Renal System

Question 1

what does the urinary system consist (in order)

Answer 1

2 Kidneys - directly connected into the abdominal aorta via the renal artery= good blood supply.

2 Ureters - kidneys drain down the urine through the ureters to the bladder.

Bladder- stores urine

Urethra-once urine is ready to be released it goes out through the urethra.

Question 2

Be able to identify the components of the renal system + label the kidneys.

Answer 2

Lighter areas = renal cortex
Darker areas = renal medulla

Question 3

what is the function of Kidneys?

Answer 3

Filter the blood (good
blood supply)- the kidneys create urine .

Urine drains from the
nephrons into collecting
ducts

Collecting ducts merge
into the renal pelvis which
then goes on to the
ureter to be stored in the bladder.

Question 4

where is the renal medulla?

Answer 4

In the centre of the kidney

Question 5

what are the renal corpuscles found in the kidney.

what part of the kidney acts as a barrier to protect the kidney from infections?

Answer 5

Renal Cortex

Renal capsule

Question 6

what is the the Nephron.

How much Nephrons per kidney?

what is the affect of low nephron count?

Answer 6

it is the functional unit of the kidney- filters out the bad stuff in the blood that need to be excreted AND retain things like nutrients and ions.

approx. 1 milllion

its associated with CKD (chronic kidney disease) and hypertension (high blood pressure).

Question 7

Label the Nephron

Question 8

Overview of Nephron functions

Answer 8

Proximal= near
Distal= away

The starting point.

The “sieve”:
- Bowman’s Capsule (tubular- sieves out the proteins, hormones, red blood cells, etc from the blood flow into the nephron)
- Glomerulus (vascular-network of capillaries which is part of the vascular system.)

2nd point
Proximal Convoluted tubule- main site of reabsorption e.g. glucose and amino acids

3rd Point
Loop of Henle- sets up a concentration gradient (osmolarity difference in the kidneys)- more concentration of ions in the middle compared to the outer edge top.
- Descending limb
- Ascending limb

4th point
Distal Convoluted tubule + Collecting duct= Reabsorption of water and adjusting concentration of the urine before it is excreted.
- the distal convoluted tubule drains into the collecting duct.

Question 9

The Glomerulus
What is it?
Where?
Afferent arteriole?
Efferent arteriole?
why is one arteriole bigger than the other?

Answer 9

Bundle of flattened out capillaries.

sits in Bowmans Capsule

Afferent
- carries blood to the glomerulus
- Larger diameter = maintains high blood pressure in glomerulus= facilitating efficient filtration.

Efferent
- carries blood away from the glomerulus after filtration
- smaller diameter = maintain the pressure gradient necessary for filtration.

To create a pressure difference= raises the blood pressure within the glomerulus= This positive pressure helps force out the filtrate (plasma) from the blood into the Bowman’s Capsule.

Question 10

Glomerular Filtration- How does it work?

Answer 10

The plasma enters through 3 layers to enter the tubule:

1- Capillary wall
A single layer of flattened epithelial cells with lots of pores/gaps to make it more permeable than normal capillaries.

2- Basement membrane
- is acellular (not made up of cells), gelatinous layer of collagen and glycoproteins.
-provides structural integrity - Negatively charged so it repels most of the smaller plasma proteins such as albumin (also negatively charged) to stop from passing through.

3- Inner layer of Bowman’s Capsule- made up of specialised cells call PODOCYTES. The cells have processes (primary foot and secondary foot) that interdigiate and form filtration sites.

Question 11

The proximal Convoluted Tubule (PCT).

Site of Tubular Reabsorption for what?

is it selective?

Answer 11

• Nutrients (glucose, ions, amino acids etc.)
  – Electrolytes (Na+, K+, CI-, etc.)

yes, it has highly selective ion channels and pores.

Question 12

what type of transport happens in the PCT.

Answer 12

Transepithelial Transport

Question 13

what does the Transepithelial transport in PCT involve and why?

Answer 13

movement of substances across the Luminal (inside the tubule) epithelial cells which are connected with tight junctions which prevent substances from passing between them. Therefore, anything that needs to be absorbed or transported must cross several barriers:

1. Luminal membrane- the membrane facing the filtrate.
2. Cytosol- the fluid inside the epithelial cell.
3. Basolateral membrane= the membrane facing the interstitial fluid.
4. Interstitial fluid (or extracellular fluid - ECF)= the fluid surrounding the cells.
5. Capillary epithelial cells- the cells lining the blood capillaries.

Question 14

Is Transepithelial Transport active or passive?

Answer 14

BOTH

Active transport - against a concentration gradient

– E.g. Na+ transport into the ECF via Na+/K+ pump

The concentration gradient can set up by active transport can be used to transport other things with passive transport.

Passive transport - with a concentration gradient

– E.g. Na+ transport into the luminal cells due to concentration gradient set up by Na+/K+ pump

– Symport channel with glucose (SGLT) and amino acids (SSS)

Question 15

The podocytes are cells associated with which structure?

