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SEMEY STATE MEDICAL UNIVERSITY
LECTURE COMPLEX
1. Theme 7: Development and peculiarities of the structure of urinary organs. Age properties.
2. Object: To acquaint students with questions of development and peculiarities of the structure
of urinary organs in different age.
3. Thesis of lectures:
• Anatomy of urinary organs
• Development of urinary organs
• Age peculiarities
STRUCTURE OF URINARY SYSTEM
• The urinary system consists of a pair of kidneys, which remove substances from blood, form
urine, and help regulate certain metabolic processes; a pair of tubular ureters, which
transport urine from the kidneys; a saclike urinary bladder, which stores urine; and a
tubular urethra, which conveys urine to the outside of the body.
• Kidneys are uriniparous organs
• Ureters urinary bladder, urethra are urinoexcretory organs
The kidney is a compound tubular gland containing about 1.2 million nephrons. Each kidney
weighs about 150 g and measures about 11 cm long, 6 cm wide, and 3 cm thick. Each kidney has
a smooth anterior and posterior surface covered by a fibrous capsule, which is easily removable.
The lateral surface is convex, whereas the medial surface is concave and has a slit, the hilum,
where it receives the renal nerves, blood vessels, lymphatics, and ureter.
Topography
• The kidneys lie on either side of the vertebral column in a depression high on the posterior
wall of the abdominal cavity. The upper and lower borders of the kidneys are generally at the
levels of the twelfth thoracic and third lumbar vertebrae, respectively. The left kidney is
usually 1.5–2.0 centimeters higher than the right one. The anterior surface of the right kidney
is related to numerous structures, some of which are separated from the kidney by a layer of
peritoneum and some of which are directly against the kidney. Posteriorly, the right and left
kidneys are related to similar structures. Superiorly is the diaphragm and inferior to this,
moving in a medial to lateral direction, are psoas major, quadratus lumborum, and
transversus abdominis muscles.
The fixing apparatus of kidney
• Renal bed
• Renal pedicle
• Renal coats (fibrous, fat, renal fascia)
• Intrabdominal pressure
Gross anatomy of kidney
Each kidney consists of an outer renal cortex and an inner renal medulla. Extensions of the
renal cortex (the renal columns) project into the inner aspect of the kidney, dividing the renal
medulla into discontinuous aggregations of triangular-shaped tissue (the renal pyramids).
The bases of the renal pyramids are directed towards the renal cortex, while the apex of each
renal pyramid projects towards the renal sinus. The apical projection (renal papilla) is
surrounded by a minor calyx. Several minor calices unite to form a major calyx, and two or
three major calices unite to form the renal pelvis.
• The nephron is the structural & functional unit of the kidney
A nephron consists of two principal parts:
• a renal corpuscle, which filters the blood plasma
• a long renal tubule, which converts the filtrate to urine.
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A renal corpuscle consists of a glomerulus surrounded by a Bowman’s capsule.
The glomerulus is a capillary network that arises from an afferent arteriole and empties into
an efferent arteriole. The diameter of the efferent arteriole is smaller than that of the afferent
arteriole, which helps maintain a fairly high blood pressure in the glomerulus.
Bowman’s capsule is the expanded end of a renal tubule; it encloses the glomerulus. The
inner layer of Bowman’s capsule is made of podocytes; and the “feet” of the podocytes are
on the surface of the glomerular capillaries. The arrangement of podocytes creates pores,
which make this layer very permeable. The outer layer of Bowman’s capsule has no pores
and is not permeable. The space between the inner and outer layers of Bowman’s capsule
contains primary urine.
• The renal tubule is a duct that leads away from the glomerular capsule and ends at the tip of
a medullary pyramid. It is about 3 cm long and divided into four major regions:
• the proximal convoluted tubule
• nephron loop
• distal convoluted tubule
• collecting duct
Only the first three of these are parts of an individual nephron; the collecting duct receives
fluid from many nephrons.
Functions of kidneys
• Urine formation
• Regulation the osmolarity of the body fluids
• Regulation of blood volume and pressure
• Participation in hemopoesis (secretion of the hormone erythropoietin)
• Contribution in calcium homeostasis.
