6.6 Hormones, homeostasis, and reproduction Flashcards
(136 cards)
1
Q
Diagram showing the organs involved in the production of hormones needed to maintain homeostasis
A
2
Q
What are the limits bewteen which blood glucose need to be kept?
A
For most people those values are between 70 to 130 milligrams per decilitre (mg/dl).
3
Q
Why do blood gluose values need to be kept within certain limits?
A
Your body needs to maintain these values so that your blood has a certain osmotic balance; as well as ensuring that the cells of your body, especially your brain cells, have an ample supply of glucose for cellular respiration.
4
Q
What happens if sensors detect blood glucose levels that are above or below the required limits?
A
Two hormones, insulin and glucagon, are produced by the Islets of Langerhans in the pancreas and are responsible for maintaining and controlling blood glucose concentrations.
5
Q
What hormone is secreted when blood glucose level is higher than normal and what effect does this have on blood glucose concentration?
A
- Hormone: Insulin – produced and secreted by β-cells of Islets of Langerhans in the pancreas.
- Effect: Levels fall : insulin stimulates glucose uptake into muscles and liver cells, where it is converted into glycogen.
6
Q
What hormone is secreted when blood glucose level is lower than normal and what effect does this have on blood glucose concentration?
A
- Hormone: Glucagon – produced and secreted by α-cells of Islets of Langerhans in the pancreas.
- Effect: Levels rise : Glucagon stimulates glycogen hydrolysis to glucose in the liver, which in turn releases glucose into the blood.
7
Q
Describe the endocrine and exocrine functions of the pancreas
A
- The pancreas has both exocrine and endocrine functions.
- As an exocrine gland (gland associated with a duct), it secretes enzymes that help in digestion; while as an endocrine gland (ductless gland) it secretes hormones that regulate blood sugar levels.
8
Q
Diagram showing control of blood glucose by insulin and glucagon
A
9
Q
What is the difference between glucagon and glycogen?
A
- Glucagon is a protein-based hormone released from the pancreas.
- Glycogen is not a hormone; it is a carbohydrate found in the liver that is the form that glucose takes when stored there.
10
Q
Symptoms of diabetes
A
- In patients with this disease, the blood glucose levels are consistently too high and their urine has elevated glucose levels.
- Other symptoms include frequent urination, increased thirst, and hunger.
11
Q
Graph showing the blood glucose concentration after a meal in pre-diabetic and diabetic patients compared with a control group.
It is clear that it takes the most time for the blood glucose level to come back to normal in diabetics, followed by pre-diabetics.
A
12
Q
What serious long-term complications can diabetes lead to if left untreated?
A
Heart disease, kidney failure and retinal damage
13
Q
What are the two types of diabetes?
A
- Type 1
- Type 2
14
Q
Type I diabetes
A
- Type I results from the body’s failure to produce sufficient insulin.
- Sometimes this form of diabetes is referred to as insulin-dependent diabetes mellitus (IDDM) or juvenile diabetes.
- It is caused by the destruction of beta cells (autoimmune)
15
Q
Type II diabetes
A
- Type II results from insulin resistance, a condition in which body cells fail to use insulin properly.
- It often begins later in life.
- Prolonged overproduction of insulin leads to desensitization of the insulin receptors, so glucose is not removed from the bloodstream.
16
Q
Describe the treatment of Type I diabetes
A
This involves injecting insulin into the body on a daily basis.
17
Q
Describe the treatment of Type II diabetes
A
It may be treated by eating food with low levels of carbohydrates, eating frequent but small meals and doing strenuous exercise, as well as losing weight.
18
Q
Analysis of a blood sample from someone who had not eaten for 24 hours would be expected to reveal high levels of ___
A
Glucagon
Someone who fasts does not get enough glucose, so the body needs to produce glucose itself from the glycogen stores in the liver. Glucagon stimulates the conversion of glycogen to glucose.
19
Q
What happens when the β-cells of the pancreas release insulin into the blood?
A
The skeletal muscles and liver take up glucose at a faster rate.
