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Which of the following secretes the hormone, relaxin, during the later phase of pregnancy?
NCERT states verbatim: "In the later phase of pregnancy, a hormone called relaxin is also secreted by the ovary." Within the maternal ovary, the persistent endocrine glandular tissue responsible for relaxin secretion is the Corpus Luteum of pregnancy! Mark Option (2) in under 15 seconds.
During human pregnancy, the placenta acts as a temporary endocrine gland producing hormones essential for fetal maintenance: human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens, and progesterone. - In the later phase of pregnancy, a peptide hormone called relaxin is secreted by the maternal ovary, specifically by the corpus luteum (and in minor amounts by the placenta/decidua). - Physiological Action: Relaxin loosens and relaxes the fibrous pubic symphysis (interpubic fibrocartilage) and softens the cervix, expanding the pelvic outlet to facilitate unimpeded passage of the foetus during parturition.
- Graafian follicle: Matures during the follicular phase of the non-pregnant menstrual cycle and ruptures at ovulation; it does not exist in late pregnancy. - Foetus: Does not secrete maternal relaxin to prepare maternal pelvic ligaments. - Uterus (Myometrium/Endometrium): Acts as the target organ responding to oxytocin, prostaglandins, and relaxin, not the source designated in NCERT.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Incorrect. Graafian follicles are pre-ovulatory ovarian follicles; during pregnancy, high progesterone blocks folliculogenesis.
Correct. The corpus luteum of the ovary secretes relaxin in late pregnancy to relax pelvic ligaments.
Incorrect. The fetus secretes ACTH and cortisol to trigger the fetal ejection reflex, not relaxin.
Incorrect. The uterus is the mechanical and target muscular organ, not the primary endocrine source of relaxin.
Many students believe the corpus luteum degenerates into a corpus albicans after 3 months of pregnancy. While the placenta assumes primary progesterone synthesis, the corpus luteum of pregnancy persists and continues to secrete relaxin into late pregnancy.
"In the later phase of pregnancy, relaxin is secreted by the ovary (corpus luteum)."
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