CHAPTER 12
Homeostasis
12.1 The Need for Homeostasis
12.2 Structure of the Human Skin
12.3 Temperature Regulation
Chapter
12
Homeostasis
Learning Outcomes
After this section, you should be able to:
• define homeostasis and explain its importance in living
org...
Maintaining a constant internal environment
Homeostasis is the maintenance of internal conditions
of an organism at all ti...
Importance of homeostasis
12.1 The Need for Homeostasis
A stable internal environment allows an organism to
be independent...
Internal conditions that should be kept constant include:
• Temperature
• pH
• Water potential
• Concentration of metaboli...
Temperature and pH level
• Enzymes require an optimum temperature and
pH to function properly.
• Below the optimum tempera...
Water potential
• The composition of tissue fluid has to be
maintained to ensure that the water potential of cells
is kept...
Blood glucose level
• Glucose in food is required for tissue respiration
which releases energy for cells to carry out thei...
Principles of homeostasis
• A stimulus is a change from normal conditions in the
internal environment.
• Receptors detect ...
What happens when a condition rises
above normal?
12.1 The Need for Homeostasis
Normal condition or set point
Stimulus
(in...
12.1 The Need for Homeostasis
Stimulus
(decreases below norm)
Receptor
(detects the stimulus)
Self-regulatory
corrective m...
brain
12.1 The Need for Homeostasis
Receptor
Hypothalamus in brain
detects stimulus
Stimulus
Water potential of blood
incr...
brain
12.1 The Need for Homeostasis
Receptor
Hypothalamus in brain
detects stimulus
Stimulus
Water potential of blood
decr...
excess glucose  glycogen
liver
pancreas
Regulating blood glucose concentration
12.1 The Need for Homeostasis
Receptor
Isl...
glycogen  glucose
liver
pancreas
12.1 The Need for Homeostasis
Receptor
Islets of Langerhans in
pancreas stimulated
Stimu...
12.1 The Need for Homeostasis
12.2 Structure of the Human Skin
12.3 Temperature Regulation
Chapter
12
Homeostasis
Learning Outcome
After this section, you should be able to:
• identify the different structures in the human skin
and unde...
Epidermis
(outermost layer)
Dermis
Subcutaneous
(consisting of
fatty tissue)
12.2 Structure of the Human Skin
Main parts o...
• The dermis has
numerous blood
capillaries
supplying blood to
skin.
• When blood
vessels dilate,
more blood flows
to the ...
• When blood vessels
constrict, less blood
flows to the skin
surface
(vasoconstriction).
• Vasodilation and
vasoconstricti...
• Hairs are embedded
within the dermis.
• Malpighian layer sinks
into dermis to form a
hair follicle.
12.2 Structure of th...
• Hair papilla is found
at the base of the hair
follicle and consists of
blood capillaries and
nerves.
• Hair erector
musc...
• Sweat gland is a
coiled tube formed by
the downgrowth of the
epidermis.
• It is richly surrounded
by blood capillaries.
...
12.1 The Need for Homeostasis
12.2 Structure of Mammalian Skin
12.3 Temperature Regulation
Chapter
12
Homeostasis
12.3 Temperature Regulation
Learning Outcomes
After this section, you should be able to:
• describe the role of the skin i...
Heat gain by the body
12.3
• Heat produced is a result of metabolic activities in
the body.
• From the Sun and warm air on...
Heat loss by the body
12.3
• From the skin surface via convection, radiation and
conduction.
• Evaporation of sweat.
• Exp...
How the body temperature is regulated
12.3
Normal body
temperature (37°C)
Body temperature rises
(heat gain greater than
h...
12.3
brain
Receptor
Temperature receptors in
skin and hypothalamus
of brain stimulated
Stimulus
Blood and skin
temperature...
12.3
arteriole
capillaries
skin surface
Arterioles
in skin
dilate
1
More blood flows
to capillaries in
skin
2
3
Greater he...
Increased production of sweat
12.3
• Sweat glands become more active.
• More sweat is produced.
• As sweat evaporates from...
Relaxation of hair erector muscles
12.3
• Hair erector muscles relax when body temperature
increases.
• Hairs lie flat, al...
Reduced metabolic rate
12.3
• Rate of metabolic activities slow down.
• Less heat is produced within body.
Temperature Reg...
12.3
brain
Receptor
Temperature receptors in
skin and hypothalamus
of brain stimulated
Stimulus
Blood and skin
temperature...
12.3
Arterioles
in skin
constrict
1
Less blood flows
to capillaries in
skin
2
3
Less heat loss
4
Vasoconstriction
• Arteri...
