Structural basis of kidney function Flashcards
(24 cards)
Function of kidney
Production of urine: Filtration of blood plasma Selective reabsorption of contents to be retained Tubular secretion of some components Concentration of urine as necessary
Endocrine function e.g. Renin, erythropoietin, 1,25 (OH)2- vitamin D
How is kidney sensitive to body’s needs?
Hormones
Nerves
Blood supply of kidneys
At pyramids (medulla), minimal blood supply If blood supply cut off they are affected first
Cortex= lots of blood supply because a lot happens there (proximal + distal convoluted)
Parts of kidney
slide 4, lecture 2
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Where are nephron units in the kidney?
Tubules?
Throughout the cortex
In medulla, tubules are straighter
Mechanism of urine production in kidney (Steps)
Filtraton Reabsorption Creation of hyper-osmotic extracellular fluid Adjustment of ion content of urine Concentration of urine
Filtration- Renal corpuscle
Weight of filtrate?
Components of renal corpuscle?
Blood supply to renal corpuscle? (Location, components, features?)
Filtration barrier layers?
Feature of fluid?
Drainage of filtrate? (Location, where does it drain?)
Blood passing glomerulus filtered under pressure
All components < about 50 000 molecular weight
Bowman’s capsule- collects fluid
Glomerulus- consists of capillaries
Podocytes associated with glomerulus
At vascular pole of corpuscle
From afferent arteriole to efferent arteriole
Glomerular capillaries at high pressure
- Fenestrated endothelial surface of capillaries= fluid can pass through
- Specialised basal lamina (basement membrane)
- Podocytes on outside of capillaries= filtration slits between foot processes of podocytes
Fluid coming out of afferent arteriole into proximal convoluted tubule= ISOTONIC, same conc. as blood
At urinary pole of corpuscle
Drains to proximal convoluted tubule
Anatomy of glomerulus
Features of arterioles?
(slide 8, lecture 2)
Arterioles= high pressure
Afferent arteriole= larger than efferent= pressure gradient to squeeze fluid out
Reabsorption
Material to be retained? Components?
% of glomerular filtrate reabsorped?
Function of proximal convoluted tubules?
Material to be retained= reabsorbed in proximal convoluted tubule- includes ions, glucose, amino acids, small proteins, water
70%
Na+ uptake by basolateral Na+ pump
Water+ anions follow Na+
Glucose uptake by Na+/glucose co-transporter
Amino acid uptake by amino acid/ glucose co-transporter
Protein uptake by endocytosis
Anatomy of proximal convoluted tubules?
Type of epithelium?
Cuboidal epithelium
Sealed with fairly water-permeable tight junctions
Brush border at apical membrane+ interdigitations of lateral membrane= high SA for reabsorption
Membrane= aquaporins= membrane protein mediating transcellular water diffusion
Lots of mitochondria= ATP requirement
Vesicles for reabsorption products
Creation of hyper-osmotic extracellular fluid
Parts of kidney for this?
Mechanism?
Descending limb of loop of Henle? (water, epithelium, function?)
Ascending limb of loop of Henle? (function, features)
Vasa recta? (arrangement, features, function?)
Main function of loop of Henle+ vasa recta (blood vessles)
Countercurrent mechanism
Passive osmotic equilibrium (aquaporins present)
Simple sqamous epithelium
Descending limb= hyperosmotic fluid so water moves out passively
Na+, Cl- actively pumped out of tubular fluid (Cl- follows Na+ which is being actively transported)
Very water impermeable tight junctions+ membranes lack aquaporins- low permeability to water= hypo-osmotic tubular fluid+ hyper-osmotic extracellular fluid
Cuboidal epithelium, few microvilli
Mitochondria= high energy requirement
Blood vessels also arranged in loop
Blood= rapid equilibrium with extracellular fluid
Loop structure stabilises hyper-osmotic Na+
Anatomy of descending limb of loop of Henle?
Thin
Not many mitchondria (passive processes)
Anatomy of collecting duct?
More mitochondria than descending limb
Tight gap junctions= don’t want reabsorption so need good barrier
Adjustment of ion content of urine Which components are part of this? Control levels of? Where in kidney? Why? Distal convoluted tubule/ Collecting duct (function, features. hormones, specialisation)?
Principally a function of distal convoluted tubule
Control levels of Na+, K+, H+, NH4+
Comes back to cortex at this point because cells working harder= better blood supply here
Site of osmotic re-equilibriation (control by vasopressin for BP)
Adjustment of Na+, K+, H+, NH4+ (control by aldosterone from adrenal glands)
Cuboidal epithelium
Few microvilli
Complex lateral membrane interdigitations with Na+ pumps
Numerous large mitochondria
Specialisation at macula densa part of juxtaglomerular apparatus
Anatomy of distal convoluted tubule?
No brush border
Invaginations in surface with pumps that require:
Some mitochondria
Why can you spot more proximal than distal tubules in the microscope?
Distal length= shorter than proximal+ not as much work to do as proximal
Concentration of urine Where does it occur? What does it involve? What is controlled by? Collecting duct (functions, features, affected by?) Drains into? Features?
Collecting tubule
Movement of water down osmotic gradient into extracellular fluid
Controlled by vasopressin (ADH)
Passes through medulla with hyper-osmotic extracellular fluid
Water moves down osmotic gradient to concentrate urine
Rate of water movement depends on aquaporin-2 in apical membrane (pituitary hormone vasopressin affects this): Content varied by exo-/endocytosis mechanism
Basolateral membrane has aquaporin-3, not under control
Duct has simple cuboidal epithelium
Cell boundaries don’t interdigitate
Little active pumping so fewer mitochondria
Drains into minor calyx at papilla of medullary pyramid
Minor and major calyces and pelvis have urinary epithelium
Juxtamedullary apparatus?
Location?
Endocrine function
Next to afferent arteriole
Secretes renin to control BP via angiotensin
Senses stretch in arteriole wall+ Cl- in tubule
Cellular components: macula densa in distal convoluted tubule+ juxtaglomerular cells of afferent arteriole
Lots of Na+= decreased renin production= decrease angiotensin 1= decrased angiotensin 2= vessels vasodilate= more urine produced
ACE inhibitors= inhibit Angiotensin II
Anatomy of kidneys in relation to each other
Left kidney is higher than right (because liver pushes down right)
Difference between males+ females urethra
Male is longer (females= increase risk of UTI)
Male has 2 right angles (harder to catherterise)
Bladder contraction occur in response to
distension from bladder filling not SNS (SNS controls sphincters not bladder)
Angiotensinogen found in
Liver
ACE found in
Lungs
Blood pressure of afferent arteriole =
blood pressure in heart
