Topic 6- 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

Maintains the rate of enzyme controlled reaction and prevent damage to membranes

• Make sure that enzyme substrate molecules have sufficient kinetic energy to collide
• when temp is too high enzymes denature

Question 3

Why is it important that blood pH remains stable

Answer 3

Maintain stable rate of enzyme controlled reactions and optimum conditions for other proteins

• acidic ions interact with H bonds and ionic bonds in tertiary structures of enzymes and this causes the active site of the enzyme to change shape so no ES complexes form

Question 4

Why is it important that blood glucose concentration remains stable

Answer 4

• maintains constant blood water potential and prevents osmotic lysis and plasmolysis of cells
• maintains constant concentration gradient 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

Outline the general stages involved in negative feedback

Answer 7

Receptors —> coordinator—-> correcting mechanism by effectors —-> receptors detect that conditions have returned to normal

Question 8

Suggest why separate negative feedback mechanisms control fluctuations in different directions

Answer 8

Provides more control, especially in the case of overcorrection which leads to a deviation in the opposite direction from the original one

Question 9

Suggest why coordinators analyses inputs from several receptors before sending an impulse to an effector

Answer 9

Receptors may find conflicting information

Optimum response may require multiple types of effectors

Question 10

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

Answer 10

• takes time to produce hormone
• transport hormone in the blood
• cause required change to the target protein

Question 11

Name the factors that effect blood glucose concentration

Answer 11

Amount of carbs digested from food

Rate of glycogenolysis

Rate of gluconeogenesis

Question 12

Define glycogenesis

Answer 12

Liver converts glucose into the storage polymer 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

Outline the role of glucagon when blood glucose concentration decreases

Answer 15

1. The alpha cells in islets of langerhans in pancrease detect the low concentration and secrete glucagon into blood
2. Glucagon binds to surface of liver cells and activates enzymes for glycogenolysis and gluconeogenesis
3. Glucose diffuses from liver into bloodstream

Question 16

Outline the role of adrenaline when blood glucose concentration decreases

Answer 16

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

Question 17

Outline what happens when blood glucose concentration increases

Answer 17

1. B cells in the islets of langerhans detect the change and secrete insulin into bloodstream
2. Insulin then binds to surface receptors on target cells which increases glucose uptake by cells and activates enzymes for glycogenesis

Question 18

Describe how insulin leads to a decrease in blood glucose concentrations

Answer 18

Increase 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

Increase number of glucose carrier proteins

Triggers change which opens glucose carrier proteins

Question 20

How does insulin increase the glucose concentration gradient

Answer 20

Activates enzymes for glycogenesis in liver and muscle

Stimulates fat synthesis in fat tissue

Question 21

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

Answer 21

1. Hormone receptor complex is formed
2. Conformational change to receptor activates G protein
3. Activates adenylate cyclase which converts ATP to cyclic AMP
4. cAMP activates proteins kinase
5. Results is glycogenolysis

Question 22

Explain the causes of Type 1 diabetes and how it is controlled

Answer 22

Body cannot produce insulin and this is thought to be due to an autoimmune response which attacks B cells of islets of langerhans

Treat by insulin injection

Question 23

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

Answer 23

Glycoprotein receptors are damages or become less resonsive to insulin

Strong correlation with poor diet and obesity

Treat by controlling diet and exercise regime

Question 24

Name some symptoms of diabetes

Answer 24

1. High glucose concentration in blood
2. Glucose in urine
3. Blurred vision
4. Sudden weight loss

Question 25

How can a student produce a desired concentration of glucose solution from a stock solution

Answer 25

Required concentration x (final volume needed/ concentration of stock solution ) Volume of distilled water = volume needed - stock solution volume

Question 26

Define osmoregulation

Answer 26

Control of blood water potential via homeostatic mechanisms

Question 27

Describe the gross structure of a mamalian kidney

Answer 27

Cortex- consists of the bowman’s capsule, convoluted tubules and blood vessels Medulla- collecting ducts, loops of henle and blood vessels Renal artery- supplied kidney with oxygenated blood Renal vein- returns deoxygenated blood from kidney to heart

