Lecture 6 Flashcards
What is chronobiology
Study of timescales and cycles in biology
Branch of biology concerned with natural physiological rhythms
What are the 3 types of biological rhythms
- Ultradian (less than 24hrs)
- Circadian (24hr)
- Infradian (more than 24hr)
Example of ultradian rhythm
Appetite e.g. ghrelin (meals); cortisol (pulse)
Example of circadian rhythm
Cortisol: lowest @ midnight (sleep), peak @ 8am (after awakening)
Example of Infradian rhythm
Menstral Cycle
What are circadian rhythms controlled by
Controlled by peripheral “clocks” that are governed by a “master or central clock”
What do circadian rhythms control
Controls: gene expression, regulation of enzyme activities, neural function, hormone secretion
What do circadian rhythms coordinate
Coordinate: Sleep, nutrient supply, activity patterns with metabolic processes required throughout the day
What does the disruption of circadian rhythms cause
Disruption of circadian rhythms in experimental animals lead to health issues and premature aging, specifically:
- Elevated inflammatory cytokines
- Gastrointestinal function (ulcer, irritable bowel)
- Obesity
- Metabolic syndrome
What is the suprachiasmatic nucleus
Master or general clock is region of brain called “suprachiasmatic nucleus” which keeps time based on light signals from retina
– Every cell in body has subsidiary (peripheral) clock that coordinates its metabolism with the rest of the body (slave to central clock)
What controls metabolic clocks
- This is a process that’s not very well underwood
- Entrained with light and dark cycles (Still intact in most blind individuals as the retina still detects light)
- Likely that chemical signals are involved (but not proven)
– Probably involves melatonin (hormone produced by pineal gland of brain) - Blue spectrum light (screens/monitors) inhibit melatonin release
What are impacts of disrupting circadian rhythms in shift works
Shift works have greater incidences of:
- Heart attacks
- Obesity
- Diabetes
- Cardiovascular complications
- Cancer
- Alzhiemer’s disease
What are impacts of disrupting circadian rhythms in night owls
Night owls are more likely to suffer from mental stress or be smokers
How are Circadian Rhythms related to health
Risk of heart attacks are greatest in the morning
- No clear answer why yet BUT
- May be due to protein Klf15 (affects K+ efflux in heart)
- May be confination of caffeine, stress, high fat fast food, ect
How is height used as a biomarker
Heights charted over years by doctors to aller of possible osteoporosis development and increased risk of bone fracture
Whats the criteria for osteoporosis
Criteria for osteoporosis is losing more than 2 cm per year
Issues with height as a biomarker
Criteria for osteoporosis is losing more than 2 cm per year
HOWEVER there is a diurnal (daily) variation of about 2 cm in height
Limitations of using height as biomarker for osteoporosis
Varies during day
– Timing of measurements needs to be standardized
Needs to be measured overtime in each individual
Does Not change that much during disease process
– Low sensitivity
Does Not directly precede, or predict disease state
Better biomarkers for determining osteoporosis
- Dual energy X-ray absorptiometry (DEXA)
- Used to determine bone material density in more definitive approach
- Generally safe
- Commonly done in femar and back
What do bones do
Bones full of living cells - some building mineral structure some destroying
Whats the relation between Ca and bones
- Serve as functional Ca store for body
– When Ca is needed for non-bone tissues, its gained from the breakdown of mineral in bone AND when there is excess Ca in the bloodstream, it forms minerals in the bone
– Mineral structure in bone composed of hydroxyapatite - insoluble deposit of calcium and phosphate within extracellular protein matrix
How does DEXA calculate bone density
DEXA estimates the amount of x ray absorbing dense material, hydroxyapatite, packed in extracellular space of bone
Whats the use of plasma Ca
Allow normal cell signaling and generation of action potentials
What hormones regulate Ca2+
PTH prevents decrease in plasma Ca2+
Calcitonin prevents increase in plasma Ca2+
How does age relate to bone density loss
Women and men have different bone density and patterns of bone loss as they age
Age of peak bone mass is 20 to 30
How is BMD via DEXA used as a biomarker
Is based on T-scores
Biomarker as time of day and low sensitivity is not an issue
How to maximize bone density as a 20-30 year old
- Consume sufficient Ca in food and supplements in adolescence and early adulthood
- Get adequate VD from sun exposure, diet and supplements
- Participate in weight bearing physical activity or exercise most days of meek
- Maintain stable body mass
Get plenty of sleep
What hinders maximal bone density
Smokin, alcohol, caffeine
High phosphate
Drugs, eg corticosteroids
