NEET-PG 2015 - Physiology Practice Questions

Q: Miracle fruit is used to change the taste from?

Sour to Sweet. ***Sour to Sweet*** - The **miracle fruit** (Synsepalum dulcificum) contains a glycoprotein called **miraculin**. - Miraculin binds to taste receptors on the tongue and modifies their perception, making **sour foods taste sweet**. *Sour to Bitter* - The primary effect of miracle fruit is to convert **sour tastes into sweet tastes**, not bitter ones. - No known natural compound consistently changes sour perception to bitter. *Bitter to Sweet* - While miraculin makes sour foods sweet, it does not typically convert **bitter tastes into sweet sensations**. - Bitter taste perception involves different receptor pathways that are not significantly altered by miraculin. *Salty to Sweet* - Miracle fruit primarily targets **sour taste receptors**. - It does not have a significant effect on altering the perception of **salty tastes to sweet**.

Q: What is the most common mechanism responsible for causing arrhythmias in the heart?

Re-entry. ***Re-entry*** - **Re-entry** is the most common mechanism for arrhythmias and involves a re-excitation of cardiac tissue due to a circulating electrical impulse. - This requires at least two pathways with differing conduction velocities and refractory periods, creating a path for the impulse to re-excite an area after its normal refractory period has ended. *Early after depolarization* - **Early afterdepolarizations (EADs)** occur during phase 2 or 3 of the action potential when repolarization is incomplete, often due to prolonged action potential duration. - They are typically associated with conditions like **long QT syndrome** and can trigger polymorphic ventricular tachycardia, but are less common than re-entry. *Late after depolarization* - **Late afterdepolarizations (DADs)** occur during phase 4 of the action potential, after repolarization is complete, due to excessive intracellular calcium. - They are often seen in conditions like **digoxin toxicity** or **catecholaminergic polymorphic ventricular tachycardia**, but are not the most prevalent mechanism. *Automaticity* - **Abnormal automaticity** refers to pacemaker activity arising in non-pacemaker cells or an acceleration of normal pacemaker activity. - While it can cause arrhythmias such as accelerated idioventricular rhythm, re-entry is far more frequently implicated in the etiology of clinical arrhythmias.

Q: All are true about GFR except:

Best estimated by creatinine clearance. ***Best estimated by creatinine clearance*** - While **creatinine clearance** can be used as a measure of GFR, it is not the *best* estimate; it tends to slightly **overestimate** GFR due to tubular secretion of creatinine. [1] - The gold standard for measuring GFR involves methods like **inulin clearance**, but in clinical practice, GFR is often *estimated* using equations based on **serum creatinine** (e.g., CKD-EPI, MDRD). [2] *30-40% decrease after 70 years of age* - **Aging** is associated with a physiological decline in GFR, with a general decrease often cited as 30-40% after the age of 70 years. - This decline is part of the normal **age-related changes in renal function**. *GFR is dependent on height in children* - In children, GFR is often adjusted for **body surface area (BSA)**, which is calculated based on both **height and weight**, making height an important factor. [1] - This adjustment is crucial for accurate assessment of renal function in a growing pediatric population. *Chronic Kidney Disease (CKD) is defined as GFR < 60 ml/min/1.73 m² for 3 months or more.* - This statement accurately reflects the widely accepted definition of **Chronic Kidney Disease (CKD)** according to clinical guidelines. [3] - A GFR below this threshold sustained for more than three months indicates persistent kidney damage or dysfunction.

Q: What is the average survival time of a person without food and water under normal conditions?

3 to 5 days. ***3 to 5 days*** - When deprived of **both food and water**, the human body can typically survive for **3 to 5 days** under normal conditions. - **Water is the critical limiting factor** - while the body can tolerate food deprivation for weeks, lack of water becomes life-threatening within days. - Water is essential for cellular metabolism, temperature regulation, waste elimination, and cardiovascular function. *1 to 3 days* - This represents the **absolute minimum survival time** without water, particularly under harsh environmental conditions (heat, physical exertion, humidity). - However, under normal/average conditions, most individuals can survive slightly longer than this range. *10 to 12 days* - This duration is **not possible** without water, even with optimal conditions. - This timeframe is more consistent with survival **without food but WITH water**, which can extend to 3-4 weeks or more. *5 to 10 days* - While exceptional cases might approach 5-7 days without water in cool, resting conditions with low metabolic demands, **10 days is physiologically implausible**. - Severe dehydration typically causes death by day 5-7 maximum, with most succumbing earlier.

