6.6 Homeostasis Flashcards
Will the body always need to produce the same amount of ATP?
The body needs glucose to make ATP (via cell respiration), however the amount required will fluctuate according to demand
What can high levels of glucose in the blood do to an organism?
High levels of glucose in the blood can damage cells (creates hypertonicity) and hence glucose levels must be regulated
What are the two hormones controlling blood sugar concentration?
Two antagonistic hormones are responsible for regulating blood glucose concentrations – insulin and glucagon
Where are insulin and glucagon released from and where do they act?
These hormones are released from pancreatic pits (called the islets of Langerhans) and act principally on the liver
What is released when blood glucose levels are high?
Insulin is released from beta (β) cells of the pancreas and cause a decrease in blood glucose concentration
What does insulin promote?
This may involve stimulating glycogen synthesis in the liver (glycogenesis), promoting glucose uptake by the liver and adipose tissue, or increasing the rate of glucose breakdown (by increasing cell respiration rates)
What is released in response to low blood glucose concentration?
Glucagon is released from alpha (α) cells of the pancreas and causes an increase in blood glucose concentration
What is diabetes mellitus?
Diabetes mellitus is a metabolic disorder that results from a high blood glucose concentration over a prolonged period
What are the 2 different causes of diabetes mellitus?
It is caused by the body either not producing insulin (Type I) or failing to respond to insulin production (Type II)
How are the 2 different types of diabetes treated?
It is treated with either insulin injections (Type I only) or by carefully monitoring and controlling dietary intake (Type II)
When do the different types of diabetes develop?
1: usually occurs during childhood (early onset)
2: usually occurs during adulthood (late onset)
How do the different types of diabetes respond to insulin?
1:body does not produced sufficient insulin
2:body does not respond to insulin production
How do the two types of diabetes differ in terms of cause?
1: caused by the destruction of beta cells (autoimmune)
2: caused by down-regulation of insulin receptors
How do the two types of diabetes differ in treatment?
1: requires insulin injections to regulate blood glucose
2: controlled by managing lifestyle and diet
What is thyroxin?
Thyroxin is a hormone secreted by the thyroid gland in response to signals initially derived from the hypothalamus
Where does thyroxin act?
Thyroxin acts on nearly every tissue in the body and is essential to the proper development and differentiation of cells
What is the primary role of thyroxin?
The primary role of thyroxin is to increase the basal metabolic rate (amount of energy the body uses at rest)
How does thyroxin achieve its primary role?
This can be achieved by stimulating carbohydrate and lipid metabolism via the oxidation of glucose and fatty acids
What is the secondary role of thyroxin, as a side-effect of its primary function?
A consequence of increasing metabolic activity is the production of heat – hence thyroxin helps to control body temperature
When will thyroxin be released in regard to body temperature?
Thyroxin is released in response to a decrease in body temperature in order to stimulate heat production
A deficiency of what nutrient may lead to a thyroxine deficiency?
Thyroxin is partially composed of iodine and hence a deficiency of iodine in the diet will lead to decreased production of thyroxin
What disease will an iodine deficiency lead to?
Iodine deficiency will cause the thyroid gland to become enlarged, resulting in a disease known as goitre
What produces leptin and what is its role?
Leptin is a hormone produced by adipose cells that regulates fat stores within the body by suppressing appetite
Where does leptin bind and why?
Leptin binds to receptors located within the hypothalamus to inhibit appetite and thereby reduce food intake
What does overeating cause in relation to leptin?
Overeating causes more adipose cells to formed and hence more leptin is produced, suppressing further appetite
What do periods of starvation cause in relation to leptin?
Conversely, periods of starvation lead to a reduction in adipose tissue and hence less leptin is released, triggering hunger
When may a person become desensitised to leptin?
As obese people are constantly producing higher levels of leptin, their body becomes progressively desensitised to the hormone
What may leptin resistance in obese people lead to?
This means they are more likely to feel hungry, less likely to recognise when they are full and are hence more likely to overeat
What may leptin resistance increase with, other than weight?
Leptin resistance also develops with age, increasing the potential for weight gain later in life (e.g. the ‘middle-age spread’)
What was leptin thought to be a treatment for?
Because leptin suppresses appetite, it was considered as a form of treatment for individuals with clinical obesity
Theoretically, how should leptin treat obesity?
Theoretically, leptin injections would reduce hunger and limit food intake in obese individuals, leading to weight loss
How were leptin trials initially conducted?
Leptin trials were initially conducted by surgically fusing the blood circulation of obese and healthy mice (parabiosis)
What mice were used for experiments on leptin?
This experiment was conducted using mice that were either obese due to a leptin gene mutation or a defective leptin receptor
What were the two findings when the leptin-deficient mouse and healthy mouse were parabiotically fused?
Leptin in the blood of the healthy mouse was transferred to the obese mouse
What were the two findings when the no leptin mouse and healthy mouse were parabiotically fused?
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, demonstrating the potential viability of leptin treatment
What were the two findings when the mouse with defective leptin receptors and healthy mouse were parabiotically fused?
Leptin was transferred to the healthy mouse (the obese mouse overproduced leptin to compensate for low receptor sensitivity)
The obese mouse remained obese as its body could not respond to leptin
What happened to the healthy mouse when the mouse with defective leptin receptors and healthy mouse were parabiotically fused?
The healthy mouse became emaciated due to the abnormally high levels of leptin transferred into its bloodstream
Do humans naturally have high/low levels of leptin?
Most humans have naturally high levels of leptin in the bloodstream
Are most cases of obesity caused by an unresponsiveness to leptin or a leptin deficiency?
When linked to leptin activity, most cases of obesity are caused by an unresponsiveness to leptin and not a leptin deficiency
Were clincial trails with leptin efficient?
Hence, in clinical trials, very few participants experienced significant weight loss in response to leptin injections
What did patients experience in the clinical trial for leptin?
However, many patients did experience adverse side effects from leptin injections, including skin irritations
Therefore, can leptin be considered an effective way of controlling obesity?
NO!!!
For these reasons, leptin treatments are not considered to be an effective way of controlling obesity
Where is melatonin produced?
Melatonin is a hormone produced by the pineal gland within the brain in response to changes in light
When is melatonin secreted?
Melatonin is therefore secreted in response to periods of darkness, resulting in higher concentrations at night
What is the mechanism of melatonin inhibition?
Light exposure to the retina is relayed via the suprachiasmatic nucleus (in the hypothalamus) and inhibits melatonin secretion
What does melatonin secretion play a pivotal role in?
Melatonin secretion by the pineal gland of the brain plays a pivotal role in the control of circadian rhythms
What are circadian rhythms?
Circadian rhythms are the body’s physiological responses to the 24 hour day-night cycle
What are circadian rhythms controlled by?
Circadian rhythms are driven by an internal (endogenous) circadian clock, although they can be modulated by external factors
What is melatonin’s role in relation to circadian rhythms?
Melatonin is the hormone responsible for synchronising circadian rhythms and regulates the body’s sleep schedule
What is melatonin secretion suppressed by?
Melatonin secretion is suppressed by bright light (principally blue wavelengths) and hence levels increase during the night
Over a prolonged period of time, what does melatonin secretion become entrained to?
Over a prolonged period, melatonin secretion becomes entrained to anticipate the onset of darkness and the approach of day
Therefore what is the function of melatonin, for nocturnal and diurnal animals?
Melatonin functions to promote activity in nocturnal animals and conversely promotes sleep in diurnal animals (like humans)
What changes during sleep?
During sleep, necessary physiological changes occur in body temperature, brain wave activity and hormonal production