Decreased production of sweat
12.3
• Sweat glands become less active.
• Less sweat is produced.
• Less latent heat is remo...
Contraction of hair erector muscles
12.3
• Hair erector muscles contract when body temperature
decreases.
• Hairs “stand u...
Increased metabolic rate
12.3
• Rate of metabolic activities increase.
• More heat is produced within body.
Shivering
• Oc...
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  • Notes:
    The external environment is the environment in which an organism lives.
    In a mammal, the internal environment consists of the blood and tissue fluid.
  • Note:
    Cells are made of biological molecules such as proteins, which make them very sensitive to slight fluctuations in temperature and pH.
  • Note:
    Point out that an animal cell will swell or even burst when it is placed in a solution of high water potential. When it is placed in a solution of low water potential, it will shrink in size.
  • Notes:
    Water potential of blood can increase due to an increased intake of water.
    The pituitary gland protrudes from the hypothalamus which is found at the base of the brain.
  • Notes:
    Water potential of blood can decrease due to loss of water through profuse sweating.
  • Note:
    Blood glucose concentration increases some time after a meal.
    The increased permeability of the cell surface membranes of the liver and muscle cells is caused by insulin.
    This enables glucose to be taken up more quickly by the liver and muscles.
  • Note:
    Blood glucose concentration decreases during vigorous muscular contraction or during starvation.
  • Note:
    Click on the Video-URL button to be directed to a website where an animation on the structure of the human skin can be found.
    This animation introduces the main characteristics of the different layers of the skin. (The animation lasts for about 55 seconds.)
  • Note:
    Vasodilation causes a person to blush or flush after vigorous exercise.
  • Note:
    Vasoconstriction causes a person to become pale.
  • Note:
    A hair follicle is a hollow tube
  • Note:
    Ask students to think about why they experience pain when a hair is pulled out but no pain is experienced when their hair is cut by a hair stylist. Follow up by explaining that when the cells covering the hair papilla are pushed upwards, they die and harden, forming hair. Thus, the hair shaft consists of dead cells. This is why no pain is experienced when hair is being cut. However, when hair is pulled out, it tugs onto the hair papilla where nerves are found, thus causing pain.
  • Notes:
    Point out that the skin is considered an excretory organ because along with sweat, a small amount of urea is removed through sweating.
    When sweat evaporates from the body surface, it removes heat from the body and thus produces a cooling effect on the body.
  • Note:
    Heat loss at the skin surface occurs mainly by convection and radiation.
  • Notes:
    When the temperature receptors in the skin sense a change in the temperature, nerve impulses are sent to the brain. This stimulates the hypothalamus to send nerve impulses to relevant parts of the body.
  • Note:
    Latent heat is the energy that is absorbed or released when a substance undergoes a change of state.
  • Note:
    The relaxation of the hair erector muscles does not have much effect in increasing heat loss in humans.
  • Note:
    We can counter the heat by putting on clothing made of materials that absorb sweat better, moving to a cool place or drinking cold water.
  • Note:
    The contraction of the hair erector muscles does not have much effect in increasing heat production in humans.
  • Note:
    We can counter the cold by putting on extra clothing, moving to a warmer place or drinking warm water.
  • 5094 homeostasis 2014

    1. 1. CHAPTER 12 Homeostasis
    2. 2. 12.1 The Need for Homeostasis 12.2 Structure of the Human Skin 12.3 Temperature Regulation Chapter 12 Homeostasis
    3. 3. Learning Outcomes After this section, you should be able to: • define homeostasis and explain its importance in living organisms; • explain the concept of negative feedback; • describe the maintenance of blood glucose levels; and • describe the process of osmoregulation. 12.1 The Need for Homeostasis
    4. 4. Maintaining a constant internal environment Homeostasis is the maintenance of internal conditions of an organism at all times. 12.1 The Need for Homeostasis Large external fluctuations External environment Homeostatic mechanism Internal environment Small internal fluctuations body cells
    5. 5. Importance of homeostasis 12.1 The Need for Homeostasis A stable internal environment allows an organism to be independent of changes in the external environment.
