Urinary System

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Urinary System
Kidneys formation of urine -contains the
functional unit for filtration
Nephron -production of urine, absorption of
water and salts Ureters transfer of urine from
kidneys to bladder Urethra transfer of
urine from bladder to outside - longer into
the male (20 cm vs. 4 cm in the female)

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Kidneys

• 10-12 cm
• retroperitoneal behind the peritoneum
• not part of peritoneal cavity
• surrounded by three layers of tissue
• 1. deepest layer renal capsule transparent
  sheet of dense irregular connective tissue
• 2. middle layer adipose capsule
• 3. outer layer renal fascia
• divided internally into an outer cortex and an
  inner medulla
• medulla consists of 8 to 18 cone-shaped regions
  called renal pyramids
• the wider base faces towards the cortex, the
  narrow region (renal papilla) projects down into
  a cup-like structure called a minor calyx
• renal cortex is divided into an outer cortical
  zone and a deeper juxtamedullary zone
• the cortex also extends down in between the
  pyramids to form the renal columns
• renal lobe renal pyramid the overlying renal
  cortex ½ the adjacent renal colum

-the renal cortex and renal pyramids constitute
the functional portion of the kidney
parenchyma -this parenchyma is comprised of
the nephrons
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kidney
URETER
URETER
BLADDER
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Renal Papilla
Renal Pyramid
Minor Calyx
Major Calyx
Renal Cortex
Renal Pelvis
Renal Medulla
URETER
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Blood supply

• supplied by a renal artery and drained by a renal
  vein(s)
• kidney receives 20-25 of the resting cardiac
  output through the renal arteries (1200mL per
  minute)
• renal artery divides into segmental arteries
  supply segments of the kidney
• the segmental arteries give off branches that
  pass through the renal columns interlobar
  arteries
• at the base on the renal pyramids between the
  medulla and cortex they are called arcuate
  arteries
• divisions from the arcuate are called the
  interlobular arteries (pass between the renal
  lobes)
• the afferent arterioles are derived from the
  interlobular arteries
• afferent arteriole supplies one nephron and forms
  the glomerulus (capillary network)
• drainage of the glomerulus is via the efferent
  arteriole
• efferent arteriole forms the peritubular
  capillary network which surround the upper
  portions of the nephron
• an extension of this network covers the lower
  portion of the nepron vasa recta
• the peritubular capillaires form the interlobular
  veins arcuate veins interlobar veins renal
  vein

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The Nephron
-about one million nephrons -kidneys filter 180 L
fluid per day!!!! -each nephron is a renal
corpuscle renal tubules -renal corpuscle
filtering unit consisting of a tangled cluster of
capillaries -gt glomerulus -tubules for
reabsorption of water and ions leading to final
urine volume and composition
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Glomerulus

• glomerulus capillary tangle derived from
  afferent arterioles (into) and lead into efferent
  arterioles (out)
• surrounded by a glomerular capsule (Bowmans
  capsule) layer of epithelial cells
• glomerular capsule site of initial filtration
  and the first step in the formation of urine
• consists of visceral and parietal layers
• visceral layer consists of modified epithelial
  cells on top of the glomerulus podocytes
• the podocytes wrap around the endothelial cells
  of the glomerular capillaries and forms the
  filtration membrane together with the endothelial
  cell wall
• space between the visceral and parietal layers
  glomerular capsule

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PCT

• proximal convoluted tubule first area of
  reabsorption into blood -gt Loop of Henle
  -gt distal convoluted tubule -gt collecting
  duct -gt union of ducts into ureter
• PCT and DCT surrounded by the peritubular network
  of capillaries for reabsorption back into the
  blood, LH is covered with the vasa recta
• PCT is the site of water reabsorption (PASSIVE) -
  associated with the ACTIVE reabsorption of sodium
  and potassium ions
• active Na and K uptake into the blood is by
  sodium pumps in the cells of the PCT- sodium
  pumped from the PCT and chloride, bicarbonate and
  phosphate ions follow it - salt reabsorption
• the active transport of ions into the blood
  plasma increases osmotic pressure within the
  blood
• therefore water moves out of the PCT into the
  capillaries PASSIVELY!
• PCT reabsorbs about 70 of filtered Na, ions and
  water
• the apical surface of the PCT epithelium forms
  microvilli which increases the surface area of
  this region

