Download Urinary System Notes - Hastings High School

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Urinary / Excretory System
Majors Organs of the Urinary System include:
 Kidneys
 Ureters
 Urinary Bladder
 Urethra
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nary_system.jpg
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The main goal of the Urinary System is HOMEOSTASIS of the body’s fluid and solute levels. Homeostasis is maintaining a
constant ideal environment for the cells of the body to live in. Without functioning kidneys our cells could shrivel and
die, expand and burst, or die from high concentrations of toxic wastes!
The kidneys are the primary organ of the urinary system, regulating levels of the following:
water
regulates how much body needs; gets rid of extra
sodium ions
regulates how much body needs; gets rid of extra
potassium ions
regulates how much body needs; gets rid of extra
calcium ions
regulates how much body needs; gets rid of extra
magnesium, phosphate, sulfate ions
regulates how much body needs; gets rid of extra
hydrogen and bicarbonate ions (influence pH)
regulates how much body needs; gets rid of extra
glucose
keeps
amino acids
keeps
triglycerides (fats)
keeps
vitamins
keeps
urea (from the breakdown of proteins)
gets rid of (21 g per day)
creatinine
gets rid of (1.8 g per day)
uric acid (from the breakdown of RNA)
gets rid of (480 mg per day)
Kidney
1. Gross Anatomy of Kidney:
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located behind peritoneum to the left and right of the spine between the 12th thoracic vertebrae and the 3rd
lumbar vertebrae
weigh less than 150 g each
hilus (indentation in kidney where the renal artery enters and the renal vein and ureter exit)
renal capsule (tougher outside of kidney)
cortex (outer layer)
medulla (inner layer)
o renal pyramids (produce and drain the urine)
o papillae (tips of pyramids that empty into minor calyces)
o renal columns (area between the renal pyramids for blood vessels to pass)
o minor and major calyces (drains urine from medulla)
o renal pelvis (where urine drains into the ureter)
http://www.webbooks.com/eLibrary/
Medicine/Physiology
/Urinary/kidney.jpg
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2. The Nephron
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Urine production begins in the nephrons
Approx. 1.25 million nephrons per kidney (85 miles worth)
Nephrons filter about 1200 ml of blood per minute, 20-25% of the cardiac output!
Nephrons are located partly in the cortex and partly in the medulla pyramids.
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3. Parts of a Nephron
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afferent arteriole (arteriole = small artery)
efferent arteriole – note that the diameter is smaller than the afferent arteriole
Glomerulus – high pressure forces smaller molecules out of blood
Bowman’s capsule – captures the filtrate
Proximal convoluted tubule – absorbs 60 – 70 % of the filtrate produced at the glomerulus
Loop of Henle: descending limb – removes additional H20 from filtrate
Loop of Henle: ascending limb – removes additional Na+ and Cl- from filtrate
Distal convoluted tubule – makes final changes to the concentration of urine in response to
hormones
http://www.bioengine
ering.canterbury.ac.nz/
graphics/nephron.jpg
proximal convoluted tubule
glomerulus (inside the
Bowman’s capsule)
January 30, 2009
efferent arteriole
collecting duct
afferent arteriole
distal convoluted tubule
cortex
Loop of Henle:
descending limb
and ascending
limb
Afferent arteriole
Efferent arteriole
Glomerulus
Bowman’s capsule
Proximal convoluted tubule
Loop of Henle: descending limb
Loop of Henle: ascending limb
Distal convoluted tubule
Collecting duct
medulla
brings unfiltered blood to glomerulus
carries filtered blood out of glomerulus
filters blood by allowing many molecules through capillary walls–
only blood cells and proteins (which are too large) stay in blood
holds water and small molecules filtered from blood
reabsorbs ions, all organic molecules, vitamins, and some water
reabsorbs water
reabsorbs ions
gets rid of acids, ammonia, and drugs; reabsorbs sodium ions
may reabsorb additional water, sodium ions, and bicarbonate ions
4. Blood Flow within the Kidneys
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renal artery branches off of the descending abdominal aorta (from the
heart) – the renal artery enters at the hilus
within the kidney the renal artery branches into the interlobar arteries
these become the arcuate arteries that run in arches along the boundary
between the medulla and the cortex
interlobular arteries branch off into the cortex from the arcuate arteries
afferent arteries branch off of the interlobular arteries
the afferent arteries bring blood to the working part of the kidney, the
nephron
blood travels through the capillaries within the glomerulus and out the
narrower efferent artery
from here the blood travels to the peritubular capillaries around the
proximal and distal convoluted tubules and to the vasa recta around the
Loop of Henle
the blood finally leaves the nephron and begins a reverse journey out of
the kidney by way of the interlobular veins, arcuate veins, interlobar
veins, and renal vein
the renal vein joins with the inferior vena cava to return to the heart
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5. How Urine is Formed
The overall goal of the kidney is to get rid of urea, creatinine, and uric acid while trying to keep as much H2O and
other desirable molecules as possible. This is accomplished by 3 processes: filtration, reabsorption, and
secretion
1. The glomerulus is mainly responsible for filtration
a. Filtration pushes out of the blood molecules that are small enough to fit
through small pores within the glomerular capillaries. The water and
molecules that are no longer part of the bloodstream are called filtrate
b. The glomeruli filter out about 50 gallons worth of filtrate per day!
