GENERAL PHYSIOLOGY Flashcards

Question

It is also known as the 1,25-dihydroxycholecalciferol A. Vitamin D B. Vitamin A C. Vitamin C D. Vitamin B

Answer 1

A. Vitamin D Explanation: 1,25-Dihydroxycholecalciferol is the active form of Vitamin D, also known as calcitriol. Steps of Vitamin D Activation: 1. Skin (UV light exposure) → Converts 7-dehydrocholesterol into cholecalciferol (Vitamin D3). 2. Liver → Converts cholecalciferol into 25-hydroxycholecalciferol (25(OH)D or calcidiol). 3. Kidney (via 1-alpha hydroxylase) → Converts calcidiol into 1,25-dihydroxycholecalciferol (1,25(OH)₂D or calcitriol), the biologically active form. Function of Calcitriol (1,25(OH)₂D): - Increases calcium and phosphate absorption in the intestines. - Regulates bone mineralization to maintain strong bones. - Works with parathyroid hormone (PTH) to regulate calcium homeostasis. Why the other options are incorrect: ❌ B. Vitamin A → Retinol, important for vision and skin health, not related to calcium metabolism. ❌ C. Vitamin C → Ascorbic acid, essential for collagen synthesis and immune function. ❌ D. Vitamin B → Group of B-complex vitamins, involved in metabolism and energy production, but not calcium regulation.

Answer 2

C. Parathyrin Explanation: Parathyrin (Parathyroid Hormone, PTH) is the primary hormone responsible for regulating serum calcium levels. It is secreted by the parathyroid glands in response to low blood calcium levels. Functions of PTH: 1. Increases calcium absorption in the intestines (by stimulating Vitamin D activation). 2. Stimulates calcium release from bones (by activating osteoclasts to break down bone tissue). 3. Increases calcium reabsorption in the kidneys (reducing calcium excretion). 4. Decreases phosphate reabsorption in the kidneys, preventing calcium-phosphate precipitation. Why the other options are incorrect: ❌ A. Calcitonin → Opposes PTH by decreasing blood calcium levels (secreted by the thyroid gland when calcium is high). It plays a minor role in calcium regulation. ❌ B. Thyroid hormones → Regulate metabolism, not calcium homeostasis. ❌ D. ADH (Antidiuretic Hormone) → Regulates water balance, not calcium levels.

Answer 3

D. Kidneys Explanation: The kidneys are the primary organs responsible for regulating the osmotic pressure of body fluids by controlling water and electrolyte balance. How the Kidneys Regulate Osmotic Pressure: 1. Regulation of Water Balance The kidneys adjust urine concentration based on the body's hydration status. Antidiuretic Hormone (ADH) from the pituitary gland signals the kidneys to retain water when osmotic pressure is high. 2. Regulation of Electrolytes (Sodium, Potassium, etc.) The renin-angiotensin-aldosterone system (RAAS) helps control sodium and water retention, affecting blood volume and osmotic balance. Aldosterone promotes sodium reabsorption, leading to water retention and increased blood pressure. 3. Filtration and Excretion The kidneys filter excess solutes (like sodium, potassium, and urea) and regulate their excretion to maintain osmotic balance. Why the other options are incorrect: ❌ A. Lungs → Regulate gas exchange (oxygen and CO₂) and acid-base balance, but not osmotic pressure. ❌ B. Liver → Plays a role in metabolism, protein synthesis, and detoxification, but does not directly regulate osmotic pressure. ❌ C. Heart → Produces Atrial Natriuretic Peptide (ANP), which influences kidney function, but it is not the primary regulator of osmotic pressure.

Answer 4

B. Movement of fluid from the blood to the interstitial tissues Explanation: Blood hydrostatic pressure (BHP) is the pressure exerted by blood against the walls of capillaries. It plays a key role in the movement of fluids between the blood and interstitial tissues. - If BHP increases excessively, it forces more fluid out of the capillaries into the interstitial space, leading to edema (swelling). - This occurs because capillary filtration increases while reabsorption remains the same or decreases, leading to fluid accumulation in tissues. Why the other options are incorrect: ❌ A. Movement of fluid from the interstitial tissues to the blood → This would happen if plasma oncotic pressure (due to albumin) increased or if BHP decreased, which is not the case here. ❌ C. Non-movement of fluid between the blood and the interstitial tissues → This would occur only if BHP and oncotic pressure were perfectly balanced, which does not happen with an excessive increase in BHP.

Answer 5

D. Arterioles Explanation: Arterioles are the primary regulators of blood flow to peripheral tissues because they have smooth muscle in their walls, allowing them to constrict or dilate to control blood flow and resistance. Why Arterioles Regulate Blood Flow: 1. Greatest Resistance to Blood Flow Arterioles are known as resistance vessels because they contribute the most to vascular resistance and blood pressure regulation. 2. Vasoconstriction & Vasodilation Vasoconstriction (narrowing) → Reduces blood flow to tissues. Vasodilation (widening) → Increases blood flow to tissues. 3. Autoregulation of Blood Flow Arterioles respond to hormonal and neural signals (e.g., epinephrine, norepinephrine) as well as local metabolic needs (oxygen, CO₂, pH). Why the other options are incorrect: ❌ A. Large-sized arteries → Transport high-pressure blood from the heart (e.g., aorta), but do not regulate flow to specific tissues. ❌ B. Medium-sized arteries → Distribute blood to organs, but do not play a major role in fine regulation of blood flow. ❌ C. Small-sized arteries → While they help with distribution, arterioles are the main regulators of peripheral blood flow.

Answer 6

C. The first statement is true, the second statement is false. Explanation: ✅ First statement: "The principal ECG or EKG intervals are P, QRS, and T waves." → (True) - The electrocardiogram (ECG or EKG) records the electrical activity of the heart. The main waves seen in an ECG are: - P wave → Atrial depolarization (atrial contraction). - QRS complex → Ventricular depolarization (ventricular contraction). - T wave → Ventricular repolarization (ventricles reset for the next cycle). ❌ Second statement: "The QRS complex represents atrial repolarization." → (False) The QRS complex represents ventricular depolarization, not atrial repolarization. Atrial repolarization does occur, but it is hidden within the QRS complex and not separately visible on the ECG because the electrical activity of the ventricles is much stronger. Why the other options are incorrect: ❌ A. Both statements are true. → The second statement is false. ❌ B. Both statements are false. → The first statement is true. ❌ D. The first statement is false, the second statement is true. → The first statement is actually true, and the second is false.

