GENERAL PHYSIOLOGY

Dr. Pavithran.PAssistant Professor in PhysiologyA J Institute of Medical Sciences, Mangalore

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What is PhysiologyPhysiology is the study of

life, specifically, how cells, tissues, and organisms function. 

Pronounced “fizzy-aw-low-jee”

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Q: Why do we shiver, when we feel cold?

A. To help us warm up, as shivering

increases body temp

How does this happen – not answeredWhat is the cause – not answeredWhat will be its effect - answered

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Temperature sensitive nerve cells detects fall in

temperatureImpulses transmitted to

brain Hypothalamus

Brain areas gets activated

Involuntary, oscillating muscle contraction

(Shivering)

Increases body temperature

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INTERNAL ENVIRONMENT&

HOMEOSTASIS

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External environment –

surrounding environment.

Amoeba- Unicellular Organism

Takes nutrients and expels waste –

external environment

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Cells in human body – all does not

have contact with external

environment.

How do they support their vital

activities?

Extra cellular fluid-the internal

environment.

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Majority inside the cells –

intracellular fluid (ICF).

1/3rd – out side the cells-

Extracellular fluid (ECF).

ECF contains ions and nutrients

ECF – internal environment for the

cells – Milieu Intérieur

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(1813-1878)

Milieu Interieur

Milieu- Environment

Interieur – Internal

19th French Physiologist.

Concept of the internal

environment of an

organism.

Blood- as the internal

environment.

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Homeostasis:Homeo: same; stasis: stayThe word does not imply something set and immobile, a stagnation. It means a condition — a condition which may vary, but which is relatively constantWalter Cannon

Homeostasis: maintenance of a constant internal environment. An extension of Claude Bernard idea

(1871–1945)

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Homeostatic mechanismThree part mechanism

1. Receptor

2. Control center

3. Effector

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The internal state of the body - dynamic

equilibrium (balanced change).

There is a certain set point or average

value for a given variable (such as 37°C for

body temperature).

Conditions fluctuate slightly around this

point.

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Regulatory Mechanism

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Negative feedback mechanismPositive feedback mechanisms

Feedforward mechanism

NEGATIVE FEEDBACK MECHANISM

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Most of the control mechanisms in human

body

The body senses an internal change and

activates mechanisms that reverse, or

negate, that change.

Arterial blood pressure regulation

Increase in BP is detected by various

mechanism that lead to a decrease in BP

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• Increase in Co2 – increases

ventilation- decreases Co2

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POSITIVE FEEDBACK MECHANISM

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A process in which the body senses a change and activates mechanisms that accelerate or increase that change.

Child birth (Parturition reflex)◦Uterine contractions due to Oxytocin◦Baby’s head pushes against the cervix -

stretch◦Sends impulse to the uterus◦Stimulates further contractions of the

uterus◦Pushing the baby out.

Milk ejection reflex

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FEEDFORWARD MECHANISM

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Body responds in anticipation of a change in

regulated variable.

In GIT- insulin secretion is increased

Insulin increases cellular uptake and storage of

ingested nutrients after they are absorbed.

This limits the rise in blood sugar/nutrients

after absorption

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Disruption

System malfunction

Homeostasis not maintained

Pathophysiology

Severe - death