However, 99% of this will be reabsorbed. If we did not reabsorb most
of this, we would probably die of severe dehydration
2. The proximal convoluted tubule is mainly responsible for reabsorption
a. Reabsorption brings the desired molecules, including much of the
water, back into the bloodstream (into the peritubular capillaries)
b. 60 to 70% of the filtrate is reabsorbed by the proximal convoluted
tubule
c. 10 to 25% of the filtrate is reabsorbed by the Loop of Henle
d. another 9 to 14% of the filtrate is reabsorbed by the distal convoluted
tubule and collecting duct, depending on hormone levels
e. The Loop of Henle and the collecting duct both “tweak” the production of urine by controlling how
many water molecules, sodium ions, and potassium ions are reabsorbed vs. lost to the urine
3. The distal convoluted tubule is mainly responsible for secretion
a. Secretion takes undesirable molecules that were not filtrated and are still in the bloodstream and forces
them out of the peritubular capillaries and into the filtrate
4. Final urine properties (vary somewhat depending on what you have been eating and drinking)
a. pH 6.0 (range 4.5 – 8)
b. water content 93-97%
c. sterile
d. 1200 ml/day on average
e. yellow color varies in intensity
5. Two hormones account for the differences in urine composition
a. aldosterone
 The distal convoluted tubule contains a ion pump that exchanges sodium ions for potassium
ions
 The more aldosterone present, the more sodium ions are reabsorbed into the blood and
potassium ions are secreted into the filtrate
b. ADH = antidiuretic hormone
 If ADH is present, the distal convoluted tubule and collecting duct are permeable to water
so the water leaves the filtrate and your urine is more concentrated
 If ADH is absent, the distal convoluted tubule and collecting duct are impermeable to water
so the water stays in the filtrate and your urine is more dilute
 Some substances like caffeine are diuretics which have the opposite effect as ADH, making
your urine more dilute and causing you to have to urinate more often
Ureters
1. Gross Anatomy of Ureters
a. 2 muscular tubes
b. about 30 cm (12 inches)
c. connect the renal pelvis of each kidney to the posterior wall of the urinary bladder
2. Histology
a. inner transitional epithelium (tissue can expand to stretch)
b. middle layer of smooth muscle – longitudinal and circular bands
 peristaltic contractions about every 30 seconds to force urine into bladder
c. outer connective tissue
3. Kidney Stones
a. calcium deposits, magnesium salts, or crystals of uric acid that form solids in the urine
b. also known as calculi
c. obstruct flow, cause extreme pain, and can even cause the kidney to not function properly
Urinary Bladder
1. Gross Anatomy of Urinary Bladder
a. muscular organ
b. size depends on how full it is, but can hold up to 1 liter
c. found in pelvic cavity
d. held in place by umbilical ligaments (connect to umbilical cord)
e. contains a triangular area on the called the trigone – apexes are the 2 ureteral openings and the
urethral opening at the lowest point in the bladder
f. contains the internal urethral sphincter where the urinary bladder connects with the urethra
2. Histology
a. inner transitional epithelium (expands to stretch)
b. Detrusor muscle = middle layer of smooth muscle including a circular layer inside 2 longitudinal
bands
 contracts to expel contents during urination
c. outer connective tissue
Urethra
1. Differences in length between sexes
a. females 2.5 to 3.0 cm (about 1 inch)
b. males 18 to 20 cm (7-8 inches)
2. contains an internal urethral sphincter (involuntary muscle) at the junction between the urinary bladder and
the urethra
3. also contains an external urethral sphincter (voluntary muscle) distal to the internal sphincter
4. both muscles must relax to let urine pass
5. Urinary tract infections occur when bacteria or yeast enter the urethra
a. Symptoms: painful and frequent urination, fever
b. Intestinal E. coli the most common pathogen
c. More common in women due to proximity of urethral opening to anus
d. Infection can become more serious if not treated as the infection travels up the urinary system
Urination
1. Micturition = Urination
2. Stretch receptors in the bladder send a signal to the brain about the need to urinate
3. Volume of 200 ml is usually the amount of “stretch” that signals the brain
4. You can “hold it” until your bladder reaches about 500 ml, but then the fluid pressure in the bladder will
force its way through the internal urethral sphincter and the external urethral sphincter opens reflexively
5. Incontinence is the inability to control when you urinate
a. Babies and small children lack this control because their brains are not developed enough yet
b. Elderly can be incontinent due to poor muscle tone
c. Damage to the sphincters can cause incontinence in adults
6. Injury to the pelvic nerves can cause the inability to relax the two sphincters, causing extreme stretching of
the urinary bladder and pain - requires catheterization