BIOL 2312.003 Introduction to Modern Biology II Dr. Mazambani Spring 2024 Lecture 1 – Chapter 38 Introduction to Animal Organization and Physiology Understanding organisms • Anatomy is the study of the structures of organisms – What does it look like? – What is it made of? • Physiology is the study of the functions of organisms – What does it do? – How does it do it? – What is its purpose? Homeostasis Cells • Cells are the basic structural and functional units of all living organisms • Cells carry out the essential processes of life. • Movement • Reproduction • Sensitivity • Nutrition • Excretion • Repiration • Growth Multicellular Organisms • Can create an internal environment – fluid that supplies all the needs of individual cells: • nutrient supply • waste removal and • osmotic balance – allows occupation of diverse external environments that would be lethal to single cells • can become relatively large – because their individual cells are small enough to exchange materials with the internal environment • major life functions to be subdivided among specialized groups of cells – with each group concentrating on a single activity Question Multicellularity allows major functions to be subdivided among specialized groups of cells. Why is this beneficial? Requirements of individual animal cells Must be surrounded by an aqueous solution containing ions and molecules in concentrations that maintain osmotic balance Organic molecules as an energy source Oxygen for oxidative reactions Removal of waste molecules and other by-products Environmental conditions within tolerable limits Levels of organization A tissue is a group of cells with the same structure and function, working together as a unit to carry out one or more specialized activities An organ integrates two or more different tissues into a structure that carries out a specific function (e.g., eye, liver) An organ system (body system) coordinates the activities of two or more organs to carry out a major body function such as movement, digestion, or reproduction Animal Tissues • The structure and function of a tissue is determined by: – Properties of the individual cells that make up the tissue – Structure and organization of the cytoskeleton – Type and organization of the extracellular matrix (ECM) surrounding the cell – The junctions holding cells together Types of Cell Junctions • Anchoring junctions form buttonlike spots or belts that weld cells together – most abundant in tissues subject to stretching, such as skin and heart muscle • Tight junctions seal spaces between cells, keeping molecules and ions from leaking between cells – e.g. in tissue lining the urinary bladder • Gap junctions open channels between cells in the same tissue, allowing ions and small molecules to flow freely from one to another – e.g., between muscle cells Animals have four basic tissue types: Animal Tissues • epithelial • connective • muscle • nervous Question There are 4 primary tissue types, based on structure and function Cell Functions Organ system: A set of organs that interacts to carry out a major body function Organ: Body structure that integrates different tissues and carries out a specific function Stomach Epithelial tissue: Protection, secretion, and absorption Connective tissue: Structural support Muscle tissue: Movement Nervous tissue: Communication, coordination, and control Stepped Art Epithelial Tissues • Consist of sheet-like layers of cells, usually connected by tight junctions with little extra cellular matrix (ECM) between them • Cover body surfaces and the surfaces of internal organs, and line cavities and ducts within the body Epithelial Tissue Organization The epithelium’s outer, apical surface may be exposed to water, air, or fluids within the body The inner, basal surface adheres to a layer of ECM secreted by epithelial cells called the basal lamina, which fixes the epithelium to underlying connective tissues Epithelial Tissue Apical Features • In internal cavities and ducts, the apical surface is often covered with cilia, which move fluids through the cavity or duct (e.g., epithelium lining the oviducts in mammals) • In some epithelia, including the lining of the small intestine, the free surface is covered with microvilli – fingerlike extensions of the plasma membrane that increase the area available for secretion or absorption Types of Epithelium Epithelia are classified as • simple (formed by a single layer of cells) or • stratified (formed by multiple cell layers) Cell shapes within an epithelium may be • squamous (flattened) • cuboidal (cube-shaped) • columnar (elongated) Four principal types of epithelium are found in the body: • simple squamous epithelium • stratified squamous epithelium • cuboidal epithelium • columnar epithelium Simple Squamous Epithelium • Description: Layer of flattened cells • Common locations: Blood vessel walls; air sacs of lungs • Function: Diffusion Stratified Squamous Epithelium • Description: Several layers of flattened cells • Common locations: Skin and other surfaces subject to abrasion, such as the mouth, esophagus, and vagina • Function: Protection against abrasion; typically not