Insulin has the effect of lowering blood glucose by increasing glucose uptake in the muscles and the liver, where it is converted into glycogen.
20
Q
In a diabetic patient, blood glucose levels after a meal would return to normal more ___ than in a non-diabetic patient.
A
Slowly
Because diabetic patients either do not make, or do not respond to insulin, blood sugar after a meal would rise quickly to a higher level than normal and decrease slowly as insulin cannot remove glucose from the blood effectively.
21
Q
In a diabetic patient, blood glucose levels after a meal would ___
A
Return to normal more slowly than in a non-diabetic patient.
Because diabetic patients either do not make, or do not respond to insulin, blood sugar after a meal would rise quickly to a higher level than normal and decrease slowly as insulin cannot remove glucose from the blood effectively.
22
Q
What is thyroxin?
A
The main hormone that regulates your metabolism and body temperature.
23
Q
Where is thyroxin produced?
A
In the thyroid gland
24
Q
Thyroxin
A
- Thyroxin is a hormone secreted by the thyroid gland in response to signals initially derived from the hypothalamus
- Thyroxin acts on nearly every tissue in the body and is essential to the proper development and differentiation of cells
- The primary role of thyroxin is to increase the basal metabolic rate (the amount of energy the body uses at rest)
- This can be achieved by stimulating carbohydrate and lipid metabolism via the oxidation of glucose and fatty acids
- A consequence of increased metabolic activity is the production of heat – hence thyroxin helps to control body temperature
- Thyroxin is released in response to a decrease in body temperature in order to stimulate heat production
- Thyroxin is partially composed of iodine and hence a deficiency of iodine in the diet will lead to decreased production of thyroxin
- Iodine deficiency will cause the thyroid gland to become enlarged, resulting in a disease known as goitre
25
What are some of the effects of thyroxine?
- Increased rate of utilization of foods for energy
- Increased breathing rate to obtain oxygen and get rid of carbon dioxide
- Increased rate of protein synthesis and protein catabolism
- Increased number and size of mitochondria in most cells of the body
- Increased growth rate of children and adolescents
- Growth and development of the brain during fetal life and for the first few years of post-natal life
- Enhanced carbohydrate metabolism
- Enhanced fat metabolism.
26
How can goitre be treated?
By consuming iodine tablets
27
What are the symptoms of thyroxine deficiency (low thyroxine concentration in the blood)
- Fatigue
- Depression
- Forgetfulness
- Feeling cold
- Constipation
28
What can thyroxine deficiency lead to in young children?
Impaired brain development
29
Iodine is added to table salt to help prevent deficiencies of an essential mineral needed for the proper function of the ___
Thyroid gland
30
If the body temperature drops below normal, the thyroid gland helps to control the body temperature by producing ___
More thyroxine
31
History of being overweight
- We have evolved systems to prevent the frequent overeating that leads to obesity.
- During the era that humans were still hunters and gatherers, being overweight would increase your chances of becoming prey yourself.
- Besides, excessive food intake in those days would have been far more difficult than today, where there is, at least in some parts of the world, access to large amounts of food, some of it of poor nutritional quality.
32
What are adipose tissues?
Fatty tissues mainly composed of fat cells (adipocytes) that are specialised in the synthesis and storage of fat globules.
33
What is leptin?
A hormone produced and secreted by cells in adipose tissues (these tissues store lipids in your body).
34
What are the two factors that control blood leptin concentration?
- Food intake
- The number of adipose tissues in the body.
35
Where are leptin receptors found?
In the hypothalamus of the brain.
36
What happens when leptin binds to leptin receptors in the hypothalamus of the brain?
It causes appetite inhibition.
37
What happens when fat mass decreases?
- When fat mass decreases, the level of plasma leptin falls (that is, only a few of the leptin receptors bind to leptin in the hypothalamus) so that appetite is stimulated until the fat mass is recovered.
- There is also a decrease in body temperature and energy expenditure is suppressed.
38
What happens when fat mass increases?
