Transcript Urinary System and Excretion 1

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
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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
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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
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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
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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
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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
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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
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Urine formation is divided into three steps.
– Glomerular filtration.
– Tubular reabsorption.
– Tubular secretion.
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Maintaining Water-Salt Balance
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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
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Reabsorption of Salt.
– Kidneys regulate blood’s 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
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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
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The kidneys are primary organs of
homeostasis because they maintain acidbase 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
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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
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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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