The following are the functions of the yolk sac, EXCEPT?

UPUMS Nsg officer-2023

Obstetrics & Gynaecology

Easy

Appeared in: UPUMS Nsg officer-2023

Explanation

The yolk sac's primary roles are nutritive, hematopoietic, and as a source of germ cells; it does not have a primary function in protecting the embryo from microorganisms.
The main protective barriers for the embryo and fetus are the amniotic sac (physical barrier) and the placenta (immunological barrier).
Protecting the embryo from the invasion of microorganisms matches the defining clue or classification criterion in the stem.
Supporting mechanism: The option aligns with the governing rule, pattern, sequence, classification, or exam logic being tested.
Key differentiator: It fits the one fact that separates the correct response from the closest distractor.

Option B: This is a primary function of the yolk sac. It is the first site of hematopoiesis (blood cell formation) in the early embryo.
Option C: This is a key function of the yolk sac. Primordial germ cells, the precursors to sperm and eggs, originate in the endodermal lining of the yolk sac.
Option D: This is a vital function of the yolk sac, especially during the second and third weeks of development, before the uteroplacental circulation is established.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Functions of the yolk sac in early embryonic development as background academic context rather than a clinical decision trigger.
The yolk sac is one of the first structures visible on an early pregnancy ultrasound, helping to confirm an intrauterine pregnancy and assess its viability.
Abnormalities in the size or shape of the yolk sac on an early scan can be an indicator of potential pregnancy complications or embryonic demise.
Yolk sac tumors (endodermal sinus tumors) are a rare type of germ cell cancer, underscoring the yolk sac's role as the origin of primordial germ cells.

How to Approach the Question

First, identify the keywords in the question: 'yolk sac', 'functions', and 'EXCEPT'.
The word 'EXCEPT' is critical. It signals that three of the options are true functions, and your task is to find the one that is false.
Systematically review each option, recalling the main roles of the extraembryonic membranes.
Evaluate Option A: Is protection from microbes a yolk sac function? Recall that the amnion and placenta are the main protective barriers.
Evaluate Options B, C, and D: Are blood cell formation, germ cell origin, and nutrient supply functions of the yolk sac? Yes, these are its three classic, well-established roles.
Conclude that the statement in Option A is the incorrect one, making it the correct answer for this 'EXCEPT' question.

Concept Tested & Keywords

Concept Tested: Functions of the yolk sac in early embryonic development.
Stem keywords: yolk sac, functions
Lead-in keywords: EXCEPT
Negative lead-in flag: The question asks to identify the option that is NOT a function of the yolk sac.

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E6 Anatomy Grays 43e Vol 1 Part 2 pp. 9-11, 48-50