- When fat mass increases, such as in the case of weight gain, so do leptin levels and appetite is suppressed until weight loss occurs.
- In this way, leptin regulates energy intake and fat stores so that weight is maintained within a relatively narrow range.
39
Diagram showing the conditions that affect the level of leptin production and action in the body
40
What kind of mice were discovered in the 1950s?
- In the 1950s, a strain of mice was discovered with a mutation that made the mice greedy.
- These mice quickly became obese. Instead of a normal mass range of 20–25 g, these mice had a mass of up to 100 g.
- The equivalent in humans would be males with a mass between 320–350 kg.
41
What was found out about the obese mice?
- It turned out that these mice were homozygous for the ob (stands for obese) allele.
- Mice with two of the recessive alleles cannot produce leptin and have no appetite inhibition, so they eat voraciously.
- In further experiments, the ob/ob mice were given injections of leptin, and their body mass was reduced by about 30% within a month.
42
How was the effect of leptin injections different in humans than in mice?
- Although the leptin injections appeared to work in mice, they did not have the same effect when tested on humans.
- A small subset of people are also homozygous for the ob allele and these people are frequently obese.
- In a double-blind trial (neither researchers nor patients knew if they are given a placebo or the real drug), the results were disappointing, as some participants did lose body mass but others gained in mass.
- Furthermore, any loss in mass was quickly regained after the trial was stopped.
- Human physiology seems to be more complex than that of mice.
43
Why did leptin not have the same effect in humans as it did in mice?
- Unlike mice, obese people have very high leptin levels in their blood.
- This implies that receptor cells in the hypothalamus may no longer be sensitive and responsive to leptin, thus they do not induce appetite inhibition.
44
What still needs to be found out about leptin?
- Although it is known that leptin is essential for normal body weight balance, the exact mechanisms by which it activates hypothalamic neurons to suppress appetite are not yet fully understood.
- In order to find pharmaceutical approaches to treating obesity, further studies are required to understand the exact mechanisms by which leptin lowers body weight and the role leptin and leptin receptors have in the development of obesity in humans.
45
Leptin is a hormone that is released from ___
Adipose tissue
46
How does the body keep track of a circadian rhythm and know the day/night pattern?
- Through the controlled secretion of a hormone called melatonin from the pineal gland.
- Melatonin levels are high at night and low during the day.
47
When are melatonin levels high and low?
High during the night and low during the day
48
What is the pineal gland?
- A small endocrine gland found near the center of the brain between the two hemispheres.
- It is reddish-grey and shaped like a pine cone about 0.8 cm long.
49
Melatonin
- Melatonin is the hormone responsible for synchronizing circadian rhythms and regulates the body's sleep schedule
- Melatonin secretion is suppressed by bright light (principally blue wavelengths) and hence levels increase during the night
- Over a prolonged period, melatonin secretion becomes entrained to anticipate the onset of darkness and the approach of day
- Melatonin functions to promote activity in nocturnal animals and conversely promotes sleep in diurnal animals (like humans)
- During sleep, necessary physiological changes occur in body temperature, brain wave activity, and hormonal production
- Melatonin levels naturally decrease with age, leading to changes in sleeping patterns in the elderly
50
Why does the day/night cycle completely reversing not happen to those living outside the cave?
- Because of certain receptor cells in the retina that signal dawn and dusk to the pineal gland.
- Actually, the impulses from the retina are first channeled to a group of cells in your anterior hypothalamus named the suprachiasmatic nuclei (SCN), which then pass on the information to the pineal gland.
- The pineal gland then adapts the melatonin concentrations in the blood to coincide with a normal 24-hour cycle.
51
Negative feedback loop in the regulation of melatonin
Melatonin receptors are also present on the neurons of the suprachiasmatic nuclei of most species, implying the possible involvement of a negative feedback loop in the regulation of melatonin.
52
Where is melatonin synthesized and what factor has a negative effect on its release?
- Melatonin is synthesized from the amino acid tryptophan and its production is dictated by light.
