Chapter 1.1 Principles of Homeo

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Biology Unit AACB 1223

Homeostasis and Excretion

Learning Outcomes

Students will be able to:

Acquire scientific knowledge through application ofscientific method.

Interpret information presented in graphs, tables and

diagrams.

Application of biological knowledge to disease e.g.

diabetes mellitus, AIDS, kidney failure. Recognize the importance of homeostatic control in

animals.

Describe the functions of vertebrate kidney.


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Syllabus

Chapter 1: Homeostasis

Principles of homeostasis Maintenance of stable internal environment

Mechanism of homeostasis

Homeostatic control of blood glucose level

Role of pancreas

Diabetes mellitus The mammalian liver and functions


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Chapter 2: Temperature Regulation

Relate the mechanisms of heat input and output in

a mammal.

Chapter 3: Control of Respiratory Gases Carbon dioxide as a stimulus

Adjustments to altitudes

Chapter 4: Excretion and Osmoregulation

Mammalian kidney Structure of nephron

Processes of urine formation, glomerular

filtration, tubular reabsorption, tubular

secretion.

Kidney failure


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Chapter 5: Defense System

Non-specific defense responses

Specific defense responses immune system

Primary response: antibody mediated immunity, cellmediated immunity

Secondary immune response

Immunization and allergies

Rejection of grafts, transplantation

Deficient immune responses_____________________________


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Reading List

Raven, H.R. &

Johnson, G.B.

Biology McGraw-Hill

Solomon, E.P.;

Berg, L.R. &

Martin, D.W.

Biology Brooks/Cole

Campbell, N.A.;

Reece, J.B. &

Michael, L.G.

Biology Benjamin/

Cummings

Mader, S.S. Biology Oxford UniversityPress

Green N.P.O.;

Stout, G.W. &

Taylor, D.J.

Biological Science Cambridge

University press


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The Principles of Homeostasis1. Homeostasis is the process of

maintaining constant physical and

chemical factors within an internalbody environment.

2. The internal environment refers to the

environment surrounding the cells i.e.the tissue fluids that envelope each

cell.


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The Principles of Homeostasis

- The formation of tissue fluid

The tissue fluid is formed from the blood by aprocess ofultra-filtration.

When blood reaches the

arterial end of a capillary, it is

under pressure

because of the pumping

action of the heart and theresistant to the blood flow due

to the narrow capillaries.


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Endothelium

Basement membrane of

capillary wall act as filter to

hold back large protein

molecules and blood cells,but allowing water, ions and

smaller molecules to pass

through tissue fluid.

The hydrostatic pressure

forces water and smallermolecules through thecapillary walls into theintercellular spaces.


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Smoothmuscle

Elasticlayer

Connectivetissue

Connectivetissue

Smoothmuscle

Elasticlayer

Once formed, tissue fluid circulates amongstthe cells and eventually returns to the blood

system. At the venous end of the capillary, the

hydrostatic pressure is relatively low

because venules have wider diameter thus,giving less resistance to blood flow.


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The residual tissue fluid is drainedinto the lymph vessels which

eventually passes into the veins.

The pressure causing this flow is

relatively small, so not all tissue

fluid follow this route.


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Fig. 44.10(TE Art)

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

Arteriole

Bloodflow

Venule

Capillary

Lymphaticcapillary

Excess interstitial fluidbecomes lymph

Osmosis due to plasmaproteins causes net

absorptionBlood pressurecauses net filtration

Interstitial

fluid


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Physical factors

include temperature,blood pressure and

osmotic pressure.

Chemical factors

include pH value and

the concentrations ofsugar and salt.


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Physical and chemical factors are

usually maintained at a balancedlevel and controlled closely through ahomeostatic mechanism to preventsudden changes.

Any variation will initiate

homeostatic reactions, where a

series of correction mechanismswill act to restore the physical and

chemical compositions of the

tissue fluids to normal conditions.


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The importance of homeostatic control:

a) The life of the organism become lessdependent on the external environment.

This is because the organism is able to

control changes in its internal

environment to compensate forchanges in external conditions.

