Kingdom of Bahrain Arabian Gulf University College of

Kingdom of Bahrain Arabian Gulf University College of Medicine & Medical Sciences Anatomy, Embryology and Histology of Urinary System Prepared by: Ali Jassim Alhashli Year III - Unit V – Gastrointestinal and Renal Systems

Anatomy of Urinary System

Gross Anatomy of Kidneys • • • Location of Kidneys: – Retroperitoneally. – In posterior abdominal wall. – On each side of vertebral column What are the functions of urinary organs? – Remove excess water, salts and wastes of protein metabolism. – Returning nutrients and chemicals to the blood. Renal fascia and fat: – Perinephric fat (perirenal fat capsule): • Surrounding kidneys and suprarenal (adrenal) glands. • Continuous with fat in renal sinus. • Kidneys, adrenal glands and perinephric fat surrounding them are enclosed (except inferiorly) by a membranous layer of renal fascia. – Paranephric fat (pararenal fat body): • External to the renal fascia. • Most obvious posterior to the kidney.

Gross Anatomy of Kidneys • Movement of the kidneys occurs during respiration and when changing from supine to erect positions (notice that normal renal mobility is about 3 cm). • Superiorly, the renal fascia is continuous with the diaphragmatic fascia on the inferior surface of the diaphragm. • Inferiorly, the anterior and posterior layers of renal fascia are loosely united, if attached at all!

Gross Anatomy of Kidneys • Kidneys (bean-shaped appearance) lie at the level of T 12 -L 3 vertebrae. Notice that the right kidney lies at a slightly lower level than the left kidney (due to the presence of the liver). • Each kidney has: – Anterior and posterior surfaces. – Medial (concave) and lateral (convex) margins. – Superior and inferior poles. • Renal hilum (on the medial aspect) is the entrance to the space within the kidney known as the renal sinus. At the hilum, renal vein is anterior to the renal artery, which is anterior to the renal pelvis.

Gross Anatomy of Kidneys • • • Superiorly, kidneys are related to the diaphragm. Inferiorly, the posterior surface of the kidney is related to the quadratus lumborum muscle. The posterior aspect of the kidney is related to: – Subcostal nerve and vessels. – Iliohypogastric nerve. – Ilio-inguinal nerve. The anterior aspect of the right kidney is related to: – Liver. – Duodenum. – Ascending colon. The anterior aspect of the left kidney is related to: – Stomach. – Spleen. – Pancreas. – Jejunum. – Descending colon.

Gross Anatomy of Kidneys • Vasculature of kidneys: – Arterial supply: • Renal arteries arise at the level of IV disc between the L 1 and L 2 vertebrae. • The longer right renal artery passes posterior to the inferior vena cava. • Typically, each artery divides close to the hilum into five segmental arteries that are end arteries- that is, they do not anastomose. – Venous drainage: • Renal veins lie anterior to the renal arteries, and the longer left renal vein passes anterior to the aorta. • Each renal vein drains into the inferior vena cava.

Gross Anatomy of Ureters • What are ureters? – Muscular ducts with narrow lumina carrying urine from the kidneys to the urinary bladder. • The renal pelvis is formed through the merging of two or three major calices, each of which was formed by the merging of two or three minor calices. • Each minor calyx is indented by the apex of the renal pyramid – the renal papilla.

Gross Anatomy of Ureters • The abdominal parts of ureters are retroperitoneal, running inferomedially beyond the bifurcation of the common iliac artery. Then, they run along the lateral wall of the pelvis to enter the urinary bladder. • Ureters constriction sites: – Junction of ureters and renal pelves. – Where ureters cross the brim of the pelvic inlet. – During passage of ureters through the wall of urinary bladder. Notice that these constriction areas are potential sites of obstruction by ureteric (kidney) stones.

Gross Anatomy of Ureters • In males, ureters lie posterolateral to the ductus deferens. • In females, it is crossed superiorly by the uterine artery. • Vasculature of ureters: – Arterial supply: arteries of ureters are arising mainly from three sources: • Renal artery. • Testicular arteries (in males) or ovarian arteries (in females). • Abdominal aorta. – Venous drainage: veins of ureters drain into renal and testicular/ ovarian veins.