Question 28

Describe the structure of a nephron

Answer 28

At the start is the Bowman’s capsule which surrounds to glomerulus and has an inner layer of podocytes Then the proximal convoluted tubules which are series of loops surrounded by capilleries Loop of henle which are hairpin loops extending from the cortex into medulla Distal convoluted tubule similar to PCT but fewer capilleries Collecting duct which is where the distal convoluted tubule from several nephrons empty into collecting duct which

Question 29

Describe the blood vessels associated with a nephron

Answer 29

Wide afferent arteriole is the end of the renal artery where the renal artery enters the renal capsule and forms the glomerulus Efferent arteriole branches to form capillary network that surrounds tubules

Question 30

Explain how glomerular filtrate is formed

Answer 30

Ultrafiltration in Bowman’s capsule which surrounds High hydrostatic pressure in glomerulus forces small molecules like water, glucose and urea out of capillary Basement membrane acts as a filter and the blood cells and larger molecules remain in capillary

Question 31

How are cells in Bowman’s capsule adapted for ultrafiltration

Answer 31

They have capilleries with tiny pores called fenestrations between the epithelial cells of capilleries Fluids can pass between and under folded membrane of podocytes

Question 32

State what happens during selective reabsorption and where is occurs

Answer 32

Useful molecules from golermular filtrate and reabsorbed into the blood in the proximal convoluted tubule

Question 33

Outline the transport processes involved in selective reabsorption

Answer 33

1. Glucose from glomerular filtrate are co transported with Na+ ions into the cells lining the proximal convoluted tubule 2. The glucose is then actively transported from cells lining convoluted tubules into intercellular species 3. Then the glucose diffuses into the blood capilleries lining the tubule

Question 34

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

Answer 34

Microvilli which creates a large SA for cotransporter proteins Many mitochondria to provide ATP needed for active transport of glucose from the proximal convoluted tubule into intercellular spaces Folded basal membrane that provides large SA

Question 35

What happens in the loop of Henle

Answer 35

2. Active transport of Na+ ions and Cl- ions out of the ascending limb 2. This decreases the water potential of the interstitial fluid 3. Osmosis of water out of the descending limb 4. Water potential of filtrate decreases going down descending limb and is lowest in the medulla region and highest at the top of the ascending limb

Question 36

Explain the role of the distal convoluted tubule

Answer 36

Reabsorption of water (osmosis) and ions (active transport)

Question 37

Why do hormones have an effect on the walls of the distal convoluted tubule

Answer 37

They effect the permeability of the walls

Question 38

Explain the role of the collecting duct

Answer 38

Reabsorption of water form filtrate into intersisital fluid via osmosis through aquaporins

Question 39

Expand why it is important to maintain an Na+ gradient

Answer 39

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

Question 40

Might cause blood water potential to change

Answer 40

Water intake Ions intake in diet Ions used in metabolic processes or excreted Sweating

Question 41

Explain the role of the hypothalamus in osmoregulation

Answer 41

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

Question 42

Explain the role of the posterior pituitary gland in osmoregulation

Answer 42

Stores and secretes the ADH produced by the hypothalamus

Question 43

Explain the role of ADH in osmoregulation

Answer 43

1. Makes cells lining collecting ducts more permeable to water - binds to receptor —> activates phosphorylase —> vesicles with aquaporins fuse with cell-surface membrane 2. Makes cells lining collecting duct more permeable to urea - water potential in interstitial fluid decreases - more water reabsorbed and more concentration urine

Question 44

Describe the role of receptors and the nervous system in increasing heart rate due to exercise

Answer 44

1. The chemoreceptors detect change in CO2 concentration in blood 2. Signal sent to the medulla 3 sympathetic NS causes the SAN valve to send more electrical impulses