BIOL202 - Human Physiology: Endocrine, Renal & Respiratory Systems Flashcards

Question 1

RAAS Pathway: Trigger and Initial Cascade

Accepted Answer

Triggered by decreased renal perfusion, low $	ext{Na}^+$ delivery to macula densa, or sympathetic drive. Juxtaglomerular (JG) cells release **renin**, which converts liver-derived angiotensinogen into **Angiotensin I**. **ACE** (primarily in pulmonary capillaries) converts Ang I into **Angiotensin II**.

Question 2

Angiotensin II: Physiological Actions

Accepted Answer

1. Preferentially constricts **efferent arterioles** to maintain GFR during low perfusion.  
2. Stimulates **aldosterone** secretion from adrenal cortex.  
3. Stimulates **ADH** secretion from posterior pituitary.  
4. Promotes systemic vasoconstriction and hypothalamic thirst drive.

Question 3

GFR Autoregulation: Myogenic Mechanism

Accepted Answer

Intrinsic vascular response to systemic pressure changes. Increased blood pressure stretches renal vascular smooth muscle, activating stretch-sensitive ion channels $\rightarrow$ depolarization $\rightarrow$ **afferent arteriole constriction**, keeping renal blood flow and GFR stable.

Question 4

GFR Autoregulation: Tubuloglomerular Feedback (TGF)

Accepted Answer

Elevated GFR increases $	ext{NaCl}$ delivery to the **macula densa** in the distal nephron. Macula densa cells release **adenosine** (and ATP), causing **afferent arteriole constriction** to lower hydrostatic pressure in the glomerulus and normalize GFR.

Question 5

Glomerular Net Filtration Pressure (NFP) Formula

Accepted Answer

Formula: $NFP = (P_{GC} - P_{BS}) - \pi_{GC}$  
- $P_{GC}$: Glomerular Capillary Hydrostatic Pressure ($\sim 55 	ext{ mmHg}$, favors filtration)  
- $P_{BS}$: Bowman's Space Hydrostatic Pressure ($\sim 15 	ext{ mmHg}$, opposes filtration)  
- $\pi_{GC}$: Glomerular Capillary Oncotic Pressure ($\sim 30 	ext{ mmHg}$, opposes filtration)  
*Normal $NFP \approx 10 	ext{ mmHg}$*

Question 6

Countercurrent Multiplication Mechanism

Accepted Answer

Establishes the medullary osmotic gradient in the Loop of Henle:  
- **Descending Limb**: Permeable to $	ext{H}_2	ext{O}$ (via AQP1), impermeable to solutes.  
- **Thick Ascending Limb (TAL)**: Impermeable to $	ext{H}_2	ext{O}$; actively reabsorbs $	ext{Na}^+/	ext{K}^+/2	ext{Cl}^-$ via the **NKCC2** cotransporter, creating a hypertonic interstitium (up to $\sim 1200 	ext{ mOsm/L}$).

Question 7

Countercurrent Exchange in Vasa Recta

Accepted Answer

Passive exchange mechanism in hair-pin shaped peritubular capillaries (vasa recta). Allows blood flow to supply medullary tissue with $	ext{O}_2$ and nutrients **without washing out** the hyperosmotic medullary gradient established by countercurrent multiplication.

Question 8

Oxygen-Hemoglobin Dissociation Curve: Bohr Effect

Accepted Answer

Shift of the $O_2$-hemoglobin curve to the **right**, decreasing hemoglobin's affinity for $O_2$ to facilitate unloading at metabolic tissues.  
Triggered by **"CADET, face Right"**:  
- **C**o2 increase  
- **A**cid (low pH / high $	ext{H}^+$)  
- **D**PG (2,3-BPG) increase  
- **E**xercise  
- **T**emperature increase

Question 9

Haldane Effect

Accepted Answer

Describes how $O_2$ saturation affects hemoglobin's affinity for $	ext{CO}_2$ and $	ext{H}^+$. Oxygenation of hemoglobin in pulmonary capillaries promotes the displacement of $	ext{CO}_2$ from hemoglobin, facilitating $	ext{CO}_2$ exhalation into alveoli.

Question 10

Carbon Dioxide Transport & Bicarbonate Buffer Equation

Accepted Answer

$	ext{CO}_2 + 	ext{H}_2	ext{O} ightleftharpoons 	ext{H}_2	ext{CO}_3 ightleftharpoons 	ext{HCO}_3^- + 	ext{H}^+$  
Approximately $70\%$ of $	ext{CO}_2$ is transported as plasma bicarbonate ($	ext{HCO}_3^-$). In systemic RBCs, carbonic anhydrase converts $	ext{CO}_2$ to $	ext{HCO}_3^-$, which exits the RBC in exchange for $	ext{Cl}^-$ (**chloride shift**).

