Lecture 4 the nephron and its actions Flashcards
What does the glomerulus do?
Produces filtrate by creating a sieve which the blood pressure pushes against.
What type of capillary is the glomerulus?
It is called a fenestrated capillary
What stay in blood?
albumin, platelets and proteins and anything large
What goes into primary filtrate?
Small molecules, salts and electrolytes
What does the nephron do?
Converts decellulised blood into urine and retains protein, amino acids sugars and the majority of salts
What gets reabsorbed at the proximal convoluted tubule?
Most nutrients (protein, amino acids, glucose etc) is absorbed and returned into blood. Salt and water are not reabsorbed much at the proximal tubule
Sodium pumps are present but nothing for water reabsorbtion here.
Why are salts removed at the renal medulla?
Increase salt content outside of the loop of henle to allow for easier reabsorbtion by osmosis.
How is the concentration of salt maintained outside of the loop of henle?
Through active transport
Where can we find a large number of mitchondria on the nephron? Why?
Proximal convoluted tubule
Thick ascending limb of loop of henle
Distal convoluted tubule
We see a large number of mitochondria to facilitate active transport of salts (Sodium primarily) into the medulla to create a rich osmotic gradient.
What are the 2 different types of nephrons?
Cortical nephrons (filter blood and generally get everything back not very useful and make up 80% of nephrons)
Juxtamedullary nephrons (present near medulla and are very important for urine production. They make up 20% of nephrons)
What do the vasa recta do?
Collects everything resorbed from kidneys
Does each collecting duct get a single nephron?
No, Each nephron gets several juxtamedullary and cortical nephrons reaching into it
What is the juxtamedullary apparatus?
Region where glomerulus and ascending tubule/distal convoluted tubule is located
How does juxtaglomerular apparatus respond to high salt concentration?
High salt concentration means we need less blood in the glomerulus
What gets secreted into nephron?
Potassium
Urea
Metabolites and drugs
How much blood do we filter per day?
180L per day
What happens in the collecting duct?
fine tunes reabsorption
What are the 2 functions of renal blood flow?
Provides blood to be filtered
Reclaims reabsorbed blood
What kind of pressure is maintained at the glomerulus?
High pressure (approx 55mmHg)
What kind of pressure is maintained at peritubular capillaries?
Very low pressure (approx 13 mmHg)
What is Starling’s Law? (in layman’s terms)
When squeezing a capillary blood will flow out of it. When squeeze is released things flow back into it
What happens when blood moves through glomerulus?
Concentration of proteins increases due to drop in volume of smaller molecules which increases Protein osmotic gradient is very high.
How is pressure maintained in glomerulus?
Afferent and efferent arteriole diameter
What does GFR amount depend on?
Permeability of membrane
Filtration pressure
Surface area
What is basement membrane made of?
Sugars and lipopolysaccharides and this carries a bit of charge
What is basement membrane made of?
Sugars and lipopolysaccharides and this carries a bit of charge
What does the basement membrane prevent passage of as a result of its charge?
anions due to negative charge
What determines glomerular permeability?
Molecular weight
Charge
What is GFR?
Amount of filtrate formed in all the renal corpuscles of both kidneys in one minute
Why must kidneys maintain a relatively constant GFR?
Too low we need enough reabsorbtion and enough blood flow. If glomerular filtration was too low hypoxic kidney could result
Too high and we lose too much water
GFR is related directly to?
net filtration rate
How to increase filtration rate?
enlarge afferent arteriole
narrow efferent arteriole
How to decrease filtration rate?
Narrow afferent arteriole
Enlarge efferent arteriole
How is GFR regulated?
Nervous system
Hormonal system
Renal system (juxtaglomerular apparatus and relex contraction if smooth muscle)
What are the types of renal autoregulation?
Myogenic mechanism: this occurs when stretching triggers contraction of smooth muscle cells in afferent arterioles which reduces GFR. (most regulation is here this is a local effect intrinsic to the kidneys)
Tubuloglomerular mechanism
Which arteriole uses myogenic autoregulation?
Mainly the afferent arteriole
What happens when the afferent arteriole constricts?
1 - Drop in glomerular capillary blood pressure
2 - Drop in net filtration pressure
3 - Drop in GFR
Describe the passage of Filtrate through the nephron and the tubuloglomerular feedback:
GFR enters the proximal tubule where salt is reabsorbed, water is reabsorbed at the loop of henle creating a salty fluid at the distal convoluted tubule.
The distal convoluted tubule has salt sensors and these sensors detect an increase in GFR and cause glomerulus to decrease amount of filtrate. Salt is then pulled out in a time-dependent manner which is what the salt sensors are based on in macula densa cells.
Macula densa cells detect salt levels through NaCl2k. If tubular fluid is too salty everything is going too fast meaning blood pressure is too high and we want to constrict. If fluid is not salty then fluid is moving too slowly which means the afferent arteriole should be dilated.
`How does macula densa salt receptor make sense?
High salt concentration means not enough time for fluid to pass through nephron and have its salt absorbed. This means net hydrostatic pressure at glomerulus is too high. This leads to constriction of afferent arteriole.
Low salt concentration indicates lots of time available for salts to be reabsorbed meaning not enough GFR is being produced meaning blood pressure is so low. This leads to dilation of afferent arteriole.
