What Is a Juxtamedullary Nephron?

The renal tubule is an elongated epithelial tubule with a length of 30-50 mm connected to the wall of the renal capsule. It has reabsorption and excretion functions, and plays a key role in excretion of metabolites, maintenance of body fluid balance and acid-base balance.

Basic Information

Chinese name

Renal tubule

Structure

Proximal tubule, medullary ridge and distal tubule

Clinical significance

With reabsorption and excretion functions

Renal tubule structure and function

According to different morphological structures, distribution positions and functions, the renal tubules are mainly divided into three parts: proximal curved tubule, medullary ridge and distal curved tubule.
1. The proximal tubule is connected to the renal capsule space, which is the thickest section of the renal tubule, coiled around the renal corpuscle. The wall is composed of a single layer of cubic epithelial cells. The lumen is small and irregular and is an important part of renal tubular reabsorption function. The free surface of the cell has a brush-like margin, which is composed of microvilli. This structure can expand the cell surface area and facilitate reabsorption.
2. The descending and ascending branches of the medulla are "U" -shaped tubules, which are mainly composed of three sections: the first section is a thick section of the descending branch, that is, a nearly straight tubule; the second section is a thin section, showing a "U" shape ; The third section is a thick ascending branch, that is, a long straight small tube. It consists of flat and cubic epithelium, with different lengths of nephron pith from different parts. Cortical nephron myelin is short, thin-walled segments are short or absent, near medullary nephron is long and penetrates into the medulla to reach the pyramidal papilla. This type of myelin has special functions for urine concentration.
3. The distally curved tubules are short, meandering coiled around the nephron, and adjacent to the proximally curved tubules. The wall is composed of cubic epithelial cells with a large and regular lumen. Its end is connected to the collecting tube. Myelinary ridges and distal tubules are collectively called distal nephrons, which are important places for ion transport and secretion. They can absorb water, sodium ions, excrete potassium ions, hydrogen ions, NH3, and are regulated by aldosterone and antidiuretic hormones. Urine is concentrated.
4. Collecting tube The collecting tube is a small tube that runs from the cortex to the medullary pyramidal papillary orifice. There are many nephric tubules connected to it along the way. The diameter of the tube gradually becomes thicker, the tube wall becomes thicker, and the tube wall is cubic or columnar. Epithelial composition. In the past, it was thought that the collecting tube only had the function of transporting urine. Now it is thought that the collecting tube also has the same reabsorption and secretion functions as the distal curved tubule.

Clinical significance of renal tubules

Ischemia, infection and poisons can cause degeneration and necrosis of renal tubular epithelial cells, leading to renal dysfunction. Certain drugs and hormones, such as aldosterone, antidiuretic hormone, atrial natriuretic peptide (atrial natriuretic peptide), and parathyroid hormone can also cause changes in renal tubular function.