Physiology Block 4

Sequence the pathway of fluid/filtrate flow and regulated reabsorption through the renal nephron starting with blood entering the renal corpuscle.

1. Afferent arteriole

2. Glomerulus

3. Bowman's capsule

4. Proximal convoluted tubule (~60–66% obligate Na+ & water reabsorption)

5. Loop of Henle (~25% Na+ reabsorption via NaK2Cl)

6. Distal convoluted tubule (~10% Na+ reabsorption via NaCl)

7. Collecting duct (2–5% hormone-regulated reabsorption via Aldosterone/ADH)

Select the correct statement regarding glomerular filtration and renal blood flow: A. 100% of renal blood flow is filtered into Bowman's capsule at the glomerulus

• B. Glomerular colloid osmotic pressure (32 mmHg) drives filtration of plasma into Bowman's capsule

  C. The efferent arteriole is the primary regulator of Glomerular Filtration Rate (GFR)

  D. Constriction of the afferent arteriole decreases glomerular hydrostatic pressure and decreases GFR

  E. Tubular secretion moves solutes from the tubule lumen into the peritubular capillaries

  
  

• D. Constriction of the afferent arteriole decreases glomerular hydrostatic pressure and decreases GFR

Select all that would be occurring in response to a DECREASE in blood pressure and blood volume:

• A. Granular cells release renin, leading to increased Angiotensin II

• B. Aldosterone inserts ENaC channels into principal cells of the collecting duct

• C. Afferent arterioles dilate to increase GFR and urine output

• D. Angiotensin II causes vasoconstriction, increasing Total Peripheral Resistance (TPR)

• E. Osmoreceptors are inhibited, decreasing ADH release

• A. Granular cells release renin, leading to increased Angiotensin II

• B. Aldosterone inserts ENaC channels into principal cells of the collecting duct

• D. Angiotensin II causes vasoconstriction, increasing Total Peripheral Resistance (TPR)

Renal Transporters & Hemodynamics: Key pairings include

SGLT/NHE in the proximal tubule, NaCl cotransporters in the DCT, and ENaC regulation by aldosterone in principal cells. Glomerular filtration is heavily influenced by afferent/efferent tone and the macula densa via tubuloglomerular feedback.

Potassium & Calcium Homeostasis: Intracellular fluid (ICF) serves as the

primary reservoir for potassium (\(K^{+}\)), which shifts due to insulin, epinephrine, and pH changes. Parathyroid hormone (PTH) and vitamin D reciprocally manage calcium and phosphate balances, while free ionized calcium is altered during acid-base disturbances.

Fluid Balance & Osmolality: Plasma osmolality is governed primarily by

sodium levels, driving hypothalamic osmoreceptors, thirst, and ADH-mediated aquaporin-2 insertion in the collecting ducts.

Acid-Base Regulation: Buffering systems rely on

weak acids and intracellular proteins alongside rapid respiratory adjustments (\(PCO_{2}\)) and slower renal management (\(HCO_{3}^{-}\) and \(H^{+}\) handling). Carbonic anhydrase facilitates these shifts across red blood cells and renal tubules.

Respiratory Control: Alveolar ventilation responds to

arterial and cerebrospinal fluid \(H^{+}\) via central and peripheral chemoreceptors, balancing uncompensated and compensated acid-base states like respiratory acidosis and alkalosis.

Sequence the pathway of the Renin-Angiotensin-Aldosterone System (RAAS) starting with a drop in blood pressure.

1. Decreased blood pressure / renal blood flow

2. Granular cells in the kidney release Renin

3. Angiotensinogen (from liver) is converted to Angiotensin I

4. ACE (in the lungs) converts Angiotensin I to Angiotensin II

5. Angiotensin II stimulates vasoconstriction and Aldosterone release

6. Aldosterone inserts ENaC channels in collecting duct principal cells

7. Increased Na+ and water reabsorption restores blood volume

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Of the listed physiological pairs, select the pair that does NOT directly go together:

• A. Proximal tubule: SGLT and NHE transporters

• B. Ascending limb of Loop of Henle: Na+K+2Cl- cotransporter

• C. Principal cells: H+ secretion and K+ reabsorption (Correct — this is Intercalated cells; Principal cells reabsorb Na+ and secrete K+)

• D. Posterior pituitary: Antidiuretic Hormone (ADH) release

• C. Principal cells: H+ secretion and K+ reabsorption (Correct — this is Intercalated cells; Principal cells reabsorb Na+ and secrete K+)

Select the FALSE answer regarding Carbonic Anhydrase:

• A. It catalyzes the conversion of CO2 and H2O into carbonic acid (H2CO3)

• B. It is found inside red blood cells

• C. It is found in renal tubules

• D. It is found freely circulating in blood plasma

• D. It is found freely circulating in blood plasma - it is in RBCs and renal tubules, NOT plasma)

Most of the potassium (K+) in the body is found:

Inside cells (intracellular fluid)

Match the nephron segment or cell type with its key transport feature:

• Afferent arteriole

• Proximal convoluted tubule

• Macula densa

• Collecting duct principal cells

• Afferent arteriole: Primary regulator of Glomerular Filtration Rate (GFR)

• Proximal convoluted tubule: ~60–66% obligate reabsorption of Na+ and water

• Macula densa: Senses distal tubule NaCl flow for tubuloglomerular feedback

• Collecting duct principal cells: Hormone-regulated Na+ reabsorption via ENaC

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Which two events do NOT happen at the same time?

