2Overall Functions Excretion – remove nitrogenous wastes from blood Osmoregulation – maintain proper balance of ionsVolume regulation – maintain proper balance of waterRegulation of pHDetoxify superoxides, free radicals and some types of drugs.
3Why are nitrogenous wastes a problem? Ammonia is a moderately strong base (elevates blood pH).Urea is a weaker base made from ammonia and carbon dioxide in the liver – less toxic than ammonia (NH3)Uric Acid is a waste produced from the metabolism of nucleic acidsCreatinine is a waste product from creatine metabolism.
4The kidneys only comprise about 0.5% of the total body weight, butthey receive 1,200 mL of bloodper minute; about 20% of theTotal cardiac output.Kidneys are constantly cleaning,balancing ions and water, and adjusting thepH of the blood.
6Tubule system(produces urine)Calyx(funnel-likeStructure thatCollects urine fromTubules)Pelvis of theKidneyCortexMedullaureter
7The Nephron is the Functional Unit of the Kidney Proximal Convoluted tubuleBowman’s CapsuleGlomerulusAfferentArterioleCollecting DuctEfferentArterioleDistalConvolutedTubuleUrine is carried to Calyx,Pelvis and then the UreterLoop of Henle
8Functions of the Nephron 1. Filtration The glomerulus is made of “fenestratedcapillaries” that are unusually permeable.All of the following substances can easily filter out of the glomerulus and into Bowman’s capsule.waterglucose (and other sugars)amino acidssmall organic moleculesammonia, urea, uric acidsalts, H+, HCO3The only substances that are not usually filtered out are blood cells, proteins and larger organic molecules.Notice that several important nutrients are filtered out of the blood duringthe filtration process.
9Functions of the Nephron 2. Reabsorption Reabsorption is a process that1. Utilizes active transport pumps2. Occurs in the proximal and distal tubules3. Reclaims nutrients that were lostduring the filtration process.4. Returns the nutrients to the bloodExamples of reabsorbed substances1. glucose2. amino acids3. NaClNOTE: water is reabsorbed passively by osmosis.
10Functions of the Nephron 3. Tubular secretion Secretion is a process that1. Utilizes active transport pumps2. Occurs in the proximal and distal tubules3. Adds wastes from the blood that were noteffectively filtered at the glomerulus.4. Increases the concentration of wastes inthe urineExamples of secreted substances1. Ammonia, H+ (smaller ionic)2. histamine, creatinine (larger, organic)3. penicillin
11Glomerular Filtration Rate The two kidneys produce nearly 45 gallons (180 liters) of filtrate per day.Glomerular Filtration Rate (GFR) depends almost completely on hydrostatic pressure in the glomerulus.* dilation or constriction ofafferent and efferent arterioles.* overall blood pressureWhat happens in exercise when blood pressure may increase up to 200 mm Hg or more?During exercise, the sympathetic nervous system comes into play. Symp. Nerves stimulate the afferent arteriole and it constricts.
12Regulation of Na+ Reabsorption If blood pressure is low for an extended period of time, the kidney reacts by releasing an enzyme called renin.Renin is involved in a series of reactions that ultimately lead to the release of a hormone called Aldosterone from the adrenal gland.Aldosterone is a steroid that acts on the distal convoluted tubule and increases the rate of NaCl reabsorption.As the concentration of NaCl increases in the blood, water is reabsorbed at a faster rate (osmosis).With more salt and water in the blood, the volume of blood goes up and blood pressure goes up.Impact of diet and strenuous exercise
13Regulation of Urine Volume coordinate function of Loop of Henle and the Collecting Duct Four Times SaltierThan the Blood