Lecture 6

Question 1

What is chronobiology

Answer 1

Study of timescales and cycles in biology

Branch of biology concerned with natural physiological rhythms

Question 2

What are the 3 types of biological rhythms

Answer 2

1. Ultradian (less than 24hrs)
2. Circadian (24hr)
3. Infradian (more than 24hr)

Question 3

Example of ultradian rhythm

Answer 3

Appetite e.g. ghrelin (meals); cortisol (pulse)

Question 4

Example of circadian rhythm

Answer 4

Cortisol: lowest @ midnight (sleep), peak @ 8am (after awakening)

Question 5

Example of Infradian rhythm

Answer 5

Menstral Cycle

Question 6

What are circadian rhythms controlled by

Answer 6

Controlled by peripheral “clocks” that are governed by a “master or central clock”

Question 7

What do circadian rhythms control

Answer 7

Controls: gene expression, regulation of enzyme activities, neural function, hormone secretion

Question 8

What do circadian rhythms coordinate

Answer 8

Coordinate: Sleep, nutrient supply, activity patterns with metabolic processes required throughout the day

Question 9

What does the disruption of circadian rhythms cause

Answer 9

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

Question 10

What is the suprachiasmatic nucleus

Answer 10

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)

Question 11

What controls metabolic clocks

Answer 11

• 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

Question 12

What are impacts of disrupting circadian rhythms in shift works

Answer 12

Shift works have greater incidences of:
- Heart attacks
- Obesity
- Diabetes
- Cardiovascular complications
- Cancer
- Alzhiemer’s disease

Question 13

What are impacts of disrupting circadian rhythms in night owls

Answer 13

Night owls are more likely to suffer from mental stress or be smokers

Question 14

How are Circadian Rhythms related to health

Answer 14

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

Question 15

How is height used as a biomarker

Answer 15

Heights charted over years by doctors to aller of possible osteoporosis development and increased risk of bone fracture

Question 16

Whats the criteria for osteoporosis

Answer 16

Criteria for osteoporosis is losing more than 2 cm per year

Question 17

Issues with height as a biomarker

Answer 17

Criteria for osteoporosis is losing more than 2 cm per year
HOWEVER there is a diurnal (daily) variation of about 2 cm in height

Question 18

Limitations of using height as biomarker for osteoporosis

Answer 18

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

Question 19

Better biomarkers for determining osteoporosis

Answer 19

• Dual energy X-ray absorptiometry (DEXA)
• Used to determine bone material density in more definitive approach
• Generally safe
• Commonly done in femar and back

Question 20

What do bones do

Answer 20

Bones full of living cells - some building mineral structure some destroying

Question 21

Whats the relation between Ca and bones

Answer 21

• 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

Question 22

How does DEXA calculate bone density

Answer 22

DEXA estimates the amount of x ray absorbing dense material, hydroxyapatite, packed in extracellular space of bone

Question 23

Whats the use of plasma Ca

Answer 23

Allow normal cell signaling and generation of action potentials

Question 24

What hormones regulate Ca2+

Answer 24

PTH prevents decrease in plasma Ca2+
Calcitonin prevents increase in plasma Ca2+

Question 25

How does age relate to bone density loss

Answer 25

Women and men have different bone density and patterns of bone loss as they age

Age of peak bone mass is 20 to 30

Question 26

How is BMD via DEXA used as a biomarker

Answer 26

Is based on T-scores

Biomarker as time of day and low sensitivity is not an issue

Question 27

How to maximize bone density as a 20-30 year old

Answer 27

1. Consume sufficient Ca in food and supplements in adolescence and early adulthood
2. Get adequate VD from sun exposure, diet and supplements
3. Participate in weight bearing physical activity or exercise most days of meek
4. Maintain stable body mass
   Get plenty of sleep

Question 28

What hinders maximal bone density

Answer 28

Smokin, alcohol, caffeine
High phosphate
Drugs, eg corticosteroids