NEPHRONS :
Nephrons are structural and functional unit of kidney .
each human kidney contains about 1 million ( 10 lakhs ) nephrons
The nephron is the basic structural and functional unit of the kidney. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. A nephron eliminates wastes from the body, regulates blood volume and blood pressure, and regulates blood pH. Its functions are vital to life and are regulated by the endocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone. In humans, a normal kidney contains 1 million nephrons.
Structure of nephrons :
The two general classes of nephrons are cortical nephrons and juxtamedullary nephrons, both of which are classified according to the length of their associated Loop of Henle and location of their renal corpuscle. All nephrons have their renal corpuscles in the cortex. Cortical nephrons have their Loop of Henle in the renal medulla near its junction with the renal cortex, while the Loop of Henle of juxtamedullary nephrons is located deep in the renal medulla; they are called juxtamedullary because their renal corpuscle is located near the medulla (but still in the cortex). The nomenclature for cortical nephrons varies, with some sources distinguishing between superficial cortical nephrons and midcortical nephrons, depending on where their corpuscle is located within the cortex.
The majority of nephrons are cortical. Cortical nephrons have a shorter loop of Henle compared to juxtamedullary nephrons. The longer loop of Henle in juxtamedullary nephrons create a hyperosmolar gradient that allows for the creation of concentrated urine.
Kidney nephron drawing with labels of the following: the Bowman's capsule, proximal convoluted tubule, loop of Henle, descending limb of loop of Henle, ascending limb of loop of Henle, distal convoluted tubule, and collecting duct.
Each nephron is composed of an initial filtering component (the "renal corpuscle") and a tubule specialized for reabsorption and secretion (the "renal tubule"). The renal corpuscle filters out solutes from the blood, delivering water and small solutes to the renal tubule for modification .
The glomerulus is a capillary tuft that receives its blood supply from an afferent arteriole of the renal circulation. The glomerular blood pressure provides the driving force for water and solutes to be filtered out of the blood and into the space made by Bowman's capsule. The remainder of the blood (only approximately 1/5 of all plasma passing through the kidney is filtered through the glomerular wall into the Bowman's capsule) passes into the efferent arteriole.The diameter of efferent arteriole is comparatively less than that of afferent arteriole, increasing the hydrostatic pressure in the glomerulus. It then moves into the vasa recta, which are only found in juxtamedullary nephrons and not cortical nephrons. The vasa recta are collecting capillaries intertwined with the loop of Henle through the interstitial space, in which the reabsorbed substances will also enter. This then combines with efferent venules from other nephrons into the renal vein, and rejoins the main bloodstream.
The Bowman's capsule, also called the glomerular capsule, surrounds the glomerulus. It is composed of a visceral inner layer formed by specialized cells called podocytes, and a parietal outer layer composed of simple squamous epithelium. Fluids from blood in the glomerulus are filtered through the visceral layer of podocytes, and the resulting glomerular filtrate is further processed along the nephron to form urine .
Function :
Secretion and reabsorption of various solutes throughout the nephron.
The nephron carries out nearly all of the kidney's functions. Most of these functions concern the reabsorption and secretion of various solutes such as ions (e.g., sodium), carbohydrates (e.g., glucose), and amino acids (e.g., glutamate). Properties of the cells that line the nephron change dramatically along its length; consequently, each segment of the nephron has highly specialized functions.
The proximal tubule as a part of the nephron can be divided into an initial convoluted portion and a following straight (descending) portion.[8] Fluid in the filtrate entering the proximal convoluted tubule is reabsorbed into the peritubular capillaries, including approximately two-thirds of the filtered salt and water and all filtered organic solutes (primarily glucose and amino acids).
The loop of Henle, is a U-shaped tube that extends from the proximal tubule. It consists of a descending limb and an ascending limb. It begins in the cortex, receiving filtrate from the proximal convoluted tubule, extends into the medulla as the descending limb, and then returns to the cortex as the ascending limb to empty into the distal convoluted tubule. The primary role of the loop of Henle is to concentrate the salt in the interstitium, the tissue surrounding the loop.
