Endocrine and reproductive physiology
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| hypothalamus/ˌhaɪpəʊˈθælæməs/ | A brain region that helps regulate homeostasis and links nervous control with hormonal signalling. |
| pituitary/pɪˈtjuːɪtəri/ | pituitary |
| target gland | target gland |
| primary/ˈpraɪməri/ | primary |
| secondary/ˈsekəndəri/ | secondary |
| menstrual cycle/ˈmenstruːəl ˈsaɪkl/ | menstrual cycle |
| ovulation/ˌɒvjʊˈleɪʃn/ | The release of an egg cell from an ovary. |
The slow control layer
- Hormones are the body's slow control layer: they signal along an axis, act at a distance and feed back at the top.
- Every axis follows one grammar, so learning it once explains a dozen syndromes.
The axis
- The hypothalamus 下丘脑 releases a releasing hormone; the pituitary 垂体 answers with a trophic hormone; the target gland 靶腺 makes the effector hormone.
- The effector hormone feeds back negatively on both the pituitary and the hypothalamus.
Put the thyroid axis in order.
Độ khó 3/5 · 200 xu + phần thưởng nhỏ khi hoàn thành lần đầu tiên hôm nay
Releasing, trophic and effector hormones, then negative feedback to both higher levels.
Which level failed?
- In primary 原发性 failure the target gland fails: the effector hormone is low and the trophic hormone is HIGH, because feedback is released.
- In secondary 继发性 failure the pituitary fails: both are low. One pattern pair works for every axis.
Low cortisol with a high ACTH points to failure where?
Độ khó 1/5 · 100 xu + phần thưởng nhỏ khi hoàn thành lần đầu tiên hôm nay
The pituitary is responding to the low cortisol by raising ACTH, so the gland it drives has failed.
Why TSH is the screen
- TSH responds very steeply to free T4: a small fall in T4 makes TSH rise many-fold.
- So the axis amplifies an early thyroid failure before symptoms or a clearly low T4 appear. Feedback, not assay sensitivity, makes TSH the screening test.
TSH can rise above normal while free T4 is still within its normal range.
Độ khó 1/5 · 100 xu + phần thưởng nhỏ khi hoàn thành lần đầu tiên hôm nay
TSH responds very steeply to small T4 changes, so it signals early thyroid failure before T4 leaves its range.
The reproductive axis
- GnRH → LH and FSH → ovaries or testes → sex steroids, with inhibin feeding back on FSH alone. The menstrual cycle 月经周期 is this axis on a monthly rhythm.
- Once per cycle, rising oestradiol flips from negative to positive feedback and triggers the LH surge: ovulation 排卵. The phase after it lasts about 14 days.
The phase after ovulation lasts about 14 days. In a regular 35-day cycle, on about which day does ovulation happen?
Độ khó 2/5 · 140 xu + phần thưởng nhỏ khi hoàn thành lần đầu tiên hôm nay
35 − 14 = day 21. Cycle length varies mostly in the phase before ovulation.
What triggers the LH surge?
Độ khó 1/5 · 100 xu + phần thưởng nhỏ khi hoàn thành lần đầu tiên hôm nay
Sustained high oestradiol flips the axis's sign once per cycle, releasing a burst of LH that triggers ovulation.
Worked example: reading thyroid labs
- (Fictional labs) Low free T4 with high TSH: the thyroid has failed (primary). The pituitary is shouting at a gland that cannot answer.
- Low free T4 with low or normal TSH: the pituitary or hypothalamus has failed (secondary). Same hormone, opposite partner, different disease.
Match each pattern to the failing level.
Độ khó 2/5 · 140 xu + phần thưởng nhỏ khi hoàn thành lần đầu tiên hôm nay
Read each effector hormone with its trophic partner and the level of the fault follows.
Worked example: high LH without ovulation
- (Fictional work-up) No periods and a high LH. Without ovulation there is little progesterone, and progesterone normally slows the hypothalamus's GnRH pulses.
- Faster pulses favour LH over FSH, so LH runs high (the PCOS pattern). Oestrogen without progesterone also explains the risk to the uterine lining.
Three common slips
- Reading one hormone alone. A cortisol or T4 means little without its trophic partner.
- The posterior pituitary as a gland. It stores and releases ADH and oxytocin made in the hypothalamus; it is neural tissue.
- Mixing the cycle's phases. Oestrogen leads before ovulation; progesterone leads after it.
Recap
- Releasing → trophic → effector hormone, with feedback to both higher levels.
- Primary failure: trophic high. Secondary failure: both low. TSH's steep response makes it the screen.
- Ovulation is oestradiol's switch to positive feedback, driving the LH surge.