1. The nephron and kidney function
HBS3

2. The nephron

3. The nephron - structure
The base unit of the kidneys is the nephron. The main parts of the nephron are
Glomerular capsule
Proximal convoluted tubule
Distal convoluted tubule
Loop of Henle
Collecting tubule (or duct)
The blood vessels associated with the nephron are the
Renal artery and vein
Afferent arteriole
Efferent arteriole
Glomerulus
Capillary network

4. 1: efferent arteriole
2: glomerulus
3: glomerular capsule
4: afferent arteriole
5: branch of renal artery
6: capillary
7: branch of renal vein
8: ascending limb of loop of Henle
9: loop of Henle
10: collecting duct
11: descending limb of loop of Henle
12: distal convoluted tubule
13: proximal convoluted tubule

5. The mammalian nephron

6. Nephron function
There are three main processes involved in the formation of urine
Filtration is separation of particles by passing them through small pores (sieving)
It occurs in the renal corpuscle between the glomerulus and the glomerular capsule.
Some substances filtered include anything small & soluble – water, nutrients (eg glucose, amino acids, vitamins), ions, wastes (eg urea), drugs, hormones
The resultant fluid is called filtrate
Reabsorption is the return of substances from the nephron back into the blood
It occurs in the proximal convoluted tubule, loop of Henle & distal convoluted tubule - along the length of the nephron
Some substances reabsorbed include urea, some ions, water glucose, amino acids, vitamins
Water is reabsorbed either by facultative reabsorption, which is an active process under the control of the hormone ADH, in which the amount of reabsorption can be controlled, or obligatory reabsorption, which is a passive process due to osmotic pressure (not controlled).
Secretion is removal of substances from the blood into the nephron
It occurs in the distal convoluted tubule
Some substances secreted include urea, creatinine, some ions, drugs

7. How the nephron works

8. Nephron adaptations
Some of the ways the nephron is related to its function include
Renal capsule:
High pressure differential between glomerulus & capsule due to short renal artery, and afferent arteriole being wider than efferent arteriole
Large surface in the glomerulus due to large number of coils in glomerulus and many nephrons
Extremely permeable (leaky) capillaries
Extremely thin membranes lining capillaries & capsule so very close contact
Rest of nephron
Large exchange area due to length of nephron and number of capillaries
favourable concentration gradients due to active transport of some substances such as glucose and amino acids, and due to the flow of blood in capillaries being in the opposite direction to the flow of filtrate in the nephron (counter current).

9. Urine formation
The amount of urine produced each day is about L. Of this, about 96% is water.
Urine normally contains no glucose and very little protein.
The rest of the urine is mainly made up of ions and nitrogenous wastes (eg urea, uric acid and creatinine).
Nitrogenous wastes are products from the breakdown of proteins or amino acids. The main one is urea, which is made in the liver from amino acids by the process of deamination.