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Loop of Henle

• active transport of Na continues through the
  loop of Henle and DCT
• descending loop of Henle is quite permeable to
  water but impermeable to solute movement urine
  becomes hypertonic (increased ions within the
  urine, decreased water)
• ascending loop is the opposite permeable to
  salt (salt pumped out of the urine back
• into the blood plasma)

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DCT and Collecting Duct

• two types of cells found in the DCT
• principal cells receptors for ADH and
  aldosterone
• intercalated cells play a role in the
  homeostasis of blood pH
• DCT and collecting duct are impermeable to water
  !!!!
• the DCT and CD become permeable upon action of
  hormones

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Renal Physiology

• 1. Glomerular filtration
• water and most solutes ion the blood plasma move
  across the glomerular capillaries into the
  Bowmans capsule and then into the renal tubule
• 2. Tubular reabsorption
• tubule cells reabsorb about 99 of the filtered
  water and many of the solutes
• return to the blood through reabsorption into the
  peritubular capillary network
• reabsorption return to the blood
• absorption entrance of new materials into the
  blood (e.g. via digestive absorption)
• 3. Tubular secretion
• tubular cells also secrete other materials
  wastes, drugs, excess ions into the urine
• this also removes these materials from the blood

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Urinary System Function 1. Excretion of
Metabolic Wastes nitrogenous wastes -Urea
by-product of amino acid metabolism
-produced when ammonia carbon
dioxide -Creatinine produced by breakdown of
creatine phosphate (high energy molecule
reserve of muscles) -Uric acid by-product of
nucleotide breakdown -insoluble and ppts in the
blood, concentrates in joints - gout 2.
Water-Salt balance of blood reabsorption into
blood from the descending Loop of Henle, from
collecting duct -reclaim salt from the ascending
portion of Loop of Henle -reclaim urea from
bottom section of collecting duct -release of
anti-diuretic hormone by pituitary increase
reabsorption of water 3. Acid-Base balance of
blood reabsorption of bicarbonate ions from
urine in the nephron decreases levels in blood
(decreases carbonic acid levels) -movement of
hydrogen ions from blood into the nephron,
combines with ammonia to form ammonium (NH4)
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4. Secretion of hormones release of renin by
kidneys which leads to release of aldosterone
by adrenal glands (reabsorption of salts by
kidneys) -release of erythropoietin by kidneys
(stimulates RBC production) -activation of
vitamin D produced by the skin
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WATER BALANCE -average intake - 2.5 L (60 from
drinking water, 30 from moist foods, 10
byproduct of metabolism) -regulation of intake -
thirst center within the hypothalamus e.g. as
body loses water - osmoreceptors within the
thirst center detects increase in osmotic
pressure within the ECF tells us to drink to
decrease OP into normal range -drinking distends
the stomach which inhibits signalling from the
thirst center PLUS osmotic pressure becomes
normal again -water is lost through urine, feces
and sweat plus respiration and skin
evaporation -2.5 L of water must be lost for
water balance -60 lost in urine, 6 in feces,
6 in sweat, 28 evaporation from skin and
lungs -primary means of controlling output is
through urine production
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Water Balance -extracellular fluids/ECF blood
plasma, interstitial fluids, CSF, lymph
etc. -intracellular fluids/ICF cytosol -of the
40 liters of water in the average male - 37 is
ECF and 63 is ICF -blood pressure and osmotic
pressure control the movement of fluid between
ECF and ICF e.g. blood pressure causes the
movement of fluid out of the capillaries into
the interstitial spaces of the tissue (between
cells) some will move into the cells and
become cytosol -BUT osmotic pressure causes
fluids to leave the cells and tissues and enter
the capillaries -dehydration blood plasma loses
water (becomes concentrated) - increases osmotic
pressure/OP of the plasma -OP increase is
detected by osmoreceptors in hypothalamus -poster
ior pituitary gland releases anti-diuretic
hormone (ADH) -ADH causes distal convoluted
tubule and collecting duct to increase water
reabsorption back into blood and OP comes back
down to normal urine volume drops -excess
water intake plasma less concentrated - decrease
in OP -osmoreceptors signal to the post.
pituitary- decreases ADH release and nephrons
decrease water reabsorption urine volume goes
up