1 1.0 Module 1 – Introduction and Human Organisation 1.1 Human Biology 1.1.1 The Characteristics of Life • • • • • • • Living things and non-living things have different molecular composition ◦ living things are organised from atom to biosphere ◦ molecules of life – proteins, carbohydrates, lipids, and nucleic acids Living things require energy and raw materials from environment ◦ metabolism – physical and chemical processes involved in transforming energy and molecules so that life can be maintained Living things are composed of one or more cells ◦ cell – smallest unit that exhibits all the characteristics of life ▪ unicellular organisms – single cell organisms ▪ multicellular organisms – organisms composed of many cells or many different types of cells Living things maintain homeostasis – capability in regulating and maintaining internal environment despite dramatic changes in the external environment Living things respond to external environment Living things grow and reproduce ◦ DNA – deoxyribonucleic acid, genetic materials in cells which allow the cells to have the capacity to grow and reproduce ◦ non-living things, such as glaciers and volcanic mountains, can grow, but cannot reproduce themselves Populations of living things evolve 1.1.2 Classification of Living Things Living things are grouped according to their characteristics – domain, kingdom, phylum, order, class, family, genus, and species. Fundamental criteria used for classification includes: presence or absence of a nucleus, number of cells, and mode of nutrition. 2 • • • Domain Bacteria – single cells, no nucleus Domain Archaea – primitive single cells, no nucleus, live in extreme conditions Domain Eukarya ◦ Kingdom Protista – unicellular and relatively simple multicellular eukaryotes such as protozoa, algae, and slime molds ◦ Kingdom Animalia – animals, multicellular, eukaryotic, heterotrophic (retrieve energy from plants or other animals) ▪ Phylum Chordata – animals with neural cords • Class Mammalia – chordates with mammary glands for nursing their young ◦ Order primates – humans, lemurs, monkeys and apes ▪ Family Hominidae – ancient and modern humans • Genus and Species – Homo sapiens ◦ Kingdom Fungi – eukaryotic decomposers like yeasts, molds and mushrooms ◦ Kingdom Plantae – plants, multicellular, eukaryotic, photosynthetic (retrieve energy from sunlight) Note: • Species – smallest unit of classification system ◦ similar physical and functional characteristics ◦ can interbreed and produce fertile offspring • Genus – second smallest unit ◦ all living human beings belong to the same genus and species – homo sapiens 1.1.3 Defining Features of Humans • • • • Bipedalism – ability and preference to stand upright and walk on two legs Opposable thumbs – ability to grasp objects between tip of the thumb and tips of fingers ◦ well-developed muscles to exert a certain type of precise control over the thumb and fingers Large brain – relative to body size; required for complex motion control and language which is fundamental to advanced social interactions Capacity for complex language – both spoken and written; vocal, signs, symbols, and gestures for communicating concepts and emotions 3 1.1.4 Biological Organisation and Structural Organisation Biological Organisation: • • • • • • • • • • • Atom – smallest unit of an element of matter Molecule – more than one atom in a stable association Cell – smallest unit of life Tissue – an association of cells with the same general structure and function Organ – an association of several tissue types that carry out a specific function Organ system – two or more organs that work together to carry out a general function Organism – an individual living being composed of several organs or organ systems Population – a group of individuals of the same species living in the same area Community – several populations of different species who inhabit the same area and interact with each other Ecosystem – all of the organisms in a given area plus all of the nonliving matter and energy Biosphere – all ecosystems combined 4 Structural Organisation: 1.1.5 Basic Anatomical Terminology 1.1.5.1 Anatomical position Standardised