Category: Biology Second Paper Lecture Sheet

Chemicals that prevent the pH of a solution from changing are called buffers. Blood buffers are NaHCO3, Na2HPO4, KHCO3 etc. Nephron tubular cells reabsorb ions such as Na+, K+, HC3-, PO43- etc. from the glomerular filtrate into the blood. These ions participate in the formation of buffers in the blood and prevent changes in blood pH.
Na+ + HCO3- → NaHCO3
2Na+ + HPO43- → Na2HPO4
K+ + HCO3- → KHCO3

1. Buffer method: Chemicals that prevent the pH of a solution from changing are called buffers. Blood buffers are NaHCO3, Na2HPO4, KHCO3 etc. Nephron tubular cells reabsorb ions such as Na+, K+, HC3-, PO43- etc. from the glomerular filtrate into the blood. These ions participate in the formation of buffers in the blood and prevent changes in blood pH.
Na+ + HCO3- → NaHCO3
2Na+ + HPO43- → Na2HPO4
K+ + HCO3- → KHCO3
2. Ammonia method: When blood pH value (acidity) decreases, NH4+ is produced by the reaction of NH3 and hydrogen ion (H+) in plasma and renal tubule cells. This results in a decrease in the concentration of H+ ions in the plasma and a change in the pH value of the blood. Again, increasing alkalinity has the opposite reaction.
3. Iron exchange method: If the acid level increases in the blood, the concentration of ions increases. Meanwhile, a Na+ ion enters the blood in exchange for an H+ ion. This results in a decrease in the concentration of H+ ions in the plasma and a change in the pH value of the blood. Again, when the blood alkalinization level increases, the rate of exchange of H+ and Na+ ions between the blood and the glomerular filtrate decreases and the blood pH changes.

pH is a measure of hydrogen ion (H+) concentration. A measure of the concentration of hydrogen ions (H+) in a solution is called the pH of the solution. The neutral pH value of the body is 7.0. Body fluids are acidic if the pH value is less than 7.0 and alkaline if it is higher. The ideal blood pH value is 7.4. A pH value below or above 7.4 can cause death in humans.
Buffer solutions can resist pH value changes.

The hormone aldosterone regulates sodium levels in the blood. When the amount of sodium in the blood decreases, the amount of water entering the body decreases. Blood volume and blood pressure decrease. As a result, the juxtaglomerular sensory cells are stimulated and the renin enzyme is produced. Renin converts the blood plasma protein into the hormone angiotensin. The hormone angiotensin stimulates the secretion of the hormone aldosterone from the adrenal cortex. The hormone aldosterone stimulates the sodium-potassium pump of the renal tubular cells. In this, sodium enters the blood from the distal convoluted tubule and potassium enters the distal convoluted tubule from the blood. Increased sodium in the blood increases water absorption. As a result, blood volume and blood pressure increase.

The process of producing large amounts of concentrated urine is called diuresis and the opposite process is called antidiuresis. When the amount of water in the body increases, the blood becomes more liquid. The amount of antidiuretic hormone (ADH) or vasopressin in the blood decreases. Water reabsorption from the glomerular filtrate in the distal convoluted tubule ceases. As a result, the concentration of urine decreases and more urine is produced. It causes frequent and large amounts of urine to be passed out of the body. Low-concentration urine continues to be excreted until the water balance in the body is restored.
Again, dehydration occurs when excess water is lost through excess sweat and urine. It increases blood density. Osmoreceptors of the hypothalamus are stimulated due to this change in blood. Antidiuretic hormone (ADH) production increases. ADH is released into the blood through the posterior pituitary gland in the process of neurosecretion. Water is reabsorbed from the glomerular filtrate by the distal convoluted tubule and returned to the blood. As a result, urine concentration increases and less urine is produced. It results in less number of times and less amount of urine is excreted from the body. More concentrated urine continues to be released until the water balance in the body.

Angiotensin-II is an active peptide hormone. Angiotensin-I is secreted inactively from the liver. Inactive Angiotensin-I is then converted to active Angiotensin-II. It increases aldosterone hormone synthesis and secretion. Increases secretion of pituitary gland. Causes constriction of blood vessels and increases blood pressure. Stimulates sodium reabsorption in the proximal convoluted tubule.

Atrial natriuretic hormone is secreted from the cells of the wall of the atrium of the heart. It increases renal sodium excretion and lowers blood pressure and blood volume. When excess blood flows into the atria, the heart wall expands. As a result, ANH is secreted from the heart wall. ANH dilates the afferent arterioles and increases the glomerular filtration rate. The collecting ducts of the nephron block sodium reabsorption. Renin inhibits angiotensin secretion.

Aldosterone hormone is produced from the cortex of the adrenal gland. It increases the ion and water reabsorption capacity of the kidney. Regulates renal sodium conservation, water retention and increased blood pressure.

Antidiuretic hormone is produced from the pituitary gland. It is also called vasopressin. When the water level in the blood decreases, more ADH is secreted. It increases the water absorption capacity of the renal tubules. As a result, the volume of urine decreases and the concentration of urine increases. The quantity and number of urine released from the body decreases. On the other hand, when the water level in the blood increases, the amount of ADH secretion decreases. This reduces the water absorption capacity of the renal tubules. As a result, urine volume increases and urine concentration decreases. The quantity and number of urine released from the body increases. Human diabetes insipidus occurs when the ADH production of the pituitary gland decreases.

Four hormones regulate urine concentration and blood sodium levels in humans.
1. Antidiuretic hormone (ADH): Antidiuretic hormone is produced from the pituitary gland. It is also called vasopressin. When the water level in the blood decreases, more ADH is secreted. It increases the water absorption capacity of the renal tubules. As a result, the volume of urine decreases and the concentration of urine increases. The quantity and number of urine released from the body decreases. On the other hand, when the water level in the blood increases, the amount of ADH secretion decreases. This reduces the water absorption capacity of the renal tubules. As a result, urine volume increases and urine concentration decreases. The quantity and number of urine released from the body increases. Human diabetes insipidus occurs when the ADH production of the pituitary gland decreases.
2. Aldosterone hormone: Aldosterone hormone is produced from the cortex of the adrenal gland. It increases the ion and water reabsorption capacity of the kidney. Regulates renal sodium conservation, water retention and increased blood pressure.
3. Atrial natriuretic hormone (ANH): Atrial natriuretic hormone is secreted from the cells of the wall of the atrium of the heart. It increases renal sodium excretion and lowers blood pressure and blood volume. When excess blood flows into the atria, the heart wall expands. As a result, ANH is secreted from the heart wall. ANH dilates the afferent arterioles and increases the glomerular filtration rate. The collecting ducts of the nephron block sodium reabsorption. Renin inhibits angiotensin secretion.
4. Angiotensin-II: Angiotensin-II is an active peptide hormone. Angiotensin-I is secreted inactively from the liver. Inactive Angiotensin-I is then converted to active Angiotensin-II. It increases aldosterone hormone synthesis and secretion. Increases secretion of pituitary gland. Causes constriction of blood vessels and increases blood pressure. Stimulates sodium reabsorption in the proximal convoluted tubule.