CELL STRUCTURES AND THEIR FUNCTIONS CELL STRUCTURE NA+ -substances must pass through transmembrane protein channels Cell- Smallest units of life ➢ ORGANELLES- specialized structures in cells that perform specific functions Example: nucleus, mitochondria, ribosomes CYTOPLASM- jelly-like substance that holds organelles -the living material surrounding the nucleus CELL MEMBRANE -also termed the plasma membrane - a structure that encloses the cytoplasm Cell metabolism and energy use • Synthesis of molecules • Communication • Reproduction and inheritance ➢ Some substances require a vesicular transport across the membrane PASSIVE MEMBRANE TRANSPORT -does not require the cell to expend energy mechanisms: diffusion, osmosis, and facilitated diffusion CELL MEMBRANE - outermost component of a cell. - forms a boundary between material inside the cell and the outside. Intracellular -materials inside the cell Extracellular- materials outside the cell -acts as a selective barrier. -contains phospholipids, cholesterol, carbohydrates. GLUCOSE - substances require carrier molecules to transport them across the cell membrane ACTIVE TRANSPORT AND PASSIVE TRANSPORT FUNCTIONS OF THE CELL • The route of transport through the membrane depends on the size, shape, and charge of the substance. ACTIVE MEMBRANE TRANSPORT -does require the cell to expend energy, usually in the form of ATP. mechanisms: active transport, secondary endocytosis, and exocytosis active transport, DIFFUSION proteins, and FLUID-MOSAIC MODEL- model used to describe the cell membrane structure. -Generally involves movement of substances in a solution down a concentration gradient. -movement from concentration high concentration to a low -An example of diffusion is the distribution of smoke throughout a room in which there are no air currents. -Another example of diffusion is the gradual spread of salt throughout a beaker of still water. SOLUTION -generally composed of two major parts: • SOLUTES -substances dissolved in a predominant liquid or gas Nonpolar tail- hydrophobic (water-fearing) Polar head- hydrophilic (water-loving) MOVEMENT THROUGH THE CELL MEMBRANE SELECTIVE PERMEABILITY -allows only certain substances to pass in and out of the cell ENZYMES, GLYCOGEN, POTASSIUM -found in higher concentrations inside the cell SODIUM, CALCIUM, CHLORIDE - found in higher concentrations outside the cell • SOLVENT CONCENTRATION GRADIENT - A concentration gradient is the difference in the concentration of a solute in a solvent between two points divided by the distance between the two points. - The concentration gradient is said to be steeper when the concentration difference is large and/or the distance is small. LEAK AND GATED CHANNELS - Two classes of cell membrane channels include leak channels and gated channels. CELL MEMBRANE PASSAGE O2, CO2 -can pass directly through the cell membrane's phospholipid bilayer LEAK CHANNELS -constantly allow ions to pass through. GATED CHANNELS - limit the movement of ions across the membrane by opening and closing. CARRIER-MEDIATED TRANSPORT CARRIER MOLECULES -proteins within the cell membrane involved in carriermediated transport. -Some water-soluble, electrically charged or large sized particles cannot enter or leave through the cell membrane by diffusion. -These substances include amino acids, glucose, and some polar molecules produced by the cell. • Carrier-mediated transport mechanisms include: ➢ FACILITATED DIFFUSION -does not require ATP for energy. ➢ ACTIVE TRANSPORT -does require ATP for transport LIPID SOLUBLE SUBSTANCES -can diffuse directly through the phospholipid bilayer. WATER SOLUBLE SUBSTANCES -such as ions, can diffuse across the cell membrane only by passing through cell membrane channels. OSMOSIS FACILITATED DIFFUSION -carrier-mediated transport process that moves substances across the cell membrane from an area of higher concentration to an area of lower concentration of that substance. -diffusion of water (a solvent) across a selectively permeable membrane from a region of higher water concentration to one of lower water concentration, ACTIVE TRANSPORT -carrier-mediated process, requiring ATP, that moves substances across the cell membrane from regions of lower concentration to those of higher concentration against a concentration gradient. OSMOTIC PRESSURE - the force required to prevent movement of water across cell membrane -depends on the difference of solution concentrations inside a cell relative to outside the cell SODIUM-POTASSIUM PUMP • A major example of active transport is the action of the sodium-potassium pump present in cell membranes. A cell may be placed in solutions that are either hypotonic, isotonic, or hypertonic compared to the cell cytoplasm. ➢ HYPOTONIC -A hypotonic solution has a lower concentration of solutes and a higher concentration of water relative to the cytoplasm of the cell. -The solution has less tone, or osmotic pressure, than the cell. - Water moves by osmosis into the cell, causing it to swell. • If the cell swells enough, it can rupture, a process called lysis. ➢ ISOTONIC -A cell immersed in an isotonic solution has the same solute concentrations inside and outside the cell. -The cell will neither shrink nor swell. • The sodium-potassium pump moves Na+ out of cells and K+ into cells. • The result is a higher concentration of Na+ outside cells and a higher concentration of K+ inside cells. Cystic Fibrosis- a genetic disorder that affects the active transport Cl into cells. SECONDARY ACTIVE TRANSPORT -uses the energy provided by a concentration gradient established by the active transport of one substance, such as Na+ to transport other substances. -No additional energy is required above the energy provided by the initial active transport pump. ➢ COTRANSPORT -the diffusing substance moves in the same direction as the initial active transported substance. ➢ HYPERTONIC -The cytoplasm of a cell in a hypertonic solution has a lower solute concentration and higher water concentration than the surrounding solution. ➢ COUNTERTRANSPORT -the diffusing substance moves in a direction opposite to that of the initial active transported substance. -Water moves by osmosis from the cell into the hypertonic solution, resulting in cell shrinkage, or crenation. ENDOCYTOSIS AND EXOCYTOSIS ENDOCYTOSIS • process that that brings materials into cell using vesicles. RECEPTOR-MEDIATED ENDOCYTOSIS - occurs when a specific substance binds to the receptor molecule and is transported into the cell. ➢ PHAGOCYTOSIS (cell-eating) -often used for endocytosis when solid particles are ingested. ➢ PINOCYTOSIS (cell-drinking) -has much smaller vesicles formed, and they contain liquid rather than solid particles. EXOCYTOSIS -involves the use of membrane-bound sacs called secretory vesicles that accumulate materials for release from the cell. -The vesicles move to the cell membrane and fuse, ultimately releasing the material by exocytosis. -Examples of exocytosis are the secretion of digestive enzymes. ORGANELLES - include the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria, cytoskeleton, centrioles, cilia, flagella, and microvilli. RIBOSOMES -Ribosome components are produced in the nucleolus. -Ribosomes are the organelles where proteins are produced. -may be attached to other organelles, such as the endoplasmic reticulum. -Ribosomes that are not attached to any other organelle are called free ribosomes. ENDOPLASMIC RETICULUM - The endoplasmic reticulum (ER) is a series of membranes forming sacs and tubules that extends from the outer nuclear membrane into the cytoplasm. The rough ER is involved in protein synthesis and is rough due to attached ribosomes. The smooth ER has no attached ribosomes and is a site for lipid synthesis, cellular detoxification, and it stores calcium ions in skeletal muscle cells. NUCLEUS - large organelle usually located near the center of the cell. - contains most of the genetic material of the cell - bounded by a nuclear envelope, which consists of outer and inner membranes with a narrow space between