The structural basis of kidney function Flashcards
Describe homeostasis
The constancy of the internal environment is the condition of free life
The ability to create our own internal environment- separate from the external environment
What happens when too much ADH is secreted
Thirst centres no longer activated- thirst stops- dehydrated- die
What happens to the food and drink once it enters the body
Some may be lost in faces as undigested residue before it enters the body
Body
Regulation of osmolarity, [Na+], [K+], pH, nitrogen etc
Control of body fluid volume
From here: It can be exhaled (H20, CO2) Lost in Urine H2O, Na+, K+, H+, urea
Lost in sweat- water and Na+
Describe the functions of the kidneys
Function
Production of urine:
Filtration of blood plasma (glomerulus)
Selective reabsorption of contents to be retained (PCT)
Tubular secretion of some components (collecting duct)
Concentration of urine as necessary (DCT)
Describe the endocrine function of the kidney
Sensitive to body needs via hormones, nerves
Endocrine function - signals to rest of body (hormones include renin, erythropoietin, 1,25-OH vitamin D)
Describe the consequences of shock on the kidney
Blood supply reduced to bowels and kidneys
Cortex- supply is good
Pyramids- supply is limited
part of kidney which dies first is the pyramid- may see a necrosis in the urine
Why does the cortex appear granulated
due to the presence of the glomerulus in the cortex
Describe the role of filtration in urine production
Blood passing through glomerulus is filtered
Filtrate consists of all components
Describe the role of reabsorption in urine production
Material to be retained is reabsorbed in proximal convoluted tubule
Includes ions, glucose, amino acids, small proteins, water, etc
Describe the role of the creation of hyper-osmotic extracellular fluid in urine production
Main function of loop of Henle and vasa recta (blood vessels)
Countercurrent mechanism creates the hyper-osmolar ECF
Describe the role of adjusting the ion content in the urine in urine production
Principally a function of distal convoluted tubule- but also takes place in collecting duct
Controls amounts of Na+, K+, H+, NH4+
Describe the role of concentrating the urine in urine production
Occurs at collecting tubule
Movement of water down osmotic gradient into extracellular fluid
Controlled by vasopressin (=ADH, antidiuretic hormone)
Why does the medullar appear striated
Due to the loop of Henlé there
How may proteins get in the urine
Hyperfiltration
High blood pressure damages the capillaries- destroying the filter- allowing larger particles such as proteins to enter the urine
How is a pressure gradient created in the glomerulus
Afferent arteriole- big
efferent arteriole- small
creates a pressure gradient for fluid to be squeezed out
Describe filtration in the glomerulus
§ Fenestrae exist in the capillary endothelium.
§ A specialised basal lamina exists- allowing substances to pass through
§ There are filtration slits between the foot processes of the podocytes which allows passage of ions and molecules ONLY less than 50,000 Da.
What are the components of the renal corpuscle
Bowman’s capsule
glomerulus consists of capillaries
podocytes associated with glomerulus
Describe the blood supply to the renal corpuscle
§ Blood supplied at the vascular pole of the corpuscle by the AFFERENT which leaves via the EFFERENT.
§ The glomerular capillaries are at a HIGH pressure.
§ The afferent arteriole is LARGER than the efferent arteriole
What does the filtration barrier consist of in the renal corpuscle
fenestrae (“windows”) in capillary endothelium
specialised basal lamina
filtration slits between foot processes of podocytes
allows passage of ions and molecules
Describe the drainage of the filtrate fluid
at urinary pole of corpuscle
drains to proximal convoluted tubule
Describe the characteristics of this filtrate
Fluid is isotonic with the blood- except for the absence of cellular components
Describe the functions and actions of the PCT
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
Describe the structural features of the PCT
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 (apical membrane)
Prominent mitochondria reflect high energy requirement
Describe the role of the descending thin tubule
Water reabsorbed into ECF
Passive osmotic equilibrium (aquaporins present)
Simple squamous epithelium
Describe the action of the ascending thick limb
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
Describe the vasa recta
Blood vessels also arranged in loop
Blood in rapid equilibrium with extracellular fluid
Loop structure stabilises hyper-osmotic [Na+]
Where is the DCT found
Back at the glomerulus
Describe the structural features of the DCT
Cuboidal epithelium, few microvilli
Complex lateral membrane interdigitations with Na+ pumps
Numerous large mitochondria
Specialisation at macula densa, part of juxtaglomerular apparatus
No brush border
Describe the functions of the DCT/ cortical collecting duct
Site of osmotic re-equilibration (control by vasopressin)
Adjustment of Na+/K+/H+/NH4+ (control by aldosterone)
Which is longer the DCT or PCT
DCT- doesn’t have as much to do
Describe the structural features of the medullary collecting duct
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
Describe the functions of the medullary collecting duct
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
Describe the formation of the juxta-glomerular apparatus
Loops back round to the glomerulus to form the juxta-glomerular apparatus (has macula densa cells).
Next to afferent arteriole- to sense blood pressure close to the site of its generation
What happens if there is lots of Na+
No renin released- no aldosterone
less reabsorption of salt and water
Describe the juxta-glomerular apparatus
§ Endocrine organ comprised of the macula densa in the distal convoluted tubule, glomerulus and afferent arteriole.
§ This organ can secrete renin to alter blood pressure by angiotensin and ADH.
What does the juxta-glomerular apparatus respond to
Endocrine specialisation
Secretes renin to control blood pressure via angiotensin
Senses stretch in arteriole wall and [Cl-] in tubule
Cellular components are
macula densa of distal convoluted tubule
juxtaglomerular cells of afferent arteriole
What is the capacity of the bladder
§ The urine drains through the ureters into the bladder (capacity ~500ml).
