Formation of Urine

Question 1

Where are 80% of the glomeruli found?

Answer 1

In cortex

Question 2

What does sensory mechanism in the macula densa and juxtaglomerular apparatus do?

Answer 2

Senses changes in blood in sodium and chloride conc

Stimulates release of renin

Question 3

How does blood enter the kidneys? What does this divide into?

Answer 3

Via the renal artery, divides to smaller arteries and finally arterioles

Question 4

What are the arterioles in contact with?

Answer 4

Functional units of the kidneys –> nephrons

Question 5

What happens in the nephrons?

Answer 5

Where blood filtration and urine formation takes place

Question 6

Where is filtered blood then collected into?

Answer 6

Series of large veins –> leaves via renal vein

Question 7

Where is urine collected?

Answer 7

In collecting ducts, leaves via ureter

Question 8

Where does glomerular filtration take place?

Answer 8

Bowman’s capsule

Question 9

How does blood enter the Bowman’s capsule? What then happens to this blood?

Answer 9

Via afferent arteriole

Passes through ball of capillaries called the glomerulus

Leads via efferent arteriole

Question 10

What is the size of the afferent arteriole compared to the efferent?

Answer 10

Afferent much wider –> blood hydrostatic pressure in these capillaries is higher than normal

Question 11

What is effect of high hydrostatic pressure in glomerulus?

Answer 11

Drives water and solutes (glucose, amino acids, urea, creatinine) from blood through filtration membrane

This forms glomerular filtrate

Question 12

Where does filtrate then pass after exiting the glomerulus?

Answer 12

It flows into a duct in the nephron called the renal tubule

The first part of this tubule is the proximal convoluted tubule

Question 13

What occurs in the proximal convoluted tubule?

Answer 13

Reabsorption occurs

Water and solutes are driven through the epithelial cells that line the tubule into the extracellular space. They are then taken up by the peritubular capillaries

(Na+, water, Cl-, urea, glucose, amino acids)

Question 14

Why is Na+ reabsorption important?

Answer 14

Creates osmotic pressure that drives water and electrical gradient that drives Cl-

Question 15

How is Na+ levels in the epithelial cells kept low? What is result of this low level?

Answer 15

Due to Na+/K+ pump

This creates conc gradient that allows Na+ diffusion from tubular fluid into cell

Question 16

How is Na+ absorbed?

Answer 16

By symporter proteins that also bind glucose etc

Question 17

What is a symporter?

Answer 17

An integral membrane protein that is involved in the transport of many differing types of molecules across the cell membrane

Is a type of cotransporter

Question 18

How else does reabsorption occur (other than symporters)?

Answer 18

Via paracellular route through tight junction between epithelial cells

Question 19

What is also occurring at the same time as reabsorption?

Answer 19

Tubular secretion

Question 20

What is tubular secretion?

Answer 20

Active secretion of additional waste (drugs, H+ etc) from blood to join tubular fluid

Question 21

Where do processes of reabsorption and secretion continue?

Answer 21

Loop of Henle, distal convoluted tubule

Question 22

What is main function of loop of Henle?

Answer 22

Create and maintain an osmotic gradient in the medulla that enables collecting ducts to concentrate urine at a later stage

Question 23

What does descending limb of loop of Henle do?

Answer 23

Water exits tubule via osmosis so filtrate gets more concentrated

Question 24

What does ascending limb of loop of Henle do?

Answer 24

Actively pumps Na+ out (urine becomes more diluted, water)

Question 25

What does the collecting duct receive?

Answer 25

Tubular fluid from several nephrons

Question 26

What is the main function of the collecting duct?

Answer 26

Concentrate urine and conserve water

Made possible by the osmolarity gradient generated by loop of Henle (as it gets saltier deep in the medulla, the filtrate loses more water as it flows down the collecting duct)

Question 27

What control is the collecting duct under?

Answer 27

Hormonal control so it can adjust amount of water reabsorbed