P1 Homeostasis: Temperature and Blood Glucose

Question 1

What is homeostasis and how is it controlled?

Answer 1

• Involves physiological control systems that maintain the internal environment, within restricted limits:
  1. Receptors - detect deviation from the optimum
  2. Coordinator - transfers information eg. CNS
  3. Effector - carries out a response

Question 2

What are the two feedback mechanisms in homeostasis?

Answer 2

1. Negative feedback: counteracts change in order to restore the system to it’s original level. Eg. osmoregulation
2. Positive feedback: exaggerates the change, increasing deviation from it’s original level. Eg. during child birth the baby stretches the cervix, stretch receptors detect this change, information transfers along the nervous system, and hormones are released, causing the cervix to stretch further.

Question 2

What are ectotherms?

Answer 2

• Animals that thermoregulate using their surroundings.
• They carry out behavioural responses to regulate their temperature, eg. to warm up they: bask in the sun, lie on warm rocks and move around more. To cool down: they lie in the shade, lie on cool ground and move around less.
• The higher the animals SA:V ratio (smaller animals), the more heat loss it has, so the more difficult it is to maintain a constant, stable core temperature. Whereas the lower the SA:V ratio (larger animals), the lower the rate of heat loss and the easier to maintain a core body temperature.

Question 3

What are endotherms?

Answer 3

• Animals that thermoregulate within the body.
• They carry out some behavioural responses, but mainly regulate core body temperature through physiological responses.
• Endotherms have thermoreceptors (eg. peripheral temperature receptors in the skin) that monitor the temperature in the environment, and have thermoreceptors in the hypothalamus that monitor temperature in the blood.

Question 4

What physiological responses do endotherms have?

Answer 4

1. To cool down, endotherms sweat more, heat energy turns this to water vapour (it evaporates) reducing their temperature. To warm up endotherms sweat less.
2. To warm up, erector pili muscles (attaches to hairs) contract, causing hairs to erect, trapping air which acts as an insulator, reducing heat loss from the skin. Whereas to cool down, erector pili muscles relax, and hairs flatten, stopping air from being trapped and increasing heat loss.
3. To warm up, arterioles close to skin dilate (vasodilation), increasing the amount of blood flowing through the capillaries, increasing the amount of heat transferred to the skin, To cool down, arterioles close to the skin constrict (vasoconstriction), decreasing the amount of blood flowing through the capillaries and decreasing the amount of heat transferred to the skin.
4. To warm up, endotherms increase the amount of metabolic reactions in their body.
5. To warm up, endotherms shiver (muscles contract rapidly) and energy required for this is provided by metabolic reactions that release heat.

Question 5

What is the endocrine system and what is it’s role?

Answer 5

• The endocrine system is composed of endocrine glands that secrete hormones into the blood. These hormones travel to target cells to trigger a response.
• Lipid-soluble hormones pass through the cell surface membrane to bind to complementary receptors within the cell.
• Lipid-insoluble hormones bind to receptors on the surface of the cell.

Question 6

Structure and function of the adrenal glands:

Answer 6

• There are two adrenal glands, both composed of the outer cortex and the inner medulla.
• The adrenal cortex secretes: 1) glucocorticoids (eg. cortisol), which regulate metabolism, 2) mineralocorticoids (eg. aldosterone) which regulate the balance of water and ions in the blood to control blood pressure, 3) androgens (eg. oestrogen) which are sex hormones involved in reproduction.
• The medulla secretes adrenaline and noradrenaline. These hormones work together to increase heart rate and blood pressure.

Question 7

Structure and function of the pancreas:

Answer 7

• The pancreas secretes hormones from clusters of cells called Islets of Langerhans.
• These clusters contain alpha cells (which secrete glucagon) and beta cells (which secrete insulin).
• Glucagon and insulin work together to regulate blood glucose concentration.
• Under a microscope (image of the pancreas), the light coloured clump of cells is an Islet of Langerhans, and each clump of dark coloured cells is called an acinus (release digestive enzymes).

Question 8

Why is it important to regulate blood glucose concentration?

Answer 8

• Too low and cells cannot respire and will die.
• Too high ad water potential of blood decreases, too much water moves out of cells.

Question 9

How do hormones affect blood glucose concentration?

Answer 9

• Alpha cells in Islets of Langerhans detect a decrease in blood glucose concentration, and release glucagon in response.
• Beta cells in Islets of Langerhans detect an increase in blood glucose concentration and release insulin in response.

Question 10

How is insulin released?

Answer 10

1. When the concentration of glucose is high, it enters beta cells by facilitated diffusion.
2. This glucose takes part in respiration and produces ATP.
3. This ATP causes potassium ion channels in the membrane to close, meaning potassium ions cannot leave the cell, so the cell membrane becomes depolarised.
4. This depolarisation causes calcium ion channels in the membrane to open, triggering an influx of calcium ions.
5. These calcium ions cause insulin containing vesicles to move towards the cell membrane, where insulin is released by exocytosis.

Question 11

Once released, how does insulin decrease blood glucose concentration?

Answer 11

• Once released, insulin binds to complementary receptors on cells throughout the body, causing vesicles in the cell to increase the number of channel proteins present in the cell membrane.
• This increases the amount of glucose that can enter the cell through facilitated diffusion, decreasing blood glucose concentration.
• When insulin binds to a liver cell, it also activates enzymes that help convert glucose into glycogen (glycogenesis), which further decreases blood glucose concentration.
• Once blood glucose concentration has returned to it’s optimum level, there is a reduction in the release of insulin.

Question 12

Once released, how does glucagon increase blood glucose concentration?

Answer 12

• When alpha cells release glucagon, it binds to receptors on the cell surface membrane of liver cells,
• Once bound, it activates enzymes that convert glycerol/amino acids into glucose (gluconeogenesis), and enzymes that convert glycogen into glucose (glycogenolysis).
• Glucose produced moves into the blood by facilitated diffusion, increasing blood glucose concentration. Once blood glucose concentration returns to optimum level, there is a reduction in the release of glucagon.

Question 13

What is the difference between type 1 and type 2 diabetes, and how are they treated?

Answer 13

• Diabetes is a condition where the body is unable to regulate blood glucose concentration.
• Type 1 occurs when the immune system attacks beta cells, preventing the pancreas from producing any insulin. Typically treated with insulin injections (which used to be taken from pigs, but now made by genetically modified bacteria).
• Type 2 occurs when the pancreas doesn’t produce enough insulin, or when receptors on the cell surface membrane loose their sensitivity to insulin. Therefore when insulin binds to receptors it may not activate processes that remove glucose from the blood. Treated by increasing exercise and reducing carbohydrate intake.