Download - 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
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What Happens When Glucose Concentration Rises?
Receptor
Islets of Langerhans in pancreas stimulated
pancreas
Stimulus
Blood glucose concentration rises above normal levels
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What Happens When Glucose Concentration Rises?
Receptor
Islets of Langerhans in pancreas stimulated
Corrective MechanismIslets of Langerhans secretes more insulin, which is transported by blood to liver and muscles
pancreas
liver
Stimulus
Blood glucose concentration rises above normal levels
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What Happens When Glucose Concentration Rises?
Receptor
Islets of Langerhans in pancreas stimulated
Permeability of cell surface membrane to glucose increases
Corrective MechanismIslets of Langerhans secretes more insulin, which is transported by blood to liver and muscles
pancreas
liver
Stimulus
Blood glucose concentration rises above normal levels
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What Happens When Glucose Concentration Rises?
Receptor
Islets of Langerhans in pancreas stimulated
Permeability of cell surface membrane to glucose increases
Corrective MechanismIslets of Langerhans secretes more insulin, which is transported by blood to liver and muscles
Liver and muscles convert excess glucose to glycogen. Glycogen is stored in liver and muscles
pancreas
excess glucose glycogen
liver
Stimulus
Blood glucose concentration rises above normal levels
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What Happens When Glucose Concentration Rises?
Receptor
Islets of Langerhans in pancreas stimulated
Permeability of cell surface membrane to glucose increases
Corrective MechanismIslets of Langerhans secretes more insulin, which is transported by blood to liver and muscles
Liver and muscles convert excess glucose to glycogen. Glycogen is stored in liver and muscles
Blood glucose concentration decreases and insulin production falls
pancreas
excess glucose glycogen
liver
Stimulus
Blood glucose concentration rises above normal levels
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What Happens When Glucose Concentration Rises?
Receptor
Islets of Langerhans in pancreas stimulated
Permeability of cell surface membrane to glucose increases
Corrective MechanismIslets of Langerhans secretes more insulin, which is transported by blood to liver and muscles
Liver and muscles convert excess glucose to glycogen. Glycogen is stored in liver and muscles
Blood glucose concentration decreases and insulin production falls
pancreas
excess glucose glycogen
liver
Blood glucose concentration returns to normal
Stimulus
Blood glucose concentration rises above normal levels
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What Happens When Glucose Concentration Rises?
Receptor
Islets of Langerhans in pancreas stimulated
Stimulus
Blood glucose concentration rises above normal levels
Permeability of cell surface membrane to glucose increases
Corrective MechanismIslets of Langerhans secretes more insulin, which is transported by blood to liver and muscles
Liver and muscles convert excess glucose to glycogen. Glycogen is stored in liver and muscles
Blood glucose concentration decreases and insulin production falls
Negative feedback
Blood glucose concentration returns to normal
excess glucose glycogen
pancreas
liver
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What Happens When Glucose Concentration Rises?
Chapter 12 HomeostasisWhat Happens When Glucose Concentration Falls?April 8, 2023
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Stimulus
Blood glucose concentration falls below normal levels
What Happens When Glucose Concentration Falls?
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Receptor
Islets of Langerhans in pancreas stimulated
Stimulus
Blood glucose concentration falls below normal levels
pancreas
What Happens When Glucose Concentration Falls?
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Stimulus
Blood glucose concentration falls below normal levels
pancreas
liver
Corrective MechanismIslets of Langerhans secretes more glucagon, which is transported by blood to liver and muscles
Receptor
Islets of Langerhans in pancreas stimulated
What Happens When Glucose Concentration Falls?
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Glucagon converts stored glycogen back to glucose. From liver, glucose enters bloodstream
Stimulus
Blood glucose concentration falls below normal levels
pancreas
liver
glycogen glucose
Corrective MechanismIslets of Langerhans secretes more glucagon, which is transported by blood to liver and muscles
Receptor
Islets of Langerhans in pancreas stimulated
What Happens When Glucose Concentration Falls?
April 8, 2023 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 27
Glucagon converts stored glycogen back to glucose. From liver, glucose enters bloodstream
Stimulus
Blood glucose concentration falls below normal levels
pancreas
liver
glycogen glucoseReceptor
Islets of Langerhans in pancreas stimulated
Corrective MechanismIslets of Langerhans secretes more glucagon, which is transported by blood to liver and muscles
Blood glucose concentration rises and glucagon production decreases
What Happens When Glucose Concentration Falls?
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Glucagon converts stored glycogen back to glucose. From liver, glucose enters bloodstream
Stimulus
Blood glucose concentration falls below normal levels
pancreas
liver
glycogen glucoseReceptor
Islets of Langerhans in pancreas stimulated
Corrective MechanismIslets of Langerhans secretes more glucagon, which is transported by blood to liver and muscles
Blood glucose concentration rises and glucagon production decreases
Blood glucose concentration returns to normal
What Happens When Glucose Concentration Falls?
liver
Receptor
Islets of Langerhans in pancreas stimulated
Glucagon converts stored glycogen back to glucose. From liver, glucose enters bloodstream
Corrective MechanismIslets of Langerhans secretes more glucagon, which is transported by blood to liver and muscles
Negative feedback
Stimulus
Blood glucose concentration falls below normal levels
Blood glucose concentration returns to normal
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What Happens When Glucose Concentration Falls?
