Do you know the kidney structure in human body? The kidney is one of the Endocrine glands. It is making “Kinins”, secreting “Rennin“, and “erythropoietin”, forming “1,25-dihydroxy cholecalciferol”. Kidneys are made comprise many functional microscopic units called “Nephrons”.
They perform excretory and homeostatic functions, which are 1.3 million nephrons in each human kidney. The function of the medulla in the kidney 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
Which occupies the outer two-thirds of the cortex and made up of about 85% of the total number, which is smaller and is functioning under normal conditions.
2. The Juxta-Medullary Nephrons
These are occupied in the inner third of the cortex and make up about 15% of the total number. This nephron is large and works only in 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 is about 200µm in diameter. It is formed by the invagination of a tuft of capillaries into dilated. 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 starts with a tuft of 6 to 8 renal blood capillaries investigated into the end of a tubule. This structure is named “Glomerulus”.
Mesangial cells are common between two neighboring capillaries, and in these locations, the base membrane forms a sheath shared by both capillaries. 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 8nm.
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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 This up of the typical squamous epithelium of flat polygonal cells. It gradually becomes continuous with the tubular epithelium at the tubular end of Bowman’s capsule.
b. Visceral layer
During development undergo extensive modification and are known as “podocytes” (Glomerular epithelial cells). These give rise to several radiating “tentacle-like” cytoplasmic processes which 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”.
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3. Renal tubule
They describe the glomerulus to have two poles. At one pole–the vascular pole attaches the blood vessels. At the opposite pole–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 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 5mm long. Its epithelium is lower than that of the PCT, and although there are a few microvilli, there is no distinct brush border. The distal tubules coalesce to form “Collecting ducts” that are about 20mm 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.
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Functions of Nephrons:
- Nephrons are the primary filtering organs in the body known as kidney filtration units.
- They are responsible for removing toxins and excess salt from blood plasma.
- There are two types of nephrons: proximal and distal nephrons.
- Proximal nephrons have three segments: Bowman’s capsule, Loop of Henle and Distal Tubule.
- Distal nephrons has four segments: medullary ray, loop of Henle, distal tubule, and collecting duct.
- These nephrons filter out the wastes from blood plasma and excrete them through urine.