Chapter 12 Homeostasis

Chapter 12

Homeostasis

ObjectivesStudents should be able to:

• Define homeostasis as the maintenance of a constant internal environment

• Explain the basic principles of homeostasis in terms of stimulus resulting from a change in the internal environment, a corrective mechanism and a negative feedback

Objectives continue…• Identify on a diagram of the skin: hairs,

sweat glands, temperature receptors, blood vessels and fatty tissue

• Describe the maintenance of a constant body temperature in humans in terms of insulation and the role of: temperature receptors in the skin, sweating, shivering, blood vessels near the skin surface and the co-ordinating role of the brain

Introduction

• Textbook Pg 239

• How does animals such as penguins keep their body temperature at 38 °C when their surrounding temperature could be as low as -20 °C?

The need of Homeostasis

• Conditions outside our body are changing all the time.

• But conditions within our body must be kept constant e.g pH and body temperature. Why?

• Why does body temperature have to be kept constant?• Ensure that enzymes do not get inactivated or

denatured since enzymes only work within a a certain temperature range

• Why must tissue fluid be kept at a constant pH and water potential?• Change in pH affects enzyme reactions in the

cells• Change in water potential affects the cells

(cells can be crenated or burst)

What is homeostasis?

• Homeostasis is the maintenance of a constant internal environment [body fluids (tissue fluid & blood)]

• Once the internal environment is stable, it allows an organism to be independent from changes in the external environment

Homeostasis involves Negative Feedback

• Homeostatic control involves a principle called negative feedback

• E.g. water potential of blood increases above normal (norm), it is detected by a receptor (detector). Your body respond by returning the water potential back to the normal condition. If water potential goes too low, the body responds and the water potential rises to normal again

• That is, the body always reacts to bring about an opposite effect to changes

• If the system is disturbed, the disturbance sets in motion a sequence of events that tends to restore the system to its original state Negative feedback process

• Can you think of other examples where the body uses the principle of negative feedback to regulate changes?

Occurrence of homeostatic control

• There must be :• A stimulus which is a change in the internal

environment

• A receptor which can detect the stimulus

• An automatic or self-regulatory corrective mechanism, which brings about

• A negative feedback to the stimulus

Fig. 12.2

Examples of Homeostasis in Man

• Regulation of blood glucose concentration (will be covered again)

• Regulation of blood water potential (covered in Excretion)

• Temperature Regulation (will study in details)

Chapter 12 HomeostasisWhat Happens When Glucose Concentration Rises?April 8, 2023

Stimulus

Blood glucose concentration rises above normal levels

April 8, 2023 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 14

What Happens When Glucose Concentration Rises?

Receptor

Islets of Langerhans in pancreas stimulated

pancreas

Stimulus




Receptor


Corrective MechanismIslets of Langerhans secretes more insulin, which is transported by blood to liver and muscles

pancreas

liver

Stimulus




Receptor


Permeability of cell surface membrane to glucose increases


pancreas

liver

Stimulus




Receptor




Liver and muscles convert excess glucose to glycogen. Glycogen is stored in liver and muscles

pancreas

excess glucose glycogen

liver

Stimulus




Receptor





Blood glucose concentration decreases and insulin production falls

pancreas


liver

Stimulus




Receptor






pancreas


liver

Blood glucose concentration returns to normal

Stimulus




Receptor


Stimulus






Negative feedback



pancreas

liver



Chapter 12 HomeostasisWhat Happens When Glucose Concentration Falls?April 8, 2023


Stimulus

Blood glucose concentration falls below normal levels

What Happens When Glucose Concentration Falls?


Receptor


Stimulus


pancreas



Stimulus


pancreas

liver

Corrective MechanismIslets of Langerhans secretes more glucagon, which is transported by blood to liver and muscles

Receptor




Glucagon converts stored glycogen back to glucose. From liver, glucose enters bloodstream

Stimulus


pancreas

liver

glycogen glucose


Receptor





Stimulus


pancreas

liver

glycogen glucoseReceptor



Blood glucose concentration rises and glucagon production decreases




Stimulus


pancreas

liver

glycogen glucoseReceptor






liver

Receptor




Negative feedback

Stimulus






glycogen glucose

pancreas

The Mammalian Skin

• Functions:1. Protective covering

2. Excretory organ

3. Regulator of body temperature

• Any change in the temperature of the surroundings can be detected by the skin

Figure 12.4 A section of the human skin

Functions of the different parts of skin

• Blood vessels – to bring oxygen to the cells in the skin. The arterioles can dilate or constrict to regulate the amount of blood flowing through the skin. This helps to regulate body temperature

• sweat gland – produces sweat which can help to cool down the body temperature

• Hair - can help to trap air to insulate the body

• Nerve endings (temperature receptors) – detect changes in temperature of the external environment

