Homeostasis

Question 1

What is homeostasis?

Answer 1

Internal environment is maintained

Question 2

Why is it important that core temperature remains stable?

Answer 2

Maintain a stable rate of enzyme controlled reactions and prevent damage membranes
Low temperature= insufficient kinetic energy
High temperature= enzymes denature

Question 3

Why is it important that blood pH remains stable?

Answer 3

Maintain stable rate of enzyme controlled reactions

Acidic pH = shape of active sites change

Question 4

Why is it important that blood glucose remains stable?

Answer 4

Maintain a constant blood water potential- stops osmotic lysis
Maintain a constant concentration of respiratory substrate

Question 5

What is negative feedback?

Answer 5

Self regulatory mechanisms return internal environment to optimum when there is fluctuations

Question 6

What is positive feedback?

Answer 6

A fluctuation triggers changes that result in an even greater deviation from the normal level

Question 7

Outline the stages involved in negative feedback

Answer 7

Receptors detect changes > Coordinator > effector > receptors detect change is back to normal

Question 8

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

Answer 8

It takes time to:
Produce the hormone
Transport the hormone in the blood
Cause required change to the target protein

Question 9

Name the factors that affect blood glucose concentration?

Answer 9

Amount of carbohydrate in diet
Rate of glycogenolysis
Rate of gluconeogenesis

Question 10

What is glycogenesis?

Answer 10

Liver converts glucose into glycogen

Question 11

What is glycogenolysis?

Answer 11

Liver hydrolyses glycogen into glucose which can diffuse into blood

Question 12

What is gluconeogenesis?

Answer 12

Liver converts glycerol and amino acids into glucose

Question 13

Outline the role of glucagon when blood glucose concentration decreases

Answer 13

1. a cells in Islets of Langerhans in pancreas detect decrease and secrete glucagon into bloodstream
2. Glucagon binds to surface cell receptors on liver cells and activates enzymes for glycogenolysis and gluconeogenesis
3. Glucose diffuses from liver into blood stream

Question 14

Outline the role of adrenaline when blood glucose concentration decreases

Answer 14

1. Adrenal gland produces adrenaline. It binds to surface receptors on liver cells and activates enyzmes for glycogenolysis
2. Glucose diffuses from liver into bloodstream

Question 15

Outline what happens when blood glucose concentration increases

Answer 15

1. B cells in islets of langerhans in pancreas detect increase and secrete insulin into bloodstream
2. Insulin binds to receptor cells on target cells to increase glucose uptake and activate enzymes for glycogenesis

Question 16

Describe how insulin leads to a decrease in blood glucose concentration

Answer 16

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

Question 17

How does insulin increase permeability of cells to glucose?

Answer 17

Increases number of glucose carrier proteins

Opens more glucose carrier proteins

Question 18

How does insulin increase the glucose concentration gradient?

Answer 18

Activates enzymes for glycogenesis in liver and muscles

Stimulates fat synthesis in adipose tissue

Question 19

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

Answer 19

1. Hormone receptor complex forms
2. Change to receptor activates G-Protein
3. Activates adenylate cyclase which converts ATP to cyclic AMP
4. cAMP activates protein kinase A pathway
5. Results in glycogenolysis

Question 20

Explain the causes of type 1 diabetes and how it can be controlled

Answer 20

The body cannot produce insulin e.g due to an autoimmune response which attacks B cells in Islets of Langerhans
Treat by injecting insulin

Question 21

Explain the causes of type 2 diabetes and how it can be controlled

Answer 21

Glycoprotein receptors are damaged or become less responsive to insulin
Correlation with poor diet/obesity
Treat by controlling diet and exercise regime

Question 22

Name some symptoms of diabetes

Answer 22

High blood glucose concentration
Glucose in urine
Blurred vision
Sudden weight loss

Question 23

What is osmoregulation?

Answer 23

Control of blood water potential

Question 24

Describe the structure of the kidney

Answer 24

Fibrous capsule
Cortex 
Medulla
Renal pelvis
Ureter
Renal artery
Renal Vein

Question 25

Describe the structure of a nephron

Answer 25

``` Bowmans capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct ```

Question 26

Describe the blood vessels associated with a nephron

Answer 26

Afferent arteriole- Wide | Efferent arteriole- Narrow

Question 27

Explain how glomerular filtrate is formed

Answer 27

Ultrafiltration in Bowmans capsule High hydrostatic pressure in the glomerulus forces small molecules out of capillary fenestrations against osmotic gradient Basement membrane acts a filter

Question 28

How are cells of the Bowmans capsule adapted for ultrafiltration?

Answer 28

Fenestrations between epithelial cells or capillaries | Fluid can pass between podocytes

Question 29

State what happens during selective reabsorption and where it occurs

Answer 29

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

Question 30

Outline the transport processes involved in selective reabsorption

Answer 30

Glucose from glomerular filtrate > co transport with Na+ > cells lining proximal convoluted tubule > active transport > intercellular spaces > diffusion > blood capillary lining tubule

Question 31

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

Answer 31

Microvilli Many mitochondrion Folded basal membrane

Question 32

What happens in the loop of henle?

Answer 32

1. Active transport of Na+ and Cl- out of ascending limb 2. Water potential of interstitial fluid decreases 3. Osmosis of water out of descending limb 4. Water potential of filtrate decreases going down the descending limb

Question 33

Explain the role of the distal convoluted tubule

Answer 33

Reabsorption of water via osmosis and of ions via active transport Permeability is determined by action of hormones

Question 34

Explain the role of the collecting duct

Answer 34

Reabsorption of water from filtrate into interstitial fluid via osmosis through aquaporins

Question 35

Why is it important to maintain an Na+ concentration gradient?

Answer 35

Countercurrent multiplier - filtrate in collecting duct is always beside an area of interstitial fluid that has a lower water potential Maintains water potential gradient for maximum reabsorption of water

Question 36

What might cause blood water potential to change?

Answer 36

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

Question 37

Explain the role of the hypothalamus in osmoregulation

Answer 37

1. Osmosis of water out of osmoreceptors in hypothalamus causes them the shrink 2. This triggers the production of antiduretic hormone (ADH)

Question 38

Explain the role of the posterior pituitary gland

Answer 38

Stores and secretes ADH produced by the hypothalamus

Question 39

Explain the role of ADH in osmoregulation

Answer 39

1. Makes cells lining collecting duct more permeable to water: binds to receptors > activates phosphorylase > vesicles with aquaporins on membrane fuse with cell surface membrane 2. Makes cells lining collecting duct more permeable to urea: Water potential in interstitial fluid decreases, more water reabsorbed = more concentrated urine