Download NOTES: The Excretory System

Anatomy & Physiology of the
Excretory System
Anatomy & Physiology 13-14
Why Are We Not Advised To Drink Seawater?
Water Balance
• Need appx. 3L/day
• Without water, no
hydrolysis,
temperature
regulation, transport of
materials
HYPONATREMIA
• 3 Gal/1hr = death due to loss of electrolytes
(salts), causing nervous conductivity and
muscle contraction to cease
HYPONATREMIA
• 3 Gal/1hr = death due to loss of electrolytes
(salts), causing nervous conductivity and
muscle contraction to cease
Physiological Functions of Excretory System
• The main function of the urinary system is to
maintain homeostasis within the body by:
– Eliminating nitrogenous wastes, toxins, and drugs
from the body
– Regulate the blood’s volume and chemical
makeup so there is a proper balance between
water & salts, and between acids and bases
– Produce the enzyme renin (regulates blood
pressure) and the hormone erythropoietin
(stimulates RBC production in bone marrow)
– Converts vitamin D to its active form
External Anatomical Features of Kidney
• Two bean shaped organs in
the dorsal wall of the body
• The right kidney is slightly
lower than the left, due to
crowding from the liver
• 12th rib corresponds to
middle of kidney
Renal Capsule & Perirenal Adipose
• Kidneys are retroperitoneal
(i.e. not protected by
peritoneum like other
abdominal organs)
• Renal Capsule = Fibrous
connective tissue that protects
the kidney
• Perirenal Adipose = protective
layer of fat around kidney
Hydronephrosis
• Ptosis = Rapid decline in
extra-renal adipose may
cause the kidneys may
descend.
• Descended kidney may lead
to ureters become
distended, backing up
drainage to the urinary
bladder.
• This exerts pressure on the
kidney tissues, a condition
called hydronephrosis,
which can severely damage
the kidney
Internal Anatomy of Kidney
Renal Divisions
•
•
•
•
•
Renal Capsule
Renal Cortex
Renal Medulla
Renal Calyces
Renal Pelvis
Renal Medulla & Renal Cortex
• Regions of filtration and
reabsorption
• Medulla – comprised of
Malpighian Pyramids
(site of reabsorption)
• Cortex – contains
Malpighian Corpuscle
(site of filtration)
The Nephron
• Nephrons are the
functional units of the
kidneys
• Located in renal
cortex with
extensions into the
renal medulla
• Comprised of
Malpighian
Corpuscles and Distal
Convoluted Tubules
Malpighian Corpuscle
• Glomerulus = bundle of
capillaries containing
waste-rich blood
• Bowman’s Capsule =
epithelial space
surrounding glomerulus
that receives wastes via
filtration
Distal Convoluted Tubule
• Long extension into the
renal medulla for the
process of reabsorption
• Highly vascularized with
capillaries
Renal Circulation
• Blood from the aorta enters the Renal Hilum
via the renal artery
• Filtered of blood occurs in the glomerulus
(bundles of capillaries) that are part of the
nephrons in the renal medulla
• Filtered blood exits via renal vein, to return to
the heart via the inferior vena cava.
Urine Formation
• Urine formation is a two step process:
• (1) Filtration:
– Nonselective, passive process that occurs in the
glomerulus
– Filtrate is essentially blood plasma, minus blood
proteins (i.e. albumin)
– Waste, excess ions, water, glucose, amino acids, and
other key ions are part of this filtrate
– Not producing enough filtrate for healthy volumes of
urine, or blood cells/proteins in the urine can indicate
problems with the glomerular filters
Urine Formation, Reabsorption
• (2) Reabsorption:
– Takes place in the renal tubules; reclaiming important
substances from the filtrate to put back into the blood
stream
– Some reabsorption is passive (requires no ATP)
• EX: Water, NaCl
– Most reabsorption is active (requires ATP)
• EX: Glucose, amino acids
– Nitrogenous waste products are poorly reabsorbed, so
found in high concentrations in filtrate (urine)
• EX: urea (from liver), uric acid (from metabolism of nucleic
acids), and creatinine (creatine metabolism of muscle tissue)
Renal Calyces & Pelvis
• Renal Calyces – collect filtrate
from the renal papillae at the
end of the Malpighian
Pyramids
• Renal Pelvis – collect filtrate
from the renal calyces and
direct it towards the ureter
(exiting the renal hilus)
Ureters
• Slender tubes that drain the urine
from renal pelvis to urinary bladder
• Though gravity does most of the
work, the ureters are composed of
visceral muscle that actively
transport urine to the bladder via
peristaltic waves
• Urine backflow is prevented by
valve-like folds of bladder mucosa
that flap over the ureter openings
Renal Calculi
Renal Calculi
• When urine becomes extremely concentrated, solutes
such as uric acid salts form crystals that precipitate in
the renal pelvis
• These crystals are called renal calculi ( “kidney stones”)
• They cause excruciating pain when the walls close in on
the sharp calculi as they are passed through the ureter,
or get wedged in a ureter
• Frequent UTIs, urinary retention, and alkaline urine can
lead to the formation of calculi
• Kidney stones may pass naturally, be removed
surgically, or, more recently, shattered with ultrasound
waves (the fragments pass painlessly)
Urinary Bladder
• Located just posterior to
the pubic symphysis
• Smooth, collapsible,
muscular sac that stores
urine temporarily
• Bounded by visceral
detrusor muscle
• Empty bladder 2-3 inches
• Full bladder 5 inches
Urethra
• Thin-walled tube that carries urine
by peristalsis from the bladder to
outside of the body
• The internal urethral sphincter is
composed of smooth muscle, and
prevents urine from exiting the
bladder (involuntary)
• The external urethral sphincter is
composed of skeletal muscle, and
controls the rate at which urine
leaves the urethra (voluntary)
• In females, the external orifice is
anterior to the vaginal opening; in
males, the external orifice is at the
tip of the penis
Male Urinary Tract
Female Urinary Tract
Micturition
• “Voiding” (emptying bladder)
• When ~200mL of urine have collected in the
bladder, this stretching activates receptors
• The pelvic splanchnic nerves trigger the
internal urethral sphincter to open, allowing
urine into the upper part of the urethra
• This is when you feel the urge to go to the
bathroom; however, you control the external
urethral sphincter (to a point)
Urinary Tract Infections (UTIs)
• Bacterial infection of one part of the urinary tract
• Cystitis is a bladder infection; typically
accompanied by frequent urges, burning
sensation during urination, cloudy urine
• Urethritis is inflammation of the ureters; marked
by frequent urges to urinate & painful urination
• Women are 30 times more likely to develop a UTI
than men, due to anatomical differences in the
opening of the urethra
• Cranberries contain a substance that helps
prevent bacteria from adhering to the bladder
walls