Bowman's capsule - surrounds glomerulus, inner layer of podocytes
Proximal convoluted tube (PCT) - loops surrounded by capillaries, walls made of epithelial cells with microvilli
Loop of Henle - hairpin loop
Distal convoluted tube (DCT) - fewer capillaries than PCT
Collecting duct - DCT from several nephrons empty into collecting duct
Describe the blood vessels associated with a nephron?
Afferent arteriole is wide in diameter
Efferent arteriole is narrow diameter
Glomerulus capillaries
Explain how glomerular filtrate is formed?
Ultrafiltration in Bowman's capsule
Highhydrostaticpressure in glomerulus forces small molecules (urea, water, glucose, mineral ions) out of capillary pores/fenestrations against osmotic gradient
Basement membrane acts as filter, plasma proteins remain is capillary as they are too large to leave
State what happens during selective reabsorption and where it occurs?
Useful molecules (e.g., glucose) are reabsorbed into the blood.
Occurs in PCT
Outline the transport processes involved in selective reabsorption?
Glucose from glomerular filtrate moves to cells lining PCT by co-transport with Na+ ions
From PCT to intercellular spaces by active transport
From intercellular spaces to capillaries by diffusion
How are cells in the PCT adapted for selective reabsorption?
Microvilli - large surface area
Many mitochondria - produce ATP for active transport of glucose
Many carrier proteins - foractive transport of glucose
What happens in the loop of Henle?
Active transport of Na+ & Cl- out of ascending limb
Water potential of tissue fluid decreases
Osmosis of water out of descending (ascending limb is impermeable to water)
Water potential of filtrate decreases going down descending limb
Explain the role of the DCT?
Reabsorption:
of water via osmosis
of ions via active transport
Explain the role of the collecting duct?
Reabsorption of water from filtrate into tissue fluid via osmosis through aquaporins
Explain why it is important to maintain an Na+ gradient?
Countercurrent multiplier - filtrate in collecting ducts is always beside an area of tissue fluid that has a lower water potential.
Maintains water potential for maximum reabsorption of water
Explain the role of the hypothalamus in osmoregulation?
Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
This triggers hypothalamus to produce more ADH
Explain the role of the posterior pituitary gland?
Stores and secretes the ADH produces by the hypothalamus
Explain the role of ADH in osmoregulation?
Stimulates addition of channel proteins (aquaporins) into membrane
Make cells/membranes more permeable to water
More water reabsorbed by osmosis
Name the two parts of a nephron where osmoreceptors are found?