Anatomy Urinary System 2022-2023(01).pdf
- 2. RecommendedBooks: ? Fundamentals of Anatomy & Physiology.Martini F, Nath JL, Bartholomew EF. 10th Edition ? Principles of Anatomy and Physiology.TortoraGJ,DerricksonB. 13th Edition
- 3. Urinary System The organs of the urinary system 1. Paired kidneys: The excretory functions of the kidneys produce urine; a fluid that contains water, ions, and small soluble compounds. 2 . paired ureters, Urine leaving the kidneys flows along the paired tubes called ureters, to reach the urinary bladder, 3. urinary bladder: a muscular sac for temporary storage of urine 4. urethra. . After leaving the urinary bladder, urine passes through the urethra, which conducts the urine to the exterior. The process of eliminate urine from urinary bladder is called urination or micturition. In this process, the muscular urinary bladder contracts and forces urine through the urethra and out of the body.
- 4. Urinary System Anatomy of Kidneys The kidneys are located just above the waist on either side of the vertebral column, between vertebrae T12 and L3. They are partially protected by 11th and 12th pairs of ribs. The left kidney lies slightly superior to the right kidney. The right kidney is slightly inferior due to the position of the right lobe of the liver. The superior surface of each kidney is capped by an adrenal gland. Because, the kidneys and adrenal glands are located posterior to peritoneal cavity, they are said to be the retroperitonealorgans.
- 5. Urinary System The kidneys are covered by three concentric layers of connective tissue that protect and stabilize each kidney: 1. The fibrous capsule, a layer of collagen fibers that covers the outer surface of the entire organ. 2. The perinephric fat, a thick layer of adipose tissue that surrounds the fibrous capsule. 3.The renal fascia, a dense, fibrous outer layer that anchors the kidney to surrounding structures. Collagen fibers extend outward from the fibrous capsule through the perinephric fat to this layer. Posteriorly, the renal fascia is fused with the deep fascia surrounding the muscles of the body wall. Anteriorly, the renal fascia is fused with the peritoneum. In effect, each kidney hangs suspended by collagen fibers from the renal fascia and is packed in a soft cushion of adipose tissue. This arrangement prevents the jolts and shocks of day to-day living from disturbing normal kidney function. If the suspensory fibers break or become detached, a slight bump or hit can displace the kidney and stress the attached vessels and ureter.This condition is called a floating kidney. It may cause pain or other problems from the distortion of the ureter or blood vessels during movement.
- 6. Urinary System A typical adult kidney is reddish- brown and about 10 cm (4 in.) long, 5.5 cm (2.2 in.) wide, and 3 cm (1.2 in.) thick. Each kidney weighs about 150 g (5.25 oz). The hilum, a prominent medial indentation, is the point of entry for the renal artery and renal nerves. The hilum is also the point of exit for the renal vein and the ureter.
- 7. Urinary System Sectional anatomy of the Kidneys Kidney has two distinct regions: an outer cortex and an inner medulla. The renal cortex is the superficial portion of the kidney, in contact with the fibrous capsule. The cortex is reddish brown and granular. Bands of cortical tissue called renal columns extend into the renal medulla and separate into 6 to 18 distinct triangular structures called renal pyramids. The base of each pyramid touches the cortex. The tip of each pyramid¡ªa region known as the renal papilla¡ªprojects into the renal sinus, an internal cavity within the kidney. The columns have a distinctly granular texture, similar to that of the cortex. A kidney lobe consists of a renal pyramid, the overlying area of renal cortex, and adjacent tissues of the renal columns.
