PSIO 305 TEST PAPER 2025/2026 QUESTIONS WITH
ANSWERS GRADED A+
✔✔what is the function of the chief cells in the parathyroid? - ✔✔to secrete parathyroid
hormone (PTH)
✔✔what is the function of PTH? - ✔✔to *raise* blood calcium levels
✔✔how does PTH increase blood calcium levels? - ✔✔by triggering:
1. ↑ osteoclast activity/bone resorption of calcium
2. ↑ renal reabsorption of calcium
3. ↑ intestinal absorption of calcium
✔✔summarize the hormones released by the thyroid and parathyroid glands for calcium
homeostasis - ✔✔1. thyroid gland:
a. follicular cells: T3 & T4
b. *parafollicular cells: calcitonin*
2. parathyroid gland:
a. oxyphil cells: unknown
b: *chief cells: PTH*
✔✔recall: what is the function of calcitonin released by parafollicular cells in the thyroid
gland? - ✔✔decrease blood calcium levels
✔✔recall: what is the the function of PTH released by chief cells in the parathyroid
glands? - ✔✔increase blood calcium levels
✔✔why is calcium homeostasis important? (hint: what are 5 physiological roles of
calcium?) - ✔✔calcium plays important roles in:
1. bone formation
2. muscle contraction
3. membrane excitability
4. blood coagulation
5. intracellular second messenger cascades
✔✔recall: what is an effector organ? - ✔✔it is an organ that receives information from
the control center and adjusts the regulated paramter
✔✔what are the 3 effector organs involved in calcium homeostasis? - ✔✔1. bone
2. kidney
3. intestines
✔✔what is the stimulus in calcium homeostasis? - ✔✔1. falling blood calcium levels
2. rising blood calcium levels
,✔✔if blood calcium levels were falling, receptors in what gland would detect this
change? - ✔✔parathyroid gland
✔✔what would the parathyroid gland secrete in response to falling blood calcium
levels? - ✔✔PTH (increases blood calcium)
✔✔what 3 effector organs would be affected by PTH? - ✔✔1. kidneys
2. bone
3. intestines
✔✔how does PTH affect the kidney? - ✔✔it stimulates calcium reuptake in the kidneys
✔✔how does PTH affect the bone? - ✔✔it stimulates osteoclast activity to release
calcium from the bones
✔✔how does PTH affect the intestines? - ✔✔kidney absorption of calcium activates
vitamin D, which indirectly increases calcium uptake in the intestines
✔✔is blood calcium homeostasis an example of a negative or positive feedback circuit?
- ✔✔negative feedback
✔✔calcitonin is secreted by the parafollicular cells in the thyroid gland when blood
calcium levels are rising or falling? - ✔✔when blood calcium levels are rising because
calcitonin decreases blood calcium levels
✔✔PTH is secreted by the chief cells in the parathyroid gland when blood calcium
levels are rising or falling? - ✔✔when blood calcium levels are falling because PTH
increases blood calcium levels
✔✔what organ is important for the regulation of blood glucose? - ✔✔pancreas
✔✔the pancreas is a part of what organ system? - ✔✔endocrine system
✔✔what microorgan within the pancreas is responsible for its hormone-secreting
(endocrine) function? - ✔✔the islets of Langerhans (which make up only 2% of the
pancreas, 98% is made up of the exocrine acinar cells)
✔✔what is the goal of blood glucose homeostasis? - ✔✔to keep blood glucose in a
normal range
✔✔what is the normal range for blood glucose levels? - ✔✔~90 mg/dL
,✔✔why is glucose homeostasis important? (hint: what is the function of gluose?) -
✔✔glucose in the presence of O2 can be converted into energy, H2O, and CO2 (called
*aerobic respiration*)
✔✔what 2 hormones secreted by the endocrine pancreas (islets of Langerhans) are
important for glucose homeostasis? - ✔✔1. glucagon
2. insulin
✔✔what cells within the islets of Langerhans secrete glucagon? - ✔✔α cells
✔✔what is the function of glucagon? - ✔✔raising blood glucose levels
✔✔what cells within the islets of Langerhans secrete insulin? - ✔✔β cells
✔✔what is the function of insulin? - ✔✔decreasing blood glucose levels
✔✔insulin and glucagon target what effector organ? - ✔✔liver
✔✔how does insulin affect the liver? - ✔✔it triggers the liver to take up glucose and
store it as glycogen (*glycogenesis*)
✔✔how does glucagon affect the liver? - ✔✔it triggers the liver to break down glycogen
and release glucose (*glycogenolysis*)
✔✔what is the goal of pH homeostasis? - ✔✔to keep blood pH constant
✔✔what is the normal blood pH? - ✔✔7.35-7.45 (7.4 in notes)
✔✔why is pH homeostasis important? - ✔✔pH plays a role in:
1. enzyme activity (enzymes operate best at a particular pH)
2. hemoglobin saturation of oxygen
✔✔what does the hemoglobin-oxygen dissociation curve show? - ✔✔it shows that as
