Homeostasis

Question 1

Define homeostasis

Answer 1

Physiological control systems that maintain a constant internal environment

Question 2

Summarise negative feedback system

Answer 2

Receptors detect change away from normal and mechanism activated to return body to normal

Question 3

Summarise positive feedback system

Answer 3

A response resulting in effectors further amplifying the change away from the normal

Question 4

Summarise how the body reacts to high blood glucose

Answer 4

• Receptors in pancreas detect increase
• Beta cells in islets of langerhans secrete insulin
• Insulin binds to receptor is liver and muscle to increase glucose permeability
• More glucose absorbed by diffusion
• Glycogenesis occurs and respiration increased

Question 5

Summarise how the body reacts to low blood glucose

Answer 5

• Receptors in pancreas detect decrease
• Alpha cells islets of langerhans secrete glucagon
• Glucagon binds to receptors on liver cells
• Decrease in rate of respiration
• Gluconeogensis
• Glycogenolysis

Question 6

Define glycogenesis

Answer 6

Breaking down of glycogen into glucose promoted by glucagon and adrenaline

Question 7

Define glycogenolysis

Answer 7

The making of glycogen promoted by insulin

Question 8

Define gluconeogenesis

Answer 8

The formation of glucose from other molecules promoted by glucagon

Question 9

Summarise glucagon in the control of blood glucose

Answer 9

• Secreted by A cells the islets of langerhans
• When blood glucose low
• Attaches to liver receptors
• Increase blood glucose
• Decreases rate of respiration, causes glycogenesis and gluconeogensis

Question 10

Summarise adrenaline in the control of blood glucose

Answer 10

• Secreted by adrenal glands
• When blood glucose low
• Attaches to liver receptors
• Increases blood glucose
• Causes glycogenolysis due to secretion of glucagon and inhibits glycogenesis due to inhibitng insulin

Question 11

Summarise insulin in the control of blood glucose

Answer 11

• Secreted by B cells in the islets of langerhans
• When blood glucose high
• Attaches to liver and muscle cells
• Decrease blood glucose levels
• Causes glycogenesis and increase liver and muscle cell permeability to glucose

Question 12

How does insulin increase cell permeability to glucose

Answer 12

• Glucose carrier proteins stored in vesicles within cell
• Insulin binds with receptors on the cell membrane
• Causes vesicle to fuse with cell membrane
• Carrier protein joins membrane and glucose absorbed by facilitated diffusion

Question 13

Summarise the process of second messengers

Answer 13

• Hormone (adrenaline or glucagon) binds to receptors on target cell
• Enzyme on inside of the cell called adenyl cyclate activated and hydrolyses ATP into cyclic AMP
• AMP acts as non-competitive inhibitor and activates protein kinase A by changing tertiary structure
• Causes break down of glycogen (glycogenolysis)

Question 14

Define diabetes

Answer 14

When blood glucose levels are not controlled fully

Question 15

Distinguish between hyper and hypoglycaemia

Answer 15

Hyper = too much glucose and hypo = too little

Question 16

Summarise Type I diabetes

Answer 16

• Immune system kills B cells so lack of insulin
• Occurs in children and young adults
• Hyperglycaemia after eating carbs
• Stays high and so glucose removed by kidneys in urine
• Insulin injections/pump
• Avoid simple carbohydrates
• Eat regular intervals and regular exercise

Question 17

Summarise Type II diabetes

Answer 17

• Obesity, lack of exercise and poor diet
• Not enough insulin produced and liver and muscle cells do not respond due to lack of receptors
• Hyperglycaemia after eating carbs
• Stays high and so glucose removed by kidneys in urine
• Eat healthy, lose weight, regular exercise
• Drugs to reduce glucose, increase insulin production and sensitivity to insulin

Question 18

Summarise the structure of a nephron

Answer 18

Afferent arteriole, bowman capsule containing glomerulus, efferent arteriole, proximal convoluted tubule, descending loop of henley, ascending loop of henley, distal convoluted tubule and collecting duct

Question 19

Summarise ultrafiltration

Answer 19

• Blood flows into bowman capsule from afferent arteriole
• Glomerulus under high hydrostatic pressure due to wide afferent and thin efferent
• Small molecules and liquid are forced out of glomerulus into bowman capsule forming filtrate
• Large molecules do not fit through gaps in capillary walls, basement membrane and podocytes
• Filtrate moves into nephron

Question 20

What does kidney filtrate contain

Answer 20

Glucose
H2O
Amino acids
Ions
Urea

Question 21

Define selective reabsorption

Answer 21

When useful products are reabsorbed from the glomerulus filtrate by the PCT, loop of henley, distal convoluted tubule and collecting duct

Question 22

Summarise selective reabsorption

Answer 22

• Capillaries wrap around nephron and useful substances reabsorbed
• Microvilli increase SA for absorption
• Urine produced once useful molecules removed
• Glucose and amino acids absorbed by facilitated diffusion, some urea remains due to simple diffusion and water moves in by osmosis
• Rest of glucose, amino acids and ions absorbed by active transport

Question 23

How are substances absorbed in the proximal convuluted tubule

Answer 23

 all the glucose/amino acids and some of the salts/water are sent back into blood
(from lumen of PCT, through cells lining PCT, into blood)
how:
 salts (sodium ions) are actively transported from cells lining the PCT into the blood
 this lowers sodium ion concentration in the cells, so sodium ions diffuse from the lumen of the PCT into the cells
 as sodium ions move, they pull in glucose and amino acids with them via co-transport
 glucose and amino acids build up in the cell, then diffuse into the blood
 the movement of salt/glucose/amino acids into the blood, lowers it’s water potential, so water follows into blood by osmosis

Question 24

Summarise how the function of the loop of henle

Answer 24

• Sodium and chloride ions actively transported out of ascending limb into medulla
• Lowers water potential of medulla
• Ascending limb impermeable to water
• Water moves out of descending limb by osmosis due to salty medulla and absorbed by capillaries
• Urine hence more concentrated

Question 25

What is the effect of a long loop of henle?

Answer 25

• More ions removed, more concentrated medulla, so more water absorbed so more concentration urine e.g desert animals

Question 26

Summarise ADH in osmoregulation

Answer 26

• Dehydrated so lower water potential, detected by osmoreceptors in hypothalamus
• Posterior pituitary secretes antidiuretic hormone
• ADH carried in blood and binds to receptors
• Increases permeability to water
• Water moves out of collecting duct by osmosis due to medulla have lowing water potential