Answer 7

A. S-T segment Explanation: The S-T segment represents the period between the end of ventricular depolarization and the beginning of ventricular repolarization. Key ECG Components & Their Meaning: 1. P wave → Atrial depolarization (atrial contraction). 2. P-R interval → Time between atrial depolarization and ventricular depolarization. 3. QRS complex → Ventricular depolarization (ventricular contraction). 4. S-T segment → End of ventricular depolarization & beginning of ventricular repolarization (important in detecting ischemia or myocardial infarction). 5. T wave → Ventricular repolarization (ventricles reset for the next cycle). 6. Q-T interval → Duration of ventricular depolarization & repolarization. Why the Other Options Are Incorrect: ❌ B. P-R interval → Represents the time between the start of atrial depolarization and the start of ventricular depolarization, not ventricular repolarization. ❌ C. Q-T interval → Represents the total time for both ventricular depolarization and repolarization, not just the transition from depolarization to repolarization.

Answer 8

B. P-R interval Explanation: The P-R interval represents the time between atrial depolarization (P wave) and ventricular depolarization (QRS complex). It measures the delay in electrical conduction through the AV node, allowing time for the atria to contract before the ventricles are activated. Key ECG Components & Their Functions: 1. P wave → Atrial depolarization (atrial contraction). 2. P-R interval → Time between atrial depolarization and ventricular depolarization. 3. QRS complex → Ventricular depolarization (ventricular contraction). 4. S-T segment → Transition between ventricular depolarization and repolarization. 5. T wave → Ventricular repolarization (ventricular recovery). 6. Q-T interval → Total time for both ventricular depolarization and repolarization. Why the Other Options Are Incorrect: ❌ A. S-T segment → Represents the transition from ventricular depolarization to repolarization, not atrial to ventricular depolarization. ❌ C. Q-T interval → Measures total ventricular activity (depolarization + repolarization), not just the delay between atrial and ventricular depolarization.

Answer 9

C. Q-T interval Explanation: The Q-T interval represents the total time it takes for the ventricles to depolarize and then repolarize. It starts from the beginning of the QRS complex (ventricular depolarization) and extends to the end of the T wave (ventricular repolarization). Key ECG Components & Their Functions: 1. P wave → Atrial depolarization (atrial contraction). 2. P-R interval → Time between atrial depolarization and ventricular depolarization. 3. QRS complex → Ventricular depolarization (ventricular contraction). 4. S-T segment → Time between ventricular depolarization and the start of repolarization. 5. T wave → Ventricular repolarization (ventricular recovery). 6. Q-T interval → Total time for ventricular depolarization and repolarization. Why the Other Options Are Incorrect: ❌ A. S-T segment → Represents the period between ventricular depolarization and the beginning of repolarization, but does not include the entire repolarization phase. ❌ B. P-R interval → Measures the time between atrial depolarization and ventricular depolarization, not ventricular repolarization.

Answer 10

B. Isovolumetric contraction Explanation: The aortic valve opens just after the isovolumetric contraction phase of the cardiac cycle. This happens when the pressure in the left ventricle exceeds the pressure in the aorta, allowing blood to be ejected into the systemic circulation. Phases of the Cardiac Cycle: 1. Atrial systole (Presystole) → The atria contract, pushing blood into the ventricles. 2. Isovolumetric contraction → The ventricles begin to contract, causing a rapid rise in pressure. All valves are closed, and no blood is ejected yet. 3. Ventricular ejection → When ventricular pressure exceeds aortic pressure, the aortic valve opens, and blood is ejected into the aorta. 4. Isovolumetric relaxation → The ventricles begin to relax, the aortic valve closes, and pressure drops without a change in volume. 5. Ventricular filling (Prediastole/Diastole) → The ventricles relax, and blood flows passively from the atria. Why the Other Options Are Incorrect: ❌ A. Isovolumetric relaxation → This occurs after the aortic valve closes, not before it opens. ❌ C. Presystole (Atrial systole) → This occurs before ventricular contraction and does not lead directly to aortic valve opening. ❌ D. Prediastole → This refers to the early phase of diastole, after the aortic valve has already closed.

Answer 11

B. Lipogenesis Explanation: During moderate to extreme physical activity, the body shifts its metabolism to prioritize energy production. This means: ✅ Increased energy-releasing processes like glycogenolysis (breaking down glycogen) and fat oxidation. ❌ Decreased energy-storing processes like lipogenesis (fat synthesis). Analysis of Each Option: ✅ A. Oxidation of fatty acids → Increases during prolonged exercise to provide energy, especially when glycogen stores start depleting. ❌ B. Lipogenesis → Decreases, since the body is focused on breaking down stored energy (glycogen and fat) rather than storing it as fat. ✅ C. Glucagon release → Increases because glucagon stimulates glycogenolysis and gluconeogenesis to maintain blood glucose levels during exercise. ✅ D. Glycogenolysis → Increases to quickly provide glucose for energy.

Answer 12

B. Oxytocin Explanation: The let-down reflex (milk ejection reflex) is triggered by the hormone oxytocin, which is released from the posterior pituitary gland in response to infant suckling or other stimuli (such as hearing a baby cry). How Oxytocin Works in Milk Ejection: - Oxytocin causes contraction of the myoepithelial cells surrounding the alveoli of the mammary glands, leading to milk ejection from the ducts. - It works alongside prolactin, but while prolactin is responsible for milk production, oxytocin is responsible for milk release. Why the Other Options Are Incorrect: ❌ A. Prolactin → Stimulates milk production, but does not cause milk ejection. ❌ C. Oxyphilic → Not a hormone related to lactation. ❌ D. Prolacton → Not a real hormone (likely a misspelling of prolactin).

Answer 13

D. Pulmonary semilunar and aortic semilunar valves Explanation: The second heart sound (S₂), also known as the "dub" sound, is produced by the closure of the semilunar valves: 1. Aortic valve (between the left ventricle and aorta) 2. Pulmonary valve (between the right ventricle and pulmonary artery) Phases of the Heart Sounds: 1. First heart sound (S₁) → Closure of the mitral and tricuspid valves (AV valves) at the beginning of systole. 2. Second heart sound (S₂) → Closure of the aortic and pulmonary valves (semilunar valves) at the end of systole, marking the beginning of diastole. Why the Other Options Are Incorrect: ❌ A. Mitral and tricuspid valves → These close during S₁ (first heart sound), not S₂. ❌ B. Aortic semilunar and mitral valves → The aortic semilunar valve closes during S₂, but the mitral valve closes during S₁. ❌ C. Tricuspid and pulmonary semilunar valves → The tricuspid valve closes during S₁, while only the pulmonary semilunar valve closes during S₂.

