1. Homeostasis

2. Learning objectives
The human body needs to maintain and regulate a steady state in order to function correctly
Homeostasis involves interactions between various systems of the body

3. Homeostasis
“the tendency of a system, esp. the physiological system of higher animals, to maintain internal stability, owing to the coordinated response of its parts to any situation or stimulus tending to disturb its normal condition or function” - Dictionary.com Unabridged (v 1.1)
“The ability or tendency of an organism or a cell to maintain internal equilibrium by adjusting its physiological processes.” - American Heritage Stedman's Medical Dictionary

4. Homeostasis
There are several examples of homeostasis and the processes involved
We have already looked at the reproductive hormones and how oestrogen and LH are linked through NEGATIVE FEEDBACK – i.e. as one gets more it causes the other to get less
Here are 3 more commonly used examples

5. Temperature Control Also known as THERMOREGULATION
The enzymes in our bodies work best at around 37°C
we need to be able to keep our bodies as close to this temperature as possible
The body will react if it gets too hot or if it gets too cold
It will adjust the temperature back to where it should be

6. Thermoregulation
Involves receptors linked to the HYPOTHALAMUS located in the brain
Nerve impulses are sent from here to the SKIN
Skin reacts to change body temperature

7. Too Hot…? VASODILATION – blood vessels near the skin get wider
This allows more warm blood to flow near the surface and lose heat, cooling you down
Muscles controlling the hairs on your skin relax – causing the hairs to lie flat
Sweat is secreted from sweat glands – as it evaporates, this cools you down

8. Too Hot…?

9. Too Cold…? VASOCONSTRICTION – blood vessels near the skin get smaller
Less blood flows near the surface, keeping the heat closer to your body core
Erector muscles contract, pulling your hairs up on end
This traps warm air close to your skin
Sweat glands no longer secrete sweat
Shivering also helps to warm you up – your muscles generate more heat through respiration

10. Water Control Also known as OSMOREGULATION
Controlled by the hypothalamus using negative feedback
Involves the pituitary gland and the kidneys

11. Osmoregulation
Water is very important to the body, but it must maintain the right amount
If there is a problem, it is spotted by OSMORECEPTORS in the hypothalamus
A message is sent through nerve impulses to the pituitary gland
This changes the amount of a particular hormone it releases
The change in hormone level causes the kidneys to react

12. Not Enough Water..? Hypothalamus signals the pituitary gland
Pituitary increases its release of the hormone ADH (ANTI-DIURETIC HORMONE)
More ADH enters kidney, stimulating it to reabsorb more water
Smaller amounts of more concentrated urine are produced

13. Osmoregulation

14. Too Much Water..? Hypothalamus signals the pituitary gland
Pituitary slows down its release of the hormone ADH
Less ADH enters kidney, which then absorbs LESS water
More urine is produced
Urine is LESS concentrated

15. Blood Sugar levels
When food is digested, sugar – glucose – is produced
It is important that blood sugar levels do not get too high – HYPERGLYCEMIA – or too low – HYPOGLYCEMIA
It involves the hormone INSULIN

16. Too much glucose Receptors in the blood sense high levels of glucose
Nerve impulses sent to the PANCREAS
Insulin is released into the blood
Triggers an increase in glucose being converted in glycogen by the LIVER
Glucose levels drop to normal
Insulin no longer produced and degrades

17. Not Enough Glucose Receptors in the blood sense low levels of glucose
Nerve impulses sent to the pancreas
Insulin stops being released into the blood
Less glucose is converted in glycogen by the liver
Less glucose absorbed by the cells
Glucose levels return to normal

18. Glucose Regulation
Insulin crystals

19. Glucose Regulation
People who cannot naturally control their blood sugar levels are called DIABETIC
They must control their blood sugar manually by controlling their diet, and by injecting themselves regularly with insulin