- Exposure to light has a negative effect on the release of melatonin.
53
How does your body react to melatonin?
Your body core temperature drops and receptors in the kidney cause decreased urine production, all of which increases sleepiness.
54
Why is some readjustment needed when you travel?
- When you travel between time zones, the level of light you are exposed to is no longer matched up with the levels of melatonin in your body.
- Thus, in the first few days, some readjustment is needed to ensure that melatonin production matches the light and dark period of your current time zone.
- After this period, your body will be tuned to a normal sleep/wake cycle again.
55
What is the effect of jetlag and how can melatonin help this?
- Jet lag upsets our normal circadian rhythm forcefully and artificially.
- It makes us irritable, gives us headaches, and indigestion, and makes us want to sleep in the middle of the day.
- Melatonin intake can help people sleep and alleviate some of the symptoms of jet lag.
56
How does melatonin affect the body?
By increasing the likelihood of sleeping
57
How does a growing embryo start out for all humans?
As female
58
Why is it that for all humans, a growing embryo in the uterus starts out as female?
- Two hormones, estrogen, and progesterone are continually present during pregnancy because the mother's ovaries and placenta keep secreting these two hormones.
- Estrogen and progesterone start the embryo on the path to becoming a female with the gonads developing into ovaries
59
What happens if a human embryo has the sex chromosomes XX?
Development is completed to form the female genitalia.
60
When do the seconday female sexual characteristics develop and what are these?
The secondary female sexual characteristics, including the development of breasts and pubic hair, broadening of hips, and start of menstruation, then develop during puberty when there is a rise in the blood concentration of estrogen and progesterone.
61
How do the male and female reproductive systems follow a similar pattern of development?
- Sexual distinction comes about as a result of the influence of hormones.
- The first sign of development of reproductive organs occurs during the 5th week and sexual distinction of the external genitalia becomes apparent in the 10th to 12th week.
62
What is TDF and what is its effect?
- In males, a protein named TDF (Testis Determining Factor), coded for by the SRY gene on the Y chromosome, triggers the development of testis and, indirectly, the production of testosterone.
- TDF is a DNA-binding protein that regulates the transcription of a number of genes involved in the differentiation of the gonads into the testis.
- This happens around week 8 of pregnancy.
63
What happens once the testes have developed?
- They start to produce testosterone.
- This triggers the development of the male genitalia.
64
What happens when testosterone production further increases during puberty?
- This gives rise to secondary male sexual characteristics, such as pubic hair, enlargement of the penis, and deepening of the voice.
- Testosterone is also responsible for triggering the production of sperm.
65
A gene on the Y chromosome causes ___
Embryonic gonads to develop as testes and secrete testosterone.
66
Diagram of the female reproductive system (side view)
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Diagram of the female reproductive system (front view)
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Female sexual organs
- Ovary
- Fallopian tubes (oviduct)
- Uterus
- Cervix
- Vagina
- Vulva
69
What is the function of the ovaries?
Estrogen, progesterone and ovum (egg) production
70
What is the function of the fallopian tubes (oviduct)?
Collects eggs from ovary and carries them to uterus
71
What is the function of the uterus?
Place for the gestation of the embryo and fetus
72
What is the function of the cervix?
Blocks the entry to the uterus during pregnancy and dilates during birth
73
What is the function of the vagina?
Canal connecting cervix and outside of body: forms birth canal and is the receptacle for penis during heterosexual intercourse
74
What is the function of the vulva?
External parts for the protection of the internal reproductive system
75
Diagram of the male reproductive system (side view)
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Diagram of the male reproductive system (front view)
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Male sexual organs
- Testis
- Epididymis
- Sperm duct
- Seminal vesicles
- Prostate gland
- Urethra
- Penis
78
What is the function of the testis?
Sperm and testosterone production
79
What is the function of the epididymis?
Stores sperm until ejaculation
80
What is the function of the sperm duct?
Transfers sperm during ejaculation
81
What is the function of the seminal vesicles?
