Kidney Function: Urine Produciton

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Kidney Function Urine Produciton

• Three main mechanisms for waste elimination
• ________________ of blood
• ________________of useful substances into
  bloodstream
• ______________ of waste products from blood into
  tubules of nephron.

Step 3 Step 2 Step 1
Peritubular capillary
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Terminology

• ____________- passage of water from weaker to a
  stronger solution across a semi-permeable
  membrane.
• ____________- passage of a substance from a high
  concentration to a low concentration.
• ________________-passage of a substance from the
  lumen of the renal tubules into the renal
  capillaries and so back into circulation this is
  an active process and requires energy.
• ________________- passage of a chemical substance
  from the renal capillaries into the lumen of the
  tubules and out of the body in the urine this is
  an active process and requires energy.

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Step 1 Filtration of the Blood

• Occurs in ___________ ______________
• Glomerular capillaries contain large
  fenestrations in the epithelium. Higher blood
  pressure in the glomerulus, plus the large
  fenestrations, allow fluid (plasma) to enter the
  capsular space, but do not allow blood cells or
  large proteins to pass through.
• ______________ _______________ when it enters
  capsular space.
• Similar to plasma except contains very little or
  no proteins.
• Proteins in urine are an abnormality and may be
  due to capillary damage in the glomerulus.

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Glomerular Filtration Rate

• Speed (ml/min) that plasma is filtered as it
  passes through the glomerulus.
• Depends on rate of blood flow to the kidneys
• Reabsorption helps reduce volume of glomerular
  filtrate.
• For every 100L of fluid filtered from the blood
  only 1 L is produced as urine.
• Ex a 180 lb man produces 280 L of glomerular
  filtrate daily, but only urinates 2 L daily
• 99 of original filtrate is reabsorbed back into
  blood.

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Step 2 Reabsorption

• __________________ takes useful substances from
  the tubules back into the blood.
• Most takes place in the ______ (65) but may also
  take place in Loop of Henle (10), or DCT and
  collecting ducts (24).
• Many substances in tubular filtrate are still
  useful
• Na, K, Ca, Mg, Cl-, HCO3-, Glucose, acids,
  H2O
• Substances to be reabsorbed pass out of tubular
  lumen thru or between tubular epithelial cells
• Enter interstitial fluid ? peritubular
  capillaries

capillary
H2O Ions Na, K, Ca, Mg Glucose, AA, Vit
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Na Reabsorption

• Sodium is the most abundant ion in the tubular
  filtrate
• Attaches to a carrier protein that carries it
  from the tubular filtrate, into the cytoplasm of
  the PCT epithelial cell, into the interstitial
  fluid, and finally the peritubular capillaries.
• _______ ions are also reabsorbed in ascending
  loop of Henle and DCT
• ____________ and _______________ attach to same
  carrier protein and follow Na into cell (Na
  cotransport no extra energy required)
• _____ then diffuses out thru K channels (leakage
  channels)
• _______ follows cations
• _______ follows Na via osmosis
• ________ also gets reabsorbed

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Potassium Reabsorption

• Diffuses out of tubular filtrate by moving
  between epithelial cells and into interstitial
  fluid before into peritubular capillaries.
• Takes place in the PCT, ascending part of Loop of
  Henle, and DCT.

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Reabsorption Continued

• Calcium Reabsorption
• Takes place in the PCT, the ascending Loop of
  Henle, and the DCT.
• Influenced by ___________, ___________,
  ____________
• Magnesium Reabsorption
• Takes place in the PCT, the ascending Loop of
  Henle, and the collecting duct.
• Influenced by ______

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Glucose Reabsorption

• There is a limit to the amount of glucose that
  can be reabsorbed by the PCT (_________
  Threshold)
• Due to a limited number of carrier proteins
• In cases of extremely high blood glucose levels
  (________ ___________), the amount of of glucose
  in the tubular filtrate exceeds the amount that
  can be reabsorbed.
• Glucose is then seen in the urine
  (glycosuria/glucosuria)
• Glucose pulls water out with it, increasing the
  total volume of urine, making the animal polyuric
• Increased water loss will make the animal
  polydipsic