blood partial pressure of O2 (PO2) increases, the percentage of hemoglobin (Hb)
saturation increases
✔✔what is the shape of the Hb-O2 dissociation curve? - ✔✔sigmoidal
✔✔at rest, hemoglobin is at what saturation? - ✔✔70-80% saturation
✔✔what 2 organ systems are important for regulation blood pH? - ✔✔1. respiratory
system
2. renal system
, ✔✔which system (respiratory or renal) is a slower but more powerful means to regulate
pH? - ✔✔renal system
✔✔what is the bohr shift? - ✔✔it is the effect of increased CO2 on the oxygen
dissociation curve for Hb
✔✔what would cause an increase in CO2? - ✔✔a decrease in blood pH (an increase in
H+/blood acidity)
✔✔why would an increase in blood acidity/a decrease in blood pH lead to an increase in
blood CO2? - ✔✔CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
✔✔how does the bohr shift affect the oxygen dissociation curve for hemoglobin? - ✔✔it
causes the sigmoidal cuve to shift *↓*
✔✔what changes would cause a decrease in Hb saturation (a downward shift in the Hb-
O2 dissociation curve)? - ✔✔1. an increase in CO2 (bohr shift)
2. a decrease in pH/an increase in H+
3. a decrease in HCO3-
✔✔at any given PO2, an increase in CO2 would lead to what on the Hb-O2 dissociation
curve? - ✔✔at any given PO2, Hb binds more H+ and less O2 (it cannot hold onto O2
as tightly)
✔✔why would an increase in H+/an increase in CO2 cause Hb to not hold onto O2 as
tightly? - ✔✔H+ stabilizes hemoglobin in the T (inactive) state, which has a lower affinity
for O2
✔✔true/false: at increased CO2, Hb cannot achieve 100% saturation - ✔✔false,
although Hb is not able to hold onto O2 as tightly at any given PO2 when CO2 levels
are increased, Hb can still achieve 100% saturation
✔✔the downward bohr shift has what effect on hemoglobin-O2 dissociation? - ✔✔at
any given partial pressure of O2 (PO2), hemoglobin has as lower saturation of O2 and a
higher tendency to release O2 (more free O2) and bind H+
✔✔when blood gets to an area of the body that is producing CO2 (rich in CO2), what
happens to hemoglobin? - ✔✔Hb dumps off O2 (more free O2)
✔✔when blood gets to an area of the body that is low inC CO2 (e.g. lungs), what
happens to hemoglobin? - ✔✔Hb binds more O2 (less free O2, higher O2 saturation)
ANSWERS GRADED A+
✔✔what is the function of the chief cells in the parathyroid? - ✔✔to secrete parathyroid
hormone (PTH)
✔✔what is the function of PTH? - ✔✔to *raise* blood calcium levels
✔✔how does PTH increase blood calcium levels? - ✔✔by triggering:
1. ↑ osteoclast activity/bone resorption of calcium
2. ↑ renal reabsorption of calcium
3. ↑ intestinal absorption of calcium
✔✔summarize the hormones released by the thyroid and parathyroid glands for calcium
homeostasis - ✔✔1. thyroid gland:
a. follicular cells: T3 & T4
b. *parafollicular cells: calcitonin*
2. parathyroid gland:
a. oxyphil cells: unknown
b: *chief cells: PTH*
✔✔recall: what is the function of calcitonin released by parafollicular cells in the thyroid
gland? - ✔✔decrease blood calcium levels
✔✔recall: what is the the function of PTH released by chief cells in the parathyroid
glands? - ✔✔increase blood calcium levels
✔✔why is calcium homeostasis important? (hint: what are 5 physiological roles of
calcium?) - ✔✔calcium plays important roles in:
1. bone formation
2. muscle contraction
3. membrane excitability
4. blood coagulation
5. intracellular second messenger cascades
✔✔recall: what is an effector organ? - ✔✔it is an organ that receives information from
the control center and adjusts the regulated paramter
✔✔what are the 3 effector organs involved in calcium homeostasis? - ✔✔1. bone
2. kidney
3. intestines
✔✔what is the stimulus in calcium homeostasis? - ✔✔1. falling blood calcium levels
2. rising blood calcium levels
,✔✔if blood calcium levels were falling, receptors in what gland would detect this
change? - ✔✔parathyroid gland
✔✔what would the parathyroid gland secrete in response to falling blood calcium
levels? - ✔✔PTH (increases blood calcium)
✔✔what 3 effector organs would be affected by PTH? - ✔✔1. kidneys
2. bone
3. intestines
✔✔how does PTH affect the kidney? - ✔✔it stimulates calcium reuptake in the kidneys
✔✔how does PTH affect the bone? - ✔✔it stimulates osteoclast activity to release
calcium from the bones
✔✔how does PTH affect the intestines? - ✔✔kidney absorption of calcium activates
vitamin D, which indirectly increases calcium uptake in the intestines
✔✔is blood calcium homeostasis an example of a negative or positive feedback circuit?
