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1. 1
Higher Biology
Homeostasis in humans- part 1

2. 2
Human Homeostasis
By the end of this lesson you should be
able to:
 Know the principle of negative feedback
 Know how the water concentration of the blood is
maintained.
 Explain the role of ADH in osmoregulation
 Know how the blood sugar concentration is maintained.
 Explain the role of insulin, glucagon and adrenaline in
controlling blood sugar levels.

3. 3
Physiological Homeostasis
 Physiological homeostasis- body’s
ability to maintain relatively stable
internal conditions even though the
outside world changes continuously.
 dynamic vs. steady state is
constant (example- water bath
temperature control)

4. 4
Physiological Homeostasis
What do we mean by internal
environment?
 The millions of cells that make up our
body and the tissue fluid that bathes
them is the internal environment.

5. 5
Physiological Homeostasis
We will look at how the body regulates:
1. Water concentration of the blood
2. Blood glucose levels
3. Internal body temperature.

6. 6
Physiological Homeostasis
Why do we need to regulate
1. Water concentration of the blood?
Otherwise many physiological and
biochemical functions would be
impaired.
e.g. nervous co-ordination and
membrane permeability.

7. 7
Physiological Homeostasis
Why do we need to regulate:
2. Blood glucose levels?
 To provide the energy needed by
cells to perform energy demanding
jobs.
 e.g. synthesis of protein, active
transport, muscle contraction.

8. 8
Physiological Homeostasis
Why do we need to regulate:
3. Internal body temperature?
 To provide the optimum conditions
for enzyme-catalysed reactions to
be carried out.

9. 9
Water Bath
Temperature set on thermostat
Too cool? Heater kicks on and temperature goes up
Too warm? Heater stays off until bath cools down
Constant checking and turning on and off

10. 10
Control of homeostasis through
feedback
 Feedback system- cycle of events in which the
status of a body condition is continually
monitored, evaluated, changed, re-monitored,
re-evaluated, etc.

11. 11
 1) receptor
 sensor that responds to changes (stimuli)
 2) control centre
 sets range of values, evaluates input and
sends output
 3) effector
 receives output from control centre and
produces a response
3 basic components of a feedback system

12. 12

13. 13
Osmoregulation
 This is where the
body maintains its
concentration of
water, salts and ions
at the correct level.
 The receptors are
in the
hypothalamus-
called
osmoreceptors.

14. 14
Osmoregulation
 The control centre
is the pituitary
gland.
 It responds by
producing ADH
(Anti-Diuretic
Hormone).

15. 15
Osmoregulation
 ADH travels in the
blood to the kidney.
 The effector is the
tubules in the
kidney.
 They responds by
changing their
permeability to
water.

16. 16
Osmoregulation-increase in water
concentration of the blood.
 The water concentration of the blood can
increase due to:
 Drinking lots of dilute liquids.

17. 17
Osmoregulation-increase in water
concentration of the blood.
1. Detected by osmoreceptors in the
hypothalamus.
2. Causes pituitary gland to release less ADH.
3. ADH travels in blood.
4. Kidney tubules become less permeable to
water.
5. Less water reabsorbed by osmosis into the
blood.
6. Large volume of dilute urine produced.
7. Water concentration of the blood falls back to
normal.

18. 18
Osmoregulation-decrease in water
concentration of the blood.
 The water concentration
of the blood can decrease
due to:
 Sweating.
 Eating salty food
 Lack of drinking water

19. 19
Osmoregulation-decrease in water
concentration of the blood.
1. Detected by osmoreceptors in the
hypothalamus.
2. Causes pituitary gland to release more ADH.
3. ADH travels in blood.
4. Kidney tubules become more permeable to
water.
5. More water reabsorbed by osmosis into the
blood.
6. Small volume of concentrated urine produced.
7. Water concentration of the blood rises back
to normal.

20. 20
Osmoregulation
1. Insert and complete the “Control of Blood
Water Concentration” diagram

21. 21
Control of Blood sugar
 All cells need a continuous supply of energy-
glucose is therefore constantly being used up by
cells.
 Glucose is only supplied to the body during
eating.
 Stored glucose can be broken down as required
to meet the cells demands.

22. 22
Stored glucose
 Glucose is stored as
glycogen in the liver.
 Two hormones are
involved:
INSULIN
 Activates the enzyme
for this reaction:
Glucose glycogen

23. 23
Stored glucose
 Two hormones are involved:
GLUCAGON
 Activates the enzyme for this
reaction:
Glycogen glucose

24. 24
Control of Blood Glucose Levels
 The receptors are in the Islets of Langerhans
in the pancreas.
 They produce insulin or glucagon

25. 25
Control of Blood Glucose Levels
 The target organ for these hormones is the
liver.

26. 26
Increase in glucose concentration of
the blood.
 The blood glucose levels (BGL) can increase
due to:
 Eating a meal

27. 27
Increase in BGL
1. Detected by receptors in the Islets of
Langerhans.
2. These receptors cells produce insulin.
3. Insulin travels in the blood to the liver
4. At the liver an enzyme stores excess glucose
as glycogen.
5. BGL falls back to normal.

28. 28
Decrease in glucose concentration of
the blood.
 The blood glucose levels (BGL) can decrease
due to:
 Between meals
 During the night

29. 29
Decrease in BGL
1. Detected by receptors in the Islets of
Langerhans.
2. These receptors cells produce glucagon.
3. Glucagon travels in the blood to the liver
4. At the liver an enzyme stores breaks down
glycogen to glucose.
5. BGL increases back to normal.

30. 30

31. 31
What about Adrenaline?

32. 32
Practice Questions
 Torrance
1. TYK page 277 Q1-4

33. 33
Human Homeostasis
Can you do it?
 Know how the water concentration of the blood is
maintained.
 Explain the role of ADH in osmoregulation
 Know how the blood sugar concentration is maintained.
 Explain the role of insulin, glucagon and adrenaline in
controlling blood sugar levels.