    6. 6. Internal conditions that should be kept constant include: • Temperature • pH • Water potential • Concentration of metabolic wastes • Blood glucose concentration • Carbon dioxide concentration 12.1 The Need for Homeostasis
    7. 7. Temperature and pH level • Enzymes require an optimum temperature and pH to function properly. • Below the optimum temperature, enzymes are inactivated. Beyond the optimum temperature, enzymes are denatured. • Drastic changes in pH level in the blood affect the activity of enzymes and the rate of cellular reactions. 12.1 The Need for Homeostasis
    8. 8. Water potential • The composition of tissue fluid has to be maintained to ensure that the water potential of cells is kept constant. • Changes in the water potential affect the body cells. • Body cells will either shrink or burst in solutions with water potentials different from that in the cytoplasm. 12.1 The Need for Homeostasis
    9. 9. Blood glucose level • Glucose in food is required for tissue respiration which releases energy for cells to carry out their activities. • Glucose levels increase after a meal and decrease following physical exertion. • If blood glucose concentration changes drastically, it can be dangerous. 12.1 The Need for Homeostasis
    10. 10. Principles of homeostasis • A stimulus is a change from normal conditions in the internal environment. • Receptors detect stimulus. • A corrective mechanism brings about the reverse effect of the stimulus. • Negative feedback ‘tells’ the receptors that the condition has been restored back to normal state. 12.1 The Need for Homeostasis
    11. 11. What happens when a condition rises above normal? 12.1 The Need for Homeostasis Normal condition or set point Stimulus (increases above norm) Receptor (detects the stimulus) Self-regulatory corrective mechanism Condition decreases Negative feedback
    12. 12. 12.1 The Need for Homeostasis Stimulus (decreases below norm) Receptor (detects the stimulus) Self-regulatory corrective mechanism Negative feedback Normal condition or set point Condition increases What happens when a condition decreases below normal?
    13. 13. brain 12.1 The Need for Homeostasis Receptor Hypothalamus in brain detects stimulus Stimulus Water potential of blood increases above the norm Water potential of blood returns to normal Less water is reabsorbed by kidney tubules Corrective Mechanism Pituitary gland releases less anti-diuretic hormone (ADH) More water is excreted and urine produced is more dilute Water potential of blood decreases Negative feedback Regulating body water potential
    14. 14. brain 12.1 The Need for Homeostasis Receptor Hypothalamus in brain detects stimulus Stimulus Water potential of blood decreases below the norm Water potential of blood returns to normal More water is reabsorbed by kidney tubules Corrective Mechanism Pituitary gland releases more anti-diuretic hormone (ADH) Less water is excreted and urine produced is more concentrated Water potential of blood increases Negative feedback Regulating body water potential
    15. 15. excess glucose  glycogen liver pancreas Regulating blood glucose concentration 12.1 The Need for Homeostasis Receptor Islets of Langerhans in pancreas stimulated Stimulus Concentration of blood glucose increases above the norm Concentration of blood glucose returns to normal Permeability of cell surface membrane to glucose increases Corrective Mechanism Islets 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. Concentration of blood glucose decreases and insulin production falls. Negative feedback
    16. 16. glycogen  glucose liver pancreas 12.1 The Need for Homeostasis Receptor Islets of Langerhans in pancreas stimulated Stimulus Concentration of blood glucose decreases below the norm Concentration of blood glucose returns to normal Corrective Mechanism Islets of Langerhans secretes more glucagon, which is transported by blood to liver and muscles. Glucose is released into the bloodstream. Concentration of blood glucose decreases and insulin production falls. Negative feedback Glycogen stored in liver is converted to glucose. Regulating blood glucose concentration
    17. 17. 12.1 The Need for Homeostasis 12.2 Structure of the Human Skin 12.3 Temperature Regulation Chapter 12 Homeostasis
    18. 18. Learning Outcome After this section, you should be able to: • identify the different structures in the human skin and understand their functions. 12.2 Structure of the Human Skin
    19. 19. Epidermis (outermost layer) Dermis Subcutaneous (consisting of fatty tissue) 12.2 Structure of the Human Skin Main parts of the skin URL
    20. 20. • The dermis has numerous blood capillaries supplying blood to skin. • When blood vessels dilate, more blood flows to the skin surface (vasodilation). 12.2 Structure of the Human Skin arterioles capillaries
    21. 21. • When blood vessels constrict, less blood flows to the skin surface (vasoconstriction). • Vasodilation and vasoconstriction play a role in the regulation of body temperature. 12.2 Structure of the Human Skin
    22. 22. • Hairs are embedded within the dermis. • Malpighian layer sinks into dermis to form a hair follicle. 12.2 Structure of the Human Skin hair hair follicle
    23. 23. • Hair papilla is found at the base of the hair follicle and consists of blood capillaries and nerves. • Hair erector muscles contract and cause hairs to stand, resulting in appearance of goose pimples. 12.2 Structure of the Human Skin hair erector muscle hair papilla
    24. 24. • Sweat gland is a coiled tube formed by the downgrowth of the epidermis. • It is richly surrounded by blood capillaries. • It secretes sweat which flows through the sweat duct and sweat pore to the skin surface. 12.2 Structure of the Human Skin sweat gland sweat pore sweat duct blood capillaries
    25. 25. 12.1 The Need for Homeostasis 12.2 Structure of Mammalian Skin 12.3 Temperature Regulation Chapter 12 Homeostasis
    26. 26. 12.3 Temperature Regulation Learning Outcomes After this section, you should be able to: • describe the role of the skin in the maintenance of a constant body temperature in humans.
