Homeostasis DR QAZI IMTIAZ RASOOL H.O.D GOVT MEDICAL COLLEGE KASHMIR

How does the organism stay alive?

Keeping our cells happy1.Cells work best at certain temperatures and with the right amount of hydration (water present)

2.The levels of glucose, salts, urea, oxygen and carbon dioxide must also be controlled

3.The control of these factors should occur via control systems.

04/07/23 DR. QAZI IMTIAZ RASOOL 1

Factors to be regulated includee.g

1.Concentration of nutrient molecules2.Concentration of water, salt, and

other electrolytes3.Concentration of waste products

4.Conc; of O2 = 100mmHg and CO2 = 40 mmHg

5.pH = 7.356.Blood volume 4-6 L and pressure

110/707.Temperature = 37o C

Where we are and what we do affect our levels…

Which internal factors are being stressed in each picture?

Control

1.External stimuli 1. heat, cold, lack of oxygen, pathogens, toxins

2.Internal stimuli1. Body temperature2. Blood pressure3. Concentration of water, glucose, salts, oxygen,

etc.4. Physical and psychological distresses

3.Disruptions can be mild to severe

4.If not maintained, death may result04/07/23 DR. QAZI IMTIAZ RASOOL 4

Claude Bernard (1872)The milieu interieur

Walter B. Cannon (1871-1945)

“Homeostasis”

Homeostasis

GREEK ‘’ HOMOI= SAME”

STASIS= ‘’ STANDING STILL”

HOMEOSTASIS

Definitionthe maintenance of a

relatively constant steady stable state

of internal environment

1. Central concept of physiology

2.Maintenance of the relative stable “internal environment” in an ever changing world.

3.Balance or equilibrium of all functions.

4.It is a dynamic steady state.

5.Dynamic: parameters do change04/07/23 DR. QAZI IMTIAZ RASOOL 11

.6.Steady state: parameters change in very narrow limits.

7.It has to respond to both internal and external threats to that stability

8.Disease, by and large, is a failure of homeostasis

9.Excessive perturbations result ultimately in death of the organism

.6.Steady state: parameters change in very narrow limits.

7.It has to respond to both internal and external threats to that stability

8.Disease, by and large, is a failure of homeostasis

9.Excessive perturbations result ultimately in death of the organism

Internal environment

Extracellular fluid directly baths body cells

Internal environment = Extracellular fluid

Pl asmaPl asma

I ntersti t i al fl I ntersti t i al flui dui d

Intracellularfluid

Extracellular fluids

Intracellularfluid

2 . Plasma 2 . Plasma

1 . Interstitial fluid 1 . Interstitial fluid/tissue fluid/tissue fluid 3. Fluid of special compartments 3. Fluid of special compartments : pe : pe

ricardial fluid, pleural fluid, cerebrospinal fl ricardial fluid, pleural fluid, cerebrospinal fluiduid ,plasma ,lymph,plasma ,lymph04/07/23 DR. QAZI IMTIAZ RASOOL 14

In fasting blood In fasting blood

Arterial pHArterial pH 7.35-7.457.35-7.45

BicarbonateBicarbonate 24-28 mEq/L24-28 mEq/L

OO22 content content17.2-22.0 ml/100 ml17.2-22.0 ml/100 ml

Total lipidTotal lipid 400-800 mg/100 ml400-800 mg/100 ml

GlucoseGlucose 75-110 mg/100 ml75-110 mg/100 ml

Normal Normal Physiological rangesPhysiological ranges

Fluid homeostasisFluid homeostasisComponentComponent ExtracellularExtracellularaa IntracellularIntracellular

CaCa2+2+ (mM) (mM) 2.52.5 1x101x10-4-4

ClCl-- (mM) (mM) 110110 ~10~10

HCOHCO33--(mM)(mM) 2020 ~10~10

KK++ (mM) (mM) 44 120120

NaNa++ (mM) (mM) 140140 1414

Osmolarity Osmolarity (mOsm/l)(mOsm/l)

295295 295295

pHpH 7.47.4 7.1-7.27.1-7.2aSmall differences between plasma and ISF due to protein 04/07/23 DR. QAZI IMTIAZ RASOOL

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

2.The intracellular fluid is “conditioned by”…

3. the interstitial fluid, which is “conditioned by”

4. the plasma, which is “conditioned by” …

5. the organ systems it passes through.

