CH16 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 temperatures remain stable

Answer 2

Maintains stable rate of enzyme-controlled reactions and prevents damage to membranes

Question 3

Why is it important that blood pH remains stable

Answer 3

Maintain stable rate of enzyme-controlled reactions

Question 4

Why is it important that blood glucose remains stable

Answer 4

Maintain constant blood water potential to prevent lysis of cells
Maintain constant concentration of respiratory substrate

Question 5

Define negative feedback

Answer 5

Self-regulatory mechanisms return internal environment to optimum when there is a fluctuation

Question 6

Define positive feedback

Answer 6

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

Question 7

Stages of negative feedback

Answer 7

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

Question 8

Suggest why separate negative feedback mechanism control fluctuations in different directions

Answer 8

Provides more control, especially in case of ‘overcorrection’ which would lead to deviation in the opposite direction from the original one

Question 9

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

Answer 9

Receptors may send conflicting information

Optimum response may require multiple types of effector

Question 10

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

Answer 10

Takes time to:
Produce hormone
Transport hormone in blood
Cause required change to target protein

Question 11

Name factors that affect blood glucose concentration

Answer 11

Amount of carbohydrate digested
Rate of glycogenolysis
Rate of gluconeogenesis

Question 12

Define glycogenesis

Answer 12

Liver converts glucose into glycogen

Question 13

Define glycogenolysis

Answer 13

Liver hydrolyses glycogen into glucose which can diffuse into blood

Question 14

Define gluconeogenesis

Answer 14

Liver converts glycerol and amino acids into glucose

Question 15

Role of glucagon when blood glucose concentration decreases

Answer 15

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

Question 16

Role of adrenaline when blood glucose concentration decreases

Answer 16

1. Adrenal glands produce adrenaline. It binds to surface receptors on liver cells and activates enzymes for glycogenolysis
2. Glucose diffuses from liver into bloodstream

Question 17

What happens when blood glucose concentration increases

Answer 17

1. Beta cells in Islets of Langerhans in pancreas detect increase and secrete insulin into bloodstream
2. Insulin binds to surface receptors on target cells to:
   - increase cellular glucose uptake
   - active enzymes for glycogenesis
   - stimulate adipose tissue to synthesise fat

Question 18

How does insulin lead to a decrease in blood glucose concentration

Answer 18

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

Question 19

How does insulin increase permeability of cells to glucose

Answer 19

Increases number of glucose carrier proteins

Triggers conformational change which opens glucose carrier proteins

Question 20

How does insulin increase glucose concentration gradient

Answer 20

Activates enzymes for glycogenesis in liver and muscles

Stimulates fat synthesis in adipose tissue

Question 21

How do glucagon and adrenaline work

Answer 21

Secondary messenger model

1. Hormone-receptor complex forms
2. Conformational 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 22

Explain causes of type 1 diabetes

Answer 22

Body cannot produce insulin

Treated by injection of insulin

Question 23

Explain causes of type 2 diabetes

Answer 23

Glycoprotein receptors are damaged or become less responsive to insulin
Treated by controlling diet and exercise regime

Question 24

Signs and symptoms of diabetes

Answer 24

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

Question 25

How could colorimetry be used to identify the glucose concentration in a sample

Answer 25

1. Benedict's test on solutions of known conc - use colorimeter to record absorbance 2. Plot calibration curve 3. Benedict's test and absorbance of unknown sample and use calibration curve

Question 26

Define osmoregulation

Answer 26

Control of blood water potential via homeostatic mechanisms

Question 27

Describe gross structure of kidney

Answer 27

Fibrous capsule - protects kidney Cortex - Consists of Bowman's capsules, convoluted tubules and blood vessels Medulla - consists of collecting ducts, loop of Henle and blood vessels Renal pelvis - cavity collects urine into ureter Ureter - tube carries urine to bladder Renal artery - supplies kidney with oxygenated blood Renal vein - returns deoxygenated blood from kidney to heart

Question 28

Describe structure of nephron

Answer 28

``` Bowman's capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct ```

Question 29

Blood vessels associated with nephron

Answer 29

Wide afferent arteriole from renal artery enters renal capsule and forms glomerulus Efferent arteriole branches to form capillary network that surrounds tubule

Question 30

How is glomerular filtrate produced

Answer 30

Ultrafiltration in Bowman's capsule High hydrostatic pressure in glomerulus forces small molecules out of capillary fenestrations against osmotic gradient Basement membrane acts as filter

Question 31

How are cells of Bowman's capsule adapted for ultrafiltration

Answer 31

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

Question 32

What happens during selective reabsorption

Answer 32

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

Question 33

How are cells in proximal convoluted tubule adapted for selective reabsorption

Answer 33

Microvilli - large SA for co-transporter proteins Many mitochondria - ATP for AT of glucose Folded basal membrane - large SA

Question 34

What happens in loop of Henle

Answer 34

1. AT 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 descending limb

Question 35

Role of distal convoluted tubule

Answer 35

Reabsorption of water via osmosis and ions via AT | Permeability of walls determined by action of hormones

Question 36

Role of collecting duct

Answer 36

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

Question 37

Importance of maintaining Na+ gradient

Answer 37

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

Question 38

What might cause blood water potential to change

Answer 38

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

Question 39

Role of hypothalamus in osmoregulation

Answer 39

Osmosis of water out of osmoreceptors in hypothalamus cause them to shrink Triggers hypothalamus to produce antidiuretic hormone (ADH)

Question 40

Role of posterior pituitary gland in osmoregulation

Answer 40

Stores and secretes ADH produced by hypothalamus