Ch 31 lecture

Copyright © 2009 Pearson Education, Inc..

Lectures by

Gregory AhearnUniversity of North Florida

Chapter 31

Homeostasis and the Organization

of the Animal Body

Copyright © 2009 Pearson Education Inc.

How Is The Animal Body Organized?

The cells of a body are arranged into numerous different body parts, with a distinctive size, shape, and combination of specialized cell types.



Body structure and organization can be described at different levels of organization.• Tissues: the basic building blocks of bodies

whose cells perform specific functions• Organs: a combination of tissues, such as the

stomach, small intestine, and urinary bladder• Organ systems: the arrangement of organs

such as occurs in the digestive system, which includes the stomach, small intestine, large intestine, and other organs


connective

muscle

largeintestine

pancreasstomach

mouth

pharynx

epithelialCells:epithelial cells

liversmall intestine

esophagusgallbladder

Tissues: Organ:stomach

Organ system:digestive system


Cells, tissues, organs, and organ systems

Fig. 19-1


How Do Tissues Differ?

There are four types of animal tissue:• Epithelial tissue• Connective tissue• Muscle tissue • Nerve tissue



Epithelial tissue forms sheets that cover the body and line cavities, such as the mouth, the stomach, and the bladder.• There are many types of epithelial tissues,

and the structure of each type is related to its function.



Lung epithelium consists of flattened cells in a single layer that gas molecules can easily cross.

Another type of lung epithelium consists of elongated cells, with cilia that secrete mucus to trap dust particles.

Fig. 19-2

(a) Thin epithelial tissue

(b) Ciliated epithelial tissue



Epithelial tissues are continuously lost and replaced by mitotic cell division.• The lining of our mouths, our stomachs, and

our skin’s outer surface are continuously replaced.

• Some epithelial tissues form glands, which are clusters of cells that are specialized to secrete substances.



There are two types of glands:• Exocrine glands: remain connected to the

epithelium by a passageway, such as with sweat glands and salivary glands

• Endocrine glands: are not connected to an epithelium by a duct, and secrete hormones into the extracellular fluid and blood



Connective tissues have diverse structures and functions.• Connective tissue serve mainly to support and

bind other tissues.• Connective tissues include large quantities of

extracellular substances that are secreted by the connective tissues themselves.



Connective tissues have diverse structures and functions (continued).• A connective tissue, called the dermis, lies

beneath the epithelial tissue of the skin and contains capillaries that nourish the epithelium.

• Other fibrous connective tissues, known as tendons and ligaments, attach muscles to bones and bones to bones; these structures are held together by strands of an extracellular protein called collagen.



Connective tissues have diverse structures and functions (continued).• Cartilage is a flexible and resilient connective

tissue that consists of widely spaced cells surrounded by a thick, nonliving matrix.



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

Fig. 19-3

cartilage cells

collagen


centralcanal

bone cells

concentricbone matrix


Bone resembles cartilage but is enhanced by deposits of calcium phosphate.

Fig. 19-4



Adipose tissue provides long-term energy storage and insulation for animals adapted to cold environments.

Fig. 19-5



Connective tissues have diverse structures and functions (continued).• Blood and lymph are considered connective

tissues even though they are liquids.• Lymph is a fluid that has leaked out of

blood vessels and is returned to the blood through the lymphatic system.


platelets

white blood cell

red blood cells


Blood has three types of cells: red blood cells, white blood cells, and platelets suspended in a fluid called plasma.

Fig. 19-6


striations

muscle fiber


Muscle tissue has the ability to contract.• The long, thin cells of muscle tissue contract

when stimulated, then relax passively.

Fig. 19-7



There are three types of muscle tissue: • Skeletal: under voluntary control, it has a

striped appearance and moves the skeleton • Cardiac: located only in the heart, its cells are

electrically connected so that they contract as a unit

• Smooth: lacks stripes and is embedded in the walls of the digestive tract, the uterus, the bladder, and large blood vessels; it produces slow, involuntary contractions



Nerve tissue transmits electrical signals.• Nerve tissue allows the body to sense and

respond to the world around it.• Transmission of electrical signals from the

brain and spinal cord occurs from them to nerves that travel to all parts of the body.



There are two types of nerve tissue cells:• Neurons generate electrical signals and

conduct these signals to other neurons, muscles, or glands.

• Glial cells surround, support, and protect neurons and regulate the extracellular fluid, allowing neurons to function optimally.



A neuron has four parts, each with a specialized function.• The dendrites receive information from other

neurons or from the external environment.• The cell body directs the maintenance and

repair of the cell.• The axon conducts the electrical signal to its

target cell.• The synaptic terminals transmit the signal to

the target cell.



