Chapter 26: Urinary System
By: Eddie Tribiana and Piers Frieden
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The urinary system is important because it performs vital excretory functions
Takes blood from renal arteries into the kidney to filtrate any liquid wastes
Creates urine
7 functions of urinary system (pg. 688)
1. Regulates plasma concentration of sodium, potassium, chloride, calcium and other
ions.
2. Regulates blood volume and blood pressure (when you drink you increase blood
volume because it is absorbed into the bloodstream)
3. Controls blood pH via control of ion concentration. (pH of blood is 7.4)
4. Conserves valuable nutrients
5. Eliminates organic waste products
6. Synthesizing calcitrol, a derivative of vitamin D, that stimulates calcium ion
absorptions
7. Assists the liver in detoxifying poisons, drugs and hormones
*If a person is diabetic, their urine is sweet due to sugar.
Organs of urinary system
1. 2 kidneys (that are retroperitoneal) (right kidney is lower because of the liver, it
also pushes the lungs up, therefore right lung is smaller and fatter)(innervated by
vagus)(a solid organ)
2. ureter (tube connecting to the bladder from the kidney)(innervated by vagus at the
top and pudendal at the bottom)
3. bladder (bag that stores urine; stores about 500 ml or ½ liter)
4. urethra – (conducts urine out)
Micturition – process of urinating (controlled by pudendal nerve)
Surface Anatomy of Kidney (pg. 690)
• The Kidney is a solid organ
*If structure has a cortex and a medulla, it is in most cases considered a solid organ.
• The whole kidney is contained by the renal capsule, which itself is epithelium
supported by connective tissue.
Structure of Kidney (pg. 691)
• Cortex (on the periphery)(lighter area)
• Medulla (triangular shaped, darker area) also called Renal Pyramid)
• Renal columns (area between renal pyramids that separate them from each other;
part of the renal cortex)
• Renal papilla (apex of the pyramid that empties into a renal cup)
• Minor calyx (cup that renal papilla empties to)
• Major calyx (2 or more minor calyx that join)
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Renal pelvis (2 or more major calyx that join)
Pathway of urine
urine (formed by kidney)> minor calyx > major calyx > renal pelvis > ureter > urinary
bladder > urethra > external urethral sphincter > out
Hilus (medially located in the kidney)
• Artery (at apex)
• Vein (ventrally located)
• Renal Pelvis (posteriorly located)
Arterial supply (pg. 692)
• Receives blood from renal arteries
• Kindeys drain to renal veins
• Renal veins drain into IVC
• Renal arteries are branching off from aorta
Renal arteries > Segmental arteries > Interlobar arteries > Arcuate arteries > Interlobular
arteries > Afferent arterioles > Glomerulus
Glomerulus – a tuft of capillaries
Glemerulus is part of the Nephron
Nephron – functional unit of the urinary system. Without nephron, we cannot make urine.
Nephron (pg.694)
Glomerulus is kept in a capsule made up of epithelium called the Glomerular capsule.
Glomerular capsule = Bowman’s capsule
Glomerulus + Bowman’s capsule = Renal corpuscle
Capillaries have simple squamous epithelium for gas exchange to occur.
Renal corpuscle is where the first process of urine formation occurs. That process is
called filtration.
Second part of nephron looks like a corrugated board and is convoluted. It is called the
Proximal Convoluted Tubule (PCT). The PCT handles the bulk of the second step in
urine formation… Reabsorption
PCT has simple cuboidal epithelium necessary for secretion and absorption.
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Reabsorption occurs along all the tubules but mainly in the PCT (80 –85%)
The ascending limb of loop of henle has cuboidal epithelium for absorption
The collecting duct also has cuboidal epithelium for absorption
Loop of Henle
• Thin descending limb – has simple squamous epithelium for secretion and
absorption. Water is reabsorbed.
• Thick ascending limb – has cuboidal epithelium for absorption. Sodium and
cloride ions are reabsorbed.
