1
Exam questions and detailed answers
1.Describe the process of reabsorption of Na+, glucose and water in the kidney(10mks).
SODIUM
90% of the filtered sodium is reabsorbed in the early region of the nephron. In absence of
aldosterone 80% of the remaining is reabsorbed through the wall of the tubule into the
peritubular blood representing 8% of the amount filtered.2% of the amount filtered is excreted
without aldosterone. When aldosterone is secreted in maximal amounts, all the Na+ delivered to
the distal tubule is reabsorbed. Aldosterone stimulates the activity of Na+/K+(ATPase) pumps in
the basolateral membrane of the cortical collecting ducts cells which is its primary site. This
increases the electrochemical gradient for the passive movement of Na+ from the filtered
through Na+, Cl- cotransporters in the apical membrane facing the filtrate in the lumen.
GLUCOSE
Occurs in the proximal tubule by secondary active transport which is mediated by membrane
carriers that cotransport glucose and Na+ carrier transport displays the property of saturation.
This means that when the transported molecules present in sufficiently high concentrations, all of
the carriers become occupied and the transport rate reaches a maximum value (transport
maximum) TM. When the blood plasma glucose can be completely reabsorbed. However, when
the plasma concentration is sufficient high, the filtered glucose can saturate the carriers. When
the rate of glucose filtration is greater than the transport maximum of the carriers become
, 2
saturated and the excess glucose will continue its journey through the renal tubules and spill over
into the urine.
WATER.
The reabsorption of water in the kidney is under the control of ADH. It triggers the release of
aldosterone which increase the concentration of sodium ions in blood. The increased sodium
concentration in the blood increases the blood osmotic potential which further increases the
reabsorption of water into the collecting tubule. ADH also makes tubules more permeable to
water reabsorption.
2.Describe the influence of ADH, the Renin- Angiotensin Aldosterone system and anti-
natriuretic peptides on the regulation of extracellular fluid and volume composition
(10mks)
ADH.
Aldosterone is produced by adrenal cortex and it's stimulated when potassium levels or sodium
levels falls by adrenal cells.
When blood volume drops for any reason (hemorrhage or excessive water loss through sweating
or diarrhea) arterial blood pressure drops, which in turn decreases the amount of filtrate formed
by the kidneys. In addition highly sensitive cells in the hypothalamus called osmoreceptors react
to change in blood composition by becoming very irritable the result is nerve impulse are sent to
the posterior pituitary which then release antidiuretic hormone (ADH) which travels in the blood
to the kidney to collecting duct that which is also main target where it causes the Duct cells to
Exam questions and detailed answers
1.Describe the process of reabsorption of Na+, glucose and water in the kidney(10mks).
SODIUM
90% of the filtered sodium is reabsorbed in the early region of the nephron. In absence of
aldosterone 80% of the remaining is reabsorbed through the wall of the tubule into the
peritubular blood representing 8% of the amount filtered.2% of the amount filtered is excreted
without aldosterone. When aldosterone is secreted in maximal amounts, all the Na+ delivered to
the distal tubule is reabsorbed. Aldosterone stimulates the activity of Na+/K+(ATPase) pumps in
the basolateral membrane of the cortical collecting ducts cells which is its primary site. This
increases the electrochemical gradient for the passive movement of Na+ from the filtered
through Na+, Cl- cotransporters in the apical membrane facing the filtrate in the lumen.
GLUCOSE
Occurs in the proximal tubule by secondary active transport which is mediated by membrane
carriers that cotransport glucose and Na+ carrier transport displays the property of saturation.
This means that when the transported molecules present in sufficiently high concentrations, all of
the carriers become occupied and the transport rate reaches a maximum value (transport
maximum) TM. When the blood plasma glucose can be completely reabsorbed. However, when
the plasma concentration is sufficient high, the filtered glucose can saturate the carriers. When
the rate of glucose filtration is greater than the transport maximum of the carriers become
, 2
saturated and the excess glucose will continue its journey through the renal tubules and spill over
into the urine.
WATER.
The reabsorption of water in the kidney is under the control of ADH. It triggers the release of
aldosterone which increase the concentration of sodium ions in blood. The increased sodium
concentration in the blood increases the blood osmotic potential which further increases the
reabsorption of water into the collecting tubule. ADH also makes tubules more permeable to
water reabsorption.
2.Describe the influence of ADH, the Renin- Angiotensin Aldosterone system and anti-
natriuretic peptides on the regulation of extracellular fluid and volume composition
(10mks)
ADH.
Aldosterone is produced by adrenal cortex and it's stimulated when potassium levels or sodium
levels falls by adrenal cells.
When blood volume drops for any reason (hemorrhage or excessive water loss through sweating
or diarrhea) arterial blood pressure drops, which in turn decreases the amount of filtrate formed
by the kidneys. In addition highly sensitive cells in the hypothalamus called osmoreceptors react
to change in blood composition by becoming very irritable the result is nerve impulse are sent to
the posterior pituitary which then release antidiuretic hormone (ADH) which travels in the blood
to the kidney to collecting duct that which is also main target where it causes the Duct cells to
