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Introduction
The fundamental structural and operational unit of the kidney is nephron. Each human kidney has millions of nephrons. They are a tiny structure made up of renal tubules and corpuscles.


Functions of Nephron
Conversion of blood into urine, elimination of all waste, including solid waste and excess water, as well as the reabsorption, secretion, and excretion of a variety of compounds.
The process of ultrafiltration is when the cell in each tube absorbs different molecules except glucose and returns others molecules. A significant percentage of ultrafiltration is extracted before it leaves the nephron as a result of the ultrafiltration particles becoming increasingly hypertonic as they go through the tubes.
The tiny molecules are pushed into the glomerular capsules and travel through a twisting sequence of tubules when the blood travels through the glomerulus under high pressure.
Through the renal blood vessels, which are devoid of toxins and other extra substances, the blood close to the nephron returns to the body. Urine, the acquired ultrafiltrate, passes through the collecting duct to the bladder, where it is stored before being expelled by the urethra.

Structure of  Nephron
The nephrons structure is divided into two main parts :
Renal Tubule: Is a long and convoluted structure that emerges from the glomerulus and can be divided into three parts based on function :
1-    The first part is called the proximal convoluted tubule (PCT) duo to its proximity to the glomerulus; it stays in the renal cortex.
2-    The second part is called the loop of Henle, or nephritic loop because it forms a loop (with descending and ascending limbs) that goes through the renal medulla.
3-    The third part of the renal tubule is called the distal convoluted tubule (DCT) and this part is also restricted to the renal cortex.
The major function of tubules is:Selective reabsorption of substances from glomerular filtrate.

1-    Proximal Convoluted Tubule (PCT)
The glomerulus filters the blood delivered by the renal artery before it is sent to the PCT. Maximum reabsorption occurs in the nephrons PCT. The renal tubules PCT is where vital molecules including glucose , proteins, amino acids, a significant amount of electrolytes, and water are reabsorbable. The lining of the simple cuboidal epithelium in them increases the surface area for reabsorption. Reabsorption uses energy to occur, indicating that the process is active. PCT selectively secretes ions into the filtrate, including hydrogen, ammonia, and potassium , and absorbs HCO3- from it. Thus, PCT keeps the bodily fluids electrolyte and acid-base balance in check.

2-    Henles Loop
The ascending and descending limbs of Henles loop are distinct. The ascending and descending arms of the same loop exhibit varying degrees of permeability. The ascending limb is impermeable to water and permeable to electrolytes, whereas the descending limb is impervious to both. As the filtrate proceeds towards the ascending limb, it becomes diluted because the electrolytes are reabsorbed at the ascending loop of Henle. However, reabsorption is constrained in this region.

3-    Distal Convoluted Tubule (DCT) 
The DCT, the nephrons last component, joins and discharges its contents into collecting ducts that surround the medullary pyramids.  The collecting ducts combine when they enter the papillae of the renal medulla, amassing material from several nephrons. In the DCT, sodium and water ions undergo conditional reabsorption. As a result, it keeps the blood cells pH and salt and potassium levels stable.

Collecting Duct
H+ and K+ ions are secreted into the collecting duct, along, straight tube, to keep the bloods electrolyte  balance. Additionally, the greatest amount of water is reabsorbable in this area, leading to the production of concentrated urine.

Renal Corpuscle
The Bowmans capsule encloses the glomerulus, which makes up the renal corpuscle. An efferent arteriole receives the glomeruluss discharge after it emerges from an afferent arteriole. The smaller diameter of the an efferent arteriole aids in preserving the glomeruluss high blood pressure. The Bowmans capsule is divided into three layers:
1-    The outer parietal layer is composed of epithelial cells with very small pores of 12 nm in width.
2-    Middle Basement Membrane : this stratum is partially permeable.
3-    Inner Visceral Layer: this layer is made up of huge nucleated cells termed podocytes that include podocels, or finger like projections.
The major function of corpuscle is : Filtration of substances from plasma.