Considerable differences aid in distinguishing the descending and ascending limbs of the loop of Henle. The descending limb is permeable to water and noticeably less impermeable to salt, and thus only indirectly contributes to the concentration of the interstitium. As the filtrate descends deeper into the hypertonic interstitium of the renal medulla, water flows freely out of the descending limb by osmosis until the tonicity of the filtrate and interstitium equilibrate. The hypertonicity of the medulla (and therefore concentration of urine) is determined in part by the size of the loop of Henle.[citation needed]
Unlike the descending limb, the thin ascending limb is impermeable to water, a critical feature of the countercurrent exchange mechanism employed by the loop. The ascending limb actively pumps sodium out of the filtrate, generating the hypertonic interstitium that drives countercurrent exchange. In passing through the ascending limb, the filtrate grows hypotonic since it has lost much of its sodium content. This hypotonic filtrate is passed to the distal convoluted tubule in the renal cortex.
The distal convoluted tubule has a different structure and function to that of the proximal convoluted tubule. Cells lining the tubule have numerous mitochondria to produce enough energy (ATP) for active transport to take place. Much of the ion transport taking place in the distal convoluted tubule is regulated by the endocrine system. In the presence of parathyroid hormone, the distal convoluted tubule reabsorbs more calcium and secretes more phosphate. When aldosterone is present, more sodium is reabsorbed and more potassium secreted. Atrial natriuretic peptide causes the distal convoluted tubule to secrete more sodium
Juxtaglomerular apparatus :
The juxtaglomerular apparatus is a specialized region of the nephron responsible for production and secretion of the enzyme renin, involved in the renin-angiotensin system. This occurs near the site of contact between the thick ascending limb and the afferent arteriole. It contains three components: the macula densa, juxtaglomerular cells, and extraglomerular mesangial cells
Renal Tubule :
The renal tubule is the part of the kidney nephron into which the glomerular filtrate passes after it has reached the Bowman's capsule. The first part of the renal tubule is called the proximal convoluted tubule (PCT), which is shown on the right-hand side of the diagram above.
The water and solutes that have passed through the proximal convoluted tubule (PCT) enter the Loop of Henle, which consists of two portions - first the descending limb of Henle, then the ascending limb of Henle. In order to pass through the Loop of Henle, the water (and substances dissolved in it) pass from the renal cortex into the renal medulla, then back to the renal cortex. When this fluid returns to the renal cortex (via the ascending limb of Henle) it passes into the distal convoluted tubule (DCT), which is shown on the left-hand side of the diagram above.
The distal convoluted tubules of many individual kidney nephrons converge onto a single collecting duct. The fluid that has passed through the distal convoluted tubules is drained into the collecting duct (far left-hand-side of the diagram above). Many collecting ducts join together to form several hundred papillary ducts. There are typically about 30 papillary ducts per renal papilla (the renal papillae being the tips of the renal pyramids - which point towards the centre of the kidney). At each renal papilla the contents of the papillary ducts drain into the minor calces - the channels through which the fluid passes, via the major calyx, into the centre of the kidney - called the renal pelvis.
Collecting duct system :
Each distal convoluted tubule delivers its filtrate to a system of collecting ducts, the first segment of which is the connecting tubule. The collecting duct system begins in the renal cortex and extends deep into the medulla. As the urine travels down the collecting duct system, it passes by the medullary interstitium which has a high sodium concentration as a result of the loop of Henle's countercurrent multiplier system.
Though the collecting duct is normally impermeable to water, it becomes permeable in the presence of antidiuretic hormone (ADH). ADH affects the function of aquaporins, resulting in the reabsorption of water molecules as it passes through the collecting duct. Aquaporins are membrane proteins that selectively conduct water molecules while preventing the passage of ions and other solutes.