- 8. Urinary System Sectional anatomy of the Kidneys Urine is produced in the kidney lobes. Ducts within each renal papilla discharge urine into a cup-shaped drain called a minor calyx. Four or five minor calyces merge to form a major calyx, and two or three major calyces combine to form the renal pelvis, a large, funnel-shaped chamber. The renal pelvis fills most of the renal sinus and is connected to the ureter, which drains the kidney. Urine production begins in microscopic, tubular structures called nephrons in the cortex of each kidney lobe. The fibrous capsule covering the outer surface of the kidney also lines the renal sinus, an internal cavity within the kidney. The fibrous capsule is bound to the outer surfaces of the structures within the renal sinus. In this way, it stabilizes the positions of the ureter, renal blood vessels, and nerves. Each kidney has about 1.25 million nephrons, with a combined length of about 145 km (85 miles).
- 9. Urinary System Blood Supply of the Kidneys The kidneys receive 20¨C25 percent of the total cardiac output. In normal, healthy people, about 1200 ml of blood flow through the kidneys each minute¡ªa phenomenal amount of blood for organs with a combined weight of less than 300 g (0.2% of body wt.)! Each kidney receives blood through a renal artery. This vessel originates along the lateral surface of the abdominal aorta near the level of the superior mesenteric artery. As it enters the renal sinus, the renal artery provides blood to the segmental arteries. Segmental arteries further divide into a series of interlobar arteries. These arteries radiate outward through the renal columns between the renal pyramids. The interlobar arteries supply blood to the arcuate arteries, which arch along the boundary between the cortex and medulla of the kidney. Each arcuate artery gives rise to a number of cortical radiate arteries, also called interlobular arteries. They supply the cortical portions of the adjacent kidney lobes. Branching from each cortical radiate artery are numerous afferent arterioles. These vessels deliver blood to the capillaries supplying individual nephrons.
- 12. Urinary System BloodSupply of the Kidneys After passing through the capillaries of the nephrons, blood enters a network of venules and small veins that converge on the cortical radiate veins, also called interlobular veins. The cortical radiate veins deliver blood to arcuate veins. These veins in turn empty into interlobar veins, which drain directly into the renal vein. There are no segmental veins.
- 13. Urinary System Innervation/Nerve supply of the kidney Renal nerves innervate the kidneys and ureters. Most of the nerve fibers involved are sympathetic postganglionic fibers from the celiac plexus and the inferior splanchnic nerves. A renal nerve enters each kidney at the hilum and follows the branches of the renal arteries to reach individual nephrons. The sympathetic innervation (1) adjusts rates of urine formation by changing blood flow and blood pressure at the nephron; and (2) stimulates the release of renin, which ultimately restricts water and salt loss in the urine by stimulating reabsorption by the nephron. When a substance is reabsorbed, it is ¡°reclaimed,¡± eventually reentering the blood.
- 14. The Nephron Nephron is the functional units¡ªthe smallest structures that can carry out all the functions of a system. . Each nephron consists of two parts: 1. a renal corpuscle and 2. a renal tubule. The renal corpuscle is a spherical structure consisting of the glomerular (Bowman¡¯s) capsule, a cup-shaped chamber approximately 200 ?m in diameter, and a capillary network known as the glomerulus. The renal tubule begins at the renal corpuscle. It is a long tubular passageway that may be 50 mm (1.97 in.) in length. The renal tubule has two convoluted (coiled or twisted) segments the proximal convoluted tubule (PCT) and the distal convoluted tubule (DCT). They are separated by a simple U-shaped tube, the nephron loop, also called the loop of Henle. The convoluted segments lie in the cortex of the kidney, and the nephron loop dips at least partially into the medulla. The Collecting system of kidney Each nephron empties into the collecting system, a series of tubes that carry tubular fluid away from the nephron. Collecting ducts receive this fluid from many nephrons. Each collecting duct begins in the cortex and descends into the medulla, carrying fluid to a papillary duct that drains into a minor calyx.
