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Eric P. WidmaierBoston University

Hershel RaffMedical College of Wisconsin

Kevin T. StrangUniversity of Wisconsin - Madison

*See PowerPoint Image Slides for all

figures and tables pre-inserted into

PowerPoint without notes.

Chapter 01

Lecture Outline*

Homeostasis:

A Framework for Human

Physiology

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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1. Cells, the fundamental units of life, exchange nutrients

and wastes with their surroundings:

The intracellular fluid isconditioned by

the interstitial fluid, which is conditioned by

the plasma, which is conditioned by

the organ systems it passes through.

Chapter 1 Homeostasis:

A framework for human physiology

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Homeostasis refers to the dynamic mechanisms

that detect and respond to deviations in

physiological variables from theirset point valuesby initiating effector responses that restore

the variables to the optimal physiological range.

Homeostasis:

A framework for human physiology

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Most of the common physiological variables ofthe body are maintained within a predictable

range.

Examples of such physiological variables:

Blood pressure

Body temperature

Blood glucose levels

Homeostasis

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Figure 1-1

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Muscle Cells and Tissues

There are 3 types of muscle cells in thehuman body: Cardiac, Skeletal and Smooth.

Control of the cardiac and smooth muscle isinvoluntary, while skeletal is voluntary.

Muscle cells with be covered in depth in

Chapter 9.

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Neurons and Nervous Tissue

A neuron is a cell of the nervous system that is specialized

to initiate, integrate and conduct electrical signals to other

cells.

A collection of neurons forms nervous tissue (brain or

spinal cord).

Axons from many neurons are packaged together along

with connective tissue to form a nerve.

Neurons, nervous tissue, and the nervous system will be

covered in Chapter 6.

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Epithelial cells and epithelial tissue Epithelial cells are specialized for the selective secretion and absorption of

ions and organic molecules, and for protection.

These cells are characterized and named according to their unique shapes,

including cuboidal (cube-shaped), columnar (elongated), squamous

(flattened) and ciliated.

Epithelial tissue (known as an epithelium) may form from any type of

epithelial cell. Epithelia may be arranged in single-cell thick tissue, called a

simple epithelium, or a thicker tissue consisting of numerous layers of

cells, called a stratified epithelium.

The type of epithelium that forms in a given region of the body reflects the

function of that particular epithelium. For example, the epithelium that

lines the inner surface of the main airway, the trachea, consists of ciliated

epithelial cells (see Chapter 13).

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Epithelial cells and epithelial tissue Epithelia are located at the surfaces that cover the body or individual

organs, and they line the inner surfaces of the tubular and hollowstructures within the body.

Epithelial cells rest on an extracellular protein layer called the

basement membrane. The side of the cell anchored to the basement

membrane is called the basolateral side; the opposite side, whichtypically faces the interior, is called the apical side.

A defining feature of many epithelia is that the two sides of all the

epithelial cells in the tissue may perform different physiological

functions.

In addition, the cells are held together along their lateral surfaces by

extracellular barriers called tight junctions Tight junctions enable

epithelia to form boundaries between body compartments and to

function as selective barriers regulating the exchange of molecules.

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Figure 1-2

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Connective tissue cells and connective tissue

Connective tissue cells connect, anchor, andsupport the structures of the body.

Types of connective tissues include: Loose Connective

Dense Connective

Blood

Cartilage

Adipose

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What surrounds the cells? The immediate environment that surrounds each individual cell in the body is

the extracellular fluid and extracellular matrix (ECM).

ECM consists of a mixture of proteins, polysaccharides, and in some cases,

minerals.

The matrix serves two general functions: (1) It provides a scaffold for cellular

attachments, and (2) it transmits information, in the form of chemical

messengers, to the cells to help regulate their activity, migration, growth, and

differentiation.

The proteins of the extracellular matrix consist of fibersropelike collagen

fibers and rubberband-like elastin fibersand a mixture of nonfibrous

proteins that contain carbohydrate.

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Organs and Organ Systems

Organs are composed of multiple tissuetypes (example: blood vessels have layers

of smooth muscle cells, endothelial cells

and fibroblasts).

Organ systems contain multiple organs that

work together (example: the urinary systemhas the kidney, ureters, urethra, bladder).

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Table 1-1, on page 5 in the text, outlines

the structural components and functions of

the major organ systems in the body.

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Body Fluids and Compartments The term body fluids, is used to refer to the watery solution of

dissolved substances (oxygen, nutrients, etc.) present in the body.

