Homeostasis and the kidney

Question 1

homeostasis definition

Answer 1

the maintenance/control of an internal environment at a constant/set point by negative feedback

Question 2

what internal factors may change due to changes in our activity or external environment

Answer 2

• core body temp
• pH
• blood glucose conc
• blood solute potential
• water potential

Question 3

describe dynamic equilibrium

Answer 3

constant changes occur, but corrective mechanisms bring the internal environmental conditions back towards a set point

Question 4

what does negative feedback do

Answer 4

restores conditions back to their set point when there is a deviation

Question 5

describe the negative feedback loop

Answer 5

• receptor detects a deviation from set point in internal environment
• receptor sends instructions to co-ordinator
• co-ordinator communicates with effectors which make corrective responses
• factor returns to normal (set point)
• receptor feeds info back to effectors which stop making the correction

Question 6

examples of effectors

Answer 6

muscle or gland

Question 7

positive feedback

Answer 7

effector increases change (causes further movement away from the norm)

Question 8

4 excretory organs

Answer 8

1. lungs
2. kidneys
3. skin
4. liver

Question 9

2 functions of the kidney and brief descriptions of them

Answer 9

excretion = removal of nitrogenous waste from body
osmoregulation = control of water potential of the body’s fluids

Question 10

what happens in the medulla

Answer 10

reabsorption of water

Question 11

what happens in the cortex

Answer 11

ultrafiltration and selective reabsorption

Question 12

how is urea formed

Answer 12

• excess aa’s deaminated in liver
• amino group removed and converted into ammonia and then to urea

Question 13

what is the nephron?

Answer 13

functional unit of the kidney which filters blood

Question 14

what is the vasa recta?

Answer 14

a capillary network surrounding the loop of Henle

Question 15

what is ultrafiltration?

Answer 15

filtration under high pressure

Question 16

Blood enters capillaries of glomerulus from afferent arteriole and leaves via efferent. Blood has high hydrostatic pressure because :

Answer 16

1. heart’s contraction increases pressure of arterial blood
2. afferent has wider diameter than efferent

Question 17

what does the glomerular filtrate contain?

Answer 17

water, glucose, salts, urea, aa’s

Question 18

how do SMALL molecules and ions enter Bowman’s capsule and tubule as filtrate?

Answer 18

• through 3 filtration layers
• high hydrostatic pressure forces molecules through :
  *fenestrations of endothelial cells
  *selective molecular filter of basement membrane
  *filtration slits of pedicels into Bowman’s space

Question 19

3 layers separating the blood in glomerulus from the space inside Bowman’s capsules

Answer 19

• capillary walls
• basement membrane
• podocytes = squamous epithelial cell layer of Bowman’s capsule wall

Question 20

capillary cell walls purpose in blood filtration

Answer 20

have tiny pores/fenestrations between cells which allow solute to pass to basement membrane

Question 21

basement membrane purpose in blood filtration

Answer 21

selective molecular filtrate

Question 22

podocytes purpose in blood filtration

Answer 22

have extensions = pedicels which wrap round a capillary, pulling it closer to basement membrane
- gaps between pedicels = filtration slits

Question 23

where and by what processes does selective reabsorption happen?

Answer 23

proximal convoluted tubule in cortex
facilitated diffusion & active transport and osmosis & co-transport

Question 24

what is selective reabsorption?

Answer 24

useful substances (glucose, aa’s, salts) are reabsorbed from glomerular filtrate back into bloodstream

Question 25

5 adaptations to the cells lining the wall of PCT

Answer 25

1. microvilli = increase SA 2. lots of mitochondria = produce ATP for AT 3. tight junctions between cells = prevent molecules from diffusing between cells 4. basal channels = increase SA at the basement membrane 5. cells are closely associated with blood capillaires of vasa recta

Question 26

how does selective reabsorption happen?

Answer 26

- nephrom closely associated with vasa recta - reabsorbed substances pass from PCT into blood plasma in vasa recta capillaries

Question 27

where does reabsorption of water happen?

Answer 27

loop of Henle

Question 28

descending and ascending limb of loop of Henle : which is permeable and which is impermeable to water?

Answer 28

descending = permeable to water ascending = impermeable to water

Question 29

what happens in the descending limb of the loop of Henle during reabsorption of water?

Answer 29

- water leaves filtrate and enters blood by osmosis - Na+ & Cl- diffuse into descending limb from medulla

Question 30

where does the filtrate reach its maximum concentration?

Answer 30

apex of the loop of Henle

Question 31

what happens in the ascending limb of the loop of Henle during reabsorption of water?

Answer 31

- initially Na+ & Cl- leaves ascending limb by FD - as conc of solutes decrease AT takes over

Question 32

filtrate in the limbs of the loop of Henle flow in opposite directions there fore it is a :

Answer 32

counter current multiplier

Question 33

long loops of Henle

Answer 33

- higher conc of solutes at the apex - animals adapted to dry environments e.g camels

Question 34

short loops of Henle

Answer 34

animals adapted to fresh water environment e.g otters

Question 35

osmoregulation = (x2)

Answer 35

- the control of body fluid water potential by negative feedback - under hormonal control

Question 36

what causes a decrease in blood plasma water potential?

Answer 36

- low water intake - high intake of solutes - sweating

Question 37

osmoregulation process

Answer 37

1. osmoreceptors in hypothalamus detect decrease in blood plasma WP 2. signal sent to posterior lobe of pituitary galnd (co-ordinator) which releases ADH into bloodstream 3. ADH carried to kidneys and binds to receptor proteins on wall of collecting duct and DCT (effectors) 4. aquaporins added to cell membs of effectors --> allow more H2O to be reabsorbed => WP in blood increases back to set point 5. info fed back to hypothalamus and less ADH produced

Question 38

ADH (antidiuretic hormone) purpose

Answer 38

increases permeability of collecting duct and distal covoluted tubule cells to water

Question 39

what happens if more ADH is secreted

Answer 39

more H2O reabsorbed by osmosis => urine produced is more conc, less volume

Question 40

where is ADH produced and secreted

Answer 40

hypothalamus, posterior lobe of pituitary gland

Question 41

process of ADH increasing the permeability of cell membranes to water

Answer 41

- ADH binds to ADH receptor proteins in cell membrane - causes vesicles containing aquaporins to fuse with cell memb - increases permeability of cell memb to water => more H2O is reabsorbed into blood of vasa recta capillaries