- 16. The Nephron The Renal Corpuscle Each renal corpuscle is 150¨C250 ?m (0.2 mm) in diameter. It includes both the glomerular capsule and the capillary network known as the glomerulus. The glomerular capsule is connected to the initial segment of the renal tubule and resembles a dilated blind end of the renal tubule invaginated by golmerulus to form a double walled capsule like structure. The outer layer/parietal layer of this capsule is made up of a simple squamous capsular epithelium. This outer layer is continuous with the inner layer/visceral epithelium, which covers the glomerular capillaries. The visceral layer is made up of the large cells with complex feet like processes, that wrap around the dense layer of glomerular capillaries. These unusual cells are called podocytes. Their feet are known as pedicels. The narrow gaps between adjacent pedicels are called filtration slits. Materials passing out of the blood at the glomerulus must be small enough to pass through filtration slits. The outer and inner layers are separated by a space called as the Bowman¡¯s space.
- 17. The Nephron Mesangial cells are special supporting cells that lie between adjacent capillaries. Actin-like filaments in these cells enable them to contract. In this way these cells control capillary diameter and the rate of capillary blood flow. Several substances, including angiotensin II, ADH (vasopressin), and histamine, affect mesangial cell contraction. Some evidence suggests that these cells also make renin. The glomerular capillaries are fenestrated capillaries. That is, their endothelium contains large-diameter pores. The basement membrane underlying the capillary endothelium is called as lamina propria or dense layer. Together, the fenestrated endothelium, the lamina propria, and the filtration slits form the filtration membrane. During filtration, blood pressure forces water and small solutes across this membrane and into the capsular space. The larger solutes, especially plasma proteins, do not pass through. Fenestrated capillary Basement membrane Filtrationmembranecomponents
- 18. The Nephron Renal Tubule The proximal Convoluted Tubule The proximal convoluted tubule (PCT) is the first segment. Its entrance lies almost directly opposite the point where the afferent and efferent arterioles connect to the glomerulus. The lining of the PCT is a simple cuboidal epithelium whose apical surfaces have microvilli. The tubular cells reabsorb organic nutrients, ions, water, and plasma proteins (if present) from the tubular fluid and release them into the peritubular fluid, the interstitial fluid surrounding the renal tubule. The reabsorbed substances in the peritubular fluid eventually reenter the blood. Reabsorption is the primary function of the PCT, but the epithelial cells can also secrete substances into the lumen of the renal tubule. Loop of Henle The PCT makes an acute bend that turns the renal tubule toward the renal medulla. This turn leads to the nephron loop, or loop of Henle. The nephron loop is divided into a descending limb and an ascending limb. Fluid in the descending limb flows toward the renal pelvis. Fluid in the ascending limb flows toward the renal cortex. Each limb contains a thick segment and a thin segment. The terms thick and thin refer to the height of the epithelium, not to the diameter of the lumen:
- 19. The Nephron Thick segments have a cuboidal epithelium. Thin segments are lined with a squamous epithelium The Distal Convoluted Tubule The thick ascending limb of the nephron loop ends where it forms a sharp angle near the renal corpuscle. The distal convoluted tubule (DCT), the third segment of the renal tubule, begins there. The initial segment of the DCT passes between the afferent and efferent arterioles. In sectional view, the DCT differs from the PCT in that the DCT has a smaller diameter, and its epithelial cells lack microvilli. The Juxtaglomerular Complex. The epithelial cells of the DCT near the renal corpuscle are taller than those elsewhere along the DCT, and their nuclei are clustered together.This region is called the macula densa. The cells of the macula densa are closely associated with unusual smooth muscle fibers in the wall of the afferent arteriole. These fibers are known as juxtaglomerular cells. Together, the macula densa and juxtaglomerular cells form the juxtaglomerular complex (JGC), an endocrine structure that secretes the hormone erythropoietin and the enzyme renin.
- 20. The Nephron The Juxtaglomerular Complex.
