1

Dr. Niveen M. DaoudAss. Prof. clinical pathology

Chapter 01Chapter 01**

Homeostasis: A Framework for Human

Physiology

2

Section I What is Physiology?What is Physiology?• PhysiologyPhysiology: biological sciences : biological sciences

• dealing with the normal life phenomena dealing with the normal life phenomena exhibited by all living organisms.exhibited by all living organisms.

• Human physiologyHuman physiology: basic sciences : basic sciences • dealing with normal life phenomena of dealing with normal life phenomena of

the human body. the human body. • Goal of physiologyGoal of physiology::

• explain the physical and chemical factors explain the physical and chemical factors that are responsible for the origin, that are responsible for the origin, development and progression of life.development and progression of life.

1-3

Physiology—The Study of Function

• Sub disciplines– Neurophysiology (physiology of nervous system)

– Endocrinology (physiology of hormones)

– Pathophysiology (mechanisms of disease)

1-4

The Birth of Modern Medicine• Christian culture of Europe in Middle Ages

– Science severely repressed– Taught medicine primarily as dogmatic commentary on Galen and

Aristotle– Crude medical illustrations

• In Jewish and Muslim cultures free inquiry was less inhibited

• Jewish physician Maimonides (Moses ben Maimon) – Wrote 10 influential medical texts – Was physician to Egyptian sultan, Saladin

• Avicenna (Ibn Sina) from Muslim world– “The Galen of Islam”– Combined Galen and Aristotle findings with original discoveries– Wrote The Canon of Medicine, used in medical schools for 500 years

HomeostasisA framework for human

physiology• homeo = same; stasis = standing• Homeostasis is the term we use to describe

the constant state of the internal environment.• Homeostasis is a state of

balance in the body.• The processes and activities

that help to maintain homeostasis are referred to as homeostatic mechanisms.

6

Homeostasis & Controls

•Successful compensation

•Homeostasis reestablished

•Failure to compensate

•Pathophysiology

•Illness

•Death

7

Organization of the human body

CellsTissues

Organs

Organ systems

Organisms (Human body)

8

Figure 1-1

1-9

The Hierarchy of Complexity

• Organism is composed of organ systems

• Organ systems composed of organs

• Organs composed of tissues

• Tissues composed of cells

• Cells composed of organelles

• Organelles composed of molecules

• Molecules composed of atoms

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

Organism

Cell

TissueOrgan system

Macromolecule

Organelle

AtomMolecule

Organ

Section II Internal Environment and Homeostasis

10

1. Cells, the fundamental units of life, exchange nutrients and wastes with their surroundings:

The intracellular fluid is “conditioned by”… the interstitial fluid, which is “conditioned by” … the plasma, which is “conditioned by” … the organ systems it passes through.

11

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 20–25 percent is in the fluid portion of blood (plasma) and the remaining 75–80 percent of the extracellular fluid lies around cells and in special compartments is known as the interstitial fluid.

• The total volume of extracellular fluid is the sum of the plasma and interstitial volumes.

12

Interstitial fluidInterstitial fluid

Blood Plasma Blood Plasma

Intracellular fluidIntracellular fluid

Total body water = 60 %Total body water = 60 % BWBW

= 40 % BW= 40 % BW

Extracellular fluidExtracellular fluid

2/2/

33

1 /1 /33

15/15/

45/45/

13

Extracellular fluids

Intracellularfluid

2. Plasma 2. Plasma

IIIIIIIIIIII IIIII1 IIIIIIIIIIII IIIII1

3 . Fluid of special compartments 3 . Fluid of special compartments : pe : pe ricardial fluid, pleural fluid, cerebrospinal fl ricardial fluid, pleural fluid, cerebrospinal fl

uid uid

14

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. WHY and HOW????

• Maintaining differences in fluid composition across the cell membrane is an important way in which cells regulate their own activity.

Differences Between Extracellular and Intracellular Fluids.

 *The extracellular fluid contains large amounts of sodium,

chloride, and bicarbonate ions plus nutrients ….. 

*The intracellular fluid differs significantly fromthe extracellular fluid; specifically, it contains large

amounts of potassium, magnesium, ………… 

16

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. explain ???

• When homeostasis is maintained, we refer to physiology; when it is not, we refer to pathophysiology.

17

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, but

remain relatively

constant over long

periods of time.

18

Contribution of Organ Systems to the Maintenance of Homeostasis

• Nervous system• Regulates muscular activity and glandular secretion; responsible for all activities associated

with the mind• Endocrine system• Regulates metabolic processes through secretion of hormones• Muscular system• Allows for body movement; contributes to thermoregulation• Circulatory system

• Transports nutrients, O2, waste, CO2, electrolytes, and hormones throughout the body

• Respiratory system• Obtains oxygen and eliminates carbon dioxide; regulates acid-base balance (pH)• Gastrointestinal tract• Digests food to provide nutrients to the body• Renal system• Eliminates waste products from the body; regulates blood volume and blood pressure;

regulates acid-base balance

19

20

21

Regulation of the Body FunctionsRegulation- the ability of an organism to maintain a stable internal conditions in a constantly changing environment

-Three types:

1. Chemical (hormonal) Regulation- a regulatory process performed by hormone or active chemical substance in blood or tissue.

-It response slowly, acts extensively and lasts for a long time.

