10/27/2010
Functions of the
Excretory System
Objectives
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.
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.
Amazing Facts
Hepatic veins (cut)
Esophagus (cut)
Inferior vena cava
Renal artery
Adrenal gland
About 1100-1200 liters of blood pass through the
capillaries in our kidneys every day.
Renal hilum
Renal vein
Aorta
Kidney
Iliac crest
Ureter
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.
Rectum (cut)
Uterus (part
of female
reproductive
system)
Urinary
bladder
Urethra
Figure 25.1
Position said to be
Retroperitoneal
Renal
hilum
Renal cortex
Anterior
Inferior vena cava
Peritoneum
Peritoneal cavity
(organs removed)
Renal
vein
Renal
artery
Body of
vertebra L2
Body wall
(a)
Renal medulla
Aorta
Supportive
tissue layers
Major calyx
• Renal fascia
anterior
posterior
• Perirenal
fat capsule
• Fibrous
capsule
Renal pelvis
Minor calyx
Ureter
Renal pyramid
in renal medulla
Renal column
Fibrous capsule
Posterior
(a) Photograph of right kidney, frontal section
Figure 25.2a
(b) Diagrammatic view
Figure 25.3
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10/27/2010
Blood and Nerve Supply
Function of the Nephron
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.
The functional unit of the kidney.
Primary role is to filter the blood.
Produces concentrated urine.
Location of the Nephron
More than 1 million nephrons are
packed into each kidney!
Primary parts of Nephron
o
Found in the renal
cortex.
1. Glomerulus: a tuft of capillaries
o
Cortical nephrons
account for 85% in
human kidney.
2. Renal tubule: begins as cup-shaped
glomerular (Bowman’s) capsule
surrounding the glomerulus
o
Portions of the
nephron
extend into the renal
medulla.
Urinary 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
Figure 25.5
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Urinary 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
Sphincters
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
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