Balancing the Internal and External Environment

ICF ISF plasma organs

external environment internal environment

Fluid homeostasis r balanced between three major

compartments separated by 2 membranes

Fluid homeostasis r balanced between three major

compartments separated by 2 membranes

Comparable composition due to high permeability of endotheliumComparable composition due to high permeability of endothelium

Specific composition -selective permeability of membrane; active transport mechanisms

1.Plasma 2.ISF 3.ICF

Control Systems1. In order to maintain homeostasis, control

system must be able to

2. Detect deviations from normal in the internal environment that need to be held within narrow limits

3.Integrate this information with other relevant information

4.Make appropriate adjustments in order to restore factor to its desired value

Feedback Loops

1.Sensor: Detects deviation from set point.

2.Integrating center: Determines the response

ACCORDING TO THE SET-PIONT

3.Effector: Produces the response.

Stimulus:Produceschangein variable

Changedetectedby receptor

Input:Informationsent alongafferentpathway to

5 Response ofeffector feedsback to influencemagnitude of stimulus andreturnsvariable tohomeostasis

Variable (in homeostasis)

Imbalance

Receptor (sensor)

Controlcenter 4 Output:

Information sentalong efferentpathway to

Effector

Homeostatic Control Mechanisms

Control SystemsControl Systems

Reference Signal ComparatorComparator ControllerController EffectorsEffectors Regulated

Variable

SensorSensor

FeedbackSignal

Error Signal

Properties/FeaturesFeatures of loop regulatory systemsregulatory systems

1. SINGLE LOOP USUALLY DOES NOT OPERATE IN ISOLATION BUT COMPLEX INTERPLAY.(coupling)

2.MUST DETERMINE THE RELATIVE WEIGHT OF LOOP FEEDBACK IN COMPETITION WITH 1 ANOTHER

3 HIERACHY MUST BE ESTABLISHED AMONG VARIOUS OPERATING LOOPS

4.REDUNDANCY –MORE VITAL A PARAMETER MORE SYSTEMS R INVOLVED

5. EQUILIBRIUM =STATE IN WHICH NO ENERGY IS USED TO MAINTAIN THE STEADY STATE

Law of Mass Balance

Most simply, ins = outs

Homeostasis is not the same as equilibriumE.g., membrane

potentials

6.PRIORITY-CELLS/SYSTEM SHOULD NOT RUN AMOK FOR ITS OWN GREED

7. ADAPTABILITY- ON ABILITY TO ALTER THE RESPONSE

8. Adaptive control as an example of delayed negative feedback

9. Most control systems display negative feedback

10 .Not all control systems are equally effective e.g Concept of gain( variable gain)

6.PRIORITY-CELLS/SYSTEM SHOULD NOT RUN AMOK FOR ITS OWN GREED

7. ADAPTABILITY- ON ABILITY TO ALTER THE RESPONSE

8. Adaptive control as an example of delayed negative feedback

9. Most control systems display negative feedback

10 .Not all control systems are equally effective e.g Concept of gain( variable gain)

11. .Excessive perturbations may lead to positive feedback and instability

Some are useful e.g., blood clotting,

12. Undamped oscillations e.g, clonus

1. BASED ON VOLUNTARY CONTROL

1. Non-automatic Control

Open-loop system

2.Automatic Control

“feedback” means a process in which a part of output (feedback signal) from controlled organ returns to affect or modify the action of the control system.