Produce an alkaline, sugar-rich fluid (fructose) that provides sperm with a source of energy to help them move
82
What is the function of the prostate gland?
Produces an alkaline fluid, rich in proteins, which together with seminal vesicles' secretion and sperm makes semen
83
What is the function of the urethra?
Transfers semen during ejaculation and is the passage of urine during urination
84
What is the function of the penis?
Becomes erect during sexual arousal: penetrates the vagina during heterosexual intercourse to deposit semen close to the cervix
85
Which labeled structures represent the epididymis and the prostate gland?
I: epididymis
IV: prostate gland
86
Women should periodically have a Pap smear test performed to detect cervical cancer.
Which roman numeral indicates the cervix in the diagram below?
iii
87
What is the menstrual cycle?
The cyclic and periodic change in ovarian and pituitary hormones that controls when a woman is fertile, meaning when she can become pregnant.
88
When does the menstrual cycle occur in most women?
Between the onset of puberty and the end of menopause.
89
What are the two fazes that the menstrual cycle can be roughly divided into?
Follicular and luteal
90
What does follicular refer to and what does each follicle contain?
- Follicular refers to the formation of follicles in the ovaries.
- Each follicle contains one egg during its development until ovulation.
91
What does the luteal phase refer to?
The transformation of a follicle into a corpus luteum once ovulation has taken place around day 14.
92
What does the menstrual cycle also control?
The timing of menstruation and the release of blood and tissue from the uterus through the vagina, also called the period.
93
Define puberty
- The phase of adolescence when the individual reaches sexual maturity and becomes capable of reproducing.
- It is accompanied by maturation of the genital organs, development of secondary sexual characteristics and, in humans and some primates, by the first occurrence of menstruation in the female.
94
Define menopause
The phase in a woman's life (around the age of 45–50) when her menstruation stops.
95
What do the follicular and luteal phases coincide with?
The first and second 14-days of a 28-day cycle.
96
Irregularity of menstrual cycles
- Not all women have these regular cycles; some may have a cycle as short as 21 days, while others have a cycle with a 35-day pattern.
- The length of the cycle can also change during the woman's life.
97
When does the menstrual cycle begin and how long does menstruation last?
- The cycle begins with the start of the menstrual period (menstruation), when the lining of the uterus is shed and bleeding starts.
- Menstruation normally lasts around 3–5 days.
98
Diagram showing the levels of the ovarian and pituitary hormones, as well as the changes in the lining of the uterus and in the ovaries.
99
What are the two hormones secreted by the pituitary gland that control mensturation?
Luteinising hormone (LH) and follicle-stimulating hormone (FSH)
100
Which gland secretes luteinising hormone (LH) and follicle-stimulating hormone (FSH)?
The pituitary gland
101
What are the hormones produced by the ovaries?
Estrogen and progesterone
102
Describe phase a of the menstrual cycle: the follicular phase
- FSH causes several follicles in the ovary to begin to develop.
- Usually, only one matures.
- As the follicle develops, it secretes estrogen.
- The estrogen stimulates the uterine lining (endometrium) to thicken with mucus and a rich supply of blood vessels.
- These changes last about 10 days and prepare the uterus for a possible pregnancy; the endometrium is where a fertilised ovum will implant in order to further develop during pregnancy.
103
Describe phase b of the menstrual cycle: ovulation
- A high level of estrogen in the blood (produced by the follicle) causes the pituitary gland to reduce the secretion of FSH (by negative feedback) and begin secretion of LH (by positive feedback).
- The decrease in FSH will, in turn, decrease the production of estrogen.
- LH stimulates the follicle cells to secrete more estrogen, promoting a surge in LH (positive feedback)
- When the concentration of LH in the blood reaches a certain level, ovulation occurs; that is, one mature follicle (a Graafian follicle) ruptures, releasing a mature egg. Ovulation usually occurs at about the middle of the menstrual cycle.
104
Decribe phase c of the menstrual cycle: luteal stage
- After ovulation, LH causes the ruptured follicle to fill with cells, forming the corpus luteum (yellow body).
