Category: Biology Second Paper Lecture Sheet

According to Scottish scientist A. R. Cushney, urine is produced in 3 stages in the human body. namely-
1. Ultrafiltration: The process by which nitrogenous wastes are filtered by the Malpighian body is called ultrafiltration. Blood enters the glomerulus through the afferent arteriole. Water, salt, sugar, urea, uric acid, creatinine, hormones, metal ions etc. are filtered from glomerulus under hydrostatic pressure. All these filtrates are called glomerular filtrate or primary urine. Glomerular filtrate accumulates in the capsular space. The hydrostatic pressure of the glomerulus is 70 mm/Hg. Other pressure against this pressure is 35 mm/Hg. As a result, the glomerular filtrate is filtered as the actual filtration pressure (70-35 = 35) is 35 mm/Hg.
For filtration, the capillary wall of the glomerulus and the wall of Bowman’s capsule together form a three-layer filter. The layers that make up the filter are the endothelium layer of the glomerular blood vessels, the basement membrane layer of the glomerular blood vessels and the endothelium layer of Bowman’s capsule. Two kidneys in the human body pump about 1,200 ml of blood per minute and filter about 125 cc of glomerular filtrate.
2. Selective reabsorption: As the glomerular filtrate flows through the renal tubules, various substances are reabsorbed by the cells of the tubular wall and enter the blood. This is called selective reabsorption. 80% of the required material is reabsorbed from the glomerular filtrate.
(i) Proximal tubular reabsorption: The proximal tubule reabsorbs 60% of the glomerular filtrate. It reabsorbs water, glucose, amino acids, vitamins, hormones, sodium, potassium, chloride, phosphate, bicarbonate, urea etc. These substances are called high quality storable substances.
(ii) Reabsorption of Henle’s loop: Water, sodium, potassium, magnesium, calcium, chloride etc. are reabsorbed by the loop of Henle.
(iii) Distal tubular reabsorption: Water, sodium, potassium, hydrogen and chlorine ions are reabsorbed by the distal tubule. These substances are called intermediate quality storable substances.
(iv) Reabsorption of collecting ducts: Water, urea, sodium and chlorine ions are reabsorbed by collecting ducts.
After 4-5 minutes the blood of the body passes through the kidneys to filter it. Human body filters 170 liters of water in 24 hours. Of this, 99% or 168.50 liters of water is reabsorbed by the renal tubules. The remaining 1.5 liters of water is excreted as urine. 80% of water is reabsorbed by the proximal convoluted tubule and 20% by the loop of Henley and distal convoluted tubule. Sulfate and creatinine are not reabsorbed. For this reason, they are called non-preservable substances.
3. Active secretion: Creatinine and some urea are secreted from the capillary network of the proximal tubule. These substances mix with the glomerular filtrate and are carried in the urine. Hydrogen ions, potassium ions, ammonium ions, serotonin, choline, histamine etc. are secreted from the distal tubule. All these substances mix with the filtrate and become urine.

The process by which nitrogenous waste products are produced and excreted from the body is called excretion. The main nitrogenous excretions of humans are urea, uric acid, ammonia, creatinine etc.

Inorganic phosphate, ammonia, hippuric acid etc. are created in epithelial cells. All these substances mix with other substances and become urine.

Creatinine and some urea are secreted from the capillary network of the proximal tubule. These substances mix with the glomerular filtrate and are carried in the urine. Hydrogen ions, potassium ions, ammonium ions, serotonin, choline, histamine etc. are secreted from the distal tubule. All these substances mix with the filtrate and become urine.

Proximal tubule reabsorbs water, glucose, sodium bicarbonate, chloride, calcium, sodium chloride and distal tubule reabsorbs potassium, urea, uric acid, phosphate etc.

The glomerulus of the nephron filters water, salt, sugar, urea, uric acid, creatinine, hormones, metal ions etc. from the blood. These filtrates are called glomerular filtrates. Glomerular filtrate accumulates in the capsular space.

1. Filtration: The glomerulus of the nephron filters water, salt, sugar, urea, uric acid, creatinine, hormones, metal ions etc. from the blood. These filtrates are called glomerular filtrates. Glomerular filtrate accumulates in the capsular space.
2. Reabsorption: Proximal tubule reabsorbs water, glucose, sodium bicarbonate, chloride, calcium, sodium chloride and distal tubule reabsorbs potassium, urea, uric acid, phosphate etc.
3. Active secretion: Creatinine and some urea are secreted from the capillary network of the proximal tubule. These substances mix with the glomerular filtrate and are carried in the urine. Hydrogen ions, potassium ions, ammonium ions, serotonin, choline, histamine etc. are secreted from the distal tubule. All these substances mix with the filtrate and become urine.
4. Creation of new substances: Inorganic phosphate, ammonia, hippuric acid etc. are created in epithelial cells. All these substances mix with other substances and become urine.
5. Acid production: Nephron produces different types of acid in the human body. The main acids produced by the nephron are sulfuric acid and lactic acid.
6. pH control: Nephron regulates pH in the body by storing alkaline substances and excreting acidic substances.
7. Controlling sodium levels: Sodium is an important buffer in our body. Nephrons regulate sodium levels in the human body.
8. Control of urine concentration: When the nephron tubules absorb water from the glomerular filtrate, the urine thickens. Again, if water is not absorbed from the glomerular filtrate, the urine becomes diluted.
9. Regulation of ion level: Kidney regulates the level of sodium, potassium, chloride etc. ions in the body.
10. Regulation of Osmosis: It regulates the osmotic pressure of blood and cells.

The part from the loop of Henley to the collecting duct is called distal convoluted tubule. Its length is 5 mm and diameter is 22.5 μ. It is surrounded by peritubule capillary or epithelial cells. It is located in the cortex. The next part of the distal patchy duct is called the collecting duct. Several collecting ducts join to form the Duct of Bellini.

The U-shaped tube extending from the proximal convoluted tubule to the distal convoluted tubule is called loop of Henle. This is called nephron leakage. It is located in the medulla and cortex. Its length is 11 mm and diameter is 20 μm. It consists of two parts. Descending limb and Ascending limb. The descending arm extends from the end of the proximal tubule to the medulla and the ascending arm is located in the cortex region. It is called loop of Henle after German medical scientist Friedrich Henle.

The tubule associated with Bowman’s capsule is called proximal convoluted tubule. Its length is about 14 cm and diameter is 57-60μ. These peritubules are covered by epithelial cells with capillaries or brush borders. At one end of the cells are numerous microscopic finger-like projections or microvilli. It is located in the cortex. This duct carries the filtrate from the glomerulus to the loop of Henley. The proximal tubule reabsorbs water, sodium ions, potassium, amino acids, glucose, chloride, peptide creatine and bicarbonate ions from the glomerular filtrate.