homeostasis 3.6

Question 1

what is homeostasis

Answer 1

internal environment is maintained within set limits around an optimum

Question 2

what is the role of the pancreas (3)

Answer 2

detects blood glucose concentration
produces digestive enzymes
produces insulin and glucagon

Question 3

which enzymes does the pancreas produce

Answer 3

protease
amylase
lipase

Question 4

effects of high blood glucose (5)

Answer 4

lowers water potential in blood- water leaves cells via osmosis
thirst + urine
can damage brain cells
encourages bacteria growth- infection
clouded vision

Question 5

effects of low blood glucose

Answer 5

fatigue, trembling, sweating, shaking
confusion, blurred vision, headache, difficulty focusing
loss of consciousness

Question 6

why is it important that blood glucose concentration remains stable (2)

Answer 6

• maintains constant blood water potential to prevent osmotic lysis of cells
• maintains constant concentration of respiratory substrate

Question 7

define negative feedback

Answer 7

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

Question 8

define positive feedback

Answer 8

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

Question 9

outline the general stages involved in negative feedback

Answer 9

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

Question 10

suggest why separate negative feedback mechanisms control fluctuations in different directions

Answer 10

provides more control
especially in case of overcorrection
which would lead to a deviation in the opposite direction

Question 11

which 3 factors affect blood glucose concentration

Answer 11

amount of carbohydrate digested
rate of glycogenolysis
rate of guconeogenisis

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 gluconeogenisis

Answer 14

liver converts glycerol and amino acids into glucose

Question 15

what is the role of glucagon when blood glucose concentration decreases

Answer 15

alpha cells in islets of langerhans 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 16

outline the role of adrenaline when blood glucose concentration decreases

Answer 16

adrenal glands produce adrenaline
it binds to surface receptors on liver cells
activates enzymes for glycogenolysis
glucose diffuses from liver into bloodstream

Question 17

outline what happens when blood glucose concentration increases

Answer 17

beta cells in islets of langerhans in pancreas detect increase
secrete insulin into bloodstream
insulin binds to surface receptors on target cells

Question 18

describe how insulin leads to a decrease in blood glucose concentration (3)

Answer 18

increases permeability of cells to glucose by binding to cell-surface glycoprotein receptors
increases glucose concentration gradient
triggers inhibition of enzymes for glycogenolysis

Question 19

how does insulin increase permeability of cells to glucose (2)

Answer 19

increases number of glucose carrier proteins
triggers conformational change which opens glucose carrier proteins

Question 20

how does insulin increase the glucose concentration gradient (decrease glucose in cells)

Answer 20

activates enzymes for glycogenesis in liver and muscles
stimulates fat synthesis in adipose tissue

Question 21

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

Answer 21

hormone receptor complex forms
conformational change to receptor activates G-protein
activates adenylate cyclase
converts ATP to cyclic AMP
cAMP activates protein kinase A pathway
results in glycogenolysis

Question 22

explain the cause of type 1 diabetes and how it can be controlled

Answer 22

body cannot produce insulin
(eg due to autoimmune response which attacks beta cells of islets of langerhans)
treat by injecting insulin

Question 23

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

Answer 23

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 24

signs/symptoms of diabetes (4)

Answer 24

high blood glucose concentration
glucose in urine
blurred vision
sudden weight loss

Question 25

define osmoregulation

Answer 25

control of blood water potential via homeostatic mechanisms

Question 26

what are the 2 structures in the kidney that the nephron spans

Answer 26

cortex medulla

Question 27

what are the structures in a nephron

Answer 27

Bowmans capsule proximal convoluted tubule loop of henle distal convoluted tubule collecting duct

Question 28

describe blood vessels associated with a nephron (Bowmans capsule)

Answer 28

wide afferent arteriole from renal artery forms glomerulus which combine to form narrow efferent arteriole

Question 29

how is glomerular filtrate formed

Answer 29

ultrafiltration in bowman's capsule high hydrostatic pressure in glomerulus forces small molecules out against concentration gradient basement membrane acts as a filter blood cells and large molecules remain in capillary

Question 30

how are cells of the Bowmans capsule adapted for ultrafiltration

Answer 30

fenestrations between epithelial cells of capillaries fluid can pass between and under folded membrane of podocytes

Question 31

what are the three functions of the kidney

Answer 31

ultrafiltration selective reabsorption osmoregulation

Question 32

where does ultrafiltration occur

Answer 32

Bowmans capsule

Question 33

where does selective reabsorption occur

Answer 33

proximal convoluted tubule

Question 34

how is water reabsorbed

Answer 34

passively by osmosis

Question 35

how are glucose and sodium ions reabsorbed

Answer 35

actively by active transport/co-transport

Question 36

how are cells in the proximal convoluted tubule adapted for selective reabsorption (3)

Answer 36

microvilli - large surface area for co-transporter proteins many mitochondria- ATP for active transport of glucose into intercellular spaces folded basal membrane- large surface area

Question 37

what happens in the loop of henle

Answer 37

active transport of Na+ and Cl- out of ascending limb water potential of interstitial fluid decreases osmosis of water out of descending limb ascending limb is impermeable to water water potential of filtrate decreases going down the descending limb lowest in medullary region, highest at top of ascending limb

Question 38

explain the role of the distal convoluted tubule

Answer 38

reabsorption of water via osmosis and ions via active transport

Question 39

what is the permeability of the distal convoluted tubule dependant upon

Answer 39

ADH hormone

Question 40

explain the role of the collecting duct

Answer 40

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

Question 41

why is it important to maintain an Na+ gradient

Answer 41

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

Question 42

explain the role of the hypothalamus in osmoregulation

Answer 42

osmosis of water out of osmoreceptors in hypothalamus causes them to shrink this triggers hypothalamus to produce more ADH

Question 43

explain the role of the posterior pituitary gland in osmoregulation

Answer 43

stores and secretes the ADH produced by the hypothalamus

Question 44

explain the role of ADH in osmoregulation

Answer 44

ADH binds to receptors activates phosphorylase vesicles with aquaporins on membrane fuse with cell-surface membrane makes cells in collecting duct more permeable to urea