CIRCADIAN RYTHMS BY BAMIDELE OLUBAYODE - PowerPoint Presentation

Slide1

CIRCADIAN RYTHMS

BYBAMIDELE OLUBAYODEBOWEN UNIVERSITY, IWOCOLLEGE OF HEALTH SCIENCESPHYSIOLOGY PROGRAMME

INTRODUCTION

Most organisms have evolved to coordinate their activities within the day-night cycle caused mainly by the earth rotation rather than simply responding to the day light transition.It would appear that such organisms have evolved real clocks to the biological processes.The biological clock keeps record of the event that occurs once in a day.Even in the absence of environment time cues, it maintains a period close to 24 hours.

The term Circadian comes from two Latin words namely:

- “Circa” means around/about - “diem/ dies” means dayCircadian means “about a day”

source: Premnath

MEANING OF CIRCADIAN RHYTHM

It is any biological process that displays an endogenous, entrainable oscillation of about 24 hours. Although circadian rhythms are endogenous (built-in, self sustained), they are adjusted (entrained) to the local environment by external cues called Zeitgebers, commonly the most important of which is day light.Chronobiology is the study of circadian rhythms.

HISTORY OF CIRCADIAN RHYTHM

The first written record was in the 4th century BC. Adrosthenes, a scribe for Alexander the great, wrote that he observed on the march to India that the leaves of the tamarind tree always opened during the day and closed at night.The first recorded observation of an endogenous circadian rhythm took place in 1729 by the French scientist Jean Jacques de Mairan.In 1832 de Candolle discovered

that

the Mimosa

opens it’s leaves 1-2 hours earlier each day

HISTORY OF CIRCADIAN RHYTHM CONT'D

In 1896, Patrick and Gilbert observed that during a prolonged period of sleep deprivation, sleepiness increase and decreases with a period of about 24 hours. Simpson and Gailbraith in 1906 found daily temperature rhythms in monkeys persist in constant darkness

.

In 1918, J.S Szymanski showed that animals are capable of maintaining 24-hour activity pattern in the absence of external cues.

HISTORY OF CIRCADIAN RHYTHM CONT'D

In 1922, Richter shows persistent rhythms of activity in animals (rats).Joseph Takahadi discovered the first mammalian “clock gene” (clock) using a 24-hour biological rhythm controlled by a “pacemaker”in the brain that sends messages to other systems in the body.

BIOLOGICAL CLOCK

Biological clocks are organisms'natural timing devices, regulating the cycle of circadian rhythms.They are made up of specific molecules that interact with cells throughout the body.Almost every tissue and organ contains biological clocks.Genes that make the clocks'molecular components have been identified in humans, fruit flies, mice, plants and other organisms.

MASTER CLOCK CONTROLLING CIRCADIAN RHYTHM

A master clock in the brain coordinates all the biological clocks in a living thing, keeping the clocks in synchrony.In vertebrates, the master clock is a group of approximately 20,000 nerve cells that form a structure called the suprachiasmtic nucleus (SCN).The SCN is in a part of the brain called the hypothalamus and receives direct input from the eyes.

IMPORTANCE OF CIRCADIAN RHYTHM

It has been shown to regulate various aspects of : - Metabolism - Sleep-wake cycle - Body temperature - Behaviour in humans as well as other organisms -Pattern of activity such as: eating habits and digestion Hormonal secretion

Neurotransmitter secretion

In plants, circadian clock control processes such as leaves and petals movement, closing of stomata & metabolic activities associated with photosynthesis.

IMPORTANCE OF CIRCADIAN RHYTHM

The photoperiodic system appears to depend on circadian clock to measure the duration of the day and night, thus maintaining the passages of the day and season.Arabidopsis thaliana a model species for plant genetics exhibits visible circadian rhythm in the leaves movements and less obvious rhythm in the expression of many genes.However, the daily rhythm of life is maintained by the circadian clock.

ELEMENTS OF CIRCADIAN RHYTHM

Circadian rhythms are believed to have three elements1 The input pathway which relay environmental information to a pacemaker.2. The circadian pacemaker which is also called Oscillator that generate the oscillation.3. The

output

pathway through which the pacemaker regulates various output rhythms.

The input and output of the circadian system are specific to each organism but the mechanism of the pacemaker appears to be similar in all organisms.

CIRCADIAN RHYTHMS AND SLEEP PATTERNS

Circadian rhythm has effect on the sleep patterns.The SCN controls the production of melatonin, a hormone that causes sleepiness. It receives information about the incoming light from the optic nerves which relay information from the eyes to the brain.When there is less light - for example, at night - the SCN signals the brain to make more melatonin to cause drownsiness.

MOLECULAR MECHANISM

In 2017, researchers Jeffrey C. Hall, Michael Rosbash and Michael W. Young won the prestigious Nobel Prize for their work on molecular mechanism of circadian rhythms.They carried out the research on fruit flies which have a very similar genetic make up to humans. In them, they isolated a gene that helps control the body's clock. They demonstrated that the gene produces a protien that builds up in cells overnight, then breaks down during the day.The process can affect sleep and brain functions.

FACTORS AFFECTING CIRCADIAN RHYTHM

Changes in the body and environmental factors can cause circadian rhythm and natural light- dark to be out of sync.- Mutations or change in certain genes can affect biological clocks- Jet lag or shift work causes changes in the light- dark cycle.- Light from electronic device at night can confuse human biological clocks.

FACTORS AFFECTING CIRCADIAN RHYTHM

Changes in the body and environmental factors can cause circadian rhythm and natural light- dark to be out of sync.- Mutations or change in certain genes can affect biological clocks- Jet lag or shift work causes changes in the light- dark cycle.- Light from electronic device at night can confuse human biological clocks.

EFFECT OF CHANGES IN CIRCADIAN RHYTHM

Changes in the natural light- dark cycle can cause sleep disorder which may lead to: ObesityDiabetesDepressionBipolar disorderSeasonal affective disorder

EFFECT OF CHANGES IN CIRCADIAN RHYTHM

Changes in the natural light- dark cycle can cause sleep disorder which may lead to: ObesityDiabetesDepressionBipolar disorderSeasonal affective disorder

CIRCADIAN RHYTHM AND JET LAG

When you pass through different time zones, your biological clock will be different from the local time.For instance, if you fly East from California to New York, you lose 3 hours when you wake up at 7:00am on the east coast, your biological clock is still running on West coast time, so you feel the way you might at 4:00am.Your biological clock will reset, but it will do so at a different rates. It often takes a few days for your biological clock to align with a new time zone.Adjusting after gaining time may be slightly easier than after losing time because the brain adjusts differently in the two situations

REFERENCES

National Institute of General Medical Sciences: Circadian Rhythm.www.slide share.net. circadian rhythm by Premnath Ramachandranpillai.

REFERENCES

National Institute of General Medical Sciences: Circadian Rhythm.www.slide share.net. circadian rhythm by Premnath Ramachandranpillai.

THANK YOU