Svintsitskaya N. L., Hryn V. H., Katsenko A. L.
Anatomy of the Urinary and Reproductive Systems.
Structural Features in Childhood.
УДК 611.6-053.2](075.8) С24
Рекомендовано вченою радою Української медичної стоматологічної академії як навчальний посібник (протокол №6 від 10 лютого 2021 року)
Kovalchuk O. I., Head of the Department of Anatomy and Pathological Physiology of the Educational and Scientific Center " Institute of Biology and Medicine" of the Taras Shevchenko National University of Kyiv, Doctor of Medicine, Professor.
Pliten O. M., Associate Professor of Pathological Anatomy, Kharkiv National Medical University, Candidate of Medical Sciences, Associate Professor.
Yeroshenko G. A., Head of the Department of Medical Biology of Poltava State Medical University, Doctor of Medical Sciences, Professor.
Kostenko V. G., Associate Professor of the Department of Foreign Languages with Latin Language and Medical Terminology of Poltava State Medical University, Candidate of Philological Sciences, Associate Professor.
N. L. Svintsitskaya, Associate professor of the Department of Human Anatomy, Candidate of Medical Sciences, Poltava State Medical University.
V. H. Hryn, Associate professor of the Department of Human Anatomy, Candidate of Medical Sciences, Poltava State Medical University.
A. L. Katsenko, Lecturer of the Department of Human Anatomy, Poltava State Medical University.
Svintsitskaya N. L.
Anatomy of the Urinary and Reproductive Systems.Structural Features in Childhood. Abnormalities = Анатомія сечової та статевої систем. Осо- бливості будови в дитячому віці. Аномалії : навчальний посібник / Svintsitskaya N. L., Hryn V. H., Katsenko A. L. – Вінниця : Нova Кnyha, 2021. – 160 p.
The study giude logically combines modern scientific data relating to the normal anatomy of the urinary and genital systems of an adult, as well as children. The mechanisms of developmental anomalies and pathologies of the human urogenital system are thoroughly elucidated. All this should greatly facilitate students of the international faculty to find the necessary information in preparation for practical classes in anatomy, histology, pathological anatomy, urology, gynecology and other clinical disciplines.
УДК 611.6-053.2](075.8) У посібнику логічно об'єднані сучасні наукові дані, що стосуються нормальної ана- томії сечової й статевої систем дорослої людини, а також дитячого періоду. Досконально освітлені механізми виникнення аномалій розвитку й патологій сечостатевої системи людини. Все це повинно значно полегшити студентам міжнародного факультета пошук необхідної інформації при підготовці до практичних занять з анатомії, гістології, патоло- гічної анатомії, урології, гінекології та інших клінічних дисциплін.
the urinary system, systema urinarium ...6
Development of the urinary organs in human ...6
the kidney, ren ... 11
Functions of the kidneys... 16
Clinical applications ... 16
The nephron ... 19
Juxtaglomerular Apparatus ... 22
Types of nephrons ... 23
Anatomical features of children’s kidneys ... 26
Developmental anomalies of kidneys ... 28
Elimination of Urine ... 37
the ureter, ureter ... 38
Clinical applications ... 40
Ureters anomalies ... 41
the urinary bladder; vesica urinaria ... 45
Clinical applications ... 45
Micturition ... 47
Anomalies of the urinary bladder ... 51
the genital system, systema genitalia ... 54
Evolution of reproductive organs ... 54
Anomalies of testis development ... 59
the male internal genitalia, organa genitalia masculina interna ... 62
The testis, testis ... 62
Clinical applications ... 64
Formation of Sperm Cells ... 68
Structure of a Sperm Cell ... 70
Anomalies of the testes ... 71
The spermatic cord, funiculus spermaticus ... 73
The ductus deferens, ductus deferens ... 73
The seminal gland, vesicula seminalis ... 75
The prostate, prostata ... 77
Clinical applications ... 80
Anomalies of the prostate ... 82
the male external genitalia, organa genitalia masculina externa ... 85
The penis, penis ... 85
The scrotum, scrotum ... 89
The male urethra, urethra masculina ... 90
Clinical applications ... 93
Anomalies of the penis ... 94
Anomalies of the urethra ... 94
the female genital system, systema genitale femininum ... 98
The female internal genitalia, Organa genitalia feminina interna ... 98
Clinical applications ...100
Anomalies of the ovary ...102
Fallopian tube, Tuba uterina ...103
The uterus, uterus ...105
Anomalies of the uterus ...113
The vagina, vagina ...116
Clinical application ...119
Abnormal development of the vagina ...120
the female external genitalia, organa genitalia feminina externa ...121
The pudendum, pudendum femininum ...121
Clinical applications ...123
the structure of the pelvis ...125
The hip bone ...125
The sacrum ...126
The functions of the pelvis ...127
Joints and ligamentous connections of the pelvis...128
Differences between the male and female pelvis ...129
Obstetrical pelvic measurements ...129
Clinical applications ...134
The perineum, perineum ...134
Clinical applications ...142
Practice questions ...143
Situation tasks ...146
This textbook is intended for undergraduate, postgraduate and continuing educa- tion for health care professionals from a variety of clinical disciplines (medicine, pedi- atrics, dentistry) as it includes the basic concepts of human anatomy of genitourinary system in adults and newborns. The neonatal period is the most crucial one in the hu- man life as well as the critical and determinative period for the postnatal ontogenesis.
This textbook covers not only the normal anatomy of genitourinary system in neo- nates but its variants and abnormalities which seem to be the commonest in medical practice.
Anomalies of kidneys and excretory organs are much more common in humans that in any other species. For the last decades due to the wide application of new di- agnostics techniques these abnormalities have being increasingly detected in the ear- ly age that is of great medical and social significance.
This textbook comprises scientific data referring the normal anatomy of genito- urinary system in adults and neonates as well as outlines the mechanisms triggering human genitourinary abnormalities. This might be helpful and supportive for the readers in searching the information needed for the lectures and practical training in anatomy, histology, anatomical pathology, urology, gynecology, and some other medical disciplines.
At the end of each chapter there are review questions, tests, and clinical case stud- ies designed for self-study to control and to stimulate thought about the issues and problems described. 118 illustrations occur in each chapter to present pertinent data.
We hope the textbook helps medical students to master the basic concepts of hu- man anatomy that are needed before progressing to more difficult material. It also meets Bologna requirements of ECTS for teaching and learning.
