Download Urinary Bladder

Chapter 15
Urinary System
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1
Pretest
True or False
•
•
•
•
•
The functional unit of the kidney is the nephron.
The outer portion of the kidney is known as the
renal medulla.
The indentation in the kidney is known as the
hilum.
The glomerulus is made up of loose connective
tissue.
The double-layered epithelial cup that surrounds
the glomerulus is Bowman’s capsule.
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Pretest, cont.
True or False
6. The ureters transport urine from the urinary
bladder to the outside.
7. Rugae located in the wall of the urinary bladder
allow the bladder to expand.
8. The urethra in a male functions only in the
transport of urine.
9. Glucose is reabsorbed into the body in the renal
tubule.
10. Micturition is the act of expelling urine.
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Introduction to the Urinary System
• Functions of the urinary system
– Rids body of waste products
– Maintains appropriate fluid volume
• By regulating amount of water excreted in the urine
– Maintains normal pH of the blood
– Secretes erythropoietin: controls red blood cell
production
– Secretes rennin: helps maintain normal blood
pressure
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Components of the
Urinary System
• Consists of:
– Kidneys: produce urine
– Ureters: transport the urine away from kidneys
to urinary bladder
– Urinary bladder: stores urine until it is excreted
from the body
– Urethra: tubular structure that carries urine
from urinary bladder to the outside of body
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Components of the
Urinary System, cont.
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Components of the
Urinary System, cont.
Kidneys
• Primary organs of the urinary system
• Functions:
– Filter the blood
– Remove wastes
– Excrete the wastes in the urine
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Components of the
Urinary System, cont.
Location
• Located between T-12 and L-3 vertebrae
• Right kidney: slightly lower than left
– Liver displaces it downward
3. Renal fascia: connective tissue that holds
kidney in place
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Components of the
Urinary System, cont.
4. Perirenal fat: thick layer of adipose tissue
that surrounds each kidney
5. Renal capsule: tough, fibrous connective
tissue
– Encases each kidney
– Provides support for the soft tissue inside
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Components of the
Urinary System, cont.
Macroscopic Structure
• Bean-shaped
2. Hilum: indentation in kidney
– Where ureter and renal vein leave the
kidney
– Where renal artery enters the kidney
– Leads to a large cavity within the kidney
(renal sinus)
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Components of the
Urinary System, cont.
3. Renal cortex: outer, reddish region of kidney
4. Renal medulla: inner, reddish-brown region
of kidney
– Consists of a series of renal pyramids
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Components of the
Urinary System, cont.
5. Renal pyramids
– Appear striated
• Contain straight tubular structures and blood
vessels
– Wide bases of pyramids: are adjacent to
the cortex
– Pointed ends of pyramids: renal papillae
• Directed toward center of kidney
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Components of the
Urinary System, cont.
6. Renal columns: formed by portions of the
renal cortex
– Extend into spaces between adjacent pyramids
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Components of the
Urinary System, cont.
7. Renal pelvis: central region of kidney
–
–
Continuous with ureter
Consists of a large cavity: collects urine as it is
produced
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Components of the
Urinary System, cont.
c. Calyces: cuplike projections of the renal pelvis
• Minor calyx: surrounds the renal papillae of each
pyramid
– Collects urine from that pyramid
• Major calyx: made up of several minor calyces
– From the major calyces: urine flows into renal pelvis
1)Then flows into ureter
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Components of the
Urinary System, cont.
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Components of the
Urinary System, cont.
Nephrons
• Functional unit of the kidney
• Each kidney: contains over a million
nephrons
• Located in the cortex and medulla of kidney
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Components of the
Urinary System, cont.
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Components of the
Urinary System, cont.
