Homeostasis - Questions and Answers
1. Describe how the loop of Henle maximizes the absorption of water by using a
countercurrent multiplier system
The thick ascending loop of Henle is impermeable to water. It uses energy (ATP molecules)
to establish an electrochemical gradient and increases the amount of ions and solutes in the
interstitium of the medulla. This makes the surrounding tissue in the medulla hypertonic and
increases the osmotic pressure. As a result, the descending loop of Henle, which is
permeable to water but impermeable to ions, uses the gradient established by the thick
ascending loop of Henle to passively move water out of the tubule and into the surrounding
tissue. As water continually moves out of the descending loop of Henle, this concentrates
the filtrate and makes it hypertonic towards the bottom of the Henle.
2. Describe how a hormone released from a posterior gland regulates an increase in blood
osmolarity above its setpoint
The hypothalamus controls the mechanisms of ADH secretion, either by regulating blood
volume or the concentration of water in the blood. Dehydration or physiological stress can
cause an increase of osmolarity above 300 mOsm/L, which in turn, raises ADH secretion and
water will be retained, causing an increase in blood pressure. ADH travels in the
bloodstream to the kidneys. Once at the kidneys, ADH changes the kidneys to become more
permeable to water by temporarily inserting water channels, aquaporins, into the kidney
tubules. Water moves out of the kidney tubules through the aquaporins, reducing urine
volume. The water is reabsorbed into the capillaries lowering blood osmolarity back toward
normal.
3. How sweating reduces body temperature in endotherms
Terrestrial animals lose water by evaporation from their skin and respiratory surfaces
resulting in a cooling effect.
4. How selective reabsorption occurs in proximal convoluted tubule
NaCl in the filtrate enters the cells of the transport epithelium by the facilitated diffusion
and cotransport mechanism. Glucose, amino acids, potassium ions, and other essential
substances are also actively or passively transported from the filtrate to the interstitial fluid
and then into the peritubular capillaries.
5. Significance of angiotensin II preventing excessive blood loss from the body
Angiotensin II constrict arterioles, which decreases blood flow to capillaries in the kidney to
raise blood pressure and stimulate adrenal gland to release aldosterone
6. Importance of homeostasis in living organisms
Maintains optimal conditions for enzyme action, body temperature and glucose level
7. How glomerular filtrate is produced in the body
Bowman’s capsule envelops the glomerulus. Blood flows through the glomerular capillaries
under high pressure, forcing more than 10% of the plasma out of the capillaries and into the
Bowman ‘s capsule.
1. Describe how the loop of Henle maximizes the absorption of water by using a
countercurrent multiplier system
The thick ascending loop of Henle is impermeable to water. It uses energy (ATP molecules)
to establish an electrochemical gradient and increases the amount of ions and solutes in the
interstitium of the medulla. This makes the surrounding tissue in the medulla hypertonic and
increases the osmotic pressure. As a result, the descending loop of Henle, which is
permeable to water but impermeable to ions, uses the gradient established by the thick
ascending loop of Henle to passively move water out of the tubule and into the surrounding
tissue. As water continually moves out of the descending loop of Henle, this concentrates
the filtrate and makes it hypertonic towards the bottom of the Henle.
2. Describe how a hormone released from a posterior gland regulates an increase in blood
osmolarity above its setpoint
The hypothalamus controls the mechanisms of ADH secretion, either by regulating blood
volume or the concentration of water in the blood. Dehydration or physiological stress can
cause an increase of osmolarity above 300 mOsm/L, which in turn, raises ADH secretion and
water will be retained, causing an increase in blood pressure. ADH travels in the
bloodstream to the kidneys. Once at the kidneys, ADH changes the kidneys to become more
permeable to water by temporarily inserting water channels, aquaporins, into the kidney
tubules. Water moves out of the kidney tubules through the aquaporins, reducing urine
volume. The water is reabsorbed into the capillaries lowering blood osmolarity back toward
normal.
3. How sweating reduces body temperature in endotherms
Terrestrial animals lose water by evaporation from their skin and respiratory surfaces
resulting in a cooling effect.
4. How selective reabsorption occurs in proximal convoluted tubule
NaCl in the filtrate enters the cells of the transport epithelium by the facilitated diffusion
and cotransport mechanism. Glucose, amino acids, potassium ions, and other essential
substances are also actively or passively transported from the filtrate to the interstitial fluid
and then into the peritubular capillaries.
5. Significance of angiotensin II preventing excessive blood loss from the body
Angiotensin II constrict arterioles, which decreases blood flow to capillaries in the kidney to
raise blood pressure and stimulate adrenal gland to release aldosterone
6. Importance of homeostasis in living organisms
Maintains optimal conditions for enzyme action, body temperature and glucose level
7. How glomerular filtrate is produced in the body
Bowman’s capsule envelops the glomerulus. Blood flows through the glomerular capillaries
under high pressure, forcing more than 10% of the plasma out of the capillaries and into the
Bowman ‘s capsule.
