Urinary System 2 - Sructural basis of kidney function Flashcards
List the functions of the kidneys
- Filtration of blood plasma
- Selective reabsorption of contents to be retained
- Tubular secretion of some components
- Concentration of urine as necessary
- Sensitive to body needs via hormones, nerves
- Endocrine function - signals to rest of body (hormones include renin, erythropoietin, 1,25-OH vitamin D
List the stages of urine production
- Filtration
- Reabsorption
- Creation of hyper-osmotic extracellular fluid
- Adjustment of ion content of urine
- Concentration of urine
List the components of the renal corpuscle
- Bowman’s capsule
- Glomerulus consists of capillaries
- Podocytes associated with glomerulus
Describe the blood supply of the renal corpuscle
- At vascular pole of corpuscle
- From afferent arteriole, exit to efferent arteriole
- Glomerular capillaries at high pressure
List 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
- Amino acids by Na+/amino acid co-transporter
- Protein uptake by endocytosis
List the structural features of the proximal convoluted tubule
- Cuboidal epithelium
Sealed with (fairly water-permeable) tight junctions - Membrane area increased to maximise rate of resorption brush border at apical surface interdigitations of lateral membrane
- Contains aquaporins - membrane protein mediating transcellular
water diffusion - Prominent mitochondria reflect high energy requirement
What happens in the descending loop of henle?
- Passive osmotic equilibrium
- Simple squamous epithelium
What happens in the ascending limb of the loop of henle?
- Na+ and Cl- actively pumped out of tubular fluid
- Very water-impermeable tight junctions
- Membranes lack aquaporins - low permeability to water
- Results in hypo-osmotic tubular fluid, hyper-osmotic extracellular fluid
- Cuboidal epithelium, few microvilli
- High energy requirement - prominent mitochondria
Where is the vasa recta and what is its structure?
- Straight capillaries in the medulla parallel to the loop of henle
- Blood is in equilibrium with extracellular fluid
- Loop structure stabilises hyper-osmotic
What is the function of the distal convoluted tubule?
- Osmotic re-equilibration (controlled by vasopressin)
- Adjustmant of ions (control by aldosterone)
Describe the structure of the distal convoluted tubule
- Cuboidal epithelium, few microvilli
- Lateral membrane interdigitations with Na+ pumps
- Numerous mitochondria
- Specialisation at macula densa (part of the juxtaglomerular apparatus)
What process happens in the collecting duct of the kidney?
- Passes through medulla with its hyper-osmotic extracellular fluid
- Water moves down osmotic gradient to concentrate urine
- Rate of water movement depends on aquaporin-2 in apical membrane (content varied by exo-/endocytosis mechanism)
- Under control from the pituitary hormone vasopressin
Describe the structure of the medulla collecting duct
- Basolateral membrane has aquaporin 3
- Duct has simple cuboidal epithelium
- Cell boundaries dont interdigitate
- Little active pumping so fewer mitochindria
Describe the pathway of urine from the collecting duct
- Drains into minor calyx at the papilla of medullary pyramid
- Drains into major calyces
- Drains into the ureter
Describe the function of the juxtaglomerular apparatus
- Secretes renin to control blood pressure via angiotensin, causing vasoconstriction (due to SNS, low Na+, low BP, low fluid volume)
- Senses stretch in the arteriole wall and Cl- in the tubule
