In the context of human reproduction, the 'Placenta' is fully formed and functional by the end of which trimester of pregnancy? MCQ with Answer and Explanation

Question

In the context of human reproduction, the 'Placenta' is fully formed and functional by the end of which trimester of pregnancy?

A. First trimester (end of 12 weeks)

B. Third trimester (end of 36 weeks)

C. Second trimester (end of 24 weeks)

D. At the time of birth

Answer: Option A

Solution (By JKSSB Mock Tests)

The placenta begins to form immediately after implantation of the blastocyst. By the end of the first trimester (around 12 weeks of gestation), the placenta is fully formed and takes over the primary role of hormone production (progesterone and estrogen) from the corpus luteum. It is fully functional in providing oxygen, nutrients, and waste removal for the developing fetus for the remainder of the pregnancy. It is not fully formed at conception, nor does it wait until the second or third trimester.

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Question #1

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Consider the following statements about the skin:
1. The epidermis is the outermost layer.
2. Melanin protects against UV radiation.
3. Sebaceous glands produce sweat.
Which of the above is/are correct?

A. 1 and 3 only

B. 1 and 2 only

C. 1, 2, and 3

D. 2 and 3 only

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Correct Answer: Option B

Explanation:
Epidermis is outer layer, melanin absorbs UV. Sebaceous glands produce sebum (oil), sweat is from sudoriferous glands. So 3 is incorrect.

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Question #2

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The nephron structure that measures the concentration of sodium chloride in the filtrate and regulates GFR is the:

A. Juxtaglomerular apparatus

B. Bowman's capsule

C. Collecting duct

D. Proximal convoluted tubule

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Correct Answer: Option A

Explanation:
The juxtaglomerular apparatus (JGA) is formed by the macula densa cells of the distal tubule and granular cells of the afferent arteriole. It detects NaCl concentration in the filtrate and releases renin, which regulates GFR and systemic blood pressure via the renin-angiotensin-aldosterone system. Bowman's capsule collects filtrate, PCT reabsorbs, collecting duct concentrates urine.

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Question #3

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The 'Hormone Oxytocin' is synthesized in the hypothalamus and released by the posterior pituitary. Its two primary physiological roles in females are:

A. Stimulating milk production and inhibiting uterine contractions

B. Stimulating uterine contractions during childbirth and milk ejection (let-down reflex) during lactation

C. Stimulating follicle growth and ovulation

D. Maintaining the uterine lining and preventing menstruation

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Correct Answer: Option B

Explanation:
Oxytocin is a peptide hormone produced by the paraventricular nucleus of the hypothalamus and released by the posterior pituitary. In females, it has two major roles: 1) During childbirth, it stimulates powerful contractions of the uterine smooth muscle, facilitating labor and delivery (this is a positive feedback loop). 2) During lactation, it stimulates the contraction of myoepithelial cells surrounding the alveoli in the mammary glands, causing the ejection (let-down) of milk into the ducts in response to suckling. It does not produce milk; prolactin does that.

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