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The Kidney

Table of Contents
The Lungs
The Trachea
The Testes
The Submaxillary Gland
The Liver
The Stomach and Duodenum
The Blood
The Arteries and Veins
The Adipose Tissue
The Skin
The Pituitary Gland
The Pancreas
The Thyroid
The Kidney
The Spinal Cord
The Cerebellum
The Elastic Cartilage
The Bone
The Smooth Muscle
The Striated Muscle


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The kidneys serve as the body’s filtration system, purifying and filtering bodily fluids, such as blood, as it circulates through the tissues.


The kidneys are located in the anterior region of the abdominal cavity, in front of the 12th ribs, behind the liver and stomach. They are about 12 cm long, 6 cm wide, bean-shaped and of a dark reddish hue. The kidneys are surrounded by a mass of fatty tissue which protects and insulates it, while keeping it in place along the abdominal wall.


The kidneys receive their blood supply through the renal arteries. Blood is carried towards the outer edges of the organs, into the capillaries where wastes are taken in by the nephrons, and then leaves the kidneys purified via the renal veins.


The kidneys can be separated into three regions; the lighter colored renal cortex, the darker renal medulla, and finally, the innermost region, the renal pelvis.


The nephrons, the specialized cells of the kidneys, are the filtration unit of the organ. Tubular in shape, the nephron is responsible for the formation of urine after collecting waste from the blood.


Blood approaches the nephrons via the afferent capillaries, which branches into a structure called the glomerulus and wraps around the top portion of the nephron, called the Bowman’s capsule. Here, solutes in the blood diffuse into the nephron, and are now known as the glomerulus filtrate.


The filtrate travels into the proximal tube of the nephron, where nutrients that are essential to the blood are reabsorbed into the peritubular capillaries. The filtrate travels down the descending and ascending loops of the nephron, called the Loop of Henle, where water and salt are reabsorbed into the capillaries.


Excess solutes and wastes travel across the distal tube and down the nephron into the collecting duct which leads the ureters, and ultimately the bladder, where the urine is expelled into the outside environment.


The kidney maintains homeostasis of internal fluids with the help of aldosterone and the antidiuretic hormone (ADH). ADH is sent to the kidneys in response to changes in osmotic pressure and signals the kidney to either accelerate or stop reabsorbtion of water. Aldosterone works with the kidneys to monitor and maintain the salt and water balance, and works in response to changes in blood pressure. The kidneys maintain the pH balance of the blood by regulating the carbonic acid and bicarbonate buffer system in the blood.

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