THE URINARY SYSTEM

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THE URINARY SYSTEM
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Components

• 2 Kidneys
• 2 ureters
• Bladder
• Urethra

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Functions of the Kidneys

• Filter blood
• Form urine

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Contributions to Homeostasis

• Regulate blood ions sodium, chloride, potassium,
  calcium, phosphate
• Maintain osmolarity of blood
• Regulate blood volume
• Regulate blood pressuresecretes renin and can
  change renal resistance to blood flow
• Produce hormones calcitriol and erythropoetin
• Regulate blood glucose gluconeogenesis
• Excrete wastes and foreign substances

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Kidney Anatomy and Histology

• Retro peritoneal
• Between T5 and L3 vertebrae

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External Anatomy of Kidney

• Hilus
• Ureter
• Blood vessels
• Lymph vessels
• Nerves
• Renal capsule
• Adipose capsule
• Renal fascia

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Internal Kidney Anatomy

• Minor calyx
• Major calyx
• Pelvis
• Ureters
• Nephrons
• Sinus
• Calyces
• Pelvis
• Blood vessels
• Nerves
• Fat

• Cortex
• Medulla
• Pyramids
• Papillae
• Columns
• Lobes

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Internal Anatomy
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Blood Supply of Kidney

• Kidneys receive 20-25 cardiac output
• 1200 ml of blood/minute through kidneys

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Kidney Blood Supply
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Innervation of kidney

• Renal nerves
• Mostly sympathetic postgangionic nerves from
  celiac ganglion and inferior splanchnic nerves
• Changes amount of blood flow and blood pressure
• Results in changes in urine volume
• Stimulates release of renin
• RAA pathway leads to increase in sodium ion,
  chloride ion and water reabsorption
• Decreases urine volume
• Increases blood volume

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The Anatomy of the Nephron Functional Unit of
the Kidney

• Renal corpuscle
• Glomerulus
• Renal capsule (Bowmans capsule)
• Renal tubule
• PCT
• LOH
• DCT
• The DCTs empty into collecting ducts, which
  empty into papillary ducts

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Function of the Nephron

• Filters blood
• Returns useful substances to the blood.
• Removes unneeded substances.

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Functions of Corpuscle and Tubules

• Renal corpuscle
• Plasma is filtered
• Renal tubules
• filtered fluid passes through
• Some substances are returned to the blood, others
  are added from the blood.
• The final result after the fine tuning in the
  tubules is urine.

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Flow of Fluid
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Differences Between Cortical and Juxtamedullary
Nephrons (nephrons)

• Cortical nephrons have glomeruli in the cortex
  and short loops of Henle that penetrate only
  into the superficial medulla.
• Juxtamedullary have glomeruli deep in the cortex.
  They have long loops of Henle that extend deep
  into the medulla almost to the renal papilla.

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Location of Corpuscles

• Always in cortex
• Deeper cortex contains corpuscles of
  juxtamedullary nephrons

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Corpuscle Anatomy

• Glomerulus
• Fenestrated capillaries
• Afferent arteriole leads in
• Efferent arteriole leads out narrower than
  afferent to raise b.p. in glomerulus
• Bowmans capsule
• Parietal layer SSE
• Bowmans space
• Visceral layer SSE
• Podocytes
• Pedicels
• Filtration slites between pedicels

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The Corpuscle Glomerulus and Bowmans Capsule
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NET FILTRATION PRESSURE
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• Compare these values to a typical systemic
  capillary

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The Filtration Membrane

• Fenestrated endothelium
• Cells
• Basal lamina (basement membrane encircling one or
  more capillaries)
• Large proteins
• Filtration slits
• Medium sized proteins

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Filtration

• High blood pressure in the glomerulus forces
  fluid through the filtration membrane
• Filtrate is trapped in Bowmans space
• Filtrate contains metabolic waste, but also
  useful substances like water, sodium, amino acids
  that must be reclaimed
• Cells and most proteins are stopped by the
  filtration membrane and remain in the capillary

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• Filtrate is squeezed out of the glomerulus into
  the capsule.
• About 180 liters/day is produced in the male, and
  about 150 liters in the female.
• Ninety nine percent of the filtrate is returned
  to the blood through reabsorption.

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The Juxtaglomerular Apparatus

• Macula densa (cells of the DCT next to the
  afferent and efferent arterioles)
• Juxtaglomerlular cells (modified smooth muscle
  cells in the afferent and efferent arterioles)

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Function of Juxtaglomerular Apparatus

• Detects blood pressure changes
• Secretes renin when blood pressure falls
• This begins the renin-angiotensin II- aldosterone
  pathways that raise blood pressure by increasing
  blood volume.

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Relation of Blood Volume and Blood Pressure to
Urine Volume

• Raising blood volume, which increases blood
  pressure, is accomplished by creating a more
  concentrated urine, and returning as much water
  as possible to the blood.

