Lecture 4 the nephron and its actions

Question 1

What does the glomerulus do?

Answer 1

Produces filtrate by creating a sieve which the blood pressure pushes against.

Question 2

What type of capillary is the glomerulus?

Answer 2

It is called a fenestrated capillary

Question 3

What stay in blood?

Answer 3

albumin, platelets and proteins and anything large

Question 4

What goes into primary filtrate?

Answer 4

Small molecules, salts and electrolytes

Question 5

What does the nephron do?

Answer 5

Converts decellulised blood into urine and retains protein, amino acids sugars and the majority of salts

Question 6

What gets reabsorbed at the proximal convoluted tubule?

Answer 6

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.

Question 7

Why are salts removed at the renal medulla?

Answer 7

Increase salt content outside of the loop of henle to allow for easier reabsorbtion by osmosis.

Question 8

How is the concentration of salt maintained outside of the loop of henle?

Answer 8

Through active transport

Question 9

Where can we find a large number of mitchondria on the nephron? Why?

Answer 9

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.

Question 10

What are the 2 different types of nephrons?

Answer 10

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)

Question 11

What do the vasa recta do?

Answer 11

Collects everything resorbed from kidneys

Question 12

Does each collecting duct get a single nephron?

Answer 12

No, Each nephron gets several juxtamedullary and cortical nephrons reaching into it

Question 13

What is the juxtamedullary apparatus?

Answer 13

Region where glomerulus and ascending tubule/distal convoluted tubule is located

Question 14

How does juxtaglomerular apparatus respond to high salt concentration?

Answer 14

High salt concentration means we need less blood in the glomerulus

Question 15

What gets secreted into nephron?

Answer 15

Potassium

Urea

Metabolites and drugs

Question 16

How much blood do we filter per day?

Answer 16

180L per day

Question 17

What happens in the collecting duct?

Answer 17

fine tunes reabsorption

Question 18

What are the 2 functions of renal blood flow?

Answer 18

Provides blood to be filtered

Reclaims reabsorbed blood

Question 19

What kind of pressure is maintained at the glomerulus?

Answer 19

High pressure (approx 55mmHg)

Question 20

What kind of pressure is maintained at peritubular capillaries?

Answer 20

Very low pressure (approx 13 mmHg)

Question 21

What is Starling’s Law? (in layman’s terms)

Answer 21

When squeezing a capillary blood will flow out of it. When squeeze is released things flow back into it

Question 22

What happens when blood moves through glomerulus?

Answer 22

Concentration of proteins increases due to drop in volume of smaller molecules which increases Protein osmotic gradient is very high.

Question 23

How is pressure maintained in glomerulus?

Answer 23

Afferent and efferent arteriole diameter

Question 24

What does GFR amount depend on?

Answer 24

Permeability of membrane

Filtration pressure

Surface area

Question 25

What is basement membrane made of?

Answer 25

Sugars and lipopolysaccharides and this carries a bit of charge

Question 26

What is basement membrane made of?

Answer 26

Sugars and lipopolysaccharides and this carries a bit of charge

Question 27

What does the basement membrane prevent passage of as a result of its charge?

Answer 27

anions due to negative charge

Question 28

What determines glomerular permeability?

Answer 28

Molecular weight

Charge

Question 29

What is GFR?

Answer 29

Amount of filtrate formed in all the renal corpuscles of both kidneys in one minute

Question 30

Why must kidneys maintain a relatively constant GFR?

Answer 30

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

Question 31

GFR is related directly to?

Answer 31

net filtration rate

Question 32

How to increase filtration rate?

Answer 32

enlarge afferent arteriole

narrow efferent arteriole

Question 33

How to decrease filtration rate?

Answer 33

Narrow afferent arteriole

Enlarge efferent arteriole

Question 34

How is GFR regulated?

Answer 34

Nervous system

Hormonal system

Renal system (juxtaglomerular apparatus and relex contraction if smooth muscle)

Question 35

What are the types of renal autoregulation?

Answer 35

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

Question 36

Which arteriole uses myogenic autoregulation?

Answer 36

Mainly the afferent arteriole

Question 37

What happens when the afferent arteriole constricts?

Answer 37

1 - Drop in glomerular capillary blood pressure

2 - Drop in net filtration pressure

3 - Drop in GFR

Question 38

Describe the passage of Filtrate through the nephron and the tubuloglomerular feedback:

Answer 38

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.

Question 39

`How does macula densa salt receptor make sense?

Answer 39

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.