involved in secretion or absorption Cuboidal Epithelium • Description: Layer of cube-like cells; free surface may have microvilli • Common locations: Glands and tubular parts of nephrons in kidneys • Function: Secretion, absorption Columnar Epithelium • Description: Layer of tall, slender cells; free surface may have microvilli • Common locations: Lining of gut and respiratory tract • Function: Secretion, absorption Epithelial Stem Cells Some epithelial cells divide constantly – new cells are produced by division of stem cells in the basal layer of the skin Stem cells are undifferentiated cells that divide to produce more stem cells or differentiating cells that become specialized body cells Stem cells are found in adults and embryos – adult stem cells are also found in the brain, bone marrow, blood vessels, skeletal muscle, and liver Glands • Epithelia give rise to cells specialized for secretion – some are scattered among nonsecretory cells within the epithelium, others form glands • Endocrine glands are ductless – they release hormones which are distributed by the circulatory system (e.g., pituitary gland, adrenal gland, and thyroid gland) • Exocrine glands are connected to the epithelium by a duct, which empties their secretion at the epithelial surface (e.g., mucus, saliva, sweat, earwax, oils, and milk) Question Identify the different types of squamous epithelia below Connective Tissue • Connective tissues consist of cells that form networks or layers in and around body structures. • Functions: provide support, protection, connecting structures, storage of fats, producing blood cells, aiding tissue repair. • Mechanical properties depend on type and quantity of extracellular matrix (ECM) present in the tissue. • Many forms of connective tissue have more ECM (by weight and volume) than cellular material • Connective tissues contain several cell types. Most common cell type is the fibroblast which secretes proteins in the ECM. These proteins assemble into fibers Six Types of Connective Tissues Extra-Cellular Matrix (ECM) Mechanical properties of a connective tissue depend on the type and quantity of its ECM Consistency of ECM ranges from fluid (blood and lymph), through firm gels (tendons), to hard and crystalline (bone) Extracellular Matrix proteins • ECM in most connective tissues consists primarily of the fibrous glycoprotein collagen embedded in a network of proteoglycans • In bone, the glycoprotein network is impregnated with mineral deposits that produce a hard, somewhat elastic structure • Another family of glycoproteins, fibronectin, aids in attachment of cells to ECM and helps hold cells in position • Elastin fibers help some connective tissues return to their original shape when pulled or stretched (e.g., skin, lungs) • The protein resilin, found only in insects and some crustaceans, is the most elastic material known Loose Connective Tissue • Loose connective tissue consists of sparsely distributed fibroblast cells surrounded by an open network of collagen and other glycoprotein fibers • Loose connective tissues support epithelia and form a band around blood vessels, nerves, and some internal organs – they also reinforce deeper layers of the skin • Sheets of loose connective tissue form mesenteries, which hold abdominal organs in place and provide lubricated, smooth surfaces that prevent chafing or abrasion Dense Connective Tissue • Fibroblasts are sparsely distributed among dense masses of collagen and elastin fibers that are lined up in highly ordered, parallel bundles • The parallel arrangement produces maximum tensile strength and elasticity • Examples: tendons, ligaments, cornea of the eye • Function: Strength, elasticity Cartilage • Cartilage consists of sparsely distributed chondrocytes surrounded by networks of collagen fibers embedded in a tough elastic matrix of the glycoprotein chondroitin sulfate • Elastin is also present in some forms of cartilage – elasticity allows cartilage to resist compression and stay resilient • In humans, cartilage is found in the ears, nose, larynx, trachea, intervertebral disks, and ends of bones in joints • Cartilage also serves as a precursor to bone during embryonic development • Common locations: Ends of long bones, ears, nose, parts of airways, skeleton of vertebrate embryos • Function: Support, flexibility, low-friction surface for joint movement Bone Bone forms the skeleton, which supports and protects the body and contributes to body movements Mature bone consists primarily of osteocytes embedded in an ECM containing collagen fibers and glycoproteins impregnated with hydroxyapatite Bone is reshaped continuously by osteoblasts, which produce collagen and minerals, and osteoclasts, which remove minerals and recycle them through the bloodstream This Photo by Unknown Author is licensed under CC BY-SA-NC Bone Anatomy • The structural unit of bone, the osteon, consists of a minute central canal surrounded by osteocytes embedded in concentric layers of mineral matter • Blood vessels and extensions of nerve cells run through the central canal, which is connected to the spaces containing cells by radiating canals filled with