Homeostasis and the Organization of the Animal Body

Chapter 31pages 604 - 618

Hierarchy of Structures

Tissues are composed of similar cells that perform a specific function

Organs perform complex functions and include two or more interacting tissue types

Organ systems consist of two or more interacting organs that function in a coordinated manner

Cells, Tissues, Organs, Organ Systems

How Is the Animal Body Organized?

Animal tissues are composed of similar cells that perform a specific function There are four categories of animal tissues

Epithelial tissue Connective tissue Muscle tissue Nerve tissue

Epithelial Tissue

Covers the body, lines cavities, and forms glands

All body surfaces — skin, digestive, respiratory, and urinary tracts, and circulatory system

Epithelial tissue is sheets of cells firmly attached to one another by connections such as desmosomes and tight junctions

Attached to an underlying layer of fibrous proteins or basement membrane - provides support, flexibility, and strength

Cells are continuously lost and replaced

Types of Epithelium

Simple epithelium is one cell thick and lines the respiratory, urinary, reproductive, and circulatory systems

Stratified epithelium is found in the skin and just inside body openings that are continuous with the skin (mouth and anus) and are continuously lost and replaced

Several cells thick and can withstand considerable wear and tear

Epithelial Tissue

(a) Lining of the lungs (simple epithelium)

basementmembrane

mucus

cilia

mucus- producing cells

flattenedcells

basementmembrane

(b) Lining of the trachea (simple epithelium)

basementmembrane

(c) Skin epidermis (stratified epithelium)

flatteneddyingcells

deadcells

dividingcells

differentiatingcells

Skin - Epithelial Tissue

Glands Glands are cells or groups of cells specialized to secrete

large quantities of substances outside the cell

Two categories Exocrine glands secrete substances into a body cavity or

onto the body surface, usually through a duct Sweat glands, mammary glands, salivary glands, and

glands that secrete digestive enzymes

Endocrine glands lack ducts, and release hormones into the extracellular fluid, diffuses into capillaries Hormones are chemicals produced in small quantities and

transported thru the bloodstream to regulate the activity of other cells

Connective Tissues

Diverse structures and functions Support and strengthen other tissues, binding the cells

of other tissues into coherent structures, such as skin or muscle

They consist of fluid containing proteins, especially collagen

Three categories of connective tissue Loose connective tissue Dense connective tissue Specialized connective tissue

Loose Connective Tissue

The most abundant form of connective tissue, consisting of a thick fluid containing scattered cells that secrete protein

Flexible tissue connects, supports, and surrounds other tissue types, forming a framework for organs such as the liver

Dense Connective Tissue

Packed with collagen fibers that provide flexibility and strength, but only in the direction in which the collagen fibers are arranged

Tendons, which connect bones to muscles

Ligaments, which connect bones to bones

Specialized connective tissues

Diverse functions and structures

Cartilage Bone Fat (adipose tissue) Blood Lymph

Cartilage

Widely spaced cells surrounded by thick, nonliving matrix composed of collagen

It covers the ends of bones at joints, provides the supporting framework for the respiratory passages, supports the ear and nose, and forms shock-absorbing pads between the vertebrae

Flexible, but can break if bent too far

Bone

Bone resembles cartilage, but its matrix is hardened by deposits of calcium phosphate

It forms in concentric rings around a central canal, which contain blood vessels

Adipose

Adipose tissue is made up of fat cells that are modified for long-term energy storage

Can serve as insulation for animals living in a cold environment

Blood and Lymph Blood and lymph are specialized forms

of connective tissue because they are composed largely of extracellular fluids in which proteins are suspended

The cellular portion of blood - Red blood cells transport oxygen White blood cells fight infection Platelets are cell fragments that aid in

blood clotting

The blood cells are suspended in a fluid called plasma

Lymph

Lymph is fluid that has leaked out of blood capillaries, it enters the lymph vessels and is carried back to the circulatory system

Muscle Tissue

Have the ability to contract The long, thin cells of muscle tissue contract when

stimulated and then relax when the stimulation stops

There are three types of muscle tissue Skeletal muscle Cardiac muscle Smooth muscle

Skeletal Muscle

Skeletal muscle is stimulated by the nervous system and is under voluntary, or conscious, control

Its main function is to move the skeleton

Cardiac Muscle

Cardiac muscle spontaneously active, not under conscious control

Interconnected by gap junctions, through which electrical signals spread, stimulating cardiac muscles cells to contract in a coordinated fashion

Smooth Muscle

Found throughout the body, in the walls of the digestive and respiratory tracts, uterus, bladder, and larger blood vessels

Produces slow, sustained, involuntary contractions that are stimulated by the nervous system, by stretch, or by hormones or other chemicals

Nervous Tissue

Specialized to produce and conduct electrical signals

Brain, spinal cord, and nerve cells (neurons) Neurons are specialized to

generate electrical signals and conduct signals to other neurons, muscles, or glands

Glial cells surround, support, insulate, and protect neurons

How Is the Animal Body Organized?