• A. High plasma osmolality and decreased ADH secretion

• B. Aldosterone secretion and K+ secretion into urine

• C. Acidemia and K+ shifting out of cells into plasma

• D. Hyperventilation and decreased arterial PCO2

• A. High plasma osmolality and decreased ADH secretion (— high osmolality stimulates osmoreceptors to INCREASE ADH)

To restore homeostasis when plasma calcium (Ca2+) is too low, select all of the following that should happen:

• A. Parathyroid gland releases Parathyroid Hormone (PTH)

• B. Bone releases Ca2+ into the blood

• C. Thyroid parafollicular cells release Calcitonin

• D. Kidneys increase Ca2+ reabsorption and increase phosphate (PO4-) excretion (Correct)

• E. Active Vitamin D (Calcitriol) increases intestinal Ca2+ absorption

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• A. Parathyroid gland releases Parathyroid Hormone (PTH)

• B. Bone releases Ca2+ into the blood

• E. Active Vitamin D (Calcitriol) increases intestinal Ca2+ absorption

From the options of physiological pairs, which option DOES NOT belong together?

• A. Chemical buffers: act within seconds to minutes

• B. Respiratory compensation: acts within 1 to 15 minutes

• C. Renal compensation: acts within hours to days

• D. Phosphate buffer system: unlimited buffering capacity

D. Phosphate buffer system: unlimited buffering capacity (Correct — Bicarbonate has unlimited capacity because CO2 is exhaled; Phosphate and Ammonia have limited capacity)

Select the correct statement regarding respiratory control and gas exchange:

• A. Oxygen (O2) is the primary regulator of resting respiratory rate

• B. Hydrogen ions (H+) easily cross the blood-brain barrier to stimulate central chemoreceptors

• C. Peripheral chemoreceptors in the carotid bodies trigger a hypoxic drive when PO2 drops below 70 mmHg

• D. Normal arterial PCO2 is 100 mmHg and arterial PO2 is 40 mmHg

• C. Peripheral chemoreceptors in the carotid bodies trigger a hypoxic drive when PO2 drops below 70 mmHg

Select all that would be occurring during uncompensated Respiratory Acidosis:

• A. Decreased blood pH (below 7.38)

• B. Elevated arterial PCO2

• C. Hyperventilation blowing off excess CO2

• D. The law of mass action drives the carbonic acid equation toward H+ and HCO3-

• A. Decreased blood pH (below 7.38)

• B. Elevated arterial PCO2

• D. The law of mass action drives the carbonic acid equation toward H+ and HCO3-

Sequence the pathway of respiratory compensation for metabolic acidosis starting with elevated plasma

1. Increased plasma H+ (decreased pH) drives the law of mass action toward CO2

2. CO2 diffuses across the blood-brain barrier into cerebrospinal fluid (CSF)

3. CO2 reacts with H2O to increase H+ in brain interstitial fluid

4. Central chemoreceptors in the medulla are stimulated

5. Respiratory control centers increase action potentials in somatic motor neurons

6. Rate and depth of breathing increase, lowering plasma CO2

Of the listed physiological pairs, select the pair that does NOT directly go together:

• A. Insulin: shifts K+ into cells (lowers plasma K+)

• B. Epinephrine: stimulates Na+K+ ATPase}\) to move K+ into cells

• C. Acidemia: shifts K+ ,into cells (causes hypokalemia)

• D. Hyperkalemia: depolarizes resting membrane potential

• C. Acidemia: shifts K+ into cells (causes hypokalemia) (Correct — acidemia causes \H+ to enter cells and K+ to exit, raising plasma K+

Select the FALSE answer regarding Parathyroid Hormone (PTH) and Calcium regulation:• A. PTH is released when plasma \(\text{Ca}^{2+}\) levels are low

• B. PTH stimulates the release of \(\text{Ca}^{2+}\) from bone

• C. PTH stimulates renal activation of Vitamin D (Calcitriol)

• D. PTH increases renal reabsorption of both \(\text{Ca}^{2+}\) and phosphate (\(\text{PO}_{4}^{-}\))

• D. PTH increases renal reabsorption of both Ca2+ and phosphate (Correct — PTH increases Ca2+ reabsorption, but INCREASES renal loss/excretion of phosphate)

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Which two events do NOT happen at the same time?

