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
What may melatonin levels decrease alongside with?
Melatonin levels naturally decrease with age, leading to changes in sleeping patterns in the elderly
What is jet lag?
Jet lag is a physiological condition resulting from a change to the body’s normal circadian rhythm
What is jet lag caused by? basic
This alteration is caused by the body’s inability to rapidly adjust to a new time zone following extended air travel (‘jet’ lag)
What is jet lag causes by, hormonally?
The pineal gland continues to secrete melatonin according to the old time zone so that the sleep schedule is not synchronised to the new timezone
What are the symptoms of jet lag?
As a result of these sleep disturbances, individuals suffering from jet lag will often experience symptoms associated with fatigue
Symptoms of jet lag include headaches, lethargy, increased irritability and reduced cognitive function
How long should jet lag last?
Jet lag should only last a few days and symptoms should resolve as the body resynchronises its circadian rhythm
What do some health professionals recommend to combat jet lag?
Some health professionals recommend taking melatonin near the sleep time of the new time zone to help recalibrate the body
How does taking melatonin help jet lag?
By artificially increasing melatonin levels at the new night time, the body can respond quicker to the new day-night schedule
What was the earliest theory for sexual reproduction?
One of the earliest theories as to how animals reproduce sexually was the ‘soil and seed’ theory proposed by Aristotle
What is the “seed and soil theory”, proposed by Aristotle?
According to this theory, the male produces a ‘seed’ which forms an ‘egg’ when mixed with menstrual blood (the ‘soil’)
The ‘egg’ then develops into a fetus inside the mother according to the information contained within the male ‘seed’ alone
Who debunked the “soil and seed” theory?
The ‘soil and seed’ theory was a popular doctrine for hundreds of years before it was eventually debunked by William Harvey
How did Harvey debunk the “soil and seed” theory?
William Harvey studied the sexual organs of female deer after mating in an effort to identify the developing embryo
He was unable to detect a growing embryo until approximately 6 – 7 weeks after mating had occurred
He concluded that Aristotle’s theory was incorrect and that menstrual blood did not contribute to the development of a fetus
Harvey was unable to identify the correct mechanism of sexual reproduction and incorrectly asserted that the fetus did not develop from a mixture of male and female ‘seeds’
How was our current understanding of sexual reproduction developed?
Our current understanding of the mechanism of sexual reproduction is based on evidence discovered using light microscopes
Viable microscopes for such investigations were not invented until 17 years after the death of William Harvey
What is our modern understanding of the mechanism of sexual reproduction?
Based on available evidence, it is now known that a fetus forms from a combination of both male and females ‘seeds’ (gametes)
How many chromosomes do humans have in diploid osmatic cells, what two categories are there?
Humans have 46 chromosomes in all diploid somatic cells – 22 pairs are autosomes and the 23rd pair are the sex chromosomes
What chromosome combinations do women and men have?
Females possess two copies of the X chromosome (XX), while males possess one X and a shorter Y chromosome (XY)
What does the Y chromosome contain and what is its role?
The Y chromosome includes a gene called the SRY gene (Sex Determining Region Y), which leads to male development
What does the SRY gene code for?
The SRY gene codes for a testis-determining factor (TDF) that causes embryonic gonads to form into testes (male gonads)
What will happen in the absence of the TDF protein?
In the absence of the TDF protein (i.e. no Y chromosome), the embryonic gonads will develop into ovaries (female gonads)
What do male and female gametes produce to promote further development of sex characteristics?
hormones
What do testes produce and what is its role in the development of sex characteristics?
The testes produce testosterone to promote the further development of male sex characteristics
What do ovaries produce and what is its role in the development of sex characteristics?
The ovaries will produce estrogen and progesterone to promote the development of female sex characteristics
What are the 4 roles of testosterone?
- It is responsible for the pre-natal development of male genitalia
- It is involved in sperm production following the onset of puberty
3.It aids in the development of secondary sex characteristics - It helps to maintain the male sex drive (libido)
What are secondary sex characteristics in males?
including body hair, muscle mass, deepening of voice
What are the 3 roles of estrogen and progesterone?
1.They promote the pre-natal development of the female reproductive organs
2. They are responsible for the development of secondary sex characteristics (including body hair and breast development)
3. They are involved in monthly preparation of egg release following puberty (via the menstrual cycle)
What initially secretes estrogen and progesterone, and how does this change?
nitially, estrogen and progesterone are secreted by the mother’s ovaries and then the placenta – until female reproductive organs develop (this occurs in the absence of testosterone)
What does the male reproductive system contain?
