The kidneys and osmoregulation

Describe the structure of a nephron

Blood enters at Afferent arteriole

Glomerulus capillaries

Efferent arteriole

Renal capsule

Proximal convoluted tubule

Distil convoluted tubule

Collecting duct

Describe ultrafiltration

• Afferent arteriole has wider diameter than efferent arteriole an glomerular capillaries

• Generates high hydrostatic pressure in the glomerular capillaries-pressure higher than bowman’s capsule

• forces ions water glucose urea and other small molecules out of the capillaries down pressure gradient

• Through fenestrations of the endothelium,basement membrane

• Which acts as a filter

• Through gaps between podocytes

• Into lumen of bowman’s capsule

• Large proteins cannot pass so reman in blood

• This is glomerular filtrate

Describe how urea is removed from the blood

Hydrostatic pressure

Causes ultrafiltration at renal capsule

Through basement membrane

Enabled my small size of urea molecule

Describe how substances are transported from PCT to capillary

• Na+ are actively transported out of PCT into epithelial cell into the blood which carry them away,lowers the concentration of Na+ in these cells

• Na+ diffuse down conc gradient from lumen to epithelial cells through a co transport proetien bringing a glucose amino acid or cl-

• Co transported molecules diffuse into the blood down their conc gradient blood low conc because removed at renal capsule

• As ions leave the lumen of the PCT the water potential drops and water moves by osmosis through aqaporins into epithelial cell and then into blood

-ALL OF GLUCOSE REABSORBED

How are epithelial cells of PCT adapted to absorb

Microcilli large SA

lots of mitochondria -ATP FOR AT

Co transport carrier proteins

Specific carrier proteins for facilitated diffusion and active transport of specific molecules

Specific channel proteins for facilitated diffusion of specific molecules

Explain the role of the loop of henle in absorption of water from filtrate

In ascending limb sodium ions actively transported out of loop

Ascending limb impermeable to water

Lower water potential of medulla

Descending limb water moved out by osmosis

Longer the loop lower the water potential in tissue fluid of medulla

Water leaves DCT by osmosis

Describe importance of countercurrent multiplier

Filtrate flows in an opposite direction to blood

Maintains concentration gradient

Along whole LOH and capillaries so water and ions can be reabsorbed

Describe what occurs in DCT

all sodium ions actively transported out of loop filtrate is dilute

Medulla concentrated low wp

More water moves by osmosis out of tubules

All water reabsorbed into capillary

Explain the role of ADH in production of concentrated urine

When blood WP too low

Detected by osmoreceptors in hypothalamus

Pituitary secretes more ADH

ADH increases permeability of DCT by vesicles containing aquaporins fusing with the membrane

More water leaves DCT and is reabsorbed into the blood

By osmosis down WP gradient

Explain how ADH increases the movement of water from the lumen of the collecting duct into the blood

ADH releases vesicles containing aquaporins inserted in membrane

Water enters cell through aquaporins

By osmosis to capillary

Via interstitial fluid

Describe adaptations of glomerulus capillaries

Fenestrations between glomerular capillary endothelial cells

Gaps between podocytes

Basement membrane

Acts as a filter

Explain why urine concentration increases with thickness of medulla

Thicker medulla =longer loop of Henle

Increased concentrations of Na+ in medulla

Gradient maintained for longer/WP gradient maintained

More water reabsorbed fro. Loop

So urine more concentrated

Explain why the concentration of fluid in the PCT remains constant despite 99%of biological molecules being reabsorbed

Water is also reabsorbed

Describe how the secretion of ADH affects urine produced by kidneys

ADH increases permeability of cells in DCT /COLLECTING DUCT

More water absorbed from dct into blood

filtrate /urine more concentrated

Urine smaller volume

Explain how urea is concentrated in the filtrate

reabsorbtion of water by osmosis

At PCT/descending LOH

Due to active transport of Na+ions which creates gradient

Explain how lack of insulin affects reabsorbtion of glucose in the kidneys of a person who does not secrete insulin

High concentration of glucose in the blood

High concentration of filtrate

Not all glucose reabsorbed into blood by

Facilitated diffusiom/active transport by carrier proteins

Because they are occupied

The urine of a non diabetic person does not contain glucose explain why

leaves blood at kidney

Reabsorbed im proximal convoluted tubule

Some desert mammals have long loops of henle and secrete large amounts of Adh

Explain how these features are adaptations to living in desert

More water reabsorbed

By osmosis

From collecting duct/distil convoluted tubule

Due to longer LOH

Sodium ions absorbed from filtrate in ascending limb

Gradient established in medulla

ADH acts om collecting duct/distal convoluted tubule Due to

Makes cells more permeable /inserts aquaporins into plasma membrane

High blood glucose cause glucose to be present in the urine suggest how 6bii

Large amount /high conc of glucose in filtrate

If glomerular filtrate contains high conc of glucose produces larger volume of urine explain why

Glucose in filtrate lowers water potential

Lower after potential gradient