Formation of Urine Flashcards
Where are 80% of the glomeruli found?
In cortex
What does sensory mechanism in the macula densa and juxtaglomerular apparatus do?
Senses changes in blood in sodium and chloride conc
Stimulates release of renin
How does blood enter the kidneys? What does this divide into?
Via the renal artery, divides to smaller arteries and finally arterioles
What are the arterioles in contact with?
Functional units of the kidneys –> nephrons
What happens in the nephrons?
Where blood filtration and urine formation takes place
Where is filtered blood then collected into?
Series of large veins –> leaves via renal vein
Where is urine collected?
In collecting ducts, leaves via ureter
Where does glomerular filtration take place?
Bowman’s capsule
How does blood enter the Bowman’s capsule? What then happens to this blood?
Via afferent arteriole
Passes through ball of capillaries called the glomerulus
Leads via efferent arteriole
What is the size of the afferent arteriole compared to the efferent?
Afferent much wider –> blood hydrostatic pressure in these capillaries is higher than normal
What is effect of high hydrostatic pressure in glomerulus?
Drives water and solutes (glucose, amino acids, urea, creatinine) from blood through filtration membrane
This forms glomerular filtrate
Where does filtrate then pass after exiting the glomerulus?
It flows into a duct in the nephron called the renal tubule
The first part of this tubule is the proximal convoluted tubule
What occurs in the proximal convoluted tubule?
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)
Why is Na+ reabsorption important?
Creates osmotic pressure that drives water and electrical gradient that drives Cl-
How is Na+ levels in the epithelial cells kept low? What is result of this low level?
Due to Na+/K+ pump
This creates conc gradient that allows Na+ diffusion from tubular fluid into cell
How is Na+ absorbed?
By symporter proteins that also bind glucose etc
What is a symporter?
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
How else does reabsorption occur (other than symporters)?
Via paracellular route through tight junction between epithelial cells
What is also occurring at the same time as reabsorption?
Tubular secretion
What is tubular secretion?
Active secretion of additional waste (drugs, H+ etc) from blood to join tubular fluid
Where do processes of reabsorption and secretion continue?
Loop of Henle, distal convoluted tubule
What is main function of loop of Henle?
Create and maintain an osmotic gradient in the medulla that enables collecting ducts to concentrate urine at a later stage
What does descending limb of loop of Henle do?
Water exits tubule via osmosis so filtrate gets more concentrated
What does ascending limb of loop of Henle do?
Actively pumps Na+ out (urine becomes more diluted, water)
What does the collecting duct receive?
Tubular fluid from several nephrons
What is the main function of the collecting duct?
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)
What control is the collecting duct under?
Hormonal control so it can adjust amount of water reabsorbed
