Which of the following is ectodermal in origin:

Correct Answer: C

Rationale: Ectoderm forms the epidermis (C), the skin's outer layer, via surface ectoderm differentiation into stratified squamous epithelium. Blood (A) originates from mesoderm, specifically hemangioblasts in the yolk sac and later bone marrow. The dermis (B), beneath the epidermis, is mesodermal, arising from fibroblasts and connective tissue. The spleen (D) is also mesodermal, from mesenchyme in the dorsal mesogastrium. C is correct epidermis' ectodermal lineage, forming skin and neural structures, distinguishes it from the mesodermal origins of the others.

Correct Answer: D

Rationale: In anemia (Hb = 5 g/100 ml), choice D (PₙO₂ decreased) is incorrect. PₙO₂ (assumed PaO₂, arterial pO₂) remains normal (≈100 mmHg) because lung function isn't impaired; only O₂-carrying capacity drops. Choice A (decreased TPR) is correct; reduced blood viscosity lowers total peripheral resistance. Choice B (increased cardiac output) is true; the heart compensates for lower O₂ content by pumping more blood. Choice C (increased 2,3-DPG) is accurate; RBCs produce more 2,3-DPG to shift the O₂ dissociation curve rightward, enhancing O₂ unloading to tissues. Choice E (curve shifts right) supports this adaptation. PaO₂ reflects dissolved O₂, not Hb-bound O₂, so it's unaffected by anemia unless hypoxemia coexists. The body's compensatory mechanisms focus on delivery, not arterial pO₂, making D the false statement here.

Correct Answer: C

Rationale: Carbon monoxide (CO, choice C) doesn't shift the Oâ‚‚ dissociation curve right, making it the exception. Decreased pH (choice A), increased temperature (choice B), and increased pCOâ‚‚ (choice D, repeated as E) all reduce Hb-Oâ‚‚ affinity (Bohr effect), shifting the curve right to favor Oâ‚‚ unloading. CO binds Hb with high affinity, forming COHb, which left-shifts the curve for unbound Hb, increasing Oâ‚‚ affinity and impairing release opposite to a right shift. Acidosis (A), heat (B), and COâ‚‚ (D) enhance tissue Oâ‚‚ delivery, adaptive in exercise or hypoxia. CO's toxic effect mimics high Oâ‚‚ saturation, masking hypoxia, and doesn't aid unloading. Thus, C's distinct leftward action excludes it from right-shift factors.

Correct Answer: A

Rationale: cholinergic discharge (acetylcholine, parasympathetic) causes bronchoconstriction, not bronchodilation. Choice B is true; β₂-agonists (e.g., albuterol) activate adrenergic receptors, relaxing bronchial smooth muscle. ' β₂-agonists increase mucus secretion, a secondary effect to dilation. Choice D is true; vasoactive intestinal peptide (VIP) promotes bronchodilation by relaxing smooth muscle. Cholinergic stimulation, via vagus nerve, contracts bronchioles, increasing resistance opposite to bronchodilation's airway widening. This reflects autonomic balance: parasympathetic constricts, sympathetic (β₂) dilates. A's reversal of this physiology misrepresents airway control, where bronchodilation aids airflow (e.g., asthma treatment), while cholinergic effects narrow airways for rest or protection. Thus, A is the incorrect pairing.

Correct Answer: B

Rationale: DₗO₂ rises from ≈25 to 65 ml/min/mmHg in exercise via increased surface area and perfusion. Choice A is false; pulmonary capillary PaO₂ (≈100 mmHg) exceeds aortic (≈95 mmHg) due to shunts. Choice C is wrong; beryllium poisoning and sarcoidosis reduce DₗO₂ via fibrosis. Choice D is true; fibrosis impairs CO₂ diffusion, causing retention. Choice E is false; decreased PDGF doesn't cause fibrosis increased does. Exercise triples DₗO₂, enhancing O₂ uptake (e.g., VO₂ max), making B the accurate physiological change.