Lecture Notes in Human Anatomy - Hryhorieva O.A., Svitlytskyi A.O. 2020

The Study of Viscera (Splanchnologia)
Anatomy of Internal Organs
Urinary System

Lecture Plan:

1. General structural plan of the Urinary system.

2. Kidneys and their Structure.

3. Ureter,

4. Urinary Bladder,

5. Urethra.

The urinary system is an organ system that eliminates nitrogenous Metabolic waste products and excess fluid from the bodies of animals and humans. In vertebrates, it consists of two kidneys where urine is produced, the urethra, and (in bony Fishes, amphibians, some reptiles, and mammals) a urinary bladder, where urine is stored prior to elimination.

The urinary system comprises Organs that produce urine, as well as organs that store and excrete it. The Urinary Organs include the kidneys, Ureters, urinary bladder, and urethra. Urinary organs have a tubular or hollow structure. In females, the URINARY AND REPRODUCTIVE organs are completely separate, whereas in males, they merge in the prostatic part of the urethra, where the paired deferent ducts and 15–20 excretory ducts of the Prostate Gland open.

The kidneys are paired bean-shaped organs; the outer border of the Kidney is convex, while the inner border is concave. They are reddish-brown in color and weigh about 120 g.

The kidneys are located in the lumbar region on both sides of THE Vertebral Column, at the level of the 12th thoracic, 1st, and 2nd lumbar vertebrae. The right kidney lies 2–3 cm lower than the left one. An Adrenal gland adheres to the upper pole of each kidney.

There is a deep indentation on the concave inner border of the kidney. This is the renal hilum, where the renal artery enters, and the renal vein and ureter exit.

The renal parenchyma is covered by a dense, easily detachable fibrous capsule. Externally, the kidney is surrounded by a layer of adipose tissue—the adipose capsule (perirenal fat).

a paired organ located on either side of the spine at the level of the 12th thoracic to 2nd lumbar vertebrae, adjacent to the posterior abdominal wall; the right kidney is positioned lower than the left one.

Kidney fixation:

✵ in place, maintained primarily by intra-abdominal pressure resulting from the contraction of the abdominal wall Muscles;

✵ to a lesser extent, by the renal fascia, which fuses with the renal sheaths;

✵ the renal muscular bed, formed by the psoas major and quadratus lumborum muscles;

✵ and the renal vessels, which prevent the Displacement of the kidney away from the aorta and INFERIOR VENA CAVA.

The kidney lies within a muscular bed formed by the psoas major and quadratus lumborum muscles. The mass of each kidney is 110–140 g, length 9–12 cm, width 4.5–6.5 cm. The kidneys are bean-shaped; they feature anterior and posterior surfaces, upper and lower poles, and lateral and medial borders; the adrenal gland is situated on the upper pole of the kidney. The anterior surface of the right kidney is adjacent to the Liver, the right colic flexure, and the descending part of the duodenum; the anterior surface of the left kidney is adjacent to The Stomach, Pancreas, loops of the jejunum, Spleen, and left colic flexure. On the medial, concave border facing the vertebral column lies the renal hilum, which leads into the renal sinus. The hilum contains the renal artery, renal vein, Lymphatic vessels, Lymph Nodes, nerves, and renal pelvis. The kidney is covered by membranes that contribute to its fixation. It is surrounded by the adipose capsule, which protects the kidney from injury during jolts. The kidney substance is differentiated into the renal cortex (5–7 mm), located peripherally, and the renal medulla, which consists of 7–12 pyramids with their apices directed toward the renal sinus and bases toward the cortex; the cortical substance extends between the pyramids, forming the renal columns.

The Structural and functional unit of the kidney is the nephron, with approximately 1 million nephrons per kidney.

✵ The structural and functional unit of the kidney is the renal corpuscle (nephron). Each kidney contains about 1 million microscopic corpuscles.

✵ The renal corpuscle begins in the cortex as a small double-walled cup-shaped capsule enclosing a glomerulus of Blood capillaries. There is a space between the walls of the capsule, which gives rise to the renal tubule. The tubule becomes convoluted and then extends into the medullary layer, forming the proximal convoluted tubule.

✵ In the medullary layer, the tubule straightens, forms a loop, and returns to the cortical layer. Here, the urinary tubule becomes convoluted again and empties into an excretory duct—the collecting duct of the kidney. Collecting ducts merge to form larger papillary ducts. These ducts pass through the medullary layer of the kidney toward the apices of the pyramids.