method of observing or imaging the body • person stands facing the observer • upper extremities places at the sides • palms forward • feet flat on the floor 5 1.1.5.2 Regional names Names given to specific regions of the body for reference 1.1.5.3 Directional terms Terms to precisely locate one part of the body relative to another 6 • Planes and sections – imaginary flat surfaces that are used to divide the body Note: • Anatomy – the study of structure • Physiology – the study of how body structures function 1.1.6 Homeostasis Homeostasis is a condition of equilibrium, or balance, in the body’s internal environment. • Maintained by regulatory processes • Extracellular fluid – precise regulation of their chemical composition to maintain homeostasis • disease, disorder and death are often as a result of homeostatic imbalance • Negative Feedback Loop – a change in a given direction causes change in the opposite direction ◦ an increase in the concentration of a substance causes feedback that ultimately causes the concentration of the substance to decrease. • Positive Feedback Loop – a change in a given direction causes additional change in the same direction ◦ an increase in the concentration of a substance causes feedback that produces continued increases in concentration ◦ has the potential to produce a runaway process ◦ eg. - blood clotting, labour contractions, lactation, blood loss due to trauma ◦ require an external factor to interrupt the loop – baby born, blood clotted, or death 7 1.2 The Scientific Method • • • • • Observe and generalise Formulate a hypothesis Make a testable prediction Experiment or observe ◦ controlled experiment – all but one variable are accounted for ◦ randomised controlled trials (RCTs) ◦ blinding of participants and/or researchers/assessors results in blind or doubleblind studies Modify the hypothesis as necessary and repeat 1.3 Body Chemistry 1.3.1 Atoms and Atomic Structure Atoms join together to form chemicals with different characteristics which determine physiology at the molecular and cellular levels. • • • • Atom ◦ nucleus – protons (positive charge), neutrons (no charge) ◦ shells – electrons (negative charge) ▪ determine the reactivity of an atom ▪ valence shell – outermost shell which determines bonding Dalton (or AMU) – units to measure the mass of subatomic particles, atoms or molecules Avogadro’s number – 6.022 x 1023 Isotopes – atoms of the same element that have a different number of neutrons ◦ radioisotopes – unstable isotopes which give off particles and energy in the form of radiation ◦ medical use of radioisotopes – carbon-14 for dating fossils, diagnostic imaging, cancer treatment, power supply for implants 1.3.2 Molecules and Compounds Chemical bonds involve the sharing, gaining, and losing of electrons in the valence shell. Molecules are formed by two or more atoms joined by strong bonds. Compounds are formed by two or more atoms of different elements joined by strong or weak bonds. • • • Ionic bonds – attraction between cations (electron donor) and anions (electron acceptor) ◦ due to cations loosing electrons to anions, the two atoms are attracted due to opposing charges Covalent bonds – strong electron bonds involving shared electrons ◦ one bond is a pair of electrons donated by each atom ▪ single covalent bond – sharing one pair of electrons ▪ double covalent bond – sharing two pair of electrons ▪ triple covalent bond – sharing three pair of electrons ◦ non-polar bonds – equal sharing of electrons (equal pull) ◦ polar bonds – unequal sharing of electrons, one of the atoms involved has a disproportionately strong pull on the elctrons Hydrogen bonds – weak polar bonds based on partial electrical attractions ◦ bonds between adjacent molecules ◦ results in surface tension in water molecules 8 1.3.2.1 The Water Molecule Key features of water in life science: • excellent biological solvent ◦ solvent – liquid in which other substances dissolve ◦ solute – any dissolved substance ◦ colloid – a solution of very large organic molecules, eg. blood plasma ◦ suspension – a solution in which particles settle (sediment), eg. whole blood ◦ concentration – amount of solute in a