Urinary System Flashcards
Which urea transporters are used where?
UT-A2 = thin descending limb (allows urea to flow into lumen of thin descending limb).
UT-A1 / A3 = medullary collecting duct cells. A1 transports urea across apical membrane into cell. A3 transports urea across basolateral membrane into interstitium.
How does the vasa recta maintain the hyperosmolar environment established in the renal medulla?
Counter-current and is freely permeable to salts and water: on its descending portion, water diffuses out and solutes are reabsorbed; on the ascending portion, water is reabsorbed and solutes secreted.
Blood flow is also slow through the vasa recta, to prevent dissipation of the gradient.
What happens in a collecting duct cell in response to ADH binding?
ADH causes AQ2 to be inserted into the apical membrane for water reabsorption.
UT-A1 inserted into apical membrane, UT-A3 inserted into basolateral membrane, increasing permeability to urea. This makes the interstitium even more hyperosmolar, so more water is reabsorbed.
What stimuli stimulate vasopressin release from the hypothalamus?
Osmoreceptors detect when the blood becomes >300mOs.
Also stimulates when blood volume or pressure decreases (detected by stretch receptors and baroreceptors).
What surround the dense, fibrous capsule of the kidney?
A fascial pouch (renal fascia).
Where do the superior poles of the kidneys lie?
Right kidney: 11 ICS. Left kidney: 11 Rib
Left kidney sits slightly higher than the right
Describe how renal arteries and veins cross the midline.
AA lies to the left of the IVC.
Right renal artery is longer and runs posterior to the IVC.
Left renal vein is longer, anterior to AA and deep to superior mesenteric artery.
Describe the difference in appearance of the renal cortex and medulla.
Cortex is granular looking because of random organisation.
Medulla striated because of radial arrangement of tubules and micro-vessels.
Describe simply the passage of urine out of the kidney.
Medulla drains into minor calyx via renal papilla. Roughly 3 minor calyces converge to form a major calyx, which all drain into the renal pelvis for urine to be drained via the ureter.
Describe the passage of the ureters.
Run vertically down posterior abdominal wall in vertical plane of the tips of transverse processes of lumbar vertebrae.
Cross the pelvic brim anterior to bifurcation of common iliac arteries & sacroiliac joint.
Enter the bladder at the level of the ischial spine.
Take blood supply from arteries they cross.
Where are the 3 sites of ureteric constriction?
- Pelviureteric junction
- Where the ureter crosses the pelvic brim
- Where the ureters traverses the bladder wall.
(Kidney stones likely to get stuck at these places).
Describe the shape of the bladder.
A triangular pyramid, with its apex anterior and base posterior.
Apex is supported by median umbilical ligament. The posterior surface is known as the fundus (base).
Describe the epithelium of the ureter and bladder.
Transitional epithelium (urothelium). This is a 3-layered epithelium with very slow cell turnover.
Large luminal cells have highly specialised low-permeability luminal membrane.
Prevents dissipation of urine-plasma gradient.
What is the trigone?
A smooth triangle on the base of the bladder, formed by the entry of the 2 ureters and exit of urethra (at the neck of the bladder).
Describe the sphincter vesicae.
The internal sphincter of the urethra - smooth muscle.
Situated at the neck of the bladder.
Reflex opening in response to bladder wall tension
Relaxed by PNS, contracted by SNS.
Describe the sphincter urethrae.
External sphincter of urethra - striated muscle. Located in perineurium. Tone maintained by somatic nerves in pudendal nerves (s2,3,4).
Opened by voluntary inhibition of nerves.
Compare the male and female urethra.
Female urethra is straight and short - roughly 4cm. Male urethra is much longer: Internal urethral orifice (bladder neck/outlet) / preprostatic urethra Prostatic urethra Membranous urethra (urogenital diaphragm) Ext Sph Spongy urethra Navicular fossa (widening at head of the penis) External urethral meatus.
Describe the epithelium of the PCT.
Cuboidal. Water-permeable tight junctions. Brush border (increase SA). Aquaporins for transcellular water diffusion. Lots of mitochondria.
What are the cellular components of the JGA and its function?
Macula densa of DCT.
Juxtaglomerular cells of afferent arteriole.
Endocrine functions. Secretes renin to control BP via angiotensin in response to LESS perfusion, LESS Na+ in the DCT and an INCREASE in B1 sympathetic activity.
What is the definition of renal failure?
An abrupt fall in glomerular filtration.
What is the equation for net ultrafiltration pressure? (Puf).
Puf = Pgc - Pt - πgc.
Net ultrafiltration pressure = hydrostatic pressure in glomerular capillaries - hydrostatic pressure of tubule - osmotic pressure of plasma proteins in glomerular capillary.
Roughly 10-20 mmHg.
What is the equation for glomerular filtration rate?
GFR = Puf x Kf GFR = net ultrafiltration pressure * ultrafiltration coefficient (membrane permeability).
How can the ultrafiltration coefficient, Kf, change?
Kidney disease may reduce the number of functioning glomeruli = reduced surface area = reduced Kf.
Dilation of arterioles by drugs/inflammation = increased Kf
What is the definition of glomerular filtration rate?
Amount of fluid filtered from the glomeruli into the Bowman’s capsule per unit time (ml/min).
It is used as an index of kidney function.
