Unit Two Essays in Higher Human Biology

CFE Higher Human Biology: Physiology & Health

This essay booklet covers the essential physiological processes that keep your body functioning properly. You'll explore how hormonal control systems regulate reproduction, how your cardiovascular system adapts to different needs, and the various medical procedures that support human health.

The topics connect closely with real-world applications, from fertility treatments to antenatal care. Understanding these processes will help you see how your body maintains balance through complex feedback mechanisms.

Key insight: Most physiological processes involve negative feedback - your body's way of maintaining stability by responding to changes.

Hormonal Control: First Half of the Menstrual Cycle

The menstrual cycle begins with menstruation - the breakdown of the endometrium (uterus lining). This seemingly destructive process actually sets up the next cycle perfectly.

Your pituitary gland kicks things off by secreting FSH (follicle-stimulating hormone), which stimulates a follicle in your ovary to grow. This growing follicle produces oestrogen, which has multiple jobs: repairing the endometrium, changing cervical mucus consistency, and triggering LH production.

LH (luteinising hormone) from the pituitary causes ovulation around day 14. Meanwhile, rising oestrogen levels create a negative feedback loop by inhibiting FSH production - your body's clever way of preventing too many eggs from developing at once.

Remember: The first half is all about preparing for ovulation - FSH grows the follicle, oestrogen repairs the lining, and LH triggers egg release.

Complete Menstrual Cycle Control

The pituitary gland acts as the master controller of your menstrual cycle through negative feedback control. It produces both FSH and LH, which work together to coordinate ovarian and uterine changes.

FSH stimulates the Graafian follicle to mature and release oestrogen. Oestrogen repairs the endometrium after menstruation and triggers LH release. When LH surges, it causes ovulation and transforms the empty follicle into the corpus luteum.

The corpus luteum secretes progesterone, which maintains and thickens the uterine lining. Progesterone also inhibits FSH and LH production. When progesterone levels drop (if pregnancy doesn't occur), the corpus luteum degenerates, triggering menstruation and starting the cycle again.

Top tip: Think of it as a perfectly timed relay race - each hormone passes the baton to the next, with feedback loops ensuring everything stays coordinated.

Events Before and After Ovulation

Leading to ovulation: Your pituitary gland releases FSH, stimulating follicle growth in the ovary. The follicle produces oestrogen, which repairs the endometrium and stimulates LH production. The LH surge triggers ovulation, while rising oestrogen creates negative feedback to prevent excessive FSH release.

After ovulation: The empty follicle transforms into the corpus luteum, which secretes progesterone (and some oestrogen). Progesterone maintains and thickens the endometrium, preparing it for potential pregnancy.

Progesterone also inhibits FSH and LH production, preventing further ovulation. Towards cycle's end, progesterone levels drop, causing corpus luteum degeneration. This triggers menstruation - the breakdown of the endometrium - and the cycle begins again.

Key point: Ovulation marks the transition from oestrogen dominance (building up) to progesterone dominance (maintaining).

Hormonal Control of the Testes

Male hormone control is simpler but just as important as the female cycle. Your pituitary gland produces FSH and LH (sometimes called ICSH in males), which work together to maintain sperm production and testosterone levels.

FSH promotes sperm production in the seminiferous tubules, whilst LH stimulates testosterone production in the interstitial cells. Testosterone has dual roles - it supports sperm production and influences semen production from the prostate gland and seminal vesicles.

Negative feedback keeps everything balanced: higher testosterone levels inhibit both LH and FSH production. This ensures testosterone stays within normal range and prevents overproduction of sperm.

Remember: Unlike the female cycle's monthly changes, male hormone control maintains steady levels through continuous negative feedback.

Treating Male and Female Infertility

Modern fertility treatments work by either boosting natural processes or bypassing problems altogether. Drug treatments can stimulate ovulation by preventing oestrogen's negative feedback on FSH or by mimicking FSH and LH effects.

Artificial insemination helps when men have low sperm counts - multiple sperm samples are collected and inserted directly into the female reproductive tract. ICSI (intra-cytoplasmic sperm injection) takes this further by injecting a single sperm head directly into an egg.

IVF (in vitro fertilisation) involves fertilising eggs outside the body, then transferring resulting embryos into the uterus. Pre-implantation genetic diagnosis (PGD) can identify genetic disorders before embryo transfer, helping prevent inherited conditions.

Hope factor: These treatments give many couples realistic chances of pregnancy, even when natural conception seems impossible.

Biological Basis of Contraception

Contraception prevents fertilisation by targeting the fertile period around day 14 of the menstrual cycle. You can detect this fertile window through rising body temperature or changes in cervical mucus (it becomes thinner).

Hormonal contraceptives (pills, injections, implants) contain oestrogen and progesterone. Taking these hormones daily for three weeks increases blood hormone concentrations, creating negative feedback that inhibits the pituitary gland.

This reduced FSH and LH production prevents egg maturation and ovulation - no egg means no pregnancy. Interestingly, prolonged breastfeeding also acts as contraception through similar hormonal suppression.

Science fact: The contraceptive pill essentially tricks your body into thinking it's already pregnant, preventing further ovulation.

Antenatal Screening and Testing

Antenatal care involves multiple screening procedures to monitor both maternal and foetal health. Basic checks include blood pressure, blood type, urine tests, and general health monitoring throughout pregnancy.

Ultrasound scans serve different purposes: dating scans (8-14 weeks) determine pregnancy stage and due dates, while anomaly scans (18-20 weeks) detect serious physical problems. Biochemical tests identify marker chemicals that indicate medical conditions, though these can sometimes give false positives.

Diagnostic testing follows concerning results. Amniocentesis analyses cells from amniotic fluid, whilst chorionic villus sampling (CVS) uses placental cells. Both create karyotypes to detect chromosome abnormalities like Down's syndrome. CVS occurs earlier but carries slightly higher miscarriage risk.

Important: These procedures help identify potential problems early, allowing parents to make informed decisions about pregnancy management.

Substance Exchange Between Plasma and Cells

Plasma (blood's liquid component) carries dissolved substances like oxygen, carbon dioxide, glucose, amino acids, and urea around your body. The actual exchange happens at capillaries, which have large surface areas, thin walls, and narrow diameters for efficient transfer.

High pressure at capillaries' arterial end forces plasma out (except plasma proteins and blood cells, which stay in blood), creating tissue fluid that bathes your cells. Substances diffuse between tissue fluid and cells - nutrients in, waste products out.

Most tissue fluid returns to blood, but excess enters lymphatic vessels as lymph, which eventually returns to your bloodstream. This system ensures cells get nutrients whilst removing metabolic waste for excretion.

Key concept: Think of capillaries as tiny distribution centres where your blood delivers supplies and collects rubbish from every cell.

Control of Heart Rate

Your heart rate adjusts constantly through negative feedback control, responding to changing body needs. Receptors in your carotid arteries and aorta detect changes in blood pressure and CO₂ concentration.

When CO₂ increases or blood pressure drops, the cardio-acceleratory centre in your brain's medulla activates. Sympathetic nerves release noradrenaline at the heart, increasing heart rate and stroke volume (cardiac output).

Conversely, when CO₂ decreases or blood pressure rises, the cardio-inhibitory centre activates. Parasympathetic nerves release acetylcholine, decreasing heart rate and contraction force. Adrenaline from adrenal glands can also boost cardiac output during stress ('fight or flight').

Amazing fact: Your heart adjusts its rhythm thousands of times daily without you thinking about it - that's automatic nervous system control at its finest.