Paper I — Q2
A middle-aged female notices a lump in the midline of the neck. She notices it moves with swallowing. The surgeon gives a…
A middle-aged female notices a lump in the midline of the neck. She notices it moves with swallowing. The surgeon gives a tentative diagnosis of goitre.
Describe the thyroid gland under the following headings: Gross anatomy and relations
Blood supply and lymphatic drainage
Surgical anatomy of thyroid gland
Explain why vitamin D can be considered to be a 'hormone'. Describe the role of vitamin D in calcium homeostasis.
Discuss the sources and Recommended Daily Allowance (RDA) of vitamin B12. Briefly discuss the absorption of vitamin B12 in the GIT and the clinical manifestations of the disorder of absorption of vitamin B12.
Define the Frank-Starling law. State the significance and causes of shift of Frank-Starling curve to right and left.
What is the role of baroreceptors and chemoreceptors in the regulation of blood pressure?
हिंदी में प्रश्न पढ़ें
एक मध्यमवय महिला को ग्रीवा की मध्यरेखा में अपृदुर्द दिखाई दी। यह अपृदुर्द निगलने की क्रिया के साथ स्थान बदलती थी। शल्यचिकित्सक ने इसे देख गलगंड का प्रारंभिक निदान दिया।
अवटु ग्रंथि का निम्नलिखित शीर्षकों के अंतर्गत वर्णन कीजिए : सकल शारीर एवं संबंध
रक्त आपूर्ति तथा लसीका जल-निकासी
अवटु ग्रंथि का शल्यतंत्री शारीर
समझाइए कि क्यों विटामिन D को 'हार्मोन' माना जा सकता है। कैल्शियम की समस्थिति बनाए रखने में विटामिन D की भूमिका का वर्णन कीजिए।
विटामिन B12 के स्रोत तथा अनुशंसित दैनिक भत्ते (आर० डी० ए०) की व्याख्या कीजिए। विटामिन B12 के जी० आई० टी० में अवशोषण तथा विटामिन B12 के अवशोषण के विकार की रोगलाक्षणिक अभिव्यक्तियों की संक्षेप में व्याख्या कीजिए।
फ्रैंक-स्टारलिंग नियम को परिभाषित कीजिए। फ्रैंक-स्टारलिंग वक्र की दायीं तथा बायीं ओर स्थानांतरित होने के महत्व तथा कारणों को लिखिए।
रक्तदाब के नियमन में दाबग्राहियों तथा रसायनग्राहियों की क्या भूमिका है?
Model answer
Drafted with AI by UPSC Answer Check against this question's marking rubric, to the expected length. UPSC does not publish answers for Mains — this is one way to score well, not an official key. How we build rubrics and answers.
A midline neck lump that moves with swallowing suggests thyroid pathology, often goitre, because the gland is bound to the trachea by pretracheal fascia.
(a)(i) Gross anatomy and relations. The thyroid has two lateral lobes over the trachea, connected by the isthmus over the 2nd–4th tracheal rings; a pyramidal lobe may be present. Anteriorly it lies deep to infrahyoid/strap muscles; posteriorly it relates to trachea, oesophagus, recurrent laryngeal nerve in the tracheoesophageal groove, and parathyroid glands.
(a)(ii) Blood supply and lymphatic drainage. Arterial supply is from superior thyroid artery (external carotid), inferior thyroid artery (thyrocervical trunk), and variable thyroid ima artery. Veins drain via superior, middle and inferior thyroid veins. Lymphatics pass to prelaryngeal, pretracheal and lateral deep cervical nodes.
(a)(iii) Surgical anatomy. Danger zones include the recurrent laryngeal nerve, external branch of the superior laryngeal nerve, and parathyroid glands, which must be preserved with their blood supply. Berry’s ligament fixes the gland to the trachea and is a key landmark. The gland has a true capsule and a false capsule from the pretracheal fascia. The inferior thyroid artery is ligated away from the gland because of its close relation to the recurrent laryngeal nerve, while the superior thyroid artery is ligated close to the upper pole to protect the external laryngeal nerve. The tubercle of Zuckerkandl points to the recurrent laryngeal nerve.