interstitial fluid • Blood vessels supply nutrients to cells that build bone, and nerve cells connect bone cells to the body’s nervous system Adipose Tissue • Adipose tissue contains large, densely clustered adipocytes that are specialized for fat storage – it has little ECM • Excess carbohydrates are converted into fats and stored in adipocytes • Adipose tissue is richly supplied with blood vessels, which move fats or their components to and from adipocytes • Adipose tissue also cushions the body and, in mammals, forms an insulating layer under the skin Blood Blood is the major transport vehicle of the body: • Carries oxygen and nutrients to body cells • Removes wastes and byproducts such as carbon dioxide • Maintains the internal fluid environment, including the osmotic balance between cells and interstitial fluid • Transports hormones and other signal molecules that coordinate body responses Blood Blood cells are suspended in a fluid ECM – plasma – a solution of proteins, nutrient molecules, ions, and gases Erythrocytes (red blood cells) are packed with hemoglobin that binds and transports oxygen Leukocytes (white blood cells) protect the body against invading viruses, bacteria, and other pathogens Platelets (membrane-bound fragments of specialized blood cells) participate in blood clotting Muscle Tissue • Muscle tissue consists of cells that have the ability to contract (shorten) • Contractions are produced by the interaction of two proteins: – actin – myosin • Muscles move body limbs and other structures, pump blood, and produce a squeezing pressure in internal organs • Vertebrates have three types of muscle tissue: – Skeletal – Cardiac – Smooth Skeletal Muscle Attached by tendons to the skeleton and helps move body parts and maintain posture Cells (muscle fibers) are multinucleate and striated (actin and myosin molecules are arranged in parallel units that give the tissue a banded appearance) Contracts voluntarily in response to signals carried by the nervous system Contractions release heat that helps mammals, birds, and some other vertebrates maintain their body temperatures Cardiac Muscle • Striated muscle that contracts spontaneously (involuntary) • Cells are short and branched, with each cell connected to neighboring cells at intercalated disks • Cells form an interlinked network, stabilized by anchoring junctions and gap junctions, which enables heart muscle to contract in all directions Smooth Muscle • Found in the walls of tubes and cavities, including blood vessels, stomach, intestine, and bladder • Cells are small and spindle-shaped, and their actin and myosin molecules are arranged in a loose network (smooth rather than striated) • Cells are connected by gap junctions that allow them to contract as a unit – contractions can be maintained at steady levels for a long time Question Identify the different muscle types Nervous Tissue • Contains nerve cells (neurons) that serve as lines of communication and control between body parts and glial cells • Glial cells physically support and provide nutrients to neurons, provide electrical insulation between them, and scavenge cellular debris and foreign matter • A neuron consists of a: – cell body – dendrites (highly branched extensions that receive signals) – axons (longer extensions that send signals) Coordination of Tissues in Organs and Organ Systems • In tissues, organs, and organ systems, each cell engages in basic metabolic activities for its own survival, and performs one or more functions for the system to which it belongs • All vertebrates (and most invertebrates) have eleven major organ systems whose functions are coordinated and integrated to accomplish vital tasks in the organism • Together these tasks maintain homeostasis, preserving the internal environment required for survival of the body Functions of Organ Systems Integrated functions of organ systems: • Acquiring, processing, and distributing required substances, and disposing of wastes • Synthesizing protein, carbohydrate, lipid, and nucleic acid molecules required for body structure and function • Sensing and responding to changes in the environment (e.g., temp., pH, ion concentrations) • Protecting the body against injury or attack from other animals, and from disease-causing agents • Reproducing, nourishing and protecting offspring through their early growth and development ECF and ICF • Each cell in a multicellular organism receives nutrients and O2, and eliminates wastes, via the extracellular fluid (ECF) • The ECF has two components: – Plasma, the fluid portion of blood – Interstitial fluid, the fluid that surrounds the cells • The ECF is the transitional zone connecting the intracellular fluid (ICF) to the external environment • Nutrients and O2 in the plasma reach the interstitial fluid through capillaries – waste moves in the opposite direction Question Which of these is responsible for bone resorption? a. b. c. d. Osteocytes Osteclasts Osteoblasts Osteons Homeostasis • The composition of ECF and other aspects of the internal environment (such as temperature) must be regulated within a narrow range • Maintenance of the internal environment in