homeostasis

Question 1

Define homeostasis

Answer 1

involves physiological control systems that maintain the internal environment within restricted limits.

Question 2

What is homeostasis important in maintaining?

Answer 2

core temperature and blood pH in relation to enzyme activity

Question 3

Explain negative and positive feedback

Answer 3

-=restores system to original level, receptors detect when change is too high or low,communication system is via NS or hormones and effectors counteract the change.(having only one means a change in only one direction)

+=amplify change from normal to rapidly activate something e.g. blood clots and platelets after an injury (often occurs when homeostasis breaks down)

Question 4

Define glycogenesis

Answer 4

formation of glycogen from glucose

Question 5

Define glycogenolysis

Answer 5

breakdown/hydrolysis of glycogen to glucose

Question 6

Define gluconeogenesis

Answer 6

formation of new glucose molecules from non-carbohydrates (usually amino acids and glycerol)

Question 7

Define Islets of Langerhans

Answer 7

group of pancreatic cells secreting insulin and glucagon

Question 8

What is insulin?

Answer 8

a hormone released when blood glucose levels are too high and causes a decrease in blood glucose levels.

Question 9

What is glucagon?

Answer 9

hormone released when blood glucose levels are too low and causes an increase in blood glucose levels.

Question 10

what can increase/decrease blood glucose levels?

Answer 10

I=ingestion of food or drink containing carbohydrates

D=following exercise or if you’ve not eaten

Question 11

How does insulin decrease the blood glucose concentration?

Answer 11

• secreted by beta cells in Islets of Langerhans and travel through blood to liver and muscle cells binding to the receptors on the cell-surface membrane
• increases muscle cell membranes permeability to glucose by increasing GLUT4 channel protein no. so cells take up more glucose via facilitated diffusion
• it activates enzymes that lets glycogenesis occur in liver where cells store more glycogen as an energy source
• lipid formation from glucose stimulated

Question 12

How does glucagon raise the blood glucose concentration?

Answer 12

• secreted by alpha cells in Islets of Langerhans into blood to liver cells and binds to the receptors on cell-surface membrane
• activates enzymes in liver which allow glycogenolysis to occur and also enzymes involved in gluconeogenesis
• it decreases rate of respiration in cells (insulin increases rate of respiration in muscle cells)

Question 13

How does adrenaline increase the blood glucose concentration?

Answer 13

• released from adrenal glands during stress or exercise to make more glucose available for muscles
• binds to receptors on liver cell membranes
• activates glycogenolysis but inhibits glycogenesis
• activates glucagon secretion but inhibits insulin secretion

Question 14

How do adrenaline and glucagon act via a second messenger?

Answer 14

• bind to receptors on cell-surface membrane
• activates adenylate cyclase (an enzyme) to convert ATP into cyclic AMP (cAMP the second messenger)
• cAMP activates enzyme protein kinase A that activates a series of reactions breaking down glycogen into glucose.

Question 15

What is type I diabetes?

Answer 15

unable to produce insulin, tends to start in childhood and could be the result of an autoimmune disease where the beta cells are attacked. Treatment tends to be injections of insulin.

Question 16

What is type II diabetes?

Answer 16

receptors on target cells lose responsiveness to insulin tends to occur in adults due to poor diet and/or obesity. Treatment or controlling it involves regulating carbohydrate intake,increasing exercise and sometimes insulin injections.

Question 17

What are the consequences of hypertonic/hypotonic blood?

Answer 17

hyper-too much water leaves the cells and enters the blood via osmosis and cells will shrivel/crenate.
hypo-too much water enters the cells and leaves the blood via osmosis and cells will burst(lysis)

Question 18

What can cause hypertonic blood and what is the corrective mechanism?

Answer 18

-too much sweating
-not drinking enough water
-lots of ions/salt in diet
CM-more water reabsorbed via osmosis into blood from the tubules of the nephrons. Urine more concentrated as less water lost in urine.

Question 19

What can cause hypotonic blood and what is the corrective mechanism?

Answer 19

-drinking too much water
-not enough salt in diet
CM-less water reabsorbed via osmosis into blood from the tubules of the nephrons. Urine more dilute as more water lost in urine.

Question 20

Define osmoregulation

Answer 20

control of the water potential of the blood and maintaining the balance of water and dissolved solutes.

Question 21

What are the two main functions of the kidney?

Answer 21

• removal of urea from the body

- osmoregulation

Question 22

Explain the nephron

Answer 22

• produces urine and excretes urea whilst playing a role in osmoregulation
• microscopic structure making up most of the kidney (one million per kidney and is also close to the blood capillaries)

Question 23

Explain the process of ultrafiltration in the Glomerulus/Bowman’s capsule(in the cortex)

Answer 23

• filtration under high hydrostatic pressure created in glomerulus due to different diameters in arterioles as afferent arteriole wider than efferent arteriole so high blood pressure in renal artery greater than water potential of blood.
• capillary endothelial walls contain pores which form a filter between blood and nephron.
• podocytes create filtration slits on the epithelial layer of the capsule acting as a molecular sieve where blood cells and large proteins remain in the blood.
• most of blood plasma(e.g. ‘small’ glucose and urea) pass through Bowman’s capsule as filtrate.

Question 24

What is absorbed in the proximal convoluted tubule?

Answer 24

glucose,amino acids,most of water, and many salt ions by facilitated diffusion and active transport

Question 25

adaptations of proximal convoluted tubules and what useful substances are selectively reabsorbed?

Answer 25

-many microvilli=large surface area
-lots of mitochondria to synthesise ATP for active transport
-close to blood capillaries=maintains a concentration gradient for diffusion
all the glucose via active transport and facilitated diffusion AND most of the water via osmosis.

Question 26

How does the loop of henle provide an osmotic gradient in the medulla for reabsorption of water?

Answer 26

• creates high salt conc. with a low wp in medulla for water reabsorption via osmosis from the descending limb and collecting duct which reduces the volume of the filtrate.
• ascending limb impermeable to water and cells actively transport Na+ into tissue fluid of medulla
• descending limb cells permeable to water so water moves out of filtrate by osmosis down wp gradient.

Question 27

Name adaptations of the loop of henle

Answer 27

• reduces wp of medulla by losing ions via diffusion (at bottom of loop) and active transport
• longer loop loses more ions and creates lower wp in medulla than other organisms
• shorter loop loses less ions and creates higher wp in medulla than other organisms

Question 28

Explain how negative feedback works in osmoregulation-low water potential (due to dehydration)

Answer 28

• low wp detected by hypothalamus and more ADH is secreted by the posterior pituitary gland
• cells of collecting duct more permeable to water so more water reabsorbed from filtrate back into the medulla then blood to dilute it more
• wp back to normal, urine volume reduced

Question 29

Explain how ADH works

Answer 29

makes walls of collecting duct/distal convoluted tubule more permeable by inserting aquaporins so that more water is reabsorbed and urine is hypertonic compared to general body fluids.

Question 30

Explain how negative feedback works in osmoregulation-higher water potential

Answer 30

• high wp detected by hypothalamus and the posterior pituitary gland secretes less ADH
• cells of collecting duct less permeable to water so less water is reabsorbed from the filtrate back into the medulla so its more concentrated
• wp now normal and urine volume increased