(b)(i) Vitamin D as a hormone and calcium homeostasis. Vitamin D can be considered a hormone because it is synthesised in skin by UV-B, hydroxylated in liver to 25-hydroxyvitamin D and in kidney to 1,25-dihydroxyvitamin D (calcitriol), and acts through nuclear vitamin D receptors in target tissues. In calcium homeostasis calcitriol increases intestinal calcium absorption, renal tubular reabsorption, and, with PTH, promotes bone resorption/mobilisation of calcium into plasma; bone mineralisation is a separate bone-health effect that can lower plasma calcium. It also suppresses PTH secretion.
(b)(ii) Vitamin B12: sources, RDA, absorption and deficiency. B12 occurs in animal products—meat, fish, eggs, dairy—and fortified foods in India. The ICMR-NIN (2020) RDA is 2.2 µg/day for adults (EAR 2.0 µg/day; higher in pregnancy and lactation), and the corresponding US RDA is 2.4 µg/day. Absorption requires intrinsic factor from parietal cells; the B12–intrinsic factor complex is absorbed in the terminal ileum via cubilin–amnionless receptors and transported by transcobalamin II. Malabsorption (pernicious anaemia, gastrectomy, ileal disease or resection, fish tapeworm, bacterial overgrowth) causes megaloblastic anaemia, glossitis, subacute combined degeneration of the cord, peripheral neuropathy and neuropsychiatric changes.
(c)(i) Frank-Starling law. Stroke volume increases as end-diastolic volume/preload increases, allowing matched output of ventricles. A rightward shift indicates decreased contractility, as in heart failure; a leftward shift indicates increased contractility, as with catecholamines or exercise. Its significance is that it matches the outputs of the two ventricles and adapts stroke volume to venous return. An increase in afterload also shifts the curve down and to the right.
(c)(ii) Baroreceptors and chemoreceptors. Carotid sinus and aortic arch baroreceptors provide rapid short-term blood pressure regulation by altering sympathetic and parasympathetic outflow from the medullary vasomotor centre. Carotid and aortic bodies respond to hypoxia, hypercapnia and acidosis, increasing ventilation and reflex vasoconstriction to maintain perfusion.
How this answer will be evaluated
Framework: Medical Science, Paper 1
What earns full marks: Comprehensive, accurate, with diagrams and clinical correlations
Evaluation rubric
Each sub-part is marked on its own, against the marks and word limit printed on the paper.
- (a)(i) Thyroid: gross anatomy and relations. 5 marks
describe— define → structure or process in order → labelled diagram → significance
Must cover
- Two lobes, isthmus over tracheal rings 2–4, pyramidal lobe
- Capsules: true and false (pretracheal fascia); movement with swallowing
- Anterior relations: strap muscles, sternocleidomastoid
- Posterior/medial relations: trachea, oesophagus, larynx, RLN, parathyroids, carotid sheath laterally
Loses marks
- Wrong tracheal ring level
Earns more
- Weight and extent (C5–T1)
Extra mark
- Ligament of Berry
- (a)(ii) Blood supply and lymphatic drainage of thyroid. 5 marks
describe— define → structure or process in order → labelled diagram → significance
Must cover
- Superior thyroid artery (ECA), inferior thyroid artery (thyrocervical trunk), thyroidea ima (variable)
- Veins: superior and middle to IJV, inferior to brachiocephalic
- Lymphatics: prelaryngeal (Delphian), pretracheal, paratracheal, deep cervical nodes
- Clinical relevance of venous/lymphatic routes
Loses marks
- Inferior thyroid artery from ECA
Earns more
- Accessory arteries (tracheal/oesophageal)
Extra mark
- Metastasis pattern in papillary carcinoma
- (a)(iii) Surgical anatomy of thyroid. 5 marks
describe— define → structure or process in order → labelled diagram → significance
Must cover
- RLN in tracheo-oesophageal groove; relation to inferior thyroid artery (ligate away from gland)
