Topic 6.6 Hormones, Homeostasis, and Reproduction Flashcards
Blood glucose function
Glucose needed to make ATP via cell respiration, but high levels of glucose can damage cells due to hypertonicity.
Hormones regulating blood glucose concentrations
Insulin and glucagon and released from the islets of Langerhans in pancreatic pits to act on the liver.
- Insulin: released from beta cells and cause a decrease in blood glucose concentration, stimulating glycogen synthesis in the liver and promoting glucose uptake by the liver/adipose tissue
Hormones regulating blood glucose concentrations
Insulin and glucagon are released from the islets of Langerhans in pancreatic pits to act on the liver by means to regulate blood glucose concentration.
Insulin
- Utilized when glucose levels are high (decreases blood glucose concentration)
- Released from beta cells
- Can stimulate glycogen synthesis in the liver and promote glucose uptake by the liver/adipose tissue
- Can also increase the rate of glucose breakdown
Glucagon
- Utilized when glucose levels are low (increases blood glucose concentration)
- Released from alpha cells
- Can stimulate glycogen breakdown in the liver and promote glucose release by the liver/adipose tissue
- Can also decrease the rate of glucose breakdown by reducing cell respiration rates
Diabetes
A metabolic disorder that results from a high blood glucose concentration over a prolonged period.
- Caused by the body either not producing insulin (Type I) or failing to respond to insulin production (Type II)
Type I diabetes
Insulin-dependent diabetes mellitus (IDDM)
- Body does not produce sufficient insulin
- Early onset
- Caused by the destruction of beta cells (autoimmune)
- Requires insulin injections to regulate blood glucose
Type II diabetes
Non-Insulin dependent diabetes mellitus (NIDDM)
- Body does not respond to insulin production
- Late onset
- Caused by the down-regulation of insulin receptors
- Controlled by diet and lifestyle
Thyroxin
A hormone secreted by the thyroid gland in response to signals initially derived from the hypothalamus.
- Acts on nearly every tissue in the body and is essential to the proper development and differentiation of cells
- Primary role: to increase the basal metabolic rate by stimulating carbohydrate and lipid metabolism
- Released in response to a decrease in body temperature to stimulate heat production
- Partially composed of iodine (decrease in diet will lead to decreased production of thyroxin)
Iodine deficiency
Thyroxin is partially composed of iodine, so a decrease of iodine in the diet will lead to decreased production of thyroxin (hypothyroidism). Conversely, too much iodine in the diet will lead to increased production of thyroxin (hyperthyroidism).
Leptin
A hormone produced by adipose cells that regulates fat stores within the body by suppressing appetite.
- Binds to receptors located within the hypothalamus to inhibit appetite, reducing food intake
- Overeating: more adipose cells formed (more leptin produced)
- Starvation: reduction in adipose tissue (less leptin released)
Obesity and leptin
Obese people are constantly producing higher levels of leptin, so their body becomes progressively desensitized to the hormone.
- More likely to feel hungry and less likely to recognize that they are full
- Resistance develops with age, increasing potential for weight gain later in life
Leptin trials on mice
Theory: leptin injections would reduce hunger and limit food intake in obese individuals, leading to weight loss. Therefore, an experiment was conducted using mice that were obese due to leptin gene mutation/ with a defective leptin receptor.
- Leptin defect: began responding to injections
- Receptor defect: remained obese
Leptin trials on humans
Cases of obesity are caused by an unresponsiveness to leptin, not a deficiency.
- In clinical trials, very few individuals experienced weight loss in response to injections
- Side effects: skin irritations, etc.
- Concluded to be ineffective
Melatonin
A hormone produced by the pineal gland within the brain in response to changes in light.
- Exposure to the retina is relayed via the hypothalamus, inhibiting melatonin secretion
- Melatonin secreted in response to periods of darkness, resulting in higher concentrations at night
Circadian rhythms
The body’s physiological responses to a 24-hour day/night cycle.
- Controlled by melatonin secretion by the pineal gland
- Driven by an internal (endogenous) circadian clock (but can be affected by external factors)
Melatonin’s role in regulating sleep schedules
- Secretion is suppressed by bright light (thus, levels increase at night)
- Over a prolonged period, melatonin secretion becomes entrained to anticipate the onset of darkness/daylight
- Functions to promote activity in nocturnal animals and sleep in diurnal animals (humans)
- During sleep, necessary physiological changes occur in body temperature, brain wave activity, and hormonal production
- Melatonin levels naturally decrease with age
Jet lag
A physiological condition resulting from a change to the body’s normal circadian rhythm.
- Caused by the body’s inability to rapidly adjust to a new time zone
- Pineal gland continues to secrete melatonin according to the old time zone so that the sleep schedule is not synchronized to the new timezone
Symptoms of jet lag
Headaches, lethargy, increased irritability, and reduced cognitive function.
- Should only last a few days, as symptoms resolve as the body resynchronizes
Melatonin and jet lag
Taking melatonin near the sleep time of the new time zone can help recalibrate the body, as artificially increasing melatonin levels at the new night time allows the body to respond quicker to the new day/night schedule.
“Seed and Soil” theory by Aristotle
Male produces a “seed”, which forms an “egg” when mixed with menstrual blood (“soil”). The “egg” then develops into a fetus inside the mother according to the information contained within the male “seed” alone.
Debunking the “Seed and Soil” theory
William Harvey studied the sexual organs of female deer after mating in an effort to identify the developing embryo.
- Unable to detect a growing embryo until approximately 6 to 7 weeks after mating
- Concluded that Aristotle’s theory was incorrect and that menstrual blood did not contribute to the development of a fetus
- Was however unable to identify the correct mechanism of sexual reproduction (incorrectly asserted that the fetus did not develop from a mixture of male and female “seeds”)
Modern theory of sexual reproduction
A fetus forms from a combination of both male and female gametes.
- Based on evidence discovered using light microscopes (invented 17 years after the death of Harvey)
Human sex chromosomes
46 chromosomes in all diploid somatic cells; 22 pairs are autosomes, the 23rd being sex chromosomes
- Females: XX
- Males XY (shorter)