BIO224 unit 5: nephron

renal cortex

• glomerulus

• bowman’s capsule

• afferent and efferent arteriole

• proximal and distal convoluted tubule

renal medulla

• descending and ascending loop of henle

• peritubular capilaries

renal cortex

collecting duct

1. glomerular filtration

non-selective filtering of blood into tubule forming the primary urine

2. tubular reabsorption

absorption of substances needed by body from tubule to blood

3. tubular secretion

selective secretion of substances to be eliminated from the body into tubule from blood

4. excretion

the resulting fluid, containing waste is urine

glomerular filtration

• separation of plasma fraction of the blood

• driven by blood hydrostatic pressure

• ultrafiltration

• leaky capillaries

• podocytes

forces in glomerular filtration

• determined by opposing forces

• blood pressure favors filtration

• high conc of proteins opposes filtration

• hydrostatic pressure opposes filtration

proximal tubule

• reabsorbs filtered water, Na and Cl, and glucose and amino acids

• secretion of organic ions and certain protons

• exchange done through single layer of epithelial cells

• exchange is transcellular (through cell) or paracellular (between cells)

loop of henle

• establishes osmotic gradient in medulla

• reduces osmotic pressure of filtrate to 100 mOsm

loop of henle: descending limb

• permeable to water

• NOT permeable to NaCl

• filtrate concentrates in medulla

loop of henle: ascending limb

• activate Na and Cl reabsorption

• impermeable to water

• concentrate the interstitial fluid in medulla

• dilute the ultrafiltrate

role of urea

• contributes to the osmotic gradient

• produced and accumulates in the medulla

distal convoluted tubule

• fluid that reaches it is 20% of the original filtered vol

• fluid is hypotonic relative to plasma

• 7.5% of filtered Na id reabsorbed here and in the collecting tubule

• not usually permeable to water but later nephron segments are

collecting duct

• concentrates the urine by exploiting the osmotic gradient in the medulla

• permeable to water

antidiuretic hormone regulatory system

• influences water and permeability in the collecting duct and distal convoluted tubule

• negative feedback when high salt or alcohol consumed

protonephridia

• network of closed tubules throughout the body

• interstitial fluid filters into the lumen at flame bulb

• freshwater flatworms: osmoregulation, most waste diffuses out of body

• parasitic flatworm: isotonic environment, secretes N wastes

metanephridia

• annelids, mollusks, arthropods

• filters coelomic fluid

• takes small solutes and wastes

• tubules reabsorb NaCl and other solutes

• osmoregulation and nitrogenous wastes

malpighian tubules

• insects

• no tubules, part of hind gut

• closed tubules that secrete K and Cl into the lumen

• osmoregulation and nitrogenous waste excretion

salt glands

• found in elasmobranchs, birds, reptiles that live in saltwater or deserts

• secrete hyperosmotic NaCl solution

• active NaCl transport