Renal Physiology Flashcards
What percentage of cardiac output does each kidney receive?
20%
What is the total renal blood flow of both kidneys (L per min)
1L/min
9 divisions of renal artery
- Renal artery
- Segmental artery
- Interlobar artery
- Arcuate artery
- Interlobular artery
- Afferent arteriole
- Glomerular capillary (nephron)
- Efferent arteriole
- Peritubular capillary (nephron)
How many capillary beds does each nephron have and where are they?
One at the glomerulus and one at the peritubular area
Within each nephron what connects the two sets of capillaries?
efferent arteriole
Within each nephron what connects the two sets of capillaries?
efferent arteriole
Which comes before the other - afferent or efferent arteriole?
afferent (a before e)
What kind of cells is the entire capillary covered by?
podocytes
What is the name for the entire unit of the glomerular tuft and bowman capsule?
renal corpuscle
What is filtrate free of?
cells, larger polypeptides and proteins
Each renal corpuscle contains a compact tuft of interconnected capillary loops called the …
glomerulus
What is the blood supply to the glomerulus from?
afferent arteriole
As blood flows through the glomerulus, how much of the plasma is filtered into Bowman’s capsule? Where does the remaining blood leave the glomerulus by?
- 20%
- The remaining blood then leaves the glomerulus by the efferent arteriole
What is Bowman’s capsule covered by? (histology)
parietal epithelium
What is ‘Bowman’s space’?
The part of Bowman’s capsule that comes in contact with the glomerulus becomes pushed inward slightly but does not make contact with the opposite side of the capsule because a fluid-filled space called Bowman’s space exists within the capsule. The filtrate from the glomerulus collects in Bowman’s space before flowing into the proximal convoluted tubule.
Blood in the glomerulus is separated from the fluid in Bowman’s space by a filtration barrier consisting of 3 layers:
- Single-celled capillary epithelium
- Basement membrane (basal lamina)
- Single celled epithelial lining of Bowman’s capsule
What epithelial cells are in the filtration barrier?
podocytes
How are podocytes different from the rest of the cells lining the rest of Bowman’s capsule?
They have an octopus-like structure in that they possess a large number of foot processes which act as glomerular filtration barrier
Fluid filtration (which layers does it pass through) (3)
- Across endothelial cells
- Across basement membrane
- Between the foot processes of the podocytes
Efferent arterioles carry blood away from the glomerulus and then supply the X capillaries which supply A and B.
Efferent arterioles carry blood away from the glomerulus and then supply the peritubular capillaries which supply the proximal and distal convoluted tubules
Efferent arterioles also supply the — — which supply blood to the …
- vasa recti
- loop of Henle
Both peritubular and vasa recti supply:
- water and solutes to be secreted into the filtrate
- blood to carry away water and solutes reabsorbed by the kidneys
Which of the convoluted tubules is longest and most coiled?
proximal
What is the histology of the brush border of the proximal convoluted tubule?
simple cuboidal
What is the portion of the tubule after the PCT?
loop of Henle
What is the histology of the distal convoluted tubule?
cuboidal epithelium with minimal microvilli
Where does fluid flow to from the distal convoluted tubule?
collecting duct system
What is the collecting duct system comprised of?
cortical collecting duct
medullary collecting duct
From Bowman’s capsule to the collecting-duct system, each nephron is completely separate from the others. This separation ends when …
multiple cortical collecting ducts MERGE
What is the result of additional merging after multiple cortical collecting ducts merge ?
urine drains into the kidney’s central cavity - the RENAL PELVIS - via several hundred large medullary collecting ducts
What is the renal pelvis continuous with?
the ureter draining that kidney
Outer and inner portion of kidney
Outer portion = renal cortex
Inner portion = renal medulla
What does the renal cortex contain?
all the renal corpuscles
What extends from the cortex for varying distances down into the medulla?
the loop of Henle
Types of nephron (+%)
Juxtamedullary - 15%
Cortical - 85%
What is the juxtamedullary part of the nephron?
The renal corpuscle lies in the part of the cortex closes to the cortical-medullary junction
What is the part of the loop of Henle in the juxtamedullary part of the nephron responsible for?