Glomerulus
Bowman’s Capsule
Proximal Convoluted Tubule

Answer 15

Bowmans’s Capsule- Although they are involved in the Glomerulus filtration, they are specialised cells located in the inner layer of the Bowman’s Capsule.

Question 16

Loop of Henle.

what are the two different nephrons which function in the loop of Henle.
Location
loop of Henle
function

Answer 16

Cortical nephron ( make up 80% of the kidney)
Location= Glomeruli is on the outer layer of renal cortex.
Loop of Henle= short and extends a short distance into the outer medulla.
Capillaries= have capillaries wrapped around the loop to help with their function of reabsorbing nutrients and electrolytes.

Juxtamedullary nephron (20% of the kidney)
Location: glomeruli is located in the inner layer of the renal cortex.
Loop of Henle= long and extends deep into the inner medulla.
capillaries: have capillaries form the vasa recta

Question 17

what is the function of the juxtamedullary nephron?

Answer 17

set up a vertical osmotic gradient in the interstitial fluid (the concentration of solutes (ions,salt) is lower in the cortex (outer edge)and higher in the medulla (centre) of the kidney.

This gradient allows controlled water reabsorption in the PCT and the collecting duct.

This is called the counter current multiplication system - use of energy to make a concentration gradient.

Question 18

where is the Ascending Limb and descending limb on the Nephron?

Answer 18

Descending Limb
- starts from the PCT and extends into the medulla.

Ascending Limb
- Rises back up from the medulla towards the DCT.

Question 19

how does the structure of the loop of Henle facilitate the Counter current Multiplication system?

Answer 19

By having different ion channels in the Descending Limb compared to the Ascending Limb= fluid can move in opposite directions= different concentration gradients.

Descending Limb:
has lots if AQP-1 water channels making it permeable to water= water leaves via osmosis , down its concentration gradient= so as you move down the PCT, the filtrate becomes more concentrated.

Because the Descending limb has no Na+/K+ ATPase, ONLY water leaves!

Ascending limb:
- Lots of Na+/K+ ATPase in the Basolateral membrane to help set up the concentration gradient (Na+ out of the filtrate and into the interstitial fluid)
- NKCC2 channels in the luminal membrane transports 1x Na+ 1xCl- and 2x K+ out of the filtrate in the tubule into the interstitial fluid.

NO AQP-1 channels so it is COMPLETELY Impermeable to water so water has to stay in the tubule while NaCI moves out, making urine more dilute.

Therefore as the filtrate travels up towards the DCT, the concentration leaves more dilute than it came in.

Question 20

what is the Vasa Recta and what is its function?

Answer 20

The vasa recta are straight blood vessels that run parallel to the loop of Henle. They help maintain the osmotic gradient in the medulla by allowing water and solutes to move in and out of the blood as it descends and ascends.

Question 21

How does the Vasa Recta help maintain Osmotic gradient?

Answer 21

Descending Limb: As blood flows down the descending limb of the vasa recta, it becomes progressively more concentrated (or “salty”) because water leaves the blood and enters the interstitial fluid, following the osmotic gradient.

Ascending Limb: As blood flows up the ascending limb of the vasa recta, it becomes less concentrated because salt leaves the blood and enters the interstitial fluid, following the concentration gradient.

Question 22

Does Urine get more or less Concentrated in the Loop of Henle?

what is the Osmotic gradient set up by?

how is osmotic gradient maintained?

Answer 22

Urine leaves MORE DILUTE than when it entered.

countercurrent multiplication in the loop of Henle.

By the countercurrent exchange in the Vasa Recta

Question 23

once the water is reabsorbed from the filtrate, what happens to the remaining (20%) of fluid ?

Answer 23

it is controlled by Vasopressin or Antidiuretic Hormone (ADH) released from the posteriorly pituitary. .

Question 24

Mechanism of Action of Vasopressin/ADH.

Answer 24

1- Osmoreceptors in hypothalamus detect increase in osmolarity of blood (dehydration)

2- ADH released from posterior pituitary

3- ADH acts on V2 receptors on DCT and CD

4- AQP-2 channels inserted into luminal membrane

5- Water diffuses into cell via AQP-2 and out into blood via AQP-3 or AQP-4 .

6- Urine is concentrated and osmolarity decreased

Question 25

what does the insertion of AQP-2 related to

Answer 25

to the amount of ADH

Question 26

How is water Reabsorption Regulated/

Answer 26

Initial Osmolarity:
The dilute filtrate enters the PCT with low osmolarity (around 100 mOsm/L).

Excess Water (Low Osmolarity):
No (ADH) so the collecting ducts remain impermeable to water= dilute urine.

Dehydration (High Osmolarity):
ADH Released so the collecting ducts are more permeable to water= more water reabsorbed back into the bloodstream= concentrated urine.