We will be particularly grateful for endorsements, suggestions, and critical re- marks.
the urinary system, systema urinarium
The urinary system consists of the following parts: a pair of glandular kidneys, which remove substances from the blood, form urine, and help regulate various metabolic processes; a pair of tubular ureters, which transport urine away from the kidneys; a saclike urinary bladder, which serves as a urine reservoir; and a tubular urethra, which conveys urine to the outside of the body (Fig. 1).
Fig. 1. The view of the urinary system
Development of the urinary organs in human
excretory organs in vertebrates. Evolution of excretory organs in vertebrates features a successive development and replacement of three different types of or- gans – the pronephros (primary kidney), mesonephros (intermediate kidney), and me- tanephros (definitive kidney).
structure of pronephros. The pronephros forms in all vertebrates but persists only in cyclostomes.
Pronephros is a system of segmental convoluted tubules (nephridia). Proximal ends of tubules open into the body cavity and distal merge to form the excretory ca- nal, which terminates in the caudal segment of digestive tube. The orifices of proxi-
mal ends feature cilia that direct the flow to nephridia. Subserous blood vessels form glomerules that filter the fluid. The fluid therefore first collects in the body cavity and then proceeds to the canaliculi. The canaliculi are responsible for urine concentration due to epithelium functioning.
structure of mesonephros. Further development of renal canaliculi leads to de- generation of the orifices that open into the body cavity. Mesonephral canaliculi thus come into intimate contact with capillary glomerules. Each canaliculus develops a blind double-walled capsule, which enfolds the glomerule to form a renal corpuscle well resembling that of the definitive kidney. The canaliculi become longer, convolut- ed and acquire more complex structure. They open into common mesonephric duct, ductus mesonephricus, which in turn opens into the cloaca. Generally, the mesone- phros appears as a paired elongated organ, which runs along the body. It lies retro- peritoneally on the dorso-lateral wall of the body cavity. Mesonephros persists in fish, amphibians and some reptiles.
relations of the mesonephros to the genitals. The internal genital organs are closely related to the mesonephros. The mesonephric duct in male fish, amphibians and reptiles communicates with the genitals and thus serves to transport semen. Fe- males develop paired paramesonephric ducts, which serve to transport the oocytes.
The mesonephros separates into two compartments – the cranial, which loses excre- tory function and becomes related to the genital organs and caudal, which retains ex- cretory function.
the definitive kidney (metanephros). The birds and mammals develop the de- finitive kidney appearing as a compact bean-shaped organ. The metanephros retains only excretory function leaving transporting of reproductive products to mesone- phros.
The definitive kidney arises from two sources. The projection in the caudal com- partment of the mesonephric duct (the ureter) grows cranially and enters the nephro- genic mass where venal corpuscle and tubules form. The metanephros thus separates from the mesone phros, which in turn becomes responsible for reproductive products transport. In view of the fact that the definitive kidney forms in the lesser pelvis cavity it is also called the pelvic kidney.
formation of the urinary organs from mesoderm. Formation of the renal cana- liculi is observed by the 4th week of development in so-called intermediate mesoderm (which lies between the ventral and dorsal mesoderm). The canaliculi lie in each seg- ment and generally appear as dense mass called the nephrogenic strand. The nephro- genic mass is a source for all kidney generations.
recapitulation of kidney phylogeny. During embryonic period, the kidneys suc- cessively pass through all evolutional stages i.e. embryo develops the pronephros, mesonephros and metanephros. As development progresses, the pronephric canalic- uli degenerate rapidly to become replaced with mesonephric canaliculi. Finally, the metanephros develops so the most part of mesonephros also degenerates except for the canaliculi that give rise to seminiferous tubules.
the pronephros. At the beginning of the 4th week of development, the embryo develops 7 pairs of pronephric canaliculi. They form at the level of cervical and upper thoracic somites. The canaliculi open into the common duct that grows lengthwise and terminates in the cloaca. Orifices of the proximal ends open into the coelomic cavity. Very soon, the pronephros undergoes involution and completely disappears by the 1st month of development.
the mesonephros in human embryo exhibits intensive development and unlike pronephros fully performs excretory function. The mesonephros also arises from the nephrogenic strand. It forms as paired S-shaped convoluted canaliculi, which join the pronephric duct. The latter henceforth is called the mesonephric duct, ductus me- sonephricus (the Wulfs duct). The nephrogenic strand gives rise to approximately 30 canaliculi but they do not exist simultaneously because as new canaliculi appear in the caudal portion of mesonephros the older ones undergo involution.
Blood vessels of mesonephros. The intermediate kidney receives numerous seg- mental arterial branches that arise from aorta. Inside the organ, each branch forms a capillary glomerule. The dilated proximal ends of the canaliculi enfold the glomerules and form double-walled capsule. Another arteriole leaves the capsule and again splits into capillary network that enfolds the canaliculi. These capillary collect into the effer- ent veins.
maximum development and degeneration of mesonephros. By the end of the 2nd month of embryo life, the mesonephros reaches maximum development. At this period, it appears as an elongated organ, which runs along the body cavity by its dorsal wall. Protruding into the body cavity, the mesonephros gives rise to paired urogenital ridge, plica urogenitales that run along the dorsal mesentery. Further, each ridge splits into lateral mesonephric fold and medial genital fold. The latter gives rise to genitals.
After formation of the metanephros, the mesonephros undergoes involution yet its duct and canaliculi residua give rise to genitals.
Double source of metanephros formation. The metanephros appears caudally to the mesonephros and arises from two sources:
projection of the mesonephros gives rise to the ureter, renal calices, pelvis, papil- lary ducts and collecting ducts;
the metanephrogenic mass gives rise to nephron ducts.
formation of the voiding passages. By the end of the 4th week, the caudal portion of mesonephric duct develops a projection, which is the ureter primordia. Very soon, the end of projection becomes dilated; this dilation corresponds to renal pelvis and calices. The primordia grows cranially and incorporates into the caudal portion of the nephrogenic strand. The metanephrogenic mass enfolds the primordia from all sides.
Further, the renal calices primordias give rise to the papillary ducts and collecting ducts.
formation of the nephrons. Internal differentiation of the metanephrogenic mass constitutes formation of nephron ducts. The renal artery incorporates into the mass and branches off to form the glomerules. The ducts enfold glomerules and form
the double-walled capsule. Growing on, the ducts develop segments and eventually join the collecting ducts that arise from calices primordias (Fig. 2–4).