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Step 3 Secretion

• Many waste products are not filtered in adequate
  amounts from the glomerular capillaries. The body
  still needs to get rid of them, so they are
  transferred from the peritubular capillaries, to
  the interstitial fluid, to the tubular epithelial
  cells, into the tubular filtrate (__________
  ___________)
• Primarily occurs in the ________.
• Hydrogen, potassium, ammonia/urea are eliminated
  via secretion.
• Some medications are eliminated by secretion as
  well.
• Useful for urinary tract infections

capillary
Secreted substances urea, uric acid Drugs Pen,
Phenobarb Excess K, H
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Urine Volume Regulation

• Determined by amount of water contained in
  tubular filtrate when it reaches renal pelvis.
• Regulated by two hormones
• ____________________(ADH)- released by posterior
  pituitary gland.
• Acts on DCT and collecting ducts to promote water
  reabsorption and prevent water loss.
• If not present will result in polyuria.
• ____________________- secreted by adrenal cortex.
• Increases reabsorption of sodium into the
  bloodstream in the DCT and collecting duct.
• Causes osmotic imbalance in which water follows
  sodium out of tubular filtrate into blood.
• However, ADH must be sufficient to move water out
  of DCT.

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Ureters

• Tube that exits the kidney at the hilus and
  connects to the urinary bladder
• Are a continuation of renal ________.
• Outer fibrous layer, middle smooth muscle layer,
  and inner layer lined with transitional
  epithelium
• Transitional epithelium allows ureters to stretch
  as urine passes thru on way to urinary bladder
• Smooth muscle layer propels urine through ureter
  by peristaltic contractions

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Function of the Ureters

• Connect the kidney to the urinary bladder at the
  TRIGONE (near the neck of the bladder at its
  caudal end)
• Continuously move urine from the kidneys to the
  urinary bladder.
• Smooth muscle propels urine through peristaltic
  contractions.
• Enables urine to be moved regardless of position
  of animals body
• Ureters enter bladder at ___________ angle, so
  that when bladder is full will collapse to
  prevent urine from backing up into ureters.
• This will not keep ureters from pushing urine
  into bladder

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Urinary Bladder

• Lined with _____________ epithelium that
  stretches as the bladder fills
• Walls of bladder contain smooth muscle
  (________________ muscle)
• Function is to store, collect and release urine.
• Bladder keeps urine from constantly being
  released from the body
• Has two parts
• Muscular sac
• Position and size vary depending on amount of
  urine it contains.
• Lined with transitional epithelium.
• Lined with smooth muscle bundles that run in all
  directions.
• As these muscles contract, urine is squeezed out
  into urethra.
• Neck
• Is a muscular sphincter of skeletal muscle
  fibers.
• Under voluntary control and open and close to
  allow urine to leave bladder and go into urethra.

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Urinary Bladder

• Rests on pubic bones when empty.
• Walls become thinner as the bladder fills
• Urination (_____________ or uresis) is the
  expulsion of urine from the urinary bladder into
  the urethra

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Process of Urination

• Urine Accumulation
• Urine is constantly accumulated in bladder until
  pressure activates stretch receptors in bladder
  wall
• Muscle contraction
• When trigger point is reached, spinal reflex
  sends impulse to bladder muscles
• Muscles in bladder wall contract and give
  sensation of needing to urinate.
• Sphincter Muscle Control
• Sphincter at neck of bladder provides temporary
  control of urine.
• If enough pressure is exerted on sphincter, will
  eventually relax and release urine.
• RUPTURE can occur if bladder is not emptied in
  timely fashion.
• Use caution when manually expressing or palpating
  bladder

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Urethra

• Continuation of the neck of the urinary bladder
  that runs through pelvic canal.
• Carries urine from bladder to external
  environment.
• Lined with transitional epithelium.
• Female
• _________ and ______________ urethra
• Opens on the ventral portion of the vestibule of
  the vulva.
• Only carries urine
• Male
• _________ and _____________ urethra
• Runs down center of penis
• Also serves in reproductive role to carry semen,
  however during ejaculation, sphincter at urinary
  bladder closes to prevent urine from mixing with
  seminal fluid.