Ahmed Salam Medical Student “TSU” kidney Ahmed Salam Medical Student “TSU”
Embryology of Kidneys and Ureter: Renal development is characterized by 3 successive, slightly overlapping kidney systems: pronephros Mesonephros metanephros.
What is the kidney? The kidneys are a pair of bean-shaped organs approximately 12 cm long and weigh about 150 g in the male and about 135 g in the female. They extend from vertebral level T12 to L3 when the body is in the erect position. They are located retroperitoneally on either side of the aorta and inferior vena cava. The right kidney is positioned slightly lower than the left because of the mass of the liver. Both kidneys are in contact with the diaphragm, psoas major, and quadratus lumborum. Right kidney: contacts the above structures and the 12th rib Left kidney: contacts the above structures and the 11th and 12th ribs.
Kidney: the kidney is divided into two major structures: the outer renal cortex and the inner renal medulla. Grossly, these structures take the shape of eight to 18 cone- shaped renal lobes, each containing renal cortex surrounding a portion of medulla called a renal pyramid. Between the renal pyramids are projections of cortex called renal columns. papilla of each pyramid empties urine into a minor calyx, minor calyces empty into major calyces and major calyces empty into the renal pelvis.
NEPHRON: The functional unit within the kidney is the nephron. Each kidney contains 1–1.3 million nephrons. Each nephron consists of a glomerulus, which is responsible for ultrafiltration of blood, a proxi mal renal tubule, a loop of Henle, a distal renal tubule and a collecting duct, which together are responsible for selective reabsorption of water and electrolytes that have been filtered at the glomerulus
Glomerulus: The glomerulus comprises a tightly packed loop of capillaries supplied by an afferent arteriole and drained by an efferent arteriole. It is surrounded by a cup shaped extension of the proximal tubule termed Bowman’s capsule. Blood that enters the glomerulus undergoes ultrafiltration across the glomerular basement membrane (GBM). The glomerular capillary endothelial cells contain pores (fenestrae), through which circulating molecules can pass to reach the underlying GBM, As well as maintaining a selective barrier to filtration, Glomerular epithelial cells (podocytes) are involved in regulating turnover of the GBM. Mesangial cells lie in the central region of the glomerulus. They have contractile properties similar to those of vascular smooth muscle cells but also have macrophage like properties. The cells of the macula densa are sensitive to the concentration of sodium chloride in the distal convoluted tubule, macula densa that has two effects: decreases resistance to blood flow in the afferent arterioles, which raises glomerular hydrostatic pressure and helps return the glomerular filtration rate(GFR) toward normal. increases renin release from the juxtaglomerular cells of the afferent and efferent arterioles
Blood Circulation: The kidneys receive 25% of total cardiac output, 1,700 liters in 24 hours through the renal artery which enters the kidney at the hilum, near the ureter the renal artery then branches off into 5 segmental branches: segmental arteries, dividing further into interlobar arteries, which penetrate the renal capsule and extend through the renal columns between the renal pyramids. The interlobar arteries then supply blood to the arcuate arteries that run through the boundary of the cortex and the medulla. Each arcuate artery supplies several interlobular arteries that feed into the afferent arterioles that supply the glomeruli.
Ureters: Are fibromuscular tubes that connect the kidneys to the urinary bladder in the pelvis. They run posterior to the ductus deferens in males and posterior to the uterine artery in females. They begin as continuations of the renal pelves and run retroperitoneally, crossing the external iliac arteries as they pass over the pelvic brim. The ureter lies on the anterior surface of the psoas major muscle.
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