4. Parts of a nephron
a. Renal corpuscle consists of:
• Glomerulus: cluster of capillaries
• Glomerular capsule (Bowman’s capsule): doublelayered epithelial cup that surrounds glomerulus
• Pathway of blood through glomerulus
– Blood enters glomerulus through an afferent arteriole
– Blood is filtered in glomerulus: filtrate enters glomerular
capsule
– Blood leaves glomerulus through an efferent arteriole
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Components of the
Urinary System, cont.
b. Renal tubule: carries fluid away from Bowman’s
capsule
• Proximal convoluted tubule: highly coiled
• Nephron loop (Henle’s loop): descends, makes a U-turn,
ascends back toward the cortex
• Distal convoluted tubule: highly coiled
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Components of the
Urinary System, cont.
Collecting Ducts
1. Urine passes from nephrons into collecting
ducts
a. Flows from collecting ducts into minor calyces
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Components of the
Urinary System, cont.
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Components of the
Urinary System, cont.
Ureters
• Transport urine from renal pelvis to
urinary bladder
• Descend from renal pelvis
• Enter urinary bladder on the posterior
inferior surface
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Components of the
Urinary System, cont.
4. Wall of ureter
a. Fibrous coat: outer layer consisting of fibrous
connective tissue
b. Muscular layer: middle layer consisting of
smooth muscle
• Function: peristalsis to propel the urine through the
ureter
c. Mucosa: inner layer
• Function: secretes mucus to coat and protect
surface of the cells
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Components of the
Urinary System, cont.
Urinary Bladder
• Located in pelvic cavity
• Temporary storage reservoir for urine
• Size and shape varies with:
– Amount of urine it contains
– Pressure from surrounding organs
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Components of the
Urinary System, cont.
4. Layers of urinary bladder
a. Mucosa: consists of a mucous membrane
• Rugae: folds that occur when bladder is empty
– Allow bladder to expand as it fills
b. Submucosa: consists of connective tissue with
elastic fibers
c. Muscularis: composed of smooth muscle
interwoven in all directions
• Collectively called the detrusor muscle
– Contraction: expels urine from bladder
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Components of the
Urinary System, cont.
5. Trigone: formed by three openings in the
floor of the urinary bladder
– Two openings: from ureters
• Small flaps of mucosa: cover openings
– Act as valves: allow urine to enter bladder
– Prevent it from backing up from bladder into ureters
– Third opening: urethra
• Band of the detrusor muscle: encircles this opening
– Forms the internal urethral sphincter
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Components of the
Urinary System, cont.
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Components of the
Urinary System, cont.
Urethra
• Thin-walled tube
• Conveys urine from urinary bladder to
outside of body
• Sphincters that control flow of urine
through urethra:
a. Internal urethral sphincter: surrounds
urethra where it leaves the urinary bladder
• Consists of smooth (involuntary) muscle
b. External urethral sphincter: encircles
urethra where it passes through pelvic floor
• Consists of skeletal (voluntary) muscle
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Components of the
Urinary System, cont.
4. Females: urethra is short
– External urethral orifice
• Opens to outside just anterior to vaginal opening
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Components of the
Urinary System, cont.
5. Males: urethra is much longer
– Transports both urine and semen
– Parts of the male urethra:
• Prostatic urethra: passes through the prostate gland
• Membranous urethra: short region that penetrates
pelvic floor and enters penis
• Spongy urethra: longest region
– Extends the entire length of the penis
– External urethral orifice: opens to the outside at the tip of
penis
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Components of the
Urinary System, cont.
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Urine Formation
Glomerular Filtration
• Blood plasma
– Moves across filtration membrane in
the renal corpuscle
– Enters glomerular capsule
• Filtration membrane consists of:
– Capillary endothelium of the
glomerulus
– Endothelium of the capsule
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Urine Formation, cont.
3. Filtration pressure: force that moves
the fluid across the membrane
4. Filtrate: fluid that enters the capsule
5. Blood flows through the kidneys: at a
rate of 1200 ml per minute
6. Filtration membrane: acts as a barrier
– Prevents blood cells and protein
molecules from entering the capsule
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Urine Formation, cont.