The fluid in the blood and surrounding cells is called

extracellular fluid (i.e., outside the cell).

About 2025 percent is in the fluid portion of blood (plasma) and

the remaining 7580 percent of the extracellular fluid lies around

and between cells and is known as the interstitial fluid.

The space containing interstitial fluid is called the interstitium.

Therefore, the total volume of extracellular fluid is the sum of the

plasma and interstitial volumes.

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Body Fluids and Compartments

Intracellular fluid is the fluid located inside the cells.

The composition of the extracellular fluid is very different from

that of the intracellular fluid.

Maintaining differences in fluid composition across the cell

membrane is an important way in which cells regulate their own

activity.

Fi 1 3

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Exchange and communication are key concepts

for understanding physiological homeostasis.

ICF ISF plasma organs

externalenvironment

internal environment

Figure 1-3

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Homeostasis

Homeostasis is a dynamic, not a static, process.

Physiological variables can change dramatically

over a 24-hr. period, but the system is still in

overall balance.

When homeostasis is maintained, we refer to

physiology; when it is not, we refer to

pathophysiology.

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Blood glucose levels

increase after eating.

Levels return to their set

point via homeostasis.

This is an example of

dynamic constancy.

Levels change over short

periods of time, butremain relatively

constant over long

periods of time.

Figure 1-4

Fi 1 5

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Interpret the arrows intextbooks flow charts as

leads to orcauses.

(e.g., decreased roomtemperature causes

increased heat loss

from the body, which

leads to a decrease in

body temperature, etc.)

Figure 1-5

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System Controls

Feedback loops or systems are a commonmechanism to control physiological processes.

A positive feedback system (also called a feedforward) enhances the production of the

product.

A negative feedback system shuts the system

off once the set point has been reached.

Fi 1 6

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Active product controls the sequence of chemical reactions

by inhibiting the sequences rate-limiting enzyme, Enzyme A.

Negative

Feedback

Figure 1-6

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example: concentration of glucose in the blood

example: 70 to 110 mg glucose/dL of blood

example: diet and energy metabolism

A strategy for exploring homeostasis

(see Tables 1-2 & 1-3)

Identify the internal environmental variable.

Establish the set point value for that variable.

Identify the inputs and outputs affecting the variable.

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example: resting versus exercising

example: certain endocrine cells in the pancreas

sense changes in glucose levels

example: a hormone that increases glucose

synthesis by the liver

Many homeostatic mechanisms utilize neural

communication.

Examine the balance between the inputs and outputs.

Determine how the body monitors/senses the variable.

Identify effectors that restore the variable to its set point.

A strategy for exploring homeostasis

(see Tables 1-2 & 1-3)

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Reflexes

A reflex is a specific involuntary,

unpremeditated, unlearned built-in response

to a particular stimulus.

Example: pulling your hand away from a hot

object or shutting your eyes as an object rapidly

approaches your face.

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Reflexes The pathway mediating a reflex is known as the reflex arc.

An arc has several components: stimulus, receptor, afferent (incoming)

pathway, integration center, efferent (outgoing) pathway, and effector.

A stimulus is defined as a detectable change in the internal or external

environment. A receptor detects the change. The pathway the signal

travels between the receptor and the integrating center is known as the

afferent pathway. The pathway along which information travels away

from the integration center to the effector is known as the efferent

pathway

An integrating center often receives signals from many receptors, some

of which may respond to quite different types of stimuli. Thus, the

output of an integrating center reflects the net effect of the total

afferent input; that is, it represents an integration of numerous bits of

information.

Figure 1 7

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30Afferent and efferent pathways in temperature homeostasis.

Figure 1-7

Figure 1 8

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31Communication systems use signals that bind to receptors.

Figure 1-8

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Non-nerve Reflexes Almost all body cells can act as effectors in homeostatic

reflexes.

There are, however, two specialized classes of tissuesmuscle

and glandthat are the major effectors of biological control

systems.

In the case of glands, the effector may be a hormone secreted

into the blood.

A hormone is a type of chemical messenger secreted into the

blood by cells of the endocrine system (see Table 11).

Hormones may act on many different cells simultaneously

because they circulate throughout the body.

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Types of Signals

Hormones are produced in and secretedfrom endocrine glands or in scattered cells

that are distributed throughout another

organ.

Neurotransmitters are chemical messengers

that are released from the endings ofneurons onto other neurons, muscle cells, or

gland cells.

