Biological rhythms

Question 1

What is a biological rhythm?

Answer 1

Any change in physiological activity that repeatedly becomes a pattern (daily, monthly, annually).

Question 2

What are the 3 biological rhythms?

Answer 2

1. Circadian
2. Infradian
3. Ultradian

Question 3

What is a circadian rhythm?

Answer 3

24 hour cycles that are part of the body’s internal clock.

• sleep wake cycle
• body temperature cycle
• hormones

Question 4

What is an infradian rhythm?

Answer 4

Rhythms that are naturally occurring cycles in the human body that last longer than 24 hours.

• menstruation
• seasonal affective disorder
• hibernation

Question 5

What is an ultradian rhythm?

Answer 5

Cycle has a period shorter than a day but longer than an hour.

• blood circulation
• pulse
• heart rate
• feeding
• sleep stages

Question 6

Explain the menstrual cycle as an infradian rhythm

Answer 6

Divided into 2 phases

1. Follicular phase:
   - Lasts 10-14 days.
   - Oestrogen and progesterone levels are at their lowest.
   - When bleeding stops, this phase begins, causing endometrium to grow and thicken to prepare for pregnancy.
   - FSH levels rise, causing maturation of several ovarian follicles and egg size triples
2. Ovulatory phase:
   - FSH signals ovaries to produce oestrogen, stimulating LH levels to surge at day 14 of cycle, triggering 1 follicle to burst and the largest egg is released into Fallopian tube.
   - Lasts 14 days.
   - After ovulation, LH causes corpus leuteum to develop from ruptured follicle.
   - Oestrogen and progesterone stimulate endometrium to prepare thick blanket of blood vessels that support the fertilised egg.
   - When pregnancy occurs, the blanket of blood vessels become placenta which surrounds the foetus until birth

Question 7

What is the main circadian rhythm?

Answer 7

The sleep/ wake cycle