solvent (mol/L, mg/mL) ▪ 1 Molar (M) solution – 1 mole in 1 L ◦ hydrophilic compounds – interacts with water, eg. ions and polar molecules ◦ hydrophobic compounds – does not interact with water, eg. non-polar molecules, fats and oils ◦ electrolytes – inorganic ions that conduct electricity in solution • liquid form at body temperature ◦ important transport function in the blood (90% water) ◦ 60% of body weight • absorbs and holds heat energy ◦ prevents rapid changes in body temperature • evaporation of water takes away heat energy ◦ regulate body temperature • participates in essential chemical reactions ◦ synthesis of carbohydrates, proteins, and lipids – produce water molecules ◦ breakdown of carbohydrates, proteins, and lipids – consumes water molecules 1.3.3 Chemical Reactions • • • • • Energy – the power to do work Work – the movement of an object, a change in the physical structure of matter Kinetic energy – energy of motion Potential energy – stored energy Chemical energy – potential energy stored in chemical bonds 1.3.3.1 Types of Chemical Reactions • • • • • • Decomposition Reaction – Catabolism ◦ Breaks chemical bonds – AB → A + B ◦ Hydrolysis – AB + H2O → AH + OHB Synthesis Reaction – Anabolism ◦ Formation of chemical bonds – A + B → AB ◦ Dehydration synthesis – AH + OHB → AB + H2O Exchange Reaction ◦ Decomposition followed by synthesis – AB + CD → AD + CB Reversible Reaction ◦ A + B ↔ AB ◦ concentration of each substance does not change at equilibrium ◦ reactions are still constantly occurring ◦ reaction rates adjust to reach a new equilibrium upon adding or removing reactants Exergonic (Exothermic) Reaction – amount of energy released is greater than the activation energy Endergonic (Endothermic) Reaction – activation energy is greater than amount of energy released 9 1.3.3.2 Enzymes • Enzymes – protein catalysts that lower the activation energy of reactions ◦ activation energy – the amount of energy needed to get a reaction started 1.3.4 Acid and Base • • pH – the concentration of hydrogen ions in a solution ◦ -log[H+] - negative logarithm of the hydrogen ion concentration in mol/L ◦ pH 7 – neutral ◦ acid – pH < 7.0 ▪ proton donor ▪ strong acids dissociate completely in solution ◦ base – pH > 7.0 ▪ proton acceptor ▪ strong bases dissociate completely in solution ◦ pH of blood – between 7.35 to 7.45 Weak acids and bases fail to dissociate completely and help to balance the pH ◦ buffers – weak acid/salt compounds ▪ neutralise either strong acid or strong base, eg. sodium bicarbonate (NaHCO3) ▪ carbonic acid-bicarbonate buffer – H2CO3 ↔ H+ + HCO3◦ antacids – neutralise acid to form a salt 1.3.5 Carbohydrates • Contain C, H, O in a 1:2:1 ratio ◦ Monosaccharide – simple sugar, an energy source, with 3 to 7 Cs ▪ glucose, fructose, galactose ◦ Disaccharide – two simple sugars, also an energy source, condensed by dehydration synthesis ▪ sucrose, maltose Dehydration Synthesis: Hydrolysis: 10 ◦ Polysaccharide – many monosaccharides (a storage of glucose) condensed by dehydration synthesis ▪ glycogen, starch, cellulose – carbohydrate storage • glycogen is the short-term energy storage in animals, stored in muscle cells and liver cells • 1% of total energy reserves 1.3.6 Lipids • • Made mostly of C and H, with some O atoms mainly hydrophobic molecules – fats, oils, and waxes ◦ Fatty acids – energy source, long chains of C and H with a carboxyl group (COOH) ▪ absorbed from food or synthesized in cells ▪ transported in the blood ▪ relatively nonpolar except the carboxyl group ▪ eg. lauric acid 11 ◦ Eicosanoids – chemical messengers coordinating local cellular activities ▪ prostaglandins, leukotrienes ◦ Glycerides – energy source and storage, insulation, physical protection ▪ fatty acides attached to a glycerol molecule ▪ must be broken down to fatty acids and glycerol before they can be used as an energy source ▪ monoglycerides, dilycerides, triglycerides • triglycerides are long-term energy storage in animals and have twice the energy of carbohydrates • 78% of total energy reserves ◦ Steroids – structural components of plasma membranes, hormones, digestive secretions in bile ▪ four rings of C and H with an assortment