ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Forty-Three Outline INTRODUCTION All Vertebrates Share the Same Body Plan and Operation Humans Are Representative Vertebrates of Special Importance THE HUMAN ANIMAL General Body Architecture fig 43.1 Digestive tube suspended within internal body cavity Coelom divided into two parts Thoracic cavity: heart and lungs Abdominal cavity: stomach, intestines and liver Supported by internal skeleton of jointed bones Bony skull surrounds brain Column of hollow vertebrae surrounds dorsal spinal nerve cord Levels of Organization in the Body Four levels: cells 9 tissues 9 organs 9 organ systems Groups of cells with similar structure and functions are called tissues Three fundamental embryonic tissues: endoderm, mesoderm and ectoderm Four principal adult tissues: epithelial, connective, muscle, nerve fig 43.2 Organs are a structural and functional unit composed of different tissues tbl 43.1 Example: the heart Contains cardiac muscle tissue wrapped in connective tissue Embedded with nerves and blood vessels Work together to pump blood through the body Organ system is group of organs that function together to carry out body activities Example: digestive system Humans contain eleven principal organ systems tbl 43.2 EPITHELIAL TISSUE FORMS MEMBRANES AND GLANDS Epithelium Covers Every Surface of the Body Examples Epidermis derived from embryonic ectoderm, comprises outer layer of skin Inner surface of digestive tract lined with endoderm derived epithelium Inner surface of Body cavities lined with mesoderm derived epithelium Functions of epithelial tissues Provide selectively permeable barrier Facilitate or impede passage of materials into underlying tissues Any entering or exiting substance must cross an epithelial layer that covers or lines all body surfaces Protect underlying tissue from dehydration and mechanical damage Provide surface for sensory nerve to act Secrete materials via glands Characteristics of epithelial layers Are only a few cell layers thick Cells contain little cytoplasm and have low metabolic rates Possess few blood vessels, transport materials via diffusion Readily regenerated Two general classes Simple epithelium Stratified epithelium Further subdivided by cell shape Simple squamous: flat cells Simple cuboidal: equal height and width Columnar: height greater than width Simple Epithelium fig 43.3 A single cell layer thick Simple squamous cells Line lungs and major cavities Have irregular, flattened shape with tapered edges Permit rapid passage of molecules across membrane Simple cuboidal cells line small ducts inside glands Simple columnar cells line respiratory and gastrointestinal tract Interspersed with goblet cells Respiratory tract cells have cilia Surface of intestine is highly infolded to increase surface area Stratified Epithelium Several cell layers thick, named according to features of uppermost layers Epidermis is a stratified squamous keratinized epithelium Has an upper layer of squamous cells Superficial cells are dead and filled with keratin Glands Derived from invaginated epithelia,produce various substances Two categories of glands Exocrine glands: connected to epithelium by a duct Product channeled to outside or to body cavity Includes sweat and oil glands (external), accessory digestive glands (internal) Endocrine glands: connection with epithelium lost, ductless Secretions called hormones Hormones enter blood capillaries, don't leave body CONNECTIVE TISSUE S PERFORM A VARIETY OF FUNCTIONS Structural Building Blocks fig 43.4 Derived from mesoderm Divided into two categories Connective tissue proper: loose and dense Special connective tissue: cartilage, bone, blood Composed of widely-spaced cells imbedded in an extracellular matrix Loose Connective Tissues fig 43.5 Cells scattered within amorphous, protein ground substance Strengthened by collagen, elastin and/or reticulin fig 43.5 Fibroblasts secrete collagen and fibrous proteins fig 43.6 Contains other living cells Mast cells produce histamine and heparin Phagocytic macrophages defend against invading organisms fig 43.7 Aided by cells that leave blood capillaries and enter loose connective cells May contain adipose cells Each cell stores a droplet of fat Number of fat cells in an adult is usually fixed, can change in size Dense Connective Tissue Contains tightly packed collagen fibers May be regular or irregular In regular tissue collagen fibers are lined up in parallel Tendons bind bone to bone Ligaments bind muscle to bone In irregular tissue fibers have different orientations Tough coverings of organs like capsules of kidneys and adrenal glands Perimysium covers muscles, perineurium covers nerves, periosteum covers bones Cartilage Has special ground substance made from characteristic glycoprotein Collagen fibers laid down along lines of stress Produces firm, flexible tissue that is tough and doesn't stretch Cushions bone joints, makes up skeleton of agnathans, cartilaginous fishes Chondrocytes remain alive even with no blood vessels Bone Cartilage hardened by calcification, cells die, replaced by living bone Osteoblasts are bone cells that remain alive even though matrix is hardened with calcium phosphate Hardest tissue in body may be organized into a delicate lacework fig 43.8 Blood fig 43.8 Contains abundant matrix material: fluid plasma Cells include erythrocytes (red cells) and leukocytes (white cells) fig 43.9 Thrombocytes or platelets are fragments of a type of bone marrow cell Erythrocytes are the most common blood cells Lose nucleus, mitochondria and ER during maturation Metabolically are relatively inactive Has iron-containing hemoglobin protein, carries oxygen Several types of leukocytes Neutrophils, eosinophils, basophils have special affinity to biological stains Neutrophils are most abundant, phagocytic Mononuclear phagocyte system: During