- 21. The Collecting System The distal convoluted tubule, the last segment of the nephron, opens into the collecting system. Individual nephrons drain into a nearby collecting duct. Several collecting ducts then converge into a larger papillary duct, which in turn empties into a minor calyx. The epithelium lining the papillary duct is typically columnar. Two main types of cells are found in the collecting duct: intercalated cells and principal cells. Together, these cells regulate the acid¨Cbase balance in the blood. Alpha-intercalated cells and beta-intercalated cells make up the population of intercalated cells. Alpha-intercalated cells secrete hydrogen ions and reabsorb bicarbonate ions, while beta- intercalated cells secrete bicarbonate ions and reabsorb hydrogen ions. Principal cells that reabsorb water and secrete potassium. Collecting System
- 23. Lengths of different parts of nephron Renal corpuscle ¨C 0.2 mm in diameter -Glomerulus- a tuft of capillaries -Bowman¡¯s capsule Renal tubule ¨C roughly 50-55 mm long -Proximal convoluted tubule ¨C 14 mm / 150-250 ?m -Loop of Henle ¨C 30 mm / 15 and 30 ?m -Distal convoluted tubule ¨C 5 mm / 30-50 ?m The Collecting system -Collecting tubule ¨C variable length / 50 ?m -Collecting duct ¨C 15 mm / 50-100 ?m -Papillary duct ¨C 5 mm / 100-200 ?m
- 24. Types of nephrons Nephrons from different locations within a kidney differ slightly in structure. Approximately 85 percent of all nephrons are cortical nephrons, located almost entirely within the superficial cortex of the kidney. In a cortical nephron, the nephron loop is relatively short, and the efferent arteriole delivers blood to a network of peritubular capillaries, which surround the entire renal tubule. These capillaries drain into small venules that carry blood to the cortical radiate veins. The remaining 15 percent of nephrons, termed juxtamedullary nephrons, have long nephron loops that extend deep into the medulla. In juxtamedullary nephrons, the peritubular capillaries are connected to the vasa recta (vasa, vessel + recta, straight)¡ªlong, straight capillaries that parallel the nephron loop.
- 26. The Ureters The ureters are a pair of muscular tubes that extend from the kidneys to the urinary bladder¡ªa distance of about 30 cm (12 in.). Each ureter begins at the funnel-shaped renal pelvis. The ureters then passes down and slightly medially, over the anterior surfaces of the psoas major muscles. The ureters are retroperitoneal and are firmly attached to the posterior abdominal wall. The paths taken by the ureters in men and women are different, due to variations in the nature, size, and position of the reproductive organs. In males, the base of the urinary bladder lies between the rectum and the pubic symphysis. In females, the base of the urinary bladder sits inferior to the uterus and anterior to the vagina. The ureters penetrate the posterior wall of the urinary bladder without entering the peritoneal cavity. They pass through the bladder wall at an oblique angle. The ureteral openings are slit-like rather than rounded. This shape helps prevent the backflow of urine toward the ureter and kidneys when the urinary bladder contracts.
- 27. The Ureters
- 28. Histology of the Ureters The wall of each ureter consists of three layers: (1) an inner mucosa, made up of a transitional epithelium and the surrounding lamina propria; (2) a middle muscular layer made up of Inner longitudinal and outer circular layers of smooth muscle; and (3) an outer connective tissue layer (adventitia), that anchors the ureters in place About every 30 seconds, a peristaltic contraction begins at the renal pelvis. As it sweeps along the ureter, it forces urine toward the urinary bladder.