• Fatty/adipose tissue – stores fat and serves as an insulating layer, preventing heat loss

Heat Production and Heat Loss

• Heat is produced in the body:• Due to metabolic activities (e.g. tissue

respiration). Esp in liver and muscles whereby lots of heat are produced in these organs

• Extra heat in Man is gained by eating hot food, from the sun, warm air, by exercising

• Heat is lost:• Through the skin by convection, radiation

and conduction

• By evaporation of sweat from skin

• In the faeces and urine

• In the exhaled air coming from lungs

Regulating Body Temperature

• Hypothalamus in the brain • monitors and regulates the body

temperature

• receives information about the heat changes in the external environment from the temperature receptors in the skin

• Monitors the temperature of blood that passes through it

Chapter 12 HomeostasisRegulating Body Temperature - on a Hot DayApril 8, 2023


Stimulus

Blood and skin temperatures rise

Regulating Body Temperature - on a Hot Day


Stimulus


Receptor

Temperature receptors detect changes and send nerve impulses to the brain



Stimulus


blood capillaries

hair folliclehair

arteriole

erector muscle

Receptor


Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts



Stimulus


Receptor



arteriole

capillariesskin surface

Arterioles in skin dilate

1

More blood flows to capillaries in skin

2

3

Greater heat loss

4

Shunt vessels constrict



Stimulus



sweat duct

sweat pore

sweat gland

Sweat glands more active

Sweat production increases

More latent heat lost as sweat evaporates

6

7

5


Receptor



Stimulus


Hair erector muscles in skin relax

erector muscle

blood capillaries

hair folliclehair

arteriole

8

Receptor





Stimulus


Receptor



Corrective Mechanism

Increase in heat loss and decrease in heat production



Stimulus


Receptor





Decreased metabolic rate reduces heat production



Stimulus


Receptor





Blood temperature returns to normal levels




Stimulus


Receptor






Negativefeedback



Regulating Body Temperature - on a Cold Day

Chapter 12 Homeostasis

April 8, 2023


Stimulus

Blood and skin temperatures fall



Stimulus


Receptor




blood capillariesarteriole

hair hair follicle

Stimulus


Receptor



erector muscles



Stimulus


Receptor


Less blood flows to capillaries in skin

Arterioles in skin constrict

Shunt vessels dilate

skin surfacecapillaries

arteriole

1

2

3

Less heat loss

4




Sweat glands less active

Sweat production decreases

Less latent heat lost

sweat pore

sweat duct

sweat gland

Stimulus


Receptor



56

7


Hair erector muscles in skin contract


erector muscles

blood capillariesarteriole

hair hair follicle

Stimulus


Receptor



8



Shivering occurs when insufficient heat is produced

Stimulus


Receptor


Hypothalamus of brain is

stimulated and sends nerve impulses to relevant body parts


Decrease in heat loss and increase in heat production



Stimulus


Receptor




Increased metabolic rate increases heat production





Stimulus


Receptor












Negativefeedback


Stimulus


Receptor



What happens when body temperature drops?

• Heat lost by body activates the temperature receptors in the skin nerve impulses sent to heat gain centre of the hypothalamus. Following mechanisms take place:

1. Vasoconstriction

2. Sweat glands become less active

3. Metabolic rate increases

4. Contraction of hair erector muscle

5. Shivering (if the above reactions are not sufficient)

When body temperature begins to rise….

• Vigorous muscular activities heat produced rise in blood temperature heat loss centre in hypothalamus activated nerve impulses sent to different body parts following mechanisms take place :

Vasodilation sweat glands increases activity rapid breathing metabolic rate slows down

• Hence body temperature remains constant as extra heat is removed

Chapter 12 HomeostasisHomeostasis (Concept Map)April 8, 2023


HOMEOSTASIS

The maintenance of a constant internal environment


Principles of Homeostasis

HOMEOSTASIS



Stimulus

Change in internal environment

HOMEOSTASIS




Stimulus


HOMEOSTASIS



Receptors

Detect the change


Stimulus


HOMEOSTASIS



Receptors

Detect the change

Self-corrective Mechanism

To rectify the change


Stimulus


HOMEOSTASIS



Receptors

Detect the change



Examples

Regulation of blood glucose concentration


Stimulus


HOMEOSTASIS



Receptors

Detect the change



Examples


Regulation of blood water potential


Stimulus


HOMEOSTASIS



Receptors

Detect the change



Examples



Regulation of body temperature



Stimulus Receptors Self-corrective Mechanism Negative Feedback


Detect the change


Examples



Regulation of body temperature

The reverse effect of the change

HOMEOSTASIS


Workbook

MCQ

Q1 – 5

Structured Questions

1, 2, 3

Chapter 12 Homeostasis

Health & Medicine

Transcript of Chapter 12 Homeostasis