human anatomy, first edition mckinley&o'loughlin€¦ · · 2015-04-08major homeostatic...
TRANSCRIPT
27-2
General Structure and Functions of the Urinary System
General Concept: Waste products accumulate in blood
Are toxic
Must be removed to maintain homeostasis
Urinary System organs remove waste products from the blood
then from the body
Major homeostatic system
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General Structure and Functions of the Urinary System
Organs of the Urinary System: Kidneys
Ureters
Urinary Bladder
Urethra
Primary organs: kidneys filter waste products from the bloodstream
convert the filtrate into urine.
The Urinary Tract: Includes:
ureters
urinary bladder
urethra
Because they transport the urine out of the body.
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Functions of the Urinary System
Removing waste products from the bloodstream.
Storage of urine. the urinary bladder is an expandable, muscular sac that can store as
much as 1 liter of urine
Excretion of urine.
Blood volume regulation. the kidneys control the volume of interstitial fluid and blood under the
direction of certain hormones
Regulation of erythrocyte production. as the kidneys filter the blood, they are also indirectly measuring the
oxygen level in the blood
Erythropoietin (EPO): hormone produced by kidney
Released if blood oxygen levels fall
Stimulates RBC production in red bone marrow
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Kidneys: Gross and Sectional Anatomy
Retroperitoneal
Anterior surface covered with peritoneum
Posterior surface against posterior abdominal wall
Superior pole: T-12
Inferior pole: L-3
Right kidney ~ 2cm lower than left
Adrenal gland on superior pole
Surface anatomy of the Kidney
• Hilum is concave
located on the medial
surface.
• The renal sinus is a
cavity within the
kidney which is
occupied by the renal
pelvis, renal calyces,
blood vessels, nerves
and fat.
10 cm
5.5cm
3cm
10
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Kidneys: Gross and Sectional Anatomy
Renal sinus: internal space
Houses blood vessels, lymphatic vessels, nerves
Houses renal pelvis, renal calyces
Also fat
kidneys are covered by 4 layers: 1- the inner layer is called renal capsule 2-the middle layer is called perirenal fat (Perinephric) 3-the outer layer is called renal fascia. Paranephric fat
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Kidneys: Gross and Sectional Anatomy • Surrounding tissues, from deep
to superficial: – Fibrous capsule (renal capsule)
• Dense irregular CT
• Covers outer surface
– Perinephric fat (adipose capsule)
• Also called perirenal fat
• Completely surrounds kidney
• Cushioning and insulation
– Renal fascia
• Dense irregular CT
• Anchors kidney to posterior wall and peritoneum
– Paranephric fat
• Between renal fascia and peritoneum
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Kidneys: Gross and Sectional Anatomy
Sectioned on a coronal plane: Renal Cortex
Renal arches
Renal columns
Renal Medulla Divided into renal pyramids
8 to 15 per kidney
Base against cortex
Apex called renal papilla
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Kidneys: Gross and Sectional Anatomy
• Minor calyx: – Funnel shaped
– Receives renal papilla
– 8 to 15 per kidney, one per pyramid
• Major calyx – Fusion of minor calyces
– 2 to 3 per kidney
• Major calyces merge to form renal pelvis
• Renal Lobe – Pyramid plus some
cortical tissue
– 8 to 15 per kidney
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Blood Supply to the Kidney
About 20 to 25% of cardiac output to kidneys
Path: Renal artery to segmental arteries to
interlobar arteries to arcuate arteries to interlobular arteries to:
Afferent arteriole to glomerulus to efferent arteriole to peritubular capilaries and vasa recta
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Blood Supply to the Kidney
Blood plasma is filtered across the glomerulus into the glomerular space.
Once the blood plasma is filtered
blood leaves the glomerulus
enters an efferent arteriole.
efferent arteriole is still carrying oxygenated blood
a gas and nutrient exchange with the kidney tissues has not yet occurred.
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Blood Supply to the Kidney
The efferent arterioles branch into one of two types of capillary networks:
peritubular capillaries
vasa recta
these capillary networks are responsible for the actual exchange of gases and nutrients
Peritubular capillaries: primarily in cortex
Vasa recta: surround the thin tubes that project into the medulla.