Answer 14

D. Both statements are false. Explanation: 1. The posterior cricoarytenoid muscle → ABDUCTS (opens) the vocal cords, not adducts them. ❌ (First statement is false) 2. The lateral cricoarytenoid muscle → ADDUCTS (closes) the vocal cords, not abducts them. ❌ (Second statement is false) Correct Muscle Functions: ✅ Posterior cricoarytenoid → ONLY muscle that abducts (opens) the vocal cords. ✅ Lateral cricoarytenoid → Adducts (closes) the vocal cords. ✅ Transverse & oblique arytenoid muscles → Assist in adduction. ✅ Cricothyroid muscle → Tenses and elongates the vocal cords (affecting pitch). Why "Both Statements Are False" is Correct: - The posterior cricoarytenoid does NOT close (adduct) the vocal cords. It actually opens them. ❌ - The lateral cricoarytenoid does NOT open (abduct) the vocal cords. It actually closes them. ❌

Answer 15

B. Pepsinogen Explanation: Trypsin is a key digestive enzyme in the small intestine that activates several other proenzymes (zymogens) by cleaving them into their active forms. Enzymes Activated by Trypsin: ✅ Prolipase → Activated into lipase (digests fats). ✅ Chymotrypsinogen → Activated into chymotrypsin (digests proteins). ✅ Proelastase → Activated into elastase (digests elastin and proteins). Why Pepsinogen is the Exception: ❌ Pepsinogen is activated into pepsin, but this activation occurs in the stomach and is triggered by hydrochloric acid (HCl), not by trypsin.

Answer 16

B. ATG Explanation: In the genetic code, STOP codons signal the termination of protein synthesis during translation. The three standard STOP codons in mRNA are: ✅ UAA – Stop codon ✅ UGA – Stop codon ✅ UAG – Stop codon However, ATG is NOT a stop codon. Instead: ❌ ATG (in DNA) corresponds to AUG in mRNA, which is the START codon coding for methionine (Met).

Answer 17

A. SA node Explanation: The SA node (sinoatrial node), located in the right atrium, is known as the natural pacemaker of the heart because it initiates the cardiac impulse. It generates electrical impulses that spread through the atria, causing them to contract and sending signals to the AV node. Role of Other Structures: - AV node (Atrioventricular node) → Delays the impulse slightly before passing it to the ventricles to allow the atria to complete contraction. - AV bundle (Bundle of His) → Conducts impulses from the AV node to the ventricles. - Left/Right Bundle Branches → Carry impulses down both sides of the interventricular septum. - Purkinje Fibers → Distribute impulses to the ventricles, causing ventricular contraction.

Answer 18

A. Submandibular Explanation: The submandibular lymph nodes are responsible for draining: ✅ Lower eyelids ✅ Maxillary sinus ✅ Palate ✅ Most maxillary teeth (except third molars, which drain into the superior deep cervical nodes) Why Not the Other Options? ❌ Submental nodes → Drain the central lower lip, floor of the mouth, tip of the tongue, and mandibular incisors. ❌ Sublingual nodes → Not a primary lymphatic drainage site in the head and neck. ❌ Submaxillary nodes → The term "submaxillary" is outdated; it refers to the submandibular nodes.

Answer 19

B. Submental Explanation: The submental lymph nodes are responsible for draining: ✅ Lower lip ✅ Mandibular incisors ✅ Floor of the mouth ✅ Apex (tip) of the tongue ✅ Chin Why Not the Other Options? ❌ Submandibular nodes → Drain the lower eyelids, maxillary sinus, palate, and most maxillary teeth but NOT the chin or apex of the tongue. ❌ Sublingual nodes → This is not a primary lymph node group involved in drainage. ❌ Submaxillary nodes → This term is outdated and usually refers to the submandibular nodes.

Answer 20

A. Deep cervical node Explanation: The submandibular and submental lymph nodes are superficial lymph nodes that eventually drain into the deep cervical nodes, which are located along the internal jugular vein. The deep cervical nodes are divided into: ✅ Superior deep cervical nodes → First major secondary drainage site for submandibular and submental nodes. ✅ Inferior deep cervical nodes → Receive lymph from the superior deep cervical nodes and drain into the jugular trunk, eventually leading to the thoracic duct or right lymphatic duct. Why Is This the Correct Answer? - The deep cervical nodes serve as the secondary drainage site for most superficial lymph nodes in the head and neck. - The submandibular and submental nodes first drain into the superior deep cervical nodes, which are part of the deep cervical chain.

Answer 21

A. Gene Explanation: A gene is the smallest hereditary unit because it is the fundamental unit of inheritance. It consists of DNA sequences that code for proteins or functional RNA molecules. Genes are passed from parents to offspring and determine hereditary traits. Why Not the Other Options? ❌ Cell → The cell is the basic unit of life, but it is much larger than a gene and is not the direct hereditary unit. ❌ Chromosome → A chromosome is a structure made of DNA and proteins that contains many genes, so it is larger than a gene. ❌ Nucleotide → A nucleotide is a building block of DNA and RNA, but it is not a hereditary unit by itself. Genes are made up of sequences of nucleotides.

Answer 22

C. Osteogenesis imperfecta Explanation: Osteogenesis imperfecta (OI) is a genetic disorder characterized by defective collagen formation, leading to: ✅ Bluish sclera – Due to thinning of the sclera, making the underlying choroidal veins visible. ✅ Frequent fractures – Bones are fragile and prone to fractures with minimal trauma. ✅ Odontogenesis anomalies – Many patients also have dentinogenesis imperfecta, leading to weak, discolored teeth. Why Not the Other Options? ❌ Dentinogenesis imperfecta (A) → Affects only the teeth, causing opalescent teeth and weak dentin but does not cause fractures or bluish sclera. ❌ Amelogenesis imperfecta (B) → Affects only the enamel formation of teeth but has no bone or sclera involvement. ❌ Osteopetrosis imperfecta (D) → Osteopetrosis is a condition of excessively dense bones, not fragile bones. Also, there is no bluish sclera associated with it.

Answer 23

C. Neurotmesis Explanation: Neurotmesis is the most severe type of nerve injury, involving damage to: ✅ Myelin sheath ✅ Axon ✅ Endoneurium (and often the perineurium and epineurium) This leads to complete loss of nerve function and requires surgical intervention for recovery. Why Not the Other Options? ❌ Neuropraxia (A) → Mildest form of nerve injury, affecting only the myelin sheath without damage to the axon. Recovery is spontaneous and occurs within weeks. ❌ Axonotmesis (B) → Involves damage to the axon and myelin sheath but endoneurium remains intact. The nerve can regenerate over time without surgery.