• Regulation of acid–base balance of the body fluids
• They detoxify free radicals and drugs.
Urinoexcretory ways
URETERS are muscular ducts (25-30 cm long) with narrow lumina that carry urine from the
kidneys to the urinary bladder. They run inferiorly from the apices of the renal pelves at the hila
of the kidneys, passing over the pelvic brim at the bifurcation of the common iliac arteries. They
then run along the lateral wall of the pelvis and enter the urinary bladder.
The urinary bladder is an expandable, muscular container that serves as a reservoir for urine.
• The bladder is postioned immediately posterior to the pubic symphysis. The empty bladder is
shaped like a three-sided pyramid. It has an apex, a base, a superior surface, and two
inferolateral surfaces.
• In females, the bladder is anteroinferior to the uterus and directly anterior to the vagina. The
urinary bladder is a retroperitoneal organ, since only its superior surface is covered with
peritoneum. In males, the bladder is anterior to the rectum and superior to the prostate gland.
The urethra is a tube that conveys urine from the urinary bladder to the outside. Its wall is lined
with mucous membrane and has a thick layer of smooth muscle tissue, whose fibers are generally
directed longitudinally. The urethral wall also has abundant mucous glands, called urethral glands,
which secrete mucus into the urethral canal. In a female, the urethra is about 4 centimeters long.
Its opening, the external urethral orifice (urinary meatus) is anterior to the vaginal opening and
posterior to the clitoris.
Prenatal Development of kidneys
• The embryonic urinary system develops two pairs of primitive, temporary kidneys before
“settling down” and producing the permanent pair. The system develops as if replaying the
evolutionary history of the vertebrate urinary system.
• Early in week 4, a rudimentary kidney called the pronephros appears in the cervical region,
resembling the kidneys of many fish and amphibian embryos and larvae. The pronephros
disappears by the end of that week. As it degenerates, a second kidney, the mesonephros,
appears in the thoracic to lumbar region.
•
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•
The mesonephros functions in the embryos of all vertebrates, but is of minor importance in
most mammals, where wastes are eliminated via the placenta. Most of the mesonephros
disappears by the end of month 2, but its collecting duct, the mesonephric duct, remains and
contributes importantly to the male reproductive tract.
• The final kidney, the metanephros, appears in week 5 and thus overlaps the existence of the
mesonephros. Each collecting duct has a cap of metanephric kidney tissue over its tip. The
duct induces this cap to differentiate into an S-shaped tubule. Blood capillaries grow into one
end of the tubule and form a glomerulus as the tubule grows around it to form the doublewalled glomerular capsule. The other end of the tubule breaks through to become continuous
with the collecting duct. The tubule gradually lengthens and differentiates into the proximal
convoluted tubule, nephronloop, and distal convoluted tubule.
Peculiarities of structure of newborn’s kidneys
• Roundish shape
• Tuberous surface
• Lobular structure
• Insufficient development of cortex (2 mm VS 8 mm of medulla)
• Wide renal pelvis
• Fibrous capsule becomes observable to 5 y.o.
• Adipose capsule is absent, it starts to form to the period of first childhood
• Leaves of renal fascia are thin
Syntopy of newborn’s kidneys
• Upper poles are attached with adrenal glands almost up to hilum
• Right kidney attaches with liver, cecum with appendix
• Left kidney attaches spleen & pancreatic tail
• Longitudinal axis of kidney is parallel to vertebral column
• Axis has inclination up to 5-6 y.o.
4. Supporting data: slides in Power Point Presentation, questions of feedback control
5. Literature:
1. "Gray's Anatomy of the Human Body – 6. Surface Markings of the Thorax". Bartleby.com.
Retrieved 2010-10-18.
2. Marieb, Elaine N. (2009). Essentials of Human Anatomy & Physiology 9th Edition. San
Francisco, CA: Pearson Benjamin Cummings.
3. D.Chaurasia’s Human Anatomy. Regional and Applied, Dissection аnd Clinical. Fourth
Edition, 2004.
4. Frank H. Netter, M.D. Atlas of Human Anatomy. Fourth Edition, 2004.
6. Advancement questions (followed up)
1. Name inrarenal and extrarenal pathways of the urina.
2. Features of a structure of urinary organs at children's age.