- External laryngeal nerve with superior thyroid artery (ligate close to upper pole)
- Parathyroid preservation with blood supply
- Berry's ligament, capsules, tubercle of Zuckerkandl
Loses marks
- No nerve-protection principles
Earns more
- Complications of thyroidectomy
Extra mark
- Non-recurrent laryngeal nerve
- (b)(i) Why vitamin D is a hormone; role in calcium homeostasis. 10 marks
explain— definition/context → points in order → small example → short close
Must cover
- Synthesised in skin; 25-hydroxylation in liver, 1α-hydroxylation in kidney (regulated by PTH)
- Acts via nuclear VDR on distant targets — hormone criteria
- Actions: ↑ intestinal Ca/P absorption, ↑ renal Ca reabsorption, bone mobilisation with PTH, mineralisation
- Feedback: suppresses PTH; FGF-23 regulation
Loses marks
- Calling it a vitamin only
Earns more
- Deficiency: rickets/osteomalacia
Extra mark
- Non-classical actions (immunity)
- (b)(ii) Vitamin B12 sources, RDA, absorption and malabsorption manifestations. 10 marks
discuss— intro → 3-4 dimensions → example → balanced close
Must cover
- Sources: animal foods; vegetarians at risk; RDA ≈ 2.2 µg/day (ICMR-NIN 2020) / 2.4 µg
- Absorption: release by pepsin, R-binder (haptocorrin), intrinsic factor, terminal ileum cubilin, transcobalamin II
- Causes of malabsorption: pernicious anaemia, gastrectomy, ileal disease/resection, fish tapeworm, bacterial overgrowth
- Manifestations: megaloblastic anaemia, glossitis, SACD, neuropathy, neuropsychiatric changes
Loses marks
- Absorption in jejunum
Earns more
- Schilling test/methylmalonic acid
Extra mark
- Indian vegetarian context
- (c)(i) Frank-Starling law; significance and causes of right/left shift. 10 marks
define— precise definition → the distinguishing feature → one example
Must cover
- Definition: stroke volume rises with end-diastolic volume (sarcomere length–tension)
- Significance: matches outputs of two ventricles; adjusts to venous return
- Left/upward shift: positive inotropes, sympathetic stimulation, catecholamines, digoxin
- Right/downward shift: heart failure, negative inotropes, ischaemia, acidosis, increased afterload
Loses marks
- Confusing preload with afterload shift
Earns more
- Graph sketch
Extra mark
- Molecular basis (Ca²⁺ sensitivity)
- (c)(ii) Role of baroreceptors and chemoreceptors in BP regulation. 5 marks
explain— definition/context → points in order → small example → short close
Must cover
- Baroreceptors: carotid sinus (IX), aortic arch (X); stretch-sensitive
- Reflex via NTS and vasomotor centre: ↑BP ⇒ ↑vagal, ↓sympathetic ⇒ ↓HR, vasodilatation
- Chemoreceptors: carotid/aortic bodies respond to hypoxia, hypercapnia, acidosis ⇒ vasoconstriction, ↑BP (esp. BP < 80 mmHg)
- Short-term vs long-term regulation; baroreceptor resetting
Loses marks
- Chemoreceptors as primary regulators at normal BP
Earns more
- Reflex arc diagram
Extra mark
- Cushing reflex mention
What "Describe" is asking you to do
Give a full, ordered account of the thing named — its parts, stages or mechanism — in the sequence in which it actually exists or occurs. Most describe questions come from the science optionals, where the marks sit in correct technical detail and, where the stem says so, a labelled diagram.
Structure that answers it
One-line identification of the subject → the parts or stages in their real order, each with its defining detail → labelled diagram where the subject is structural → closing line on function or significance
Where marks are lost
Loose general prose where the examiner is ticking named parts, correct terminology and their sequence; and in the General Studies papers, turning to evaluation before the description is finished.
Practice this exact question
Write your answer and it is marked point by point against the model answer above — what you covered, what you missed, what you got wrong.
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