✵ Every 2–3 renal pyramids fuse together by their apices to form a renal papilla. The papillae feature numerous openings where the excretory collecting ducts terminate, opening into the calyces. The calyces mark the beginning of the Urinary Tract. Minor renal calyces, fusing with one another, form 2–3 major renal calyces, which in turn lead into the renal pelvis.

✵ The renal pelvis is a funnel-shaped, flattened cavity with thin walls. Urine flows from the renal pelvis into the ureters, which connect to the urinary bladder.

✵ Two Types of nephrons are distinguished in the human kidney: cortical nephrons (80%), whose renal corpuscles are located in the outer zone of the cortex, and juxtamedullary nephrons (20%), whose renal corpuscles are localized in the inner zone of the cortex near the border with the medullary substance.

Class="center">

The nephron consists of a capillary glomerulus and a renal (urinary) tubule. The blind (closed) end of the renal tubule forms Bowman's capsule (the capsule of Shumlyansky-Bowman), which consists of two layers—visceral and parietal—with a capsular space (slit) between them. Inside the capsule lies the vascular glomerulus, which closely adjoins the visceral layer of the capsule. The vascular glomerulus is a tuft of capillaries formed by the branching of the afferent arteriole that brings blood into the kidney. The renal tubule continues from the space between the two layers of the capsule as a thin, single-layered tubular structure. Thus, the nephron is composed of the vascular glomerulus, Bowman's capsule, and the renal tubules. Each tubule extending from the nephron is divided into three sections: 1) the proximal tubule, located near the vascular glomerulus, consisting of convoluted and straight parts (the thick descending limb of the Loop of Henle); 2) the thin segment of the loop of Henle; and 3) the distal tubule, consisting of a straight part (the thick ascending limb of the loop of Henle). The distal portion of the tubule empties into the collecting duct. The collecting ducts form short excretory ducts that open through punctate orifices at the apex of the renal pyramid's papilla, which transitions into the renal calyces, and subsequently into the renal pelvis and ureter.

The Fornical Apparatus

✵ Smooth Muscle fibers in the wall of the renal fornix are arranged so that some of them function as the elevator of the fornix, while others act as its sphincter. The flow of urine from the papillary ducts (ducts of Bellini) into the minor calyces is not a passive process, but rather the result of the fornical apparatus function.

✵ The fornical apparatus includes: the fornix with its epithelial lining, the elevator and sphincter of the fornix, the adipose and Connective Tissue of the renal sinus surrounding the fornix (rich in elastic fibers, Blood Vessels, and nerves), as well as the renal papilla and the perifornical venous plexus.

✵ In the walls of the minor calyces, muscle fibers are also arranged longitudinally (the longitudinal muscle) and circularly around the calyx (the spiral muscle). The elevator of the fornix and the longitudinal muscle widen the cavity of the calyx, thereby facilitating urine accumulation. The sphincter of the fornix and the spiral muscle narrow the calyx, emptying it.

The ureter (one originating from each kidney) is a hollow tube connecting the kidney (renal pelvis) to the urinary bladder; the wall of the ureter consists of three layers: mucosal, muscular, and adventitial (connective tissue) tunics.

✵ The ureter is a urine-conveying tube measuring 30–35 cm in length with a lumen of 5–7 mm.

✵ Topographically, the ureter is divided into abdominal, pelvic, and intramural parts.

✵ The lumen of the ureter is uneven.

✵ The ureter features three narrowings: the first at the Water/144.html">Origin of the ureter (lumen 2–4 mm); the second at the site of transition into the lesser pelvis (lumen 4–6 mm); and the third in the intramural part (lumen 4 mm). Kidney stones (calculi) can become trapped in any of these narrowings during urolithiasis.

✵ Throughout almost its entire length, the Muscles of the ureter consist of two layers: an outer longitudinal layer and an inner circular layer. In the lower part of the organ, there is a third muscular layer—the longitudinal layer—which extends here from the trigone of the urinary bladder.

✵ The Movements of the ureter are peristaltic in nature, with contraction waves running at intervals of 1/4 to 1 minute; during these intervals, mucosal folds close off the lumen of the organ. Consequently, urine enters the urinary bladder in discrete portions of 8–10 drops twice a minute.