For e.g. if the temperature of the

environment rises, the organism canactivate various reactions to cool thebody, such as: perspiration, increasingblood flow to the skin or by increasing

the respiration rate.


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b) The organism can live in a wider

range of habitats and the species can

live in areas variable conditions.

c) The organism can increase or

decrease the metabolic rate of its body

according to its requirements.


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All homeostatic control processesinclude corrective mechanisms thatuse the principles ofnegativefeedback and positive feedback.

What is negative feedback?

Mechanism of Homeostasis


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Negative feedback of a regulatorymechanism means that when

something changes, the oppositeeffect is produced.

This means any increase in the value

of a physical or chemical factors in theinternal environment will trigger a

correction mechanism to reduce that

value.


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Conversely, a reduction in the valueof the physical or chemical factor willtrigger a mechanism to increase theamount of that factor. This controlprinciple is called negative feedback.

What about positive feedback?


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If the control centre or correctionmechanism is disrupted, the changeoccurring in the factor cannot be

reversed. This results in the value ofthe factorcontinuing to rise or fall.This is called positive feedback.

It is usually harmful but in certaincircumstances it becomes useful.


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Example : childbirth.

During childbirth, the fetus exerts pressure

on the wall of its mothers uterus. Pressurestimulates the production and secretion of

oxytocin. Oxytocin causes wall muscles to

contract and exert pressure on the fetus,

which exerts more pressure on the walland so on until the fetus is expelled.


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Fig. 49.07(TE Art)

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

Integratingcenters in brain Increasedneuraland hormonalsignals

Continuedincreasedneuralstimulation

Receptors detectincreased stretch

The fetus ispushed againstthe uterine opening,causing the inferioruterus to stretch

Increasedcontractionforce andfrequencyin smooth

muscles ofuterus


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Disturbance Set point

Receptor Control centre Effector

Further increase

Positive feedback

Receptor Control centre Effector

Further decreasePositive feedback


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For the corrective mechanism to work,

there must be:

(a) receptors which are capable ofdetecting changes ( e.g. sensory cells

in eye, tongue and ear).

(b) effectors that carry out the corrective

process (e.g. muscles, glands).(c) control centre coordinating the overall

response (brain, spinal cord).

As a summary..


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Input

Receptor(sensor) Coordinator(control centre) Effector(output)

Feedback loop

Corrective Mechanism


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Self Quiz

1. Which of the following are examples of integrators?

a. brain, spinal cordb. muscles, glands

c. sensory cells in eye, tongue, and ear

d. bones

e. none of these

2. Which of the following is most directly associated

with a stimulus?

a. integrators

b. receptorsc. effectors

d. central nervous system

e. all of these


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Self Quiz

3. Which of the following is the correct sequence

involved in the regulation of organ systems?a. stimulus, receptor, integrator, response, effector

b. stimulus, response, integrator, receptor, effector

c. stimulus, receptor, integrator , effector, response

d. stimulus, integrator, receptor, effector, responsee. stimulus, effector, integrator, receptor, response

4. An effector can be

a. muscle.

b. nerve.c. gland.

d. receptor.

e. both muscle and gland.


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Self Quiz

5. Control of body temperature is an example of which

of the following?

a. homeostatic mechanism

b. positive feedback system

c. endocrine function

d. negative feedback system

e. both homeostatic mechanism and negativefeedback system

6. In feedback systems,

a. two sets of organ may act in opposition to each other.

b. a set point may be established.c. receptors are required to monitor changing condition.

d. changes in either internal or external environment

result in a response by the organism.

e. all of these.


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1. (a) Define homeostasis.

(b) What is:

(i) internal environment ?

(ii) physical factors?(iii) chemical factors?

2. Why is homeostatic control important to organisms?

3. (a) What is the difference between the process of negative

feedback and the process of positive feedback?

(b) Give suitable examples to support your answer.


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HAPPY DEEPAVALI

SELAMAT HARI RAYA

AIDILFITRI

&

Dearest DCB1 students:

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Chapter 1.1 Principles of Homeo