homeostasis

Question 1

Responding to an increase in blood glucose levels:

Answer 1

• After a meal, blood glucose concentrations rise as a result of the digestion of carbohydrates
• when blood glucose levels rise, the islet cells of the pancreas detect the change and secrete insulin in response
• the insulin is transported to the liver in the blood plasma where it stimulates liver cells to take up the glucose from the blood and convert it to glycogen
• insulin also stimulates other body cells to take up more glucose for use in respiration

Question 2

Responding to a decrease in blood glucose levels:

Answer 2

• if the levels of glucose in the blood fall below normal, e.g. during vigorous exercise or a lengthy period without food, the islet cells in the pancreas are stimulated to release the hormone glucagon.
• the glucagon is transported to the liver in the blood plasma where it stimulates liver cells to convert stored glycogen back to glucose in order to raise blood glucose levels

Question 3

type 1 diabetes

Answer 3

• inability of the pancreatic islet cells to secrete enough insulin to control blood glucose correctly
• hyperglycemia (high blood glucose levels)
• juvenile, non-obese
• insulin-dependant

Question 4

type 2 diabetes

Answer 4

• body doesn’t use insulin properly
• glucose does not enter cells effectively
• hyperglycemia
• mid-age, obese
• non-insulin dependant

Question 5

diabetic nephropathy

Answer 5

• affects both type 1 and 2 diabetes

- impaired filtration so bigger molecules can pass into urine eg. glucose, proteins, blood

Question 6

causes of type 1 diabetes

Answer 6

• can be inherited
• can be triggered by an event such as a viral infection which causes the body’s immune system to attack the islet cells of the pancreas, so they stop producing sufficient insulin (autoimmune)

Question 7

type 1 diabetes symptoms

Answer 7

• tiredness
• feeling very thirsty
• frequent urination
• weight loss
• glucose present in the urine
• eating a meal high in carbohydrates/a shortage of food can result in the diabetic falling into a coma

Question 8

control of type 1 diabetes

Answer 8

• a carefully regulated diet to stop blood glucose levels from fluctuating too much
• regular blood tests to monitor blood glucose levels
• regular injections of insulin to control blood glucose levels

Question 9

how is water gained and lost from the body?

Answer 9

• gain: metabolism, food, drinking

- loss: faeces, sweat, breathing, urine

Question 10

ADH

Answer 10

• antidiuretic hormone
• hormone that signals to the kidneys how much water they should excrete/absorb
• high levels of ADH cause the kidneys to reabsorb more water
• Low levels of ADH cause the kidneys to reabsorb less water
• this is because ADH binds to the collecting ducts of nephrons, making them more permeable to water
• the water is reabsorbed by osmosis

Question 11

osmoregulation

Answer 11

• too much water drunk
• water content of the blood HIGH
• hypothalamus instructs the pituitary gland to secrete less ADH
• low volume of water reabsorbed by kidney
• high volume of dilute urine produced
• water content of blood normal
• too much sweating or salt
• water content of blood LOW
• hypothalamus instructs the pituitary gland to secrete more ADH
• high volume of water reabsorbed by kidney
• low volume of concentrated urine produced
• water content of blood normal

Question 12

thermoregulation

Answer 12

• body temp rises above normal
• thermoregulatory centre in hypothalamus instructs arterioles (not capillaries as they don’t have muscles in their walls so can’t dilate/constrict) to dilate and sweat glands to secrete more sweat
• body heat lost to its surroundings
• body temp drops to normal
• body temp falls below normal
• thermoregulatory centre in hypothalamus instructs arterioles to constrict and sweat glands to secrete less sweat
• if body heat continues to drop, thermoregulatory centre instructs skeletal muscles to contract involuntarily (generating body heat) and triggers hair erector muscles to contract, causing hairs to stand up, trapping a layer of insulating air around the skin
• body heat is conserved
• body temp rises to normal

Question 13

Why is insulin injected by diabetics rather than taken orally in tablet form?

Answer 13

• when a tablet of insulin is swallowed, it would pass down the oesophagus into the stomach
• insulin is a protein so protease enzymes in the stomach would digest the insulin, breaking it down into amino acids
• these would have a different molecular structure to the insulin, so would not have any effect on liver cells producing glycogen.

Question 14

hydrogen bicarbonate in the blood

Answer 14

• acts as a buffer in blood
• if the pH drops below 7, the bicarbonate molecules accept H+
• if the pH rises above 7, the hydrogen bicarbonate molecules release H+