Structure and functions of organs in urinary system-2

Nephron

The kidney's functional unit, or nephron, is responsible for carrying out the actions that cause urine to be produced. Approximately one million nephrons make up each kidney. Some of the juxtamedullary nephrons extend into the medulla, while some cortical nephrons are mostly found in the cortex.

The generation of urine involves a number of different structures that make up the nephron. Here are some examples of those:

• Glomerulus
  • A group of capillaries that have been twisted together to form the glomerulus make up each nephron. The glomerulus is created when the renal artery splits into arterioles after entering the kidney. Afferent arterioles are the arterioles that bring blood to the glomerulus, and efferent arterioles are the arterioles that remove blood from the glomerulus.
•  Glomerular (Bowman's) Capsule
  • The glomerulus is fully encircled by this cup-like structure. The enclosed glomerulus and glomerular capsule are referred to as the renal corpuscle together. Visceral and parietal layers of highly specialized epithelial cells make up the glomerular capsule. Special cells called podocytes, which are composed of modified simple squamous epithelial cells, are found in the visceral layer. Simple squamous epithelium also makes up the glomerular capsule's parietal layer. The glomerular capsule's wall is made up of the parietal and visceral layers.

The proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and a collecting duct make up the continuous renal tubule, which extends from the capsule.

•  The Proximal Convoluted Tubule (PCT)
  • The cortex is where it is situated. Simple cuboidal epithelial cells make up the cells in the PCT. By osmosis and active transport, it reabsorbs water, urea, sodium, potassium, calcium, chloride, and other substances.
• The Loop of Henle
  • It penetrates the medulla before returning to the cortex of the nephron. The descending limb of the loop of Henle is the portion of the loop that first dips into the renal medulla.

It turns into a hairpin before returning to the renal cortex, where it is referred to as the ascending limb of the Henle loop. Simple squamous epithelium makes up the descending limb and the first portion of the ascending limb of the Henle loop. By means of osmosis and diffusion, the Henle loop reabsorbs water, urea, sodium, chloride, and bicarbonate.

• The Distal Convoluted Tubule (DCT)
  • It is the tubule's upward-returning portion that is found in the cortex. The final section of the DCT and the collecting ducts contain two different types of cells. They are main cells, which control aldosterone hormone and antidiuretic hormone (ADH), and intercalated cells, which support blood pH homeostasis. It reabsorbs substances by osmosis, diffusion, and active transport, including water, urea, salt, chloride, phosphate, and bicarbonate. Hydrogen ions are secreted into the tubule by the DCT.
• The Collecting Duct
  • It gets urine from a number of nephrons. It then joins together to form larger papillary ducts, which pass urine through the papillae of the pyramids into the minor calyces. Through the processes of osmosis and active transport, it reabsorbs water, sodium, and potassium. Hydrogen ions are also secreted into the tubule by the collecting ducts.

Juxtra-Glomerular Apparatus

Three distinct components combine to produce the juxtra-glomerular apparatus:

• Macula densa
• Extraglomerular mesangial cells
• Juxtraglomerular cells

• Macula Densa
  • Before it opens into the distal convoluted tubule, the thick ascending segment's end is known as the macula densa. It is located within the same nephron, between the afferent and efferent arterioles. Cuboidal epithelial cells are closely packed together to form the macula densa. It makes the change in NaCl concentration more sensitive.
• Extraglomerular Mesangial Cells
  • The triangular area bounded by the afferent arteriole, efferent arteriole, and macula densa is where extraglomerular mesangial cells are located. Agranular cells, lacis cells, and Goormaghtigh cells are further names for these cells. They assist in phagocytosis, secrete prostaglandin, and support cellular functions.
• Juxtraglomerular Cells
  • Specialized smooth muscle cells known as juxtaglomerular cells are found in the wall of an afferent arteriole immediately before it reaches the Bowman capsule. Renin is secreted by them and controls blood pressure.

Flow of Fluid (Renal Filtrate) Through the Nephron Structures

• Bowman's globular capsule
• Convoluted tubule in the vicinity
• Descending leg of Henle's loop
• Ascending branch of the Henle loop
• Convoluted distal tubule
• The duct that collects

Functions of the Kidneys

• Urine is created by the kidneys.
• By retaining or excreting water in the urine, the kidneys control the volume of blood in the body.
• The kidney controls the acid-base balance by retaining bicarbonate ions and excreting hydrogen ions (H+) (HCO3).
• The kidneys assist in maintaining normal concentrations of numerous electrolytes in the blood, including sodium (Na+), potassium (K+), calcium (Ca+), and phosphate (HPO42-).
• By manufacturing the enzyme renin, which stimulates the renin-angiotensin-aldosterone system, the kidneys also aid in controlling blood pressure.
• Nitrogenous wastes such ammonia, urea, creatinine, bilirubin, and uric acid are expelled by the kidneys.
• Two hormones are made by the kidneys. In bone marrow, erythropoietin stimulates the production of red blood cells. The body's calcium level is regulated by calcitriol.