Homeostasis

Question 1

homeostasis

Answer 1

maintaining internal environment within restricted limits
eg temp and pH need to be controlled as enzymes denature away from optimum
glucose conc needs to be controlled as it is important in respiration and in maintaining wp in blood + tissue fluid

Question 2

negative feedback

Answer 2

mechanism for stability where deviations from optimum levels are detected by receptors and trigger a corrective mechanism to bring the factor back to optimum level
amount of correction needed is reduced as the factor returns to optimum

Question 3

glyogenolysis

Answer 3

hydrolysis of glycogen to form glucose

Question 4

glycogenesis

Answer 4

formation of glycogen from glucose

Question 5

gluconeogenesis

Answer 5

non carbohydrate sources (fatty acids and amino acids) converted to glucose

Question 6

beta cells

Answer 6

on islets of Langerhan
detect high glucose levels
release insulin to lower levels

Question 7

alpha cells

Answer 7

on islets of Langerhan
detect low glucose levels
release glucagon to raise glucose levels

Question 8

insulin

Answer 8

target cells- liver, muscle and fat
insulin increases the rate at which these cells absorb glucose, lowering glucose conc in blood
insulin binds to receptors on muscle and fat cells
causes vesicles containing glucose transporter proteins (GTP) to join the cell surface membrane
increases the number of GTP on the membranes, increasing the rate of uptake of glucose by FD
results in glucose conversion to glycogen

Question 9

insulin- liver

Answer 9

in liver cells, insulin activates enzymes to convert glucose to glycogen (glycogenesis)
this lowers the glucose conc in cells which maintains a conc gradient so that more glucose can be taken up from blood

Question 10

glucagon

Answer 10

target cells- muscle + liver
glucagon raises glucose conc
attaches to receptors on target cells and stimulates:
activating enzymes that convert glycogen to glucose (glycogenolysis)
activating enzymes that convert fatty acids and amino acids to glucose (gluconeogenesis)

Question 11

adrenaline

Answer 11

secreted by adrenal glands
raises blood glucose conc ready for fight or flight
has a similar effect on liver cells as glucagon as it causes glycogenlysis
glucose is then released from the liver into the bloodstream

Question 12

second messenger model

Answer 12

adrenalin and glucagon do not enter the cell but this explains how they cause glycogenolysis
hormone binds to receptor on membrane of target cell
changes shape of membrane protein
this activates adenylate cyclase
this converts ATP to cAMP
cAMP is second messenger
cAMP activates protein kinase A
this converts glycogen to glucose
glucose moves out of liver cells by facilitated diffusion

Question 13

kidney functions

Answer 13

excretion- removal of waste products eg urea

osmoregulation- maintaining balance of dissolved substances and water

Question 14

nephron

Answer 14

each kidney contains thousands of tiny tubules called nephrons which are responsible for the formation of urine

Question 15

glomerulus

Answer 15

found in cortex of kidney
afferent arteriole- blood in
efferent arteriole- blood out
ultrafiltration occurs here
small molecules; aa, g, ions, aa are pushed out
efferent is narrower than afferent creating high pressure which forces out the small molecules, creating glomerulus filtrate
endothelium
basement membrane- mesh of protein, fine filter
podocytes

Question 16

proximal convoluted tubule

Answer 16

found in cortex of kidney
selective reabsorption from lumen to cells to blood
useful substances (g, aa, ions) reabsorbed from glomerular filtrate
Na+ reabsorbed by FD or co transport with g and aa
water reabsorbed by osmosis
Na+K+ pump maintains conc gradient (other side)- Na+ low inside

Question 17

PCT cells adapted

Answer 17

proximal convoluted tubule
microvilli on surface of cell to increase SA to reabsorb substances from filtrate
lots of mitochondria to provide ATP for active transport
folds in PCT to provide SA for reabsorption back into blood

Question 18

diabetes + reabsorption

Answer 18

glucose levels in glomerular filtrate is too high
not all glucose can be reabsorbed as glucose transporter proteins are saturated
glucose comes out in urine

Question 19

loop of Henle

Answer 19

found in medulla of kidney
aims to conserve water by creating a high conc of ions in medulla
desert animals have longer loH to conserve more water- more water can be reabsorbed

Question 20

ascending limb

Answer 20

impermeable to water
actively transports Na+ into medulla (wider part)
creates low wp in medulla

Question 21

descending limb

Answer 21

permeable to water

water leaves down wp gradient by osmosis into medulla created by AL

Question 22

distal convoluted tube + collecting duct

Answer 22

hormones control amount of water reabsorbed through DCT and CD
osmoreceptors in hypothalamus detect changes in blood wp
when wp becomes low, pituitary gland releases antidiuretic hormone (ADH)
ADH increases the permeability of DCT and CD so more water is reabsorbed

Question 23

ADH action

Answer 23

binds to ADH receptors on cells of DCT and CD
triggers aquaporins to move into cell surface membrane
increases permeability of cells to water
allows more water to be reabsorbed into blood from DCT and CD
- means smaller volume of urine

Question 24

negative feedback WP

Answer 24

as water potential in blood increases, ADH secretion decreases ( so less water is reabsorbed)
as water potential in blood decreases, ADH secretion occurs ( more water reabsorbed)
at low levels of ADH, aquaporins leave cell surface membrane

Question 25

maintaining body temp

Answer 25

thermoregulatory centre in hypothalamus contains thermoreceptors that detect changes in temp of the blood
if the blood is higher or lower than 37C, impulses will pass to skin (effector)

Question 26

high body temp

Answer 26

more heat loss
vasodilation- widening of arterioles so more blood flows through capillaries near the skin surface, to radiate hear
sweating- heat lost through evaporation
relaxation of erector hair muscles- lowers body hair to reduce air trapped and reduce insulation

Question 27

low body temp

Answer 27

less heat loss
vasoconstriction- narrowing of arterioles so less blood flows through capillaries near skin and less heat is radiated
reduction in sweat
contraction of erector hair- makes hair stand up so they can trap air and insulate the body
heat generated by shivering due to contraction and relaxation of muscles

Question 28

skin receptors

Answer 28

skin has receptors which detect external temps and pass impulses to thermoregulatory centre of brain
if external temp is cold, thermoregulatory will turn up heat production before the internal temp has time to drop

Question 29

hyper + hypothermia

Answer 29

occurs when info that blood has returned to normal temp is not fed back to thermoregulatory centre in brain
the body continues to respond which deviates the body temp further away from the norm (positive feedback)

Question 30

hypothermia

Answer 30

when the body gets too cold

body continues to increase heat loss which will lower the body temperature

Question 31

hypothermia

Answer 31

when the body gets too hot

body continues to reduce heat loss which will raise the body temperature

Question 32

loop of henle and medulla relationship

Answer 32

thicker medulla means longer loop of Henle
can conserve more water
increase in Na+ conc in medulla
maintains wp gradient for longer so more water is reabsorbed into medulla

Question 33

desert animals

Answer 33

More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
By osmosis;
From collecting duct / from end of second convoluted tubule;
Due to longer loop of Henle;
Sodium / chloride ions absorbed from filtrate in ascending limb;
Gradient established in medulla / concentration of ions increases down medulla;

For ADH,
Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
Makes cells more permeable / inserts aquaporins in plasma membranes;