THE URINARY SYSTEM| ANATOMICAL, PHYSIOLOGICAL AND CLINICAL EXPLANATION|, Study notes of Anatomy

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Urinary system

Urinary system

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Fig 159

The components of the urinary system (without the urethra) and some adjacent structures

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Fig 160

Anterior view of the kidneys, showing their sites of contact with adjacent structures

Urinary system

1. 2. Suprarenal glandsStomach 3. 4. SpleenPancreas 5. 6. JejunumLeft (splenic) colic flexure 7. 8. UreterRenal vein 10.^ 9.^ AortaInferior vena cava 11. 12. Renal arterySmall intestine 13. 14. Right (hepatic) colic flexureLiver 15. Duodenum Comments Anatomical: The bean-shaped kidneys are located on either side of the vertebral column between the 12th thoracic vertebra (T12) and 3rd lumbar vertebra (L3). The renal fascia, made up of connective tissue, surrounds each kidney and keeps it tethered in contact with the adjacent organs. The relations of the right kidney include the right suprarenal gland, the right lobe of the liver, the duodenum and the right colic flexure of the colon. Both kidneys are in contact with the diaphragm and the muscles of the posterior abdominal wall. The relations of the left kidney include the left suprarenal gland, the spleen, the stomach, the pancreas, the jejunum and the left colic flexure. The blood supply of the kidney depends on the renal artery and the renal vein, which enter or leave at the renal hilum. Clinical: Chronic renal failure is very often associated with a reduction in the size of the kidneys. Signs and symptoms of renal cancer may include lumbar pain, haematuria, weight loss and fever. It can also be detected by chance during an ultrasound or a computed tomography scan performed for some other reason.

Urinary system

1. 2. CortexMinor calyces 3. 4. Renal arteryRenal vein 5. 6. Renal pelvisUreter 7. 8. CapsuleMajor calyx 10.^ 9.^ Renal papillaMedulla (pyramids) Comments Anatomical: The kidney consists of three tissue layers. On the outside, there is a fibrous capsule that surrounds it and overlies the cortex, which is a layer of brown tissue sandwiched between the capsule and the pyramids. The medulla, the innermost layer of the kidney, consists of the renal pyramids, which appear striated because of the presence of the collecting ducts as they carry urine to the calyces. The blood vessels, the nerves and the ureter pass through the hilum, which forms a concave border in the middle of the medial aspect of the kidney. Physiological: hydrostatic pressure. It passes through a renal papilla at the apex of a pyramid, The urine formed in the nephron is moved along by intratubular drains into the calyces and the renal pelvis and enters the bladder, where it is stored until it is excreted. Clinical: lead to renal colic if the stones become impacted in the ureter and can cause very The presence of small renal stones (nephrolithiasis) in the calyces can severe acute pain in the lumbar region, radiating towards the external genitalia. The stones are formed when some normally dissolved urinary constituents precipitate as a result of some metabolic disease, dehydration or a change in the urinary pH during some infections.

Fig 162

A nephron and its associated blood vessels

Fig 163

The serial arrangement of the blood vessels in the kidney

Urinary system

1. 2. Renal arteryAfferent arteriole 3. 4. GlomerulusEfferent arteriole 5. 6. Peritubular capillaries (supplying the nephron)Renal vein

Comments Anatomical: The kidney is a very vascular organ. The renal artery divides sequentially into segmental, interlobar, arcuate and interlobular arteries before giving rise to the arterioles. The afferent arteriole enters the glomerular capsule and then divides further into small capillaries to form the glomerulus. An efferent arteriole exits the capsule to give rise to the interlobular veins and the interlobar veins, which drain into the renal vein, as it leaves the renal hilum to join the inferior vena cava. Physiological: the diameters of the afferent and efferent arterioles—and hence the difference in The renal artery supplies the kidney with blood. The difference in their intraluminal pressure—allows filtration to occur. This process does not allow large molecules such as plasma proteins and blood cells to be filtered. Clinical: of their rich vascularity. The risk of haemorrhage is higher in cases of rupture or Haematuria is a common clinical finding in diseases of the kidneys because trauma to the kidney. Gross haematuria, lumbar pain and clinical signs of shock (e.g., tachycardia, arterial hypotension) are suggestive of renal trauma. Haematuria, a sudden acute and intense pain in the flank or in the abdomen, described as a stabbing pain, nausea, vomiting and a feeling of sickness are the signs and symptoms of renal infarction.