    27. 27. Heat gain by the body 12.3 • Heat produced is a result of metabolic activities in the body. • From the Sun and warm air on hot days. • Intake of hot food and drinks. • During physical exertion or exercise. Temperature Regulation
    28. 28. Heat loss by the body 12.3 • From the skin surface via convection, radiation and conduction. • Evaporation of sweat. • Expired air from lungs. • Faeces and urine. Temperature Regulation
    29. 29. How the body temperature is regulated 12.3 Normal body temperature (37°C) Body temperature rises (heat gain greater than heat loss) Body temperature falls (heat loss greater than heat gain) • Reduce heat production • Increase heat loss to surroundings • Increase heat production • Decrease heat loss to surroundings Temperature Regulation
    30. 30. 12.3 brain Receptor Temperature receptors in skin and hypothalamus of brain stimulated Stimulus Blood and skin temperatures increase Blood and skin temperatures return to normal Corrective Mechanism • Vasodilation of arterioles near skin’s surface • Increased production of sweat • Increased rate of breathing • Metabolic rate decreases Increased heat loss and reduced heat production Body temperature decreases Negative feedback What happens on a hot day? skin Temperature Regulation
    31. 31. 12.3 arteriole capillaries skin surface Arterioles in skin dilate 1 More blood flows to capillaries in skin 2 3 Greater heat loss 4 Vasodilation 1. Dilation of arterioles 2. More blood flows to the capillaries 3. When shunt vessels constrict, more blood flows to capillaries. 4. More heat is lost from skin by radiation, convection and conduction. Shunt vessel constricts shunt vessel Temperature Regulation
    32. 32. Increased production of sweat 12.3 • Sweat glands become more active. • More sweat is produced. • As sweat evaporates from the surface of the skin, heat is lost from the body via latent heat of vaporisation. more sweat produced more active sweat gland Temperature Regulation
    33. 33. Relaxation of hair erector muscles 12.3 • Hair erector muscles relax when body temperature increases. • Hairs lie flat, allowing air to circulate over skin. This removes heat. hairs lie flat Temperature Regulation
    34. 34. Reduced metabolic rate 12.3 • Rate of metabolic activities slow down. • Less heat is produced within body. Temperature Regulation
    35. 35. 12.3 brain Receptor Temperature receptors in skin and hypothalamus of brain stimulated Stimulus Blood and skin temperatures decrease Blood and skin temperatures return to normal Corrective Mechanism • Vasoconstriction of arterioles near skin’s surface • Decreased production of sweat • Metabolic rate increases • Shivering Decreased heat loss and increased heat production Body temperature increases Negative feedback What happens on a cold day? skin Temperature Regulation
    36. 36. 12.3 Arterioles in skin constrict 1 Less blood flows to capillaries in skin 2 3 Less heat loss 4 Vasoconstriction • Arterioles in skin constrict. • Less blood flows to capillaries in the skin • When shunt vessels dilate, less blood flows to capillaries. • Less heat is lost from skin by radiation, convection and conduction. Shunt vessel dilates Temperature Regulation arteriole capillaries skin surface shunt vessel
    37. 37. Decreased production of sweat 12.3 • Sweat glands become less active. • Less sweat is produced. • Less latent heat is removed when sweat evaporates. less sweat produced less active sweat gland Temperature Regulation
    38. 38. Contraction of hair erector muscles 12.3 • Hair erector muscles contract when body temperature decreases. • Hairs “stand up”, trapping an insulating layer of warm air over skin. hairs “stand up” Temperature Regulation
    39. 39. Increased metabolic rate 12.3 • Rate of metabolic activities increase. • More heat is produced within body. Shivering • Occurs when more heat production is needed to prevent drop in temperature. • Reflex contraction of the body muscles generates heat which increases body temperature to normal. Temperature Regulation

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