Opisthonephros

Opisthonephros is a type of kidney that is found in adult amphibians, reptiles, birds, and mammals. It is the most complex and advanced type of kidney, capable of producing highly concentrated urine. The opisthonephros is derived from the mesonephros, which is the intermediate stage in the development of the vertebrate kidney.

Structure

The opisthonephros is composed of a series of tubules, each of which is connected to a nephron. The nephrons are the functional units of the kidney, responsible for filtering waste products from the blood and producing urine. Each nephron in the opisthonephros consists of a glomerulus, a Bowman's capsule, a proximal tubule, a loop of Henle, and a distal tubule. The distal tubule empties into a collecting duct, which carries the urine to the ureter for excretion.

Function

The primary function of the opisthonephros is to filter waste products from the blood and excrete them in the form of urine. This is accomplished through a process known as urine formation, which involves three main steps: filtration, reabsorption, and secretion.

Filtration

Filtration occurs in the glomerulus, a network of tiny blood vessels located within the Bowman's capsule. Here, blood pressure forces water and small solutes out of the blood and into the Bowman's capsule, forming a fluid known as glomerular filtrate.

Reabsorption

Reabsorption takes place in the proximal tubule, the loop of Henle, and the distal tubule. During this step, useful substances such as glucose, amino acids, and ions are reabsorbed back into the blood, while waste products remain in the tubule.

Secretion

Secretion is the final step in urine formation. It occurs in the distal tubule and involves the active transport of substances from the blood into the tubule. This process helps to regulate the body's pH and electrolyte balance by removing excess hydrogen ions and potassium ions from the blood.

Development

The opisthonephros develops from the mesonephros during embryonic development. Initially, the mesonephros functions as the primary excretory organ, but as the embryo grows and develops, the mesonephros gradually transforms into the opisthonephros. This process is regulated by a variety of growth factors and transcription factors, including WT1, PAX2, and GDNF.

See also

• Pronephros
• Mesonephros
• Metanephros