Surface Anatomy of Kidneys and Ureters • Hilum of the left kidney = transpyloric plane, 5 cm from the median plane. • Right kidney = 2. 5 cm lower than the left kidney. • Posteriorly, the superior parts of the kidneys lie deep to the 11 th and 12 th ribs. • Inferior pole of the right kidney = firm, smooth, rounded mass which descends during inspiration. • The left kidney is usually not palpable unless it is enlarged or displaced. • The ureters occupy a sagittal plane that intersects the tips of the transverse processes of the lumbar vertebrae.

Clinical Correlations • • • Perinephric abscess: abscess pus from an abscess (or blood from an injured kidney) may force its way into the pelvis between the loosely attached anterior and posterior layers of the pelvic fascia. Renal transplantation: transplantation done for patients with End-Stage Renal Disease (ESRD). The site for the transplanted kidney is in the iliac fossa of the greater pelvis. The renal artery and vein are joined to the adjacent external iliac artery and vein, respectively; and the ureter is sutured into the nearby urinary bladder. Renal and ureteric stones: stones excessive distention of the ureter owing to a renal calculus (kidney stone) causes severe intermittent pain, ureteric colic, as it is gradually forced down the ureter by waves of contraction. The calculus may cause complete or intermittent obstruction of urinary flow. Pain may be referred to: – Lumbar or inguinal regions. – Proximal anterior aspect of the thigh. – External genitalia and/or testis. Ureteric calculi can be observed and removed with a nephroscope. Another technique, lithotripsy fources a shock wave through the body that breaks the stones into fragments, which then pass with the urine.

Clinical Correlations • Intraperitoneal injection and peritoneal dialysis: – Fluid injected into the peritoneal cavity is absorbed rapidly. – In renal failure, waste products such as urea accumulate in the blood and tissues and ultimately reach fatal levels. – Peritoneal dialysis may be performed in which soluble substances and excess water are removed from the system by transfer across the peritoneum, using a dilute sterile solution that is introduced into the peritoneal cavity on one side and then drianed from the other side. – Diffusible solutes and water are transferred between the blood and the peritoneal cavity as a result of concentration gradients between the two fluid compartments. – Peritoneal dialysis is usually employed only temporarily; however, for the long term it is preferable to use direct blood flow through a renal dialysis machine.

Gross Anatomy of Urinary Bladder • • • Characteristics of urinary bladder: bladder hollow viscus ( )ﻋﻀﻮ ﺩﺍﺧﻠﻲ ﻣﺠﻑ , strong muscular walls, located in the lesser pelvis, inferior to peritoneum, posterior and slightly superior to the pubic bones (Notice that it is separated from these bones by the retropubic space), resting on the pelvic floor. The neck of urinary bladder is held firmly by the lateral ligmanets of the bladder and the tendinous arch of pelvic fascia (puboprostatic ligament in males and pubovesicle ligament in females). As the bladder fills, it enters the greater pelvis. A full bladder may ascend to the level of the umbilicus ! When empty the bladder is somewhat tetrahedral ( )ﺭﺑﺎﻋﻲ ﺍﻷﺴﻄﺢ. It has an apex (pointing toward the superior edge of pubic symphysis), body (between the apex and fundus), fundus (opposite the apex and formed by the convex posterior wall) and neck (where the fundus and inferolateral surfaces converge inferiorly). Urinary bladder has a superior surface, two inferolateral surfaces and a posterior surface.

Gross Anatomy of Urinary Bladder • • Bladder bed is fromed on each side by: – Pubic bones. – Fascia covering obturator internus and levator ani muscles. – Posteriorly by the rectum or vagina. The bladder is enveloped by loose connective tissue, the vesical fascia. Only the superior surface is covered by peritoneum. Walls of bladder are composed chiefly of detrusor muscle. Toward the neck of the male bladder, its muscle fibers form the involuntary internal urethral sphincter. This sphincter contracts during ejaculation to prevent retrograde ejaculation of semen into the bladder. In males, the muscle fibers in the neck of the bladder are continuous with the fibromuscular tissue of the prostate, whereas in females, these fibers are continuous with muscle fibers in the wall of the urethra. The ureteric orifices and the internal urethral orifice are at the angles of the trigone of the bladder. The ureteric orifices are encircled by loops of detrusor musculature that tighten when the bladder contracts to assist in preventing reflux of urine into the bladder. The uvula of the bladder is a slight elevation of the trigone in the internal urethral orifice.