Answer 24

B. Sternoglossus Explanation: There is no such muscle as "Sternoglossus" in human anatomy. The three true extrinsic muscles of the tongue are: ✅ Styloglossus – Retracts and elevates the tongue. ✅ Genioglossus – Protrudes the tongue and depresses the center. ✅ Palatoglossus – Elevates the posterior tongue and aids in swallowing. Why is "Sternoglossus" Incorrect? - There is no "Sternoglossus" muscle in human anatomy. - The extrinsic muscles of the tongue originate from structures outside the tongue (like the styloid process, mandible, or palate) and control tongue movement.

Answer 25

C. Calcium Explanation: Calcium (Ca²⁺) plays a crucial role in blood clot formation by: ✅ Activating several clotting factors in the coagulation cascade (e.g., Factor IV). ✅ Aiding in the conversion of prothrombin to thrombin, which is necessary for fibrin clot formation. ✅ Stabilizing platelet adhesion to the injury site. Why Not the Other Options? ❌ Sodium (Na⁺) – Important for nerve and muscle function, but not directly involved in clotting. ❌ Magnesium (Mg²⁺) – Plays a role in enzymatic reactions and muscle function, but not in coagulation. ❌ Potassium (K⁺) – Essential for nerve impulses and heart function, but does not contribute to blood clotting.

Answer 26

D. Cortisol Explanation: Cortisol is a glucocorticoid hormone released by the adrenal cortex. It plays a key role in: ✅ Suppressing the inflammatory response by inhibiting immune cell activity. ✅ Reducing the release of inflammatory cytokines like interleukins and TNF-α. ✅ Decreasing the production of prostaglandins and histamines, which are involved in inflammation. Why Not the Other Options? ❌ Aldosterone – Regulates sodium and potassium balance, but does not reduce inflammation. ❌ Epinephrine – Involved in the "fight or flight" response, increasing heart rate and blood pressure, but not directly reducing inflammation. ❌ Anti-diuretic hormone (ADH) – Helps regulate water balance in the kidneys but has no effect on inflammation.

Answer 27

A. Right lateral pterygoid muscle Explanation: The lateral pterygoid muscle is responsible for protrusion and lateral movements of the mandible. When the right lateral pterygoid muscle contracts, it: ✅ Pulls the right condyle downward, forward, and medial → this results in leftward movement of the mandible (contralateral movement). Muscle Function Breakdown: - Bilateral contraction of the lateral pterygoid muscles → moves the mandible forward (protrusion). - Unilateral contraction of the right lateral pterygoid → moves the right condyle downward, forward, and medial, causing the mandible to shift leftward. - Unilateral contraction of the left lateral pterygoid → moves the left condyle downward, forward, and medial, causing the mandible to shift rightward.

Answer 28

B. Vitamin B12 Explanation: A beefy red tongue is a hallmark symptom of Vitamin B12 deficiency, which is commonly seen in: - Pernicious anemia (autoimmune destruction of gastric parietal cells) - Malabsorption syndromes (e.g., celiac disease, Crohn’s disease) - Strict vegan diets (since B12 is primarily found in animal products) Symptoms of Vitamin B12 Deficiency: ✅ Glossitis → Smooth, swollen, "beefy red" tongue ✅ Megaloblastic anemia → Fatigue, pallor, weakness ✅ Neurological issues → Tingling, numbness, memory loss Why Not the Other Options? ❌ Vitamin A – Important for vision and skin health, but not linked to a beefy tongue. ❌ Vitamin B9 (Folate) – Also causes megaloblastic anemia, but usually does not cause glossitis as prominently as B12 deficiency. ❌ Vitamin C – Deficiency leads to scurvy (bleeding gums, poor wound healing), not a beefy tongue.

Answer 29

A. Solute Explanation: In a solution: - Solute → The substance being dissolved (e.g., salt in saltwater). - Solvent → The substance that dissolves the solute (e.g., water in saltwater). Why Not the Other Options? ❌ Precipitate – A solid that forms and separates from a solution. ❌ Solvent – The substance that dissolves the solute. ❌ Mixture – A combination of two or more substances, which may or may not be a solution.

Answer 30

B. Hypertonic solution Explanation: When two solutions are separated by a semi-permeable membrane, osmosis occurs. Osmosis is the movement of the solvent (usually water) from an area of low solute concentration (hypotonic) to an area of high solute concentration (hypertonic) to balance the concentration on both sides. Why? - Hypotonic solution → Has lower solute concentration and higher water concentration. - Hypertonic solution → Has higher solute concentration and lower water concentration. - Water moves towards the hypertonic solution to dilute it and establish equilibrium.

Answer 31

B. Lateral pterygoid Explanation: The lateral pterygoid muscle is primarily responsible for lateral movement (side-to-side) of the mandible. Functions of the Muscles of Mastication: - Lateral pterygoid → Moves the mandible laterally, depresses and protrudes the jaw. - Medial pterygoid → Elevates and protrudes the mandible but does not contribute significantly to lateral movement. - Masseter → Elevates the mandible for biting and chewing. - Temporalis → Elevates and retracts the mandible.

Answer 32

A. Opthalmic Explanation: The ophthalmic nerve (V1) is a purely sensory branch of the trigeminal nerve (Cranial Nerve V). It supplies sensation to: - The skin over the tip of the nose (via the external nasal nerve, a branch of the anterior ethmoidal nerve). - The forehead, upper eyelid, cornea, and parts of the nasal cavity. Why Not the Other Options? ❌ Maxillary (V2) – Also sensory but innervates the midface, including the upper lip and cheeks, not the tip of the nose. ❌ Mandibular (V3) – Mixed motor and sensory, mostly affecting the lower jaw. ❌ Facial (CN VII) – Primarily a motor nerve controlling facial expression, though it has some sensory function for taste.

Answer 33

B. Hydrocephalus Explanation: Hydrocephalus is a condition caused by excessive cerebrospinal fluid (CSF) accumulation in the ventricles of the brain. This can occur due to: 1. Overproduction of CSF 2. Obstruction of CSF flow 3. Impaired CSF absorption Why Not the Other Options? ❌ Encephalitis – Inflammation of the brain, usually caused by viral infections. ❌ Cerebrospinal Hydrosis – This is not a recognized medical term. ❌ Meningitis – Inflammation of the meninges, typically caused by bacterial or viral infections.

