Kidneys Flashcards
What are the functions of the kidneys?
- filtration of blood plasma (glomerulus)
- selective reabsorption of contents to be retained (PCT)
- tubular secretion of some components (LoH)
- concentration of urine as necessary (DCT)
What is the endocrine function of kidneys?
Signals to rest of body - hormones inc renin, erythropoietin, 1,25-OH Vit D
Where in the kidneys is material to be retained reabsorbed?
Proximal convoluted tubule
Where is the creation of hyper-osmotic extracellular fluid taking place in kidneys?
Main function of loop of Henle and the vasa recta (blood vessels)
When is the adjustment of ion content of urine done in the kidneys?
Principally a function of distal covoluted tubule controlling the amount of Na+, H+, NH4+ and K+
When is the concentration of urine controlled in the kidney? What happens?
Collecting tubule, movement of water down an osmotic gradient into extracellular fluid
What hormone affects the concentration of urine?
Vasopressin - ADH - antidiuretic hormone
What is the renal corpscle made out of?
Bowman’s capsule containing:
- The glomerulus consisting of capillaries
- Podocytes and mesangial cells associated with glomerulus
Where is the blood supply from and where does it leave the renal corpuscle?
- At the vascular pole of corpuscle
- From afferent arteriole and exit to efferent arteriole
- Glomerular capillaries at a high pressure
What does the filtration barrier in the renal corpuscle consist of?
- Fenestrae (windows) in capillary endothelium
- Special basal lamina
Where does the filtration happen in the renal corpusle?
Filtration slits between foot processes of podocytes - allows passage of ions and molecules less than 50,000 Da
Where is the drainage of filtrate in the renal corpuscle taking place? Where does it drain to?
At urinary pole of corpuscle
Drains to proximal convoluted tubule
What are the 5 stages of the mechanism of urine production in the kidney?
- Filtration
- Re-absorption
- Creation of hyper-osmotic extracellular fluid
- Adjustment of ion content of urine
- Concentration of urine
What are structural features of the proximal convoluted tubule? (eg epithelium/proteins)
- Cuboidal epithelium sealed by tight junctions and a brush border at apical surface
- indigitations at lateral membrane
- contains aquaproins, membrane protein mediating transcellular water diffusion and prominent mitochondria reflect high energy requirement
What are the functions of the proximal convoluted tubule?
- Reabsorption of 70% of glomerular filtrate
- Na+ uptake by basolateral Na+ pump
- Water and anions follow Na+
- Glucose uptake by Na+/glucose co-transporter
- AA uptake by Na+/aa co transporter
- Protein uptake by endocytosis
What happens in the descending thin tubule of the loop of Henle? What epithelia do they have?
- Passive osmotic equilibrium (aquaporins present)
- Simple squamous epithelium
What happens in the ascending thick limb of the loop of Henle?
Na+ and Cl- actively pumped out of tubular fluid
resulting in hyperosmotic extracellular fluid
What qualities does the ascending thick limb of the loop of Henle have that make it good for it’s job?
- Very water impermable tight junctions
- Membranes lack aquaporins making low permability to water
- results in hypo osmotic tubular fluid, hyper osmotic ECF
- high energy requirement
What kind of epithelia does the ascending thick limb of the loop of Henle have?
cuboidal epithelium with few microvilli
How are the blood vessels in the vasa recta in the Loop of Henle? eg arrangement
Arranged in loop that stabilises hyperosmotic [Na+]
In rapid equilibrium with extracellular fluid
What is the site of osmotic equilibrium in the kidneys and what hormone controls it?
Distal convoluted tubule/Cortical collecting duct
Control by vasopressin
Where does specialisation take place in the distal convoluted tubule?
Macula densa, a part of juxtaglomerular apparatus
What happens in the medullary collecting duct?
- Passes through medulla with its hyperosmotic extracellular fluid
- water moves down osmotic gradient to concentrate urine
What does water movement rate in the medullary collecting duct depend on?
Aquaporin 2 in apical membrane
- content varied by exo-endocytosis mechanism
- under control from the pituitary hormone vasopressin
What type of aquaporin does the basolateral membrane have on the medullary collecting duct?
Aquaporin 3, not under control by vasopressin
What kind of epithelium does the medullary collecting duct have?
Simple cuboidal with no indigitations and little active pumping so few mitochondria
Where does the medullary collecting duct drain into?
Minor calyx at papilla of medullary pyramid
Minor and major calyces and pelvis have urinary epithelium
What does the juxtagolmerular apparatus do?
- Secrete renin to control blood pressure via angiotensin
- senses stretch in arteriole wall and Cl- in tubule
What are the cell components of the jutaglomerular apparatus?
- macula densa of distal convoluted tubule
- juxtaglomerular cells of afferent arteriole
What’s the capacity of the bladder?
~500ml
What is the vasa recta?
Network of capillaries surrounding the LoH
What kind of epithelial cell does the distal convoluted tubule have?
Cuboidal with few microvilli and complex lateral membrane indigitations with Na+ pumps and numerous large mitochondria
How is osmotic re-equilibrium controlled in the DCT/CT?
Vasopressin
How is adjustment of Na+/K+/H controlled in DCT/CT
Aldosterone