Question 11

Pulmonary Surfactant & Law of Laplace

Accepted Answer

Law of Laplace: $P = \frac{2T}{r}$ ($P$ = collapsing pressure, $T$ = surface tension, $r$ = alveolar radius).  
**Type II alveolar cells** secrete surfactant (dipalmitoylphosphatidylcholine), which reduces surface tension ($T$) more in smaller alveoli, preventing alveolar collapse (atelectasis) and maintaining uniform lung compliance.

Question 12

Hormone Classes: Peptide vs. Steroid Signaling Mechanisms

Accepted Answer

- **Peptide/Amine Hormones** (Hydrophilic): Circulate freely, bind cell-surface receptors (GPCRs, RTKs), act rapidly via intracellular secondary messengers ($cAMP, IP_3/DAG, Ca^{2+}$).  
- **Steroid Hormones** (Lipophilic): Require transport proteins, diffuse across plasma membrane, bind intracellular/nuclear receptors, modulate gene expression (slow onset, longer duration).

Question 13

ADH (Vasopressin) Cellular Mechanism

Accepted Answer

Binds **$V_2$ receptors** ($G_{\alpha s}$-coupled GPCR) on basolateral membranes of collecting duct principal cells $\rightarrow$ increases $cAMP$ $\rightarrow$ triggers PKA phosphorylation and insertion of **Aquaporin-2 (AQP2)** water channels into the apical membrane to increase free water reabsorption.

Question 14

Aldosterone Cellular Mechanism

Accepted Answer

Mineralocorticoid from zona glomerulosa that diffuses into principal cells $ightarrow$ binds intracellular mineralocorticoid receptors $ightarrow$ increases gene expression of apical **ENaC** ($	ext{Na}^+$ channels) and basolateral **$	ext{Na}^+/	ext{K}^+$-ATPase** pumps. Result: increased $	ext{Na}^+$ reabsorption and $	ext{K}^+/	ext{H}^+$ secretion.

Question 15

Renal Clearance & Determination of GFR vs. RPF

Accepted Answer

Clearance formula: $C_x = \frac{U_x 	imes V}{P_x}$  
- **Inulin** (or Creatinine): Freely filtered, neither reabsorbed nor secreted $ightarrow C_{inulin} = GFR$.  
- **PAH (Para-aminohippurate)**: Freely filtered and completely secreted $ightarrow C_{PAH} = RPF$ (Renal Plasma Flow).

Question 16

Spirometry: Obstructive vs. Restrictive Lung Patterns

Accepted Answer

- **Obstructive** (e.g., Asthma, COPD): Impaired expiratory airflow. Reduced $FEV_1/FVC$ ratio ($< 0.70$), elevated Total Lung Capacity ($TLC$) due to air trapping.  
- **Restrictive** (e.g., Pulmonary Fibrosis): Reduced expansion. Normal or elevated $FEV_1/FVC$ ratio ($\ge 0.70$), but reduced $FVC$ and $TLC$.

Question 17

Hypothalamic-Pituitary-Adrenal (HPA) Axis Feedback Loop

Accepted Answer

Hypothalamus releases **CRH** $\rightarrow$ Anterior Pituitary releases **ACTH** $\rightarrow$ Adrenal Cortex (zona fasciculata) secretes **Cortisol**. Cortisol exerts negative feedback on both the hypothalamus and anterior pituitary to inhibit CRH and ACTH release.

Question 18

Hypothalamic-Pituitary-Thyroid (HPT) Axis & Peripheral Conversion

Accepted Answer

Hypothalamus secretes **TRH** $\rightarrow$ Anterior Pituitary secretes **TSH** $\rightarrow$ Thyroid gland releases **$T_4$ ($90\%$)** and **$T_3$ ($10\%$)**. Free $T_3$ and $T_4$ exert negative feedback on TRH and TSH. Peripheral tissue target cells convert $T_4$ into active $T_3$ via **5'-deiodinase**.

Question 19

Glomerular Filtration Barrier Components

Accepted Answer

Three-layer barrier preventing macro-molecule filtration:  
1. **Fenestrated Endothelium** (blocks blood cells).  
2. **Basement Membrane** (negatively charged heparan sulfate, repels negatively charged proteins like albumin).  
3. **Podocyte Epithelium** (interdigitating foot processes forming slit diaphragms).

Question 20

Atrial Natriuretic Peptide (ANP) Physiology

Accepted Answer

Released by atrial myocytes in response to high atrial stretch (hypervolemia).  
- **Dilates afferent** and **constricts efferent** arterioles (increases GFR).  
- Inhibits renin, aldosterone, and ADH release.  
- Decreases $	ext{Na}^+$ reabsorption in medullary collecting duct $ightarrow$ net natriuresis and diuresis.

BIOL202 - Human Physiology: Endocrine, Renal & Respiratory Systems

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