Kidney

The kidneys are two reddish-brown bean-shaped organs found in invertebrates. In adult humans, they are about 12 centimetres in size. They receive blood from the pair of renal arteries; blood exits into the paired renal veins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder. The kidneys participate in controlling the volume of various body fluids, fluid osmolality, acid-base balance, various electrolyte concentrations, and removal of toxins. Filtration occurs in the glomerulus: one-fifth of the blood volume that enters the kidneys is filtered. Examples of substances reabsorbed are solute-free water, sodium, bicarbonate, glucose, and amino acids.

Structure of Kidney

The kidneys are located on the left and right in the retroperitoneal space. Towards the middle of the inner concave surface of the kidneys is a notch called the hilum. Through the hilum, ureter, blood vessels, and nerves enter. Inner to the hilum is a broad funnel-shaped space called the renal pelvis with projections called calyces. The outer layer of the kidneys is a tough capsule. Inside the kidneys, there are two zones, an outer cortex, and an inner medulla. The medulla is divided into a few conical masses called medullary pyramids projecting into the calyces. The cortex extends in between the medullary pyramids as renal columns called Columns of Bertini. 

Each kidney has nearly one million complex tubular structures called nephrons which are the functional units. Each nephron has two parts – the glomerulus and the renal tubule. The glomerulus is a tuft of capillaries formed by the afferent arteriole – a fine branch of the renal artery. Blood from the glomerulus is carried away by an efferent arteriole. The renal tubule starts with a double-walled cup-like structure called Bowman’s capsule, which encloses the glomerulus. The glomerulus, along with Bowman’s capsule, the glomerulus is called the malpighian body or renal corpuscle. The tubule continues further to form a highly coiled network – proximal convoluted tubule (PCT). A hairpin-shaped Henle’s loop is the next part of the tubule, which has an ascending and a descending limb. The ascending limb continues as a highly coiled tubular region called the distal convoluted tubule (DCT). 

The DCTs of many nephrons open into a straight tube called a collecting duct, many of which converge and open into the renal pelvis through medullary pyramids in the calyces. The malpighian corpuscle, PCT and DCT of the nephron are situated in the cortical region of the kidney, whereas the loop of Henle dips into the medulla. In the majority of nephrons, the loop of Henle is very short and extends very little into the medulla. Such nephrons are called cortical nephrons. In some of the nephrons, the loop of Henle is very long and runs deep into the medulla. These nephrons are called juxtamedullary nephrons. The different arteriole emerging from the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries. A minute vessel of this network runs parallel to Henle’s loop forming a ‘U’ shaped vasa recta. Vasa recta is absent from the cortical nephrons.

Problems Associated With Kidneys

Acute renal failure (ARF) is a sudden failure of kidney or kidney damage that happens within a few hours or a few days. It causes a build-up of waste products in the blood and makes it hard for the kidneys to keep the right balance of fluid in the body. It can also affect other organs such as the brain, heart, and lungs. 

Causes of ARF

Following are the causes of ARF:

• Low blood pressure
• Blood or fluid loss due to bleeding or severe diarrhoea
• Heart attack, heart failure, and other conditions leading to decreased heart function
• Organ failures such as heart or liver
• Overuse of pain medicines, which are used to reduce swelling or relieve pain from headaches, colds, flu, and other ailments. For example ibuprofen, ketoprofen, and naproxen. 
• Severe allergic reactions
• Injury or Major surgery

Symptoms and Treatment of ARF

The symptoms of ARF include very less amount of urine leaving the body, swelling in the legs, ankles, and around the eyes, fatigue or tiredness, shortness of breath, nausea, chest pain, and seizures or coma in critical cases. Treatment for ARF usually requires hospitalization. In some serious cases, dialysis may be needed to help replace kidney function until the kidneys recover.

Conclusion:

The kidneys are two reddish-brown bean-shaped organs found in invertebrates. In adult humans, they are about 12 centimetres in size. They receive blood from the pair of renal arteries, purify it of waste, and blood finally exits into the paired renal veins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder. Acute renal failure is a sudden kidney failure or kidney damage that happens within a few hours or a few days. It causes a build-up of waste products in the blood and makes it hard for the kidneys to keep the right balance of fluid in the body.