of functional groups ▪ cholesterol – components of plasma membranes ▪ oestrogens/testosterone – sex hormones ▪ corticosteroids and calcitriol – metabolic regulation ▪ bile salts – derivatives of steroids ◦ Phospholipids/glycolipids – structural components of plasma membranes ▪ structural lipids – generally has hydrophilic heads and hydrophobic tails ▪ lecithin 12 1.3.7 Proteins 1.3.7.1 Protein Structure A protein is made of long chains of amino acids. Proteins have the same amount of energy as carbohydrates and make up 21% of toal energy reserves. There are five components of amino acid structure: • central carbon atom • hydrogen atom • amino group (-NH2) • carboxyl group (-COOH) • variable side chain or R group Linking amino acids together requires a dehydration synthesis between the amino group of one amino acid and the carboxyl group of another amino acid. A peptide bond is formed. Protein structure determines protein function. • • • • Primary structure – sequence of amino acids Secondary structure – hydrogen bonds forming spirals or pleats Tertiary structure – secondary structure folds into a unique shape Quaternary structure – several tertiary structures together forming the final protein shape 13 1.3.7.2 Protein Function Proteins have seven major functions: • support – structural proteins ◦ fibrous proteins • movement – contractile proteins • transport – transport/carrier proteins • buffering – regulation of pH • metabolic regulation – enzymes • coordination and control – hormones • defense – antibodies Note: Fibrous proteins are structural sheets or strands, providing support. proteins are soluble spheres with active functions Globular 1.3.7.3 Enzyme Enzymes are catalysts which lower the activation energy of a chemical reaction. They are not changed or used up in the reaction. Three characters of enzymes are: • • • specificity – only work on limited types of substrates saturation limits – limited by their concentration regulation – can be regulated by other cellular chemicals An enzyme may be inactive and requires cofactors or coenzymes to activate its function. Isozymes are two enzymes which can catalyse the same reaction. • • cofactor – an io or molecule that binds to an enzyme before substrates can bind coenzyme – nonprotein organic cofactors such as vitamins 14 1.3.7.4 Temperature/pH and Proteins Both temperature and the pH of the surrounding environment have effects on enzyme functions. A protein can be denatured, i.e. loss of shape, if the temperature or pH of the environment exceeds its tolerance. 1.3.7.5 Protein and Carbohydrate Combined • Glycoprotein – large protein + small carbohydrate ◦ enzymes, antibodies, hormones and mucus production • Proteoglycans – large polysaccharides + polypeptides ◦ promote viscosity ◦ major component of the animal extracellular matrix as the filler substance between cells 1.4 Cells and Tissues 1.4.1 The Cell Theory • • • All living things are composed of cells A single cell is the smallest unit that exhibits all of the characteristics of life All cells come only form pre-existing cells 1.4.2 Cell Size Cells remain small to stay efficient. • high surface area to promote efficiency in acquisition of nutrients and disposal of wastes, such as microvilli • can only been seen under microscopes – light microscope (1000x), transmission electron microscope (100,000x), scanning electron microscope (100,000x with 3D view) 15 1.4.3 Classification of Cells Cells are classified according to their internal organisation. • Prokaryotic cells – plasma membrane, no nucleus, cytoplasm, no true organelles • Eukaryotic cells – plasma membrane, nucleus, cytoplasm, organelles ◦ eukaryotic cells are remarkable similar, but structurally different ▪ muscle cells – organelles providing energy needed for contraction ▪ nerve cells – long and thin to carry impulses over distance 16 1.4.4 The Plasma Membrane The plasma membrane surrounds the cell and: • separates a cell from its environment • selectively permeable to permit movement of some substances into and out of the cell while blocking others • enables transfer of information between environment and cell 1.4.4.1 Plasma Membrane Structure