BIOLOGICAL RHYTHMS: IT’S A MATTER OF TIME

Text: Rhythms of Life

Russell Foster and Leon Kreitzman

• What are Biological Rhythms?

• What are Rhythms?

Pattern

Sequence

Regularity

Progression

Time

Measure

Beat

What is a rhythm?

Rhythm = sequence of events that repeat themselves in the same order and with the same time interval, over and over again.

Biological rhythm: a biological event or function with a pattern of activity that is repeated over and over again at a constant time interval.

Biological Rhythms

Heart rate

Breathing

Hormone secretion

Menstrual cycle

Body temperature

Sleep/wake cycle Time

What are examples of Biological Rhythms?

• Biological Rhythms are the product of an internal biological timekeeping system which is controlled by a biological clock

•Chronobiology

•

Two Broad Categories of Biological Rhythms

•high frequency –

•Ultradian

•Those that have a constant relationship with environmental rhythms –

•Have a geophysical counterpart

ENVIRONMENTAL RHYTHMS

Semi-Daily Rhythms•Tidal

Daily Rhythms•Solar

Monthly•Lunar

Quarterly•Seasons

Annual

Longer than a year

Spinning of earth on its axis 24h – solar day

Movement of earth around sun 365 days – year

Tilting of earth on its axis seasons

Movement of moon around earth 24.53 days – lunar month

24.8h – lunar day

Geophysical

Types of biological rhythms with a geophysical counterpart:

PeriodLength

NameChronobiological

NameExample

12.4 h tidal CIRCA TIDAL crab activity on shoreline

29 days monthly CIRCA LUNAR menstrual cycle, marine reproduction.

365 days

yearly CIRCANNUAL Hibernation, many reproductive cycles.

24 h daily CIRCADIAN (circa + diem)

sleep-wake cycle and many others

infradian

What Kind of Organisms Have Biological Rhythms?

What is the purpose of having a biological timekeeping system?

Promotes organism’s ability to survive by coordinating its activities

with changes in the environment

Coordinates internal processes

STROMATOLITE

Many organisms have several kinds of biological rhythms

Alexander the Great

4th Century BC

Tamarind Tree

de Mairan, 1729

endogenous

Du Monceau 1759

Circadian rhythms do not depend on temperature changes

Linneaeus 1751

Circadian rhythms are genetically determined

Linneaeus 1751

de Candolle 1832

When not exposed to environmental day/night rhythms plant leaves opened and closed on a 22 – 23 h cycle instead of a 24 h cycle

Free-running rhythm

•Circadian rhythms are endogenous.

•Endogenous rhythms are not exactly 24h.

•The periods of Circadian rhythms are genetically determined.

•Endogenous rhythms are temperature-compensated

Bees – 1910 Forel

1929 Beling

1950s Renner

Drosophila – 1950s Pittendrigh

PACEMAKER

TARGET TISSUE

BIOLOGICAL RHYTHMS (overt rhythms)

ZEITGEBER

TRANSDUCER

PACEMAKER

INTERMEDIATE ELEMENTS

TARGET TISSUES

BIOLOGICAL RHYTHMS

Endogenous, free-running rhythm

Activity (locomotor) rhythm

Chronobiology

Biological rhythm

Ultradian

Infradian

Circadian

Circatidal

Circalunar

Circannual

Endogenous

Free-running

Pacemaker

Target tissue

Overt rhythm

Nocturnal

Diurnal

LL

DD

LD 12:12

Study of biological timekeeping

Cyclical, repeated variation in a biological function

High frequency – repeats many times in a day

Repeats at intervals much longer than 24 hours

Approximately a day (24 hours)

Approximately every 12.4 hours ( with the tide)

Approximately once a month

Approximately once a year

Internally generated rhythm

Not synchronized to external signals

A structure that generates a rhythm

Tissue whose function is regulated by the pacemaker

A visible, measurable rhythm

Active at night

Active during the day

Constant light

Constant darkness

12 hours of light; 12 hours of dark