Cortical Nephrons are the basic units that make up the structure and function of the kidney, including renal corpuscles and tubules. Each kidney has more than one million nephrons. The renal corpuscles are composed of glomeruli and renal capsules. The renal tubules are elongated and circuitous epithelial tubes. It is usually divided into three sections: the first section is connected to the renal capsule and is called the proximal tubule.That is in the cortical nephron.
table of Contents
1 Overview
2 Composition structure
3 Physiological significance
4 Renal corpuscle
4.1 Overview
4.2 Globules
4.3 Kidney capsule
4.4 Globular basement membrane
5 Renal tubules
5.1 Summary
5.2 Proximal tubule
5.3 Details
5.4 Distal tubule
6 Etiology Guidelines
juxtamedullary nephron vs cortical nephron
Each kidney (cortical nephron) has more than 1 million renal units, which are the basic units of the structure and function of the kidney. Each cortical nephron includes two parts: renal corpuscle and tubule. According to the location of the renal corpuscles in the cortex, it is divided into superficial cortical nephron and paramedullary nephrons. The medullary loop of the superficial nephron is short and only reaches the outer medulla; the medullary loop of the paramedullary cortical nephron is long and can reach the nipple. In terms of quantity, the former is 7 times that of the latter.
cortical nephron
The renal corpuscle is composed of glomerulus and glomerulus. The glomerulus is composed of a plexus of capillary blood vessels, which originate from the glomerular arterioles, and then divide into 5 branches. Each branch is divided into capillary lobules. The capillaries of each lobule converge into a glomerular arteriole; after the latter exits the glomerulus, It branches widely, and then becomes a network of capillaries wound around the renal tubules, and the blood flow finally flows back into the interlobular veins. The glomerular sac is a concave double-layer sac that wraps around the vascular globule, with a wall layer on the outside, a visceral layer on the inside, and a balloon cavity in between. Below the parietal cells is the basement membrane around the glomerulus. The renal tubules are divided into proximal tubules, medullary loops and distal tubules. The proximal tubule is adjacent to the urinary pole of the renal capsule and is divided into two parts. The first section is the curvature of the proximal tubule, and the second section is the straight portion of the proximal tubule, which constitutes the first section of the descending branch of the medullary loop. The medullary loop is also called a thin section, which is a thin straight section connected between the straight part of the proximal tubule and the straight portion of the distal tubule. The distal tubule is composed of a straight portion and a curved portion of the distal tubule.
The renal corpuscle is located in the cortex and is composed of a glomerulus and a renal capsule surrounding it. The glomerulus is a spheroid formed by bending and coiling dozens of capillaries branched out by the small arteries that enter the bulb. These capillaries converge into a small artery before exiting the renal corpuscle. The renal capsule is the enlarged part of the blind end of the renal tubule, which is recessed into a double-layered globular capsule. The wall of the capsule is divided into two layers, the inner layer and the outer layer. The inner layer of cells is close to the outside of the capillaries of the vascular bulb, and the outer layer of cells is connected with the renal tubules. The renal capsule is divided into inner and outer layers. Between the inner and outer layers is a small renal capsule, which communicates with the renal tubules.
The glomerulus filters the blood into the renal capsule, which is the original urine. It is called the filtration effect of the glomerulus. Then it is injected into the renal tubules to reabsorb the beneficial substances in the original urine into the body. This is called the reabsorption of renal tubules.
Composition structure
The glomerulus filters the blood into the renal capsule, which is the original urine. Then it is injected into the renal tubules to reabsorb the beneficial substances in the original urine into the body. According to the location of the renal corpuscles in the cortex, it is divided into superficial nephrons and paramedullary nephrons. The medullary loop of the superficial nephron is short and only reaches the outer medulla; the medullary loop of the paramedullary nephron is long and can reach the nipple. In terms of quantity, the former is 7 times that of the latter.
