Category: Biology Second Paper Lecture Sheet

The physiological process that maintains the balance of water and mineral salts in the body is called osmoregulation.
Most of the water is excreted from the body through urine. When the amount of water in the body decreases by 20%, the physical activity is disturbed. If you take more liquids, the amount of water in the body increases.

The physiological process that maintains the balance of water and mineral salts in the body is called osmoregulation.
Most of the water is excreted from the body through urine. When the amount of water in the body decreases by 20%, the physical activity is disturbed. If you take more liquids, the amount of water in the body increases.
1. Maintaining water balance: If excess water is lost through excess sweat and urine, water deficiency occurs in the body. It increases blood density. The news of this change in blood reaches the hypothalamus and the osmoreceptors of the hypothalamus are stimulated. Therefore, antidiuretic hormone (ADH) is produced from the posterior pituitary gland in the process of neurosecretion. ADH increases renal tubular permeability. The renal tubule reabsorbs large amounts of water from the glomerular filtrate and returns it to the blood. It produces less urine and is excreted from the body. This work continues until the water balance in the body.
Again, when the amount of water in the body increases, the blood becomes more fluid. The news of this change in blood reaches the hypothalamus. As a result, the production of antidiuretic hormone (ADH) by the posterior pituitary gland stops or decreases. This causes the renal tubules to become impervious. Renal tubular reabsorption of water from the glomerular filtrate ceases (or is greatly reduced). As a result, more urine is produced and excreted from the body. Urine volume can increase up to 16 ml per minute. This process continues until the water balance in the body.
2. Maintenance of sodium ion balance: Na+ ion concentration in human body is 142 mmol/L in extracellular fluid and 10 mmol/L in intracellular fluid. In a healthy body this concentration is always constant. During intake of food and drink more Na+ ions enter the body than required. Excess Na+ ions are removed from the body through urine, feces and sweat. As a result, sodium ion balance is maintained in the body.
3. Maintenance of potassium ion balance: The concentration of K+ ions in the human body is 4 mmol/L in the extracellular fluid and 160 mmol/L in the intracellular fluid. In a healthy body this concentration is always liquid. When consuming different types of fruits, more K+ ions enter the body than required. Excess K+ ions are removed from the body through urine and feces. As a result, the balance of potassium ions in the body is maintained.

If the solute concentration of the glomerular filtrate is less than the solute concentration of the plasma, it is called a hypotonic filtrate.

If the solute concentration of the glomerular filtrate is greater than the solute concentration of the plasma, it is called a hypertonic filtrate.

If the solute concentration of the glomerular filtrate is equal to the solute concentration of the plasma, it is called isotonic filtrate.

The pressure at which the non-colloidal part of the blood separates from the colloidal part of the blood and enters the capsular space as filtered fluid is called the effective osmotic pressure. The effective osmotic pressure is determined by the capillary blood pressure of the glomerulus, the colloidal osmotic pressure of the blood, and the hydrostatic pressure of the filtrate. The effective osmotic pressure is obtained by subtracting the colloidal osmotic pressure and the hydrostatic pressure of the filtrate from the glomerular blood pressure. If the blood pressure of the glomerulus is 75 mmHg, the colloidal osmotic pressure is 30 mmHg, and the hydrostatic pressure of the filtrate is 20 mmHg, the effective osmotic pressure will be {75-(30+20)} mmHg or 25 mmHg.

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.

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.

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.

The process by which excess ammonia present in the liver cells is converted into urea is called the ornithine cycle or the urea cycle. The ornithine cycle is completed in five steps. The steps are-
1. Formation of carbamyl phosphate: Carbamyl phosphate is produced from CO2 and NH3 in the presence of carbamyl synthetase enzyme.
CO2 + NH3→ carbamyl phosphate
2. Formation of citrulline: Carbamyl phosphate reacts with ornithine in the presence of ornithine transcarbamylase enzyme to produce citrulline.
Carbamyl phosphate + ornithine → citrulline
3. Formation of argininosuccinate: Citrulline reacts with aspartate in the presence of argininosuccinate synthetase enzyme to form argininosuccinate.
Citrulline + aspartate → argininosuccinate
4. Arginine production: Argininosuccinate is cleaved to fumarate and arginine by the enzyme argininosuccinase.
Argininosuccinate → fumarate + arginine
5. Urea produced: Arginine reacts with water in the presence of arginase enzyme to produce urea.
Arginine + water → urea