2. Nervous Regulation- a process in which body functions are controlled by nerve system

- Pathway: nerve reflex

- Types: unconditioned reflex and conditioned reflex

22

3. Autoregulation – a tissue or an organ can directly respond to environmental changes that are independent of nervous and hormonal control

Characteristics：

Amplitude of the regulation is smaller than other two types.

Extension of the effects is smaller than other two types.

In the human body these three regulations have coordinated and acts as one system, “feedback control system”.

The nervous system• The nervous system is composed of excitable

cells called neurones (also neurons)

• Neurones, characteristically, have long thin extensions which carry electrical nerve impulses

• This electrical signal of the nerve impulse needs to be converted into a chemical signal (a neurotransmitter) so that it can pass from nerve cell to nerve cell

© 2008 Paul Billiet ODWS

24

Reflexes• A reflex is a specific involuntary, 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.

25

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

• .

26Afferent and efferent pathways in temperature homeostasis.

Figure 1-7

Postural Change in Blood Pressure

Figure 1.11

Baroreceptors send signalsto cardiac center of brainstem

Baroreceptors aboveheart respond to dropin blood pressure

Cardiac centeraccelerates heartbeat

Blood pressure risesto normal; homeostasisis restored

Blood drains fromupper body, creatinghomeostatic imbalance

Person risesfrom bed

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

28

Non-nerve Reflexes• Almost all body cells can act as effectors in homeostatic reflexes. • There are, however, two specialized classes of tissues—muscle and gland—

that 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 .

• Hormones may act on many different cells simultaneously because they circulate throughout the body.

29

Multi-factorial control of signal release adds more complexity.

A given signal can fit into all 3 categories:

(e.g., the steroidhormone cortisolaffects 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

Example:Regulation of Blood Glucose

Fig 2.7

31

III- System Controls • Feedback loops or systems are a common

mechanism to control physiological processes.

• A positive feedback system (also called a feed forward) enhances the production of the product.

• A negative feedback system shuts the system off once the set point? has been reached.

32

“Active product” controls the sequence of chemical reactions by inhibiting the sequence’s rate-limiting enzyme, “Enzyme A.”

Negative Feedback

Figure 1-6

33

Negative Feedback: Inhibitory mechanism .Is the mechanisms prevent small changes from becoming too large.

Non-Biological Control System in roomTemperature below 200 C

Thermostat set at 200 C

Heating System

Room temperature

Returns to 200 C

Room TemperatureSignals thermostat

To turn off heat

A Review

• Example: thermostatic heating system in a home

Components of an automatic control system

• Variable: the changeable (internal temp in this example).

• Sensor (receptor) detects changes in variable and feeds that information back to the integrator (control center) (thermometer in this example).

Example Continued

• Integrator (control center) integrates (thermostat in this example).

• Set point is the "ideal" or "normal" value of the variable.

• Effector is the mechanism that has an "effect" on the variable (internal temperature in this example).

37Communication systems use signals that bind to receptors.

Figure 1-8

http://fig.cox.miami.edu/~cmallery/150/physiol/c44x10thermo-reg.jpg

39

40

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

• Identify the internal environmental variable.

• Establish the “set point” value for that variable.

• Identify the inputs and outputs affecting the variable.

41

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

42

Positive feedback Positive feedbackThe feedback signal or output from the The feedback signal or output from the controlled system increases the action of controlled system increases the action of the control systemthe control system

• A-Sometimes Be Useful.

• Hemostasis?? • Blood clotting is an example of a valuable use of positive

feedback. When a blood vessel is ruptured and a clot begins to form, multiple enzymes called clotting factors are activated within the clot itself. Some of these enzymes act on other unactivated enzymes of the immediately adjacent blood, thus causing more blood clotting. This process continues until the hole in the vessel is plugged and bleeding no longer occurs.

 

 

43

45

Positive Feedback: Stimulatory.Stimulus trigger mechanisms that amplify the response and reinforces the stimulus.

• B-Sometimes Cause Vicious Cycles and Death:

• Hypovolemic shock  • If the person is suddenly bled 2 liters, the amount of

blood in the body is decreased to such a low level that not enough blood is available for the heart to pump effectively. As a result, the arterial pressure falls, and the flow of blood to the heart muscle through the coronary vessels diminishes. This results in weakening of the heart, further diminished pumping, a further decrease

46

• in coronary blood flow, and still more weakness of the heart; the cycle repeats itself again and again until death occurs.

47

1-48

Positive Feedback and Rapid Change

• Septic shock

• Fever > 104°F– Metabolic rate increases

– Body produces heat even faster

– Body temperature continues to rise

– Further increasing metabolic rate

• Cycle continues to reinforce itself

• Becomes fatal at 113°F

Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 8 April 2005 01:55 PM)

© 2005 Elsevier

50

Adaptation and Acclimatization• The term adaptation denotes a characteristic that favors

survival in specific environments.

• Acclimatization refers to the improved functioning of an already existing homeostatic system based on an environmental stress.

• In an individual, acclimatizations are reversible; adaptations are not.

51

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.

52

Some of the potential inputs and outputs that can affect the “pool” of a material (like glucose) that is a dynamically regulated physiological variable.

53

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.

Figure 1-12

Check your understanding

• What are the main topics of our lecture?

• Why homeostasis is frame work of physiology?

• Body deal with hypocalemia by stimulating parathyroid gland this mechanism is known as………… . Discuss this strategy , control system, feed back mechanism .

54

55

The End.