6.4 Homeostasis Is The Maintenance Of A Stable Internal Enviroment

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 reaction & prevent damage to membranes

Temperature too low = enzyme & substrate molecules have insufficient kinetic energy

Temperature too high = enzymes denature

Question 3

Why is it important that blood pH remains stable

Answer 3

Maintain stable rate of enzyme-controlled reaction (& optimum conditions for other proteins).

Acidic pH = H+ ions interact with H-bonds & ionic bonds in tertiary structure of enzymes —> shape of active site changes so no ES complexes form

Question 4

Why is it important that blood glucose concentration remains stable

Answer 4

Maintain constant blood water potential: prevent osmotic lysis / crenation of cells
Maintains constant concentration of respiratory substrate: organism maintains constant level of activity regardless of environmental conditions

Question 5

Define negative and positive feedback

Answer 5

Negative feedback: self regulatory mechanisms returns internal environment to optimum when there is a fluctuation

Positive feedback: a fluctuation triggers changes that result in an even greater deviation from the normal level

Question 6

Outline the general stages involved in negative feedback

Answer 6

Receptor detect deviation —> coordinator —> corrective mechanism by effector —> receptors detect that conditions have returned to normal

Question 7

Suggest why separate negative feedback mechanisms control fluctuations in different directions

Answer 7

Provides more control, especially 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 effector

Question 9

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

Answer 9

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

Question 10

Name the factor that affect blood glucose concentration

Answer 10

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

Question 11

Define glycogenesis, glycogenolysis and gluconeogenesis

Answer 11

glycogenesis: liver converts glucose into the storage polymer glycogen

glycogenolysis: liver hydrolyses glycogen into glucose which can diffuse into blood

gluconeogenesis: liver converts glycerol & amino acids into glucose

Question 12

Outline the role of glucagon when blood glucose concentration decreases

Answer 12

α cells in IsIets of Largerhans in pancreas detect decrease & secrete glucagon into bloodstream

Glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis and gluconeogenesis

Glucose diffuses from liver into bloodstream

Question 13

Outline the role of adrenaline when blood glucose concentration decreases

Answer 13

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 14

Outline what happens when blood glucose concentration increases

Answer 14

1. β cells in IsIets of Langerhans in pancreas detect increase & secrete insulin into bloodstream
2. Insulin binds to surface receptors on target cell to:

A) increase cellular glucose uptake
B) activate cellular glucose uptake
C) stimulate adipose tissue to synthesise fat

Question 15

Describe how insulin leads to a decrease in blood glucose concentration

Answer 15

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

Question 16

How does insulin increase permeability of cells to glucose?

Answer 16

Increases number of glucose carrier proteins

Triggers conformational change which opens glucose carrier proteins

Question 17

How does insulin increase the glucose concentration gradient

Answer 17

Activates enzymes for glycogenesis in liver & 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 cyclic AMP (cAMP)
4. cAMP activates protein kinase A pathway
5. Results in glycogenolysis

Question 19

Explain the cause of Type 1 diabeates and how it can be controlled

Answer 19

Body cannot produce insulin e.g. due to autoimmune response which attacks β cells of IsIets of Langerhans

Treat by injecting insulin

Question 20

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

Answer 20

Glycoprotein receptors are damaged or become less responsive to insulin

Strong positive correlation with poor diet / obesity

Treat by controlling diet and exercise regime

Question 21

Name some signs and symptoms of diabetes

Answer 21

• high blood glucose concentration
• glucose in urine
• polyuria
• polyphagia
• polydipsia
• blurred vision
• sudden weight loss

Question 22

Suggest how a student could produce a desired concentration of glucose solution from a stock solution

Answer 22

Volume of stock solution = required concentration X final volume needed / concentration of stock solution

Volume of distilled water = final volume needed - volume of stock solution

Question 23

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

Answer 23

1. Benedict’s test on solution of known glucose concentration. Use colorimeter to record absorbance.
2. Plot calibration curve: absorbance (y-axis), glucose concentration (X-axis)
3. Benedict’s test on unknown sample. Use calibration curve to read glucose concentration at its absorbance value

Question 24

Define osmoregulation

Answer 24

Control of blood water potential via homeostatic mechanisms

Question 25

Describe the gross structure of a mammalian kidney

Answer 25

Fibrous capsule: protects kidney Cortex: outer region consists of bowman’s capsules, convoluted tubules, blood vessels Medulla: inner region consists of collecting ducts, loops of Henle, 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 26

Describe the structure of a nephron

Answer 26

Bowman’s capsule at start of nephron: cup-shaped, surrounds glomerulus, inner layer of podocytes Proximal convoluted tubule (PCT): series of loops surrounded by capillaries, walls made of epithelial cells with microvilli. Loop of henle: hairpin loop extends from cortex into medulla Distal convoluted tubule: similar to PCT but fewer capillaries Collecting duct: DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney

Question 27

Describe the blood vessels associated with a nephron

Answer 27

Wide afferent arteriole from renal artery enters renal capsule & forms glomerulus: branched knot of capillaries which combine to form narrow efferent arteriole Efferent arteriole branches to form capillary network that surrounds tubules

Question 28

Explain how glomerular filtrate is formed

Answer 28

Ultrafiltration in bowman’s capsule High hydrostatic pressure in glomerulus forces small molecules (urea,water,glucose, minereal ions) out of capillary fenestartions AGAINST osmotic gradient Basement membrane acts as filter. Blood cells & large molecules e.g. proteins remain in capillary

Question 29

How are cells of the Bowman’s capsule adapted for ultrafiltration?

Answer 29

Fenestration between epithelial cells of capillaries Fluid can pass between & under folded membrane of podocytes

Question 30

State what happens during selective reabsorption and where it occurs

Answer 30

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

Question 31

Outline the transport process involved in selective reabsorption

Answer 31

Slide 64

Question 32

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

Answer 32

Microvilli: large surface area for co-transporter protein Many mitochondria: ATP for active transport of glucose into intercellular spaces Folded basal membrane: large surface area

Question 33

What happens in the loop of henle?

Answer 33

1. Active transport of Na+ & Cl- out of ascending limb. 2. Water potential of interstitial fluid decreases 3. Osmosis of water out of descending limb (ascending limb is impermeable to water). 4. Water potential of filtrate decreases going down descending limb: lowest in medullary region, highest at top of ascending limb

Question 34

Explain the role of the distal convoluted tuble

Answer 34

Reabsorption: a) of water via osmosis b) of ions via active transport Permeability of walls is determined by action of hormones

Question 35

Explain the role of the collecting duct

Answer 35

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

Question 36

Explain why it is important to maintain an Na+ gradient

Answer 36

Countercurrent multiplier: filtrate in collecting ducts is always besides an area of interstital fluid that has a lower water potential Maintains water potential gradient for maximum reabsorption of water

Question 37

What might cause blood water potential to change

Answer 37

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

Question 38

Explain the role of the hypothalamus in osmoregulation

Answer 38

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

Question 39

Explain the role of the posterior pituitary gland in osmoregulation

Answer 39

Stores and secretes the ADH produced by the hypothalamus

Question 40

Explain the role of ADH in osmoregulation

Answer 40

1. Makes cells lining collecting duct more permeable to water: Binds to receptors—> activates phosphorylase —> vesicles with aquaporins on membrane fuse with cell-surface memebrane 2. Makes cells lining collecting duct more permeable to urea: Water potential in interstital fluid decreases More water reabsorbed = more concentration urine