ultrafiltration

• capillary wall


  blocks cells from leaving capillaries
• podocytes

  absorbs the water and small molecules that pass through. is wrapped around capillary walls
• basement membrane

  blocks proteins due to negative charge of glycoprotein and collagen fibres
• diagram

  A) renal artery

  B) efferent arteriole

  C) lower water potential

  D) afferent arteriole

  E) higher water potential

  F) capillary wall (1 cell thick and pores)

  G) basement membrane

  H) podocytes ( cells of bowman capsule)

  I) glomerulus

  J) Bowmans capsule

  K) proximal convoluted tubule

  L) vili in the PCT

  M) where selective reabsorption takes place

  
• larger lumen of the afferent arteriole creates high pressure in the glomerulus
• fluid is forced out of the capillaries into the Bowmans capsule which creates ultrafiltration
• filtrate

  contains water, glucose, amino acids , urea, vitamins, drugs ( ethanol/ penicillin)
• selective reabsorption

  reabsorption of useful substances, takes place as the filtrate flows along the PCP
• glucose, amino acids, vitamins and some salts are reabsorbed along the PCT by active transport and facilitated diffusion. some urea also is diffused in
• water enters the blood by osmosis so water is reabsorbed from the loop of hence, DCT and collecting duct
• PCT

  A) cross-section

  B) villi

  C) capillary

  D) proximal convoluted tubule

  E) filtrate travels through PCT

  F) villi - increased surface area for reabsorption

  G) epithelium

  H) capillaries

  
• ultrafiltration is filtration under pressure and takes place in the Bowmans capsule. the latter is sometimes referred to as the renal capsule
• blood enters the glomerulus from the afferent arteriole and leaves through the efferent arteriole
• the afferent arteriole has a wider diameter than the efferent arteriole and since the diameter of these capillaries is far less than of an arteriole this creates a high hydrostatic pressure
• water and small solute molecules are forced through the walls of the glomerulus into the Bowman's capsule so forming the hydrostatic pressure. large molecules such as the blood cells and protein can not pass through
• since water is being lost from the glomerulus and the plasma proteins remain in the blood of the glomerulus, the blood that leaves the glomerulus will have a lower water potential. this will be important for reabsorbing water later in the nephron. in addition the glomerular filtrate will be reduced
• The Bowman's Capsule is a cup shaped structure which contains a mass of capillaries called the glomerulus. The capillary walls consist of a single layer of endothelial cells (the endothelium) which have gaps or pores to allow molecules through. These cells rest on a basement membrane (made of glycoprotein and collagen) and are in close proximity of the inner layer of the Bowman's capsule. The inner layer of the Bowman's capsule is made up of cells called podocytes. These cells have many tiny finger like projections ("pods") with gaps in between. These gaps allow molecules through.