The hypothalamus regulates body temperature through negative feedback by sensing blood temperature and sending signals to alter processes like shivering, sweating and blood vessel constriction/dilation. The pancreas and liver also use negative feedback to keep blood glucose levels steady by secreting insulin and glucagon which signal the liver to store or release glucose as needed. Diabetes occurs when this process is disrupted, resulting in dangerous fluctuations in blood glucose.

1. Homeostasis PART 2

2. Skin (Last Lesson)
Summary of Skin Structure
Epidermis - New cells form by mitosis.
New cells move to surface and die forming Cornified Layer. Protects
living cells below.
Contains Melanin to protect from UV rays
Hair follicles form when epidermis folds inwards
Dermis – Formed from connective tissue.
Contains Sweat Glands, blood vessels and nerve endings.
Adipose Tissue – Fatty tissue containing oil.
Insulates against the cold. Energy storage.

3. How we keep our body temperature constant
• What is the Hypothalamus?
• The Hypothalamus is a part of the brain which helps regulate body
temperature

4. How we keep our body temperature constant
• How?
• The hypothalamus co-ordinates the activities of the parts of the body
that can effect temperature changes.
• Thermostat (in your house)
- Contains temperature receptors (senses blood running through it)
- 37 degrees!!!
- Hypothalamus then sends electrical impulses to appropriate parts of
the body (along nerves)

5. How we keep our body temperature
constant
• Below 37 degrees
• Muscles relax and contract very quickly (SHIVERING).
- This causes heat to generate, which then warms the blood, and spreads the heat
around the body.
• Metabolism may increase – speed of respiration increases to release more heat.
• Hair stands up – erector muscles contract. Acts as an insulator in furry animals
by trapping warm air next to the skin. Humans (not useful)
• Vasoconstriction – causes surface capillaries to become narrower. (constricted).
- Less blood runs through, forcing blood to run through deeper cap. beneath fatty
tissue (insulation)

6. How we keep our body temperature
constant
• Above 37 degrees
• Hair lies flat – erector muscles relax.
• Vasodilation – surface capillaries widen (dilate). More blood can flow through.
- Blood is near the surface so heat is lost easily into the air.
• Sweat glands secrete sweat. Sweat on hot skin evaporates taking heat from the
skin with it.
• More blood is supplied to sweat glands to produce more sweat.

7. How we keep our body temperature constant
Hypothalamus senses
blood temperature
(receptors)
Sends electrical impulses
to necessary parts of the
body
(nervous system)
Muscles (shivering)
Erector muscles (hairs)
Capillaries constrict
Sweat glands (sweating)
Erector muscles (hairs)
Capillaries dilate

8. The role of negative feedback in homeostasis
• What is negative feedback?
• "A mechanism in which a change in parameter brings about actions
that push it back to normal"
• A stimulus causes an opposite effect to maintain the normal level
• If we are too hot mechanisms occur to cool us down, until we are back
to normal levels. Then mechanisms are stopped. And vice versa.
• Hypothalamus is constantly monitoring any small changes in the
blood temp.

9. Experiment
• Write how we could test this hypothesis:
A large body cools more slowly than a small one.
Next time?

10. How the pancreas and liver help to keep
blood glucose concentration steady
• Why is glucose concentration important?
• Cells need a steady supply of glucose for respiration (especially brain
cells)
• However
• Too much glucose can cause water to move out of cells through
osmosis. Effecting metabolic processes.

11. How the pancreas and liver help to keep
blood glucose concentration steady
• How is the glucose level controlled?
• By the pancreas and the liver.
• Negative feedback
• Glucose too high = Islets of Langerhans (pancreas) release Insulin
- Liver uses some of the glucose in resp. & stores some as glycogen.
• Glucose too low = Islets of Langerhans release Glucagon
• - Liver breaks down glycogen into glucose

12. How the pancreas and liver help to keep
blood glucose concentration steady
• Insulin hormone secreted by the pancreas to reduce glucose level
• Glucagon hormone secreted by the pancreas to raise glucose level
• IMPORTANT
• Glycogen is glucose stored in the liver.

13. How the pancreas and liver help to keep
blood glucose concentration steady
• What is Diabetes?
• A condition where a persons blood glucose concentration isn't
controlled properly.
• Type 1 Diabetes is an auto-immune disease, where the body's own
immune system attacks and destroys insulin producing cells(in
pancreas)

14. How the pancreas and liver help to keep
blood glucose concentration steady
• Person without Type 1 Diabetes:-
• Eating carbohydrates causes rise of glucose level, triggers pancreas to
release Insulin, return level to normal.
• Person with Type 1 Diabetes:-
• Glucose level rises and stays up (HYPERGLYCAEMIA)
• Signs – dry mouth, blurred vision, thirst, increased heart
rate/breathing

15. How the pancreas and liver help to keep
blood glucose concentration steady
• And vice versa
• Person without Type 1 Diabetes:-
• Not eating carbohydrates causes drop of glucose level, triggers pancreas to
release glucagon which breaks down stored glycogen, level returns to normal.
• Person with Type 1 Diabetes:-
• Glucose level drops and stay low (HYPOGLYCAEMIA) the person doesn't have
the stored glycogen levels in liver
• Signs – tired (no glucose for resp.), confusion/irrational. Eventually
unconsciousness
• People can eat something sweet when these signs start to occur.

16. How the pancreas and liver help to keep
blood glucose concentration steady
• Prolonged fluctuations of high and low glucose levels can have longterm
harmful effects on bodily organs.
• Therefore
• People check their blood regularly (blood sugar monitoring device)
• Or
• People can check their urine (dipsticks)
• Glucose should be reabsorbed by the kidneys (nephron) so urine shouldn't
contain any.
• If it does, levels are too high for the kidney to function properly.

17. How the pancreas and liver help to keep
blood glucose concentration steady
• What else doe people with type 1 Diabetes need to do?
• They need to inject themselves with Insulin
• They need to eat little and often
• They need to avoid large amounts of carbohydrates