Flashcards in Renal Structure and Function Deck (49)
Where do the renal arteries originate?
They're a branch off the abdominal aorta
What are the ureters?
Tube carrying urine to the bladder from the kidneys
What is the urethra?
The tube carrying urine from the bladder to outside of the body (excretion)
Describe the passage of the renal artery into the kidney
Renal arteries pass into the interlobar vessels and then divide into the small arcuate arteries in the renal cortex; these arteries terminate in a little clump of capillaries called a glomerulus
What is each capillary glomerulus in the kidney surrounded by?
Back of tissue known as the Bowman's capsule
How do efferent arterioles compare to the afferent arterioles at the glomerulus?
The afferent arterioles are wider than the efferent arterioles
What special type of cell covers the glomerulus (capillaries) on the capsular side and what is its function?
Cells called podocytes which have slits in them which form the filtration mechanism
Describe the flow of renal filtrate in the nephron
Glomerulus --> Bowman's capsule, PCT, loop of Henle --> DCT --> collecting duct
Why does only ~20% of the plasma from the blood leave the glomerulus in the afferent arteriole?
Too much filtration (plasma loss) would make the blood too viscous for flow in the efferent arteriole due to excessive haematocrit concentration.
How is GFR regulated and maintained?
By the balance of constriction in the smooth muscle of the afferent and efferent arterioles; this maintains constant GFR despite changes in systemic blood pressure.
How does the constrictor tone differ between the afferent and efferent arterioles and what is the consequence of this?
Constrictor tone in efferent arterioles is higher than in the afferents to produce a filtration pressure in the glomerulus
How can the afferent and efferent arterioles cause a reduction in GFR?
If afferents constrict and efferents relax --> lowered filtration pressure --> slower GFR
How can the afferent and efferent arterioles cause a increase in GFR?
If afferents relax and efferents constrict --> increased filtration pressure --> increased GFR
What controls the balance of constriction in the afferent and efferent arteriolar smooth muscle?
Juxtaglomerular apparatus, a structure where the distal tube folds back and contacts the glomerulus at the point where the afferent and efferent arterioles enter.
What are macula densa cells?
Part of the juxtaglomerular apparatus; they line the DCT where the tubule contacts the entry of the afferent and efferent arterioles. These cells sense sodium concentrations in the DCT fluid
How and why does renal flow affect sodium reabsorption?
In the PCT sodium is removed at a relatively constant rate, so if the flow of fluid through the PCT is low, more sodium is reabsorbed to cause more water to enter the blood. If the flow is high through the PCT than the sodium concentration increases to draw water into the urine, as the individual has sufficient water in their blood.
How do the macula densa cells respond if the sodium concentration is too low in the PCT?
This signals that GFR is too low (potentially due to low filtration pressure, meaning that more sodium can be reabsorbed), causing chemical factors to be released from the macula densa which cause constriction of the efferent arteriole to increase GFR to normal (by increasing filtration pressure). In addition, renin is also released from the juxtaglomerular cells simultaneously which diffuses into the blood.
Outline the RAAS system
Renin released into the blood travels to liver veins where it cleaves the protein angiotensin to release angiotensin I which then travels to the lungs where it is converted to angiotensin II by ACE (angiotensin converting enzyme). Angiotensin II then acts on the adrenal cortex to release aldosterone which increases sodium retention in the DCT.
Explain how the RAAS system is regulated by negative feedback
Works to maintain steady sodium levels in the blood; If blood sodium is too low, it’s sensed by a low sodium in the DCT which causes the juxtaglomerular cells to release renin which causes a pathway which increases sodium retention in the kidney.
What is meant by 'renal clearance'
The effective volume of plasma completely ‘cleared’ of a substance per minute
What range of values can renal clearance take?
Zero (no plasma completely cleared of substance in a minute) up to the renal plasma flow (all substances in the plasma cleared into the urine)
How may renal flow and GFR be affected by kidney damage?
Generally GFR with decrease but renal flow may remain normal
How do you calculate clearance?
(urine concentration x urine flow) / plasma concentration
Outline how you could measure renal clearance
Measure the concentration of the substance in the plasma, then collect urine for a fixed period to get the urine flow (ml/min) and then measure the concentration of the substance in the urine
What is GFR?
Glomerular filtration rate, auto-regulated in a healthy individual
What is the physical pressure ordinarily in the glomerular capillaries?
What is the net filtration pressure ordinarily in the glomerular capillaries?
Name two methods that can be used to measure GFR
Creatinine clearance and use of inulin (gold standard)
What is inulin?
A polysaccharide that is completely filtered from the plasma and not reabsorbed