Nephron
The renal corpuscle is composed of glomerulus and glomerulus sac. The glomerulus is composed of a plexus of capillary blood vessels, which originate from the glomerular arterioles, and then divide into 5 branches. Each branch is divided into capillary lobules. The capillaries of each lobule converge into a glomerular arteriole; after the latter exits the glomerulus, It branches widely, and then becomes a network of capillaries wound around the renal tubules, and the blood flow finally flows back into the interlobular veins. The glomerular sac is a concave double-layer sac that wraps around the vascular globule, with a wall layer on the outside, a visceral layer on the inside, and a balloon cavity in between. Below the parietal cells is the basement membrane around the glomerulus. The renal tubules are divided into proximal tubules, medullary loops and distal tubules. The proximal tubule is adjacent to the urinary pole of the renal capsule and is divided into two parts. The first section is the curvature of the proximal tubule, and the second section is the straight portion of the proximal tubule, which constitutes the first section of the descending branch of the medullary loop. The medullary loop is also called a thin section, which is a thin straight section connected between the straight part of the proximal tubule and the straight portion of the distal tubule. The distal tubule is composed of a straight portion and a curved portion of the distal tubule.
Renal corpuscles:
similar to a spherical shape, composed of vascular globules and renal capsules. Each renal corpuscle has two poles. The end of the arterioles is called the vascular pole, and the end connected to the renal tubules is the urinary pole.
Nephron composition
A spheroid is a group of cricket capillaries located in the renal capsule. It enters into the renal capsule from the pole of the blood vessel from the small arteries that enter the ball. It is first divided into 4-5 branches, and each branch forms many capillaries that are mutually anastomosed. The loops then converge into a small artery out of the bulb, leaving the renal corpuscle from the pole of the blood vessel. Under the electron microscope, the spheroid capillaries are porous, and most of the pores have no diaphragm, which is conducive to the filtering function.
(1) Renal capsule:
It is a double-layer cup-shaped capsule formed by the expansion and depression of the initial part of the kidney. The outer layer is called the wall layer, the inner layer is called the visceral layer, and the space between the two layers is called the renal capsule cavity. The wall layer is a single layer of flat epithelium, which is connected to the proximal tubule at the urinary pole. The visceral layer is composed of polydroid podocytes, which are tightly wrapped around the capillaries of the vascular bulbs. There is a basement membrane between endothelial cells and podocytes.
Physiological significance
According to the different depth of the renal corpuscles in the cortex, nephrons can be divided into superficial nephrons and paramedullary nephrons. Superficial nephron
cortical nephron
(Superfacialnephron) is also called cortical nephron. Its renal corpuscles are located in the superficial cortex. The renal corpuscles are small in size, and the medullary loops and segments are short. There are many superficial nephrons, accounting for about 85% of the total nephrons. The renal corpuscles are larger in size, and the medullary loops and segments are longer. The number of paramedullary nephrons is relatively small, accounting for about 15% of the total nephrons, which has important physiological significance for urine concentration.
All veins and arteries in the human body are connected by capillaries, but the glomerular arterioles and the glomerular arterioles in the glomerulus are not connected by capillaries.
(2) Renal corpuscles:
similar to a spherical shape, composed of vascular globules and renal capsules. Each renal corpuscle has two poles. The end of the arterioles is called the vascular pole, and the end connected to the renal tubules is the urinary pole.
A spheroid is a group of cricket capillaries located in the renal capsule. It enters into the renal capsule from the pole of the blood vessel from the small arteries that enter the ball. It is first divided into 4-5 branches, and each branch forms many capillaries that are mutually anastomosed. The loops then converge into a small artery out of the bulb, leaving the renal corpuscle from the pole of the blood vessel. Under the electron microscope, the spheroid capillaries are porous, and most of the pores have no diaphragm, which is conducive to the filtering function.
Overview of cortical nephron
The renal corpuscle (renalcorpuscle) resembles a spherical shape, so it is also called glomerulus, with a diameter of about 200μm, composed of renal capsule and vascular globule. The renal corpuscle has two ends or two poles. One end of the arterioles is called the vascular pole, and the other end is on the opposite side of the vascular pole. The renal capsule and the proximal tubule are connected to the urinary pole.