CLASSIFICATION OF CONTROL System

2.Based on location:1. Intrinsic or local

control Regulatory

mechanism is initiated inside an organ. (= inherent to an organ)

Ex: local vasodilationmovement of cilia

2.Extrinsic: Regulatory mechanism

is initiated outside the organ. Accomplished by nervous and endocrine systems

3.Based on kinds of response

1.Negative feedback

2.Positive feedback:

3.Feedforward:

4. Servomechanisms

Negative Feedback1. Defending the set point 2. Main form of regulation. most

feedback systems in the body are negative

3. Driving the variable in the opposite direction of the initial change.

4. Multiply the error signal by some proportionate factore.g. when you feel cold, you start shivering to raise body temperature.

Positive feedback

1. Increases (accelerates) amplifies the actions of the body

2. Produces more instability in the body

3. Produces more chaos in the body

4. There are only a few types necessary for our survival

5. Positive feedback mechanisms are short-lived

6. Controls less frequent forms of events that do not require continuous adjustments

7. Considered to be the uncommon loop8. Driving the variable in the same direction of the initial change.

04/07/23 DR. QAZI IMTIAZ RASOOL33

3. Feed-forward control

Concept: a direct effect of stimulus on the control system before the action of feedback signal occurs.

1.Less frequent form of regulation.

2.Stimulus triggers a response in anticipation of a change in a variable.

3.Here the direct effect of the stimulus is termed disturb signal or interfere signal.

4. e,g 1. Shivering before diving into the cold water.

1.2. smell of food triggers digestive juice secretion

Significance of Feedback-forward :

1.adaptive feedback control.

2.makes the human body to fore-see and adapt the environment promptly and exactly

3.(prepare the body for the change).

1.Set piont is not fixed

2. Changes from time to timee.g stretch reflex

Regulation of the Body Functions

3 regulatory systems have to coordinated and acts as one system, “feedback control system”.

1. Endocrine/ Chemical Regulation- 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

- Example: baroreceptor reflex of arterial blood pressure

- Characteristics: response fast; acts exactly or locally, last for a short time

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.

Nervous system1. Receptors input –CNS-output

2. Role of autonomic nervous system

3. Local action

4.Spatially-determined information-

5. uses nerve impulses to respond to stresses in the body

6. response is rapid compare to endocrinal system

Nervous system1. Receptors input –CNS-output

2. Role of autonomic nervous system

3. Local action

4.Spatially-determined information-

5. uses nerve impulses to respond to stresses in the body

6. response is rapid compare to endocrinal system

ENDOCRINAL SYSTEM

1.Uses hormones to responds to stresses

2.Generalized action throughout body

3.Specificity conferred by receptor distribution

4.Response is slower than nervous system an

5. also is more fine tuning

ENDOCRINAL SYSTEM

1.Uses hormones to responds to stresses

2.Generalized action throughout body

3.Specificity conferred by receptor distribution

4.Response is slower than nervous system an

5. also is more fine tuning

REGULATION OF HOMEOSTASISThe 2 work together or independently to

regulate homeostasis

REGULATION OF HOMEOSTASISThe 2 work together or independently to

regulate homeostasis

Examples of homeostasis

Why do we have an optimum temperature?

Most chemical reactions in our body rely on enzymes (biological catalysts made of

proteins)

They need a reasonably high temperature to allow enough collisions with other

molecules (substrates) but not too high in case they denature (no longer work)

body temperature over time

37.5 °

36.5 °

37.5 °

36.5 °

37.5 °

36.5 °

37.0 °04/07/23 DR. QAZI IMTIAZ RASOOL 64

37.5 °

36.5 °

37.0 °(set point)

