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30 Cards in this Set

  • Front
  • Back

What is urine?

- excretion from the body consisting of urea, excess salt and water (sterile)

What are the stages of osmoregulation in the body?

- ultrafiltration


- reabsorption of glucose and water by PCT


- maintain Na+ gradient in medulla by loop of Henle


- reabsorption of water by DCT and collecting ducts

What is the overview of ultrafiltration?

- small molecules/ions filtered out blood into the renal capsule due to pressure maintained by efferent/afferent arterioles


- forms a glomerular filtrate

How is a glomerular filtrate formed by ultrafiltration?

- blood enters kidney via renal artery/afferent arteriole/glomerulus/efferent arteriole


- wall of glomerular capillaries are epithelial with pores between them


- diameter of afferent>efferent arteriole=glomerulus hydrostatic pressure up


- water/glucose in blood squeezed out glomerulus capillaries


- glomerulus filtrate picked up by renal capsule

What is the movement of the filtrate from the glomerulus to the renal capsule resisted by?

- connective tissue/epithelial cells of glomerulus capillaries


- existing hydrostatic pressure in the renal capsule


- low water potential of blood in glomerulus

What modifications are there to reduce the barrier to the flow of the filtrate?

- inner layer of Bowman's capsule=podocytes=spaces between them=allows filtrate to pass between cells


- spaces between endothelium of glomerular capillaries allow fluid to pass through

What is the result of the resistance of movement of the glomerular filtrate combined with the modifications?

- hydrostatic pressure in glomerulus enough = filtrate passes from blood to rena (Bowman's) capsule

Which components make up the three-part filter which forms the glomerular filtrate?

- endothelium of blood capillary


- basement of membrane


- epithelium of renal capsule (podocytes)

What are the features of the endothelium of the blood capillary as part of the three-part filter?

- thin


- perforated with 1000s of pores approx 10nm


- barrier to cells, not plasma proteins

What are the features of the basement membrane as part of the three-part filter?

- meshwork of collagen/glycoprotein fibres


- water/small molecules pass through


- proteins too large=repelled by negative charge on fibres

What are the features of the epithelium of the renal capsule (podocytes) as part of the three-part filter?

- each cell has foot-like extensions from its surface


- wrap around capillaries of the glomerulus/neighbouring cells


- filtration slits 23nm wide


- filtered fluid passes through filtration slits

What is the main role of the proximal convoluted tubule (PCT)?

- absorbs 85% of the filtrate back into the blood


- includes water, amino acids, Na+ and other ions

How are the epithelial cells which line the PCT adapted for absorption?

Microvilli: large surface area for reabsorption


Infoldings on base: large SA=transfer reabsorbed substances to capillary


Lots of mitochondria: provide ATP for active transport

What is the process of reabsorption of glucose and water in the PCT?

- Na+ active transport out PCT epithelial to capillaries=carried away (Na+ conc. down)


- Na+ diffuse from lumen to epithelial (facilitated diffusion)


- carrier protein co-transports glucose with Na+ to epithelial


- NA+/glucose diffuse from epithelial to blood


- changes filtrate conc.=water moves from PCT lumen to blood (osmosis)

What is the main role of the loop of Henle?

- to increase the conc. of salts in the tubule fluid to allow the water to move out the filtrate by osmosis and be reabsorbed by the blood

What are the two regions of the loop of Henle?

Descending limb: narrow, thin walls;highly permeable to water


Ascending limb: wider, thick walls;impermeable to water

What is the 1st step of the loop of Henle?

- the filtrate arrives from the PCT at the descending limb

What is the 2nd step of the loop of Henle?

- as filtrate moves down the descending limb to the medulla, the water potential goes down


- lowest water potential at hairpin curve

Why does the water potential of the filtrate decrease as the filtrate moves down the descending limb?

- walls of the descending limb are permeable to water/Na+


- water leaves by osmosis to interstitial region to be carried away by blood capillaries


- Na+ diffuses into descending limb, maintaining the concentration gradient

What is the 3rd step of the loop of Henle?

- as the filtrate moves up the ascending limb to the cortex, the water potential increases

Why does the water potential of the filtrate increase as the filtrate moves up the ascending limb?

- Na+ diffuses out filtrate at hairpin curve


- higher up, Na+ actively transported to interstitial region


*ATP from mitochondria in cells of AL walls*


- AL wall impermeable to water=can't leave AL

What is the 4th step of the loop of Henle?

- the interstitial regions now have a lower water potential

What is the 5th step of the loop of Henle?

- At the top of the AL, the filtrate passes through the distal convoluted tubule (DCT)


- salts selectively reabsorbed into the blood through active transport


- controlled by hormones

What is the 6th step of the loop of Henle?

- water potential gradient in the interstitial region between the AL and collecting duct


- water potential up in cortex and down in medulla

What is the 7th step of the loop of Henle?

- As filtrate moves down collecting duct (permeable), water moves out (osmosis) and is carried away by blood capillaries

What is the 8th step of the loop of Henle?

- As you move from the cortex to the medulla, the water potential of the filtrate and the interstitial region decreases


counter current multiplier: constant water potential gradient allowing water to move out the collecting duct by osmosis

What is the 9th step of the loop of Henle?

- water not removed from the collecting duct enters the ureter and becomes urine

What affects the amount of water reabsorbed from the filtrate?

- the permeability of the collecting duct walls


Aquaporins: channel proteins that allow water to pass out of collecting duct (osmosis)


ADH: alters the no. aquaporins=controls water loss

What is the main role of the distal convoluted tubule?

- adjust water/salts reabsorbed=control pH of blood (select reabsorbed ions)


- permeability of walls altered by hormones

How does the distal convoluted tubule carry out its main role?

- cells of the DCT wall=microvilli/many mitochondria=reabsorb material rapidly by active transport