Which peptide hormone is produced almost exclusively by the corpus luteum during pregnancy?

MP CHO -2021 (Shift 1st)

Obstetrics & Gynaecology

Easy

Appeared in: MP CHO -2021 (Shift 1st)

Explanation

Relaxin is a peptide hormone structurally similar to insulin.
During early pregnancy, its primary source is the corpus luteum in the ovary, with its secretion stimulated by hCG.
Later in pregnancy, the placenta and decidua also contribute to its production.
Key functions include remodeling connective tissue, softening the cervix, relaxing pelvic ligaments for labor, and increasing maternal renal blood flow.

Option A: Leptin is a peptide hormone, but it is primarily secreted by adipose tissue and the placenta, not the corpus luteum. Its main role is in energy regulation.
Option C: Estriol is a steroid hormone, not a peptide hormone. It is the main estrogen of pregnancy and is produced by the placenta from fetal adrenal precursors.
Option D: PAPPA (Pregnancy-Associated Plasma Protein A) is a large glycoprotein, not a simple peptide hormone. It is produced by the placenta and used as a marker in prenatal screening.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Hormones of Pregnancy as background academic context rather than a clinical decision trigger.
Understanding the source and function of relaxin helps explain common musculoskeletal complaints in pregnancy, such as pelvic girdle pain and back pain, which result from ligamentous laxity.
Relaxin's effect on renal hemodynamics (increasing GFR and renal blood flow) is a key maternal physiological adaptation in early pregnancy.
What if the question asked about a hormone that maintains the corpus luteum in early pregnancy? The answer would be human chorionic gonadotropin (hCG), which is produced by the trophoblast and stimulates the corpus luteum to continue producing progesterone and relaxin.

How to Approach the Question

First, dissect the question to identify the key criteria: 1) Must be a peptide hormone, and 2) Must be produced 'almost exclusively' by the corpus luteum during pregnancy.
Evaluate Option A (Leptin): Recall or deduce that leptin is related to fat stores (adipose tissue) and energy balance. While it's a peptide, its primary source isn't the corpus luteum.
Evaluate Option B (Relaxin): Recall that relaxin is known for 'relaxing' ligaments in pregnancy. It is a peptide hormone, and its primary source in early pregnancy is the corpus luteum.
Evaluate Option C (Estriol): Identify 'estriol' as an estrogen. Estrogens are steroid hormones, not peptides. This disqualifies it based on the first criterion.
Evaluate Option D (PAPPA): Recognize this as Pregnancy-Associated Plasma Protein A. Its name suggests it's a protein from the placenta, and it's a large glycoprotein, not a simple peptide hormone. It's also not from the corpus luteum.
Conclude that Relaxin is the only option that fits both criteria of being a peptide hormone and being primarily produced by the corpus luteum in pregnancy.

Concept Tested & Keywords

QBt26zHPLXXgN52EQpTt6b

E6 Obstetrics Williams p. 1-9

E6 Physiology Guyton 4SAE Part 3 p. 60-62