The loop of Henle of these nephrons plunge deep into the medulla and are responsible for generating an osmotic gradient in the medulla that is responsible for the REABSORPTION OF WATER
Which vasculature is in close proximity to the juxtamedullary nephrons?
- vasa recti
- They also loop deeply into the medulla and then return to the cortico-medullary junction
What is the cortical part of the nephron?
Their renal corpuscles lie in the outer cortex and their loop of Henle do not penetrate deep into the medulla
What do some cortical nephrons not contain? What are they involved and not involved in?
- Some cortical nephrons do not have a loop of Henle at all
- They are involved in reabsorption and secretion but do not contribute to the hypertonic medullary interstitium
Near its end, the ascending limb of each loop of Henle passes between X and Y of its own nephron.
afferent and efferent arterioles
There is a path of cells in the wall of the ascending limb of the LOH as it becomes the distal convoluted tubule called the — — and the walls of the afferent arteriole contain — cells known as — cells.
- Macula densa
- Granular cells known as juxtaglomerular cells
The combination of macula densa and juxtaglomerular cells is known as the…?
juxtaglomerular apparatus
What do granular cells in the juxtaglomerular cells secrete into the blood?
renin enzyme
What do the macula densa cells detect? What is their response?
how much NaCl is passing through the distal convoluted tubule and sends signals to the granular cells to produce renin
Flow of glomerular filtrate (order of 12 sites)
- Glomerular capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct
- Papillary duct
- Minor calyx
- Major calyx
- Renal pelvis
- Ureter
- Urinary bladder
- Urethra
What are the similarities and differences between glomerular filtrate and blood plasma?
Glomerular filtrate is cell-free and has no large proteins, but other than that contains virtually all substances in virtually the same concentrations as in plasma.
What is the only exception to the rule that all non-protein plasma substances have the same concentrations in the glomerular filtrate as in the plasma?
Certain low-molecular-weight substances that would otherwise be filterable are BOUND to plasma proteins and are thus not filtered e.g. half the plasma calcium and virtually all of the plasma fatty acids are bound to plasma protein and thus are not filtered.
What can freely pass through the filtration barrier? Give 4 examples
- small molecules and ions up to 10kDa can pass freely
- glucose, uric acid, potassium, creatinine
What can’t pass through the glomerular basement membrane and why?
Fixed negative charge in the glomerular basement membrane repels negatively charged anions such as albumin
Albumin and its clinical relevance
Albumin has a molecular weight of 66kDa (>10kDa) and is negatively charged. This means it CANNOT pass through into the tubule.
Small amounts of albumin in urine is the first sign of diabetic nephropathy (damage to filtration barrier due to diabetes)
Damage to the filtration barrier can lead to protein leak and a condition known as…
nephrotic syndrome
Causes of nephrotic syndrome
- immune conditions
- genetic abnormalities
- proteins involved in podocytes/slit diaphragm
What else can damage the filtration barrier?
- Diabetes
- Early sign of diabetic nephropathy = microalbuminuria (low levels of albumin in the urine)
What determines GFR?
- pressure gradients
- size of molecule
- charge of molecule
- rate of blood flow
- surface area; GFR is directly proportional to membrane permeability and surface area
- binding to plasma proteins e.g. Ca2+, hormones, fatty acids
Measuring GFR: what is the equation?
GFR = (Urine(M) x urine flow rate)/Plasma(m)
Normal GFR
125ml/min
How many litres filtered in 24 hours?
180L
How much is reabsorbed?
99%
Total plasma volume?
3L
How many times is plasma volume filtered in a day?
~60 times
Measuring GFR: when does it fall?
disease causing loss of nephrons
What does GFR not detect?
problems in tubule function e.g. nephrotic syndrome
What is the only protein normally found in urine?
Tamm-Horsfall protein (uromodulin) which is produced by the thick ascending limb
2 mechanisms of auto-regulation
Myogenic
Tubuloglomerular feedback
What is myogenic autoregulation?
Pressure within the afferent arteriole rises, causing stretching of the smooth muscle wall which triggers the contraction of smooth muscle → arteriolar constriction
PASSIVE mechanism
Where does myogenic autoregulation occur?
capillary walls