The Urinary
System

 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).

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 Pyramids : triangular tissue
 Calyces : cup-shaped tips of pyramids
 Renal Pelvis : basin of the kidney http://www.google.com/imgres

 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 .

 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 .
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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 .

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

 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).
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 The urinary bladder i s 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
.
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 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.

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

 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.