• A. Decreased blood volume and decreased sympathetic nerve activity to the kidney

• B. Sympathetic stimulation to the kidney and constriction of the afferent arteriole

• C. Increased Angiotensin II and increased Total Peripheral Resistance (TPR)

• D. Increased Aldosterone and increased \(\text{K}^{+}\) secretion in the collecting duct

• A. Decreased blood volume and decreased sympathetic nerve activity to the kidney (Correct — low blood volume triggers baroreceptors to INCREASE sympathetic activity)

To restore homeostasis when plasma osmolality is TOO HIGH (e.g., dehydration or high salt intake), select all of the following that should happen:

• A. Osmoreceptors in the hypothalamus are stimulated

• B. Thirst is stimulated to increase water intake

• C. The posterior pituitary increases Antidiuretic Hormone (ADH) secretion

• D. Aquaporin-2 channels are inserted into the apical membrane of collecting duct cells

• E. The kidneys excrete a large volume of dilute urine

• A. Osmoreceptors in the hypothalamus are stimulated

• B. Thirst is stimulated to increase water intake

• C. The posterior pituitary increases Antidiuretic Hormone (ADH) secretion

• D. Aquaporin-2 channels are inserted into the apical membrane of collecting duct cells

Central chemoreceptors in the medulla are responsible for what percentage of the increased ventilation seen during hypercapnia (high \(\text{CO}_{2}\))?

• A. 10–20%

• B. 25–30%

• C. 50%

• D. 70–80%

D. 70–80% (Correct — peripheral chemoreceptors respond faster, while central chemoreceptors drive 70–80% of the response)

Match the respiratory term or location with its defining characteristic:

• External respiration:

• Internal respiration:

• Cellular respiration:

• Alveoli & arterial blood:

• External respiration: Ventilation and gas exchange between alveoli and pulmonary blood

• Internal respiration: Gas exchange between systemic blood and tissue cells

• Cellular respiration: Oxygen utilization by mitochondria to generate ATP

• Alveoli & arterial blood: PO2 = 100\text{ mmHg}\) and PCO2 = 40mmhg

From the options of physiological pairs, which option DOES NOT belong together?

• A. High altitude (10,000 ft): decreased total atmospheric pressure lowers alveolar PO2

• B. Lack of surfactant or fibrosis: decreased lung compliance

• C. Bronchoconstriction or excess mucus: decreased airway resistance

• D. Alcohol poisoning or drug overdose: CNS depression slows breathing rate

C. Bronchoconstriction or excess mucus: decreased airway resistance (Correct — narrowing/obstruction INCREASES airway resistance)

Select the correct statement regarding buffers and pH regulation:

• A. Strong acids are the principal chemical buffers in the human body

• B. Chemical buffer systems permanently eliminate excess acid or base from the body

• C. Roughly 60% of chemical buffering occurs inside cells via proteins such as hemoglobin

• D. At a normal blood pH of 7.4, phosphate exists primarily as PO³- 4

• C. Roughly 60% of chemical buffering occurs inside cells via proteins such as hemoglobin

Select all that are true regarding tubular reabsorption in the nephron:

• A. The basolateral Na+-K+ ATPase}\) establishes the gradient that drives secondary active Na+ reabsorption

• B. Roughly 90% of filtered Na+ and water is reabsorbed obligately before reaching the collecting duct

• C. Aldosterone regulates ~60% of total filtered sodium reabsorption

• D. In the proximal tubule, Na+ reabsorption via NHE helps reclaim bicarbonate HCO3 -

• A. The basolateral Na+-K+ ATPase}\) establishes the gradient that drives secondary active Na+ reabsorption

• B. Roughly 90% of filtered Na+ and water is reabsorbed obligately before reaching the collecting duct

D. In the proximal tubule, Na+ reabsorption via NHE helps reclaim bicarbonate HCO3 -

Which two events do NOT happen at the same time?

• A. Alkalosis (high pH) and increased free ionized plasma \(\text{Ca}^{2+}\)

• B. Acidosis (low pH) and increased free ionized plasma \(\text{Ca}^{2+}\)

• C. High plasma \(\text{K}^{+}\) and direct stimulation of aldosterone secretion from the adrenal cortex [cite: 2]

• D. Low blood pressure and increased renin secretion from granular cells

• A. Alkalosis (high pH) and increased free ionized plasma \(\text{Ca}^{2+}\) (Correct — alkalosis leaves more negative binding sites open on albumin, so more \(\text{Ca}^{2+}\) binds protein and FREE \(\text{Ca}^{2+}\) decreases)