them. - The nuclear membrane contains nuclear pores, through which materials can pass into or out of the nucleus. • The nuclei of human cells contain 23 pairs of chromosomes which consist of DNA and proteins. • During most of a cell's life, the chromosomes are loosely coiled and collectively called chromatin. • When a cell prepares to divide, the chromosomes become tightly coiled and are visible when viewed with a microscope. • Within the nucleus are Nucleoli, which are diffuse bodies with no surrounding membrane. That are found within the nucleus GOLGI APPARATUS • The Golgi apparatus, also called the Golgi complex, consists of closely packed stacks of curved, membranebound sacs. • It collects, modifies, packages, and distributes proteins and lipids manufactured by the ER. •The Golgi apparatus forms vesicles, some of which are secretory vesicles, lysosomes, and other vesicles. MITOCHONDRIA -Mitochondria (singular mitochondrion) are small organelles responsible for producing considerable amounts of ATP by aerobic (with O2) metabolism. -They have inner and outer membranes separated by a space. -The outer membranes have a smooth contour, but the inner membranes have numerous folds, called cristae, which project into the interior of the mitochondria. Secretory Vesicles -a vesicle is a small, membrane-bound sac that transports or stores materials within cells. -Secretory vesicles pinch off from the Golgi apparatus and move to the cell membrane -The material within the inner membrane is the mitochondrial matrix and contains enzymes and mitochondrial DNA (mtDNA). -Cells with a large energy requirement have more mitochondria than cells that require less energy. LYSOSOMES -Lysosomes are membrane-bound vesicles formed from the Golgi apparatus. -They contain a variety of enzymes that function as intracellular digestive systems. -One example is white blood cells phagocytizing bacteria. Pompe disease- caused by the inability of lysosomal enzymes to break down the carbohydrate glycogen produced in certain cells. CYTOSKELETON -The cytoskeleton gives internal framework to the cell. -It consists of protein structures that support the cell, hold organelles in place, and enable the cell to change shape. - These protein structures are microtubules, microfilaments, and intermediate filaments. ➢ MICROTUBULES -Microtubules are hollow structures formed from protein subunits. -The microtubules perform a variety of roles, including: • helping to support the cytoplasm of cells • assisting in cell division • forming essential components of certain organelles, such as cilia and flagella. ➢ PEROXISOMES • Peroxisomes are small, membrane-bound vesicles containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide (H202). -Hydrogen peroxide is a by-product of fatty acid and amino acid breakdown and can be toxic to a cell. -The enzymes in peroxisomes break down hydrogen. MICROFILAMENTS -Microfilaments are small fibrils formed from protein subunits that structurally support the cytoplasm, determining cell shape. -Some microfilaments are involved with cell movement. -Microfilaments in muscle cells enable the cells to shorten, or contract. ➢ INTERMEDIATE FILAMENTS -Intermediate filaments are fibrils formed from protein subunits that are smaller in diameter than microtubules but larger in diameter than microfilaments. -They provide mechanical support to the cell. - A specific type of intermediate filament is keratin, a protein associated with skin cells. FLAGELLA -Flagella have a structure similar to that of cilia but are much longer, and they usually occur only one per cell. -Sperm cells each have one flagellum, which propels the sperm cell. CENTRIOLES -The centrosome is a specialized area of cytoplasm close to the nucleus where microtubule formation occurs. MICROVILLI -It contains two centrioles, which are normally oriented perpendicular to each other. -are specialized extensions of the cell membrane that are supported by microfilaments, but they do not actively move as cilia and flagella do. -Each centriole is a small, cylindrical organelle composed of microtubules. -The centriole is involved in the process of mitosis. CILIA -Cilia project from the surface of certain cells. -Microvilli are numerous on cells that have them and they increase the surface area of those cells. -They are abundant on the surface of cells that line the intestine, kidney, and other areas in which absorption is an important function. WHOLE CELL ACTIVITY GENE EXPRESION -They are responsible for the movement of materials over the top of cells, such as mucus. - is the process by which information stored in the genes of DNA molecules directs the manufacture of the various proteins of our cells. -Cilia are cylindrical structures that extend from the cell and are composed of microtubules. -A DNA molecule consists of nucleotides joined together to form two nucleotide strands. -The two strands are connected and resemble a ladder that is twisted around its long axis. -Each nucleotide consists of a 5-carbon sugar, a phosphate group, and a nitrogenous base. -Each nucleotide on one DNA strand has a specific bonding pattern to another nucleotide on the opposite strand Genes -Sections of these DNA strands -sequences of nucleotides that provide a chemical set of instructions for making specific proteins -recipe for making proteins Amino Acids -The ingredients necessary to synthesize a protein • A cell spends most of its life cycle in interphase performing its normal functions. Transfer RNAs (tRNAs) -Specialized molecules, carry the amino acids to the ribosome. • Gene expression, which is protein synthesis, involves transcription and translation. ➢ TRANSCRIPTION - involves copying DNA into messenger RNA. ➢ TRANSLATION -involves messenger RNA being used to produce a protein. TRANSCRIPTION -Transcription takes place in the nucleus of the cell. -DNA determines the structure of mRNA through transcription. -During transcription, the double strands of a DNA segment separate, and DNA nucleotides of the gene pair with RNA nucleotides that form the mRNA. -DNA contains one of the following organic bases: thymine, adenine, cytosine, or guanine. -Messenger RNA (mRNA) contains uracil, adenine, cytosine, or guanine. • DNA nucleotides pair only with specific nucleotides. • DNA's thymine pairs with RNA's adenine. • DNA's adenine pairs with RNA's uracil. • DNA's cytosine pairs with RNA's guanine • DNA's guanine pairs with RNA's cytosine. RNA Genetic Code - The information in mRNA is carried in groups of three nucleotides called codons, where each codon specifies a particular amino acid. -There are 64 possible mRNA codons, but only 20 amino acids. As a result, more than 1 codon can specify the same amino acid. -Some codons do not specify a particular amino acid but perform other functions. For example, UAA does not code for an amino acid; instead it acts as a signal to end the translation process and therefore is called a stop codon. Translation - is the synthesis of proteins based on the information in mRNA. -Translation occurs at ribosomes. -In each tRNA there is a three-nucleotide sequence called the anticodon that pairs with the codon of the mRNA. THE CELL CYCLE -During growth and development, cell division occurs to increase the number of cells or replace damaged or dying ones. -This cell division involves a cell cycle. -The cell cycle includes two major phases: • Interphase- a nondividing phase • Mitosis- a cell dividing phase • During interphase, the DNA (located in chromosomes in the cell's nucleus) is replicated. • The two strands of DNA separate from each other, and each strand serves as a template for the production of a new strand of DNA. Interphase is divided into three phases: (1) G1 phase, during which the cell carries out normal metabolic activity (2) S phase, during which the DNA is replicated (3) G2 phase, during which the cell prepares to divide. • Nucleotides in the DNA of each template strand pair with new nucleotides that are subsequently joined by enzymes to form a new strand of DNA. • The sequence