Gross Anatomy of Urinary Bladder

Gross Anatomy of Urinary Bladder • Vasculature of bladder: – Arterial supply (branches of internal iliac arteries): • Superior vesical arteries supply the anterosuperior parts of the bladder. • In males, the fundus and neck of the bladder are supplied by the inferior vesical arteries. In females, the inferior vesicle arteries are replaced by the vaginal arteries. • Obturator and inferior gluteal arteries also supply small branches to the bladder. – Venous drainage (tributaries of internal iliac veins): • In males, the vesicle venous plexus is continuous with the prostatic venous plexus and the combined plexus envelops the fundus of the bladder, prostate, seminal glands, ductus deferens and inferior ends of the ureters. The prostatic venous plexus also receives blood from the deep dorsal vein of the penis. The vesical venous plexus mainly drains through the inferior vesical veins into the internal iliac veins; however, it may drain through the sacral veins into the internal vertebral venous plexuses. • In females, the vesicle venous plexus envelops the pelvic part of the urethra, neck of the bladder, receives blood from the dorsal veins of the clitoris and comminicates with the vaginal or uterovaginal venous plexus.

Gross Anatomy of Urinary Bladder

Gross Anatomy of Urinary Bladder • Innervation of bladder: – Sympathetic fibers: T 11 -L 2 or L 3 through the hypogastric plexuses and nerves and inferior hypogastric plexuses. • Sympathetic innervation that stimulates ejaculation simultaneously causes contraction of the internal urethral sphincter to prevent reflux of semen into the bladder. – Parasympathetic fibers are motor to the detrusor muscle in the bladder wall and inhibitory to the internal sphincter of males. • Bladder contracts, the internal sphincter relaxes in males and urine flows into the urethra.

Clinical Correlations • • • Suprapubic cystotomy: – As the bladder fills, it extends superiorly in the extraperitoneal fatty tissue of the anterior abdominal wall. – Distended bladder may be punctured (suprapubic cystotomy) or approached surgically for the introduction of indwelling catheters or instruments without traversing the peritoneum and entering the peritoneal cavity. Rupture of bladder: – The rupture of the superior part of the bladder frequently tears the peritoneum, resulting in passage of urine into the peritoneal cavity. Posterior rupture of the bladder usually results in passage of urine subperitoneally into the perineum. Cystoscopy: – The interior of the bladder and its three orifices can be examined with a cystoscope, a lighted tubular endoscope that is inserted through the urethra into the bladder. The cystoscope consists of a light; an observing lens; and various attachments for grasping, removing, cutting and cauterizing.

Gross Anatomy of Female Urethra • • • The short female urethra passes anteroinferiorly from the internal urethral orifice of the urinary bladder, posterior, and then inferior to the pubic symphysis to the external urethral orifice in the vestibule of the vagina. The urethra lies anterior to the vagina; its axis is parallel with the vagina. Paraurethral glands are homologs to the prostate. These glands have a common paraurethral duct, which opens (one on each side) near the external urethral orifice. Vasculature of female urethra: it is supplied by: – Internal pudendal artery. – Vaginal artery. Innervation of female urethra: – Vesical plexus. – Pudendal nerve.

Gross Anatomy of Male Urethra • • • The male urethra is a muscular tube that conveys urine from the internal urethral orifice of the urinary bladder to the exterior through the external urethral orifice at the tip of glans penis. The urethra also provides an exit for semen (sperm and glandular secretions). Male urethra is composed of four parts: – Intramural part: it is surrounded by an internal urethral sphincter composed of sympathetically innervated smooth muscle. This sphincter prevents semen from entering the bladder during ejaculation (retrograde ejaculation). – Prostatic urethra: it is surrounded by the prostate. – Intermediate (membranous) part: it is surrounded by the external urethral sphincter. – Spongy (penile) urethra.

