3.6.4 Homeostasis

Question 1

What is homeostasis

Answer 1

Internal environment is maintained within set limits around an optimum

Question 2

Why is it important that core temperature remains stable

Answer 2

Maintain stable rate of enzyme controlled reactions and prevent damage to membranes
Too low = insufficient kinetic energy
Too high = enzymes denature

Question 3

Why is it important that blood pH remains table

Answer 3

Maintains stable rate of enzyme controlled reactions
Acidic = H+ ions interact with H bonds and ionic bonds in tertiary structures of enzymes - shape of active site changes so no ES complexes

Question 4

Why is it important that blood glucose conc remains stable

Answer 4

Maintain constant blood wp, prevents lysis and crenation
Maintain constant conc of respiratory substrate - constant level of activity regardless of environmental conditions

Question 5

Define negative and positive feedback

Answer 5

Neg = self regulatory mechanisms return internal environment to optimum when there is a fluctuation
Pos = a fluctuation triggers changes that result in an even greater deviation from the normal level

Question 6

Outline the general stages involved in neg feedback

Answer 6

Receptors detect deviation – coordinator – corrective mechanism by effector – receptors detect that conditions have returned to normal

Question 7

Suggest why separate neg feedback mechanisms control fluctuations in different directions

Answer 7

Provides more control, esp in case of overcorrection, which would lead to a deviation in the opposite direction from the original one

Question 8

Suggest why coordinators analyse inputs from several receptors before sending an impulse to effectors

Answer 8

Receptors may send conflicting information
Optimum response may require multiple types of receptors

Question 9

Why is there a time lag between hormone production and response by an effector

Answer 9

It takes time to;
produce hormone
transport hormone in the blood

Question 10

Factors that affect blood glucose

Answer 10

Amount of carb digested from diet
Rate of glycogenolysis
Rate of gluconeogenesis

Question 11

Define glycogenesis, glycogenolysis, gluconeogenesis

Answer 11

Glycogenesis: liver converts glucose into glycogen
Glycogenolysis; liver hydrolyses glycogen into glucose
Gluconeogenesis; liver converts glycerol and amino acids into glucose

Question 12

Outline the role of glucagon when blood glucose conc decreases

Answer 12

Alpha cells in pancreas detect decrease and secrete glucagon into blood
Glucagon binds to surface receptors on liver cells and activates enzymes for glycogenolysis and gluconeogenesis
Glucose diffuses from liver into bloodstream

Question 13

Outline the role of adrenaline when blood glucose conc decreases

Answer 13

Adrenal glands produce adrenaline, binds to surface receptors on liber cells and activates enzymes for glycogenolysis
Glucose diffuses from liver into blood

Question 14

Outline what happens when blood glucose conc increases

Answer 14

Beta cells in pancreas detect increase and secrete insulin into blood
Insulin binds to surface receptors on target cells to;
a) increase cellular glucose uptake
b) activate enzymes for glycogenesis
c) stimulate adipose tissue to synthesise fat

Question 15

Describe how insulin leads to a decrease in blood glucose

Answer 15

Increases permeability of cells to glucose
Increases glucose conc gradient
Triggers inhibition of enzymes for glycogenolysis

Question 16

How does insulin increase permeability of cells to glucose

Answer 16

Increase number of glucose carrier proteins
Triggers conformational change which opens glucose carrier proteins

Question 17

How does insulin increase glucose conc gradient

Answer 17

Activates enzymes for glycogenesis in liver and muscles
Stimulates fat synthesis in adipose tissue

Question 18

Use the secondary messenger model to explain how glucagon and adrenaline work

Answer 18

1. Hormone receptor complex forms
2. Conformational change to receptor activates G protein
3. Activates adenylate cyclase which converts ATP to cAMP
4. cAMP activates protein kinase A pathway
5. Results in glycogenolysis

