urinary physiology - filtration Flashcards
What is Filtration
The formation of a protein free plasma at the glomerular capillaries
What is the normal GFR
180L/day
What happens to substances that are wanted by the body compared to those that are not in the kidney
Substances that are wanted are reabsorbed while unwanted substances stay in the tubule to be excreted out
What is the blood flow the kidney recieves
20-25% of the cardiac output - 1200 mls/min
Why are kidneys at risk to vascular disease
The high blood flow that supplies them
What is filtered through to Bowman’s capsule
Only a small amount of plasma and no red blood cells are filtered - the excess passes through the efferent arteriole into the peritubular capillaries and then into the renal vein
What determines the filterability of solutes across the glomerular filtration barrier
Molecular size, electrical charge and shape
What does the fenestration (pores) of the glomerulus do
Allow plasma to be filtered while preventing the filtration of red blood cells
What does the basal lamina of the glomerulus do
Prevent filtration of bigger solutes
What does the slit membrane at the pedicles do
Prevents filtration of medium sized proteins
Why is the glomerular capillary pressure higher than most capillaries in the body
The afferent arteriole is short and wide so does little resistance to the flow of blood and the long and narrow efferent arteriole offers a high post capillary resistance
What cis the sympathetic vasoconstrictive nerve effect on the afferent and efferent arterioles
constriction - the afferent arteriole is more sensitive so will have a greater change in constriction
What do circulating catecholamines do to the arterioles
Cause mainly the afferent arteriole to constrict
What does angiotensin II do to the arterioles of the glomerulus
At low concentrations only constricts the efferent arteriole but at high concentrations of Angiotensin II, causes both the efferent and afferent arteriole to constrict
What happens if the mean arterial pressure increases to the arterioles
The afferent arteriole constricts which prevents the glomerular capillary pressure from rising
