Lecture 2

Question 1

glucose reabsoprtion in the PCT

Answer 1

reabsorption of glucose through the sodium-glucose transporters (SGLTs) -all glucose in the filtrate is reabsorbed via PCT -it is co-transported with Na+ at the luminal membrane by Na+/glucose transporter (through the Na+/K+ pump) -then diffuses from the cell into the intestinal fluid and then into peritubular capillaries (surrounding the glomerulus) -also H+ can be transported out of the cell

Question 2

What occurs at the distal part of the PCT?

Answer 2

passive reabsorption of ions and urea, out of the intestinal fluid into the blood

Question 3

What occurs in the descending limb?

Answer 3

water is freely move out of the thin descending limb in response to surronding osmolarity as surronding tissue has higher solute concentration -in symporter, solutes (e.g, Na+/K+) are drawn into the tubule into surronding tissue -although as the thick part of the ascending limb is permaeable to water, solutes stay trapped into the surronding tissue

Question 4

What occurs in the distal convoluted and the collecting duct?

Answer 4

Na+ moves out of the tubule and K+ moves back inside -water can either be moved out to conserve water and this is used in ADH

Question 5

The control of ADH

Answer 5

it is normally used to save/preserve water and alcohol inhibits ADH 1.In the hypothalamus, there are osmoreceptors that detect dehydration 2. This stimulates the thrist sector in the brain, and makes you drink 3. This causes the release of ADH 4. There are volume receptors which can detect the low pressure and stimulate the release of ADH

Question 6

What is the aim of anti-direutic hormone( ADH) ?

Answer 6

produced in supraoptic and paraventricular nuclei of the hypothalamus -transported to the posterior pitatury where it is packaged into storage granules and released by exocytosis -has a short plasma life -released into circulation and acts on principal cells of the collecting duct also shown to reduce water excretion and stimulate vasoconstriction

Question 7

What are other uses of ADH?

Answer 7

allows water to be removed from the tubular fluid as it flows through

Question 8

How does urine production occur?

Answer 8

there is 500 mL/day of urine production a day -humans must excerte 600 mOsm/day (despite being dehydrated) -our urine can be come up to 1200 mOsm/L (concentration)

Question 9

Camels and water reabsorption

Answer 9

camels need to retain water so have a very concentrated urine

Question 10

Loop of Henle

Answer 10

Thin descending limb - permeable to water - no active reabsorption or secretion of solutes. Thin ascending limb - impermeable to water - essentially no active reabsorption or secretion of solutes. Thick ascending limb - impermeable to water - active reabsorption of sodium & other solutes.

Question 11

Can we alter water excretion independently of solute excretion?

Answer 11

Graphs show effect of sudden ingestion of 1 litre of water on plasma osmolarity, urine osmolarity, urine flow rate & solute excretion. Increase of urine volume x6 within 45 minutes to maintain body fluid volume. The amount of solutes excreted remains essentially unchanged, it is the amount of water excreted that is altered - thus plasma osmolarity remains constant ∴ shows that we can alter water excretion independently of solute excretion

Question 12

Medullary concentration gradient

Answer 12

Within the inner medulla, the concentration of urea, Na and Cl increases -the more urea surronds the nephron

Question 13

The counter-current multipler in the loop of Henle

Answer 13

formation of increasing osmoatic gradinet in the meduallry interstital fluid -there is a build up of ions from 300-1200 mOsm/L

Question 14

What occurs if we are hydrated or dehydrated?

Answer 14

If we are hydrated, we get rid of solutes. If we are dehydrated, we need to draw out water, and concentrate solutes (ADH), so low volume, leaving behind solutes that is concentrated

Question 15

Formation of dilute urine

Answer 15

1. Osmolarity of tubular fluid INCREASES as it flows down the descending limb LoH. -more solutes are pumped out of the tubule they leave behind a dilute tubular fluid when compared to plasma -leads to dilute urine exerted

Question 16

(Owing to increase in osmolarity of the surrounding interstitial tissue of renal medulla so fluid moves out of the tubule.) 2.Osmolarity of tubular fluid DECREASES as it flows up the ascending limb LoH. (Owing to the removal of ions by Na+, K+ and Cl- symporters : and retention of water because the cells of the thick limb are impermeable to water. So solutes are leaving but water can not follow.) 1.Osmolarity of tubular fluid further DECREASES as it flows through DCT and CD.

Question 17

(Some solutes are further removed and reabsorbed, in the absence of ADH the DCT and CD are impermeable to water so the tubular fluid is very dilute at this point = 65-70 mOsml/L)

Question 18

Formation of concentrated urine

Answer 18

•The distal & collecting tubules / ducts are permeable to water in the presence of antidiuretic hormone (ADH) •Water will move so that there is osmotic equilibrium with surrounding interstitium •Note osmolarity of medullary interstitum ~1200mOsm/L/H2O •This leads to a concentrated urine being excreted

Question 19

Counter current exchange

Answer 19

•Hairpin arrangement allows the nutrients to be delivered & water removed whilst minimising disruption to the medullary concentration gradient - counter current exchange •Constant flow of urea and NaCl (lumen to interstitium and via vasa recta) - stops them precipitating in medulla

Question 20

How is this system regulated?

Answer 20

through the renin-angiotensin-aldosterone system 1. decrease in Blood volume and pressure, means the afferent arteriole is less stretched 2. The juxtamedullary cells secrete renin 3. Renin leads to the production of angiotensin II, thus helping with vasoconstriction of efferent and afferent arteriole 4. This reduced GFR 5. Slows processes down so reabsorption of Na+ and Cl- and water, activating Na+/H+ anti-porters

Question 21

What is the major for hypotension drugs?

Answer 21

•ACE - produced from both renal and lung epithelia •ACE Inhibitors clinically very important. •Major target for hypertension drugs: -benazepril (Lotensin) -captopril (Capoten) -enalapril (Vasotec), -fosinopril (Monopril), -lisinopril (Prinivil, Zestril) -moexipril (Univasc), and -perindopril(Aceon), -quinapril (Accupril), -ramipril (Altace), -trandolapril (Mavik).