Question 19

Explain the cause of t1d and how it can be controlled

Answer 19

Body cannot produce insulin due to autoimmune response which attacks Beta cells
Treat by insulin injections / pump

Question 20

Explain the cause of t2d and how it can be controlled

Answer 20

Glycoprotein receptors are damaged or become less responsive to insulin
Poor diet / obesity
Treat by controlling diet and exercise

Question 21

Outline how colorimetry could be used to identify the glucose conc in a sample

Answer 21

1. Benedicts test on solutions of known glucose conc. Use colorimeter to record absorbance
2. Plot calibration curve - absorbance y and glucose conc x
3. Benedicts test on unknown sample. Use calibration curve to read glucose conc at its absorbance value

Question 22

Define osmoregulation

Answer 22

Control of blood wp via homeostatic mechanisms

Question 23

What structures does a nephron include

Answer 23

Bowmans capsule
Proximal convoluted tubule
Loop of henle
Distal convoluted tubules
Collecting duct

Question 24

Describe the blood vessels associated with a nephron

Answer 24

Wide afferent arteriole from renal artery enters renal capsule and forms glomerulus; branched knot of capillaries which combine to form narrow efferent arteriole

Efferent arteriole branches to form capillary network that surrounds tubules

Question 25

Explain how glomerular filtrate is formed

Answer 25

Ultrafiltration in bowmans capsule
High hydrostatic presssure in glomerulus forces small molecules out of capillary fenestrations against osmotic gradient
Basement membrane acts as a filter. Blood cells and large molecules remain in capillary

Question 26

How are cells of the bowmans capsule adapted for ultrafiltration

Answer 26

Fenestrations between epithelial cells of capillaries
Fluid can pass between and under folded membrane of podocytes

Question 27

State what happens during selective reabsorption and where it occurs

Answer 27

Useful molecules from glomerular filtrate eg glucose are reabsorbed into the blood
Occurs in proximal convoluted tubule

Question 28

Outline the transport processes involved in selective reabsorption

Answer 28

Glucose co transport with Na+
Active transport from cells lining PCT to intercellular spaces
Diffusion from intercellular spaces to blood capillary lining tubules

Question 29

How are cells in the proximal convoluted tubule adapted for selective reabsorption

Answer 29

Microvilli; large SA for co transporter proteins
Many mitochondria; ATP for active transport of glucose into intercellular spaces
Folded basal membrane; large SA

Question 30

What happens in the loop of henle

Answer 30

1. Active transport of Na+ and Cl- out of ascending limb
2. wp of interstitial fluid decreases
3. Osmosis of water out of DL
4. Wp of filtrate decreases going down DL; lowest in medullary region, highest at top of AL

Question 31

Explain the role of the distal convoluted tubule

Answer 31

Reabsorption of water via osmosis and of ions by active transport

Question 32

Explain the role of the collecting duct

Answer 32

Reabsorption of water from filtrate into interstitial fluid via osmosis

Question 33

Why is it important to maintain an Na+ gradient

Answer 33

Counter current multiplier; filtrate in collecting ducts always beside an area of interstitial fluid that has a lower wp
Maintains wp gradient for maximum reabsorption of water

Question 34

What might cause blood wp to change

Answer 34

Level of water intake
Level of ion intake in diet
Level of ions use in metabolic processes or excreted
Sweating

Question 35

Explain the role of the hypothalamus in osmoregulation

Answer 35

1. Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
2. This triggers hypothalamus to produce more ADH

Question 36

Explain the role of the posterior pituitary gland in osmoregulation

Answer 36

Stores and secrets the ADH produced by the hypothalamus

Question 37

Explain the role of ADH in osmoregulation

Answer 37

1. Makes cells lining CD more permeable to water
   Binds to receptor – activates phosphorylase –vesicles with aquaporins on membrane fuse with cell surface membrane
2. Makes cells lining CD more permeable to urea
   wp in interstitial fluid decreasesss
   more water reabsorbed = more conc urine