A nerve cell

Fig. 19-8

dendrites

synapticterminals

cell body

axon


How Are Tissues Combined Into Organs?

Skin is an organ that contains all four tissue types.• The epidermis, or outer skin layer, is a

specialized epithelial tissue.• Immediately below the epidermis lies the

dermis, a layer of connective tissue.



Skin is an organ that contains all four tissue types (continued).• Blood vessels spread through the dermis and

carry the blood that nourishes both the dermal and epidermal tissues.

• The dermis contains hair follicle glands that produce hair; sweat glands that secrete sweat to cool the body; and sebaceous glands that secrete oil for lubrication.



Skin

Fig. 19-9

sensorynerve ending

livingepidermalcells

dead cell layer

sebaceous gland

capillaries

arteriolevenule

hair folliclemuscle(pulls hair upright)

sweat gland

hair shaft

epidermis

dermis

subdermalconnectiveand adiposetissue

capillarybed



Organ systems consist of two or more interacting organs.• The skin is part of the integumentary system,

which includes the hair and the nails, and which serves as a barrier between the environment and the inside of the body.

• In the digestive system, the mouth, stomach, intestines, and other organs, such as the liver and pancreas, supply digestive enzymes, and all function together to convert food into nutrient molecules.




How Do Animals Maintain Internal Constancy? To function properly, an organ system must be

situated in stable environmental surroundings of just the right moisture level, temperature, and chemical composition.• However, the external environment is highly variable;

to survive, an animal’s body must be able to maintain constant internal conditions regardless of the external conditions.

• Constancy of the internal environment is called homeostasis.

• Internal homeostasis is maintained in animal bodies by a host of mechanisms called feedback systems.


How Do Animals Maintain Internal Constancy? Negative feedback reverses the effects of

changes.• The most important mechanism governing

homeostasis is negative feedback, in which the response to a change is to counteract the change.

• In other words, an input causes an output response that “feeds back” to the initial input and decreases its effects.


How Do Animals Maintain Internal Constancy? A home thermostat is a familiar example of

negative feedback.• An input, temperature, dropping below a set point, the

thermostat setting, is detected by the thermometer.• The thermometer responds with an output—switching

on the heater.• The heater restores the temperature to the set point

and the heater switches off.• The thermostat’s negative feedback mechanism

requires a control center with a set point, a sensor (thermometer), and an effector (the furnace), which accomplishes the change.


on off

controlcenter

below

aboveset

point

thermometer(sensor)

heater(effector)

(a) Maintaining a home’s temperature

How Do Animals Maintain Internal Constancy? Maintaining a home’s temperature

Fig. 19-10a


How Do Animals Maintain Internal Constancy? Negative feedback keeps a person’s body

temperature close to 98.6°F (37°C).• The center of the temperature control system is in the

hypothalamus, a region of the brain.• Nerve endings throughout the body act as

temperature sensors and transmit this information to the hypothalamus.

• When body temperature drops, the hypothalamus activates effector mechanisms that raise your body temperature.

• When normal body temperature is restored, the hypothalamus switches off these control mechanisms.


How Do Animals Maintain Internal Constancy? Maintaining a body’s temperature

Fig. 19-10b

nerve endings(sensor)

skeletalmuscles(effector)

hypothalamus(control center)

heat output(shivering)decreases

heat output(shivering)increases

setpoint

(b) Maintaining a body’s temperature


How Do Animals Maintain Internal Constancy? Positive feedback drives an event to its

conclusion.• A change in a positive feedback system

produces a response that intensifies the original change.


How Do Animals Maintain Internal Constancy? An example of positive feedback in animal

physiology are the events that control childbirth.• Early contractions of labor force the baby’s

head against the cervix, dilating the cervix.• Stretch receptors in the cervix signal the

hypothalamus, which releases the hormone oxytocin that stimulates more uterine contractions.

• The feedback cycle is terminated by the expulsion of the baby and its placenta.


How Do Animals Maintain Internal Constancy?

Animation—Feedback Loops and HomeostasisPLAYPLAY


How Do Animals Maintain Internal Constancy? The body’s organ systems act in concert.

• Numerous feedback mechanisms are constantly at work, responding to inputs that continuously change as an animal’s activities and external environment change.


How Do Animals Maintain Internal Constancy? The body’s organ systems act in concert (continued).• For example, the digestive system works in

concert with the systems responsible for transporting substances within the body, such as the circulatory system and the systems that remove waste substances from the body, including the excretory system.

• This coordinated action is possible because the body continually sends messages from sensors to effectors, which allow feedback mechanisms to maintain homeostasis.