anatomy 13-urinary-system
TRANSCRIPT
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The Department of Human anatomy
Urinary System
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Development
The development of the kidney proceeds through a series of successive phases: the pronephros, mesonephros, and metanephros.
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Pronephros It develops in the cervical region of the
embryo. During approximately day 22 of human gestation, the paired pronephron appear towards the cranial end of the intermediate mesoderm. In this region, epithelial cells arrange themselves in a series of tubules called nephrotomes and join laterally with the pronephric duct. This duct is fully contained within the embryo and thus cannot excrete filtered material outside the embryo; therefore the pronephros is considered nonfunctional in mammals.
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MesonephrosThe development of the pronephric duct
proceeds in a cranial-to-caudal direction. As it elongates caudally, the pronephric duct induces nearby intermediate mesoderm in the thoracolumbar area to become epithelial tubules called mesonephric tubules. The mesonephric tubule forms a capsule around the capillary tuft, allowing for filtration of blood. This filtrate flows through the mesonephric tubule and is drained into the continuation of the pronephric duct, now called the mesonephric duct or Wolffian duct.
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Metanephros During the fifth week of gestation, the
mesonephric duct develops an outpouching, the ureteric bud, near its attachment to the cloaca. This bud, also called the metanephrogenic diverticulum, grows posteriorly and towards the head of the embryo. As the cranial end of the bud extends into the intermediate mesoderm, it undergoes a series of branchings to form the collecting duct system of the kidney.
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Migration After inducing the metanephric mesenchyme
the lower portions of the nephric duct will migrate caudally (downward) and connect with the bladder, thereby forming the ureters. The ureters will carry urine from the kidneys to the bladder for excretion from the fetus into the amniotic sac. As the fetus develops, the torso elongates and the kidneys rotate and migrate upwards within the abdomen which causes the length of the ureters to increase.
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Development of metanephros
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General Structure and Functions of the Urinary System
Organs of the Urinary System:- Primary organs: Kidneys filter waste products from the
bloodstream convert the filtrate into urine.
- The Urinary Tract: Ureters, Urinary Bladder, Urethra
they transport the urine out of the body.
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Functions of the Urinary System
Removing waste product from the blood, then from the body
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: Th-12 Inferior pole: L-3 Right kidney ~ 2cm lower than left
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Kidneys: Gross and Sectional Anatomy Surrounding tissues, from deep to
superficial: Fibrous capsule (renal capsule) Perinephric fat (adipose capsule) Renal fascia Paranephric fat
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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
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 blood
flow to kidneys (1500-2000 L/day) 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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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.
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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
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Renal CorpuscleGlomerulus
• Capillary bed - rete mirabile arteriosum (wonderful network )• High pressure• fenestrations
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Proximal Convoluted Tubule Begins at tubular pole of the renal
corpuscle. 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
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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).
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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.
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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.
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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.
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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
four tunics mucosa submucosa Muscularis: called the detrusor muscle adventitia.
Internal urethral sphincter (smooth muscle)
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Urethra Fibromuscular tube
exits the urinary bladder through the urethral opening 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 External urethral sphincter
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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 located in the female perineum.
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Male Urethra Urinary and reproductive functions:
passageway for both urine and semen Approximately 18 to 20 centimeters long. 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.