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Urinary System Functions of the Urinary System 1. Excretion of metabolic wastes 2. Maintenance of water-salt balance 3. Maintenance of acid-base balance 4. Secretion of hormones Components Consists of organs that produce, store, and rid the body of urine Kidneys: - bean shaped, fist sized, reddish brown - produce urine - protected by lower ribs Renal Artery and Renal Vein: - enter/leave on concave side of kidney Ureter: -muscular tubes that carry urine from kidneys towards bladder by peristalsis Components Urinary Bladder: - stores urine (can hold up to 600 ml) - hollow, muscular organ - expands as urine enters - small folds of bladder mucosa act like valve to prevent urine from going back up ureters - two sphincters control the exit of urine from the bladder to the urethra - internal sphincter is composed of smooth muscle – involuntary control - external sphincter is composed of skeletal muscle – voluntarily controlled Components Urethra: - carries urine from bladder to external opening - shorter in women, thus more easily permits infection of urinary tract - in men, urethra is surrounded by prostate gland – if it enlarges, it can restrict flow of urine - in men, urethra also carries sperm during ejaculation Nervous System and Urination • Stretch receptors and sensory nerve impulses to empty bladder are sent to spinal cord when bladder fills (250 ml) • Motor nerve impulses from the spinal cord cause the bladder to contract and the sphincters to relax • Urination occurs • In older children and adults, the brain controls the reflex Functions of the Urinary System 1. Removal of the nitrogenous wastes (excretion) A. Urea - Amino acid metabolism (in liver) → ammonia ammonia + CO2 → urea - ammonia is very toxic to cells, urea is less toxic B. Creatine Phosphate - a high energy phosphate reserve molecule in muscles - break down → creatinine - Creatinine is excreted by the kidneys Functions of the Urinary System C. Nucleotides - breakdown of nucleotides = Uric Acid - excreted by kidneys - too much in blood causes it to precipitate out into crystals which accumulate in the joints = Gout Functions of the Urinary System 2. Maintain the water-salt balance - kidneys maintain the appropriate amount of ions (e.g. potassium, bicarbonate, calcium) in the blood - salts cause diffusion of water into the blood, therefore, more salts, more water, more blood… more blood pressure - in this way the kidneys are involved in regulating blood pressure Functions of the Urinary System 3. Maintain the Acid-base balance of blood - blood pH should be 7.4 - kidneys monitor and control pH by excreting H+ or reabsorbing HCO3- ions as needed - urine usually has a pH of 6 due to acidic foods in diet Functions of the Urinary System 4. Hormonal Function a. Secretes erythropoietin when oxygen carrying capacity is reduced – stimulates RBC production b. Helps activate vitamin D c. Secretes renin – leads to secretion of aldosterone from adrenal glands (on top of kidneys) which causes reabsorption of sodium ions