Urine formation

What is glomerular filtration and in what direction

• from blood to nephron

• controls the speed of filtration

  • and the amount of urine formed

• occurs in glomerulus and glomerular capsule

What is tubular reabsorption and in what direction

• from renal tubule back into blood

• controls the chemistry of the urine formed

• affected by

  • tubule permeability

  • counter current circulation

What direction is tubular secretion

from blood into renal tubule

What is the structure of the glomerulus

• a network of capillaries in the renal corpuscle

• found only in the kidney cortex

• pressurized

What is the role of podocytes and capillary walls

• create a filter with fixed openings

  • plasma and many substances dissolved in it pass through

  • blood cells, platelets and proteins don’t

What is fenestration of glomerulus endothelial cells

• prevents filtration of blood cells

• allows all components of blood plasma to pass through

What is the role of the basement membrane of glomerulus

• prevents filtration of larger proteins

What is the role of the slit membranes between pedicels

prevents filtration of medium sized proteins

What is the process of glomerular filtration

• hydrostatic pressure forces water & small solutes through filtration slits

  • requires sufficient blood flow and pressure

• large solutes are too big

• useful substances will pass through if small enough

What is the equation for glomerular filtration rate

• filtration constant

• multiplied by

• (Hydrostatic glomerulus pressure - Hydrostatic Bowman’s capsule pressure)

• subtracted by

• ( osmotic glomerulus pressure + osmotic Bowman’s capsule pressure)

What is hydrostatic pressure

• the force a fluid exerts on the walls of its compartment 

What is oncotic pressure

• the pressure exerted by plasma proteins on the walls of the compartment in which they’re contained 

What is the function of glomerular filtration

controls the speed of filtration and ultimately the amount of urine formed

What is the function of tubular reabsorption and secretion

• controls the chemistry of the urine formed

• affected by

  • tube permeability

  • counter current direction 

What is the 2 step process of reabsorption

• movement of water and dissolved substances from the fluid inside the tubule through the tubule wall into the space outside

• move through the capillary walls back into blood stream

• active or passive process

What is the structure of the proximal convoluted tubule

• simple, tall, cuboidal epithelial cells with microvilli 

What is the function of the proximal convoluted tubule

• reabsorption of salt, water and glucose from glomerular filtrate

• certain substances are actively transported from blood capillaries into tubule for excretion

• mitochondria aids active transport of Na⁺ out of cell 

What is the structure of the loop of Henle

• U-shaped

  • thick descending portion

    • pars recta

  • thin descending portion

  • thin ascending portion

  • thick ascending portion 

What is the function of the loop of henle

• recovery of water, Na⁺ and Cl^- from urine

  • making it more concentrated than blood

  • limiting the amount of water needed as intake for survival

• creates a concentration gradient to facilitate water reabsorption

  • counter-current mechanism

What is the structure of the distal convoluted tubule

• simple cuboidal epithelium 

  • few microvilli

What percentage of original filtrate reaches distal convoluted tubule

• only 15-20%

What is the function of the distal convoluted tubule

• major regulated reabsorption site

• variable reabsorption of water, Na⁺ and Ca⁺

• ^{secrete toxins, ions and drugs} 

• linked to the glomerulus forming part of juxtaglomerular apparatus

What is the macula densa cell

• modified epithelium

  • responds to NaCl level changes in distal convoluted tubule

What is the function of juxtaglomerular (granular) cell

secrete renin

What is a feature of an extraglomerular mesengial cell

contractile

What are the 3 effects of an increase in NaCl

• decrease in glomerular filtration rate through tumeruglobular feedback loop

• extraglomerular mesengial cells contact

• adjacent afferent arteriole contracts

What is the structure of the collecting duct

• simple cuboidal epithelium

• relatively impermeable to water unless anti-diuretic hormone present

What is the function of the collecting duct

• site of faculative reabsorption

  • able to adapt

  • tightly controlled

• reabsorption of water 

  • through the action of ADH and aquaporins

What is the function of ADH

• increases the number of aquaporin 2 channels in the apical membrane of collecting duct tubular cells