Hormonal Control in Humans
This topic covers how hormones act as chemical messengers in the body, focusing on adrenaline's role in the 'fight or flight' response and the complex hormonal control of the human menstrual cycle and contraception.
Part of the ESAT Biology syllabus — revision for the Engineering and Science Admissions Test (ESAT), the UAT-UK admissions test for Cambridge, Imperial, Oxford and UCL.
Key points
- Hormones are chemicals released from endocrine glands directly into the bloodstream. They travel to specific target organs where they produce a slower, longer-lasting response compared to the nervous system.
- Adrenaline is secreted by the adrenal glands during stress. It prepares the body for 'fight or flight' by increasing heart rate, breathing rate, and converting glycogen to glucose for energy.
- The menstrual cycle is regulated by four key hormones in a feedback loop: FSH matures the egg, Oestrogen rebuilds the uterine wall, LH triggers ovulation, and Progesterone maintains the uterine lining.
- Hormonal contraceptives (e.g., the pill, implant) use synthetic oestrogen and/or progesterone to inhibit FSH production, which prevents egg maturation and ovulation.
- Non-hormonal contraception methods create a physical or chemical barrier to prevent sperm meeting an egg (e.g., condoms, copper IUD) or involve permanent sterilisation.
Formulae
Menstrual Cycle Sequence: FSH → Oestrogen → LH → Progesterone To understand the sequence of hormonal peaks and their primary effects during the 28-day menstrual cycle. FSH from the pituitary starts the process. Oestrogen from the ovaries follows, triggering an LH surge from the pituitary, which causes ovulation. Finally, progesterone from the empty follicle maintains the uterus lining.
Definitions
- Hormone
- A chemical substance produced by an endocrine gland and transported via the blood to a specific target organ to exert an effect.
- Endocrine Gland
- A ductless gland that synthesises hormones and secretes them directly into the bloodstream. Examples include the pituitary and adrenal glands.
- Target Structure
- A cell, tissue, or organ that has specific receptors for a hormone, allowing it to respond to that hormone's signal.
- Ovulation
- The release of a mature egg from an ovary, which is triggered by a sharp increase in Luteinising Hormone (LH) around day 14 of the menstrual cycle.
Worked example
A hormonal contraceptive skin patch releases a steady, high level of oestrogen and progesterone into the bloodstream. Which hormone's production by the pituitary gland is most directly inhibited by this action? A) Testosterone B) Adrenaline C) FSH D) LH and Progesterone
- 1
Identify the key information:
The patch releases high levels of oestrogen and progesterone.
- 2
Recall the negative feedback mechanism in the menstrual cycle.
High levels of oestrogen and progesterone signal to the pituitary gland to stop producing other hormones.
- 3
Specifically, oestrogen and progesterone inhibit the release of Follicle-Stimulating Hormone (FSH).
- 4
By inhibiting FSH, the development of a new egg follicle in the ovary is prevented, which is the primary contraceptive effect.
- 5
Evaluate the options:
A and B are unrelated to the menstrual cycle.
D is partially correct as LH is also inhibited, but progesterone is released *from* the patch, not inhibited.
C is the most direct and primary inhibition target to prevent the cycle from starting.
Answer: C
Common mistakes
- ×Mixing up the hormonal sequence or roles in the menstrual cycle. A common error is thinking FSH causes ovulation (it's LH) or that progesterone builds the uterus lining (it's oestrogen; progesterone maintains it).
- ×Confusing the gland sources. Remember FSH and LH are released from the pituitary gland in the brain, whereas oestrogen and progesterone are primarily produced in the ovaries.
- ×Misunderstanding how hormonal contraception works. It does not create a physical barrier; it manipulates the body's natural hormone levels to prevent ovulation from occurring in the first place.
No-calculator tips
- ✓Use the mnemonic 'FOLP' (Follicle-stimulating hormone, Oestrogen, Luteinising hormone, Progesterone) to remember the order in which the four key menstrual hormones peak.
- ✓Think of hormonal contraception as creating a 'pseudo-pregnancy'. The high levels of progesterone and oestrogen mimic pregnancy, which naturally suppresses ovulation.
- ✓For Adrenaline, think of its effects as everything needed to 'run away or fight': more glucose for energy, faster heart rate to pump blood to muscles, and wider pupils to see better.