Fig. 2. The development of the urinary system
Cloaca Gonadal ridge
Mesonephric (Wolffian) duct Paramesonephric
Fig. 3. The development of the kidney
Renal pelvis Major calyx
Major calyx Minor calyx Ureter
Week 7 Week 6 Week 5
Mesonephros Degenerating pronephros
Fig. 4. The development of the urogenital organs
Paramesonephric (Mullerian) duct
Primordium of prostate (male)
or of Skene’s (female) glands Primordium of Cowper’s (male) or of Bartholin’s (female) glands
Diaphragmatic ligament (suspensory ligament of ovary)
Urogenital sinus Genital cord
Mesonephric (Wolffian) duct
the kiDney, ren
Synonym ‘nephros’ (Greek) gives birth to ‘nephritis’, nephrology’ and other medical terms (Fig. 5).
A kidney is a reddish brown, bean-shaped organ with a smooth surface. It is about 12 centimeters long, 6 centimeters wide and 3 centimeters thick in an adult, and it is enclosed in a tough, fibrous capsule (tunic fibrosa). It`s mass ranges from 120 to 200 grams. The kidneys lie on either side of the vertebral column in a depression high on the posterior wall of the abdominal cavity.
Although the positions of the kidneys may vary slightly with changes in posture and with breathing movements, their upper and lower borders are generally at the levels of the twelfth thoracic and third lumbar vertebrae, respectively. The left kidney is usually about 1.5 to 2 centimeters higher than the right one.
The kidneys are positioned retroperitoneally, which means they are behind the parietal peritoneum and against the deep muscles of the back. They are held in po- sition by connective tissue (renal fascia) and masses of adipose tissue (renal fat) that surround them.
Fig. 5. Organs of the urinary system
Hepatic veins (cut) Inferior vena cava Adrenal gland Renal artery Renal hilus Renal vein Aorta Kidney Ureter Iliac crest Rectum (cut)
Urinary bladder Urethra
Uterus (part of female reproductive system)
the exterior of the kidney. Each kidney has two borders, two surfaces and two extremities (poles):
the lateral border, margo lateralis, a convex one directed laterally and slightly pos- teriorly;
the medial border, margo medialis, the opposite concave border directed medial- ly and slightly anteriorly;
the hilum of kidney, hilum renalis, a deep notch situated in the middle of medial border; the hilum contains the vessels, nerves, the renal pelvis and ureter;
the renal sinus, sinus renalis, a cavity within the kidney, which contains the renal calices, the renal pelvis, blood and lymphatic vessels, nerves and fat;
the anterior surface, facies anterior, more convex than posterior surface;
the posterior surface, facies posterior, rather flat compared to the anterior;
the superior extremity (pole), extremitas superior, rather thin, it lies superomedially;
the inferior extremity (pole), extremitas inferior, thicker than the opposite one (Fig. 6).
skeletotopy. The kidneys are related to Thl2 through L2. The right kidney lies 1–1.5 cm lower than the left (Fig. 7, 8). The upper extremities reach the XI ribs. Relations to the XII ribs are not identical: the left kidney is crossed by the XII rib in the middle, while the right – between the upper and middle thirds. The inferior extremities lie 3–5 cm above the iliac crest. The longitudinal axes of kidneys run slantwise downwards and laterally so the upper poles approximate while the lower are distant from each other.
Apart from this the kidneys versed so that the lateral borders are directed slightly pos- teriorly and the medial – anteriorly (Fig. 9).
Fig. 6. The exterior of the kidney
Posterior Anterior superior
Anterior inferior (middle)
Anterior surface of left kidney Posterior surface of left kidney
syntopy. The right kidney neighbors the right suprarenal gland, the liver, the de- scending part of duodenum and the right colic flexure (Fig. 10).
The left kidney neighbors the left suprarenal gland, the pancreas, the stomach, the left colic flexure and the small intestine.
Peritoneal relations. The kidneys lie posterior to the visceral layer of peritoneum (extraperitoneally). Only small portions of anterior surface retain serous coating.
kidneys’ support. The most important role in support of kidneys belongs to ab- dominal pressure and to the following structures:
the renal bed – the excavation bounded by the psoas major, the diaphragm, the quadratus lumborum and the transversus abdominis;
the perinephric fat (the perirenal fat capsule), capsula adiposa, abundant fat tis- sue, which enfolds the kidney. Its medial and posterior portions are better devel- oped than the rest;
the fibrous capsule, capsula fibrosa, a dense connective tissue coating, which fixes directly to the renal substance and may easily be removed. It also fixes to the peri- nephric fat and renal fascia;
the renal stalk, a bundle of the renal vessels, which fix the kidney to large vessels and ureter. The renal vein lies anteriorly, next lies the renal artery and the renal pelvis lies posteriorly (Fig. 11);
the renal fascia, fascia renalis, which covers the perinephric fat from outside. It has two layers – the prerenal and postrenal. The layers merge superior to the suprare- nal gland and along the lateral border. Inferior edges do not merge and run down gradually thinning to disappear in the retroperitoneal fat. The prerenal layer pass- es from one kidney to another anterior to the aorta and inferior vena cava and the post-renal layer fixes to the vertebral column.
Fig. 7. The projection of the kidneys on the back
Spleen Xth rib
Left kidney Right kidney
Serratus posterior inferior muscle Lumbocostal ligament Latissimus dorsi muscle
External abdominal oblique muscle Aponeurosis of transuersus
abdominis muscle Internal abdominal
oblique muscle Iliac crest Thoracolumbar fascia (posterior layer) Fascia (gluteal aponeurosis) over gluteus medius muscle Gluteus maximus muscle
Erector spinae muscle Iliolumbar ligament Psoas major muscle Ilioinguinal nerve Iliohypogastric nerve Ascending colon Right kidney Subcostal nerve
Transuersus abdominis muscle
Quadratus lumborum muscle (cut)
Pleura (costodiaphragmatic recess)
Quadratus lumborur muscle (cut)
Fig. 8. Posterior relation of the kidneys
Area for diaphragm
Area for diaphragm Projection
of 11th rib
Projection of 12th rib
Projection of 12th rib
Area for aponeurosis of transversus abdominis muscle Area for psoas major muscle
Area for quadratus lumborum muscle
Area for quadratus lumborum muscle Inferior vena cava
Fig. 9. Anterior relation of the kidneys
Gastrophrenic ligament Gastrosplenic ligament
Left suprarenal gland Splenorenal ligament
Area for stomach Area for spleen
Tail of pancreas Area for descending colon Area for small intestine Transverse mesocolon
Area for small intestine Area for colon
Peritoneum (cut) Duodenum Area for liver Peritoneum (cut) Area for bare area of liver
Right suprarenal gland
Inferior vena cava Right suprarenal gland
Diaphragm Esophagus Left suprarenal gland
Celiac trunk Left kidney
Left renal artery and vein Superior mesenteric artery (cut)
Left subcostal nerve
Peritoneum (cut) Sigmoid mesocolon (cut) Rectum
Abdominal aorta Iliohypogastric nerve
Ilioinguinal nerve Lateral femoral cutaneous nerve Left testicular (ovarian) artery and vein Inferior mesenteric artery (out]
Right kidney Right renal artery and vein Right subcostal nerve Transversus abdominis
muscle Quadratus lumborurn muscle Iliac crest Psoas major muscle
Iliacus muscle Right ureter Right common iliac artery
Right eternal iliac artery Right internal iliac artery
functions of the kidneys
The kidneys remove metabolic wastes from the blood and excrete them to the outside. They also carry on a variety of equally important regulatory activities includ- ing helping control the rate of red blood cell formation by secreting the hormone erythropoietin, helping regulate the blood pressure by secreting the enzyme renin, and helping regulate the absorption of calcium ions by activating vitamin D. The kid- neys also help regulate the volume, composition, and pH of body fluids. These func- tions involve complex mechanisms that lead to the formation of urine.