of nucleotides in the DNA template determines the sequence of nucleotides in the new strand of DNA. • Replication of DNA gives two identical chromatids joined at a centromere; both form one chromosome. Cell division - is the formation of daughter cells from a single parent cell. -The new cells necessary for growth and tissue repair are formed through mitosis, and the reproductive cells are formed through meiosis • Each of our body cells, except for reproductive cells, contains the diploid number of chromosomes, which for humans is 46. • Each human cell (except sperm and egg) contains 23 pairs of chromosomes, a total of 46. • The sperm and egg contain 23 chromosomes total. • Of the 23 pairs, one pair of chromosomes are the sex chromosomes, which consist of two X chromosomes if the person is a female or an X and Y chromosome if the person is a male. •The remaining 22 pairs of chromosomes are called autosomes MITOSIS - involves formation of 2 daughter cells from a single parent cell. - Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase. - Recall that during the S phase of interphase, the DNA is replicated. Each chromosome is composed of two genetically identical strands of chromatin, called chromatids, which are linked by a specialized region called the centromere INTERPHASE -During interphase, DNA exists as thin threads of chromatin. During the S phase of interphase, DNA molecules are replicated. TELOPHASE -During telophase, the chromosomes in each of the daughter cells become organized to form two separate nuclei, one in each newly formed daughter cell. -The chromosomes begin to unravel and resemble the genetic material during interphase. -Following telophase, cytoplasm division is completed, and two separate daughter cells are produced. PROPHASE -During prophase the chromatin condenses to form visible chromosomes. -Each chromosome consists of two chromatids joined at the centromere -Microtubules, termed spindle fibers, form to assist in breaking the centromere between the chromatids and move the chromosomes to opposite sides of the cell. METAPHASE -During metaphase, the chromosomes align near the center of the cell. -The movement of the chromosomes is regulated by the attached spindle fibers. DIFFERENTIATION -A sperm cell and an oocyte unite to form a single cell, then a great number of mitotic divisions occur to give the trillions of cells of the body. -The process by which cells develop with specialized structures and functions is called differentiation. -During differentiation of a cell, some portions of DNA are active, but others are inactive. APOPTOSIS ANAPHASE - At the beginning of anaphase, the chromatids separate and each chromatid is called a chromosome. -Each of the two sets of 46 chromosomes is moved by the spindle fibers toward the centriole at one of the poles of the cell. -At the end of anaphase, each set of chromosomes has reached an opposite pole of the cell, and the cytoplasm begins to divide. -termed programmed cell death, is a normal process by which cell numbers within various tissues are adjusted and controlled. -In the developing fetus, apoptosis removes extra tissue, such as cells between the developing fingers and toes. - In some adult tissues, apoptosis eliminates excess cells to maintain a constant number of cells within the tissue. CELLULAR ASPECTS OF AGING There are various causes for cellular aging. • Existence of a cellular clock • Presence of death genes • DNA damage • Formation of free radicals • Mitochondrial damage TUMORS -Tumors are abnormal proliferations of cells. -They are due to problems occurring in the cell cycle. -Some tumors are benign and some are malignant (cancer). -Malignant tumors can spread by a process, termed metastasis. - The cell shapes can be squamous, cuboidal, columnar, or a special transitional shape, that varies with the degree of stretch. Cancer refers to a malignant, spreading tumor and the illness that results from it. Cancers lack the normal growth control that is exhibited by most other adult tissues. Cancer results when a cell or group of cells breaks away from the normal control of growth and differentiation. TISSUES TISSUES AND HISTOLOGY TISSUE -a group of cells with similar structure and function, plus the extracellular substance surrounding them. HISTOLOGY -Study of microscopic anatomy of normal tissues and cells FOUR CATEGORIES OF TISSUES: • Epithelial tissue • Connective tissue • Nervous tissue • Muscle Tissue Based on the number of cell layers: ➢ Simple epithelium -consists of a single layer of cells, with each cell extending from the basement membrane to the free surface. EPITHELIAL TISSUE -Epithelium, or epithelial tissue, covers and protects surfaces, both outside and inside the body. -Included under the classification of epithelial tissue are the exocrine and endocrine glands. EPITHELIAL TISSUE CHARACTERISTICS • Mostly composed of cells ➢ Stratified epithelium -consists of more than one layer of cells, but only the deepest layer of cells attaches to the basement membrane. ➢ Pseudostratified columnar epithelium -is a special type of simple epithelium. The prefix pseudo- means false, so this type of epithelium appears to be stratified but is not. It consists of one layer of cells, with all the cells attached to the basement membrane. There appear to be two or more layers of cells because some of the cell are tall and extend to the free surface, whereas other are sorter and do not extend to the free surface. • Covers body surfaces • Has an exposed surface • Attached at the basal surface • Specialized cell connections and matrix attachments • Avascular • Capable of regeneration FUNCTIONS OF EPITHELIAL TISSUES • Protects underlying structures • Acts as a barrier • Permits passage of substances • Secretes substances • Absorption of substances CLASSIFICATION OF EPITHELIA - Epithelial tissues are classified primarily according to the number of cell layers and the shape of the superficial cells. - The cell layers pseudostratified. can be simple, stratified, or There are three types of epithelium based on idealized shapes of the epithelial cells: ➢ ➢ Squamous -cells are flat or scalelike Cuboidal (cubelike) -cells are cube-shaped-about as wide as they are tall. ➢ Stratified squamous epithelium - forms a thick epithelium because it consists of several layers of cells. The deepest cells are cuboidal or columnar and are capable of dividing and producing new cells. As these newly formed cells are pushed to the surface, they become flat and thin. ➢ Transitional epithelium - is a special type of stratified epithelium that can stretch. In the unstretched state, transitional epithelium consists of five or more layers of cuboidal or columnar cells. As transitional epithelium is stretched, the cells flatten, and the number of cell layer decreases. Transitional epithelium lines cavities that expand, such as the urinary bladder. Simple Epithelium a.) Simple squamous epithelium ➢ Columnar (tall and thin, similar to a column) - cells tend to be taller than they are wide • There are also two less easily categorized types of epithelia. ➢ PSEUDOSTRATIFIED EPITHELIUM -actually a simple columnar epithelium, but its cells extend varied distances from the basement membrane, so it gives the false appearance of being stratified. ➢ TRANSITIONAL EPITHELIUM Location: Lining of blood vessels and the heart, lymphatic vessels, alveoli of the lungs, portions of the kidney tubules, lining of serous membranes of body cavities (pleural, pericardial, peritoneal) b.) Simple cuboidal epithelium -a rather peculiar stratified squamous epithelium formed of rounded, or "plump," cells with the ability to slide over one another to allow the organ to be stretched. Types of Epithelial tissues ➢ Simple squamous epithelium - is a single layer of thin, flat cells. ➢ Simple cuboidal epithelium -is a single layer of cube-like cells that carry out active transport, facilitated diffusion, or secretion. ➢ Simple columnar epithelium - is a single layer of tall, thin cells ➢ Pseudostratified columnar epithelium - is actually a single layer of cells, but the cells appear to be layered due to the differing heights of adjacent cells and positions of their nuclei. Location: Kidney tubules, glands and their ducts, choroid plexuses of the brain, lining of terminal bronchioles of the lungs, and surfaces of the ovaries c.) Simple columnar epithelium Location: Glands and some ducts, bronchioles of lungs, auditory tubes, uterus, uterine tubes, stomach, intestines, gallbladder, bile ducts, and ventricles of the brain b.) Transitional epithelium Location: Lining of urinary bladder, ureters, and superior urethra d.) Pseudostratified columnar epithelium FREE CELL SURFACES • Most epithelia have a free surface that is not in contact with other cells and faces away from underlying tissues. • The characteristics of the free surface reflect its functions. • The free surface can be smooth or lined with microvilli or cilia. • Cilia move materials over the top of the cell. • Microvilli increase surface area. CELL CONNECTIONS Location: Lining of nasal cavity, nasal sinuses, auditory tubes, pharynx, trachea, and bronchi of lungs. Stratified Epithelium a.) Stratified squamous epithelium -Cells have several structures that hold one cell to one another or to the basement membrane. -These structures do three things: • mechanically bind the cells together • help form a permeability barrier • provide a mechanism for intercellular communication DESMOSOMES -mechanical links that bind cells together -mechanically bind epithelial cells together HEMIDESMOSOMES -half desmosomes that anchor cells to the basement membrane. -bind cells to the basement membrane KERATINIZED STRATIFIED SQUAMOUS -The outer layer of the skin is comprised of a keratinized squamous epithelium. -The keratin reduces the loss of water from the body. NONKERATINIZED STRATIFIED SQUAMOUS EPITHELIA -provides protection against abrasion and acts as a mechanical barrier. Location: Keratinized-outer layer of the skin; non keratinizedmouth, throat, larynx, esophagus, anus, vagina, inferior urethra, and corneas TIGHT JUNCTIONS -prevent the passage of materials between epithelial cells because they completely surround each cell, similar to the way a belt surrounds the waist. -cell connection structures that (1) form barriers and (2) anchor cells to each other. -Tight junctions form a barrier to movement of molecules or ions between epithelial cells. -In addition, tight junctions anchor cells together. Adhesion Belts are found just below the tight junctions, and help the tight junctions anchor the epithelial cells to each other. GAP JUNCTIONS - small channels that allow small molecules and ions to pass from one epithelial cell to an adjacent one. -act as communication signals to coordinate the activities of the cells. GLANDS ➢ HOLOCRINE -secretion involves the shedding of entire cells. CONNECTIVE TISSUE -Connective tissue is a diverse primary tissue type makes up part of every organ in the body. -Glands are secretory organs that secrete substances onto a surface, into a cavity, or into the bloodstream. -Connective tissue differs from the other three tissue types in that it consists of cells separated from each other by abundant extracellular matrix. -Glands are composed primarily of epithelium, with a supporting network of connective tissue. -Connective tissue is diverse in both structure and function. There are two major types of glands in the body: -Connective tissue is comprised of cells, protein fibers, and an extracellular matrix. ➢ ENDOCRINE GLANDS -ductless glands; they secrete their products (termed hormones) into the bloodstream. FUNCTIONS OF CONNECTIVE TISSUE • Enclose and separate other tissues ➢ EXOCRINE GLANDS -produce a wide variety of products, such as saliva, sweat, and digestive tract secretions. • Connecting tissues to one another -Glands with ducts • Storing compounds -Both the gland and its ducts is lined with epithelium. • Cushioning and insulating -Most exocrine glands are multicellular, comprised of many cells. • Transporting • Supporting and moving parts of the body • Protecting -Some exocrine glands are composed of a single cell, like goblet cells, that secrete mucus. CELLS OF CONNECTIVE TISSUE -Multicellular exocrine glands can be classified according to the structure of their ducts and secretory regions. -The specialized cells of the various connective tissues produce the extracellular matrix. ➢ UNICELLULAR -Some exocrine glands are composed of only a single cell, such goblet cells that secrete mucus -The name of the cell identifies the cell functions by means of one of the following suffixes: • Blasts create the matrix •cytes maintain it • clasts break it down for remodeling. ➢ SIMPLE GLANDS -multicellular glands that have a single, non-branched duct, some have branched ducts. For bone: • Osteoblasts form it • Osteocytes maintain it • Osteoclasts break it down Major categories of exocrine glands ➢ COMPOUND GLANDS -have multiple, branched ducts Exocrine glands -Glands with secretory regions shaped as tubules (small tubes) are called tubular, whereas those shaped in saclike structures are called acinar or alveolar. -Tubular glands can be straight or coiled. -Glands with a combination of the two are called tubuloacinar or tubuloalveolar. Modes of Secretion by Exocrine Glands ➢ MEROCRINE -secretion involves the release of secretory products by exocytosis. ➢ APOCRINE -secretion involves the release of secretory products as pinched-off fragments of the gland cells. For fibrous connective tissue: • Fibroblasts form it • Fibrocytes maintain it For cartilage: • Chondroblasts form it • Chondrocytes maintain it EXTRACELLULAR MATRIX -The extracellular matrix of connective tissue has three major components: protein fibers, ground substance, and fluid. ➢ GROUND SUBSTANCE consists of non-fibrous protein and other molecules. -The structure of the matrix is responsible for the functional characteristics of connective tissues-for example, they enable bones and cartilage to bear weight. PROTEIN FIBERS OF THE MATRIX Three types of protein fibers -collagen, reticular, and elastic-help form most connective tissues. ➢ COLLAGEN FIBERS -which resemble microscopic ropes, are very flexible but resist stretching. ➢ RETICULAR FIBERS - very fine, short collagen fibers that branch to form a supporting network. Location: Widely distributed throughout the body; substance on which epithelial basement membranes rest; packing between gland muscles, and nerves; attaches the skin to underlying tissues ➢ ADIPOSE TISSUE -consists of adipocytes, or fat cells, which contain large amounts of lipids for energy storage. ➢ ELASTIC FIBERS - have the ability to return to their original shape after being stretched or compressed, giving tissue an elastic quality Ground Substance of the Matrix GROUND SUBSTANCE -consists of non-fibrous molecules and is shapeless PROTEOGLYCANS -which are large molecules that consist of a protein core attached to many long polysaccharides. -trap large quantities of water between the polysaccharides, which allows them to return to their original shape when compressed or deformed Location: Predominantly in subcutaneous areas, mesenteries, renal pelves, around kidneys, attached to the surface of the colon, mammary glands, and in loose connective tissue that penetrates into spaces and crevices ➢ RETICULAR TISSUE -forms the framework of lymphatic tissue, such as in the spleen and lymph nodes, as well as in bone marrow and the liver Classification of Connective Tissue -The two main types of connective tissue are: • Embryonic • Adult Connective Tissue - By eight weeks of development, most of the embryonic connective tissue has become specialized to form the types of connective tissue seen in adults. Adult connective tissue consists of three types: (1) connective tissue proper (loose and dense) (2) supporting connective tissue (cartilage and bone) (3) fluid connective tissue (blood). Connective Tissue Proper: Loose Connective Tissue LOOSE CONNECTIVE TISSUE -consists of relatively few protein fibers that form