Q: Testes are not palpable in

SRY deletion. ***SRY deletion*** - **SRY (Sex-determining Region Y) gene** is the master regulator of male sex determination on the Y chromosome; its deletion in 46,XY individuals results in **Swyer syndrome** (pure gonadal dysgenesis). - Without functional SRY, **testes fail to develop entirely**, and the gonads remain as non-functional **streak gonads** rather than differentiating into either testes or ovaries. - Result: **No palpable testes** because testicular tissue never forms; individuals develop female external genitalia despite XY karyotype. *DAX1 deletion* - DAX1 (NR0B1) normally **antagonizes testicular development** and supports adrenal/gonadal development. - **Deletion of DAX1** would actually **reduce anti-testis effects**, allowing testicular development to proceed more readily if SRY is present. - DAX1 **duplications** (not deletions) can impair male development; deletions cause **adrenal hypoplasia congenita** but do not prevent testicular formation. *WNT-4 gene mutation* - **WNT4** promotes **ovarian development** and opposes male differentiation pathways in normal female development. - **Loss-of-function mutations** in WNT4 do not prevent testicular development in 46,XY individuals where SRY is present and functional. - WNT4 overexpression (not loss-of-function mutation) could theoretically interfere with male development, but standard WNT4 mutations do not cause absent testes. *RSPO-1 gene mutation* - **RSPO1** (R-spondin 1) enhances **Wnt/β-catenin signaling** and supports ovarian differentiation; primarily relevant in 46,XX sex development. - Loss-of-function mutations in RSPO1 lead to **46,XX testicular/ovotesticular DSD**, where testicular tissue develops inappropriately in XX individuals. - In 46,XY individuals with functional SRY, RSPO1 mutations would **not prevent testicular development**, so testes would be palpable.

Q: What is the primary change in fetal circulation that occurs at birth?

Closure of the foramen ovale. ***Closure of the foramen ovale*** - The **foramen ovale** undergoes functional closure within minutes of birth, making it the **primary immediate circulatory change** - At birth, the first breath causes **dramatic decrease in pulmonary vascular resistance** and **increased pulmonary blood flow**, which raises **left atrial pressure** - Simultaneously, umbilical cord clamping **increases systemic vascular resistance** and **decreases right atrial pressure** (loss of placental return) - This **pressure gradient reversal** (left atrial pressure > right atrial pressure) causes the **septum primum** to be pushed against the **septum secundum**, achieving functional closure - This immediately separates the systemic and pulmonary circulations, which is the **most critical primary change** in transitioning from fetal to neonatal circulation *Closure of the patent ductus arteriosus* - The **ductus arteriosus** undergoes **functional closure over 10-15 hours** after birth, followed by **anatomical closure over 2-3 weeks** - Closure occurs due to increased arterial oxygen tension and decreased prostaglandin E2 levels, causing smooth muscle constriction - While important, this is a **secondary change** that occurs more gradually compared to the immediate foramen ovale closure *Closure of the ductus venosus* - The **ductus venosus** closes functionally within 3-7 days as umbilical venous flow ceases - This redirects portal blood through the liver but does not directly impact the critical pulmonary-systemic circulation separation *Increased activity of the right ventricle* - After birth, the **left ventricle** becomes dominant as it pumps against higher systemic vascular resistance - The right ventricle actually experiences **decreased afterload** due to falling pulmonary vascular resistance - This is a consequence of, not the primary change in, the circulatory transition

Q: Osteoclasts have all of the following functions except -

Receptor for parathormone. ***Receptor for parathormone*** - **Osteoclasts** do not directly have receptors for **parathormone (PTH)**; instead, **osteoblasts** have PTH receptors. - When PTH binds to osteoblasts, they release factors (like **RANKL**) that stimulate osteoclast activity, thus indirectly regulating bone resorption. *Bone resorption* - **Osteoclasts** are specialized cells primarily responsible for **resorbing bone matrix**, a critical process in bone remodeling. - They secrete **acids and enzymes** to break down the mineral and organic components of bone. *Ruffled border* - The **ruffled border** is a characteristic morphological feature of active osteoclasts, representing a highly folded plasma membrane. - This specialized structure increases the surface area for the secretion of **protons and lysosomal enzymes** into the bone-resorbing compartment. *RANK ligand production* - **Osteoclasts** do not produce **RANK ligand (RANKL)**; rather, they have **RANK receptors** that bind to RANKL produced by **osteoblasts and stromal cells**. - The binding of RANKL to RANK is essential for the **differentiation, activation, and survival** of osteoclasts.

Q: During pregnancy, the increased size of the pituitary gland is primarily due to the enlargement of which hormone-secreting cells?

Prolactin. ***Prolactin*** - During pregnancy, the number and size of **lactotrophs**, the cells that secrete prolactin, increase significantly due to high **estrogen** levels. - This **hyperplasia** and **hypertrophy** of lactotrophs contribute to the overall enlargement of the pituitary gland, preparing it for lactation. *Growth hormone* - While growth hormone is important, there isn't a primary enlargement of **somatotrophs** (GH-secreting cells) in the pituitary during pregnancy. - Furthermore, most circulating GH during pregnancy is **placental growth hormone**, rather than pituitary-derived. *ACTH* - Adrenocorticotropic hormone (ACTH) is secreted by **corticotrophs**, and these cells do not undergo prominent hypertrophy or hyperplasia during normal pregnancy. - While cortisol levels increase, this is largely due to factors other than increased pituitary ACTH cell size. *TSH* - Thyroid-stimulating hormone (TSH) is secreted by **thyrotrophs**, which do not notably enlarge during pregnancy. - Thyroid gland activity increases during pregnancy, but this is mediated by **hCG** and other mechanisms, not pituitary thyrotroph growth.