Nephrons are structural and functional unit of kidney .
each human kidney contains about 1 million ( 10 lakhs ) nephrons
The nephron is the basic structural and functional unit of the kidney. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. A nephron eliminates wastes from the body, regulates blood volume and blood pressure, and regulates blood pH. Its functions are vital to life and are regulated by the endocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone. In humans, a normal kidney contains 1 million nephrons.
Structure of nephrons :
The two general classes of nephrons are cortical nephrons and juxtamedullary nephrons, both of which are classified according to the length of their associated Loop of Henle and location of their renal corpuscle. All nephrons have their renal corpuscles in the cortex. Cortical nephrons have their Loop of Henle in the renal medulla near its junction with the renal cortex, while the Loop of Henle of juxtamedullary nephrons is located deep in the renal medulla; they are called juxtamedullary because their renal corpuscle is located near the medulla (but still in the cortex). The nomenclature for cortical nephrons varies, with some sources distinguishing between superficial cortical nephrons and midcortical nephrons, depending on where their corpuscle is located within the cortex.
The majority of nephrons are cortical. Cortical nephrons have a shorter loop of Henle compared to juxtamedullary nephrons. The longer loop of Henle in juxtamedullary nephrons create a hyperosmolar gradient that allows for the creation of concentrated urine.
Kidney nephron drawing with labels of the following: the Bowman's capsule, proximal convoluted tubule, loop of Henle, descending limb of loop of Henle, ascending limb of loop of Henle, distal convoluted tubule, and collecting duct.
Each nephron is composed of an initial filtering component (the "renal corpuscle") and a tubule specialized for reabsorption and secretion (the "renal tubule"). The renal corpuscle filters out solutes from the blood, delivering water and small solutes to the renal tubule for modification .
The glomerulus is a capillary tuft that receives its blood supply from an afferent arteriole of the renal circulation. The glomerular blood pressure provides the driving force for water and solutes to be filtered out of the blood and into the space made by Bowman's capsule. The remainder of the blood (only approximately 1/5 of all plasma passing through the kidney is filtered through the glomerular wall into the Bowman's capsule) passes into the efferent arteriole.The diameter of efferent arteriole is comparatively less than that of afferent arteriole, increasing the hydrostatic pressure in the glomerulus. It then moves into the vasa recta, which are only found in juxtamedullary nephrons and not cortical nephrons. The vasa recta are collecting capillaries intertwined with the loop of Henle through the interstitial space, in which the reabsorbed substances will also enter. This then combines with efferent venules from other nephrons into the renal vein, and rejoins the main bloodstream.
The Bowman's capsule, also called the glomerular capsule, surrounds the glomerulus. It is composed of a visceral inner layer formed by specialized cells called podocytes, and a parietal outer layer composed of simple squamous epithelium. Fluids from blood in the glomerulus are filtered through the visceral layer of podocytes, and the resulting glomerular filtrate is further processed along the nephron to form urine .
Function :
Secretion and reabsorption of various solutes throughout the nephron.
The nephron carries out nearly all of the kidney's functions. Most of these functions concern the reabsorption and secretion of various solutes such as ions (e.g., sodium), carbohydrates (e.g., glucose), and amino acids (e.g., glutamate). Properties of the cells that line the nephron change dramatically along its length; consequently, each segment of the nephron has highly specialized functions.
The proximal tubule as a part of the nephron can be divided into an initial convoluted portion and a following straight (descending) portion.[8] Fluid in the filtrate entering the proximal convoluted tubule is reabsorbed into the peritubular capillaries, including approximately two-thirds of the filtered salt and water and all filtered organic solutes (primarily glucose and amino acids).
The loop of Henle, is a U-shaped tube that extends from the proximal tubule. It consists of a descending limb and an ascending limb. It begins in the cortex, receiving filtrate from the proximal convoluted tubule, extends into the medulla as the descending limb, and then returns to the cortex as the ascending limb to empty into the distal convoluted tubule. The primary role of the loop of Henle is to concentrate the salt in the interstitium, the tissue surrounding the loop.