a lacy network, with numerous spaces filled with ground substance and fluid. -Three subdivisions of loose connective tissue are: o Areolar o Adipose o Reticular ➢ AREOLAR CONNECTIVE TISSUE -The extracellular matrix of areolar connective tissue primarily consists of collagen fibers and a few elastic fibers. Location: Within the lymph nodes, spleen, bone marrow Connective Tissue Proper: Dense Connective Tissue -Dense connective tissue has a relatively large number of protein fibers that form thick bundles and fill nearly all of the extracellular space. These protein fibers are produced by fibroblasts. -There are two major subcategories of dense connective tissue: (1) collagenous (2) elastic -Dense collagenous connective tissue has an extracellular matrix consisting mostly of collagen fibers. -In tendons and ligaments, the collagen fibers are oriented in the same direction, and so the tissue is called dense regular, but in the dermis and in organ capsules, the fibers are oriented in many different directions, and so the tissue is called dense irregular. -Dense elastic connective tissue has abundant elastic fibers among its collagen fibers. The elastic fibers allow the tissue to stretch and recoil. a.) Dense Regular Tissue Collagenous Connective Location: Growing long bones, cartilage rings of the respiratory system, costal cartilage of ribs, nasal cartilages, articulating surface of bones, and the embryonic skeleton ➢ Fibrocartilage -has more collagen than does hyaline cartilage, and bundles of collagen fibers can be seen in the matrix. Fibrocartilage can withstand both compression and pulling or tearing forces. Location: Tendons (attach muscle to bone) and ligaments (attach bones to each other); also found in the dermis of the skin, organ capsules, and the outer layer of many blood vessels b.) Dense Regular Elastic Connective Tissue Location: Intervertebral disks, pubic symphysis, and articular disks (e.g. knees and temporomandibular (jaw] joints) ➢ Elastic cartilage -contains elastic fibers in addition to collagen and proteoglycans. The elastic fibers appear as coiled fibers among bundles of collagen fibers. Elastic cartilage is able to recoil to its original shape when bent. Location: Elastic ligaments between the vertebrae and along the dorsal aspect of the neck (nucha) and in the vocal cords; also found in elastic connective tissue of blood vessel walls Supporting Connective Tissue: Cartilage Cartilage -is composed of chondrocytes or cartilage cells, located in spaces called lacunae within an extensive matrix. -This makes cartilage relatively rigid but still able to spring back after being compressed. -Cartilage provides support, while allowing flexibility. There are three types of cartilage: ➢ Hyaline cartilage -is the most abundant type of cartilage and has many functions. It covers the ends of bones where they come together to form joints. In joints, hyaline cartilage forms smooth, resilient surfaces that can withstand repeated compression. Location: External ears, epiglottis, and auditory tubes Supporting Connective Tissue: Bone Bone (Osseous Tissue) - is a hard connective tissue that consists of living cells and a mineralized matrix. Osteocytes or bone cells, are located within lacunae. -Two types of bone tissue exist: 1. Spongy bone has spaces between trabeculae or plates, of bone and therefore resembles a sponge. 2. Compact bone is more solid, with almost no space between many thin layers of mineralized matrix Fluid Connective Tissue: Blood Blood is unique because the matrix is liquid, enabling blood cells and platelets, collectively called formed elements, to move through blood vessels. Location: In the heart ➢ SMOOTH MUSCLE -Smooth muscle forms the walls of hollow organs (except the heart); it is also found in the skin and the eyes - Smooth muscle is responsible for a number of functions, such as moving food through the digestive tract and emptying the urinary bladder. Location: Within the blood vessels; white blood cells frequently leave the blood vessels and enter the extracellular spaces MUSCLE TISSUE -The main function of muscle tissue is to contract, or shorten, making movement possible. -Muscle contraction results from contractile proteins located within the muscle cells called muscle fibers. The three types of muscle tissue are: • SKELETAL • CARDIAC • SMOOTH ➢ SKELETAL MUSCLE -attaches to the skeleton and enables the body to move. -Skeletal muscle is described as voluntary (under conscious control) because a person can purposefully cause skeletal muscle contraction to achieve specific body movements. NERVOUS TISSUE -Nervous tissue forms the brain, spinal cord, and nerves. -It is responsible for coordinating and controlling many body activities. -Nervous tissue consists of neurons and support cells, termed glial cells. -The neuron is responsible for conducting action potentials / electrical signals -It is composed of three parts: • cell body- contains the nucleus and is the site of general cell functions • dendrites- usually receive stimuli that lead to electrical changes. • axon- conduct electrical signals, which usually originate at the base of an axon where it joins the cell body and travel to the end of the axon. Glial cells are the support cells of the nervous system. -They nourish, protect, and insulate the neurons Location: Attached to bone or other connective tissue ➢ CARDIAC MUSCLE - Cardiac muscle is the muscle of the heart; it is responsible for pumping blood. - Cardiac muscle is under involuntary (unconscious) control, although a person can learn to influence the heart rate by using techniques such as meditation and biofeedback. Location: In the brain, spinal cord, and ganglia TISSUE MEMBRANES TISSUE REPAIR -A tissue membrane is a thin sheet or layer of tissue that covers a structure or lines a cavity. -Tissue repair involves substitution of dead cells for viable cells. -Most membranes consist of epithelium and the connective tissue on which the epithelium rests. . There are four tissue membranes in the body: • CUTANEOUS -Tissue repair can occur by regeneration or by replacement/fibrosis. ➢ REGENERATION -the new cells are the same type as those that were destroyed, and normal function is usually restored. -can completely repair some tissues, such as the skin and the mucous membrane of the intestine. In these cases, regeneration is accomplished primarily by stem cells. • MUCOUS • SEROUS • SYNOVIAL ➢ CUTANEOUS MEMBRANE -also termed "skin", is an external body surface membrane ➢ MUCOUS MEMBRANES -line cavities that open to the outside of the body, such as the digestive. respiratory, and reproductive tracts. -consist of epithelial cells, their basement membrane, and a thick layer of loose connective tissue. -Many, but not all, mucous membranes secrete mucus. -The functions of mucous membranes include protection, absorption, and secretion. ➢ SEROUS MEMBRANES -line cavities that do not open to the exterior of the body, such as the pericardial, pleural, and peritoneal cavities. -consist of three components: a layer of simple squamous epithelium, its basement membrane, and a delicate layer of loose connective tissue. -do not contain glands, but they secrete a small amount of fluid called serous fluid, which lubricates the surface of the membranes ➢ SYNOVIAL MEMBRANES -line the cavities of freely movable joints. -They are made up of only connective tissue and consist of modified connective tissue cells. -produce synovial fluid, which makes the joint very slippery, thereby reducing friction and allowing smooth movement within the joint. TISSUE INFLAMMATION -Inflammation is usually a beneficial process occurring when tissues are damaged -When viruses infect epithelial cells of the upper respiratory tract, inflammation and the symptoms of the common cold are produced. -The inflammatory process occurs in stages. -Inflammation mobilizes the body's defenses and isolates and destroys microorganisms, foreign materials, and damaged cells so that tissue repair can proceed. Inflammation produces five major symptoms: • REDNESS-Rubor • HEAT-Calor • SWELLING- Tumor • PAIN-Dolor • DISTURBANCE OF FUNCTION- Functio Laesa STEM CELLS -self-renewing, undifferentiated cells that continue to divide throughout life. ➢ FIBROSIS OR REPLACEMENT -a new type of tissue develops that eventually causes scar production and the loss of some tissue function SKELETAL SYSTEM: BONES AND JOINTS FUNCTIONS OF THE SKELETAL SYSTEM -The skeletal system is the primary structure or the central framework of your body. - It is made up of bones and connective tissue, such as cartilage, tendons, and ligaments. -Sitting, standing, walking, picking up a pencil, and taking a breath all involve the skeletal system. • Body Support -Osteocytes account for 90-95% of bone cells and are long-lived with a lifespan of up to 25 years. -Can produce the components needed to maintain the bone matrix -Osteocyte cell bodies are housed within the bone matrix in spaces called lacunae -Osteocyte cell extensions are housed in narrow, long spaces called canaliculi ➢ • Organ protection Osteoclasts -Bone-destroying cells responsible for breakdown of bone (bone reabsorption) • Body Movement • Mineral Storage • Blood cell production BONE HISTOLOGY Connective tissue is characterized by having widely distributed cells separated by a non-living material called matrix. In these structures of the skeletal system, the cells produce the matrix and become entrapped within it. -important for mobilizing crucial calcium ions and phosphate ions for use in many metabolic processes. -As bone is broken down, the Ca+ goes "back" into the blood. -Osteoclasts are massive, multinucleated cells and develop from the red bone marrow cells that also differentiate into specialized white blood cells. -Ruffled border- a specialized reabsorption-specific area of the membrane. Collagen- the fibrous that provides flexibility but resists pulling or compression. SPONGY AND COMPACT BONE BONE MATRIX -Mature bone is called lamellar bone. It is organized into thin, concentric sheets or layers, called lamellae. -By weight, mature bone matrix is normally about 35% organic and 65% inorganic material. -Bone can be classified according to the amount of bone matrix relative to the amount of space within the bone: -The organic material consists primarily of collagen and proteoglycans. ➢ Spongy Bone -The inorganic material consists primarily of a calcium phosphate crystal called hydroxyapatite -which appears porous, has less bone matrix and more space than compact bone -The collagen and mineral components are responsible for the major functional characteristics of bone. -consists of interconnecting rods or plates of bone called trabeculae Brittle bone disease -A rare disorder caused by any one of a number of faulty genes that results in either too little collagen formation, or poor-quality collagen. BONE CELLS There are three types of bone cells; ·Osteoblasts ·Osteocytes ·Osteoclasts ➢ Osteoblasts -bone-building cells -have an extensive endoplasmic reticulum and numerous ribosomes -produce collagen and proteoglycans, which are packaged into vesicles by the Golgi apparatus and secreted by exocytosis -secrete high concentrations of Calcium ions and phosphate ions, forming crystals called hydroxyapatite (stimulate further hydroxyapatite formation and mineralization of the matrix). Ossification- the formation of new bone by osteoblast -occurs by appositional growth on the surface of previously existing material, either bone or cartilage. ➢ Osteocytes -Osteoblasts become osteocytes once the osteoblasts have secreted sufficient bone matrix ➢ Compact Bone (cortical bone) -compact bone has more bone matrix and less space than spongy bone -the solid, outer layer surrounding each bone -It has more matrix and is denser with fewer pores than spongy bone -The functional unit of compact bone is an osteon, or haversian system. BONE ANATOMY STRUCTURE OF THE LONG BONE A long bone is the traditional model for overall bone structure. Diaphysis- is the center portion of the bone. -It is composed primarily of compact bone tissue. surrounding a hollow center called the medullary cavity. Epiphyses- the ends of a long bone -are mostly spongy bone, with an outer layer of compact bone. Articular cartilage- the end of a long bone is covered with hyaline cartilage. Epiphyseal Plate or Growth Plate- is located between the epiphysis and the diaphysis. -Growth in bone length occurs at the epiphyseal plate. -When bone stops growing in length, the epiphyseal plate becomes ossified and is called the epiphyseal line The cavities of spongy bone and the medullary cavity are filled with marrow: Red marrow- is the site of blood cell formation. Yellow marrow- is mostly adipose tissue. Periosteum- is a connective tissue membrane covering the outer surface of a bone. Endosteum- is a single cell layer of connective tissue that lines the internal surfaces of all cavities within bones, such as the medullary cavity of the diaphysis. -includes osteoblasts and osteoclasts BONE DEVELOPMENT -Bone formation in the fetus follows two processes: Intramembranous Ossification and Endochondral Ossification. ➢ Intramembranous Ossification - starts within embryonic connective tissue membranes. -many skull bones, part of the mandible (lower jaw), and the diaphyses of the clavicles (collarbones) develop by intramembranous ossification. Centers of Ossification- locations in the membrane where intramembranous ossification. Fontanels- are the larger, membrane-covered spaces between the developing skull bones that have not yet been ossified. ➢ Endochondral Ossification - starts with a cartilage model -the formation of cartilage begins at approximately the end of the fourth week of embryonic development. BONE GROWTH -Unlike cartilage, bones do not grow by interstitial growth only. -Bones increase in size in part by appositional growth, the formation of new bone on the surface of older bone or cartilage. For example, trabeculae grow in size when osteoblasts deposit new bone matrix onto the surface of the trabeculae Growth in Bone Length -Long bones increase in length because of growth at the epiphyseal plate. In a long bone, the epiphyseal plate separates the epiphysis from the diaphysis BONE REMODELING -It is a process where bone that becomes old is replaced with new bone. - In this process, osteoclasts remove old bone and osteoblasts deposit new bone BONE REPAIR Bone is a living tissue that can undergo repair if it is damaged. 3. Callus ossification -Like the cartilage models formed during fetal development, the cartilage in the callus is replaced by spongy bone through endochondral ossification. The result is a stronger external callus. 4. Bone remodeling -Repair is complete only when the new bone of the callus and the dead bone adjacent to the fracture site have been replaced by compact bone. - In this compact bone, osteons from both sides of the break extend across the fracture line to "peg" the bone fragments together. This remodeling process takes timeas much as a year or more. CALCIUM HOMEOSTASIS Calcium is a critical physiological regulator of many processes required to achieve and maintain homeostasis. Calcium homeostasis is regulated by three hormones: ➢ PARATHYROID HORMONE (PTH) • secreted by cells in the parathyroid gland • essential for the maintenance of blood Ca²+ levels within the homeostatic limits Direct Effects of PTH Bone Cells PTH increases blood Ca2+ levels by exerting direct regulatory control of osteoblasts and osteocytes to increase formation and activation of osteoclasts, the principal bone-reabsorbing cells. Kidney Tubules PTH stimulates the reabsorption of Ca2+ from urine in the kidney tubules, which reduces the amount of Ca2+ excreted in the urine. Indirect Effects of PTH in the Small Intestine PTH regulates blood Cat levels by indirectly increasing Ca²+ uptake from the small intestine. Increased PTH promotes the activation of calcitriol in the kidneys. Calcitriol increases absorption of Ca2+ in the small intestine. ➢ Calcitriol -Calcitriol increases blood Ca² levels. -It is a steroid