039 Overivew of Kidney Function Flashcards
How much output do kidneys receive from the heart?
20-25%
How much blood do we filter per day?
180L
How long is the proximal tubule?
15mm in length
What occurs in proximal tubule?
2/3 Water, Na+, Cl- absorption, all of glucose & amino acid absorption
What occurs in the loop of henle?
This regulates whether urine is dilute
What occurs in the distal tubule and collecting duct?
Fine tuning of Na+ and water under hormonal control
How is the proximal tubule adapted for absorption?
Contains microvilli that increase absorption by rate of x200
What does calcitriol (vitamin D metabolite) help absorb from intestines?
Ca2+ and Pi
How does the kidney regulate Ca2+ and Pi
Dietary vitamin D needs to be activated by UV light on the skin. A hydroxyl group is added in the liver, and then in the kidney, the enzyme 1a-hydroxylase forms calcitriol. Calcitriol indicates to the gut to increase uptake of calcium. Parathyroid gland senses Ca2+ levels and is able to regulate 1a hydroxylase with parathyroid hormone release.
PTH has the opposing effect on phosphate – it is thought to be because calcium and phosphate can react and form a compound.
Where is enzyme 1a-hydroxylase produced and regulated?
Produced in the proximal tubules and regulated by the parathyroid hormone.
Describe the arterial vascular supply of the kidneys
Renal artery goes into kidney at hilum. This splits into interlobar arteries between renal pyramids. This splits into arcuate arteries at junction between cortex and medulla which lead to the afferent arterioles entering the glomerulus. Efferent arterioles are peritubular (go along the tubules of nephron)
Describe venous drainage of the kidneys
After peritubular arteries, blood drains into stellate veins, and then into the cortical radial veins, and then arcuate vein, interlobar veins and finally out through the renal vein.
How % much blood is filtered into the tubule from the the 100% input of afferent arterioles?
20%
What is an important transmitter found in the proximal tubules?
SGLT2
In the proximal convoluted tubule, there is low affinity high capacity.
In the proximal straight tubule, there is high affinity low capacity SGLT1 to make sure all glucose is absorbed.
How much urine do we produce per day?
1.2-2L (varies)
Where are the cortical and juxtamedullary nephron located?
Juxtamedullary is more embedded in the medulla pyramid while cortical nephrons are mainly embedded in the cortex.
What are the papillae of the kidney?
The apex of a renal pyramid which projects into the lumen of a calyx of the kidney
Where are the renal sinuses located?
In between each pyramid in the cortex region. It contains the fatty parts of the kidney.
How can differentiate the proximal from the distal tubule of the kidney on microscopic images?
Distal tubules have a narrower lumen and proximal tubules contain microvilli.
What is the functional difference between juxtamedullary and cortical nephrons?
Juxtamedullary nephrons are able to secrete either very dilute or concentrated urine.
How many juxtamedullary nephrons are there relative to cortical nephrons?
Cortical nephrons - 80%
Juxtamedullary nephrons - 20%
What is the venous saturation oxygen of the kidney and why?
It is approx. 90% because of the high cardiac output that reaches the kidney for such a small surface area.
Where do renal nerves come from?
Most come from the sympathetic autonomic nervous system. Most have vasomotor function which regulates blood flow. Renin secretion is also controlled sympathetically. There is parasympathetic nerve supply but function is still unknown.
What ion homeostasis do the kidneys regulate?
Ca2+, Pi, K+, Na+
How much Ca2+ and Pi do the kidneys secrete?
Equal amounts that are entering the body via GI tract.
How are the kidneys oxygen sensors?
85% of erythropoetin is produced by interstitial fibroblasts of the kidney. This is released due to decrease in blood PO2 and acts on bone marrow stem cells to increase RBC production.
Describe renin regulation and secretion in the kidney.
Angiotensinogen is released in the liver. Due to a signal of increased sympathetic activity, reduced afferent arteriole pressure, or decreased Na+ in distal tubule, Renin will be released by juxtaglomerular cells. This converts angiotensinogen into angiotensin I by ACE enzymes in capillary walls, which is then converted into angiotensin II and then aldosterone in suprarenal gland. Aldosterone causes Na+, H2O uptake and arteriole constriction. Angiotensin II has direct effects on arteriole constriction.
Where are juxtaglomerular cells mainly found?
In the afferent arteriole where they mainly secrete renin.
How much volume is reabsorbed and excreted from 100% entering the nephron?
99% reabsorbed
<1% excreted
What is standard GFR rate?
125ml/min
Where does blood from the descending vasa recta drain?
Directly into the arcuate vein
What ion is used as a buffer in urine?
Phosphorus
What 3 types of cells make up the juxtaglomerular aparatus?
Macula densa cells
Granular cells/ juxtaglomerular cells
Mesangial cells/ Lacis cells
What do juxtaglomerular cells do?
Specialised smooth muscle cells of the arterioles
What do macula densa cells do?
Columnar epithelial thickening of the distal convoluted tubule that senses Na+ concentration