1. Reduced perinephric fat (common in weight loss) or decreased abdominal pres- sure (in abdominal muscles weakness) may result in abnormal kidneys descent (renal ptosis). In this case, the kidney (usually right) descends between the fascial layers to the greater pelvis. Treatment of the condition is aimed at suturing the fascial layers inferior to the kidney and fixation of the organ to the XII rib (nephropexy).
2. Blood from a ruptured kidney or pus in a perinephric abscess first distend the renal fascia, then force their way within the fascial compartment downwards into the pelvis. The midline attachment of the renal fascia prevents extravasation to the oppo- site side.
3. In hypermobility of the kidney (‘floating kidney’), this organ can be moved up and down in its fascial compartment but not from side to side. To a lesser degree, it is in this plane that the normal kidney moves during respiration.
4. Exposure of the kidney via the loin. An oblique incision is usually favoured mid- way between the 12th rib and the iliac crest, extending laterally from the lateral bor-
Fig. 10. Syntopy of the kidneys (transverse sections of the kidneys)
Kidney Adipose tissue
Inferior vena cava Pancreas
Spleen Small intestine
Large intestine Aorta
Fig. 11. Syntopy of the kidneys.
a – transverse section demonstrating the fascial compartments of the kidney. B – CT scan of the same region. Note that CT scans, by convention, are viewed from below, so that the aorta, for example, is seen on the right side. The blood vessels have been enhanced by an intravenous injection of contrast
der of erector spinae. Latissimus dorsi and serratus posterior inferior are divided and the free posterior border of external oblique is identified, enabling this muscle to be split along its fibres. Internal oblique and transversus abdominis are then divided, re- vealing peritoneum anteriorly, which is pushed forward. The renal fascial capsule is then brought clearly into view and is opened. The subcostal nerve and vessels are usually encountered in the upper part of the incision and are preserved. If more room is required, the lateral edge of quadratus lumborum may be divided and also the 12th
Inferior vena cava
Transversalis fascia Peritoneum Ascending colon Renal capsule Kidney Perinephric fat Renal fascia
Right kidney Inferior vena cava with left renal vein Superior mesenteric artery Transverse colon Psoas
rib excised, care being taken to push up, but not to open, the pleura, which crosses the medial half of the rib.
interior of the kidney. The renal substance consists of the renal cortex and the renal medulla. The lateral surface of each kidney is convex, but its medial side is deep- ly concave. The resulting medial depression leads into a hollow chamber called the renal sinus. The entrance to this sinus is termed the hilum, and through it pass various blood vessels, and the ureter. The superior end of the ureter is expanded to form a funnel-shaped sac called the renal pelvis, which is located inside the renal sinus. The pelvis is subdivided into two or three tubes, called major calyces (sing. calyx), and they, in turn, are subdivided into several (eight to fourteen) minor calyces.
A series of small elevations project into the renal sinus from its wall. These projec- tions are called renal papillae, and each of them is pierced by tiny openings that lead into a minor calyx.
The substance of the kidney includes two distinct regions: an inner medulla and an outer cortex. The renal medulla is composed of conical masses of tissue called re- nal pyramids, whose bases are directed toward the convex surface of the kidney, and whose apexes form the renal papillae. The tissue of the medulla appears striated due to the presence of microscopic tubules leading from the cortex to the renal papillae.
The renal cortex, which appears somewhat granular, forms a shell around the me- dulla. Its tissue dips into the medulla between adjacent renal pyramids, forming renal columns. The granular appearance of the cortex is due to the random arrangement of tiny tubules associated with the nephrons, the functional units of the kidney.
Fig. 12. The right kidney (coronal section)
Fibrous capsule Renal cortex Renal medulla
Renal papilla Fat in renal sinus Renal sinus
Major calyx Renal column
Renal artery Renal pelvis Renal vein
Ureter Renal pyramid in renal medulla Minor calyx
The renal segments. Renal segmentation is based on arterial branching within the organs:
the superior segment, segmentum superius;
the anterior superior segment, segmentum anterius superius;
the anterior inferior segment, segmentum anterius inferius;
the posterior segment, segmentum posterius;
the inf erior segment, segmentum inferius.
the renal lobes, lobi renalis. A renal lobe is a renal pyramid together with neigh- boring segment of the cortex separated by the interlobular arteries and veins running in the renal columns.
The cortical lobules, lobuli corticales. The renal lobules are the cortical segments separated by the interlobular arteries. Each lobule consists of the radiate part, pars ra- diata surrounded by the cortex corticis (Fig. 12).
The radiate part contains the straight portions of renal tubules and collecting ducts and the cortex corticis contains the renal corpuscles and distal portions of renal tubules.
Structure of a Nephron. A kidney contains about one million nephrons, eachcon- sisting of a renal corpuscle and a renal tubule. A renal corpuscle (Malpighian corpus- cle) is composed of a tangled cluster of blood capillaries called a glomerulus, which is surrounded by a thinwalled, saclike structure called a glomerular capsule (Bowman’s capsule) (Fig. 13).
The glomerular capsule is an expansion at the closed end of a renal tubule. It is composed of two layers of squamous epithelial cells: a visceral layer that closely cov- ers the glomerulus, and an outer parietal layer that is continuous with the visceral layer and with the wall of the renal tubule. The cells of the parietal layer are typical squamous epithelial cells; however, those of the visceral layer are highly modified epi- thelial cells called podocytes (Fig. 14, 15).