Answer 34

A. Inhalation Explanation: When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity. This reduces intrapulmonary pressure, causing air to rush into the lungs—resulting in inhalation. Why Not the Other Options? ❌ Exhalation (B) – Exhalation occurs when the diaphragm relaxes and moves upward, decreasing thoracic volume and pushing air out. ❌ Hiccups (C) – Hiccups are caused by sudden involuntary contractions of the diaphragm, not normal contraction during breathing. ❌ None of the above (D) – This is incorrect because inhalation does occur.

Answer 35

B. Rheumatoid arthritis Explanation: Osteogenesis Imperfecta (OI) is a genetic disorder affecting collagen formation, leading to bone fragility and other symptoms. The classic triad of OI includes: 1. Blue sclera – Due to thin connective tissue in the eyes. 2. Fragility of bones – Increased risk of fractures. 3. Deafness – Due to abnormal ossicles in the middle ear. Why Not the Other Options? ❌ Rheumatoid arthritis (B) – This is an autoimmune disease affecting joints and is not a feature of OI.

Answer 36

A. Pharyngotympanic tube Explanation: The pharyngotympanic tube (Eustachian tube) connects the nasopharynx to the middle ear, helping to equalize pressure between the middle ear and the external environment. Why Not the Other Options? ❌ C. External auditory canal – This is the passageway that leads from the outer ear to the eardrum. ❌ D. Internal auditory canal – This transmits the vestibulocochlear nerve (CN VIII) and facial nerve (CN VII) from the inner ear to the brainstem.

Answer 37

A. Circumvallate papillae Explanation: The circumvallate papillae are located at the back of the tongue and contain the highest concentration of taste buds sensitive to bitter flavors. Bitter taste detection is crucial for survival, as many toxic substances have a bitter taste. Why Not the Other Options? ❌ B. Foliate papillae – Found on the lateral sides of the tongue and sensitive to sour tastes. ❌ C. Fungiform papillae – Located on the tip and sides of the tongue, primarily detecting sweet and salty tastes. ❌ D. Filiform papillae – Do not contain taste buds; they function primarily for texture sensation.

Answer 38

A. Iris Explanation: Heterochromia is a condition where a person has different-colored irises (the colored part of the eye) or variations in pigmentation within a single iris. It can be genetic or caused by injury, disease, or medication. Why Not the Other Options? ❌ B. Lens – The lens helps focus light but is not related to eye color. ❌ C. Ovary – Not related to eye pigmentation. ❌ D. Prostate – Unrelated to heterochromia.

Answer 39

B. Sternal angle Explanation: The carina is the point where the trachea bifurcates into the right and left primary bronchi. This anatomical landmark is located at the level of: - The sternal angle (Angle of Louis) - The intervertebral disc between T4 and T5 Why Not the Other Options? ❌ A. Costal cartilages – The tracheal bifurcation is not related to costal cartilages. ❌ C. T1 and T2 vertebra – The trachea is still superior at this level; bifurcation occurs lower. ❌ D. 7th rib – This is too low for the tracheal bifurcation.

Answer 40

C. Delta cells Explanation: Somatostatin is a hormone that inhibits several metabolic processes, including insulin and glucagon secretion, gastric acid secretion, and growth hormone release. In the pancreas, it is secreted by the delta (δ) cells of the islets of Langerhans. Why Not the Other Options? ❌ A. Alpha cells – Secrete glucagon, which increases blood glucose levels. ❌ B. Beta cells – Secrete insulin, which decreases blood glucose levels. ❌ D. Gamma cells – These cells are less common and secrete pancreatic polypeptide, which regulates pancreatic enzyme secretion and GI motility.

Answer 41

C. Terminal bronchioles Explanation: Gas exchange in the lungs primarily occurs in structures that have alveoli or are closely associated with them. These include: ✅ Alveoli (A) – The primary site of gas exchange. ✅ Alveolar ducts (B) – Tiny ducts that lead to alveolar sacs and participate in gas exchange. ✅ Respiratory bronchioles (D) – These contain some alveoli and play a minor role in gas exchange. ❌ Terminal bronchioles (C) – These are the last part of the conducting zone and do not contain alveoli, meaning they do not participate in gas exchange. Instead, they serve as a passageway for air before it reaches the respiratory bronchioles and alveoli.

Answer 42

D. Bone marrow Explanation: The primary organ responsible for the production of lymphocytes (a type of white blood cell) is the bone marrow. - Bone marrow produces all types of blood cells, including lymphocytes (T-cells, B-cells, and natural killer cells). Why Not the Other Options? ❌ A. Lymph nodes – Lymph nodes filter lymph and are involved in immune responses but do not produce lymphocytes. ❌ B. Spleen – The spleen filters blood and removes old red blood cells but does not produce lymphocytes. It stores them and helps in immune response. ❌ C. Tonsils – The tonsils are involved in immune responses but do not produce lymphocytes.

Answer 43

C. Closure of the semilunar valves Explanation: Contraction of the cardiac myocytes in the ventricles causes ventricular systole, which leads to the ejection of blood from the ventricles into the pulmonary artery and aorta. However, the semilunar valves (pulmonary and aortic valves) open during ventricular contraction, not close. A. Ejection of blood going to the pulmonary artery – During ventricular contraction, the right ventricle pumps blood into the pulmonary artery. B. Ejection of blood going to the aorta – During ventricular contraction, the left ventricle pumps blood into the aorta. D. Closure of the atrioventricular valves – During ventricular contraction, the atrioventricular (AV) valves (mitral and tricuspid) close to prevent backflow of blood into the atria. Why Not the Other Options? ❌ C. Closure of the semilunar valves – This happens during diastole after the ventricles have ejected blood and the pressure in the ventricles drops, causing the semilunar valves to close.

Answer 44

D. Circumvallate Explanation: The circumvallate papillae are the largest and least numerous papillae on the tongue. They are located at the back of the tongue, arranged in a V-shape, and contain taste buds that are sensitive to bitter flavors. Why Not the Other Options? ❌ A. Filiform – The filiform papillae are the most numerous papillae on the tongue but do not have taste buds. They are responsible for the texture of the tongue surface. ❌ B. Fungiform – The fungiform papillae are scattered across the tongue and are smaller than circumvallate papillae. They also contain taste buds. ❌ C. Foliate – The foliate papillae are found on the sides of the tongue and are not the largest or the least numerous.

