Chapter 41 Physiology, Homeostasis, and Temperature Regulation Biology 102 Tri-County Technical College Pendleton, SC

Introduction Tissue is a group of cells with common structure and function Cell  tissue  organ  organ systems  organism Epithelial tissue: cuboidal, columnar, squamous Connective tissue: adipose, cartilage, bone Muscle tissue: skeletal (striated), cardiac, smooth Nervous tissue: neurons and glial cells

Tissues Visual Lining, transport, secretion, and absorption Support, strength, and elasticity Movement Information synthesis, communication, and control

Epithelial Tissue Formed from sheets of tightly packed cells, covers outside of body & lines organs and body systems Cells closely joined and riveted by tight junctions Functions as barrier against mechanical injury, invading organisms, and fluid loss Free surface exposed to air or fluid

Epithelium, cont. Cells at base attached to basement membrane (dense layer of extracellular material) Characterized by number of layers and shape of free surface cells Simple = one layer thick Stratified = multiple tiers (layers) of cells Pseduostratified = one layer that appears to be multiple because they vary in length

Epithelium, III Cell shapes are cuboidal (dice), columnar (bricks on end), or squamous (flat tiles) Cuboidal epithelium = epithelia of kidney tubules Columnar epithelium = lining of intestines Squamous = line air sacs of lungs

Connective Tissue Characterized by sparse cell population in an extensive extracellular matrix Functions to bind and support other tissues Matrix is web of fibers embedded in homogenous ground substance Consists of loose weave of 3 types of proteinaceous fibers: collagenous, elastic, and reticular

Connective, cont. Collagenous fibers are bundles of fibers containing 3 collagen molecules each, have great tensile strength and resist stretching Elastic fibers are long threads of protein (elastin); lend tissue resilience to quickly return to original shape Reticular fibers are branched; form tightly woven fabric joining connective tissue to adjacent tissues

Major types of Connective Tissue Loose connective, adipose, fibrous connective, cartilage, bone, and blood Adipose tissue is loose connective tissue specialized to store fat in adipose cells distributed throughout its matrix Insulates body and stores fuel molecules Each adipose cell has one large fat droplet Adipose tissue covers some internal organs

Connective Types, cont. Cartilage composed of collagenous fibers embedded in chondroitin sulfate (protein- carbohydrate substance) Chondrocytes secrete both collagen and chondroitin sulfate Makes cartilage both strong and flexible Chondrocytes confined to lucunae (scattered spaces within ground substance)

Connective Types, III Cartilage composes skeleton of all vertebrate embryos Retained in some areas: nose, ears, trachea, intervertebral discs, and ends of some bones BONE is mineralized connective tissue Osteoblasts are bone forming cells Deposit matrix of collagen & calcium phosphate which hardens into mineral hydroxyapatite

Connective Types, IV Makes bones hard but not brittle Bone consists of repeating Haversian systems (concentric layers or lamellae around central canal containing blood vessels/nerves Once osteoblast trapped in secretion, called osteocyte

Connective Types, V Osteocytes located in spaces called lucunae surrounded by hard matrix and connected by extensions called canaliculi In long bones, inner area filled with spongy bone tissue called bone marrow Skeleton composed mostly on bone tissue Blood is only LIQUID connective tissue

Muscle Tissue Consists of long, excitable cells capable of contraction In muscle cell cytoplasm are parallel bundles of microfilaments made of contractile proteins actin and myosin Most abundant tissue in most animals Three types of muscle tissue: Skeletal, cardiac, and smooth

Muscle, cont. Skeletal responsible for voluntary movements Attached to bones by tendons Microfilaments aligned to form banded (striated) appearance Cardiac forms contractile wall of heart Striated and branched Each joined by intercalated disks (relay contractile impulse from cell to cell)

Muscle, III Smooth is not striated Found in walls of internal organs (digestive tract, bladder) and arteries Spindle-shaped cells contract slowly, can retain contracted condition longer than skeletal muscle Responsible for involuntary movements (churning of stomach)

Nervous Tissue Senses stimuli and transmits signals from one part of animal to another Neuron is nerve cell specialized to conduct impulse or biochemical signal Cell body (soma); dendrites (extensions that conduct impulses to cell body), and axon (extension that transmits impulses away from cell body) Cells of brain and spinal cord (CNS) and nerves (PNS)

Cell Size Must have enough surface area in contact with aqueous medium to allow for adequate exchange of dissolved oxygen, nutrients, & wastes Critical factor limiting cell size is surface area to volume ratio Most complex animals have smaller surface area to volume ratio and thus lack adequate exchange area on outer surface Instead, highly folded, moist, internal surfaces exchange materials with environment

Cell Size, cont. Circulatory system shuttles materials between these specialized exchange surfaces Environmental exchange surfaces are internal and protected from desiccation, so animal can live on land Cells bathed with internal body fluid Animal can control the quality of the cells immediate environment

Body Shapes Single-celled organisms have entire surface area in contact with environment Two-layered sac has body wall only 2 cell layers thick (body cavity of Hydra) Flat-shaped body with maximum surface area exposed to aqueous environment (tapeworm) Highly folded, moist, internal surface (most complex animals)

Interstitial Fluid Interstitial fluid is the fluid between the cells that comprise the internal environment of vertebrates Fills spaces between cells Exchanges nutrients and wastes with blood carried in the capillaries

Homeostasis Homeostasis is dynamic state of equilibrium in which internal conditions remain relatively stable “Steady state” Allows organism to maintain (fairly) constant conditions in internal environment even when external environment changes

Feedback Mechansims Negative feedback is homeostatic mechanism that stops or reduces intensity of original stimulus and consequently causes a change in the variable that is in opposite direction to initial change Most common homeostatic mechanism in animals Lag time between sensation and response so variable drifts slightly above and below set point Thermostatic control of room temperature

Feedback, cont. Positive feedback is homeostatic mechanism that enhances the initial change in a variable Rarer than negative feedback Controls “episodic events” Examples are childbirth, milk let down, and blood clotting

Body Temperature Living cells function over very narrow temperature range Below 0 o C, ice crystals damage cellular structures, possibly fatally Some animals possess “antifreeze” molecules Nearly all animal cells must remain above 0 o C to stay alive

Body Temperature, cont. Upper temperature limit is less than 45 o C for most cells Biochemical reactions and physiological processes are temperature-sensitive General rule is that reaction rates 2x or 3x as temperature >s by 10 o C Changes in temperature shifts rates of some some reactions more than others Disrupts balance and integration that processes require

Body Temperature, III For homeostasis, organisms must be able to compensate for or prevent changes in temperature Poikilotherm versus homeotherm Ectotherms versus endotherms Behavior, blood flow, heat production, shivering, decreasing heat loss, evaporation of water, fevers, daily torpor versus hibernation