Kidney physiology Flashcards
What is the main function of the kidney?
Excrete metabolic products (urea, creatinine)
Maintain internal environment (water, sodium, potassium, H+)
Secretes hormones (renin, erythropoietin, vit D)
What is glomerular filtration rate?
The amount if blood that passes through the glomeruli per unit time
What is osmolality measured in?
No. of particles per kilogram of solvent
mmol/kg
What is osmolarity measured in?
No. of particles per litre of solution
mmol/l
Draw a nephron (and label it).
:)
What is the proximal convoluted tubule’s basic function?
Most of the reabsorption and secretion
What is the loop of henle’s basic function?
Creates concentration gradient
What is the distal convoluted tubule’s basic function?
Fine tuning!
What is reabsorbed in the collecting duct?
Some urea, water and NaCl
What is reabsorbed in the PCT?
K+ NaCl water amino acids glucose bicarbonate ions
What is secreted in the PCT?
Uric acid
Organic acids
Antibiotics that need to be removed from the body
What is reabsorbed in the descending limb of the loop of Henle?
water
What is reabsorbed in the ascending limb of the loop of Henle?
NaCl
What is reabsorbed in the DCT?
NaCl and water
What is secreted in the DCT?
K+
H+
What is hydrostatic pressure?
Force that compels a fluid to move out of a vessel.
The larger the volume of blood within the capillaries and the higher the BP, the more quickly fluid will move from blood to Bowman’s.
What are podocytes?
Cells in the Bowman’s capsule that wrap around the capillaries of the glomerulus
What is the structure of podocytes and how does this help them carry out their function?
They have long processes called pedicels which wrap around the capillaries. There are slits between the pedicels which is where blood is filtered through.
What are the 2 functions of the glomerulus?
Ultrafiltration of plasma
Barrier to filtration of protein
What is oncotic pressure?
A form of osmotic pressure exerted by proteins, notably albumin.
Usually pulls water into circulatory system.
Name the three ‘pressures’ acting on the glomerulus and Bowman’s capsule.
Hydrostatic pressure of blood (Ph blood) Hydrostatic pressure of filtrate (Ph filtrate) Oncotic pressure (π)
Which pressure(s) support movement of fluid out of blood into Bowman’s?
Hydrostatic pressure of blood
Which pressure(s) support movement of fluid out of Bowman’s into blood?
Hydrostatic pressure of filtrate
Oncotic pressure
Why is there not oncotic pressure supporting movement from blood to Bowman’s?
Oncotic pressure is exerted by presence of proteins - there shouldn’t be any protein in the filtrate
What’s the equation to calculate net pressure (Pnet)?
Pnet = force out - force in
Pnet = Ph blood - (Ph filtrate + π)
Pnet = 55 - (15 + 30) = 10 mmHg
Why is it that there’s an overall movement of fluid out of the glomerulus?
Because the pressures that are acting add up to mean the there is more pressure forcing fluid out than back in.
What makes up the filtration barrier in the glomerulus?
Fenestrated endothelium of glomerular capillaries
Fused basal lamina of the endothelial cells and podocytes
Slits created by podocytes
Where is the juxtaglomerular apparatus?
Structure between Bowman’s and the distal convoluted tubule - look up a picture!
What is the juxtaglomerular apparatus made up of?
Juxtaglomerular cells
Macula densa
Mesangial cells
What do the juxtaglomerular cells look like and what do they do?
Specialised smooth muscle cells of glomerular arteries
Produce and secrete renin
What is the macula densa?
Area of closely packed specialised cells lining the thick ascending limb where it become the DCT
What do macula densa cells look like and what do they do?
Columnar epithelium
Sense increase in NaCl concentration in the distal tubule.
Secretes a locally active vasopressor - which acts to decrease GFR
What do Mesangial cells look like and what do they do?
Pericytes found outside the glomerulus near Bowman’s-ish. They resemble smooth muscle cells
Role in autoregulation of blood flow to the kidney and control of systemic blood pressure via Renin-Angio-Aldo pathway
What effect does vasoconstriction of the afferent arteriole have on GFR? Explain briefly.
Decreases GFR
Less blood gets to glomerulus - less fluid can get to
↑resistance due to arteriolar constriction
↓ renal blood flow
↓ GFR
What effect does vasoconstriction of the efferent artery have on GFR? Explain briefly.
Increases GFR
More blood gets to the glomerulus - so more fluid is forced out into Bowman’s.
↑ resistance due to arteriolar constriction
↓ renal blood flow
↑ GFR
Normal value of oncotic pressure?
30 mmHg
Normal value of hydrostatic pressure of blood?
55 mmHg
Normal value of hydrostatic pressure of filtrate?
15 mmHg