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Blood Supply to the Kidney
• Path for veins:
– Interlobular veins to arcuate veins to
interlobar veins to the renal vein
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Nephrons • The functional filtration unit in the
kidney.
• Consists of the following:
– Renal corpuscle
• Glomerulus
• Glomerular capsule (Bowman’s capsule)
– Proximal convoluted tubule (PCT)
– Nephron loop (loop of Henle)
• Ascending loop of Henle
• Descending loop of Henle
– Distal convoluted tubule (DCT)
– collectively called the renal tubule
• In both kidneys: approximately 2.5 million nephrons.
• Are microscopic: measure about 5 centimeters in length.
20
0
m
Blood vessels from a human kidney. Arterioles and peritubular capillaries appear pink; glomeruli appear yellow.
Figure 44.14e
Figure 44.14c
Nephron Types
Cortical nephron
Juxtamedullary nephron
Renal cortex
Renal medulla
Functional units of kidney are the nephrons.
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Nephrons
Cortical Nephrons Near peripheral edge of cortex
Short nephron loops
Have peritubular capillaries
Juxtamedullary nephrons Near corticomedullary border
Long nephron loops
Have vasa recta
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Urine Formation
Three processes
Filtration Renal corpuscle: forms filtrate
From blood to tubule
Reabsorption Mostly PCT
Water and salt: rest of nephron
From tubule to blood
Secretion From blood to tubule
occurs at the distal convoluted tubule.
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Renal Corpuscle
• Vascular pole – Afferent and efferent
arterioles
• Tubular pole – Connects to PCT
• Two structures: – Glomerulus and
glomerular capsule
• Glomerulus – Capillary bed
– High pressure
– fenestrations
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Renal Corpuscle • Glomerular Capsule
– Parietal layer
• Simple squamous epithelium
– Visceral layer
• Podocytes
– Pedicels
– Filtration slits
– Capsular space (Bowman’s capsule): location of filtrate
– Filtration membrane
• Fenestrations
• Filtration slits
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Proximal Convoluted Tubule
Begins at tubular pole of the renal corpuscle. Cells: simple cuboidal epithelium
actively reabsorb from the filtrate: almost all nutrients (glucose and
amino acids) electrolytes plasma proteins
Osmosis: reabsorption of 60% to 65% of the water in filtrate.
Have microvilli
Solutes and water:
moved into blood plasma
via the peritubular capillaries.
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Nephron Loop (loop of Henle)
originates at end of proximal convoluted tubule
projects toward and/or into the medulla.
Each loop has two limbs.
descending limb:
from cortex toward and/or into the medulla
ascending limb:
returns back to the renal cortex
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Distal Convoluted Tubule
• begins at the end of the thick ascending limb of the nephron loop
– adjacent to the afferent arteriole (important physiologically)
• Juxtaglomerular apparatus.
• primary function:
– Secretion
– From blood plasma to filtrate.
– secretes ions
• potassium (K+)
• acid (H+)
• Reabsorption of water also occurs:
– influenced by two hormones
• Aldosterone
• antidiuretic hormone (ADH).
juxtaglomerular (JG) apparatus, -
JG apparatus consists of
• a region of the DCT called the macula densa (simple columnar) located between the afferent & efferent arterioles.
Alteration in:
1-Blood pressure &/or
2-NaCl salt concentration in urine is detected by the JG apparatus.
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Collecting Ducts
Function in a well hydrated person:
transport the tubular fluid into the papillary duct and then into the minor calyx.
Function in a dehydrated person:
water conservation
more-concentrated urine is produced.
ADH can act on the collecting duct epithelium
Cells become permeable to water
Water moves from filtrate into blood plasma
Involves vasa recta.
Osmolarity of interstitial
fluid (mOsm/L)
Key
Active transport
Passive transport
INNER MEDULLA
OUTER MEDULLA
CORTEX NaCl H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
H2O
H2O
H2O
H2O
H2O
H2O
H2O
Urea
Urea
Urea
1,200
1,200 1,200
900
600
400
300 300
400
600
100
100
200
400
700 900
600
400
300
300
300
Figure 44.16-3
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Innervation of the Kidney
innervated by a mass of autonomic nervous system fibers
called the renal plexus.
