6.6 thyroxin, leptin and melatonin

how long does jet lag last?

JL usually lasts for a few days and symptoms resolve as the body resynchronizes it's circadian rhythm

thyroxin

a hormone responsible for increasing the basal metabolic rate by stimulating carbohydrate and lipid metabolism it acts on nearly every tissue on the body and is essential for proper development and differentiation of cells

jet lag

a physiological condition condition that is caused by a change in the body's normal circadian rhythm

where is leptin produced?

by the adipose cells in adipose tissue

why are leptin treatments not an effective way to control obesity in humans?

despite it's natural function, many patients experienced adverse side effects from leptin injections including skin irritations

symptoms of jet lag

headaches, fatigue, lethargy, increased irritability and reduced cognitive function

melatonin

hormone that controls circadian rhythms and regulates the body's sleep schedule it is most present at night time

leptin

hormone that regulates fat stores within the body by suppressing appetite

how much leptin is in the blood stream of humans?

humans have naturally high levels of leptin in the blood stream

how does melatonin help alleviate jetlag?

if a jet lagged individual takes melatonin near the sleep time of their new time zone it can help with the resynchronization by artificially increasing melatonin levels at the new night time, the body can respond quicker to the new sleep schedule

where is melatonin produced and how is production stimulated?

in the pineal gland within the brain it's production is stimulated by changes in light

how does it leptin work?

it binds on receptors within the hypothalamus to inhibit appetite and hence reduce food intake

how does iodine deficiency affect the the thyroid gland?

it causes the gland to enlarge and result in goitre

what is is secreted by?

it's secreted by the thyroid gland

leptin and age

leptin resistance also develops with age and increases the potential for weight gain later in life e.g. middle age dad bods

summary of leptin

leptin suppresses your appetite and is produced in the adipose cells more leptin means less appetite less leptin means stronger appetite

what were mice experiments to test leptin as a form of treatment for individuals with obesity like?

leptin trials on mice were intially conducted by surgically fusing the blood circulation of obese and healthy mice (parabiosis) the obese mice were obese due to either a leptin gene mutation or a defective leptin receptor

what happened when the obese mouse with a DEFECTIVE LEPTIN RECEPTOR was parabiotically fused with a healthy mouse?

leptin was transferred to the healthy mouse as the obese mouse had over produced leptin to compensate for low receptor sensitivity the obese mouse remained obese as the body is already desensitized to leptin the healthy mouse became abnormally thin (emaciated) due to the abnormally high levels of leptin transfgerred into it's blood stream

how does melatonin secretion change in response to different light exposure?

light exposure to the retina is relayed via the suprachiasmatic nucleus in the hypothalamus and inhibits melatonin secretion e.g. morning = awake non-light exposure aka darkness stimulates melatonin production in the pineal gland and results in higher concentrations of melatonin at night over some time melatonin secretion becomes trained to anticipate the onset of darkness and the approach of day time

how do melatonin levels change with age?

melatonin levels naturally decrease with age and leads to changes in sleeping patterns for the elderly

what are most cases of obesity caused by (in relation to leptin)?

most obesity cases are caused by a unresponsiveness to leptin not leptin defiency

leptin and obesity

obese people are constantly exposed to producing higher levels of leptin and so their body becomes desensitized to the hormone the desensitization causes them to feel more hungry (as the suppressant affect of leptin is not as strong) and they are less likely to recognize that they are full, causing them to further overeat

leptin production when overeating

overeating causes more adipose cells to form and hence more leptin is produced, trying to further suppress appetite

why does jet lag happen?

the body cannot rapidly adjust to a new time zone after air travel the pineal gland still continues to secrete melatonin according to the old timezone and hence the sleep schedule is adjusted to the old timezone, not the new

thyroxin release in cold temperatures

the hypothalamus sends signals in response to the cold temperatures to stimulate thyroxin release from thyroid this increases metabolic rate and generates heat (raises body temp)

circadian rhythms

these are the body's physiological responses to the 24 hour day/night cycle

what are circadian rhythms driven by?

they are driven by an internal (endogenous) circadian clock however they can also be regulated by external factors

leptin production when undereating/periods of starvation?

this causes a reduction in adipose tissue and hence less leptin is released the reduced leptin production triggers hunger

why would iodine deficiency lead to decreased production of thyroxin?

thyroxin is partially composed of iodine and hence a deficiency of iodine in the diet will lead to decreased production of thyroxin

what initiates thyroxin production?

thyroxin production occurs in response to signals from the hypothalamus about changed in body temperature this is for the purpose of stimulating heat production or reducing heat production

thyroxin release in hot temperatures

warmer temperatures cause the hypothalamus to inhibit signals for thyroxin release from the thyroid glands this decreases metabolic rate and reduces heat production

why is sleep and therefore the presence of melatonin important?

we need to sleep because during sleep physiological changes occur in body temperature, brain wave activity and hormonal production

what happened when the obese mouse with no leptin was parabiotically fused to the healthy mouse?

when the obese mouse with no leptin was parabiotically fused to a healthy mouse: - leptin in the blood of the healthy mouse was transferred to the obese mouse - the obese mouse responded to the leptin and began to lose weight - both mice healthy this demonstrated the potential viability of leptin treatment