hormone derived from vitamin D3. ➢ Calcitonin -Calcitonin is secreted from C cells in the thyroid gland when blood Ca2+ levels are too high. -Calcitonin rapidly lowers blood Ca+ levels by inhibiting osteoclast activity. DISRUPTION OF BONE HEMOSTASIS BY BACTERIA FOUR MAJOR STEPS IN BONE REPAIR OSTEOMYELITIS • bacterial infection in bone 1. Hematoma formation -A hematoma is a localized mass of blood released from blood vessels but confined within an organ or a space. -When a bone is fractured, the blood vessels in the bone and surrounding periosteum are damaged and a hematoma forms. Usually the blood in a hematoma forms a clot, which consists of fibrous proteins that stop the bleeding. • causative agent: Staphylococcus aureus 2. Callus formation -A callus is a mass of bone tissue that forms at a fracture site. Several days after the fracture, blood vessels grow into the clot. • commonly found on our skin • common treatment for osteomyelitis is a 4- to 8-week course of antibiotics. • doctor may prescribe intravenous dosing with the antibiotics SKELETAL ANATOMY OVERVIEW -The average adult has 206 bones. However, the actual number of bones varies among people and decreases with age as bones become fused. -Bones are segregated into the axial skeleton and the appendicular skeleton. -The axial skeleton consists of the bones of the skull, the auditory ossicles, the hyoid bone, the vertebral column, and the thoracic cage (rib cage). -The appendicular skeleton consists of the bones of the upper limbs, the lower limbs, and the two girdles. The term girdle, which means "belt" or "zone," refers to the two zones where the limbs are attached to the body. These two zones are the pectoral girdle and the pelvic girdle. SKELETAL TERMINOLOGY -Anatomists use several common terms to describe the features of bones. • For example, a hole in a bone is called a foramen. • If the hole is elongated into a tunnel-like passage through the bone, it is called a canal or a meatus (a passage). • A depression in a bone is called a fossa. • A rounded projection on a bone is called a tubercle (a knob) or a tuberosity, and a sharp projection from a bone is called a process. • The smooth, rounded end of a bone, where it forms a joint with another bone, is called a condyle (knuckle). AXIAL SKELETON -The axial skeleton forms the central axis of the body. It protects the brain, the spinal cord, and the vital organs housed within the thorax. BONE SHAPES There are four categories of bone, based on their shape: (1) long (2) short (3) flat (4) irregular ➢ Long bones -are longer than they are wide. This shape enhances their function in movement of appendages. -Most of the bones of the upper and lower limbs are long bones. ➢ Short bones -are approximately as wide as they are long; examples are the bones of the wrist and ankle. -Short bones help transfer force between long bones. ➢ Flat bones -have a relatively thin, flattened shape. Flat bones are well-suited to providing a strong barrier around soft organs such as the brain and heart. -Examples of flat bones are certain skull bones, the ribs, the scapulae (shoulder blades), and the sternum. ➢ Irregular bones - include the vertebrae and facial bones, which have shapes that do not fit readily into the other three categories. These bones tend to have specialized functions, such as providing protection while allowing bending and flexing of certain body regions such as the spine. SKULL -The skull consists of 8 cranial bones and 14 facial bones, a total of 22 bones. -The cranial bones, or cranium, house and protect the brain. -The cranial bones are connected by immovable joints called sutures There are four principal sutures: (1) coronal (2) sagittal (3) lambdoid (4) squamous -The top of the skull, called the calvaria, is often removed to view the interior of the skull. Cranial Bones -The 8 bones of the cranium include: • frontal bone • 2 parietal bones • 2 temporal bones • occipital bone • sphenoid bone • ethmoid bone Facial Bones The 14 facial bones of the skull include: (1 and 2) the pair of zygomatic bones (3 and 4) the pair of maxilla bones 5 and 6) the pair of palatine bones (7 and 8) the pair of lacrimal bones (9 and 10) the pair of nasal bones (11) the mandible (12) the vomer bone (13 and 14) the pair of inferior nasal conchae ➢ Zygomatic Bones -commonly known as the cheekbones ➢ Maxillae Each maxilla (upper jaw) is anterior and inferior to the zygomatic bones. ➢ Palatine Bones -The palatine bones have horizontal plates that fuse centrally to form the posterior portion of the hard palate as described earlier with the maxillae. ➢ Lacrimal Bones -The lacrimal bones are the smallest of the skull bones and house the depression through which the nasolacrimal duct enters the nasolacrimal canal, joining the orbits and nasal cavity. ➢ Nasal Bones -The nasal bones, along with the frontal processes of the maxillae, form the bridge of the nose. ➢ Mandible -The mandible (lower jaw) is the only skull bone that is freely movable relative to the other skull bones. ➢ Vomer -The vomer forms most of the posterior portion of the nasal septum ➢ Frontal Bone -The frontal bone is connected to the two parietal bones by the coronal suture. -The frontal bone is most well-known at the "forehead." ➢ Parietal Bones -The paired parietal bones form nearly half of the superior portion of the skull. ➢ Temporal Bones -The temporal bones are connected to the skull by the squamous sutures. -The term temporal means "related to time"; the temporal bone's name is derived from the observation that the hair on the temples turns gray as a person ages. ➢ Occipital Bone -The occipital bone makes up the majority of the skull's posterior wall and base ➢ Sphenoid Bone -Although appearing to be two bones, one on each side of the skull anterior to the temporal bone, the sphenoid bone is actually a single bone that extends completely across the skull. -When viewed as a whole, the sphenoid bone somewhat resembles a butterfly. ➢ Ethmoid Bone -The ethmoid bone is appropriately named because it is a very porous, fragile bone. ➢ Inferior Nasal Conchae -The inferior nasal concha, as discussed with the ethmoid bone, is one of the three conchae in the nasal cavity that provide increased surface area Hyoid Bone -The hyoid bone is important for speech and swallowing. -The hyoid bone has the unique distinction of being the only bone in the body not directly attached to another bone Vertebral Column The vertebral column performs five major functions: (1) It supports the weight of the head and trunk (2) it protects the spinal cord (3) it allows spinal nerves to exit the spinal cord (4) it pro- vides a site for muscle attachment (5) it permits movement of the head and trunk. -The vertebral column usually consists of 26 bones, called vertebrae, which can be divided into five regions: 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, 1 sacral bone, and 1 coccygeal bone. JOINTS (ARTICULATION) -Are commonly named according to the bones or portions of bones that join together. -Some joints are given the Greek or Latin name such as “cubital” joint for the elbow joint. -Classified structurally as fibrous, cartilaginous, or synovial, according to the major connective tissue that binds the bones together and whether a fluid-filled joint capsule is present. SYNOVIAL MEMBRANE -The synovial membrane is the inner layer of the joint capsule. -It lines the joint cavity, except over the articular cartilage and articular disks and is a thin, delicate membrane. -The membrane produces synovial fluid, a viscous lubricating film that covers the surfaces of a joint. -Synovial fluid is a complex mixture of polysaccharides, proteins, lipids, and cells derived from serum (blood fluid) filtrate and secretions from the synovial cells. -In general, fibrous and cartilaginous joints have little or no movement, while synovial joints have considerable movement. FIBROUS JOINT -Are the articulating surfaces of two bones united by a fibrous connective tissue. -They have no joint cavity and exhibit little or no