✵ When the urinary bladder is overly distended, the peristalsis of the ureter weakens, whereas when the ureter is obstructed by a stone, it intensifies. In cases of ureteral obstruction or compression, its proximal part dilates, Hypertrophy of the muscular tunic occurs, and prolonged impairment of urine outflow leads to muscular atrophy.

The urinary bladder is a hollow organ serving as a reservoir for urine accumulation, with a capacity of 500–700 ml, located in the cavity of the lesser pelvis posterior to the Pubic Symphysis. Inferiorly, it rests on the pelvic floor (perineal muscles). The urinary bladder comprises a base (fundus), neck, apex, and body. On the internal surface of the lower part of the urinary bladder, there is a smooth triangular area (the trigone), at the apex of which lies the internal urethral orifice, while the ureteral orifices are located at the angles of its base. Circular fibers of the muscular layer in the region of the internal urethral orifice and the ureteral orifices form the sphincter of the urinary bladder and the ureteral sphincters, respectively.

✵ The urinary bladder serves as a reservoir for urine. Its shape and size depend on its degree of filling. In newborns, the urinary bladder is spindle-shaped or pear-shaped, positioned above the pelvic inlet, with its apex located midway between the umbilicus and the pubic symphysis.

✵ The capacity of the urinary bladder (measured in cadavers) is 50–80 cm³ in newborns, 135 cm³ in 6-month-old infants, 200 cm³ at 1 year of age, 400 cm³ at 3–4 years, 500 cm³ at 8–9 years, and 900 cm³ at 12–13 years.

✵ In adults, the maximum capacity of the urinary bladder is 1500–2000 ml, being slightly greater in women than in men. The greatest bladder capacity is observed at 40–50 years of age, after which it decreases, and in old age, the organ enlarges due to weakening of the muscular tone.

✵ The structure of the urinary bladder walls exhibits certain features related to its function. The mucous membrane forms folds that smooth out and almost disappear when the organ is distended.

The urethra is a canal extending from the urinary bladder to the external urethral orifice, which in women opens into the Vestibule of the Vagina, and in men opens at the tip of the glans Penis, thereby belonging to the external genitalia. The length of the male urethra is 18–20 cm, its narrowest parts being the membranous part and the external orifice; the length of the female urethra is 3–4 cm. The urethra is divided into prostatic, membranous, and spongy parts.

The urethra is designed for the periodic excretion of urine from the urinary bladder and the expulsion of semen (in males).

The male urethra is a soft, elastic tube 16–20 cm in length. It originates at the internal urethral orifice of the urinary bladder and terminates at the external urethral orifice located on the glans penis.

The male urethra is divided into three parts: prostatic, membranous, and spongy. The prostatic part is located inside the prostate gland and is about 3 cm long. On its posterior wall, there is a longitudinal elevation known as the urethral crest. The most prominent part of this crest is called the seminal colliculus (verumontanum), at the apex of which lies a small depression—the prostatic utricle. Flanking the prostatic utricle are the openings of the ejaculatory ducts, as well as the orifices of the excretory ducts of the prostate gland. The membranous part begins at the apex of the prostate gland and reaches the bulb of the penis; its length is 1.5 cm. In this region, the canal passes through the urogenital Diaphragm, where striated muscle fibers form a voluntary urethral sphincter around it.

The spongy part is the longest section of the urethra (about 15 cm), passing through the corpus cavernosum urethrae (corpus spongiosum) of the penis.

The mucous membrane of the prostatic and membranous PARTS OF THE canal is lined with Cytology/practical/33.html">Pseudostratified columnar epithelium, the spongy part with simple columnar epithelium, and the region of the glans penis with stratified squamous epithelium.

The female urethra is wider and significantly shorter than the male urethra; it is a tube 3.0–3.5 cm long and 8–12 mm wide, opening into the vaginal vestibule. Its function is urine excretion.

In both men and women, as the urethra passes through the urogenital diaphragm, there is an external sphincter subject to voluntary control. The internal (involuntary) sphincter is located around the internal urethral orifice and is formed by a circular muscular layer.

The mucous membrane of the female urethra features longitudinal folds and depressions on its surface—urethral lacunae—while urethral glands are located within the thickness of the mucosa. A fold on the posterior wall of the urethra is particularly well-developed.