Blood glucose concentration rises and glucagon production decreases
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
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Stimulus
Blood and skin temperatures rise
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skin temperatures rise
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skin temperatures rise
blood capillaries
hair folliclehair
arteriole
erector muscle
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skin temperatures rise
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
arteriole
capillariesskin surface
Arterioles in skin dilate
1
More blood flows to capillaries in skin
2
3
Greater heat loss
4
Shunt vessels constrict
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skin temperatures rise
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
sweat duct
sweat pore
sweat gland
Sweat glands more active
Sweat production increases
More latent heat lost as sweat evaporates
6
7
5
Regulating Body Temperature - on a Hot Day
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
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Stimulus
Blood and skin temperatures rise
Hair erector muscles in skin relax
erector muscle
blood capillaries
hair folliclehair
arteriole
8
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skin temperatures rise
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
Corrective Mechanism
Increase in heat loss and decrease in heat production
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skin temperatures rise
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
Corrective Mechanism
Increase in heat loss and decrease in heat production
Decreased metabolic rate reduces heat production
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skin temperatures rise
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
Corrective Mechanism
Increase in heat loss and decrease in heat production
Blood temperature returns to normal levels
Decreased metabolic rate reduces heat production
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skin temperatures rise
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
Corrective Mechanism
Increase in heat loss and decrease in heat production
Blood temperature returns to normal levels
Negativefeedback
Decreased metabolic rate reduces heat production
Regulating Body Temperature - on a Hot Day
Regulating Body Temperature - on a Cold Day
Chapter 12 Homeostasis
April 8, 2023
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Stimulus
Blood and skin temperatures fall
Regulating Body Temperature - on a Cold Day
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Stimulus
Blood and skin temperatures fall
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Regulating Body Temperature - on a Cold Day
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blood capillariesarteriole
hair hair follicle
Stimulus
Blood and skin temperatures fall
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
erector muscles
Regulating Body Temperature - on a Cold Day
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Stimulus
Blood and skin temperatures fall
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Less blood flows to capillaries in skin
Arterioles in skin constrict
Shunt vessels dilate
skin surfacecapillaries
arteriole
1
2
3
Less heat loss
4
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
Regulating Body Temperature - on a Cold Day
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Sweat glands less active
Sweat production decreases
Less latent heat lost
sweat pore
sweat duct
sweat gland
Stimulus
Blood and skin temperatures fall
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
56
7
Regulating Body Temperature - on a Cold Day
Hair erector muscles in skin contract
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erector muscles
blood capillariesarteriole
hair hair follicle
Stimulus
Blood and skin temperatures fall
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
8
Regulating Body Temperature - on a Cold Day
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Shivering occurs when insufficient heat is produced
Stimulus
Blood and skin temperatures fall
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is
stimulated and sends nerve impulses to relevant body parts
Corrective Mechanism
Decrease in heat loss and increase in heat production
Regulating Body Temperature - on a Cold Day
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Stimulus
Blood and skin temperatures fall
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Corrective Mechanism
Decrease in heat loss and increase in heat production
Increased metabolic rate increases heat production
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
Regulating Body Temperature - on a Cold Day
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Blood temperature returns to normal levels
Stimulus
Blood and skin temperatures fall
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Corrective Mechanism
Decrease in heat loss and increase in heat production
Increased metabolic rate increases heat production
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
Regulating Body Temperature - on a Cold Day
Regulating Body Temperature - on a Cold Day
Corrective Mechanism
Decrease in heat loss and increase in heat production
Increased metabolic rate increases heat production
Blood temperature returns to normal levels
Negativefeedback
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Stimulus
Blood and skin temperatures fall
Receptor
Temperature receptors detect changes and send nerve impulses to the brain
Hypothalamus of brain is stimulated and sends nerve impulses to relevant body parts
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
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HOMEOSTASIS
The maintenance of a constant internal environment
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Principles of Homeostasis
HOMEOSTASIS
The maintenance of a constant internal environment
Principles of Homeostasis
Stimulus
Change in internal environment
HOMEOSTASIS
The maintenance of a constant internal environment
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Principles of Homeostasis
Stimulus
Change in internal environment
HOMEOSTASIS
The maintenance of a constant internal environment
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Receptors
Detect the change
Principles of Homeostasis
Stimulus
Change in internal environment
HOMEOSTASIS
The maintenance of a constant internal environment
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Receptors
Detect the change
Self-corrective Mechanism
To rectify the change
Principles of Homeostasis
Stimulus
Change in internal environment
HOMEOSTASIS
The maintenance of a constant internal environment
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Receptors
Detect the change
Self-corrective Mechanism
To rectify the change
Examples
Regulation of blood glucose concentration
Principles of Homeostasis
Stimulus
Change in internal environment
HOMEOSTASIS
The maintenance of a constant internal environment
April 8, 2023 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 69
Receptors
Detect the change
Self-corrective Mechanism
To rectify the change
Examples
Regulation of blood glucose concentration
Regulation of blood water potential
Principles of Homeostasis
Stimulus
Change in internal environment
HOMEOSTASIS
The maintenance of a constant internal environment
April 8, 2023 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 70
Receptors
Detect the change
Self-corrective Mechanism
To rectify the change
Examples
Regulation of blood glucose concentration
Regulation of blood water potential
Regulation of body temperature
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Principles of Homeostasis
Stimulus Receptors Self-corrective Mechanism Negative Feedback
Change in internal environment
Detect the change
Regulation of blood glucose concentration
Examples
To rectify the change
Regulation of blood water potential
Regulation of body temperature
The reverse effect of the change
HOMEOSTASIS
The maintenance of a constant internal environment
Workbook
MCQ
Q1 – 5
Structured Questions
1, 2, 3