2 The Structural Basis of Kidney Function Flashcards
Q: Which process is the kidney key in? What are the functions of the kidney? (6) How is it sensitive to the body’s needs? (2)
A: homeostasis- constancy of the internal environment
(creating urine)
- filtration of blood plasma (close to aorta= system under high pressure)
- selective reabsorption of contents being retained (PCT)
- tubular secretion of some components
- concentration of urine as necessary (collecting tubule)
- endocrine function: signals for the rest of body eg renin, erythropoietin, activated vitamin D
hormones, nerves
Q: Why may someone who drinks lots of water get urine infections?
A: constantly drinking loads and body is always removing and during night, still removing but no input -> concentrated urine = puts you at higher risks of getting an infection
Q: Describe the gross structure of the kidneys. (3) Urine path? Blood supply variation? (2)
A: cortex on outside = disorganised structure
medullary pyramids are striated and regular
^ come down into papilla -> urine -> expelled into renal pelvis -> ureter
- high blood supply where there’s filtration AKA outer
- lower where tubes come down… ^^
Q: What’s the result of a car accident/ lots of blood loss? (3)
A: bp drops
outer cortex is preserved
medulla is part of kidneys that die -> can lead to death
Q: What’s the renal cortex structure? (2) Why? Medulla?
A: disorganised/ granular
lots of glomeruli hence not regular structure
striated look since- lots of tubules present
Q: Describe filtration.
A: 1. blood goes through glomerulus
- filtered under pressure = hyperfiltration
- all components of filtrate =
Q: What’s the structure of the glomerulus? (3) All?
A: 1. fenestrated endothelium = leaky = specific for filtration
- basement membrane = specialised to act as filter too
- outside= podocytes (cells of bowmans)= sit on arterioles
3 fenestrated layers
Q: What are the components of the renal corpuscle? (3) Blood supply? (2) Filtration barrier made of? (3) Result? Where does the filtrate drain? (2)
A: Bowman’s capsule (collect filtrate)
glomerulus consists of capillaries
podocytes associated with glomerulus
from afferent arteriole, exit to efferent arteriole glomerular capillaries at high pressure due to pressure difference (due to differences in diameter)
fenestrae (“windows”) in capillary endothelium
specialised basal lamina
filtration slits between foot processes of podocytes
allows passage of ions and molecules
Q: Does reabsorption need energy? Where does it occur? What’s retained? (5)
A: yes
Material to be retained is reabsorbed in proximal convoluted tubule
Includes ions, glucose, amino acids, small proteins, water, etc
Q: What’s the main function of loop of Henle and vasa recta (blood vessels)? mechanism? Where in the kidney is the loop of Henle?
A: Creation of hyper-osmotic extracellular fluid
Countercurrent mechanism= concentrated twice during once cycle
medulla
Q: What is the function of the distal convoluted tubule? Eg? (4) What does it form?
A: Adjustment of ion content of urine // fine tuning
Controls amounts of Na+, K+, H+, NH4+
passes own glomerulus to form juxtaglomerular apparatus
Q: Which part of the nephron determines the concentration of urine? Describe. Controlled by? 2 example urine values?
A: collecting tubule
Movement of water down osmotic gradient into extracellular fluid
Controlled by vasopressin (=ADH, antidiuretic hormone)-> affects aquaporins
specific gravity of 1= urine with same concentration or SG above 1.0303
Q: Describe the specialised structure of the proximal convoluted tubule. (7) What type of epithelium?
A: -lots of mitochondria- reflect high energy requirement
- lots of vesicles containing what has been reabsorbed -> needs to be taken up
- 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
Cuboidal epithelium
Q: What’s the ratio between PCT and DCT?
A: 1:1
but appear to have more P as they are longer- deal with more fluid
D are shorter
Q: What’s the role of the proximal tubule? Describe (5).
A: Reabsorption of 70% of glomerular filtrate BY…
Na+ uptake by basolateral Na+ pump
Water and anions follow Na+
Glucose uptake by Na+/glucose co-transporter (active movement)
Amino acids by Na+/amino acid co-transporter (active movement)
Protein uptake by endocytosis (since they’re larger)
Q: What’s the structure of the loop of henle? (2) What else is in the same area?
A: descending limb= thin
ascending= thicker
lots of capillaries= vasa recta= reabsorbing content of extracellular fluid
Q: What’s the structure of the descending limb of the loop of henle? (2) What occurs here? Driving force?
A: (thin tubule)
Simple squamous epithelium
Passive osmotic equilibrium (aquaporins present)= passive water movement
hyperosmotic extracellular environment created by ascending limb
Q: What’s the structure of the ascending limb of the loop of henle? (3) What occurs here? (3) Result? (2) Controls? (2)
A: Cuboidal epithelium, few microvilli
High energy requirement - prominent mitochondria
- Na+ and Cl- actively pumped out of tubular fluid
- Very water-impermeable tight junctions
- Membranes lack aquaporins - low permeability to water (don’t want water to follow)
Results in hypo-osmotic tubular fluid (diluted), hyper-osmotic extracellular fluid
- activity of descending limb
- collecting duct
Q: What’s the structure of the vasa recta? Role? (2) Reason?
A: Blood vessels also arranged in loop
Blood in rapid equilibrium with extracellular fluid
Loop structure stabilises hyper-osmotic [Na+]= too high is toxic
Q: What’s the structure of the distal convoluted tubule? (4) Site of? Explain. Control?
A: -Cuboidal epithelium, few microvilli
- Complex lateral membrane interdigitations with Na+ pumps
- Numerous large mitochondria
- Site of osmotic re-equilibration (control by vasopressin) (determines how much fluid is absorbed)
Adjustment of Na+/K+/H+/NH4+ (control by aldosterone)
Specialisation at macula densa, part of juxtaglomerular apparatus
Q: What’s the structure of collecting ducts? (4) What do they drain into? Describe. (2)
A: -have aquaporins in apical and basal membrane (different ones)
- simple cuboidal epithelium
- good tight junctions
- Little active pumping so fewer mitochondria
Drains into minor calyx at papilla of medullary pyramid
Minor and major calyces and pelvis have urinary epithelium
Q: What does the medullarly collecting duct pass through? What occurs here? (2) Control of both steps?
A: 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
- Basolateral membrane has aquaporin-3
- not under control
Q: How does the juxtaglomerular apparatus work? What else affects this? (2)
A: -JM cells secrete renin to control blood pressure via angiotensin (ANG II -> vasoconstriction -> increased pressure)
Senses stretch in arteriole wall and [Cl-] in tubule
Q: What makes up the endocrine part of the nephron? (3) Describe.
A: juxtaglomerular apparatus
- macula densa= modified cells of distal convoluted tubule
- juxtaglomerular cells around afferent arteriole sense pressure and can release renin
