Download Urinary System

The Urinary System
Functions:
-Excretion of wastes from the blood
(kidneys)
-Elimination of wastes into environment
(ureters, bladder, urethra)
-Regulation of volume and solute
concentration of blood plasma
Organs of the Urinary Tract
• Kidneys
– reddish brown, bean shaped, located just below
the ribs on posterior wall of abdominal cavity
– regulate volume, composition, and pH of body
fluids (remove metabolic wastes in the
process)
– secrete hormone erythropoetin (controls rate of
RBC formation)
– secrete enzyme renin (regulates blood pressure)
– functional unit is the nephron (will discuss
later)
Organs cont.
• Ureters
– transport urine from kidneys to bladder
– 25 cm long tubes
– muscular walls help move urine by
peristalsis
– kidney stones can block this tube
Organs cont.
• Urinary bladder
– temporarily stores urine
– hollow, muscular organ composed of transitional
epithelium (stretches)
– internal urethral sphincter - muscle that surrounds the
neck of the bladder; remains contracted to prevent the
bladder from emptying until pressure increases to a
certain level – autonomic controlled
– External urethral sphincter – voluntarily controlled, ring
of muscles where urethra exits body. How you control
when you use the restroom.
Female
Male
Organs cont.
• Urethra
– conveys urine out of body
– about 4 cm long in females
– about 19 cm long in males
Urethral Sphincters
Micturition
• bladder can hold as much as 600 ml of urine
• urge to urinate occurs when it contains 200 ml
• the reflex to urinate is inhibited by the conscious
control of the external urethral sphincter
• Urine leaves the bladder by micturition (a.k.a.
urination)
Micturition Reflex
• bladder distends as it fills with urine and
stimulates stretch receptors in bladder wall
• when stretch receptors are triggered, they
stimulate muscular bladder wall to contract
• external urethral sphincter is relaxed
voluntarily, and the internal urethral sphincter
relaxes also
• urination occurs
• if ext. urethral sphincter does not relax, int.
urethral sphincter remains closed
Micturition Reflex cont.
• What happens if you “hold it” too
long?
– Once volume exceeds 500 ml, pressure
may force open internal sphincter which
causes reflexive relaxation of external
sphincter, and urination occurs
Urinary Diseases and Disorders
• UTI - urinary tract infection
– more common in women than men b/c the urethra is
shorter in females
– symptoms – burning pain during urination
– cause – bacteria spread from rectum to urethra
• Kidney Stones (a.k.a. renal calculi)
– result from chronically concentrated urine which
causes uric acid to clump and form “stones”
– Possible causes: oxalate – found in green, leafy
vegetables, coffee, and chocolate
• Gout – uric acid build up in joints
Gout
Kidney Stones
World’s Largest Kidney Stone
22 oz. 5.5 in across
The Nephron
• each kidney contains ~ 1 million nephrons
• they filter 7.5 liters of plasma each hour
• each nephron consists of a renal corpuscle (blood
vessels) and a renal tubule (tube)
• the renal corpuscle is divided into 3 parts. Renal artery,
glomerulus, and peritubular capillary.
• renal artery becomes a cluster of capillaries called a
glomerulus (surrounded by Bowman’s capsule)
• Then goes to a network of capillaries called peritubular
capillaries which surround the renal tubule
• the renal tubule is divided into 4 parts; Bowman’s
capsule, the proximal convoluted tubule, loop of Henle,
and the distal convoluted tubule
Urine Formation
• Urine formation occurs in the nephrons
• Consists of 3 processes:
– 1. glomerular filtration (collects good and bad stuff)
– 2. tubular reabsorption (removes good stuff from
filtrate and put back into body)
– 3. tubular secretion (puts in extra bad stuff into
filtrate which is going to the toilet)
1. Glomerular Filtration (collecting
good and bad stuff)
• Occurs when the renal artery delivers blood to the
glomerulus
• blood pressure forces water and small molecules
from blood plasma into the Bowman's’ capsule
• this fluid is now known as filtrate and moves into
the renal tubule
• ex. of molecules in filtrate: water, glucose, amino
acids, sodium, urea, uric acid, other minerals
• Filters both good and bad stuff for example;
water and toxic substances
2. Tubular Reabsorption (removes
good stuff from filtrate)
• occurs in the proximal convoluted tubule, loop of Henle,
distal convoluted tubule, and collecting duct
• molecules from the filtrate (in the tubule) are returned by
diffusion and active transport to the blood in the
peritubular capillaries
• ex. of molecules that are reabsorbed: glucose, amino
acids, and almost all of the water and sodium that enters
the tubule is reabsorbed
• Make a really salty place so that on the next pass by we
can remove almost all the water. (good stuff)
3. Tubular Secretion (Puts in extra
bad stuff into filtrate)
• occurs mainly at the distal convoluted
tubule
• molecules from the peritubular capillaries
(blood vessels) are actively transported into
the renal tubule (tubes)
• ex. of molecules that are secreted: uric acid,
hydrogen ions, ammonia, penicillin (and
other drugs)
Notice hormones in orange and green on right
1
2
3
Urine Formation cont.
• the distal convoluted tubule empties the fluid
(urine) into a collecting duct which carries it away
from the nephron
• Each collecting duct empties many nephrons
• Many collecting ducts empty the medullas into the
funnel-shaped central chamber of the kidney
(renal pelvis)
• the ureters drain this chamber
• the peritubular capillaries merge to form venules
that carry the filtered blood away from the
nephron and eventually out of the kidney
Urine
• Physical characteristics
– The yellow color in urine is due to chemicals called urobilins.
These are the breakdown products of the bile pigment
bilirubin. Bilirubin is itself a breakdown product of the heme
part of hemoglobin from worn-out red blood cells. Most
bilirubin is partly broken down in the liver, stored in the gall
bladder, broken down some more in the intestines, and
excreted in the feces (its metabolites are what make feces
brown), but some remains in the bloodstream to be extracted
by the kidneys where, converted to urobilins, it gives urine
that familiar yellow tint.
– pH – slightly acidic (6.0)
• Chemical composition
– 95% water, 5% solutes
Urine Components
• Urea is the body’s main waste product - formed
when amino acids are broken down into energy;
is toxic to cells in high levels
• Uric acid – a by-product of the breakdown of
nucleic acids (RNA & DNA)
• Creatinine – a by-product of muscle metabolism
• Ammonia – waste formed when bacteria break
down proteins
• Ketones – waste produced when fats are
digested (diabetes and Atkin’s diet)
Urine
• Composition affected by lifestyle and diet
• Volume varies from 0.6 to 2.5 liters/day
• Diuretics – inhibit reabsorption of water so
increase urine volume – ex. coffee, tea,
alcoholic beverages
Hormonal Regulation
• Aldosterone
– stimulates both reabsorption of Na+ and the
secretion of K+
– Na+ reabsorption increases water
reabsorption, leading to a rise in blood
volume and therefore a rise in blood
pressure
Hormonal Regulation
• ADH (antidiuretic hormone) causes increased
water absorption
– high solute conc. in blood  increased ADH
secretion
– alcohol and caffeine inhibit ADH secretion
causing excess excretion of dilute urine and
dehydration
Diuretics in orange