OSMOREGULATION

OSMOREGULATION: REGULATION OF BLOOD WATER POTENTIAL

DECREASE IN BLOOD WATER POTENTIAL

• Decrease may be due to loss of water through sweating when doing vigorous exercise or when the environmental temperature increases which causes more sweating (stimulus).
• This decrease stimulates the pituitary gland in the brain to secrete more Anti Diuretic Hormone (ADH) into the blood.
• The blood then transports this ADH to the kidneys (target organ).
• The function of ADH is to promote water reabsorption from the filtrate in the kidney tubules back into the blood capillaries which are in close contact with the kidney tubules.
• Since ADH is secreted in high concentration, more water will be reabsorbed back from the filtrate in the kidney tubules into the blood capillaries.
• As a result, urine production will decrease and hence urine becomes more concentrated.
• Reabsorption of water back into the blood capillaries, causes the water potential in the blood to increase (Negative Feedback) and eventually the level of water potential in the blood will return back to normal.

(Note: if this corrective mechanism is not functioning, red blood cells in the blood may undergo crenation and hence less oxygen will be transported)

INCREASE IN BLOOD WATER POTENTIAL

• Increase may be due to too much intake of water or lack of sweating (stimulus).
• This increase stimulates the pituitary gland in the brain to secrete less ADH into the blood.
• The blood then transports this ADH to the kidneys (target organ).
• The function of ADH is to promote water reabsorption from the filtrate in the kidney tubules back into the blood capillaries which are in close contact with the kidney tubules.
• Since ADH is secreted in low concentration, less water will be reabsorbed back from the filtrate in the kidney tubules into the blood capillaries.
• As a result, urine production will increase and hence urine becomes more dilute.
• Less reabsorption of water back into the blood capillaries, causes the water potential in the blood to decrease (Negative Feedback) and eventually the level of water potential in the blood will return back to normal.

REGULATION OF GLUCOSE CONCENTRATION

REGULATION OF BLOOD GLUCOSE CONCENTRATION

What happens if the glucose concentration in the blood increases?

• After having a meal, the glucose concentration in the blood increases (stimulus).
• This increase may caused cells in the body to undergo crenation. For example, the red blood cells in the blood may undergo crenation due to higher water potential in the red blood cells than the blood itself. As a result water molecules in the red blood cells diffuse out of the red blood cells by osmosis.
• This condition needs to be corrected. Because of this increase, the pancreas will secrete insulin into the blood (insulin is a hormone produced by the beta-cells of the islets of langerhans of the pancreas).
• The blood will then transports the insulin to the liver (target organ).
• In the liver, the excess glucose is then converted into glycogen for storage in the liver itself as well as in the muscles.
• This conversion of excess glucose to glycogen slowly lowers the blood glucose concentration (negative feedback).
• Eventually the glucose concentration in the blood will return to normal (Norm).
  

What happens if the glucose concentration in the blood decreases?

• After vigorous exercise, the glucose concentration in the blood decreases due to glucose being oxidised to release energy during cellular respiration (stimulus)
• The decreased may caused the red blood cells to haemolyse. Haemolysis occurs due to passage of water molecules into the red blood cells from the blood from higher to lower water potential by osmosis.
• This condition needs to be corrected. The pancreas responds to this by producing glucagon into the blood (Glucagon is a hormone produced by the alpha cells of the islets of langerhans of the pancreas).
• The glucagon is then transported by the blood to the liver which is the target organ.
• In the liver, the glucagon converts glycogen stored in the liver into glucose.
• This will boost the blood glucose concentration in the blood (negative feedback)
• Eventually the blood glucose concentration will return to normal.
  

Note: Before the insulin and the glucagon can be secreted into the blood, the pancreas must first be triggered or stimulated by the pituitary gland in the brain (Remember: Pituitary gland is a MASTER gland of all the endocrine glands. It controls the activities of other endocrine glands)

HORMONES

WHAT ARE HORMONES?

Hormones are chemical substances produced in minute quantities by the endocrine glands and transported by the blood to the target organs where they exert a profound effect. After exerting its effect in the target organ, it is then destroyed in the liver and then transported to the kidneys to be excreted.

DIFFERENCES BETWEEN NERVOUS CONTROL AND HORMONAL CONTROL

• NC involves nervous impulses whereas HC involves hormones

• Impulses are transmitted by neurones in NC whereas hormones are transmitted by blood in HC

• The response is very quick in NC and slower in HC

• Response in NC is usually short-lived whereas in HC it may be short-lived or long-lived

• NC may be voluntary or involuntary whereas HC is always involuntary

• NC is usually localised and in HC it may affects more than one target organ

ADRENALINE

• Adrenaline is a hormone produced by the Adrenal gland located just above each kidney
• Circumstances in which it is secreted: Usually in conditions of fear, anger and anxiety or in any other emergency situation
• Effect 1: Increases metabolic rate. This means that more energy is released in tissue respiration
• Effect 2: Increases in rate of heartbeat and rise in blood pressure so that oxygen and glucose are carried faster to the muscles
• Effect 3: Constriction of arterioles in skin which causes pallor. As a result of this more blood is sent to the muscles
• Effect 4: Causes the conversion of more glycogen stored in the liver into glucose so that the glucose can be used in tissue respiration
• Effect 5: Dilates the pupil of the eye so that more light can enter the eye. Hence this provides clearer vision
• Effect 6: Hair muscles may contract producing "goose pimples"
  

INSULIN

• Insulin is a hormone produced by the Islets of Langerhans in the pancreas
• Secretion of insulin is due to an increase in concentration of glucose in the blood
• Effect 1: Causes the conversion of glucose to glycogen for storage in the liver and muscles
• Effect 2: Enables tissue cells to oxidise glucose to produce energy in tissue respiration (Remember the "Gate Keeper")
• Both effects help to control the amount of glucose in the blood