Urinary System and Excretion

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• Urinary System and Excretion

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Outline

• Overview of the Urinary System
• Functions of the Urinary System
• Urination
• Kidney Structure
• Nephrons
• Urine Formation
• Maintaining Water-Salt Balance
• Reabsorption of Water
• Reabsorption of Salt
• Kidney Problems

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Urinary System

• Kidneys are primary organs of the urinary system.
• The concave side of a kidney has depression
  called the hilum where the renal artery enters
  and the renal vein and ureters exit the kidney.
• Urinary bladder gradually expands as urine
  enters.
• Urethra extends from the urinary bladder to an
  exterior opening.

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The Urinary System
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Functions of the Urinary System

• Function of the urinary system is to produce
  urine and conduct it outside the body.
• Excretion is the removal of metabolic wastes from
  the body.
• Defecation refers to the elimination of feces
  from the body.

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Functions of the Urinary System

• As urine is being produced, the kidneys
• Carry out excretion of metabolic wastes.
• Urea is the primary nitrogenous end product, but
  ammonium, creatinine, and uric acid are also
  excreted.
• Maintain salt-water balance of blood and thus
  blood volume and blood pressure.
• Maintain acid-base balance of the blood.
• Have a hormonal function.

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Urination
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Kidney Structure

• The kidney contains three major regions
• Renal cortex.
• Renal medulla.
• Renal pelvis.
• Microscopically, the kidney is composed of over
  one-million nephrons that produce urine.

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Kidney Gross Anatomy
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Anatomy of a Nephron

• Each nephron has its own blood supply.
• From the renal artery, afferent arteriole leads
  to the glomerulus, then to the efferent arteriole
  and then to the peritubular capillary network
  which surrounds the nephron.
• From there blood goes into a venule that joins
  the renal vein.

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Nephron Anatomy
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Parts of a Nephron

• Each nephron is composed of several parts.
• Glomerular capsule.
• Proximal convoluted tubule.
• Loop of the nephron (loop of Henle).
• Distal convoluted tubule.

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Urine Formation

• Urine formation is divided into three steps.
• Glomerular filtration.
• Tubular reabsorption.
• Tubular secretion.

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Maintaining Water-Salt Balance

• Reabsorption of Water.
• Excretion of hypertonic urine is dependent upon
  reabsorption of water from the loop of the
  nephron and the collecting duct.
• Osmotic gradient exists within the tissues of the
  renal medulla.
• Antidiuretic hormone (ADH) released by the
  posterior lobe of the pituitary causes more water
  to be reabsorbed and less urine to form.

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Reabsorption of Water
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Maintaining Water-Salt Balance

• Reabsorption of Salt.
• Kidneys regulate bloods salt balance by
  controlling excretion and reabsorption of various
  ions.
• Usually more than 99 of sodium filtered at the
  glomerulus is returned to the blood.
• Most is reabsorbed at the proximal convoluted
  tube, while a sizeable amount is reabsorbed from
  the convoluted tubule and collecting duct.

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Reabsorption of Salt

• Aldosterone regulates sodium reabsorption.
• Renin is an enzyme that converts angiotensinogen.
• Atrial natriuretic hormone promotes sodium
  excretion.
• Diuretics increase urine flow.
• Alcohol.
• Caffeine.

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Homeostasis

• The kidneys are primary organs of homeostasis
  because they maintain acid-base balance and
  water-salt balance of blood.
• Kidneys reabsorb bicarbonate ions and excrete
  hydrogen ions as needed to maintain normal blood
  pH.

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Problems with Kidney Function

• Many types of illness cause progressive renal
  disease and ultimate renal failure.
• Diabetes.
• Hypertension.
• Inherited conditions.
• Treatment of renal failure can include
  hemodialysis and kidney replacement.

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Review

• Overview of the Urinary System
• Functions of the Urinary System
• Urination
• Kidney Structure
• Nephrons
• Urine Formation
• Maintaining Water-Salt Balance
• Reabsorption of Water
• Reabsorption of Salt
• Kidney Problems

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