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10/27/2010
1
ObjectivesObjectives
To begin unit on excretory system.
I.D. elements of the gross anatomy.
- Kidney
- Bladder
- Sphincters
Introduce the nephron and its general function.
Learn some interesting facts about the excretory system.
Functions of the Functions of the Excretory SystemExcretory System�The kidneys excrete nitrogenous wastes, such as
urea, uric acid, creatinine and ammonium.
�The kidneys maintain blood volume by regulating water excreted.
�Monitor blood composition and blood pH by regulating electrolyte excretion.
�Kidneys secrete the enzyme renin, which helps maintain blood pressure.
�The kidneys secrete erythropoietin, which stimulates RBC production.
�Gluconeogenesis during prolonged fasting.
Figure 25.1
Esophagus (cut)Inferior vena cava
Adrenal gland
Hepatic veins (cut)
Renal artery
Renal hilum
Renal vein
Iliac crest
Kidney
Ureter
Urinary
bladder
Urethra
Aorta
Rectum (cut)
Uterus (part
of female
reproductive
system)
Amazing FactsAmazing Facts
About 1100-1200 liters of blood pass through the capillaries in our kidneys every day.
The kidneys filter nearly 200 liters of fluid from the bloodstream every day!
Our kidneys extract about 180 L (45 gallons) of fluid/filtrate.
The kidneys refine the filtrate, and in a typical day we excrete only about 1.5 L of urine.
Figure 25.2a
Body wall
• Perirenal
fat capsule
Renal
artery
Renal
vein
Inferior vena cava
Aorta
• Fibrous
capsule
• Renal fasciaanteriorposterior
Supportivetissue layers
Body of
vertebra L2
PeritoneumPeritoneal cavity
(organs removed)
Anterior
Posterior(a)
Position said to be
Retroperitoneal
Figure 25.3
Renal cortex
Renal medulla
Major calyx
Renal pelvis
Ureter
Minor calyx
Renal column
Renal pyramid
in renal medulla
Fibrous capsule
Renal
hilum
(a) Photograph of right kidney, frontal section (b) Diagrammatic view
10/27/2010
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Blood and Nerve SupplyBlood and Nerve Supply
� Renal arteries deliver ~ 1/4 (1200 ml) of cardiac output to the kidneys each minute.
� Most of the blood directed towards cortex, where urine production occurs.
� Nerve supply is via sympathetic fibers from the renal plexus.
Function of the NephronFunction of the Nephron
The functional unit of the kidney.
Primary role is to filter the blood.
Produces concentrated urine.
More than 1 million nephrons are packed into each kidney!
Location of the NephronLocation of the Nephron
o Found in the renal cortex.
o Cortical nephronsaccount for 85% in human kidney.
o Portions of the nephron
extend into the renal
medulla.
Primary parts of NephronPrimary parts of Nephron
1. Glomerulus: a tuft of capillaries
2. Renal tubule: begins as cup-shaped glomerular (Bowman’s) capsule surrounding the glomerulus
Figure 25.5
Urinary BladderUrinary Bladder
> Muscular sac for temporary storage of urine
> Retroperitoneal, on pelvic floor posterior to pubic symphysis
◦ Males—prostate gland surrounds the neck inferiorly
◦ Females—anterior to the vagina and uterus
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Urinary BladderUrinary Bladder
� Muscular sac for temporary storage of urine
� Retroperitoneal, on pelvic floor posterior to pubic symphysis
◦ Males—prostate gland surrounds the neck inferiorly
◦ Females—anterior to the vagina and uterus
SphinctersSphincters
I. Internal urethral sphincter
� Involuntary (smooth muscle) at bladder-urethra junction
� Contracts to open
II. External urethral sphincter
� Voluntary (skeletal) muscle surrounding the urethra as it passes through the pelvic floor