a relatively stable state is homeostasis – a dynamic process in which internal adjustments are made continuously to compensate for external changes in order to maintain a steady state • The factors controlled by homeostatic mechanisms all require energy that must be acquired from the external environment Homeostatic Control Systems Humans and other mammals maintain a consistent internal environment, but many other animals are more variable in their internal environments Regulators maintain factors of the internal environment in a relatively constant state (e.g., mammals and birds are thermoregulators) Conformers have internal environments that match the external environment (e.g., fishes, reptiles, and insects are thermoconformers) Factors of the Internal Environment Nutrient concentration Concentration of O2 Concentration of CO2 Concentration of waste chemicals Concentration of water and NaCl pH Volume and pressure of plasma Temperature (of warm-blooded animals) Local and Systemic Controls Local homeostatic controls operate only within an organ where a change in internal environment needs to be addressed (e.g., increased blood flow to a working muscle) Systemic homeostatic controls are initiated outside of an organ or organ system to control that organ’s or organ system’s activity (e.g., maintaining blood pressure) and controlled through nervous system endocrine system Negative Feedback Control Tissue or organ that detects a change A change in in factors subject the environment to triggering a homeostatic response control, that compensates such as pH or for the change temperature Stimulus Sensor A control center that receives information from the sensor and initiates steps to correct the environmental change by comparing the detected change with a set point, the level at which the condition controlled by the pathway is to be maintained. Integrator A system or systems activated by the integrator to return the condition to the set point. Effectors may include The physiological parts of actions that return essentially the condition to any body tissue or organ. the set point Effector (s) Compensatory response Environmental condition returned to set point Negative feedback cancels the system responsible for the response. Stepped Art Temperature Control in Mammals • Humans maintain body temperature near a set point by negative feedback mechanisms • If blood temperature falls, the hypothalamus activates effectors that constrict blood vessels, reducing heat loss from the skin – other effectors induce shivering to generate heat • If blood temperature rises, the hypothalamus activates effectors that dilate blood vessels, increasing heat loss – other effectors induce sweating, which cools the skin Stimulus The husky is active on a hot, dry day, and its body surface temperature rises. Sensors Response Neurons in the hypothalamus detect the increase in brain and body temperature. Integrator The network of neurons compares brain and body temperature against a set point. Temperature of brain and body decreases. Many Effectors carry out specific responses: Salivary glands Skeletal muscles Smooth muscle in blood vessels Husky starts to pant, increasing heat loss by evaporation of water from lungs, throat, mouth, and tongue. Blood carrying metabolically generated heat circulates through lungs, throat, mouth, and tongue. Secretions from glands increase evaporation of water from tongue, mouth, and throat. Temperature Control in Other Animals • While mammals and birds regulate their internal body temperature within a narrow range around a set point; other vertebrates regulate over a broader range • Snakes and lizards respond behaviorally to variations in environmental temperatures – they bask in the sun on cool days, and move to shady spots when it is hot • Dragonflies, moths, and butterflies use muscular contractions equivalent to shivering when their body temperature falls below the level required for flight Positive Feedback Mechanisms • Under certain circumstances, animals respond to a change in the internal or external environment by a positive feedback mechanism that intensifies or adds to the change – Example: Childbirth contractions trigger stretch sensors that signal the hypothalamus to release oxytocin from the pituitary gland – oxytocin then increases the uterine contractions • Because positive feedback mechanisms do not result in homeostasis, they are not as common as negative feedback Set Points Can Change • Some regulated factors change in predictable and cycling patterns called biological rhythms or biorhythms • Many biorhythms correlate with regular environmental changes – Example: In mammals, many physiological processes have a 24-hour rhythm called a circadian rhythm • When a set point changes naturally because of an alteration in environmental conditions, it is called acclimatization • Acclimatization is a temporary change in a physiological process that occurs during the life of an animal, whereas evolutionary adaptation is a change that occurs at the genetic level over many generations • When a set point changes artificially in a laboratory setting, it is called acclimation