Each podocyte has several primary processes extending from its cell body, and these processes, in turn, bear numerous secondary processes, or pedicels. The ped- icels of each cell interdigitate with those of adjacent podocytes, and the clefts be- tween them form a complicated system of slit pores.
The renal tubule leads away from the glomerular capsule and becomes highly coiled. This coiled portion of the tubule is named the proximal convoluted tubule.
The proximal convoluted tubule dips toward the renal pelvis to become the de- scending limb of the loop of Henle. The tubule then curves back toward its renal cor- puscle and forms the ascending limb of the loop of Henle (Fig. 16).
The ascending limb returns to the region of the renal corpuscle, where it becomes highly coiled again and is called the distal convoluted tubule. This distal portion is shorter than the proximal tubule, and its convolutions are less complex.
Fig. 14. A scanning electron micrograph (SEM) of a cast of the renal blood vessels associated with the glomeruli (× 260) and SEM of a glomerular capsule
arteriole Affarant arteriole Glomerulus
Glomerylus Glomerular capsula
Fig. 13. The structure of the nephrons
Interlobar vein Renal vein
Arcuate vein Interlobular vein Vasa recta (juxtamedul-
lary) nephron) Peritubular
capillaries (cortical nephron) Efferent arteriole Glomerulus Afferent arteriole Interlobular artery Arcuate artery
Cortical nephron Renal cortex
Collecting duct Nephron loop
Fibrous capsule Renal pyramid
Arcuate vessels Interlobular
Fig. 15. Glomerulus and Bowman’s capsule (renal corpuscle)
Fig. 16. Scanning electron micrograph of a glomerulus (× 8.000).
Note the slit pores between the pedicels a complicated system of slit pores
Primary process of podocyte Pedicel
Bowmans eapsule (visceral layer podocytes) Bowmans capsule
Vascular pore Efferent arteriole Arferent arteriole
Several distal convoluted tubules merge in the renal cortex to form a collecting duct, which, in turn, passes into the renal medulla, becoming larger and larger as it is joined by other collecting ducts. The resulting tube (papillary duct) empties into a minor calyx through an opening in a renal papilla (Fig. 17).
Near its beginning, the distal convoluted tubule passes between the afferent and efferent arterioles and contacts them. At the point of contact, the epithelial cells of the distal tubule are quite narrow and densely packed. These cells comprise a struc- ture called the macula densa.
Fig. 17. Structure of a nephron and the blood vessels associated with it
Ascending limb Descending limb Henle's loop
Cortical renal corpuscle Proximal convolution
Distal convolution Fibrous capsule
Subcapsular zone Distal convolution Proximal
Juxlamedullary renal corpuscle
Outerstripe Inner stripe
Collecting tubule Cribriform area
Ascending limb Descending limb
Afferent and efferent arterioles
Renal (Malpighian) corpuscle; glomerular (Bowman’s) capsule with glomerulus
PnodrnaJ segment Neck
Proximal convolution Thick segment of descending limb
Henle’s loop Henle’s
Distal segment Thick segment of ascending limb Distal convolution Macula densa Medulla (pyxarmid) Inner zoneOuter zone
Close by, in the walls of the arterioles near their attachments to the glomerulus, are some large, smooth muscle cells. They are called juxtaglomerular cells, and to- gether with the cells of the macula densa, they constitute the juxtaglomerular appa- ratus (complex). This structure plays an important role in regulating the flow of blood through various renal vessels (Fig. 18).
types of nephrons
Depending on location the nephrons are subdivided into three groups as follows:
the subcapsular nephrons (2–3 %), their glomeruli lie right under the capsule and the tubular portions (including the loop) lie within the renal cortex;
a – location of the juxtaglomerular apparatus. B – enlargement of a section of the juxtaglomerular apparatus, which consists of the macula densa and the juxtaglomerular cells
Juxtaglomerular apparatus Distal convoluted tubule Glomerulus
Glomerulus Afferent arteriole
Macula densa Distal
Loop of Henle Efferent arteriole Glomerular
the intermediate nephrons (80 %) that lie in the middle of the cortex, their loops reach the medulla;
the juxtamedullary nephrons (18 %), which have large glomeruli lying adjacent to the medulla, their nephron loops descend deep to the medulla and reach apices of pyramids (Fig. 19).
Under conditions of rapid blood loss (e.g. in hemorrhagic shock) the small arteri- oles of outer nephrons contract leaving renal circulation to juxtamedullary nephrons.
Blood circulation thus becomes restricted to the medulla. This may result in renal in- sufficiency though renal blood circulation remains undisturbed.
The most significant place among renal diseases belongs to tubular degeneration (nephrosis) and inflammatory diseases of glomerular tubular system (nephritis and glomerulonephritis). These pathologies often develop as complications of infectious diseases and intoxications. The branch of medicine that studies diagnostics and treat- ment of renal diseases is called nephrology. The renal calices, calices renales and the renal pelvis are related to the renal sinus. The calices are subdivided into the major and minor.
sphincters. Walls of the calices and pelvis contain non-striated circular muscle fi- bers, which resemble sphincters. These sphincters reside in the fornix and pelvic out- let. The sphincters assist in forcing urine through the calices and pelvis and prevent urine backflow. Pathologies of calices and pelvis may result in urinary congestion.
The calices and pelvis are the common places where renal stones (calculi) form. Dis- Fig. 19. Urine ducts
Minor calyx Major calyx Renal column Renal pyramid
Renal pelvis Renal papilla
lodged stone may block the pelvis or ureter lumen. Very often, the stone-affected pel- vis exhibits purulent inflammation complicated with nephritis (pyelonephritis). Pass- ing stone causes severe pain called the renal colic. This state requires surgery. Recent treatment modalities include ultrasound techniques of stones fragmentation suitable for outpatient use.