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Three Factors That Cause Large Volumes of
Filtrate Production

• 1. Large surface area of glomerulus the
  mesangial cells, which are located in the
  glomerulus and in the cleft between the two
  arterioles, regulate the area available by
  contracting or relaxing.

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• 2. The thinness and porosity of the filtration
  membrane
• 3. The high glomerular blood pressure due to the
  efferent arteriole having a smaller diameter.

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Glomerular Filtration Rate

• GFR refers to the amount of filtrate produced by
  both kidneys/minute.
• GFR125ml/min for males
• GFR105ml/min for females

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Regulation of GFR

• Adjusting the flow into and out of the glomerulus
  through contriction or relaxation of afferent
  arteriole or efferent arteriole.
• e.g., Constriction of afferent will reduce
  filtrate.
• Altering glomerular capillary surface area by the
  mesangial cells.

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Three Mechanisms of GFR Regulation

• 1. Autoregulation keeps GFR fairly constant,
  despite changes in BP
• Myogenic
• Tubuloglomerular feedback

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Myogenic Autoregulation

• Occurs when stretching triggers contraction of
  smooth muscle in afferent arteriole. The lumen
  constricts and GFR decreases occurs when BP is
  elevated and prevents overproduction of filtrate.
  The opposite occurs when BP if low

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Tubuloglomerular Feedback

• If BP increases,GFR increases
• Fluid flows too fast for proper reabsorption of
  sodium ion, chloride ion and water.
• The macula densa detects this, and inhibits
  release of NO, a vasodilater, from JG cells
• Afferent arterioles constrict.
• This decreases GFR.
• Urine volume decreases.
• The opposite occurs when BP falls

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• 2. Neural regulation of GFR
• Sympathetic division of ANS releases NE. This
  causes moderate constriction in both arterioles
  and a slight decrease in GFR. If a very large
  amount of NE is released, however, the afferent
  arteriole constricts the most and GFR decreases
  greatly.
• The sympathetic division also causes release of
  renin from JG cells. This leads to the
  production of angiotensin II, which decreases
  GFR.

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3. Hormonal Regulation of GFR

• Angiotensin II reduces GFR by narrowing both
  arterioles.
• ANP increases GFR by relaxing mesangial cells and
  decreasing BP.

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Reabsorption

• Removal of water and useful substances from
  filtrate through osmosis (water), diffusion or
  carrier proteins active and passive processses
  occur
• Substances enter peritubular fluid and then blood
  in these capillaries

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Secretion

• Waste, toxins, drugs move from capillaries
  surrounding tubules into peritubular fluid and
  then into the filtrate

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Mechanisms of Tubular Reabsorption and Secretion

• Movement is either transcellular or
  paracellular.
• Transport may be passive or active, depending on
  gradients.
• Active processes may involve symporters or
  antiporters

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The Tubules

• Proximal convoluted
• Loop of Henle
• Distal Convoluted
• Collecting duct

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The Ducts

• The collecting ducts receive fluid from several
  DCTs.
• Urine then goes into papillary ducts, then minor
  calyxes, major calyxes, pelvis, and ureter

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Histology of the Tubules and Collecting Ducts

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The Tubules and Their Functional Regions
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Secretion and Reabsorption

• Substances are reabsorbed into the blood. These
  are things the body needs to keep, for example
  water.
• Substances are secreted into the filtrate from
  the capillaries surrounding the tubules. This is
  the final chance to dump unneeded substances into
  the developing urine.

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2 Routes of Tubular Reabsorption

• 1. Paracellular reabsorption between adjacent
  cells
• Various ions (up to 50 of some) and the water
  that follows them
• 2. Transcellular reabsorption through tubular
  cells.
• Substances must pass from the lumen of the
  tubule through the apical membrane, cytosol, and
  basolateral membrane into the interstitial fluid,
  and then from there into the capillary.

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Two Types of Active Processes

• 1. Primary active transport works against
  gradients, uses ATP. e.g., Sodium pumps
• Secondary active transport uses the high
  gradients produced in primary active transport to
  drive another material across the membrane
  against its own gradient.
• Symporters move the two materials in the same
  direction.
• Antiporters move the two materials in opposite
  directions.

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The Transport Maximum

• Upper limit of how fast a transporter can work

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Glucosuria

• Blood Glucose Is Over 200 MG/ML. This is a sign
  of diabetes mellitis.
• It occurs because the sodium-glucose symporters
  cannot work fast enough.

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PCT

• 65 of filtrate reabsorbed and returned to blood
  water, sodium, glucose, A.A.S
• Secretion into the tubule from blood also occurs
  to remove more wastes urea, uric acid, bile
  salts, ammonia, catecholamines, creatine,
  hydrogen ion and bicarbonate ion.