movement -Joints in this group are further subdivided on the basis of structure as: • SUTURES - are fibrous joint between the bones of the skull; in a new born, some parts of the sutures are quite wide and are called fontanels (soft spot) • SYNDESMOSES - are fibrous joints in which bones are separated by some distance and held together by ligaments. • GOMPHOSES - consist of pegs fitted into sockets and held in place by ligaments.; e.g. joint between a tooth and a socket is a gomphosis. CARTILAGINOUS JOINT -Hold two bones together by a pad of cartilage. -Like fibrous joints, these joints exhibit little or no movement. Cartilaginous joints are subdivided into 2 parts on the basis of the type of cartilage as: Synchondroses - which contain hyaline cartilage Symphyses - contain fibrous cartilage SYNOVIAL JOINTS -Synovial joints contain synovial fluid and allow considerable movement between articulating bones. -Most joints that unite the bones of the appendicular skeleton are synovial joints, reflecting the far greater mobility of the appendicular skeleton compared with the axial skeleton. ARTICULAR CARTILAGE -The articular surfaces of bones within synovial joints are covered with a thin layer of hyaline cartilage called articular cartilage. -The articular cartilage provides a smooth surface where the bones meet. The space around the articular surfaces of the bones in a synovial joint is called the joint cavity. TYPES OF SINOVIAL JOINTS Synovial joints are classified according to the shape of the adjoining articular surfaces. The six types of synovial joints are: (1) plane (2) saddle (3) hinge (4) pivot (5) ball-and-socket (6) ellipsoid Movements at synovial joints are described as uniaxial, occurring around one axis; biaxial, occurring around two axes situated at right angles to each other, or multiaxial, occurring around several axes. ➢ PLANE JOINT -A plane joint, or gliding joint, consists of two flat bone surfaces of about equal size between which a slight gliding motion can occur. -These joints are considered uniaxial because some rotation is also possible but is limited by ligaments and adjacent bone. ➢ SADDLE JOINT -A saddle joint consists of two saddle-shaped articulating surfaces oriented at right angles to each other so that their complementary surfaces articulate. -Saddle joints are biaxial joints. -The carpometacarpal joint of the thumb is an example The joint cavity is filled with synovial fluid and surrounded by a joint capsule. The joint capsule helps hold the bones together while still allowing for movement. The fibrous capsule is the outer layer of the joint capsule. It consists of dense irregular connective tissue and is continuous with the fibrous layer of the periosteum that covers the bones united at the joint. ➢ HINGE JOINT -A hinge joint is a uniaxial joint in which a convex cylinder in one bone is applied to a corresponding concavity in the other bone. -Examples include the elbow and knee joints. ➢ PIVOT JOINT -A pivot joint is a uniaxial joint that restricts movement to rotation around a single axis. ➢ PLANTAR FLEXION & DORSIFLEXION -There are special cases of flexion when describing the movement of the foot. -A pivot joint consists of a relatively cylindrical bony process that rotates within a ring composed partly of bone and partly of ligament. -Movement of the foot toward the plantar surface, as when standing on the toes, is commonly called plantar flexion; movement of the foot toward the shin, as when walking on the heels, is called dorsiflexion. -The articulation between the head of the radius and the proximal end of the ulna is an example. ➢ BALL-AND-SOCKET JOINT -A ball-and-socket joint consists of a ball (head) at the end of one bone and a socket in an adjacent bone into which a portion of the ball fits. -This type of joint is multiaxial, allowing a wide range of movement in almost any direction. -Examples are the shoulder and hip joints. ➢ ELLIPSOID JOINT -An ellipsoid joint (condyloid joint) is a modified ball-andsocket joint. The articular surfaces are ellipsoid in shape, rather than spherical as in regular ball-and-socket joints. ➢ ABDUCTION & ADDUCTION -Abduction (to take away) is movement away from the median or midsagittal plane; adduction (to bring together) is movement toward the median plane. -Moving the legs away from the midline of the body, as in the outward movement of "jumping jacks." is abduction, and bringing the legs back together is adduction. -Ellipsoid joints are biaxial, because the shape of the joint limits its range of movement almost to a hinge motion in two axes and restricts rotation. TYPES OF MOVEMENT The types of movement occurring at a given joint are related to the structure of that joint. Some joints are limited to only one type of movement, whereas others permit movement in several directions. All the movements are described relative to the anatomical position. Because most movements are accompanied by movements in the opposite direction, they are often illustrated in pairs. ➢ FLEXION & EXTENSION -Flexion and extension are movements. common opposing ➢ PRONATION & SUPINATION -Pronation and supination refer to the unique rotation of the forearm. They are best demonstrated with the elbow flexed at a 90-degree angle. -When the elbow is flexed, pronation is rotation of the forearm so that the palm is down, and supination is rotation of the forearm so that the palm faces up -Flexion is a bending movement that decreases the angle of the joint to bring the articulating bones closer together. Extension is a straightening movement that increases the angle of the joint to extend the articulating bones. -These bending and extending movements can easily be seen at the elbow and knee joints. -Hyperextension is usually defined as extension of a joint beyond 180 degrees. Hyperextension can be a normal movement, such as looking up at the stars, but it can also result in injury. ➢ EVERSION & INVERSION Eversion is turning the foot so that the plantar surface (bottom of the foot) faces laterally; inversion is turning the foot so that the plantar surface faces medially. ➢ ROTATION & CIRCUMDUCTION -Rotation is the turning of a structure around its long axis, as in shaking the head "no." Rotation of the arm can best be demonstrated with the elbow flexed so that rotation is not confused with supination and pronation of the forearm. ➢ OPPOSITION & REPOSITION Opposition is a movement unique to the thumb and little finger. It occurs when the tips of the thumb and little finger are brought toward each other across the palm of the hand. The thumb can also oppose the other digits. Reposition returns the digits to the anatomical position. -Circumduction occurs at freely movable joints, such as the shoulder. In circumduction, the arm moves so that it traces a cone where the shoulder joint is at the cone's apex When the bones of a joint are forcefully pulled apart and the ligaments around the joint are pulled or torn, a sprain results. A separation exists when the bones remain apart after injury to a joint. In addition to the movements mentioned, several other movement types have been identified: ➢ PROTRACTION & RETRACTION Protraction is a movement in which a structure, such as the mandible, glides anteriorly. In retraction, the structure glides posteriorly. ➢ ELEVATION & DEPRESSION Elevation is movement of a structure in a superior direction. Closing the mouth involves elevation of the mandible. Depression is movement of a structure in an inferior direction. Opening the mouth involves depression of the mandible. ➢ EXCURSION Excursion is movement of a structure to one side, as in moving the mandible from side to side. A dislocation is when the end of one bone is pulled out of the socket in a ball-and-socket, ellipsoid, or pivot joint. Most dislocations result in stretching of the joint capsule. Once the joint capsule has been stretched by a dislocation, the joint may be predisposed to future dislocations. Some individuals have hereditary "loose" joints and are more likely to experience a dislocation.
