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

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

Celltissueorganorgan 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 VisualLining, 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 0oC, ice crystals damage cellular structures, possibly fatally Some animals possess “antifreeze” molecules

Nearly all animal cells must remain above 0oC to stay alive

Body Temperature, cont.

Upper temperature limit is less than 45oC for most cells

Biochemical reactions and physiological processes are temperature-sensitive

General rule is that reaction rates 2x or 3x as temperature >s by 10oC

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