infections monocytes enter loose connective tissue and become macrophages Monocytes, macrophages, organ-specific phagocytes Lymphocytes are second most abundant leukocytes, part of immune system fig 43.7 Blood plasma contains nutrients and metabolic wastes Also contains sodium, calcium, other inorganic salts Includes proteins like fibrinogen and albumin Contains lymphocyte-produced antibodies MUSCLE TISSUE PROVIDES FOR MOVEMENT Muscle Cells Are Motors of the Vertebrate Body Possess large numbers of actin and myosin filaments, specialized for contraction Three types of vertebrate muscle: smooth, skeletal and cardiac fig 43.10 Skeletal and cardiac are also striated muscles Smooth Muscle Earliest form to evolve, found throughout animal kingdom Cells are long and spindle-shaped, each with one nucleus Cells organized into sheets to form smooth muscle tissue Two types of contraction occur All muscles contract as a unit when stimulated by nerve or hormone: i.e. muscles lining blood vessels Individual cells contract spontaneously causing slow, steady contraction of the tissue: i.e. muscles in the walls of the gut Contraction is involuntary and cannot be consciously controlled Skeletal Muscle Attached to bones by tendons, contract and cause bones to move Numerous muscle cells called muscle fibers act in concert Stronger contractions result when more fibers within muscle contract Contraction due to substructures called myofibrils fig 43.11 Contain highly ordered arrays of actin and myosin filaments Fibers produced during development by the fusion of several cells fig 43.11 A single fiber runs the length of an individual vertebrate muscle Each fiber contains all of the original nuclei of the fused cells Cardiac Muscle Vertebrate hearts made of specially arranged striated muscle fibers Composed of interconnected cells, each with its own nucleus Interconnections appear as lines called intercalated disks fig 43.10 Lines are really regions where cells are linked by gap junctions Interconnections allow heart to contract as single unit Functioning unit called myocardium Certain muscle cells generate spontaneous electrical impulse Impulses spread across gap junction from cell to cell All cells in myocardium ultimately contract Contraction represents one heartbeat NERVE TISSUE CONDUCTS SIGNALS RAPIDLY Composition of Nerve Tissue fig 43.12,13 Neurons: specialized for transmission of nerve impulses Cell body contains the nucleus Dendrites Thin, highly branched protrusions from the cell body Receive stimulation Axon Long tubular extension of the cell body Transmit nerve impulse away from the cell body Axon can be long, resulting in long nerve cell May be covered with insulating layer called myelin sheath Derived from Schwann cells Periodic interruptions called Nodes of Ranvier Nerves Are Bundles of Axon Fibers Central nervous system (CNS): link brain and spinal cord Peripheral nervous system (PNS): nerves and ganglia Sensory neurons: conduct impulses from sensory organs to CNS Motor neurons: conduct impulses from CNS to muscles or glands Interneurons/association neurons: neither sensory or motor neurons Comprise majority of neurons in CNS Responsible for information processing Supporting Cells of the Nervous System Neuroglia are supporting cells Provide more than just physical support Essential for prop[er functioning of nervous system Example: Schwann cells in PNS that make myelin HOMEOSTASIS Cell Specialization Requires Limited Extracellular Conditions Homeostasis definition: dynamic consistency of the internal environment Conditions are not constant but fluctuate within narrow limits Regulating Levels of Glucose in Blood Large amount of glucose in body after meal Glucose absorbed by liver cells Converted to glycogen for storage When blood glucose levels fall below normal Liver converts glycogen to glucose Releases glucose into blood Little change in blood plasma glucose level over time Regulating Body Temperature Neurons detect temperature increase over 37% C (98.6% F) Input to hypothalamus Triggers mechanisms to dissipate heat Induces sweating, dilation of blood vessels in skin and other things Decrease in body temperature Induces shivering and constriction of skin blood vessels Raises body temperature, corrects challenge to homeostasis Homeostasis Is Maintained by Negative Feedback Loops Feedback loop monitors body conditions and corrects deviations Negative feedback: reverse changes to condition, reduces disturbance fig 43.14 Keep value of controlled variable close to preferred set point value Sensors monitor control variable, send data to integrator Integrator compares value to set point Deviations from set point, perturbations, cause integrator to send error signal to an effector to bring about change Example: driving a car fig 43.14b Variable = position of car in lane Sensors = eyes of driver Integrator = driver's brain Setpoint = center of lane Perturbations = bumps or curves in road Error signals = deviations from setpoint Deviations result from perturbations, car off center Opposed by system of effectors, car kept in center of lane Setpoint in physiological systems may change Body temperature lower during sleep Temperature higher during fever Controls involve complex interactions between organ systems Positive Feedback Loops Are Unstable In positive feedback the disturbance is accentuated Perturbations cause effector to drive controlled variable even farther from set point Analogous to spark that ignites an explosion Example: blood clotting One factor activates another Produces cascade that leads to formation of a clot Example: contractions of uterus during childbirth fig 43.15 Stretching of uterus by fetus stimulates contraction Stimulates further stretching, more contraction Final result: fetus expelled from uterus Positive feedback systems are part of larger mechanism that maintains homeostasis