urinary system. overall functions excretion – remove nitrogenous wastes from blood osmoregulation...
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Urinary System
Overall Functions
• Excretion – remove nitrogenous wastes from blood
• Osmoregulation – maintain proper balance of ions
• Volume regulation – maintain proper balance of water
• Regulation of pH• Detoxify superoxides, free radicals and some
types of drugs.
Why 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 acids
• Creatinine is a waste product from creatine metabolism.
The 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.
AortaInferior Vena Cava
Renal ArteryRenal Vein
Kidney
Ureter
Urinary Bladder
Urethra
Tubule system(produces urine)
Calyx(funnel-like Structure thatCollects urine fromTubules)
Pelvis of theKidney
ureter
Cortex
Medulla
The Nephron is the Functional Unit of the Kidney
GlomerulusAfferentArteriole
EfferentArteriole
Bowman’s Capsule
Proximal Convoluted tubule
Loop of Henle
DistalConvolutedTubule
Collecting Duct
Urine is carried to Calyx,Pelvis and then the Ureter
Functions of the Nephron1. 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+, HCO3
The 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.
Functions of the Nephron2. Reabsorption
Reabsorption is a process that 1. Utilizes active transport pumps 2. Occurs in the proximal and distal tubules 3. Reclaims nutrients that were lost during the filtration process. 4. Returns the nutrients to the blood
Examples of reabsorbed substances 1. glucose 2. amino acids 3. NaCl
NOTE: water is reabsorbed passively by osmosis.
Functions of the Nephron3. Tubular secretion
Secretion is a process that 1. Utilizes active transport pumps 2. Occurs in the proximal and distal tubules 3. Adds wastes from the blood that were not effectively filtered at the glomerulus. 4. Increases the concentration of wastes in the urine
Examples of secreted substances 1. Ammonia, H+ (smaller ionic) 2. histamine, creatinine (larger, organic) 3. penicillin
Glomerular Filtration RateThe 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 of afferent and efferent arterioles. * overall blood pressure
What 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.
Regulation of Na+ ReabsorptionIf 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 . . . .
Regulation of Urine Volumecoordinate function of Loop of Henle and the Collecting Duct
Na+
Na+
Na+
Na+
Na+
Four Times SaltierThan the Blood