The kidneys are bean-shaped paired-organs found on the right and left sides of the body in the posterior abdomen. They are reddish-brown in colour. The kidneys filter the blood in order to make urine, to release and retain water, and to remove waste. They also control acid-base balance and ion concentrations of the blood.
Each kidney feeds urine into the bladder by means of a tube known as the ureter. The tubes are roughly 4.3 in(11 centimetres) in length.
Anatomical Position of the Kidney
The kidneys lie behind the peritoneum in the posterior abdomen, either side of the vertebral column extends from T12 to L3. The right kidney is situated slightly lower due to the presence of the liver.
Internally, the renal parenchyma can be divided into two main areas – the outer cortex and inner medulla. The cortex elongates into the medulla, dividing it into triangular shapes – these are known as renal pyramids.
The apex of a renal pyramid is designate 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 compose a major calyx. Urine passes within the major calices into the renal pelvis, a flattened and funnel-shaped structure. From the renal pelvis, urine drains into the ureter, which conveys it to the bladder for storage.
The medial margin of each kidney is marked by a deep fissure, known as the renal hilum. This deep fissure acts as a gateway to the kidney – the renal vessels and ureter enter/exit the kidney via this structure.
Blood Supply of the Kidney
The renal arteries branch from the abdominal aorta and enter the kidneys through the renal hilus. Inside the kidneys, the renal arteries diverge into the smaller afferent arterioles. Each afferent arteriole carries blood into the renal cortex, where it separates into a bundle of capillaries known as a glomerulus. Into the glomerulus, the blood recollects into smaller efferent arterioles that descend into the renal medulla. The efferent arterioles separate into the peritubular capillaries that surround the renal tubules. The peritubular capillaries merge to form veins that merge again to form the large renal vein. The renal vein exits the kidney and joins with the inferior vena cava, which carries blood back to the heart.
Nerve Supply of the Kidney
The renal plexus is located nearby the renal artery and receive postganglionic fibres from the sympathetic nervous system (Th10 to L2). The nerve fibres of the plexus enter the kidney with the branches of the renal artery and control the vascular tone and the secretion of renin.
The kidney also receives input from the parasympathetic nervous system, the renal branches of the vagus nerve (cranial nerve X), that causes vasodilation and increased blood flow of the afferent arterioles. Due to this mechanism, sympathetic nervous stimulation will reduce urine production, whereas parasympathetic nerve stimulation will increase urine production.
Function of the Kidney
The kidneys control the balance of ions known as electrolytes in the blood, simultaneously with maintaining acid-base homeostasis. They also remove waste products out of the blood and into the urine, such as nitrogen-containing urea and ammonium. Kidneys also control fluid balance and blood pressure. They are also able for the reabsorption of water, glucose, and amino acids. The kidneys further produce hormones including calcitriol and erythropoietin. The kidneys also produce an important enzyme, renin, which control blood pressure through negative feedback.
Common Kidney Diseases
Over time, diabetes can induce kidney failure. Effective monitoring of blood glucose levels over the years can reduce the complications.
Hereditary disorders commonly engender clinical symptoms from teenage years to adulthood. The most common hereditary kidney condition is polycystic kidney disease, a kidney disorder in that many cysts form in the kidneys, provoking them to become enlarged.
High Blood Pressure (hypertension)
High blood pressure can influence to kidney disease or can be a result of a kidney disorder. Left untreated, high blood pressure can enhance the natural course of any underlying kidney disease.
Nephrotic syndrome is a group of symptoms that include protein in the urine, low blood protein levels, high triglyceride levels, high cholesterol levels, and swelling. Nephrotic syndrome is induced by different disorders that damage the kidneys and relinquish of an inordinate amount of protein in the urine.
Most kidney stones pass out of the body without help from physicians. But sometimes a stone can get stuck in the urinary tract, block the flow of urine and cause great pain.
Drugs and Toxins
Certain medications, toxins, pesticides and “street” drugs (heroin) can also engender kidney damage.