The Urinary System ANATOMY & PHYSIOLOGY

 The Urinary System removes salts and nitrogenous wastes, helps maintain water concentration, electrolyte balance, pH balance, fluid volume, control rbc production & blood pressure. Kidneys:  2 bean-shaped organs positioned retroperitoneally (in the back) Each kidney has:  an inner region called the renal medulla  an outer region called the renal cortex  within the renal cortex are the nephrons, or the functioning unit of the kidneys (more on them later). FUNCTIONAL REVIEW:

 Pyramids: triangular tissue  Calyces: cup-shaped tips of pyramids  Renal Pelvis: basin of the kidney KIDNEY ANATOMY:

 Help maintain homeostasis (regulate b.p., remove wastes for blood, control RBC formation, maintain volume of extracellular fluid) Renal Blood Vessels:  The renal arteries bring blood to the kidneys.  The afferent arterioles from the renal arteries to the nephrons.  The renal vein takes blood from the kidneys to the abdominal cavity. KIDNEY FUNCTIONS:

 Each kidney contains about 1 million nephrons.  Within the nephron is a network of blood vessels (capillaries) called the glomerulus.  The glomerular capillaries filter fluid.  The glomerulus is surrounded by the glomerular capsule. This receives the filtered fluid. NEPHRONS:

1. Glomerular filtration (within glomerular capillaries)  Glomerular capsule receives the glomerular filtrate (the tissue fluid of the body) which is mostly water & large protein molecules. 2. Tubular reabsorption is the reabsorption of water, electrolytes & glucose.  Returns substances into the internal environment that the body needs. (glucose, water, & amino acids are reabsorbed as well as vitamin C and many ions).  ADH and aldosterone (hormones) stimulate the reabsorption of Na+ and water. URINE FORMATION:

ADH and aldosterone regulate the kidneys & diuresis (urination).  Aldosterone is secreted by the adrenal gland; it stimulates the reabsorption of more Na+ and, therefore water (decrease in urination).  ADH is secreted by the hypothalamus in response to a decrease in [water] in the blood; this signals the reabsorption of water (decrease in urination).

3. Tubular secretion is last.  Wastes such as toxins (nitrogenous wastes) and hydrogen ions are eliminated.  Final product is urine. Urine is composed of water (about 95%), urea, & uric acid. URINE FORMATION: 1. Filtration 3. Secretion 2. Reabsorption

 If body fluids are in excess the filtration rate may increase.  If body fluids are low, the filtration rate may decrease (to conserve).  However, under normal circumstances filtration rate stays about the same. REGULATION OF FILTRATION RATE:

 Once urine is formed, it passes through collecting ducts through the kidney.  Urine then passes through the renal pelvis and a ureter, a tube connecting the renal pelvis to the bladder, and then to the urinary bladder.  The ureter has a flap-like mucous membrane that covers the opening which acts like a valve, preventing urine from backing up (urine goes only one way). URINE ELIMINATION:

 The urinary bladder is a muscular organ that stores urine.  It may hold up to 600 milliliters of fluid before pain receptors are triggered but usually at about 200 milliliters, the urge to urinate is triggered.  Urine then passes through the urethra.

 Micturition is urination.  This requires the relaxation of the external urethral sphincter (skeletal muscle) which is controlled voluntarily.

 Thirst mechanism: drives water intake  Osmoreceptors: w/in hypothalamus, activate thirst center (makes you thristy)  Antidiuretic hormone (ADH): prevents excess water loss (decreases urination); tells kidney to absorb more water.  Aldosterone: tells kidney to reabsorb Na+; when sodium is reabsorbed, so is water (water follows salt). Therefore, urine output is decreased. REGULATION OF WATER INTAKE & OUTPUT:

 Look up in text or online!  Know the following: anuria, kidney stones, incontinence, Addison’s disease, polyuria, & adult polycystic kidney disease

THE END!

 This slide show was developed by Dana Halloran,  Cardinal Mooney High School, Sarasota, FL.  Used with her personal permission,  adapted and amended by Rosa Whiting,  Manatee School for the Arts, Palmetto, FL.