- ✔✔negative feedback
✔✔calcitonin is secreted by the parafollicular cells in the thyroid gland when blood
calcium levels are rising or falling? - ✔✔when blood calcium levels are rising because
calcitonin decreases blood calcium levels
✔✔PTH is secreted by the chief cells in the parathyroid gland when blood calcium
levels are rising or falling? - ✔✔when blood calcium levels are falling because PTH
increases blood calcium levels
✔✔what organ is important for the regulation of blood glucose? - ✔✔pancreas
✔✔the pancreas is a part of what organ system? - ✔✔endocrine system
✔✔what microorgan within the pancreas is responsible for its hormone-secreting
(endocrine) function? - ✔✔the islets of Langerhans (which make up only 2% of the
pancreas, 98% is made up of the exocrine acinar cells)
✔✔what is the goal of blood glucose homeostasis? - ✔✔to keep blood glucose in a
normal range
✔✔what is the normal range for blood glucose levels? - ✔✔~90 mg/dL
,✔✔why is glucose homeostasis important? (hint: what is the function of gluose?) -
✔✔glucose in the presence of O2 can be converted into energy, H2O, and CO2 (called
*aerobic respiration*)
✔✔what 2 hormones secreted by the endocrine pancreas (islets of Langerhans) are
important for glucose homeostasis? - ✔✔1. glucagon
2. insulin
✔✔what cells within the islets of Langerhans secrete glucagon? - ✔✔α cells
✔✔what is the function of glucagon? - ✔✔raising blood glucose levels
✔✔what cells within the islets of Langerhans secrete insulin? - ✔✔β cells
✔✔what is the function of insulin? - ✔✔decreasing blood glucose levels
✔✔insulin and glucagon target what effector organ? - ✔✔liver
✔✔how does insulin affect the liver? - ✔✔it triggers the liver to take up glucose and
store it as glycogen (*glycogenesis*)
✔✔how does glucagon affect the liver? - ✔✔it triggers the liver to break down glycogen
and release glucose (*glycogenolysis*)
✔✔what is the goal of pH homeostasis? - ✔✔to keep blood pH constant
✔✔what is the normal blood pH? - ✔✔7.35-7.45 (7.4 in notes)
✔✔why is pH homeostasis important? - ✔✔pH plays a role in:
1. enzyme activity (enzymes operate best at a particular pH)
2. hemoglobin saturation of oxygen
✔✔what does the hemoglobin-oxygen dissociation curve show? - ✔✔it shows that as
blood partial pressure of O2 (PO2) increases, the percentage of hemoglobin (Hb)
saturation increases
✔✔what is the shape of the Hb-O2 dissociation curve? - ✔✔sigmoidal
✔✔at rest, hemoglobin is at what saturation? - ✔✔70-80% saturation
✔✔what 2 organ systems are important for regulation blood pH? - ✔✔1. respiratory
system
2. renal system
, ✔✔which system (respiratory or renal) is a slower but more powerful means to regulate
pH? - ✔✔renal system
✔✔what is the bohr shift? - ✔✔it is the effect of increased CO2 on the oxygen
dissociation curve for Hb
✔✔what would cause an increase in CO2? - ✔✔a decrease in blood pH (an increase in
H+/blood acidity)
✔✔why would an increase in blood acidity/a decrease in blood pH lead to an increase in
blood CO2? - ✔✔CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
✔✔how does the bohr shift affect the oxygen dissociation curve for hemoglobin? - ✔✔it
causes the sigmoidal cuve to shift *↓*
✔✔what changes would cause a decrease in Hb saturation (a downward shift in the Hb-
O2 dissociation curve)? - ✔✔1. an increase in CO2 (bohr shift)
2. a decrease in pH/an increase in H+
3. a decrease in HCO3-
✔✔at any given PO2, an increase in CO2 would lead to what on the Hb-O2 dissociation
curve? - ✔✔at any given PO2, Hb binds more H+ and less O2 (it cannot hold onto O2
as tightly)
✔✔why would an increase in H+/an increase in CO2 cause Hb to not hold onto O2 as
tightly? - ✔✔H+ stabilizes hemoglobin in the T (inactive) state, which has a lower affinity
for O2
✔✔true/false: at increased CO2, Hb cannot achieve 100% saturation - ✔✔false,
although Hb is not able to hold onto O2 as tightly at any given PO2 when CO2 levels
are increased, Hb can still achieve 100% saturation
✔✔the downward bohr shift has what effect on hemoglobin-O2 dissociation? - ✔✔at
any given partial pressure of O2 (PO2), hemoglobin has as lower saturation of O2 and a
higher tendency to release O2 (more free O2) and bind H+
✔✔when blood gets to an area of the body that is producing CO2 (rich in CO2), what
happens to hemoglobin? - ✔✔Hb dumps off O2 (more free O2)
✔✔when blood gets to an area of the body that is low inC CO2 (e.g. lungs), what
happens to hemoglobin? - ✔✔Hb binds more O2 (less free O2, higher O2 saturation)