Answer 45

A. Temporalis Explanation: The temporalis muscle is responsible for mandibular retrusion (pulling the jaw backward). It is a powerful muscle that plays a key role in chewing by elevating the mandible, and its posterior fibers specifically help in retrusion. Why Not the Other Options? ❌ B. Internal pterygoid – The internal (medial) pterygoid helps elevate the mandible and assists in side-to-side movements, but it is not primarily responsible for retrusion. ❌ C. Masseter – The masseter muscle is mainly responsible for elevating the mandible (closing the jaw), not for retrusion. ❌ D. External pterygoid – The external (lateral) pterygoid is responsible for protrusion and side-to-side movements of the mandible, but not retrusion.

Answer 46

C. Significant bone resorption Explanation: Excessive parathyroid hormone (PTH) secretion leads to increased bone resorption. PTH stimulates osteoclasts to break down bone tissue, releasing calcium and phosphate into the bloodstream. This process can lead to weakened bones and an increased risk of fractures. Why Not the Other Options? ❌ A. Increases the urine output – While PTH increases calcium reabsorption in the kidneys, it actually decreases phosphate reabsorption, leading to higher phosphate excretion, but it doesn't directly cause increased urine output overall. ❌ B. Better cardiopulmonary circulation – Excessive PTH does not improve cardiopulmonary circulation and may instead lead to complications like cardiovascular calcifications due to high calcium levels. ❌ D. Stimulates bone formation – Excessive PTH actually inhibits bone formation by promoting bone resorption, rather than stimulating the creation of new bone.

Answer 47

D. Spleen Explanation: The left hypochondriac region is located in the upper-left part of the abdomen, and it contains the spleen. The spleen plays a role in filtering blood, recycling iron, and storing blood cells. Why Not the Other Options? ❌ A. Sigmoid colon – The sigmoid colon is located in the left lower quadrant of the abdomen, not the hypochondriac region. ❌ B. Descending colon – The descending colon is located in the left side of the abdomen, but it is found in the left lumbar region, not the hypochondriac region. ❌ C. Small intestine – The small intestine primarily occupies the central abdominal regions, and it extends across several quadrants, but it isn't predominantly located in the left hypochondriac region.

Answer 48

B. Increases blood osmolality Explanation: Anti-diuretic hormone (ADH) has the following effects: A. Vasoconstrictor: ADH can cause vasoconstriction, helping to increase blood pressure, particularly at higher concentrations. C. Decreases blood osmolality: ADH helps to decrease blood osmolality by promoting water reabsorption in the kidneys, which dilutes the blood. D. Increases reabsorption of water in the renal tubules: One of ADH's main actions is to increase water reabsorption in the kidneys, particularly in the collecting ducts, leading to more concentrated urine and conserving water. Why Not B? B. Increases blood osmolality: This is incorrect because ADH actually works to decrease blood osmolality (by reabsorbing water), not increase it. When ADH is released, it results in water retention, which dilutes the blood and lowers its osmolality.

Answer 49

A. Tunica intima Explanation: - Tunica intima is the thinnest layer of arteries and veins. It consists of a thin layer of endothelial cells that line the lumen of the blood vessels. - Tunica media is the middle layer and is generally thicker, especially in arteries, as it contains smooth muscle and elastic fibers that allow the blood vessel to constrict and dilate. - Tunica adventitia (also known as the tunica externa) is the outermost layer and is thicker in veins compared to arteries, as it provides structural support and contains collagen and elastin fibers.

Answer 50

A. 2 to 4 mins Explanation: Bleeding time refers to the time it takes for a small standardized wound (such as a pinprick) to stop bleeding, primarily assessing platelet function. The normal range for bleeding time is typically between 2 to 4 minutes. Values outside this range may indicate platelet disorders or other hemostatic issues.

Answer 51

A. ATG Explanation: The start codon in RNA is AUG, which codes for the amino acid methionine. However, in DNA, the complementary sequence of AUG is ATG. So, ATG in DNA transcribes to AUG in mRNA, which signals the beginning of translation.

Answer 52

B. Antibody test Explanation: Antibody tests (also known as serology tests) are used to determine if a person has developed antibodies against a virus, such as COVID-19, after being infected. This can indicate previous infection and potential immunity. The rapid antigen test detects active infection, and the PCR test also identifies the presence of the virus's genetic material, but neither specifically checks for immunity.

Answer 53

A. Brainstem Explanation: The Pontine Micturition Center (PMC) is located in the brainstem, specifically in the pons. It plays a critical role in controlling bladder voiding by coordinating the contraction of the bladder and the relaxation of the external urethral sphincter. The other options (urethra, urinary bladder, and parasympathetic efferent nerve fibers) are involved in the process of micturition but are not the site where the PMC is located.

Answer 54

C. Squamous cells Explanation: The lining of the urinary bladder when it is full of urine consists of transitional epithelium, which is capable of stretching. The surface cells, when the bladder is distended (full of urine), flatten out and appear squamous. When the bladder is empty or relaxed, the transitional epithelium appears more cuboidal or columnar.

Answer 55

A. Cuboidal cells Explanation: The salivary glands are primarily lined by cuboidal cells. These cells are specialized for secretion and are typically found in the ducts of the glands, particularly in the smaller ducts and the acini (clusters of cells that produce saliva). Columnar cells can also be found in certain parts of the duct system, but cuboidal cells are the most common in the glandular structures.

Answer 56

C. Voltage-gated potassium channels Explanation: - Voltage-gated potassium channels are responsible for restoring the resting membrane potential after an action potential. When an action potential occurs, sodium ions rush into the cell, depolarizing the membrane. To repolarize and return to the resting state, potassium ions move out of the cell through voltage-gated potassium channels. - Voltage-gated sodium channels open during the depolarization phase of an action potential, allowing sodium ions into the cell, but they do not help restore the resting state. - The sodium-potassium pump (while essential for maintaining the resting membrane potential by pumping sodium out and potassium in) works gradually over time and is not directly involved in restoring the resting state immediately after an action potential. - Voltage-gated calcium channels are involved in processes such as muscle contraction and neurotransmitter release, but not in directly restoring the resting membrane potential.

Answer 57

D. Neutrophils Explanation: - Neutrophils are the most numerous and first responders in the immune system to sites of infection or inflammation. They play a crucial role in protecting periodontal tissues from microorganisms by phagocytosing bacteria and releasing enzymes to break down harmful pathogens. They are abundant in the gingival crevice (the space between the teeth and gums) to fight off microbial invasion. - Monocytes are precursor cells that differentiate into macrophages when they migrate to tissues, but they are not as numerous as neutrophils in the gingival crevice. - Basophils are involved in allergic reactions and inflammation but are not the predominant immune cells in the gingival crevice. - Eosinophils primarily deal with parasitic infections and allergic responses, but they do not play a significant role in protecting the periodontal tissues from microorganisms.

