Question

Relaxin is secreted by
A. Corpus luteum
B. Pituitary
C. Pineal
D. Ovary

Answer 1

Hint: Relaxin is a peptide hormone belonging to the insulin family. This hormone is secreted only by mammals. It facilitates the process of parturition, participates in uterine contraction, promotes spermatozoa motility and acrosome reaction.

Complete answer:
Relaxin is secreted by a number of reproductive organs and tissues that include ovary, uterus, testis, prostate and other tissues.
In females, relaxin is primarily secreted in circulation by the corpus luteum present in the ovaries of both pregnant and non-pregnant females. During pregnancy, placenta, foetal membranes and the lining of the uterus also secrete relaxin.
In men, relaxin is produced by the prostate gland and is found in the seminal fluid and not in the blood circulation.

The effect of relaxin is more profound during the female reproductive cycle and pregnancy. In the ovaries, after ovulation, the Luteal phase starts which marks the formation of corpus luteum. If fertilization has occurred, the corpus luteum continues to grow and act as a temporary endocrine gland. It secretes important hormones like Relaxin and Progesterone for the sustenance of pregnancy. Relaxin helps to relax the uterine wall by inhibiting contractions, and prepares the lining of the uterus for pregnancy. However, in the absence of fertilization corpus luteum degenerates and relaxin levels drop again.

The main role of relaxin is towards the end of pregnancy when contraction of uterine muscles initiates the process of parturition. Relaxin is released in huge amounts to soften and relax the ligaments of the pelvic region. This loosens the pubic symphysis and the cervix gets dilated. The foetus moves down the birth canal and is delivered through the vagina.

Hence, the correct answer is option (A).

Note: During the first trimester of pregnancy, high levels of relaxin inhibit contractions in the uterine wall and prevent premature labour and childbirth. It also facilitates the growth of placenta which also starts the secretion of relaxin. It regulates the mother’s cardiovascular and renal systems so that the foetal demand for oxygen, nutrients and disposal of waste are met.