Considerable differences aid in distinguishing the descending and ascending limbs of the loop of Henle. The descending limb is permeable to water and noticeably less impermeable to salt, and thus only indirectly contributes to the concentration of the interstitium. As the filtrate descends deeper into the hypertonic interstitium of the renal medulla, water flows freely out of the descending limb by osmosis until the tonicity of the filtrate and interstitium equilibrate. The hypertonicity of the medulla (and therefore concentration of urine) is determined in part by the size of the loop of Henle.[citation needed]
Unlike the descending limb, the thin ascending limb is impermeable to water, a critical feature of the countercurrent exchange mechanism employed by the loop. The ascending limb actively pumps sodium out of the filtrate, generating the hypertonic interstitium that drives countercurrent exchange. In passing through the ascending limb, the filtrate grows hypotonic since it has lost much of its sodium content. This hypotonic filtrate is passed to the distal convoluted tubule in the renal cortex.
The distal convoluted tubule has a different structure and function to that of the proximal convoluted tubule. Cells lining the tubule have numerous mitochondria to produce enough energy (ATP) for active transport to take place. Much of the ion transport taking place in the distal convoluted tubule is regulated by the endocrine system. In the presence of parathyroid hormone, the distal convoluted tubule reabsorbs more calcium and secretes more phosphate. When aldosterone is present, more sodium is reabsorbed and more potassium secreted. Atrial natriuretic peptide causes the distal convoluted tubule to secrete more sodium
Juxtaglomerular apparatus :
The juxtaglomerular apparatus is a specialized region of the nephron responsible for production and secretion of the enzyme renin, involved in the renin-angiotensin system. This occurs near the site of contact between the thick ascending limb and the afferent arteriole. It contains three components: the macula densa, juxtaglomerular cells, and extraglomerular mesangial cells
Renal Tubule :
The renal tubule is the part of the kidney nephron into which the glomerular filtrate passes after it has reached the Bowman's capsule. The first part of the renal tubule is called the proximal convoluted tubule (PCT), which is shown on the right-hand side of the diagram above.
The water and solutes that have passed through the proximal convoluted tubule (PCT) enter the Loop of Henle, which consists of two portions - first the descending limb of Henle, then the ascending limb of Henle. In order to pass through the Loop of Henle, the water (and substances dissolved in it) pass from the renal cortex into the renal medulla, then back to the renal cortex. When this fluid returns to the renal cortex (via the ascending limb of Henle) it passes into the distal convoluted tubule (DCT), which is shown on the left-hand side of the diagram above.
The distal convoluted tubules of many individual kidney nephrons converge onto a single collecting duct. The fluid that has passed through the distal convoluted tubules is drained into the collecting duct (far left-hand-side of the diagram above). Many collecting ducts join together to form several hundred papillary ducts. There are typically about 30 papillary ducts per renal papilla (the renal papillae being the tips of the renal pyramids - which point towards the centre of the kidney). At each renal papilla the contents of the papillary ducts drain into the minor calces - the channels through which the fluid passes, via the major calyx, into the centre of the kidney - called the renal pelvis.
Collecting duct system :
Each distal convoluted tubule delivers its filtrate to a system of collecting ducts, the first segment of which is the connecting tubule. The collecting duct system begins in the renal cortex and extends deep into the medulla. As the urine travels down the collecting duct system, it passes by the medullary interstitium which has a high sodium concentration as a result of the loop of Henle's countercurrent multiplier system.
Though the collecting duct is normally impermeable to water, it becomes permeable in the presence of antidiuretic hormone (ADH). ADH affects the function of aquaporins, resulting in the reabsorption of water molecules as it passes through the collecting duct. Aquaporins are membrane proteins that selectively conduct water molecules while preventing the passage of ions and other solutes.
TAGS :
COMMENTS