The structure of plasma membrane is a lipid bilayer which is consist of: • phospholipids – hydrophilic head and hydrophobic tail • cholesterol – stablise membrane structure, rigidity • proteins – for transportation of substances • carbohydrates – recognition patterns for cells and organisms 1.4.2 Membrane Transport • Passive Transport – transports a substance without having to expend energy ◦ moves with the concentration gradient ◦ diffusion – movement of molecules from high concentration to low concentration ▪ directly through the lipid bilayer – O2, CO2, urea ▪ through protein channels – water and ions ▪ facilitated diffusion – transport protein changing shape to transport molecules through the bilayer, eg. glucose 17 ◦ osmosis – diffusion of water across a selectively permeable membrane ▪ water moves from low solute concentration to high solute concentration ▪ osmotic pressure – fluid pressure required to exactly oppose osmosis • Active Transport – moves substances from low concentration to high concentration with energy ◦ moves against the concentration gradient ◦ requires a membrane protein ◦ requires ATP or other energy source • Endocytosis and exocytosis to move larger molecules or materials in bulk ◦ endocytosis – brings substances into the cell ▪ substances are surrounded by a membrane-bound vesicle ◦ exocytosis – expels substances from the cell ▪ substance is contained with a membranous vesicle which fuses with the membrane to release the substance to the external environment 18 1.4.2.1 Cell Volume Regulation The Sodium-Potassium pump maintains cell volume by expelling excess sodium ions and stockpile potassium ions. The rate of transport by the sodium-potassium pumps determines the cell volume. • increase in cell volume – more water in cytoplasm ◦ inhibit the pump activity to allow more sodium into the cell • decrease in cell volume – less water in cytoplasm ◦ promoting the pump activity to remove sodium ions from the cell The tonicity of extracellular fluid also determines cell volume. • tonicity – relative concentration of solutes in two fluids • isotonic – concentrations of both extracellular and intracellular solutes are equal ◦ normal cell volume is maintained ◦ regulatory mechanisms to maintain tonicity of extracellular fluids to be isotonic • hypertonic – solute concentration is higher in extracellular fluid ◦ water diffuse out of cell – cell shrinks and die • hypotonic – solute concentration is higher in cytoplasm ◦ water diffiuse into cell – cell swells and burst 19 1.4.5 The Nucleus The nucleus contains the genetic information of the cell and controls all of the activities of the cell. 1.4.5.1 The Nucleus Structure • • • • double-layered nuclear membrane – separates the nucleus from the cytoplasm ◦ outer membrane of the nuclear envelop is continuous with rough endoplasmic reticulum nuclear pores – control the movement of substances between the nucleus and the cytoplasm ◦ small molecules and ions move via passive diffusion ◦ most large molecules (RNAs and protein) cannot pass through the nuclear pores – requires active transport ◦ larger than a ribosome chromosomes/chromatin nucleolus – produce ribosomes ◦ prominent in cells that synthesize large amounts of protein, such as muscle and liver cells ◦ disperse and disappear during cell division 1.4.5.2 Ribosomes Ribosomes are sites of protein synthesis made of ribonucleic acid (rRNA) and can be found free floating in cytoplasm or bound to outer surface of endoplasmic reticulum. • free – synthesize proteins for immediate use in the cell • bound – synthesize proteins that will be transported to other organelles or exported form the cell. 20 1.4.6 Organelles 1.4.6.1 Endoplasmic Reticulum The endoplasmic reticulum (ER) is the manufacturing center of the cell. It is a highly folded membranous network and there are two types of ER: • Rouch ER – has ribosomes on surface ◦ protein manufacturing, particularly those that will be secreted form the cell • Smooth ER – no ribosomes on surface ◦ lipid synthesis, including the synthesis of some hormones ◦ packaging of proteins and lipids for delivery to Golgi apparatus 1.4.6.2 Golgi Apparatus The Golgi apparatus