The Glomerulus

Question 1

7 functions of the kidney

Answer 1

Remove waste
Remove excess fluid
Remove drugs
RBC production
Maintenance of healthy bones
Control bp
Balance salt, water and pH

Question 2

Renal blood flow

Answer 2

1 L/min

Question 3

Blood supply to kidneys

Answer 3

Abdominal aorta
Renal artery
Segmental artery
Interlobar artery
Arcuate artery
Afferent arteriole
Glomerular capillary

Question 4

Blood drainage of kidneys

Answer 4

Efferent arteriole
Peritubular capillaries
Vasa recta
Interlobular veins
Arcuate veins
Interlobar veins
Renal vein
Inferior Vena Cava

Question 5

Juxtaglomerular apparatus

Answer 5

Located in hillum
Consists of juxtaglomerular cells + macula densa cells
Modified muscular layer of afferent arteriole
More smooth muscle cells, thicker (more granules containing renin)
React to changes in BP

Question 6

The intrinsic autoregulation of juxtaglomerular apparatus

Answer 6

Not dependent on the brain.

Maintains constant GFR and excretion of water and waste products by…

1) Tubuloglomerular feedback
2) Myogenic mechanism

Question 7

Tubuloglomerular response to maintain GFR if bp increased

Answer 7

There is increased glomerular blood flow and increased capillary pressure.
Increased glomerular filtration rate (GFR)

Increased delivery of NaCl to macula densa cells
This sends signals for afferent arteriolar constriction

This constriction decreases glomerular blood flow and capillary pressure.

Question 8

Decreased bp to kidney causes what hormone to be released?

Answer 8

Renin

Question 9

What does renin cause?

Answer 9

Angiotensinogen (made in liver) to be converted to Angiotensin 1

Question 10

What converts Angiotensin 1 to angiotensin 2 and where is it made?

Answer 10

ACE, surface of pulmonary and renal endothelium

Question 11

What does Angiotensin II cause?

Answer 11

Increased sympathetic activity

Arteriolar vasoconstriction
*Increased bp (why is this helpful?!)

ADH secretion (posterior pituitary)

Aldosterone secretion from adrenal gland in the cortex of kidney

Increased reabsorption of sodium and chloride
Increased excretion of potassium
Water retention
(Means increased volume so perfusion of juxtaglomerular apparatus increases which prevents renin being secreted preventing more angiotensin II to be activated)

Question 12

Myogenic response to maintain GFR if increased bp

Answer 12

Increased bp means more stretch in blood vessel wall

Stretch-activated cation (+ve) channels open

Membrane depolarised

Voltage-gated calcium channels open

Increased calcium within the cell

Smooth muscle contraction

Increased vascular resistance

Minimises changes in GFR (increased bp would increase GFR but increased resistance counteracts this)

Question 13

The filtration barrier and its 3 layers

Answer 13

Filtrate moves from blood into Bowman space.

Fenestrated capillary endothelium
Glomerular basement membrane
Podocytes (visceral epithelium)

Question 14

What are the spaces called between podocytes where filtrate moves through

Answer 14

Slit diaphragm

Question 15

Factors determining filtration rate

Answer 15

Pressure
Size of molecule
Charge
Rate of blood flow
Protein binding

Question 16

What is nephrotic syndrome?

Answer 16

Damage to the filtration barrier so proteins can leak across.

This can be due to immune conditions, genetic abnormalities of proteins involved in the slit diaphragms of podocytes, diabetes.

Question 17

What is microalbuminuria an early sign of?

Answer 17

Diabetes

Causes damage to filtration barrier.
Small molecules of albumin can cross the filtration barrier and are present within the urine.

Question 18

GFR = KF (PGC - PBS) - (Pi GC)

Or in words, Glomerular filtration rate =

Answer 18

Filtration volume per unit time (mins)

KF is the filtration coefficient.

Units = ml/min/ m2

Question 19

GFR determined by

Answer 19

Net filtration pressure

Permeability of the filtration barrier

Surface area available for filtration (approx. 1.2-1.5 m2 total)

Question 20

What regulates the GFR

Answer 20

Sympathetic nervous system and Hormones / autocoids

Question 21

Sympathetic regulation of GFR

Answer 21

Afferent arterioles receive strong sympathetic stimulus

Abdominal arteries constrict

Decreased Renal blood flow

Decreased GFR

(Important in bleeding, shock, ischaemia and illness)

Question 22

Afferent and efferent arteriole actions to help increase GFR

Answer 22

Want more blood to be flowing slower near glomerulus so…

The afferent arteriole dilates and the efferent arteriole constricts

Question 23

Afferent and efferent arteriole actions to help decrease GFR

Answer 23

Want less blood to be flowing (and faster) near the glomerulus so…

Afferent arteriole would constrict and efferent would dilate.

Question 24

How do NSAIDs decrease the GFR?

Answer 24

Cause afferent arteriole to constrict

Question 25

How doe ACE inhibitors decrease the GFR?

Answer 25

Cause efferent arteriole to dilate

Question 26

Measuring GFR

Answer 26

Not measured directly.

Used by measuring how much of a marker is excreted.

compare the Urine concentration of marker and the plasma concentration of marker and the urine flow rate.

Creatinine often used as a marker.

Question 27

Properties of a good marker for measuring GFR

Answer 27

Freely filtered
Not secreted or absorbed
Not metabolised

Creatinine often used but not the best marker as it is secreted by cells (tubular secretion).

Question 28

Factors changing levels of creatinine

Answer 28

Age, gender, ethnicity, height, weight, renal tubular handling, dietary protein intake, medications, creatinine supplements.

Question 29

Gold standard marker for measuring GFR

Answer 29

Inulin

It is freely filtered
It is not secreted or absorbed
It is not metabolised.

Not very easy to use or administer. Clinically, Cystatin C used more regularly.