9.9 - osmoregulation

Question 1

structure of the kidney

Answer 1

page 131 of revision guide

Question 2

what is the kidney made up of

Answer 2

• made of millions of nephrons
• these give the kindney its distinctive layers

Question 3

nephron structure

Answer 3

page 131 revision guide

Question 4

function of structures in the cortex

Answer 4

• structures in the cortex mostly filter toxins such as urine from blood

nephron

Question 5

function of structures in the medulla

nephron

Answer 5

• tubules that extend into medulla are mostly regulate water potential in the blood

Question 6

microscopic structure of nephron

Answer 6

page 131 revision guide

Question 7

Bowman’s capsule function

Answer 7

• has little resistance to fluid leaving blood
• prevents large proteins from passing into the tubule

Question 8

wall of proximal tubule

Answer 8

• adaptations for rapid absorption
• i.e. large surface area due to microvillie
• ATP readily available from many mitochondria

Question 9

blood supply in the nephron

Answer 9

• kidney filters 180dm^3 of fluid out the blood each day
• majority returns back to blood due to a network of vessels

Question 10

vasa recta

Answer 10

• the group of capillaries that drop into the medulla and return to the cortex
• direction of blood flow is opposite to that of fluid in the tubules (countercurrent flow)

Question 11

how is urea produced in the liver

Answer 11

• excess amino acids are deaminated in the liver
• amine group is removed and forms ammonia (very toxic)
• ammonia is then converted into a less toxic urea by reacting with CO2 and energy from ATP
• urea then excreted by kidneys by ultrafiltration

Question 12

what is deamination

Answer 12

• the removal of the amino group from excess amino acids in liver

then converted to ammonia then urea which is then excreted through kidneys

Question 13

ultrafiltration

Answer 13

• the filtering of blood under high pressure from the glomerulus into the Bowman’s capsule
• due to hydrostatic pressure
• diameter of afferent arteriole is greater than the efferent arteriole

Question 14

afferent arteriole

Answer 14

blood vessel coming into the glomerulus

Question 15

efferent arteriole

Answer 15

blood vessel leaving the glomerulus

Question 16

why is filtrate formation promoted

Answer 16

• because the blood enters the glomerulus under pressure
• afferent arteriole entering glomerulus is wider than efferent vessel leaving

Question 17

process of ultrafiltration

Answer 17

• occurs in the Bowman’s capsule
• filtration is based on particle size
• filtrate produced has a composition very similar to plasma
• high blood pressure develops in glomerular capillaries
• high pressure squeezes blood out through the capillary wall through pores
• most proteins are too big to pass inot the tubule
• there is a very thin barrier between blood in the capillary and the tubule lumen

Question 18

why is there a thin barrier between blood in capillary and tubule lumen

Answer 18

due to there being many gaps between the capillary endothelium cells

Question 19

what is selective reabsorption

Answer 19

• the process by which substances needed by the body are reabsorbed from the kidney tubules into the blood

Question 20

where does selective reabsorption occur

Answer 20

at the proximal convulated tubule

Question 21

what substances are absorbed/not absorbed

Answer 21

• glucose fully reabsorbed
• waste products such as urea left in high conc in the filtrate
• water reabsorption is variable

Question 22

how are substances reabsorbed

Answer 22

• via active transport for glucose, amino acids/proteins, vitamins and hormones
• mitochondria supply the ATP needed
• sodium ions are actively reabsorbed
• water and other ions follow passively

Question 23

distal convulated tubule (DCT)

Answer 23

• secretes waste chemicals such as creatinine into the filtrate
• pumps ions to control blood pH
• helps to control blood volume

Question 24

what are the two regions of the Loop of Henle

Answer 24

1. descending limb
2. ascending limb

Question 25

# Loop of Henle descending limb

Answer 25

- has narrow thin walls - permeable to water

Question 26

# Loop of Henle ascending limb

Answer 26

- wider thicker walls - impermeable to water

Question 27

# Loop of Henle selective reabsorbption - describe

Answer 27

- as glomerular filtrate carries on down **descending limb** conc of Na+ and Cl- ions increases - **hypertonic solution** - when travelling through **ascending limb** the water permeability changes - Na+ and Cl- diffuse out and the conc of Na+ and Cl- ions starts to decrease - **hypotonic solution**

Question 28

hypertonic

Answer 28

concentrated urine

Question 29

hypotonic

Answer 29

less concentrated urine

Question 30

what is the loop of Henle ## Footnote in terms of how it works

Answer 30

- it is a **countercurrent multiplier** - the longer the loop the greater the effect on the concentration of the filtrate

Question 31

what causes the countercurrent multiplication

Answer 31

- the flow of filtrate in the two limbs is in **opposite** directions - descending limb - water moves by osmosis out of the loop down the water potential gradient - ascending limb - in the lower, thinner part, ions move out by diffusion which maintains water potential gradient in descending limb - in higher parts ions move out by active transport

Question 32

what is the main role of the loop of Henle

Answer 32

- to set up & maintain a salt gradient between the filtrate & blood so water is reabsorbed by osmosis

Question 33

explain how the Loop of Henle is involved in the production of concentrated urine ## Footnote ppq

Answer 33

- sodium/chloride ions are move out the ascending limb by active transport - ascending limb is impermeable to water which results in a low water potential in medulla - Loop of Henle acts as a countercurrent - collecting duct is permeable to water - so water moves out of collecting duct by osmosis