The male reproductive system includes all the organs responsible for the production of sperm (the male gamete)
What is the role of the organs of the male reproductive system?
It also includes the organs that are involved in synthesising the semen in which the sperm is transported during copulation
What are the 6 structures of the male reproductive system?
testis
epididymis
vas deferens
seminal vesicle
prostate gland
urethrea
What is the role of the testis?
The testis (plural: testes) is responsible for the production of sperm and testosterone (male sex hormone)
What is the role of the epidiymis?
Site where sperm matures and develops the ability to be motile (i.e. ‘swim’) – mature sperm is stored here until ejaculation
What is the role of the vas deferens?
Long tube which conducts sperm from the testes to the prostate gland (which connects to the urethra) during ejaculation
What is the role of the seminal vesicle?
Secretes fluid containing fructose (to nourish sperm), mucus (to protect sperm) and prostaglandin (triggers uterine contractions)
What is the role of the prostate gland?
Secretes an alkaline fluid to neutralise vaginal acids (necessary to maintain sperm viability)
What is the role of the urethra?
Conducts sperm / semen from the prostate gland to the outside of the body via the penis (also used to convey urine)
What are the purposes of the female reproductive system?
The female reproductive system includes all the organs responsible for the production of an oocyte (the female gamete)
It also includes the organs involved in initially developing and maintaining an embryo during the early stages of pregnancy
What is the role of the ovary?
The ovary is where oocytes mature prior to release (ovulation) – it also responsible for estrogen and progesterone secretion
What is the role of the fimbria?
Fimbria (plural: fimbriae) are a fringe of tissue adjacent to an ovary that sweep an oocyte into the oviduct
What is the role of the oviduct?
The oviduct (or fallopian tube) transports the oocyte to the uterus – it is also typically where fertilisation occurs
What is the role of the uterus?
The uterus is the organ where a fertilised egg will implant and develop (becoming an embryo)
What is the role of the endometrium?
The mucous membrane lining of the uterus, it thickens in preparation for implantation or is otherwise lost (via menstruation)
What is the role of the vagina?
Passage leading to the uterus by which the penis can enter (uterus protected by a muscular opening called the cervix)
What does the menstrual cycle describe?
The menstrual cycle describes recurring changes that occur within the female reproductive system to make pregnancy possible
How long does the menstrual cycle last?
Each menstrual cycle lasts roughly one month (~28 days) and begins at puberty (menarche) before ending with menopause
What are the two key groups of hormones which control and coordinate the menstrual cycle?
Pituitary hormones (FSH and LH) are released from the anterior pituitary gland and act on the ovaries to develop follicles
Ovarian hormones (estrogen and progesterone) are released from the ovaries and act on the uterus to prepare for pregnancy
What is the role of FSH? 2
stimulates follicular growth in ovaries
stimulates estrogen secretion (from developing follicles
What is the role of LH? 2
surge causes ovulation
results in the formation of a corpus luteum
What is the role of estrogen? 3
thickens uterine lining (endometrium)
inhibits FSH and LH for most of cycle
stimulates FSH and LH release pre-obulation
What is the role of progesterone (2)?
thickens uterine lining (endometrium)
inhibits FSH and LH
What are the 4 key events of the menstrual cycle?
There are four key events that comprise a typical menstrual cycle: follicular phase, ovulation, luteal phase and menstruation
How can the 4 key events be distinguished? MC
These events are distinguished by changes to hormonal levels, follicular development and the status of the endometrium
1.1 Follicular Phase - What hormone is first secreted?
Follicle stimulating hormone (FSH) is secreted from the anterior pituitary and stimulates growth of ovarian follicles
1.2 Follicular Phase - What does the dominant follicle produce?
The dominant follicle produces estrogen, which inhibits FSH secretion (negative feedback) to prevent other follicles growing
1.3 Follicular Phase - What does estrogen do at this stage?
Estrogen acts on the uterus to stimulate the thickening of the endometrial layer
2.1 Ovulation - What does estrogen do MIDWAY through the cycle?
Midway through the cycle (~ day 12), estrogen stimulates the anterior pituitary to secrete hormones (positive feedback)
2.2 Ovulation - What does positive feedback lead to?
This positive feedback results in a large surge of luteinizing hormone (LH) and a lesser surge of FSH