Distal Convoluted Tubule
• Secretion of toxins happens at the DCT
• The DCT is affected by hormones such as mineralocoriticoids
• End of nephron which drops urine off at the collecting duct
Part of Nephron
Renal Corpuscle
Proximal Convoluted Tubule
Loop of Henle
• Descending limb
• Ascending limb
Epithelium
Simple Squamous
Simple Cuboidal with
microvilli
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Simple Squamous
Simple Cuboidal
Function
Production of filtrate
Reabsorption of water,
ions, and all organic
nutrients
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Distal Convoluted Tubule
Simple Cuboidal
Part of Collecting System
Collecting Duct
Epithelium
Simple Cuboidal
Papillary Duct
Simple Columnar
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Reabsorption of
water
Reabsorption of
sodium and
chloride ions
Secretion of ions, acids,
drugs and toxins
Variable reabsorption of
water, sodium ions and
calcium ions.
Function
Variable reabsorption of
water and reabsorption or
secretion of sodium,
potassium, hydrogen and
bicarbonate ions
Delivery of urine to minor
calyx
Processes of urine formation
1. Filtration
a. Happens at Renal Corpuscle
b. Molecules that are big cannot cross cell membrane
c. Water, Calcium, Sodium, Potassium, Glucose, and amino acids
2. Re-absorption
a. Happens at PCT
b. About 85% of water is reabsorbed
c. About 55% of ions is reabsorbed
3. Secretion
a. Happens at DCT
b. Secretes big molecules metabolized from blood through active transport
i. Ions, acids, drugs and toxins
c. Variable reabsorption of water, sodium and calcium
d. Aldosterone controls this portion of the Nephron for salts and minerals.
There are about 3 million nephrons per kidney.
Nephrons empty into a collecting duct.
Collecting duct empties into the renal papilla. It is not part of the nephron
Nephron ends at DCT
3 types of Nephrons
1. Cortical nephrons – nephrons in the cortex (most abundant nephrons)
2. Medullary nephrons – nephrons found on the medulla
3. Juxtamedullary nephrons – nephrons found around the borders of the cortex and
medulla
Urine – fluid that is in the collecting duct
ADH (anti-diuretic hormone) controls collecting duct. If there is a lot of water in urine
and blood volume is very low, pituitary gland will secrete ADH and go to the collecting
duct to reabsorb more water until blood volume is at a homeostatic level.
Peritubular capillaries – capillaries around the loop of henle.
Venous Capillaries (pg. 692)
Efferent Arterioles > Peritubular capillaries > Venules > Interlobular veins > Arcuate
veins > Interlobar veins > Renal veins
*Reabsorption involves peritubular capillaries because reabsorption happens all along the
tube.
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Urinary bladder (pg. 699)
Rugae – folds of mucosa found in the bladder.
Center of Trigone – a triangle within the bladder that lacks the rugae, that is formed
between the openings of the 2 ureters and the neck of the urinary bladder. It does not
distend.
Bladder has transitional epithelium (when bladder is full, it looks like squamous
epithelium and when it is empty it looks like cuboidal)
The posterior wall of urinary bladder has the urethral openings.
Detrusor muscle – muscle of the bladder (smooth muscle)
At the neck of the urinary bladder, there is a sphincter called the internal urethral
sphincter that is made up of smooth muscle (involuntary control of internal urethral
sphincter).
The internal urethral sphincters is stimulated by stretch receptors in the wall of bladder
which tell the brain when the bladder is full.
Pudendal nerve has parasympathetic involuntary function and somatic voluntary
functions.
Urogenital diaphragm is made of skeletal muscle.
Male urethera: ~7” – 8” long
1. Prostatic urethra
2. Membranous urethra (~3”) (pierces urogenital diaphragm)
3. Penile urethra or Bulbo urethra
Female urethra: ~1” – 1 ½” long
1. Membranous urethra
Micturition reflex – the peristaltic movement of the urinary bladder.
The detrusor muscle has stretch receptors that send message to brain that bladder is full.
Brain sends message back to bladder to external sphincter to hold it (ability to hold for
half an hour before next message.) Sending message between brain and bladder.
Micturition reflex (pg. 705) – The process of urination that is initiated by stretch
receptors in the bladder wall.
If you can’t void urine, external urethral sphincter is spasming
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Aging and the Urinary System
Incontinence – Lack of ability to hold urine.
Men can have problems due to an enlarged prostate.
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