Only need 50% function of kidneys

I. Nephrons – filtering units 1.25 million per kidney Afferent arteriole – small branch of the renal artery at each nephron Glomerulus – capillary bed with fenestrations (small slits) that open when blood pressure increases 1. Diameter of efferent tubule smaller than that of afferent tubule – causes high pressure in the glomerulus

Ultrafiltration – process by which substances are filtered through the glomerulus Filtrate passes through basement membrane – prevents proteins and other large molecules from becoming part of the filtrate

Filtrate enters proximal convoluted tubule Portion not in filtrate exits through efferent arteriole (blood cells, proteins, etc.)

Reabsorption There is good stuff in filtrate (water, ions, glucose) that you don’t want lost in urine Moved from proximal convoluted tubule to surrounding capillary bed Proximal convoluted tubule wall is only 1 cell thick, contain microvilli Interior tube called lumen

Salt ions – active transport Water – osmosis a. As salt is transported out, water follows Glucose – active transport – 100% of glucose goes back to blood (would only be 50% if done by diffusion)

III. Osmoregulation – Control of solute concentrations and balance of water gain/loss A. Depends on volume of water ingested, perspiration rate, ventilation rate

B. Loop of Henle - extends into medulla (very hypertonic – more solutes in blood than in tubule) a. Descending loop – relatively permeable to water but mostly impermeable to salt b. Ascending loop – relatively permeable to salt but mostly impermeable to water

ADH – antidiuretic hormone 1. Secreted by pituitary gland in the hypothalamus in brain, target cells are the cells of the collecting ducts 2. Filtrate reaching collecting duct is hypotonic (high water content) – water diffuses into blood 3. Collecting ducts are in the medulla (hypertonic)

Collecting ducts permeability to water is dependent upon the presence/absence of ADH a. Absent - impermeable  water stays in (goes out with urine) b. Present - permeable  water moves out

III. Kidneys and your health Dialysis – blood taken out, run through machine that uses principles of diffusion to “clean” blood, put back into body

B. Urinalysis – used to determine kidney function 1 B. Urinalysis – used to determine kidney function 1. Glucose – active transport moves all in filtrate back into blood – should not be in urine a. Diabetes – very high sugar content in blood – too much for kidneys to actively transport back to blood – sugar in urine

2. Blood cells and proteins - too large to fit through basement membrane of glomerulus – only found in urine if infection is increasing permeability of glomerulus or bleeding is occuring in urinary tract 3. Urea – because water is reabsorbed, concentration increases in collecting ducts and is high in urine 4. Drugs – most end up in the filtrate and urine