modifies, sorts, packages, and transports proteins received from the rough ER. • vesicles – membrane-bound ◦ secretory – discharge processed proteins via exocytosis into extracellular fluid ◦ endocytic – ferry molecules to the plasma membrane or other organelles ◦ peroxisomes – contains enzymes that detoxify wastes produced by the cell ◦ lysosomes – contains digestive enzymes 1.4.6.3 Mitochondria The mitochondria is the power plant of the cell. It generates most of the ATP through aerobic respiration. The number of mitochondria within a cell will vary according to the cell’s energy requirement. • double membrane structure ◦ inner membrane is highly folded – increases surface area for chemical reactions • generates ATP using glucose, other carbohydrates, fats and protein ◦ glucose is the primary source of energy ◦ one glucose molecule yield 36 ATP ◦ ATP is required to do cellular work 21 Note: • Metabolism – sum of all chemical reactions in an organism • Two types of metabolic pathways: ◦ anabolism ▪ assembly of larger molecules from smaller ones ▪ require ATP ◦ catabolism ▪ breakdown of larger molecules to smaller ones ▪ release ATP • Cellular respiration – the breakdown of glucose in the presence of oxygen to yield ATP 1. glycolysis 2. oxidation of pyruvate 3. citric acid cyle 4. electron transport system Glycolysis: • occurs in the cytoplasm • series of 10 reactions that split glucose into two molecules of pyruvic acid (pyruvate) • net yield – 2 ATP ◦ requires investment of 2 ATP ◦ 4 ATP are produced • coenzyme NAD+ picks up high-energy electrons and H+ to form NADH 22 Oxidation of Pyruvate: • pyruvate enters mitochondria ◦ acetyl group snipped off of pyruvate and release a molecule of CO 2 ◦ oxidation of the two-carbon molecule previously to form acetyl CoA ▪ NAD+ reduced to NADH ▪ joining the acetyl group to coenzyme A ▪ enzyme required – pyruvate dehydrogenase complex ◦ Acetyle CoA then enter citric acid cycle The Citric Acid Cycle: • occurs in mitochondria • cyclic series of eight reactions which break down the acetyl CoA ◦ acetyle CoA joins with oxaloacetate to form citrate ◦ citrate converted to isocitrate ◦ isocitrate oxidised to form a five-carbon molecule (α-ketoglutarate) ▪ enzyme required – isocitrate dehydrogenzse, important regulation of the speed of the citric acid cycle ▪ NAD+ reduced to NADH ◦ α-ketoglutarate oxidised to form a four-carbon molecule (succinyl CoA) ▪ enzyme required – α-ketoglutarate dehydrogenase, also important regulation of the citric acid cyle ◦ coA group of succinal CoA replaced by phosphate group and then transferred to ADP to make ATP and form succinate ◦ succinate is oxidised to form fumarate ▪ 2 hydrogen atoms are transferred to FAD to form FADH2 ▪ enzyme required is embedded in the inner membrane of the mitochondrion – electrons are directly transferred into the electron transport chain ◦ water is added to fumarate to form malate ◦ malate is oxidised to form oxaloacetate ▪ NAD+ reduced to NADH • oxaloacetate generated at the end of one full turn of the cycle • outcome – 1 ATP, 2 NADH, 1 FADH 2 are produced and 2 CO 2 are released per cycle ◦ 2 ATP and 4 CO2 per glucose molecule 23 The Electron Transport System (Oxidative Phosphorylation): • occurs in inner mitochondrial membrane • takes electrons from NADH and FADH2 • generates ATP by moving electrons from one electron carrier to another ◦ NADH – very good electron donor (electrons at high energy level) in redox reactions ▪ transfer electrons directly to complex I ▪ energy released used to pump protons from the matrix into the intermembrane space ◦ FADH2 – poorer electron donor ▪ transfer electrons to complex II – does not pump protons across the membrane ▪ contributes less to the proton gradient ◦ final xomplext passes the electrons to O2 which splits into two oxygen atoms and accepts protons to form water • generates most of ATP in cell respiration process 24 25 Anaerobic Pathway • ATP generation without oxygen • glycolysis continues – pyruvate generates normally • pyruvate converts to lactic acid instead ◦ build up in muscles causing a burning sensation ◦ lactic acid will be metabolised aerobically once oxygen