The Glomerulus Flashcards
7 functions of the kidney
Remove waste
Remove excess fluid
Remove drugs
RBC production
Maintenance of healthy bones
Control bp
Balance salt, water and pH
Renal blood flow
1 L/min
Blood supply to kidneys
Abdominal aorta
Renal artery
Segmental artery
Interlobar artery
Arcuate artery
Afferent arteriole
Glomerular capillary
Blood drainage of kidneys
Efferent arteriole
Peritubular capillaries
Vasa recta
Interlobular veins
Arcuate veins
Interlobar veins
Renal vein
Inferior Vena Cava
Juxtaglomerular apparatus
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
The intrinsic autoregulation of juxtaglomerular apparatus
Not dependent on the brain.
Maintains constant GFR and excretion of water and waste products by…
1) Tubuloglomerular feedback
2) Myogenic mechanism
Tubuloglomerular response to maintain GFR if bp increased
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.
Decreased bp to kidney causes what hormone to be released?
Renin
What does renin cause?
Angiotensinogen (made in liver) to be converted to Angiotensin 1
What converts Angiotensin 1 to angiotensin 2 and where is it made?
ACE, surface of pulmonary and renal endothelium
What does Angiotensin II cause?
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)
Myogenic response to maintain GFR if increased bp
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)
The filtration barrier and its 3 layers
Filtrate moves from blood into Bowman space.
Fenestrated capillary endothelium
Glomerular basement membrane
Podocytes (visceral epithelium)
What are the spaces called between podocytes where filtrate moves through
Slit diaphragm
Factors determining filtration rate
Pressure
Size of molecule
Charge
Rate of blood flow
Protein binding
What is nephrotic syndrome?
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.
What is microalbuminuria an early sign of?
Diabetes
Causes damage to filtration barrier.
Small molecules of albumin can cross the filtration barrier and are present within the urine.
GFR = KF (PGC - PBS) - (Pi GC)
Or in words, Glomerular filtration rate =
Filtration volume per unit time (mins)
KF is the filtration coefficient.
Units = ml/min/ m2
GFR determined by
Net filtration pressure
Permeability of the filtration barrier
Surface area available for filtration (approx. 1.2-1.5 m2 total)
What regulates the GFR
Sympathetic nervous system and Hormones / autocoids
Sympathetic regulation of GFR
Afferent arterioles receive strong sympathetic stimulus
Abdominal arteries constrict
Decreased Renal blood flow
Decreased GFR
(Important in bleeding, shock, ischaemia and illness)
Afferent and efferent arteriole actions to help increase GFR
Want more blood to be flowing slower near glomerulus so…
The afferent arteriole dilates and the efferent arteriole constricts
Afferent and efferent arteriole actions to help decrease GFR
Want less blood to be flowing (and faster) near the glomerulus so…
Afferent arteriole would constrict and efferent would dilate.
How do NSAIDs decrease the GFR?
Cause afferent arteriole to constrict
How doe ACE inhibitors decrease the GFR?
Cause efferent arteriole to dilate
Measuring GFR
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.
Properties of a good marker for measuring GFR
Freely filtered
Not secreted or absorbed
Not metabolised
Creatinine often used but not the best marker as it is secreted by cells (tubular secretion).
Factors changing levels of creatinine
Age, gender, ethnicity, height, weight, renal tubular handling, dietary protein intake, medications, creatinine supplements.
Gold standard marker for measuring GFR
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.