Answer 58

A. External carotid artery Explanation: - The ascending pharyngeal artery is a branch of the external carotid artery. It supplies the pharynx, soft palate, and the meninges (the protective coverings of the brain and spinal cord). - The internal carotid artery supplies the brain and other parts of the head, but not the pharynx or soft palate. - The mandibular artery and maxillary artery are branches of the external carotid artery, but they supply other regions, such as the jaw, face, and deep structures of the head, not the pharynx or meninges.

Answer 59

B. Posterior cerebral artery Explanation: The posterior cerebral artery is a branch of the vertebral artery, not the internal carotid artery. It supplies the occipital lobe and parts of the temporal lobe. The major branches of the internal carotid artery include: - Anterior cerebral artery: Supplies the medial parts of the frontal and parietal lobes. - Middle cerebral artery: Supplies the lateral parts of the frontal, parietal, and temporal lobes. - Ophthalmic artery: Supplies the eye and other structures in the orbit. - Posterior communicating artery: Connects the internal carotid artery to the posterior cerebral artery (part of the Circle of Willis). - Anterior choroidal artery: Supplies structures involved in the choroid plexus and parts of the brainstem and thalamus.

Answer 60

A. Mediastinum Explanation: - The mediastinum is the space located between the right and left pleural cavities in the thoracic cavity. It contains several vital organs, including the heart, esophagus, trachea, thymus, and major blood vessels, but does not contain the lungs, which are located in the pleural cavities. - The thoracic cage refers to the bony structure formed by the ribcage, sternum, and vertebrae that protects the thoracic organs. - The manubrium is the upper part of the sternum and is part of the thoracic cage, but it is not a space or cavity.

Answer 61

E. Brachiocephalic vein Explanation: The great vessels of the heart are the major blood vessels that directly connect to the heart and are responsible for transporting blood to and from the heart. They include: - Aorta (carries oxygenated blood from the left ventricle to the body) - Pulmonary artery (carries deoxygenated blood from the right ventricle to the lungs) - Pulmonary veins (carry oxygenated blood from the lungs to the left atrium) - Vena cava (superior and inferior, carry deoxygenated blood from the body to the right atrium) The brachiocephalic vein is not a great vessel but rather a large vein that drains blood from the head and upper limbs into the superior vena cava.

Answer 62

C. Bradycardia Explanation: The carotid sinus is a dilated area at the bifurcation of the common carotid artery. It contains baroreceptors that monitor blood pressure. When there is an increase in pressure (such as from strangling), these receptors are stimulated, which triggers the baroreceptor reflex. This reflex typically leads to bradycardia (slowing of the heart rate) in an attempt to lower blood pressure.

Answer 63

D. Cochlea Explanation: The cochlea is the part of the inner ear that transduces sound waves into nerve impulses. It contains sensory cells (hair cells) that convert mechanical sound vibrations into electrical signals, which are then sent to the brain via the auditory nerve.

Answer 64

D. TMJ Explanation: The auriculotemporal nerve is a branch of the mandibular nerve (V3), which is the third division of the trigeminal nerve. It innervates several structures, including: - The temporomandibular joint (TMJ): It provides sensory innervation to the TMJ. - The skin of the temple and parts of the external ear. - The parotid gland, but it does not have motor functions like other branches of the trigeminal nerve (such as the ones innervating the muscles of mastication).

Answer 65

C. Petit Mal Explanation: Sturge-Weber Syndrome (SWS) is a neurocutaneous disorder that primarily affects the brain, skin, and eyes due to abnormal blood vessel formation (angiomas). The neurological manifestations of SWS include: ✅ Hemiparesis (A) – Muscle weakness on one side of the body due to brain involvement. ✅ Mental Retardation (B) – Cognitive impairments, learning disabilities, and developmental delays. ✅ Seizures – The most common type of seizures in SWS are focal seizures (partial seizures), which may generalize into tonic-clonic seizures. However, Petit Mal (C) refers specifically to absence seizures, which are brief, non-convulsive episodes typically seen in generalized epilepsy syndromes (e.g., Childhood Absence Epilepsy). While seizures are common in Sturge-Weber Syndrome, absence seizures (Petit Mal) are not the typical type seen in this condition. Instead, focal seizures with secondary generalization are more common.

Answer 66

B. 4 Explanation: The trigeminal nerve has four nuclei, which are divided into one motor nucleus and three sensory nuclei: 1. Motor Nucleus of V – Controls the muscles of mastication. 2. Mesencephalic Nucleus – Proprioception of the face (especially jaw muscles). 3. Principal (Chief) Sensory Nucleus – Touch and pressure sensation from the face. 4. Spinal Nucleus of V – Pain and temperature sensation from the face. These nuclei are located in different parts of the brainstem (midbrain, pons, and medulla), making the trigeminal nerve unique in its extensive distribution.

Answer 67

C. Otic ganglion Explanation: The otic ganglion is a parasympathetic ganglion that provides the postganglionic secretory motor supply to the parotid gland. Pathway of Parotid Gland Innervation: 1. Preganglionic fibers originate from the inferior salivatory nucleus in the brainstem. 2. These fibers travel via the glossopharyngeal nerve (cranial nerve IX). 3. They then pass through the tympanic plexus and the lesser petrosal nerve to reach the otic ganglion. 4. In the otic ganglion, these fibers synapse with postganglionic fibers. 5. Postganglionic fibers travel with the auriculotemporal nerve (branch of V3) to reach and stimulate the parotid gland for saliva secretion. Why Not the Other Options? A. Geniculate ganglion → This is a sensory ganglion of the facial nerve (CN VII), not related to the parotid gland. B. Spiral ganglion → This is involved in hearing and is part of the cochlea of the inner ear. D. Ciliary ganglion → This is associated with oculomotor nerve (CN III) and controls the eye muscles (pupil constriction and lens accommodation).

Answer 68

C. Glycogenesis Explanation: During heavy exercise, the body needs more energy, so it prioritizes breaking down stored fuels rather than storing them. Here's how the metabolic pathways respond: Metabolic Processes During Exercise: A. Gluconeogenesis (↑ Increases) → The liver produces glucose from non-carbohydrate sources like amino acids and lactate to maintain blood glucose levels. B. Glycogenolysis (↑ Increases) → Stored glycogen in muscles and the liver is broken down into glucose to provide energy. C. Glycogenesis (↓ Decreases) → The synthesis of glycogen from glucose decreases because the body needs glucose for immediate energy, not storage. D. Glycolysis (↑ Increases) → The breakdown of glucose for ATP production accelerates to meet the energy demands of active muscles.

