Urinary System

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BY: DR. NABIHA IQBAL

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• The urinary system is one of the excretory systems of body. It consists of the following structures:
• 2 kidneys, which secrete urine
• 2 ureters, which convey the urine from the kidneys to the urinary bladder
• 1 urinay bladder where urine collects and is temporarily stored
• 1 urethra through which the urine passes from the urinary bladder to the exterior.

Kidney

• The kidneys are bilateral bean-shaped organs, reddish-brown in color and located in the posterior abdomen.
• Kidney is 11 cm long, 6 cm wide, 3 cm thick and weigh 150 g.
• They are embedded in, and held in position by, a mass of fat.
• A sheath of fibrous connective tissue, also known as the renal fascia, encloses the kidney and the renal fat.

Function

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• To filter and excrete waste products from the blood.
• Responsible for water and electrolyte balance in the body.
• Metabolic waste and excess electrolytes are excreted by the kidneys to form urine.
• Production and secretion of erythropoietin, the hormone that stimulates formation of red blood cells.
• Production and secretion of renin, an important enzyme in the control of blood pressure

Urine:

• Urine is transported from the kidneys to the bladder by the ureters.
• It leaves the body via the urethra, which opens out into perineum in the female and passes through the penis in the male.

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Anatomy of Kidney

• The kidneys lie retroperitoneally (behind the peritoneum) in the abdomen, either side of the vertebral column.
• They extend from the level of the 12th thoracic vertebra to the 3rd lumbar vertebra, receiving some protection from the lower rib cage
• The right kidney is often situated slightly lower due to the presence of the liver. Each kidney is approximately three vertebrae in length.
• The adrenal glands sit immediately superior to the kidneys within a separate envelope of the renal fascia.

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Organs associated with the kidneys

The kidneys lie on either side of the vertebral column, each is associated with a different group of structures.

Right kidney

• Superiorly – the right adrenal gland
• Anteriorly– the right lobe of the liver, the duodenum and the hepatic flexure of the colon
• Posteriorly – the diaphragm, and muscles of the posterior abdominal wall

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Left kidney

• Superiorly – the left adrenal gland
• Anteriorly – the spleen, stomach, pancreas, jejunum and splenic flexure of the colon
• Posteriorly – the diaphragm and muscles of the posterior abdominal wall

Structure

• an outer Fibrous capsule, surrounding the kidney
• The Cortex, a reddish-brown layer of tissue immediately below the capsule and outside the pyramids.
• The Medulla, the innermost layer, consisting of pale conical-shaped striations, the renal pyramids.
• The apex of a renal pyramid is called a renal papilla.
• Each renal papilla is associated with a structure known as the minor calyx, which collects urine from the pyramids.
• Several minor calices merge to form a major calyx. 

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• Urine passes through the major calices into the renal pelvis, a flattened and funnel-shaped structure.
• From the renal pelvis, urine drains into the ureter, which transports it to the bladder for storage.
• The medial margin of each kidney is marked by a deep fissure, known as the renal hilum.
• This acts as a gateway to the kidney
• Normally the renal vessels, nerves and lymph vessel and ureter enter/exit the kidney via this structure.

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Microscopic structure of the kidney

• The kidney is composed of about 1–2 million functional units,
• the nephrons,
• Smaller number of collecting ducts.
• The collecting ducts transport urine through the pyramids to the calyces and renal pelvis, giving the pyramids their striped appearance (Fig. 13.4).
• The collecting ducts are supported by a small amount of connective tissue, containing blood vessels, nerves and lymph vessels.

Nephron

• The nephron consists of a tubule closed at one end, the other end opening into a collecting tubule.
• The closed or blind end is indented to form the cup-shaped glomerular capsule (Bowman’s capsule), which almost completely encloses a network of tiny arterial capillaries, the glomerulus.
• Remainder of the nephron is about 3 cm long have three parts:
• The proximal convoluted tubule
• The medullary loop (loop of Henle)
• The distal convoluted tubule, leading into a collecting duct.
• The collecting ducts unite, forming larger ducts that empty into the minor calyces.

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Blood supply

The kidneys are supplied with blood via the renal arteries, enter at hilus

• Divided into small Arterioles and Arteries

Afferent arteriole

• In cortex arteriole or Afferent arteriole enter into glomerular capsule------subdivided into ----cluster of capillaries ----Form Glumerulus.

Phagocytic mesangial cells

Connective tissue present between capillary loops.

Efferent arterioles

Blood vessel leading away from glomerulus ----break into second capillary

network ----supply O2 & nutrients to remaining nephron

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Venous Drainage�

• The kidneys are drained of venous blood by the left and right renal veins. They leave the renal hilum anteriorly to the renal arteries, and empty directly into the inferior vena cava.
• As the vena cava lies slightly to the right, the left renal vein is longer, and travels anteriorly to the abdominal aorta below the origin of the superior mesenteric artery. The right renal artery lies posterior to the inferior vena cava.

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Nerve & lymphatics�

• The nerve supply consist of both sympathetic and parasympathetic nerves

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• Lymph from the kidney drains into the lateral aortic (or para-aortic) lymph nodes, which are located at the origin of the renal arteries.

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Ureters

Ureters

• The ureters are the tubes that carry urine from the kidneys to the urinary bladder
• They are about 25 to 30 cm long with a diameter of about 3 mm
• the ureter is continuous with the funnel-shaped renal pelvis.
• It passes downwards through the abdominal cavity, behind the peritoneum in front of the psoas muscle into the pelvic cavity, and passes obliquely through the posterior wall of the bladder.
• Because of this arrangement, when urine accumulates and the pressure in the bladder rises, the ureters are compressed and the openings occluded. This prevents reflux of urine into the ureters (towards the kidneys) as the bladder fills and during micturition, when pressure increases as the muscular bladder wall contracts

Structure

• The walls of the ureters consist of three layers of tissue which are shown in cross-section in Figure 13.19:
• an outer covering of fibrous tissue, continuous with the fibrous capsule of the kidney
• a middle muscular layer consisting of interlacing smooth muscle fibres that form a functional unit round the ureter
• an additional outer longitudinal layer in the lower third an inner layer, the mucosa, composed of transitional epithelium