FMGE 2024 — Physiology

Q: Which of the following organs is a primary lymphoid organ?

Thymus. ***Thymus***- **Primary lymphoid organs** are the sites where lymphocytes are generated and mature into immunocompetent cells.- The **thymus** is essential for the maturation, selection, and central tolerance of **T lymphocytes**.*Lymph node*- Lymph nodes are classified as **secondary lymphoid organs** where matured lymphocytes activate and proliferate upon encountering specific antigens.- They serve as critical filters for **lymph**, organizing immune responses against pathogens draining from local tissues.*Spleen*- The spleen is a major **secondary lymphoid organ** responsible for filtering **blood** and mounting immune responses to systemic infections.- The **white pulp** contains T and B cell zones that are crucial for activating adaptive immunity against blood-borne pathogens.*MALT*- MALT (Mucosa-Associated Lymphoid Tissue) represents **secondary lymphoid tissues** found beneath epithelial surfaces.- It is responsible for initiating local immune responses at mucosal sites (e.g., **Peyer's patches** in the intestine). [Practice more Physiology PYQs on OnCourse]

Q: What is the typical Glomerular Filtration Rate (GFR) in a healthy adult?

125 ml/min. **Correct: 125 ml/min** - This is the accepted average value for **Glomerular Filtration Rate (GFR)** in a standard 70 kg healthy young adult - Represents the total volume of fluid filtered from plasma into Bowman's capsule per minute - Totals approximately **180 liters per day** *Incorrect: 150 ml/min* - Higher than the established average GFR (125 ml/min) - Indicative of **renal hyperfiltration**, often an early sign preceding kidney damage - Not the normal rate for a healthy adult *Incorrect: 100 ml/min* - Within the lower limits of normal for some demographics or mild age-related decline - Not the typical average GFR used in standard physiology - GFR below 90 ml/min suggests potential **renal impairment** (Stage 2 CKD) *Incorrect: 200 ml/min* - Significantly higher than physiological GFR - Suggests **hyperfiltration**, a pathological state associated with conditions like early **diabetes mellitus** - Indicates increased pressure or permeability in glomerular capillaries [Practice more Physiology PYQs on OnCourse]

Q: What renal function is represented by the formula UV/P?

Clearance. ***Clearance*** - The formula **(U × V) / P** represents the **renal clearance** (C) of a substance, where U is the urine concentration, V is the urine flow rate, and P is the plasma concentration of that substance - Clearance measures the virtual volume of **plasma** from which a substance is completely removed by the kidney per unit of time (typically expressed in ml/min) - This is the fundamental definition and calculation of renal clearance *Filtration* - Filtration is the bulk flow of fluid and solutes from the glomerular capillaries into Bowman's capsule, quantified by the Glomerular Filtration Rate (GFR) - The net filtration rate of a substance is calculated as GFR multiplied by the plasma concentration (P), which is distinct from the clearance formula UV/P *Tubular Secretion* - Tubular secretion is the active transfer of substances from the peritubular capillaries into the tubular lumen - While UV/P is used to calculate clearance, if a substance's clearance exceeds the GFR, it indicates that net tubular secretion has occurred *Tubular Reabsorption* - Tubular reabsorption is the process where filtered solutes move from the tubular lumen back into the peritubular capillaries - If the clearance (UV/P) of a substance is significantly less than the GFR, it signifies that net reabsorption of the substance has taken place [Practice more Physiology PYQs on OnCourse]

Q: Which of the following oxygen-sensitive channels is present in peripheral chemoreceptors?

K+. ***K+***- **Oxygen-sensitive K+ channels**, specifically members of the **TASK-like potassium channels** family, are central to the response of **glomus cells** in the carotid body to **hypoxia**.- When oxygen levels fall, these channels are **inhibited**, reducing K+ efflux and causing the cell membrane to **depolarize**, initiating the signaling cascade.*Na+*- While **voltage-gated Na+ channels** are essential for action potential generation in the afferent nerve, they are not the primary channels that directly sense changes in **pO2** within the glomus cells.- The initial depolarizing signal stems from the inhibition of K+ channels, not the activation or inhibition of Na+ channels.*Ca++*- **Voltage-gated Ca++ channels** open in response to the **depolarization** caused by K+ channel inhibition upon hypoxia.- The resulting **calcium influx** is mandatory for the final step: triggering the release of **neurotransmitters** (e.g., dopamine, ATP) that signal the brainstem.*Cl-*- **Cl- channels** (Chloride channels) are present in glomus cells and help regulate cell volume and membrane potential, but they do not function as the mechanism's primary oxygen sensor.- The entire chemosensing process is primarily governed by the modulation of **cation** movement (K+ efflux and subsequent Ca++ influx) rather than chloride flux. [Practice more Physiology PYQs on OnCourse]

4 Previous Year Questions with Answers & Explanations

Questions

Which of the following organs is a primary lymphoid organ?

What is the typical Glomerular Filtration Rate (GFR) in a healthy adult?

What renal function is represented by the formula UV/P?

Which of the following oxygen-sensitive channels is present in peripheral chemoreceptors?