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)
SRY gene
A gene on the Y chromosome called the sex determining region Y, which leads to male development.
- Codes for a testis-determining factor (TDF) that causes embryonic gonads to form into testes
- Without a TDF protein, embryonic gonads develop into ovaries
Male and female hromones
- Testes produce testosterone to promote the development of male sex characteristics
- Ovaries produce estrogen and progesterone to promote the development and female sex characteristics
Testosterone
The main male reproductive hormone secreted by testes.
- Responsible for the prenatal development of male genitalia
- Involved in sperm production following the onset of puberty
- Aids in the development of secondary sex characteristics (body hair, muscle mass, deepening of voice, etc.)
- Helps maintain libido (male sex drive)
Estrogen and progesterone
The main female reproductive hormones secreted by the ovaries.
- Promote the prenatal development of female genitalia
- Aids in the development of secondary sex characteristics (body hair, breast development, etc.)
- Involved in monthly preparation of egg release (via the menstrual cycle) following puberty
Testis
Responsible for the production of sperm and testosterone.
Epididymis
Site where sperm matures and develops the ability to be motile. Also the site where mature sperm is stored here until ejaculation.
Vas deferens
Long tube which conducts sperm from the testes to the prostate gland (which connects to the urethra) during ejaculation.
Seminal vesicle
Secretes fluid containing fructose (to nourish sperm), mucus (to protect sperm), and prostaglandin (to trigger uterine contractions).
Prostate gland
Secretes an alkaline fluid to neutralize vaginal acids (necessary to maintain sperm viability).
Urethra
Conducts semen from the prostate gland to the outside of the body via the penis. Also used to convey urine.
Ovary
Where oocytes mature prior to release (ovulation). Also responsible for estrogen and progesterone secretion.
Fimbria
A fringe of tissue adjacent to an ovary that sweep an oocyte into the oviduct.
Fallopian tube/oviduct
Transports the oocyte to the uterus. Also typically where fertilization occurs.
Uterus
The organ where a fertilized egg will implant and develop to become an embryo.
Endometrium
The mucous membrane lining of the uterus, which thickens in preparation for implantation or is otherwise lost (via menstruation).
Vagina
Passage leading to the uterus by which the penis can enter (uterus protected by a muscular opening called the cervix).
Menstrual cycle
Describes recurring changes that occur within the female reproductive system to make pregnancy possible.
- Lasts roughly one month (approx. 28 days) and begins at puberty before ending with menopause
Hormones controlling and coordinating the menstrual cycle
- Pituitary hormones (FSH and LH) are released from the anterior pituitary gland and act on ovaries
- Ovarian hormones (estrogen and progesterone) are released from the ovaries and act on the uterus
Follicle stimulating hormone (FSH)
- Stimulates follicular growth in ovaries
- Stimulates estrogen secretion from developing follicles
Luteinizing hormone (LH)
- Surge in LH causes ovulation
- Results in the formation of a corpus luteum
Estrogen
- Thickens endometrium
- Inhibits FSH and LH for most of the menstrual cycle
- Stimulates FSH and LH release before ovulation
Progesterone
- Thickens endometrium
- Inhibits FSH and LH
4 key events in the menstrual cycle
- Follicular phase
- Ovulation
- Luteal phase
- Menstruation
Follicular phase (events)
- FSH secreted from the anterior pituitary gland to stimulate the growth of ovarian follicles
- The dominant follicle produces estrogen, which inhibits FSH secretion (negative feedback) to prevent other follicles from growing
- Estrogen acts on the uterus to stimulate the thickening of the endometrium
Ovulation (events)
Midway through the cycle (approx. day 12)
- Estrogen stimulates the anterior pituitary to secrete hormones (positive feedback)
- Results in a large surge of LH and a lesser one of FSH
- LH causes the dominant follicle to rupture and release an egg (secondary oocyte)
Luteal phase
- Ruptured follicle develops into a slowly degenerating corpus luteum
- Corpus luteum secretes high levels of progesterone and lower levels of estrogen
- Estrogen and progesterone act on the uterus to thicken the endometrium (preparation for pregnancy)
- Estrogen and progesterone inhibit secretion of FSH and LH, preventing any follicles from developing
Menstruation
- If fertilization occurs, the developing embryo will implant in the endometrium and release hormones to sustain the corpus luteum
- If fertilization doesn’t occur, the corpus luteum eventually degenerates, causing estrogen and progesterone levels to drop - The endometrium can no longer be maintained, and is sloughed away and eliminated from the body as menstrual blood
- As estrogen and progesterone levels are too now low to inhibit the anterior pituitary, the cycle can now begin again
In vitro fertilization (IVF)
Fertilization outside the body involving the utilization of drugs to suspend normal ovulation (down regulation) before superovulation (hormone treatments to collect multiple eggs)
Down regulation
- Drugs halt the regular secretion of FSH and LH, inhibiting the secretion of estrogen and progesterone
- By arresting the hormonal cycle, doctors can take control of the timing and quantity of egg production by the ovaries
- Treatment usually takes about two weeks and is typically delivered in the form of a nasal spray
Superovulation
Involves using artificial doses of hormones to develop and collect multiple eggs from the woman.
- Patient injected with large amounts of FSH to stimulate the development of many follicles
- Follicles are treated with human chorionic gonadotrophin (hCG), a hormone usually produced by a developing embryo
- hCG stimulates the follicles to mature and the egg is then collected via aspiration with a needle prior rupturing
Fertilization
- Extracted eggs are incubated in the presence of a sperm sample from the male donor
- Eggs are then analyzed under a microscope for successful fertilization
Implantation
- Approx. two weeks prior to implantation, the patient takes progesterone treatments to develop the endometrium
- Healthy embryos are selected and transferred into the female uterus
- Multiple embryos are transferred to improve chances of successful implantation (multiple births can be an outcome)
- Roughly two weeks after the procedure, a pregnancy test is taken to determine success
Negative feedback
A response that is the reverse of the change detected (functions to reduce the change) to promote equilibrium.
Positive feedback
A response that reinforces the change detected (functions to amplify the change).
Androgen insensitivity syndrome
Do not respond to the production of testosterone.
- Males who suffer from androgen insensitivity do not develop external male genitalia (despite having internal testes), instead developing female sex characteristics (such as enlarged breasts)
- Thus, despite being genetically male (XY), these individuals physically resemble females and will associate with that gender
Guevedoces
“Girls” who turn into boys at puberty.
- Genetic males (XY) do not initially develop male genitals and instead develop as females
- A second hormone surge occurs with the onset of puberty, and it is at this point that the male genitals develop