- 29. The Urinary Bladder The urinary bladder is a hollow, muscular organ that serves as a temporary reservoir for urine. It is situated in the pelvic cavity posterior to the pubic symphysis. In males, it is directly anterior to the rectum; in females, it is anterior to the vagina and inferior to the uterus. The dimensions of the urinary bladder vary with its state of distension. It is rounded when slightly distended with urine but becomes pear shaped when fully distended with use. It collapses when empty. A full urinary bladder can contain as much as a liter of urine. A layer of peritoneum covers the superior surfaces of the urinary bladder. Several peritoneal folds assist in stabilizing its position. The urinary bladder¡¯s posterior, inferior, and anterior surfaces lie outside the peritoneal cavity. In these areas, tough ligamentous bands anchor the urinary bladder to the pelvic and pubic bones. In sectional view, the mucosa lining the urinary bladder is usually thrown into folds, or rugae, that disappear as the bladder fills. The triangular area bounded by the openings of the ureters and the entrance to the urethra makes up a region called the trigone of the urinary bladder. There, the mucosa is smooth and very thick.
- 31. Position of urinary bladder in pelvic cavity Female Male
- 32. The Urinary Bladder The trigone acts as a funnel that channels urine into the urethra when the urinary bladder contracts. The urethral entrance lies at the apex of the trigone, at the most inferior point in the urinary bladder. The region surrounding the urethral opening is known as the neck of the urinary bladder. It contains a muscular internal urethral sphincter. The smooth muscle fibers of this sphincter provide involuntary control over the discharge of urine from the bladder. The urinary bladder is innervated by postganglionic fibers from ganglia in the hypogastric plexus and by parasympathetic fibers from intramural ganglia that are controlled by branches of the pelvic nerves.
- 33. Histology of the Urinary Bladder The wall of the urinary bladder contains mucosa, submucosa, and muscularis layers. The muscularis layer consists of inner and outer layers of longitudinal smooth muscle, with a circular layer between the two. Together, these layers form the powerful detrusor muscle of the urinary bladder. When this muscle it compresses the urinary and expels urine into the contracts, bladder urethra.
- 34. The Urethra The urethra is a tube like structure that extends from internal urethral orifice at the neck of the urinary bladder to external urethral orifice that is opened exterior to the body. The urethrae of males and females differ in length and in function. Internal urethral orifice is surrounded by internal urethra sphincter, made up of smooth muscles, while external urethral orifice is surrounded by external urethral sphincter, made up of skeletal muscles. In males, the urethra extends from the neck of the urinary bladder to the tip of the penis. This distance may be 18¨C 20 cm. The male urethra can be divided into three segments: the prostatic urethra, the membranous urethra, and the spongy urethra. The prostatic urethra passes through the center of the prostate gland. The membranous urethra includes the short segment that penetrates the urogenital diaphragm, the muscular floor of the pelvic cavity. The spongy urethra, or penile urethra, extends from the distal border of the urogenital diaphragm to the external opening, or external urethral orifice, at the tip of the penis. In females, the urethra is very short. It extends 3¨C5 cm from the bladder to the external urethra orifice. The external urethral orifice is near the anterior wall of the vagina.
- 35. Urethra In both sexes, where the urethra passes through the urogenital diaphragm, a circular band of skeletal muscle forms the external urethral sphincter. This muscular band acts as a valve. The external urethral sphincter is under voluntary control through the perineal branch of the pudendal nerve. This sphincter has a resting muscle tone and must be voluntarily relaxed to permit micturition. Spongy urethra
- 36. Histology of the Urethra Urethral wall consists of inner mucosa, a middle of smooth muscles and outer layer of connective tissue called adventitia. Mucosa consists of a stratified epithelium that is lining the inner surface of urethra and varies from transitional epithelium at the neck of the urinary bladder, to stratified columnar epithelium at the midpoint, to stratified squamous epithelium near the external urethral orifice. Underlying the epithelial lining is the lamina propria made up of areolar tissue. Lamina propria is thick and elastic. The mucosa is folded into longitudinal creases. Mucin secreting cells are located in the epithelial pockets. In males, lamina propria contains tubules like mucous glands. In females, the lamina propria contains an extensive network of veins. Mucosa is surrounded by thin layer of smooth muscles with inner and outer longitudinal muscle layers and middle circular muscle layer. Adventitia, a thin layer of connective tissue, is situated outside the smooth muscle layer.