Tubular Reabsorption
• 180 liters (45 gallons) of filtrate are
formed in a 24-hour period
– Reduced to 1-2 liters of urine
2. Tubular reabsorption
– Movement of substances from the
filtrate in the kidney tubules: into the
blood
• Changes the volume and composition of the
filtrate
– Substances that are useful to body: are
reabsorbed (e.g., glucose, water, sodium)
– Wastes remain in the filtrate: excreted in
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Urine Formation, cont.
3. Amount of reabsorption that takes
place:
– Proximal convoluted tubule: 65%
– Nephron loop (loop of Henle): 15%
– Distal convoluted tubule: 19%
4. 1% of filtrate: excreted as urine
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Urine Formation, cont.
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Urine Formation, cont.
Tubular Secretion
1. Transport of molecules and ions into
the filtrate from the blood
– Includes:
• Waste products of cellular metabolism
(e.g., urea)
– Become toxic if allowed to accumulate in body
• Some drugs (e.g., penicillin)
• Hydrogen ions
– Helps to regulate the pH of the blood
• Potassium ions, creatinine, histamine
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Urine Formation, cont.
2. Urine consists of:
– Substances that are filtered minus the
substances that are reabsorbed in the
tubules
– Plus the substances that are added by
tubular secretion
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Urine Formation, cont.
Regulation of Urine Concentration and Volume
1. Aldosterone: secreted by adrenal
gland
– Acts on the kidney tubules: increases
reabsorption of sodium
• When sodium is reabsorbed: water follows
by osmosis
– Reduces urine output
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Urine Formation, cont.
2. Antidiuretic hormone (ADH): released from
pituitary gland
a. Presence of ADH: less water is lost from body
• Makes distal convoluted tubule and collecting duct
more permeable to water
– More water is reabsorbed
– Reduces amount of urine excreted
– Makes urine more concentrated
b. Absence of ADH: more water is lost from body
• Makes tubules less permeable to water
– Less water is reabsorbed
– Increases volume of urine
– Makes urine dilute
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Urine Formation, cont.
3. Atrial natriuretic hormone
(atriopeptin): produced by special
cells in the heart
– Promotes excretion of sodium and
water
– Acts directly on kidney tubules
• Inhibits secretion of ADH, renin, and
aldosterone
– Decreases blood volume and blood pressure
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Urine Formation, cont.
4. Renin: enzyme produced by kidney
– Secreted in response to:
• Low blood pressure
• Decreased blood sodium concentration
– Promotes production of angiotensin II
in the blood
• Powerful vasoconstrictor: increases blood
pressure
• Stimulates adrenal gland to secrete
aldosterone
– Acts on kidney tubules to conserve sodium and
water
• Increases blood volume and, consequently,
increases blood pressure
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Urine Formation, cont.
Micturition
• Act of expelling urine from the
bladder
• Bladder:
– Can hold up to 1 liter (1000 ml) of urine
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Urine Formation, cont.
3. Micturition reflex
– When bladder contains 200-400 ml of urine
• Stretch receptors in bladder wall triggers micturition
reflex
• Automatic and involuntary response
• Impulses are transmitted to detrusor muscle
– Can be inhibited or stimulated by higher brain
centers
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Posttest
True or False
•
•
•
•
The urinary system helps to regulate the blood
pressure.
The renal pelvis collects urine as it is produced.
The nephron is made up of the glomerulus and
Bowman’s capsule.
Blood enters the glomerulus through the efferent
arteriole.
•
The renal tubule carries fluid away from the
glomerular capsule toward a collecting duct.
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Posttest, cont.
True or False
6. Urine is expelled from the urinary bladder through
contraction of the detrusor muscle.
7. The calyx consists of three openings and is located
in the floor of the urinary bladder.
8. The urethral orifice controls the passage of urine
through the urethra.
9. Erythropoietin increases reabsorption of sodium
and reduces urine output.
10. In the absence of ADH, the urine is more dilute.
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