3.6.4Inquiry Process
Epinephrine and Melatonin — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 144 of 160
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.
Section 1 of 5Epinephrine in the Stress Response
Source
- Source The adrenal medulla releases epinephrine when the sympathetic nervous system signals danger or stress.
Cardiovascular effect
- Cardiovascular effect Heart rate and the strength of contraction increase, and blood is diverted to muscles from the gut and skin.
Metabolic effect
- Metabolic effect Glycogen in the liver is broken down so glucose enters the blood and fuels respiration.
Breathing
- Breathing Airways widen to allow more air in, supplying extra oxygen for the increased energy demand.
Receptors
- Receptors Epinephrine binds to G-protein-linked receptors on target cells, so a second messenger inside the cell carries out the response.
Section 2 of 5Melatonin and Circadian Rhythms
1
Light enters the eye and is detected by specialised cells in the retina, which send signals to the suprachiasmatic nucleus in the hypothalamus.
2
In daylight the signals prevent the pineal gland from secreting melatonin, so melatonin levels are low.
3
In darkness these signals fall, and the pineal gland releases melatonin into the blood.
4
Melatonin acts on the brain to promote sleep and reduce body temperature, helping to set a 24 hour rhythm.
5
Melatonin levels fall again before dawn, and light the next morning keeps the rhythm matched to the day.
Section 3 of 5Comparison and Applications
Comparison and Applications
Stimulus
- Stimulus Epinephrine release is triggered by stress, whereas melatonin release is controlled by the light-dark cycle.
Jet lag
- Jet lag Rapid travel across time zones leaves the melatonin rhythm out of step with local time until it gradually resets.
Day length
- Day length In some mammals, longer nights give a longer melatonin signal, which triggers seasonal breeding.
Duration
- Duration Epinephrine is cleared in minutes, but melatonin follows a daily cycle across hours.
Treatment
- Treatment Synthetic melatonin is sometimes taken to help reset the body clock, showing how hormone knowledge is used in medicine.
| Hormone | Source | Main effect |
|---|---|---|
| Epinephrine | Adrenal medulla | Prepares for fight or flight |
| Melatonin | Pineal gland | Sleep timing, circadian rhythm |
Section 4 of 5Worked Example
Question
- Melatonin concentration is 5 units at midday and 55 units at 02:00.
- Calculate the percentage increase and explain the pattern.
- Increase = 55 − 5 = 50 units.
- Percentage increase = 50 ÷ 5 × 100 = 1000%.
- Midday light inhibits the pineal gland, while darkness at night removes this inhibition.
Answer A 1000% increase, because melatonin is released in darkness.
Section 5 of 5Exam Checklist & Tips
3.6.4 – Key Points for the Exam
- Epinephrine Hormone from the adrenal medulla that prepares the body for action.
- Melatonin Hormone from the pineal gland that helps control sleep rhythms.
- Circadian rhythm Biological cycle of about 24 hours.
- Pineal gland Small gland in the brain that releases melatonin in darkness.
Common Mistakes
- Saying melatonin is released in daylight; darkness stimulates it.
- Mixing up the adrenal medulla (epinephrine) with the cortex (steroid hormones).
- Treating jet lag as tiredness only; it reflects an out-of-phase body clock.
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