PY 105 Chapter Notes - Chapter 12: Distal Convoluted Tubule, Proximal Tubule, Glomerular Basement Membrane
Filtration
ā¢ Blood from the renal artery flows into an afferent arteriole, which branches into a ball of
capillaries known as the glomerulus
ā¢ From there the blood flows into the efferent arteriole
ā¢ Constriction of efferent arteriole results in high pressure in the glomerulus, which causes fluid to
leak out of the glomerular capillaries
ā¢ The fluid passes through a filter known as the glomerular basement membrane and enters
Bowman's capsule
Selective Reabsorption
ā¢ The filtrate in the tubule consists of water and small hydrophilic molecules such as sugars, amino
acids, and urea
ā¢ They are extracted from the tubules, via active transport, and picked up by peritubular capillaries,
which drain into venules that lead to the renal vein
ā¢ A lot of the reabsorption occurs in the part of the tubule nearest to Bowman's capsule, called the
proximal convoluted tubule (PCT)
ā¢ A lot of water reabsorption occurs in this area too
o Selective reabsorption
ā¢ Distal convoluted tubule (DCT) - more regulated reabsorption via hormones
Secretion
ā¢ Movement of substances into the filtrate via active transport thus increasing the rate at which
they are removed from the plasma
ā¢ Most secretion takes place in the DCT and collecting ducts
Concentration and Dilution
ā¢ The distal nephron which includes the DCT and collecting duct
ā¢ Controlled by two hormones: ADH and aldosterone
o ADH: when you are dehydrated, the volume of fluid in the bloodstream is low and the solute
concentration in the blood is high
ā¢ Antidiuretic hormone (ADH or vasopressin) is released by posterior pituitary
ā¢ This prevents diuresis (water loss) by increasing water reabsorption in the distal
nephron
ā¢ This makes the distal nephron permeable to water
ā¢ Water flows out of the filtrate into the tissue of the kidney --> returned to blood
ā¢ A drop in blood pressure can also trigger ADH release
ā¢ After drinking a lot of water, the plasma volume is too high, and a large volume of
dilute urine is necessary
āŖ No ADH is secreted
āŖ The collecting duct is not permeable to water
o Aldosterone: when the blood pressure is low, aldosterone is released by the adrenal cortex
ā¢ It causes increased reabsorption of Na by the distal nephron
ā¢ Increased plasma osmolarity, which leads to increased thirst and water retention,
which raises the blood pressure
ā¢ When blood pressure is high, aldosterone is not released
āŖ Sodium is lost in the urine
o ADH and aldosterone work together to increase blood pressure
ā¢ Aldosterone causes sodium reabsorption, which results in increased plasma
osmolarity
ā¢ ADH is secreted
ā¢ Increased water reabsorption and thus increase plasma volume
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