Q: Oxygen consumption increases in pregnancy by

20%. ***20%*** - During **pregnancy**, the maternal **metabolic rate increases** to support fetal growth and the physiological changes occurring in the mother's body. - This increased metabolic demand leads to a **rise in oxygen consumption** by approximately 20% compared to the non-pregnant state. *10%* - A 10% increase is an **underestimation** of the physiological change in oxygen consumption during pregnancy. - The demands of supporting a growing fetus and increased maternal tissue mass require a more substantial metabolic adjustment. *30%* - While oxygen consumption does increase significantly, a 30% rise is generally considered an **overestimation** of the average increase. - The typical physiological adaptation usually falls within the 15-25% range. *40%* - A 40% increase in oxygen consumption would represent an **extreme physiological demand** that is not typically observed during an uncomplicated pregnancy. - Such a drastic increase might indicate underlying pathology rather than normal adaptation.

Q: The role of human placental lactogen is :

Supports fetal growth and development.. ***Supports fetal growth and development.*** - Human placental lactogen (hPL) acts as a **growth hormone** for the fetus, primarily by altering maternal metabolism to favor fetal nutrient supply. - It increases **maternal insulin resistance**, leading to higher maternal glucose and free fatty acids, which are then shunted to the fetus, supporting its growth and development. *Stimulate milk production* - **Prolactin**, secreted by the anterior pituitary, is the primary hormone responsible for stimulating milk production (lactogenesis). - While hPL has some structural similarity to growth hormone and prolactin, its primary role is not to directly stimulate milk production during pregnancy; rather, it prepares the breasts. *Promotes growth of breast for lactation.* - hPL, along with **estrogen** and **progesterone**, contributes to the **mammary gland development** during pregnancy, preparing the breasts for lactation. - However, its direct role is more about **mammary gland proliferation and differentiation** rather than initiation of milk production. *Provide fetal nutrition by antagonizing the action of insulin in maternal circulation, breakdown of fats and proteins and transport of fatty acids and amino acids from maternal to fetal circulation.* - This is a highly detailed and largely accurate description of *how* hPL supports fetal growth and development, making it a mechanism rather than the primary, concise role. - It describes the metabolic changes induced by hPL, which ultimately lead to the **support of fetal growth and development**.

Question 1

Miracle fruit is used to change the taste from?

Accepted Answer

Sour to Sweet

Answer

Sour to Bitter

Answer

Bitter to Sweet

Answer

Salty to Sweet

Question 2

What is the most common mechanism responsible for causing arrhythmias in the heart?

Accepted Answer

Re-entry

Answer

Early after depolarization

Answer

Late after depolarization

Answer

Automaticity

Question 3

All are true about GFR except:

Accepted Answer

Best estimated by creatinine clearance

Answer

30-40% decrease after 70 years of age

Answer

GFR is dependent on height in children

Answer

Chronic Kidney Disease (CKD) is defined as GFR < 60 ml/min/1.73 m² for 3 months or more.

Question 4

What is the average survival time of a person without food and water under normal conditions?

Accepted Answer

3 to 5 days

Answer

10 to 12 days

Answer

1 to 3 days

Answer

5 to 10 days

Question 5

Testes are not palpable in

Accepted Answer

SRY deletion

Answer

DAX 1 deletion

Answer

WNT- 4 gene mutation

Answer

RSPO-1 gene mutation

Question 6

What is the primary change in fetal circulation that occurs at birth?

Accepted Answer

Closure of the foramen ovale

Answer

Closure of the ductus venosus

Answer

Increased activity of the right ventricle

Answer

Closure of the patent ductus arteriosus

Question 7

Osteoclasts have all of the following functions except -

Accepted Answer

Receptor for parathormone

Answer

Ruffled border

Answer

Bone resorption

Answer

RANK ligand production

Question 8

During pregnancy, the increased size of the pituitary gland is primarily due to the enlargement of which hormone-secreting cells?

Accepted Answer

Prolactin

Answer

Growth hormone

Answer

ACTH

Answer

TSH

Question 9

Oxygen consumption increases in pregnancy by

Accepted Answer

20%

Answer

10%

Answer

30%

Answer

40%

Question 10

The role of human placental lactogen is :

Accepted Answer

Supports fetal growth and development.

Answer

Stimulate milk production

Answer

Promotes growth of breast for lactation.

Answer

Provide fetal nutrition by antagonizing the action of insulin in maternal circulation, breakdown of fats and proteins and transport of fatty acids and amino acids from maternal to fetal circulation.

NEET-PG 2015 — Physiology