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Endocrine: signal reaches often-distant targets aftertransport in blood.

Paracrine: signal reaches neighboring cells via the ISF.

Autocrine: signal affects the cell that synthesized the

signal.

Chemical Messengers

Chemical messengers participate not only in reflexes,but also in local responses.

Communication signals in three categories:

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Points to Remember

A neuron, endocrine gland cell, and other cell

types may all secrete the same chemicalmessenger.

In some cases, a particular messenger mayfunction as a neurotransmitter, as a hormone, or as

a paracrine/autocrine substance.

Example: Norepinephrine is a neurotransmitter in

the brain and is also produced as a hormone by

cells of the adrenal glands.

Figure 1-9

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Multi-factorial control of

signal release adds

more complexity.

A given signal can

fit into all 3 categories:

(e.g., the steroid

hormone cortisol

affects the very cells in

which it is made,

the nearby cells thatproduce other hormones,

and many distant targets,

including muscles and

liver.)

Figure 1 9

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Other Types of Cell Communication There are two important types of chemical communication

between cells that do not require secretion of a chemicalmessenger.

1. Gap junctions (physical linkages connecting the cytosol

between two cells) allow molecules to move from one cell toan adjacent cell without entering the extracellular fluid.

2. Juxtacrine signaling is the chemical messenger not actually

being released from the cell producing it, but rather is locatedin the plasma membrane of that cell. When the cell encounters

another cell type capable of responding to the message, the

two cells link up via the membrane-bound messenger.

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Adaptation and Acclimatization

The term adaptation denotes a characteristic thatfavors survival in specific environments.

Acclimatization refers to the improvedfunctioning of an already existing homeostatic

system based on an environmental stress.

In an individual, acclimatizations are reversible;

adaptations are not.

Bi l i l Rh th

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Biological Rhythms

Many body functions are rhythmical

changes.

Example: circadian rhythm, which cycles

approximately once every 24 h.

Waking and sleeping, body temperature,hormone concentrations in the blood, the

excretion of ions into the urine, and many

other functions undergo circadian variation.

Figure 1-10

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A full analysis of the

hormone cortisol requires

not only knowledge of the

signals that cause itssynthesis and secretion

but also consideration

of biological rhythms.

asleep asleep

Figure 1 10

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What have biological rhythms to do with homeostasis?

They add an anticipatory component to homeostatic

control systems and in effect are a feed-forward systemoperating without detectors.

The negative-feedback homeostatic responses are

corrective responses. They are initiated afterthe steady

state of the individual has been perturbed.

Biological rhythms enable homeostatic mechanisms tobe utilized immediately and automatically by activating

them at times when a challenge is likely to occur but

before it actually does occur.

Balance in the Homeostasis of

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Balance in the Homeostasis of

Chemical Substances in the Body

Many homeostatic systems regulate the balance

between addition and removal of a chemical substance

from the body.

Two important generalizations concerning the balance

concept: (1) During any period of time, total-body

balance depends upon the relative rates of net gain and

net loss to the body; and (2) the pool concentration

depends not only upon the total amount of the substance

in the body, but also upon exchanges of the substance

within the body.

Figure 1-11

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Some of the potential inputs and outputs that can

affect the pool of a material (like glucose) that is a

dynamically regulated physiological variable.

g

Figure 1-12

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Sodium homeostasis: Consuming greater amounts of dietary

sodium initiates a set of dynamic responses that include greater

excretion of sodium in the urine. Though not shown here, the

amount excreted would likely exceed the amount ingested until

the set point is restored.

g

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Clinical Correlation

A 64-year-old, fair-skinned man in good overall health spent a veryhot, humid summer day gardening in his backyard. After several hours

in the sun, he began to feel dizzy and confused as he knelt over his

vegetable garden. Although he had earlier been perspiring profusely,

his sweating had eventually stopped. Because he also felt confused and

disoriented, he could not recall for how long he had not been

perspiring, or even how long it had been since he had taken a drink of

water. He called to his wife, who was alarmed to see that his skin had

turned a pale blue color. She asked her husband to come indoors, but

he fainted as soon as he tried to stand. The wife called for an

ambulance, and the man was taken to a hospital and diagnosed with a

condition called heat stroke. What happened to this man that wouldexplain his condition, and how does it relate to homeostasis?

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You dont have a figure for this

but it would be really helpful to

have a flow chart diagram here

with the information for the

clinical correlation

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The End.