58 - Functions of the renal tubules. Transport through the different tubular sections. Excretion of diluted and concentrated urine. Renal excretion.

sections

function of renal tubule

parts of renal tubule

excretion of concentrated and diluted urine

renal excretion

function of renal tubule

1. Reabsorption: moving of solutes from the tubules back to the bloodstream

2. Secretion: transport of substances into the tubules in order to be excreted achieved by active transport.

   • These functions are regulated by the selective permeability of different parts of the tubules to water, sodium and the response of the distal tubules to hormones such as aldosterone, ADH and parathyroid hormone

parts of renal tubule

1. Proximal Convoluted Tubule: reabsorbtion of volume of solution filtered in glomerular apparatus

2. Loop of Henle: mainly located in the medulla of the kidney and has two parts - descending limb: water flows out by osmosis - ascending limb—primary role to concentrate the salt in tissue surrounding the Loop by pumping Na out of filtrate

3. Distal convoluted Tubule: located in the cortex of the kidney, reabsorbs calcium, sodium and chloride, regulates the pH of urine by secreting protons

4. Collecting duct -> passes through a renal pyramid, site of most water resorbtion by osmosis

excretion of concentrated and diluted urine

• low water intake (dehydration) -> plasma osmolality increases -> signal to osmoreceptors in the hypothalamus -> increased release of ADH from the pituitary gland into the blood stream -> kidneys will increase water absorption -> less water secreted with the urine -> concentrated urine with less water and more solute = high osmolality

• high water intake (over-hydration) -> low plasma osmolality -> signal to the osmoreceptors of the hypothalamus -> less release of ADH from the posterior pituitary gland -> kidneys will absorb less water -> more water secreted with the urine -> diluted urine with more water and less solute = low osmolality

renal excretion

• excretion of waste products is a major function of the kidneys,

• these substances are filtered through the glomerulurs into the glomerular capsule

• waste products can enter the urine when secreted out of the capillaries through the tubule cells and into the lumen.

• Clearance is the rate at which waste products are cleared from the blood by the kidney: each substance has a different rate according to its filtration characteristics