The renal plexus
accompanies each renal artery
enters the kidney through the hilum.
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Urinary Tract : Ureters
• long, fibromuscular tubes
• conduct urine from the kidneys to the urinary bladder.
• average 25 centimeters in length
• retroperitoneal.
• ureters originate at the renal pelvis
• extend inferiorly to enter the posterolateral wall of the base of the urinary bladder.
• wall is composed of three concentric tunics.
– mucosa
– muscularis
– adventitia.
Urinary Tract – Urinary Bladder
• The urinary bladder:
– expandable, muscular container
– serves as a reservoir for urine
• positioned immediately superior and posterior to the pubic symphysis.
• in females
– the urinary bladder is in contact with the uterus posterosuperiorly and with the vagina posteroinferiorly.
• in males
– it is in contact with the rectum posterosuperiorly and is immediately superior to the prostate gland.
• is a retroperitoneal organ.
• when empty exhibits an upside-down pyramidal shape.
• Filling with urine distends it superiorly until it assumes an oval shape. 27-49
Urinary Tract – Urinary Bladder • Trigone
– posteroinferior triangular area of the urinary bladder wall
– formed by imaginary lines
• connect the two posterior ureteral openings
• and the anterior urethral opening.
• The trigone remains immovable as the urinary bladder fills and evacuates.
• It functions as a funnel
– directs urine into the urethra as the bladder wall contracts
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Urinary Tract – Urinary Bladder
• four tunics
– mucosa
– submucosa
– Muscularis: called the detrusor muscle
– adventitia.
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Micturition (Urination)
The expulsion of urine from the bladder.
Initiated by a complex sequence of events called the micturition reflex.
The bladder is supplied by both parasympathetic and sympathetic nerve fibers of the autonomic nervous
system.
Urethra • Fibromuscular tube
– exits the urinary bladder
– at anteroinferior surface
• conducts urine to the exterior of the body.
• Tunica mucosa: is a protective mucous membrane
– houses clusters of mucin-producing cells called urethral glands.
• Tunica muscularis: primarily smooth muscle fibers
– help propel urine to the outside of the body.
• Two urethral sphincters:
– Internal urethral sphincter
• restrict the release of urine until the pressure within the urinary bladder is high enough
– External urethral sphincter
• and voluntary activities needed to release the urine are activated.
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Urethra
• The internal urethral sphincter
– involuntary (smooth muscle)
– superior sphincter surrounding the neck of the bladder, where the urethra originates.
– a circular thickening of the detrusor muscle
– controlled by the autonomic nervous system
• The external urethral sphincter
– inferior to the internal urethral sphincter
– formed by skeletal muscle fibers of the urogenital diaphragm.
– a voluntary sphincter
– controlled by the somatic nervous system
– this is the muscle children learn to control when they become “toilet-trained”
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Female Urethra
Has a single function:
to transport urine from the urinary bladder to the vestibule, an external space immediately internal to the labia minora
3 to 5 centimeters long, and opens to the outside of the body at the external urethral orifice
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Male Urethra
Urinary and reproductive functions:
passageway for both urine and semen
Approximately 18 to 20 centimeters long.
• Male Urethra is Partitioned into three segments:
– prostatic urethra is approximately 3 to 4 centimeters long and is the most dilatable portion of the urethra
• extends through the prostate gland, immediately inferior to the male bladder, where multiple small prostatic ducts enter it
– membranous urethra is the shortest and least dilatable portion
• extends from the inferior surface of the prostate gland through the urogenital diaphragm
– spongy urethra is the longest part (15 centimeters)
• encased within a cylinder of erectile tissue in the penis called the corpus spongiosum
• extends to the external urethral orifice
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Aging and the Urinary System • Changes in the size and functioning of the kidneys begin
at 30.
• Gradual reduction in kidney size.
• Reduced blood flow to the kidneys.
• Decrease in the number of functional nephrons.
• Reabsorption and secretion are reduced.
• Diminished ability to filter and cleanse the blood.
• Less aldosterone or antidiuretic hormone.
• Ability to control blood volume and blood pressure is reduced.
• Bladder decreases in size.
• More frequent urination.
• Control of the urethral sphincters—and micturition—may be lost.