Organs are formed from at least two types of tissues that function together; most consist of all four tissue types

Function as part of an organ system

The skin illustrates the properties of organs Outer layer of epithelial cells underlain by connective

tissue that contains a blood, nerve supply, muscle, and glandular structures derived from the epithelium

Structural Components of Skin

Epidermis, or outer layer, is specialized stratified epithelial tissue

Immediately beneath the epidermis lies a layer of loose connective tissue, the dermis, which contains blood vessels

Specialized epithelial cells dip down from the epidermis into the dermis, forming hair follicles

Below the dermis is a layer of adipose tissue

Skin is an Organ

sensory nerve endings

living epidermalcells

dead cell layer

sebaceous gland

arterioles

venules

hair follicle

muscle(pulls hair upright) sweat gland

hair shaft

epidermis

dermis

subdermalconnective and adiposetissue

capillary bed

lymph vessels

pore

Organ Systems

Two or more interacting organs, located in different regions of the body, that work together to perform a common function

Digestive system - in which the mouth, esophagus, stomach, intestines, liver and pancreas, all function together to convert food into nutrient molecules that can be absorbed into the bloodstream

Homeostasis

Animal cells need a narrow range of conditions to survive

Homeostasis is the process by which an organism maintains its internal environment, within that narrow range

How does it work?

The internal environment is maintained in a state of dynamic constancy

The internal environment is in a state of dynamic constancy

The body adjusts to ongoing internal and external changes to maintain constant conditions

Examples of Regulated Conditions

Temperature

Water and salt concentrations

Glucose concentrations

pH (acid-base balance)

Oxygen and carbon dioxide concentrations

Why is this Important?

Animal cells are constantly generating and using large quantities of ATP to sustain life processes

Continuous supplies of high-energy molecules and O2 are required to carry out the reactions that generate ATP

Energy production helps explain the importance of glucose and oxygen levels

Each of the reactions for producing ATP is catalyzed by a protein whose ability to function depends on its three-dimensional structure

This structure is maintained by hydrogen bonds, which can be disrupted if the environment is too hot, salty, acidic, or basic

The need to maintain these bonds helps explain the requirement for a narrow range of temperature, pH, and salt

Animals vary in their homeostatic abilities

Birds and mammals are efficient at maintaining homeostasis for all the internal conditions listed above

Other animals have reduced or absent homeostasis

for one or more aspects of their internal environment For example, many marine invertebrates, including

snails, crabs, and worms, cannot regulate the overall concentration of their bodily fluids

Classification

Scientists classify animals according to their major source of body warmth

Endotherms generate heat through metabolic reactions - birds and mammals Warm blooded

Ectotherms derive body heat from the environment, and maintain it by occupying a constant environment or by behavioral activities - reptiles, amphibians, fishes, and invertebrates Cold blooded

Warm-Blooded or Cold-Blooded?

Regulation

Feedback systems regulate internal conditions Homeostatic mechanisms that maintain internal

constancy are called feedback systems

Two types Negative feedback - counteracts the effects of

changes in the internal environment to maintain homeostasis

Positive feedback, - drives rapid, self-limiting changes, such as those that occur when a mother gives birth

Negative Feedback

Works by reversing the effect of a change The most important feedback mechanism A change in the environment causes responses that “feed back” to

counteract the change The overall result of negative feedback is a return to the original

condition

Three components A sensor detects the current condition A control center compares that condition to the desired state,

called the set point An effector produces an output that restores the desired condition

Animation: Elements of a Feedback System

Home temperature is regulated by negative feedback Negative feedback systems that control body temperature are similar

to those used to heat a home

The sensor is a thermometer, the control center is a thermostat, and the effector is the heater

The thermometer detects the room temperature and sends that information to the thermostat, where it is compared to the set point of the desired temperature

If the temperature is below the set point, the thermostat signals the heater to turn on and generate heat

The heater warms the room, restoring the temperature to the set point, causing the thermostat to turn off the heater

Animation: Temperature Control in Your House

Negative feedback maintains body temperature The temperature control center is located in the hypothalamus,

a part of the brain

Set point is between 97º- 99º F

Nerve endings act as temperature sensors and transmit information to the hypothalamus

If the body temperature falls below the set point, the hypothalamus activates effector mechanisms that raise body temperature Shivering, blood vessel constriction, increased metabolic rate When body temperature is restored, the sensors signal the hypothalamus

to switch off these actions

Negative Feedback Maintains Homeostasis

The body’s temperature controls system can also act to reduce body temperature if rises above set point Blood vessels leading to the skin to dilate, allowing

warm blood to flow to the skin, where heat can be radiated into the air

Sweat glands secrete fluid, cooling the body as it evaporates from the skin

Fatigue and discomfort cause the body to slow down, so the body generates less heat

Animation: The Control of Body Temperature

Positive Feedback

Positive feedback enhances the effects of changes A change produces a response that intensifies the

initial change Positive feedback is relatively rare in biological

systems, but occurs during childbirth and blood clotting

Childbirth

Labor contractions force the baby’s head against the cervix at the base of the uterus, causing it to stretch and open

Stretch-receptor neurons in the cervix signal the hypothalamus

The hypothalamus releases oxytocin, a hormone which stimulates more and stronger contractions

Stronger contractions cause the baby’s head to stretch the cervix even more, causing the release of more oxytocin

Delivery of the baby relieves the pressure on the cervix, halting the positive feedback cycle

Animation: The Control of Labor