Histology of Urinary System

Histology of Urinary System • • • Uriniferous tubules and nephrons: – Functional unit of kidney is uriniferous tubule. – It consists of a nephron and a collecting duct. Nephrons of the kidney: – There are two types of nephrons: • Cortical nephrons in the cortex. • Juxtamedullary nephrons in the medulla. – The nephron is subdivided into renal corspuscle and renal tubules. Renal corpuscle: – Blood is filtered in the glomerular capillaries of the corpuscle to form ultrafiltrate. – It consists of capillaries called glomerulus and double-layered glomerular (Bowman) capsule. – The visceral layer of the capsule contains podocytes that invest fenestrated glomerular capillaries. – Podocytes exhibit primary processes from which arise smaller pdicles. – Pedicles for filtration slits around capillaries that are spanned by filtration slit diaphragm. – Parietal layer is lined with simple squamous epithelium of the glomerular capsule. – Between parietal and visceral layers is the capsular (urinary) space for glomerular filtrate. – At vascular pole, afferent and efferent arterioles enter and exit the renal corpuscle. – At opposite urinary pole, ultrafiltrate enters the proximal convoluted tubule.

Histology of Urinary System

Histology of Urinary System • • Blood filtration: – In renal corpusclem it is through glomerular capillaries. – Consists of capillary endothelium, basement memebrane and podocytes/ pedicles. – Glomerular filtrate enters capsular space between parietal and visceral layers. Filtration barrier in glomerulus: – Glomerular endothelium is fenestrated and permeable except for blood cells and proteins. – Basement membrane restricts molecules the size of albumin. – Slit diaphragms between pedicles contain the transmembrane protein nephrin. – Filtration slits responsible for glomerular permeability due to size-selective molecular filters.

Histology of Urinary System • Renal tubules: – From capsular space, glomerular filtrate enters renal tubules that extend to collecting ducts. – Initial tubule is the proximal convoluted tubule that starts at the urinary pole of renal corpuscle. – Loop of Henle consists of thick descending tubules, a thin loop, and thick ascending tubules. – Distal convoluted tubule ascends into kidney cortex and joins the collecting tubule. – Juxtamedullary nephrons have very long loops of Henle. – Collecting tubules are not part of nephron, but join larger collecting ducts to form papillary ducts. – Deep in medulla, papillary ducts are lined with columnar epithelium and exit in area cribrosa. – Medullary rays in cortex are collecting ducts, blood vessels, and straight portions of nephrons.

Histology of Urinary System

Histology of Urinary System • Mesangial cells: – Attached to capillaries in renal corpuscle ans serve important functions. – Produce extracellular matrix and provide structural support for glomerular capillaries. – Serve as phagocytes in glomerulus and phagocytose antigen-antibody complexes. – Function as macrophages and regulate blood pressure as a result of vasoactive receptors and contractility. – Extraglomerular cells form part of the juxtaglomerular apparatus.

Histology of Urinary System • Proximal convoluted tubules: – They are lined with vrush border and absorb most of filtrate. – Basal infoldings of cells membrane contain numerous mitochondria and sodium pumps. – Mitochondria supply energy for ionic transport across cell membrane into the interstitium. – Absorb all glucose, proteins, and amino acids, almost all carbohydrates, and 75%-85% of water. – Secrete metabolic waste, hydrogen, ammonia, dyes, and drugs into the filtrate for voiding. – Longer than distal convoluted tubules and more frequently seen in cortex near renal corpuscles.

Histology of Urinary System • Loop of Henle: – In juxtamedullary nephrons, it produces hypertonic urine owing to the countercurrent multiplier system. – High interstitial osmolarity draws water from the filtrate as it flows through the loop. – Vasa recta capillaries take up water from interstitium and return it to systemic circulation.

Histology of Urinary System • Distal convoluted tubules: – Shorter than proximal convoluted tubules, less frequent in cortex, and lack brush border. – Basolateral membrane shows infoldings and contains numerous mitochondria. – Under the influence of aldosterone, sodium ions actively absorbed from the filtrate. – Peritubular capillaries return ions to systemic circulation to maintain vital acid-base balance.