arterial blood is supplied to the kidney via paired renal arteries (the branches of abdominal aorta). Within the hilum, each artery splits into three branches to both poles and central part. In the parenchyme, these branches give interlobar arteries, a. interlobares, which run to renal cortex (Fig. 20). In the area of pyramids’ bases, the
a – pathway of blood through the blood vessels of the kidney and nephron. B – the capillary loop of the vasa recta is closely associated with the loop of henle of a juxtamedullary nephron
Interlobular artery and vein Glomerulus
Proximal convoluted tubule
Efferent arteriole Glomerular capsule
Distal convoluted tubule
Loop of Henle
Collecting duct Renal pelvis RENAL ARTERY
ARCIFORM ARTERY INTERLOBULAR ARTERY
AFFERENT ARTERIOLE GLOMERULAR CAPILLARY
EFFERENT ARTERIOLE VASA RECTA AND PERITUBULAR CAPILLARY
INTERLOBULAR VEIN ARCIFORM VEIN
INTERLOBAR VEIN RENAL VEIN
interlobar arteries pass into the arcuate arteries, a. arcuatae, which in turn give nu- merous branches to cortex and medulla. Cortex related branches are the cortical radi- ate arteries, aa. corticales radiatae, which give small branches to each renal corpuscle and larger afferent glomerular arteriole, arteriola glomerularis afferens. The afferent arteriole passes into the glomerular capillaries, which again collect into arteriole – the efferent glomerular arteriole, arteriola glomerularis efferens. The efferent arteriole eventually passes into capillary network, which collects into venous system. Medulla related branches are the straight arterioles, arteriolae rectae, which run along the re- nal tubules and join the capillary network.
The blood flowing within cortex thus passes the capillaries twice: in the glomer- ules, where it slows down to ensure proper filtration and in peritubular renal capillary network.
Venous system begins in renal cortex with the stellate veins, w.stellatae well dis- tinguishable in sectioned kidney; in medulla, venous system begins with the straight venules, venae rectae. Further divisions of venous system simply accompany the ar- teries. Renal lobules and corpuscles lack lymphatic capillaries, which run only in in- terlobular connective tissue. The efferent lymphatic capillaries take their routes to the lumbar nodes, nodi lymphatici lumbales.
Innervation: branches of the renal plexus (plexus renalis), coeliac plexus, (plexus coeliacus) and the vagus nerve (nervus vagus).
anatomical features of children’s kidneys
in kidneys of newborns and infants retain rather high lobulation, which disap- pears up to the age of 2–4 years old. The kidney of children is relatively larger in size and weight than the kidney of adults, their weight is 1/100 of body weight, whereas in adults – 1/200–1/230 of body weight. Newborns have the round kid- ney. Their length does not exceed a total height of the four bodies of the lumbar vertebrae. The right kidney is larger than the left. The width of an infant’s kidney infants is 65 % of their length. With age, the growth of renal length is faster than the growth of the width. So that, the width of older children’s kidney is about 50 % of the length of the body, as for adults it is only 30–35 % (Fig. 21);
infants have their kidneys at the level of the IVth lumbar vertebrae, where as an older children, as adults have kidneys between the XIth thoracic and the IVth lum- bar vertebrae. Relatively low position of the kidneys in children determined to 7–8-year-olds. In addition, the kidneys are placed in a way that their lateral edges are turned a little posteriorly, while their medial edges are placed a bit forward;
adipose capsule is absent in infants;
infants have very thin fibrous capsule, which is directly adjacent to the paren- chyma;
fixing apparatus of infants and young children is not developed enough, which leads to greater physiological mobility of the kidneys. The kidney of newborns corresponds to the height of the body of one lumbar vertebrae and in average it is about 1–2 cm. In children of early years, the kidney may be available for palpation due to their increased mobility and correspondingly low position. The mechanism of kidney’s fixing ends by the age of 5–8 years old. The kidney displacement in a child of 1.5 and greater than the height of the lumbar vertebrae down favors pathological mobility of the kidney (nephroptosis);
in postnatal onthogenesis nephrons remain morphological signs of immaturity.
In particular, the glomeruli at the moment of birth are poorly differentiated and have a small diameter of 85 mm, whereas in adults it is about 200mm. Glomerular epithelium is not flat as in adults, but cylindrical. Tubules relatively short in length and the diameter is half of adult tubules. The loop of Henle is underdeveloped and looks like a small curl. These features of the structure of the nephrons in young children influence the functionality of the kidneys. The features of the anatomical and histological structure of the children are not specific to the kidney, but also to the urinary tract;
Fig. 21. The internal structure of the kidney
Renal capsule Medullary (renal)
Ureter Renal pelvis Renal vein Renal artery
Interlobular vein Interlobular artery Arcuate vein Arcuate artery Interlobar vein Interlobar artery Lobar artery Segmental artery
the kidneys of infants and young children are unable to concentrate urine and conserve water as effectively as those of adults. Consequently, such young per- sons produce relatively large volumes of urine and tend to lose water rapidly, which may lead to dehydration;
renal pelvises in newborn and infants are relatively large in size, the walls are weakly developed, and hypotonic due to poor development of muscle and elastic fibers. The mentioned features can favor the stagnation of urine and the appear- ance of inflammatory processes.
Developmental anomalies of kidneys
Incidence and clinical significance. Kidney development features complex pro- cesses (two different primordias, kidney ascent etc.) so renal malformations incidence constitutes 1 % of all occurrences in neonates. Some anomalies are asymptomatic and remain undiagnosed throughout the life while some require immediate treatment.
Studying of renal malformations thus is of great significance for urology (Fig. 22).
number anomalies. Absence of primordia or growth failure results in unilateral or bilateral renal agenesia (complete absence). Bilateral agenesia is a fatal pathology, while unilateral agenesia or underdevelopment is more common. It becomes import- ant in cases when pathology develops in the single kidney.
Double kidney is another common deformity, which results from unilateral forma- tion of two ureteric buds. The kidney as a rule is enlarged and has two functional ure- ters. Less common is the smaller accessory (third) kidney.
size anomalies. Unilateral reduction (hypoplasia) of one kidney as a rule com- bines with enlargement (hyperplasia) of the contralateral organ. Bilateral hypoplasia is uncommon and features severe malfunctioning.
number anomalies and position anomalies of the renal arteries. In this group, additional renal arteries are the most frequent. It has a smaller diameter and goes to the upper or lower segment of the kidney from the abdominal aorta or from the trunk of the kidney, suprarenal, common iliac arteries. Additional renal arteries can be six or more. They are one of the main causes of violation of urodynamics and development of hydronephrosis. Additional arteries can be found in 21.4 % of patients operated be- cause of hydronephrosis. The main clinical sign of additional vessels of the lower pole of the kidney is the pain syndrome of varying intensity (attack of renal colic), com- plicated by pyelonephritis. Diagnosis of additional vessel can be based on X-ray and other methods. The treatment should be surgical.
Double kidney artery. Kidney is supplied with blood by two identical diameter arteries. One of the two renal artery lies behind the pelves. It branches into the form of a network. The pelves is blocked by the renal artery and its branches of a large di- ameter. This can prevent from removing of the stone through an incision in the back of the kidney.