becomes available • outcome – 2 ATP produced per molecule of glucose 1.4.7 Cytoskeleton The Cytoskeleton forms framework to maintain the shape of the cell. It supports and anchors other cellular structures. It is also responsible for cell movements. • microtubules – hollow tubes of protein • microfilaments – thin solid fibers of protein 26 2.0 • • • Cardiovascular System Cardiovascular system – closed continuous system Blood flow – arteries → arterioles → capillaries → venules → veins → heart Heart – double pump ◦ systemic circulation ◦ pulmonary circulation 2.1 Heart • • • • • Located in the mediastinum Enclosed by the pericardium ◦ fibrous parietal layer ◦ serous visceral membrane – epicardium Heart wall – epicardium, myocardium (cardiac muscle), endocardium Right atrium (RA) – receives blood from the superior vena cava, inferior vena cava and the coronary sinus Right ventricle (RV) – receives blood from RA and sends blood to the lungs 27 6.0 Musculoskeletal System 6.1 Functions of the Skeletal System • • • • • • Support – for soft tissues and providing attachment points for the tendons of most skeletal muscles Protection – prevent important internal organs from injury Assistance in movement – movement by attaching muscles Mineral homeostasis – calcium, phosphate and fat; storage and release Blood cell production – red bone marrow, haemopoiesis ◦ has developing blood cells, adipocytes, fibroblasts and reticular fibres ◦ more red bone marrow in newborn than in adults ◦ red bone marrow turns into yellow bone marrow with age Triglyceride storage – adipose cells in yellow bone marrow 6.2 Structure of Bone • • • • • • • Diaphysis – shaft of the bone made of compact bone and filled with yellow marrow Epiphysis – ends of the bone made mostly of spongy bone ◦ contains red bone marrow Articular cartilage – hyaline cartilage found on the ends of long bones Metaphyses – between diaphysis and epiphyses ◦ epiphyseal plate – a layer of hyaline cartilage allowing the growth of diaphysis ◦ epiphyseal line – epiphyseal plate replaced by bone in adults Periosteum – outer covering of fibrous connective tissue ◦ associated with blood supply that surrounds the bone surface wherever it is not covered by articular cartilage ◦ dense irregular connective tissue - outer layer ◦ osteogenic layer – inner layer ◦ perforating fibres (Sharpey’s fibres) – attachment to bone with thick bundles of collagen that extend from the periosteum into the bone extracellular matrix ◦ protects the bone ◦ assist in fracture repair ◦ help nourish bone tissue ◦ serve as attachment point for ligaments and tendons Medullary cavity – hollow, cylindrical space within the diaphysis ◦ contains fatty yellow bone marrow and blood vessels ◦ minimise the weight of bone ◦ provide maximum strength – tubular design Endosteum – thin membrane which lines the medullary cavity 28 6.3 Histology of Bone Tissue • Osseous tissue – contains an abundant extracellular matrix ◦ 15% water, 30% collagen fibres, 55% crystallised mineral salts ◦ hydroxyapatite – mostly calcium phosphate and some calcium hydroxide ◦ other minerals – calcium carbonate, magnesium, fluoride, potassium and sulphate ◦ calcification – hardening of the collagen fibres and mineral salt deposits ▪ collagen fibres – provide tensile strength; resistance to stretch ▪ minerals – provide hardness 6.3.1 Compact Bone • • • • • • The strongest form of bone tissue Provides protection and support Resist the stresses produced by weight and movement osteon – repeating structural units ◦ concentric lamellae – circular plates of mineralised extracellular matrix ◦ central canal – small network of blood vessles and nerves ◦ lacuna – between concentric lamellae containing osteocytes ◦ canaliculi – small channels filled with extracellular fluid connecting lacunae with one another and with the central canals ▪ provides a transportation system for nutrients, oxygen and wastes for osteocytes neighbouring osteocytes communicate via gap junctions perforating canals (Volkmann’s canals) – transverse canals containing blood vessels and nerves from periosteum to medullary cavity 6.3.2 Spongy Bone • trabecular/cancellous bone tissue - 29 30
