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4.7.11Additional lessons

Hormones in Pregnancy — IB Biology HL Revision Notes & Topical Questions

5 min read 5 parts Lesson 65 of 101

📚 IB Biology HL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Maintaining Pregnancy

Without hormonal support from the embryo, the corpus luteum would degenerate and the lining would be lost.

hCG
  • hCG Secreted by the embryo's trophoblast, it stimulates the corpus luteum to continue secreting progesterone and oestradiol.
Progesterone
  • Progesterone Maintains the endometrium, inhibits FSH and LH so that no further eggs mature, and prevents uterine contractions.
Oestradiol
  • Oestradiol Stimulates growth of the uterus and mammary glands.
Placental takeover
  • Placental takeover After about the first three months the placenta produces enough progesterone and oestradiol, and the corpus luteum degenerates.

Part 2 of 5Control of Birth

1
Late in pregnancy, falling progesterone and rising oestradiol make the uterine muscle more sensitive to oxytocin.
2
Pressure of the fetus on the cervix sends nerve signals to the hypothalamus.
3
The posterior pituitary releases oxytocin, which stimulates uterine contractions.
4
Contractions push the fetus harder against the cervix, causing more oxytocin release, a positive feedback loop.
5
The cycle ends with birth, when the cervix is no longer stimulated.

Part 3 of 5Pregnancy Tests

What is detected
  • What is detected Tests detect hCG in urine, since it appears soon after implantation.
Monoclonal antibodies
  • Monoclonal antibodies Antibodies on the test strip bind hCG and trigger a colour change that shows a positive result.
Timing
  • Timing hCG levels rise rapidly in early pregnancy, so tests become reliable a few days after a missed period.
HormoneSourceRole in pregnancy
hCGEmbryo/placentaMaintains corpus luteum
ProgesteroneCorpus luteum then placentaMaintains lining, inhibits contractions
OxytocinPosterior pituitaryStimulates contractions

Part 4 of 5Why Feedback Matters

Positive feedback in birth
  • Positive feedback in birth Contractions strengthen themselves, quickly increasing the force until delivery.
Negative feedback elsewhere
  • Negative feedback elsewhere High progesterone suppresses FSH and LH, maintaining a stable hormonal state.
Clinical use
  • Clinical use Synthetic oxytocin may be given to start or strengthen labour.

Part 5 of 5Exam Checklist & Tips

4.7.11 – Key Points for the Exam

  • hCG Human chorionic gonadotrophin, a hormone made by the embryo that maintains the corpus luteum.
  • Oxytocin A hormone from the posterior pituitary that stimulates uterine contractions.
  • Positive feedback A process in which a change causes further change in the same direction.
  • Monoclonal antibody An identical antibody made by a clone of cells and specific for one antigen.

Common Mistakes

  • Saying the corpus luteum remains active throughout pregnancy.
  • Stating that oxytocin is made by the ovary.
  • Calling the control of birth negative feedback.
  • Writing that hCG is secreted by the mother's pituitary.

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