Multiple kidney arteries. There are common for the kidney in a shape of a horse- shoe and other types of dystopia kidney, but can also occur in the normally devel- oped kidney. Renal artery aneurysm are also corresponded to the anomalies of shape and structure of the renal arterial trunks. Renal artery aneurysm is represented in the shape of sack or fusiform enlargement of the vessel. Moreover, they are of an unilater- al. Aneurysms have a certain symptomatology detected in 60–80 % of cases (Fig. 23).
The absence of the kidneys on both sides is incompatible with life. The absence of one kidney or hypoplasia are frequent and have important clinical implications in cases where only one pathologic process develops in the kidney (Fig. 24).
The doubling of the kidneys also happens quite often, it is associated with two ure- teral outgrowths on one side (Fig. 25, 26). Such a kidney is enlarged and has 2 ureters.
Rare anomaly is the presence of an extra (third) kidney, which is much smaller by size (Fig. 27).
the abnormal sizes. Decrease (hypoplasia) of the size of one kidney with its nor- mal structure usually combines with an increase (hyperplasia) of the opposite kidney.
Fig. 22. The right kidney of a newborn. (Anterior surface).
a: 1 – the lower end (extremitas inferior); 2 – anterior surface (facies anterior); 3 – lateral margin (margo lateralis): 4 – the upper end (extremitas superior); 5 – medial border (margo medialis):
6 – renal artery (a. renalis); 7 – renal hilum (hilus renalis); 8 – renal vien (v. renalis); 9 – ureter (ureter).
B: 1 – the lower end (extremitas inferior); 2 – kidney’s cortex (cortex renalis); 3 – renal column (columnae renales); 4 – minor renal calyx (calices renales minores); 5 – renal pyramids (pyramides renales); 6 – lateral margin (margo lateralis): 7 – the upper end (extremitas superior); 8 – major kidney calyx (calices renales majores); 9 renal sinus (sinus renalis); 10 – renal pelvis (pelvis renalis);
11 – ureter (ureter) 2
Hypoplasia of both kidneys includes severe disruption of their functions, which is rather uncommon.
shape and position anomalies. Abnormal position (ectopia) constitutes 25 % of all congenital anomalies. Ectopia may be unilateral and bilateral. Lumbar and iliac ec- topias are the most common types of abnormal position of kidneys. Pelvic ectopia oc- curs as the result of complete ascent failure. Abnormal position usually combines with deformities and incomplete rotation (Fig. 28, 29).
Fig. 23. Aplasia of the left kidney
Fig. 24. Variants of agenesis and aplasia of the left kidney.
a – agenesis with absence of ureter. B – aplasia with the presence of a rudimentary ureter.
C – crossed dystopia of the right kidney with agenesis of left kidney
a B C
The kind of dystopia determines the blood supply of the kidney. The vessels of lumbo-dystopic kidney are placed normally, but more often they can be doubled and originate from the aorta, from the level of the second lumbar vertebra before the bi- furcation of the abdominal aorta (Fig. 30).
If the kidney is above the sacrum bone or in the pelvic cavity, the vessels may de- viate from the common iliac and the external iliac, median sacral or inferior mesen- teric arteries. The arteries are accompanied by corresponding veins. Kidney dystopia combined with anomalies of genital organs.
intrathoracic dystopia of a kidney is very rare and is called epiphrenic dystopia. A healthy kidney is placed above the diaphragm and it is not clinically detected.
Pelvic dystopia is characterized by deep-seated kidney positioned in the pelvic cavity. It can be placed in the sacral groove. In these cases, the fatty tissue, sacral ner- vous plexus, pyramidal and sacrococcygeal muscle are located between the sacral bone and the kidney (Fig. 31, 32).
Fig. 25. Variants of a double kidney and ureter.
a – full doubling of the left pelvis and ureter. B – doubling of the the left pelvis with splitting of the ureter. C – bilateral doubling of pelvises and ureters. D – bilateral doubling of pelvises and ureters splitting. e – bilateral doubling of pelvises, doubling of the right ureter and splitting of the left one
a B C
Fig. 26. Common variants of kidney doubling and renal pelvises
1 2 3 4 5 6
7 8 9 10 11 12
13 14 15 16 17
18 19 20 21 22 23
Fig. 27. Schemes of an additional (third) kidney localization
In severe pelvic kidney dystopia, the kidney is located between the rectum and the bladder in men and between the uterus and rectum in women. The upper pole of the kidney is covered by peritoneum, and the lower one is on the pelvic diaphragm, and the middle part of the kidney is bordered with the prostate gland in men or the back of the vagina in women. Pelvic dystopia can be uni- or bilateral. At bilateral dys- topia it is possible the fusion of the kidneys. The form of the kidney can be round, flat- tened, galette-like and partial (Fig. 33).
Fig. 28. Variants of kidney dystopia
In the chest
Fig. 29. The anomalies of kidney position.
a – heterolateral dystopia. B – cross iliac dystopia of the one kidney. C – pelvic dystopia of one kidney. D – pelvic dystopia
a B C D
kidneys fusion. Fusion of two renal primordia results in formation of single or- gan with two ureters. Most common is fusion of inferior poles called horseshoe kid-
Fig. 31. Intrathoracic dystopia of the right kidney Fig. 32. Pelvic dystopia of the left kidney Fig. 30. Variants of the blood supply of the anomalously located kidneys.
a – iliac dystopia of the left kidney. B – lumbar dystopia of the right kidney and pelvic dystopia of the left kidney
ney (90 % of all occurrences). This malformation as a rule is associated with lumbar or pelvic ec- topia. Less common are rosette kidney, S-shaped kidney, L-shaped kidney, hook-like kidney, etc (Fig. 34–36).
Multicystic kidney.This is a rare anomaly which amounts to 1.1 % of all the anomalies of the kidney (Fig. 37). This anomaly is characterized by a total replacement of the renal parenchyma by cystic formations. In 50 % of cases older chil- dren and adults in the projection multicystic kid- ney can be determined by round shadows, calci- fied cysts in the X-ray.
Polycystic kidney disease. This is a severe ab- normality of both kidneys, which is characterized by replacement of renal parenchyma by multi- ple cysts of different sizes (Fig. 38). There are two forms of polycystic kidney disease: the first one with increasing dimensions of the kidney (detect- ed more often) and second one with no increas- ing or with some decreasing size of the kidneys.
neonatal polycystic manifests during the first month of life cause a progressive renal and the pulmonary failure of both kidneys. For poly- cystic process of infants, in general it is character- ized by increasing of both kidneys, splenomega-
Fig. 33. The right kidney is located on the usual place. Pelvic dystopia of the left kidney. Ureter of the left kidney is compressed by one of the numerous
branches of the renal artery
Fig. 34. Anomalies of kidney interposition.