Vascular bulb
Glomerulus (glomerulus): is a group of twisted capillaries encased in the renal capsule. A ball-entering arteriole protrudes into the renal capsule from the pole of the blood vessel and is divided into 4 to 5 branches. Each branch then branches to form a reticular capillary loop. Between each loop, there is a mesangial support, and the capillaries in turn
Renal corpuscle
Converge into a bulbar arteriole and leave the renal capsule from the extreme point of the blood vessel. Therefore, the vascular globule is an arterial capillary network. Since the diameter of the arterioles entering the bulb is larger than that of the outlet arteries, the blood pressure in the bulb is higher than that of the general capillary. When the blood flows through the bulb, a large amount of water and small molecules are easy to filter out of the wall and enter the renal sac Inside. Under the electron microscope, the capillaries of the globules are porous. The pore size is 50-100nm, which is conducive to the filtering function. The cavity of endothelial cells is covered with a negatively charged glycoprotein (cell coat) rich in sialic acid, which selectively permeates substances in the blood. Most of the endothelium has a basement membrane on the outside, but there is no basement membrane on the endothelium facing the vascular mesangium, where the endothelial cells are in direct contact with the mesangium.
Mesangium (mesangium), also known as intraglomerular mesangium
(intraglomerularmesangium), is located between the vascular bulb capillaries, adjacent to the capillary endothelium or basement membrane, and is mainly composed of mesangial cells and mesangial matrix. Mesangial cells (mesangialcells) are irregular in shape, and the cell protrusions can extend between the endothelium and the basement membrane, or extend into the capillary cavity through the endothelial cells, the nucleus is small, the staining is deeper, and the cytoplasm has more developed Rough endoplasmic reticulum, Golgi complex, lysosomes and phagocytic vesicles, etc., sometimes a small amount of secretory granules can be seen; there are microtubules, microfilaments and intermediate filaments in the cell bodies and protrusions. It is currently believed that mesangial cells are derived from smooth muscle cells. Mesangial cells can synthesize the components of basement membrane and mesangial matrix, and can also swallow and degrade immune complexes deposited on the basement membrane to maintain the permeability of the basement membrane. And participate in the renewal and repair of the basement membrane. The contraction activity of the cells can adjust the diameter of the capillaries to affect the blood flow in the vascular ball. Mesangial cells can also secrete bioactive substances such as renin and enzymes, which may be related to the local regulation of blood flow in the vascular ball. Under normal circumstances, the mesangial cells renew slowly, but under pathological conditions (such as nephritis), cell proliferation is active, and phagocytosis and clearance are also enhanced. The mesangial matrix is filled between the lineage cells and plays a supporting and permeable role in the vascular ball. There are also a small number of macrophages in the mesangium.
Kidney capsule
Renal capsule, also known as Bowman’s capsule, is a double-layered capsule formed by an expansion and depression at the beginning of the renal tubule, which looks like a cup and has a vascular ball in the capsule. The outer layer of the renal capsule (or the wall layer of the renal capsule) is a single layer of flat epithelium, which is continuous with the proximal tubule epithelium at the urinary pole of the renal corpuscle, and reflexes into the inner layer of the renal capsule at the vascular pole (or Renal capsule visceral layer). The narrow space between the two layers of epithelium is called the renal capsule cavity, which is connected to the proximal convoluted small lumen. The inner cell has a special cell shape with many protrusions of varying sizes, called podocytes. The podocytes are large in size, the cell body protrudes into the small renal cyst, the nucleus is slightly stained, and there are abundant organelles in the cytoplasm. Under the scanning electron microscope, it can be seen that there are several large primary protrusions extending from the cell body, which are then divided into many fingers. The adjacent secondary protrusions are interspersed with each other to form a finger-like embedment to form a fence shape and cling to the outside of the capillary basement membrane. There are cracks with a diameter of about 25nm between the protrusions, called slitpores, and the pores are covered with a 4-6nm thick slit membrane (slitmembrane). The protrusions contain more microwires, and the shrinkage of the microwires can make the protrusions move and change the width of the slit. The surface of the podocytes is also covered with a layer of glycoprotein rich in sialic acid.