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LOH

• Reabsoprtion of water, sodium ion, potassium ion,
  chloride ion
• The loops of juxtamedullary nephrons have a thick
  and a thin segment. The thick segment is
  impermeable to water
• Secretion of urea

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LOH

• Has descending limb, hairpin turn, ascending limb
• 20 of nephrons are juxtamedullary and have long
  LOHs
• Have a thin region that can reabsorb water and
  thick region that cannot
• Served by the vasa recta, a series of long
  capillaries
• Produce very concentrated or very dilute urine
  due to osmotic differences achieved by the thick
  and thin regions of the loop.

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• The long loops of the juxtamedullary nephrons
  enabale the kidney to make concentrated or dilute
  urine. If the body is dehydrated, concentrated
  urine is produce, thus conserving water.
  Conversely, if the body is overhydrated, dilute
  urine is produced.

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DCT

• The DCT is subject to hormonal control of PTH for
  increased resorption of calcium ion
• The end of the DCT is subject to further hormonal
  control
• Angiotensin decreases filtration and decreases
  urine output
• Aldosterone also decreases urine output
• ADH decreases urine output
• ANP increases output.
• PTH increases calcium ion reabsorption

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Reabsorption and Secretion in DCT

• First part of duct
• Water sodium, chloride, calcium ions
• Late duct principal cells
• Reabsorb sodium
• Secrete potassium
• Late duct intercalated cells
• Reabsorb potassium
• Secrete hydrogen ion

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Collecting Ducts

• Principal cells
• Reabsorb sodium
• Secrete potassium
• Intercalated cells
• Reabsorb potassium
• Secrete hydrogen ion
• Final chemical composition of urine is determined
  in the collecting ducts

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Hormonal Control of Collecting Ducts

• Angiotensin II decreases filtration and decreases
  urine output
• Aldosterone also decreases urine output
• ADH decreases urine output
• ANP increases output.

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Formation of Dilute Urine

• Occurs in the absence of ADH
• Water leaves filtrate in the descending LOH,
  producing a filtrate that is more concentrated
  than blood
• Only solutes, though, leave in the ascending LOH,
  producing a dilute filtrate, whose osmolarity is
  less than blood (solute/solvent ratio is less
  than blood)
• Filtrate continues to become more dilute in DCT
  and CT as more solutes and only a little water
  leave.

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Formation of Concentrated Urine

• Involves juxtamedullary nephrons and the presence
  of ADH
• A high osmotic pressure is established deep in
  the medulla with sodium, chloride and urea
  through a process called the countercurrent
  multiplier
• The filtrate leaving the ascending LOH has the
  same osmolarity (solute/solvent) as blood
• Even more water leaves the filtrate as it passes
  through the last part of the DCT and CD.

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Pathways of Water Reabsorption

• Obligatory
• Aquaporin Is
• Facultative
• Aquaporing IIs
• In presence of ADH
• Only in distal part of DCT and CD

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Obligatory

• Obligatory water transport occurs when water
  follows the sodium ions, chloride ions, and
  glucose that is reabsorbed. This is an osmotic
  process where glucose is concerned. Owt occurs
  in the pct and des loh. These areas are always
  water permeable. 90 of water resorption occurs
  in these regions.

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Facultative

• Facultative water reabsorption means that the
  cells are capable of adapting to need by adding
  or deleting aquaporin-2s (water channels).
• Facultative water reabsorption occurs in the last
  part of the dct and in the collecting ducts
• It is dependent on ADH
• Accounts for the last 10 of water resorption

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NOTE THAT SODIUM ION AND WATER ARE REABSORBED IN
ALL PARTS OF THE TUBULES.
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Evaluating Kidney Function

• Urinalysis
• Volume, physical chemical and microscopic
  properties
• Blood tests
• BUN rises with decrease in GFR
• Plasma creatinine rises with poor renal function
• Renal plasma clearance volume of blood cleared
  of a substance per unit time
• Creatinine clearance measures GFR
• Paraaminohippuric acid administered IV and used
  to measure plasma flow through kidneys per minute

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Dialysis

• Artificial filtering of blood through a
  selectively permeable membrane.
• Osmotic pressures are created to draw wastes from
  the blood into the dialysis solution.

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Layers of the ureters, bladder and urethra

• Mucosa
• Muscularis
• Adventitia

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Anatomy beyond the kidney

• Ureters
• Carries urine to bladder
• Trigone
• Triangular region formed by ureters and urethra
• Detrussor muscle
• muscularis
• Urethra
• Has internal and external sphincters

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Female Anatomy
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Male Anatomy
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Male Urethra

• Prostatic
• Membranous
• Spongy

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One More Definition

• Micturation means to expel urine.

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