Answer 69

D. Blood pressure Explanation: Korotkoff sounds are the sounds heard while measuring blood pressure using a stethoscope and sphygmomanometer. These sounds are produced by turbulent blood flow in the arteries as the cuff pressure is gradually released. Phases of Korotkoff Sounds: 1. Phase I – First appearance of a clear tapping sound → Indicates Systolic BP 2. Phase II – Softer and longer sounds 3. Phase III – Crisper and louder sounds 4. Phase IV – Muffled and soft sounds 5. Phase V – Sounds disappear → Indicates Diastolic BP

Answer 70

C. Systolic pressure Explanation: Cardiac Output (CO) is the amount of blood pumped by the heart per minute and is calculated as: CO=Heart Rate (HR)×Stroke Volume (SV) Several factors influence cardiac output, including: ✅ Heart Rate (HR) – A higher HR increases CO, while a lower HR decreases CO. ✅ Venous Return – More blood returning to the heart (preload) increases stroke volume, boosting CO. ✅ Peripheral Resistance – Affects afterload and the workload of the heart, indirectly impacting CO. ❌ Systolic Pressure – While systolic pressure is an indicator of blood pressure, it does not directly determine cardiac output. It is more of an effect rather than a cause.

Answer 71

A. Tropomyosin moves away from blocking the myosin-binding sites and results in muscular contraction. Explanation: Muscle contraction occurs through the sliding filament theory, which involves actin, myosin, troponin, and tropomyosin. 1. Calcium Release: When a muscle cell is stimulated, calcium (Ca²⁺) is released from the sarcoplasmic reticulum into the cytoplasm. 2. Troponin Activation: Calcium binds to troponin, which causes a conformational change. 3. Tropomyosin Shift: This change moves tropomyosin away from the myosin-binding sites on actin, allowing the myosin heads to bind to actin and initiate contraction. 4. Power Stroke: Myosin heads pull actin toward the M-line, leading to muscle contraction. 5. Relaxation (if no calcium): Without calcium, tropomyosin blocks the myosin-binding sites, preventing contraction. Why the Other Choices Are Incorrect: ❌ B. Tropomyosin will block the myosin head and result in muscular relaxation. This happens in the absence of calcium, not when calcium binds to troponin. ❌ C. Myosin head will be detached from binding to actin. Myosin detaches after ATP binds, not immediately when calcium binds to troponin. ❌ D. Myosin head will move the actin away from the M line (power stroke). The power stroke happens after myosin binds to actin and ATP is hydrolyzed, but calcium binding itself only exposes the binding site.

Answer 72

C. Both statements are true. Explanation: 1. Veins - Tunica Adventitia (Thickest Layer): - Veins have a thicker tunica adventitia (also called tunica externa) compared to arteries. - This layer is composed mainly of collagen and connective tissue, providing structural support since veins have lower pressure than arteries. 2. Arteries - Tunica Media (Thickest Layer): - The tunica media is the thickest layer in arteries, consisting of smooth muscle and elastic fibers. - It allows vasoconstriction and vasodilation, which regulate blood pressure and flow. Why the Other Choices Are Incorrect: ❌ A. The first statement is true, and the second is false. The second statement is also true because arteries indeed have a thick tunica media. ❌ B. The first statement is false, and the second is true. The first statement is true because veins have a thicker tunica adventitia. ❌ D. Both statements are false. Both statements are actually correct.

Answer 73

D. Upper border of thyroid cartilage Explanation: The common carotid artery bifurcates into the internal and external carotid arteries at the level of the upper border of the thyroid cartilage, around the C3–C4 vertebral level. This is an important anatomical landmark for clinicians when assessing carotid pulse or performing surgical interventions. Why the Other Options Are Incorrect: ❌ A. Transverse process of C6 The common carotid artery is still a single vessel at C6 and hasn't bifurcated yet. ❌ B. Transverse process of C7 The bifurcation occurs higher up at C3–C4, not at C7. ❌ C. Hyoid bone The hyoid bone is located above the carotid bifurcation, at the level of C3, but the bifurcation is slightly lower, at the upper border of the thyroid cartilage.

Answer 74

D. Ligamentum teres Explanation: The umbilical vein is a fetal blood vessel that carries oxygenated blood from the placenta to the fetus. After birth, it closes and degenerates into the ligamentum teres (round ligament of the liver), which is found in the free edge of the falciform ligament of the liver. Why the Other Options Are Incorrect: ❌ A. Ligamentum venosum The ligamentum venosum is a remnant of the ductus venosus, which in fetal circulation shunted blood from the umbilical vein to the inferior vena cava. ❌ B. Ligamentum umbilicum There is no such structure called "ligamentum umbilicum." You may be thinking of the median umbilical ligament, which is a remnant of the urachus (fetal connection between the bladder and the umbilicus). ❌ C. Ligamentum arteriosum The ligamentum arteriosum is a remnant of the ductus arteriosus, which in fetal circulation shunted blood from the pulmonary artery to the aorta, bypassing the lungs.

Answer 75

A. Epicardium Explanation: Fat accumulation in the heart primarily occurs in the epicardium, which is the outermost layer of the heart wall. The epicardium contains adipose tissue, blood vessels, and nerves that supply the heart. Why the Other Options Are Incorrect: ❌ B. Myocardium The myocardium is the thick muscular layer responsible for pumping blood. While some fat can infiltrate the myocardium in certain pathological conditions (e.g., fatty infiltration of the myocardium), the primary site of fat accumulation is still the epicardium. ❌ C. Endocardium The endocardium is the innermost layer of the heart that lines the chambers and valves. It is composed of endothelial cells and connective tissue and does not store fat. ❌ D. Epiadipocardium This is not an anatomical term; it seems to be a misleading or incorrect option.

Answer 76

B. Collagen fibers Explanation: The tensile strength of bone refers to its ability to resist stretching and pulling forces. This property is primarily due to collagen fibers, which provide flexibility and resilience. Why the Other Options Are Incorrect: ❌ A. Hydroxyapatite crystals Hydroxyapatite (calcium phosphate) provides compressive strength, allowing bones to withstand weight and pressure. However, it does not contribute significantly to tensile strength. ❌ C. Osteocytes Osteocytes are mature bone cells responsible for maintaining bone tissue, but they do not contribute directly to tensile strength. ❌ D. Osteoid Osteoid is the unmineralized organic portion of bone matrix, consisting mainly of collagen and proteins. While osteoid is a precursor to bone formation, its tensile strength comes from collagen fibers within it.