А – horse-shoe kidney. B – S-shaped kidney. C – L-shaped kidney
a B C
Fig. 37. Multicystic kidney Fig. 35. A galette-shaped kidney
ly, liver failure, and progressive chronic renal failure. According to this anomaly the 25 % of the tubules replaced cysts. At polycystic kidney in adolescence parenchyma is not changed, and about 10 % of the tubules are affected by cystic dysplasia. In old- er children polycystic kidneys are small and have heavily tuberous surface with cysts ranged through the fibrous capsule. On a section kidney parenchyma is dotted with lots of cysts of varying size (Fig. 39).
Fig. 36. Anomalies of kidney interposition.
a – S-shaped. B – tumor-shaped. C – L-shaped. D – disk-shaped
a B C D
Fig. 38. Polycystic kidney
elimination of urine
After being formed by nephrons, urine passes from the collecting ducts through openings in the renal papillae and enters the major and minor calyces of the kidney.
From there it passes through the renal pelvis and is conveyed by a ureter to the uri- nary bladder. Urine is excreted to the outside by means of the urethra.
Fig. 39. A horseshoe kidney with wide isthmus (a), which compresses the urethra and narrow (B) of the isthmus
the ureter, ureter
The ureter connects the renal pelvis with the urinary bladder. It is 30 cm long, 5–6 mm of diameter and lies extraperitoneally (i.e. devoid of peritoneal investment).
relative positioning of ureters. Each ureter has three parts:
the abdominal part, pars abdominalis;
the pelvic part, pars pelvica;
the intramural part, pars intramuralis.
The abdominal part is 12–15 cm long; it runs along the anterior surface of the qua- dratus lumborum on each side. Relations of the abdominal parts of ureters are not identical. Upon leaving the sinus, the right ureter runs posterior to the descending part of duodenum and the left runs posterior to the duodenojejunal flexure. Running on, both ureters cross either ovarian (in females) or testicular vessels (in males). In the lowermost portion of abdomen, the right ureter runs posterior to the root of mes- entery while the left runs posterior to the of sigmoid mesocolon. The pelvic part is 13–14 cm long. Relations of these parts are side-independent but sex-related. Enter- ing the pelvic inlet the right ureter crosses the right external iliac artery and the left crosses the left common iliac artery (Fig. 40).
Fig. 40. Relations of pelvic viscera and perineum in male (sagittal section)
Ureter Symphysis pubis Urinary bladder
Prostate gland Parietal peritoneum
In females, the ureters run posterior to the broad ligament of uterus and then along the free border of ovary. Laterally to the cervix of uterus, the ureters loop around the inferior border of the broad ligament cross the uterine vessels at a right angle and pass between the anterior wall of vagina and the urinary bladder to reach the fornix of the latter posteriorly.
In males, the ureter on each side runs laterally to the ductus deferens then crosses it inferiorly to enter the bladder wall anteroinferiorly to the seminal vesicle.
The intramural part is 1.5–2 cm long; it takes a skewed route through the bladder wall to open in the fundus of bladder with slit-like orifice.
the constrictions of ureter. First constriction appears at the junction of the ure- ter and renal pelvis, the second – where it enters the lesser pelvis (at the terminal line) and the third – within the urinary bladder wall. Renal stones often lodge in these con- strictions. The segments between the constrictions are somewhat dilated.
Layers of ureter wall. The layers distinguishable in the ureter wall are like the following: 1) the mucosa and submucosa; 2) the muscular layer and 3) adventitia (Fig. 41).
The mucosa forms small longitudinal folds and contains mucous glands and sol- itary lymphatic nodules. The muscular tunic consists of external longitudinal and in- ternal circular layers. The lower portion features the third internal longitudinal layer.
Within the bladder wall, the muscular fibers run spirally. Contracting, the muscles cause ureter orifices to open.
Fig. 41. Cross section of a ureter (× 160)
arterial blood is supplied to the ureters from three sources:
the ureteric branches (rr. ureterici) from renal, testicular (or ovarian) arteries sup- ply the superior parts of ureters;
branches of the same name arising from the internal iliac artery and abdominal aorta supply middle part of the organs;
ureteric branches of the inferior vesical arteries (a. vesicales inferior) and middle rectal artery (a. rectalis media) supply inferior parts of the organs.
Lymph drains into lumbar and iliac lymph nodes.
innervation: branches of renal and inferior hypogastric plexuses and the vagus nerve.
Because the linings of the ureters and the urinary bladder are continuous, infec- tious agents such as bacteria may ascend from the bladder into the ureters. An inflam- mation of the bladder, which is called cystitis, occurs more commonly in women than m men because the female urethral pathway is shorter. An inflammation of the ureter is called ureteritis.
Although the ureter is simply a tube leading from the kidney to the urinary blad- der, its muscular wall helps move the urine. Muscular peristaltic waves, originating in the renal pelvis, force the urine along the length of the ureter. These waves are initiated by the presence of urine in the renal pelvis, and their frequency is related to the rate of urine formation. If the rate of urine formation is high, a peristaltic wave may occur every few seconds; if the rate is low, a wave may occur every few minutes.
When such a peristaltic wave reaches the urinary bladder, it causes a jet of urine to spurt into the bladder. The opening through which the urine enters is covered by a flaplike fold of mucous membrane. This fold acts as a valve, allowing urine to enter the bladder from the ureter but preventing it from backing up from the bladder into the ureter.
If a ureter becomes obstructed, as when a small kidney stone (renal calculus) is present in its lumen, strong peristaltic waves are initiated in the proximal portion of the tube. Such waves may help move the stone into the bladder. At the same time, the presence of a stone usually stimulates a sympathetic reflex (ureter- orenal reflex) that results in constriction of the renal arterioles and reduces the production of urine in the kidney on the affected side.
Kidney stones, which are usually composed of calcium oxalate, calcium phosphate, uric acid, or magnesium phosphate, sometimes form in the renal pelvis. If such a stone passes into a ureter, it may produce severe pain. This pain commonly begins in the region of the kidney and tends to radiate into the abdomen, pelvis, and legs. The pain may also be accompanied by nausea and vomiting. Although about 60 % of kidney stone patients pass their stones spontaneously, the others must have the stones removed. In the past, such removal required surgery or tubular instruments that could be passed through the