2.3 Ovulation - What does LH cause the dominant follicle to do?
LH causes the dominant follicle to rupture and release an egg (secondary oocyte) – this is called ovulation
3.1 Luteal Phase - What happens to the ruptured follicle?
The ruptured follicle develops into a slowly degenerating corpus luteum
3.2 Luteal Phase - What does the corpus luteum secrete?
The corpus luteum secretes high levels of progesterone, as well as lower levels of oestrogen
3.3 Luteal Phase - What is the role of the hormones secreted by the corpus luteum (effect on UTERUS)?
Estrogen and progesterone act on the uterus to thicken the endometrial lining (in preparation for pregnancy)
3.4 Luteal Phase - What is the role of the hormones secreted by the corpus luteum (effect on HORMONES)?
Estrogen and progesterone also inhibit secretion of FSH and LH, preventing any follicles from developing
4.1. Menstruation - What occurs if fertilisation occurs?
If fertilisation occurs, the developing embryo will implant in the endometrium and release hormones to sustain the corpus luteum
4.2. Menstruation - What happens if fertilisation DOESN’T occur?
If fertilisation doesn’t occur, the corpus luteum eventually degenerates (forming a corpus albicans after ~ 2 weeks)
4.3. Menstruation - What happens when the corpus luteum degenerates?
When the corpus luteum degenerates, estrogen and progesteron levels drop and the endometrium can no longer be maintained
4.4. Menstruation - What is shed due to the drop in estrogen and progesterone levels?
The endometrial layer is sloughed away and eliminated from the body as menstrual blood (i.e. a woman’s period)
4.5. Menstruation - What causes the cycle to repeat?
As estrogen and progesterone levels are too now low to inhibit the anterior pituitary, the cycle can now begin again
Very general, what is IVF?
In vitro fertilisation (IVF) refers to fertilisation that occurs outside of the body (in vitro = ‘in glass’)
It involves using drugs to suspend normal ovulation (down regulation), before using hormone treatments to collect multiple eggs (superovulation)
What are the 4 stages of IVF?
down regulation
superovulation
fertilisation
implantation
1.1. Down Regulation - What drugs are taken to start the process?
Drugs are used to halt the regular secretion of FSH and LH – this in turn stops the secretion of estrogen and progesterone
1.2. Down Regulation - What is the purpose of arresting the hormonal cycle?
By arresting the hormonal cycle, doctors can take control of the timing and quantity of egg production by the ovaries
1.3. Down Regulation - How long does this stage last and how is the drug treatment administered?
The drug treatment usually takes about two weeks and is typically delivered in the form of a nasal spray
2.1. Superovulation - What does this stage involve?
Superovulation involves using artificial doses of hormones to develop and collect multiple eggs from the woman
2.2. Superovulation - What is the woman injected with?
The patient is firstly injected with large amounts of FSH to stimulate the development of many follicles
2.3. Superovulation - What are the follicles then treated with?
The follicles are then treated with human chorionic gonadotrophin (hCG) – a hormone usually produced by a developing embryo
2.4. Superovulation - What is the role of hCG?
hCG stimulates the follicles to mature and the egg is then collected (via aspiration with a needle) prior to the follicles rupturing
3.1. Fertilisation - What happens to the extracted eggs?
The extracted eggs are then incubated in the presence of a sperm sample from the male donor
The eggs are then analysed under a microscope for successful fertilisation
4.1. Implantation - What occurs roughly two weeks before this stage?
Approximately two weeks prior to implantation, the woman begins to take progesterone treatments to develop the endometrium
4.2. Implantation - What is implanted into the uterus?
Healthy embryos are selected and transferred into the female uterus (or the uterus of a surrogate)
4.3. Implantation - How many embryos are implanted and why?
Multiple embryos are transferred to improve chances of successful implantation (hence multiple births are a possible outcome)
4.4. Implantation - What is done to check whether the procedure was successful?
Roughly two weeks after the procedure, a pregnancy test is taken to determine if the process has been successful
Mnemonic to remember the key stages of IVF
Stop normal menstrual cycle (with drugs)
Hormone treatments to promote super ovulation
Extract multiple eggs from the ovaries
Sperm collected, then prepared (via capacitation) and injected into egg
Fertilisation occurs externally under controlled conditions (in vitro)
Implantation of multiple embryos into uterus (either patient or surrogate)
Test for pregnancy after ~ two weeks
Mnemonic: SHE’S FIT