Components of a homeostatic mechanism

Stimulus

Components of a homeostatic mechanism

Stimulus

Stimulus Receptors

ControlCenter

Stimulus Receptors

ControlCenter

Stimulus Receptors

ControlCenter

Effectors

Stimulus Receptors

ControlCenter

Effectors

Stimulus Receptors

ControlCenter

EffectorsResponse

Regulation of Body Temp. Stimulus Receptors

ControlCenter

EffectorsResponse

Stimulus Receptors

ControlCenter

EffectorsResponse

Stimulus Receptors

ControlCenter

EffectorsResponse

(Various Neurons)

Stimulus Receptors

ControlCenter

EffectorsResponse

(Various Neurons)

(Hypo-thalamus)

Stimulus Receptors

ControlCenter

EffectorsResponse

(Various Neurons)

(Hypo-thalamus)

(Sweat glands, etc.)

Stimulus Receptors

ControlCenter

EffectorsResponse

(Various Neurons)

(Hypo-thalamus)

Temp04/07/23 DR. QAZI IMTIAZ RASOOL 80

Regulation of Body Temp. Stimulus Receptors

ControlCenter

EffectorsResponse

(Various Neurons)

(Hypo-thalamus)

Temp04/07/23 DR. QAZI IMTIAZ RASOOL 81

blood pH over time

7.4 04/07/23 DR. QAZI IMTIAZ RASOOL 82

Controlling Glucose levels

Your cells also need an exact level of glucose in the blood.

Excess glucose gets turned into glycogen in the liver

This is regulated by 2 hormones (chemicals) from the pancreas called:

InsulinGlucagon

Blood glucose over time

100 dl/ml 04/07/23 DR. QAZI IMTIAZ RASOOL 84

Glucose Concentration

Meal eaten

Insulin is produced and glucose levels fall to normal again.

Glucose levels rise after a meal.

Normal

Glucose Concentration

Meal eaten

Insulin is not produced so glucose levels stay high

Glucose levels rise after a meal.

Diabetic

What mechanisms are there to cool the body down?

Sweating

The skin

If the temperature rises, the blood vessel dilates (gets bigger).

This means more heat is lost from the surface of the skin

What mechanisms are there to warm the body up?

Vasoconstriction

If the temperature falls, the blood vessel constricts (gets shut off).

This means less heat is lost from the surface of the skin

STRESS AND HOMEOSTASISStress – is any stimuli (external and internal) disturbing homeostasis Examples of internal stresses - blood glucose, and acidity

Examples of external stresses - heat, cold, lack of oxygen

There are variations of stress from mild stress to extreme stress.e , g mild stress - thirst and hunger

extreme stress - poisoning, severe infection

For mild stress, cells respond quickly to restore imbalanceFor extreme stress, cells may restore incompletely the imbalance

and can result in chronic illness or even death.

DISEASE :HOMEOSTASIS and IMBALANCE Body processes remains within physiological limits body cells function well homeostasis is maintained body is

healthy.

But when body processes ( 1 or >1) loose their ability to contribute to homeostasis. The outcomes would result in;

- (if moderate) diseases results - (if severe) death results LOCAL DISEASES - disease affecting limited part/ region of the body.

SYSTEMIC DISEASE- disease affecting entire body.

SYMPTOMS - Subjective changes (complains) in the body function that a patient complains about, and is not apparent to an observer. (e.g. pain complaint by patient)

SIGNS - Objective changes that a clinician can observe and measure.

- SIGNS can be ; (ANATOMICAL changes) – Swelling, rash(PHYSIOLOGICAL changes) – Raised blood pressure and raised

body temperature

Frostbite

damage to hands

Homeostasis & Controls

•Successful compensation

•Homeostasis reestablished

•Failure to compensate

•Pathophysiology

•Illness

•Death

Homeostasis DR QAZI IMTIAZ RASOOL H.O.D GOVT MEDICAL COLLEGE KASHMIR

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HOMEOSTASIS BY DR QAZI IMTIAZ RASOOL OBJECTIVES 1.Define the terms homeostasis and steady state. 2.Identify the components of a control system. 3.Describe