Histology of Urinary System • Juxtaglomerular apparatus: – Located adjacent to renal capsule and distal convoluted tubule. – Consists of juxtaglomerular cells, macula densa and extraglomerular mesangial cells. – Juxtaglomerular cells are modified smooth muscle cells in afferent arteriole before entering glomerular capsule. – Main function is to maintain proper blood pressure for blood filtration in renal corpuscles. – Juxtaglomerular cells respond to stretching in the wall of afferent arterioles, as baroreceptors. – Macula densa responds to changes in sodium chloride concentration in glomerular filtrate. – Decreased blood pressure and ionic content causes release of enzyme renin by juxtaglomerular cells. – Renin release eventually causes plasma proteins to convert to angiotensin II, a powerful vasoconstrictor. – Angiotensin II stimulates release of aldosterone, which acts on the distal convoluted tubules. – Distal convoluted tubules absorb Na. Cl with water, increasing blood volume and pressure. – Distal convoluted tubule also eliminates hydrogen and potassium to maintain acidbase balance.

Histology of Urinary System

Histology of Urinary System • Collecting tubules, collecting ducts and antidiuretic hormone: – Glomerular filtrate flows from distal convoluted tubules to collecting tubules and ducts. – During excessive water loss or dehydration, ADH is released from the pituitary gland. – ADH causes epithelium of collecting duct to become highly permeable to water. – Water that is retained in interstitium is collected by peritubular capillaries and vasa recta. – In the absence of ADH, increased water is retained in collecting ducts and urine is dilute.

Histology of Urinary System • Ureter: – Lined with trasitional epithelium and consists of mucosa, muscularis and adeventitia. – Upper part lined with inner longitudinal and middle circular smooth muscle layers. – Third longitudinal smooth muscle layer added in the lower third of the ureter. – Connective tissue adventitia surrounds the ureter.

Histology of Urinary System • Urinary bladder: – Thick muscular wall with three indistinct layers of smooth muscle. – Serosa lines superior surface and adventitia covers the inferior surface. – Transitional epithelium in empty bladder exhibits about six layers of cells. – When stretched, transitional epithelium appears stratified squamous. – Changes in epithelium caused by thicker plasma membrane of superficial cells and plaques. – Plaques act like hinges and allow cells to expand during stretching; cells become squamous. – Thicker plasma membrane and transitional epithelium provide osmotic barrier to urine.

Histology of Urinary System

Embryology of Urinary System

Embryology of Urinary System • • Kidney embryology: – Pronephros: week 4; then degenerates. – Mesonephros: functions as interim ( )ﻣﺆﻘﺖ kidney for 1 st trimester; later contributes to male genital system. – Metanephros: permanent; first appears in 5 th week of gestation; nephrogenesis continues through 32 -36 weeks of gestation. Ureteric bud: bud derived from caudal end of mesonephric duct; gives rise to ureter, pelvises, calyces, and collecting ducts; fully canalized by 10 th week. Metanephric mesenchyme: mesenchyme ureteric bud interacts with this tissue; interaction induces differentiation and formation of glomerulus through to distal convoluted tubules. Ureteropelvic junction: junction last to canalize. It is the most common site of obstruction (hydronephrosis) in fetus.

Embryology of Urinary System • Potter sequence (syndrome): – Oligohydramnios → compression of developing fetus → limb deformities, facial anomalies (low-set ears and retrognathia), and compression of chest → pulmonary hypoplasia (cause of death). – Causes: ARPKD (Autosomal Recessive Polycystic Kidney Disease), posterior urethral valves and bilateral renal agenesis. – POTTER syndrome associated with: • P: Pulmonary hypoplasia. • O: Oligohydramnios. • T: Twisted face. • T: Twisted skin. • E: Extremity defects. • R: Renal failure.

Embryology of Urinary System • Horseshoe kidney: – Inferior poles of both kidneys fuse. – As they ascend from pelvis during fetal development, horseshoe kidney get trapped under inferior mesenteric artery and remain low in the abdomen. – Kidney functions normally. – ↑ risk for ureteropelvic junction obstruction and hydronephrosis. – Associated with Turner syndrome (X).

Embryology of Urinary System • Multicystic dysplastic kidney: – Due to abnormal interaction between ureteric bud and metanephric mesenchyme. – This leads to a non-functional kidney consisting of cysts and connective tissue. – If unilateral (most common), generally asymptomatic with compensatory hypertrophy of contralateral kidney. – Often diagnosed prenatally via ultrasound.

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