Do you know the structure of the kidneys in the human body? The kidney is one of the endocrine glands. It is making “kinins,” secreting “rennin,” and “erythropoietin,” forming “1,25-dihydroxycholecalciferol.” Kidneys are made up of many functional microscopic units called “nephrons.”
They perform excretory and homeostatic functions, and there are 1.3 million nephrons in each human kidney. The function of the medulla in the kidney is the filtering of waste materials and the elimination of fluid from the body.
What are the types of Nephrons?
A nephron is the functional unit of the kidney. There are two types of nephrons, according to their relative position in the cortex.
1. The Superficial Nephrons
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2. The Juxta-Medullary Nephrons
These make up about 15% of the total number and are found in the inner third of the cortex. This nephron is large and works only under conditions of stress.
What is the Structure of Nephron?
There are 1.3 million nephrons in each human kidney. Here we describe the structure of nephron with the help of diagrams now. The nephron comprises three parts.,
The glomerulus has a diameter of about 200 m. It is formed by the invagination of a tuft of capillaries into a dilated blood vessel. At the blind end of the nephron, the capillaries are supplied by an “afferent arteriole” and drained by a smaller “efferent arteriole.” The afferent arteriole breaks up into about fifty capillary loops and forms the glomerular tuft, which lies within Bowman’s capsule, a double-walled epithelial sac. Each nephron begins with a tuft of 6-8 renal blood capillaries that are probed into the end of a tubule. This structure is named “Glomerulus.”
Mesangial cells are shared by two capillaries that are next to each other. In these places, the base membrane forms a sheath that both capillaries share. The cells are contractile and play a role in regulating “glomerular filtration.” They also secrete various substances, take up “immune complexes,” and are involved in the production of glomerular disease. The glomerular membrane permits the free passage of neutral substances up to 4 nm in diameter and almost excludes those with diameters greater than 8 nm.
2. Bowman’s Capsule
Which is the blind dilation of renal tubule and is a crescentic cavity measuring 0.2mm in diameter? It has two layers, i.e. Visceral and parietal, each lined by flattened epithelial cells. Visceral and parietal. Each lined by flattened epithelial cells. The visceral layer covers the glomerulus and parietal layer and constituents the wall of the corpuscle being continuous with a renal tubule.
a. Parietal layer
It makes up the typical squamous epithelium of flat, polygonal cells. At the tubular end of Bowman’s capsule, it gradually joins up with the tubular epithelium.
b. Visceral layer
During development, they undergo extensive modification and are known as “podocytes” (glomerular epithelial cells). These give rise to several radiating “tentacle-like” cytoplasmic processes that give up many small branches—the “pedicels” or “end feet,” which are actually attached to the basal lamina.
The space between the basement membrane and the “pedicel” or “end feet,” which are actually attached to the basal lamina. The space between the basement membrane and the podocyte is known as the “subpodocytic space.“
3. Renal tubule
They describe the glomerulus as having two poles. At one pole–the vascular pole—the blood vessels are attached. At the opposite pole—the tubular pole—the renal tubule begins. The human tubule is about 3.0 cm long, 20 to 30 microns wide. The tubular system comprises the following serial parts.
a. First (or) Proximal Convoluted Tubule (PCT)
- The human PCT is about 15mm. Long and 55µm in diameter. These are all made up of a single layer of cells that interdigitate with one another and are united by apical tight junctions.
- PCT forms the first part of the “loop of Henle”.
- The PCT ends in the thin segment of the descending limb of the Henley’s loop, which has an epithelium made up of attached flat cells.
- Electron microscopy has revealed that they compose the brush border of processes or microvilli. In which protein, it also demonstrates enzymes are also.
- In the PCT’s cell lined, Rod-shaped mitochondria lying across the cell. The cells of PCT are very active metabolically and contain many enzymes.
- These cells absorb about 2/3 of the water of the glomerular filtrate and all the Glucose and part of sodium chloride and phosphate.
b. Henle’s Loop (Paras recta)
It is a ‘U’ shaped loop, dipping for a variable length into the medulla. Anatomically the loop of Henle can be divided into three parts
i) Descending limb
In the thin-walled descending limb being devoid of obvious intracellular structures – “Isosmotic fluid” delivered from the PCT becomes increasingly “Hypertonic fluid” as it progresses from the renal cortex towards the renal papilla. Until it reaches the maximum concentration and the membrane of this portion is more permeable to H2O than solute urea, NaCl and to affect equilibrium. It removes H2O.
ii) Thin-walled ascending limb
In this, the tubular fluid becomes progressively less concentrated because of its backflow towards the renal-cortex because of the loss of NaCl from the renal tubule.
iii) Thick-walled ascending limb
Which is known as “functional proximal tubule”. Reabsorption of NaCl from both cortical and medullary thick ascending limbs results in active chloride reabsorption. But that reabsorption of sodium occurred through a passive re-absorptive process in the maintenance of electrical neutrality.
c. Distal (or) Secondary convoluted Tubule (DCT)
The distal convoluted tubule (DCT) is about 5 mm long. It has a lower epithelium than the PCT. There are a few microvilli, but there is no clear brush border. The distal tubules coalesce to form “collecting ducts” that are about 20 mm long and pass through the renal cortex and medulla to empty into the pelvis of the kidney at the apexes of the medullary pyramids.
4. Collecting tubule
Which receives urine from the distal tubule. They line it with high column cells. They make the epithelium of the collecting ducts up of “principal cells” (P-cells) and “Intercalated cells” (I-cells).
Which predominate are relatively tall and have few organelles. It involves them in “Sodium absorption” and “Vasopressin” stimulate Water reabsorption.
which are present in a smaller number and are also found in the distal tubules, have more microvilli, cytoplasmic vesicles, and mitochondria. They are concerned with acid secretion and HCO3– transport. The total length of the nephrons, including the collecting ducts, ranges from 45 to 65 mm.
Functions of Nephrons:
Nephrons are the functional units of the kidney. They are responsible for filtering waste and excess fluids from the blood and regulating the electrolyte balance in the body. Each nephron consists of a glomerulus, a Bowman’s capsule, a proximal tubule, a loop of Henle, and a distal tubule.
- Glomerulus: This is a small network of capillaries located at the beginning of the nephron. It is responsible for filtering the blood and removing waste products, such as urea and creatinine, as well as excess water and electrolytes.
- Bowman’s capsule: This is a cup-shaped structure that surrounds the glomerulus. It is responsible for collecting the filtered fluid, known as glomerular filtrate, and passing it on to the proximal tubule.
- Proximal tubule: This is a long, convoluted tube that follows the Bowman’s capsule. It is responsible for reabsorbing important substances, such as glucose, amino acids, and electrolytes, back into the blood.
- Loop of Henle: This is a U-shaped tube that extends into the medulla of the kidney. It is responsible for regulating the concentration of electrolytes in the body by reabsorbing or secreting them as needed.
- Distal tubule: This is the final segment of the nephron. It is responsible for regulating the pH of the body by secreting or reabsorbing acid and base as needed.
Overall, the nephron plays a vital role in maintaining the balance of fluids and electrolytes in the body and removing waste products from the bloodstream.