Urinary system

1. 2. Glomerular capsuleNet filtration pressure (1.3 kPa, or 10 mmHg) 3. 4. Glomerular hydrostatic pressure (7.3Glomerular osmotic pressure (4 kPa, or 32 kPa, or 60 mmHg) mmHg) 5. Glomerular hydrostatic pressure (2 kPa, or 18 mmHg) Comments Anatomical: At the upper end of the nephron, the cup-shaped glomerular capsule or Bowman’s capsule surrounds the glomerulus, which is a network of arterial capillaries. Physiological: merular capillaries and the glomerular capsule as a result of the pressure difference Filtration occurs across the semipermeable membrane of the glo- between the osmotic pressure of the blood and the hydrostatic pressure of the filtrate. Clinical: Oedema and arterial hypertension may also be present, indicating renal insufficiency. Haematuria and proteinuria are the two main signs of glomerular disease. The predominance of one of these findings, along with a significant proteinuria and a variable rate of progression, would support a diagnosis of acute or chronic glomerulonephritis or the nephrotic syndrome.

Fig 165

The glomerulus and the glomerular capsule

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Fig 166

The ureters and their relations to the kidneys and the bladder

Urinary system

1. 2. Suprarenal glandsKidneys 3. 4. UretersBladder

Comments Anatomical: The ureters, two in number, carry urine from the kidneys to the bladder. They measure about 25 consist of three tissue layers—fibrous, muscular and mucosal. The funnel-shaped cm in length and 3 mm in diameter. Their walls ureter is continuous with the renal pelvis. It descends in the abdominal and pelvic cavities and obliquely crosses the wall of the bladder, which is balloon-shaped and is an intrapelvic urine reservoir. Physiological: The smooth muscle surrounding the ureter contracts to generate peristaltic waves to propel the urine towards the bladder in small spurts. The frequency of these contractions depends on the amount of urine to be moved. Clinical: include a burning feeling on urination, a desire to pass urine frequently, difficulty A urinary infection confined to the bladder is called cystitis. Its symptoms in passing urine and bladder pain. In some cases, the infection reaches the kidney and becomes pyelonephritis, which can be complicated by a renal abscess and septicaemia.

Urinary system

Comments Anatomical: The ureter consists of three tissue layers—an inner layer (a mucosa lined by transitional epithelium), a middle layer of smooth muscle and an outer layer made up of fibrous tissue and continuous with that of the kidney. It descends in the abdominal cavity and then in the pelvic cavity and runs obliquely through the wall of the bladder to open into its neck at the ureteric orifice. Physiological: activity of its smooth muscle. The spurt frequency depends on the volume of urine The urine is propelled in small spurts along the ureter by peristaltic available. The internal ureteric sphincter, made up of smooth muscle, controls the passage of urine into the bladder; it is not under voluntary control. The oblique path through the bladder wall taken by the ureters ensures that their orifices into the bladder are closed when the bladder is full. This prevents reflux of urine from the bladder into the ureters and towards the kidneys when the bladder is filling or emptying. Clinical: renal failure if left untreated. Vesicoureteric reflux can cause repeated renal infections and lead to chronic

1. 2. Bladder mucosa covered by transitional epitheliumUreter 3. 4. Layer of smooth muscleOuter coat of the bladder wall (fibrous tissue)

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A. Filtration(blood nephron) B. Reabsorption(filtrate blood) C. Secretion(blood filtrate)

Fig 168

Summary of the three stages of urine formation