- It begins to secrete the hormone progesterone, which maintains the continued growth of the endometrium.
- The corpus luteum also produces estrogen, which accounts for the rise in this hormone level after ovulation.
- As the concentration of estrogen and progesterone rise to a certain level, they in turn inhibit the secretion of FSH and LH, respectively (negative feedback).
- This stage lasts about 14 days.
105
How long does the luteal stage last?
About 14 days
106
Describe stage d of the menstrual cycle: menstruation
- If fertilization does not occur, the corpus luteum breaks down.
- This results in a decrease in the level of progesterone and estrogen. With a drop in the progesterone level, the thickened lining of the uterus can no longer be maintained, and it breaks down.
- As a result, the extra layers of the endometrium lining, the unfertilized egg and a small amount of blood pass out of the body through the vagina.
- This lasts about 3–5 days.
- While menstruation is occurring, the amount of estrogen in the blood falls, reducing the inhibitory effect of estrogen on FSH secretion.
- The pituitary gland then increases its output of FSH, a new follicle starts maturing, and the cycle starts again.
107
Negative feedback in the menstrual cycle
- Negative feedback generally has a stabilizing effect on systems or processes.
- In this case, the product of a process controls the rate of its own production.
- For instance, the pituitary gland secretes FSH, which stimulates the production of estrogen.
- But, an increased concentration of estrogen feeds back to inhibit the production of FSH.
- In this way, no more estrogen is produced.
108
Positive feedback in the menstrual cycle
- Positive feedback involves the enhancing or amplification of a product by its own effect on the process which gives rise to it.
- For example, positive feedback occurs during the follicular phase when rising LH levels in the blood cause the pituitary to release more LH to further increase the levels of that hormone so ovulation is triggered.
109
Where is progesterone produced?
Ovary
110
Where is estrogen produced?
Ovary
111
Where is FSH produced?
Pituitary gland
112
Where is LH produced?
Pituitary gland
113
What is the role of progesterone?
Rises at the start of the luteal phase; promotes thickening and maintenance of the endometrium (lining of the uterus)
114
What is the role of estrogen?
Rises to a peak towards the end of the follicular phase; stimulates repair of the endometrium and an increase in FSH receptors on ovary cells
115
What is the role of FSH?
Starts to rise towards the end of the cycle (day 28); stimulates the development of follicles and the production of estrogen by the follicle wall
116
What is the role of LH?
- Rises to a sudden peak towards the end of the follicular phase; stimulates completion of meiosis in the oocyte and thinning of the follicular wall, so that ovulation can occur.
- After ovulation, it stimulates the development of the remaining part of the Graafian follicle into the corpus luteum (by causing an increase in the number of follicle cells), which secretes estrogen (this is an example of positive feedback) and progesterone
117
In the human menstrual cycle, which hormone causes the wall of the follicle to develop after ovulation and secrete more progesterone?
LH
After ovulation, LH causes the ruptured (Graafian) follicle to fill with cells, forming the corpus luteum. The latter can then produce more progesterone.
118
Which hormonal event causes ovulation to occur in the human menstrual cycle?
A quick rise in LH
119
What is in vitro fertilization (IVF)?
- Artificial fertilisation.
- The name means that fertilization (joining of the sperm and the egg) takes place in 'glass' (vitro).
- Before IVF can take place, a number of steps need to be taken.
120
For what reasons may couples use IVF?
- Woman with blocked fallopian tubes
- Woman cannot produce healthy eggs
- Man does not produce enough sperm for fertilisation to take place
- Man suffering from erection problems
- Genetic predisposition of one parent toward certain health problems
- Couple is unable to conceive normally.
121
Diagram showing the steps of in vitro fertilization
122
Step 1a of IVF
- The woman is given a drug (or drugs) to suppress her natural cycle by suspending her normal secretion of hormones.
- She can administer them herself in the form of a daily injection or a nasal spray.
- The drug treatment continues for about 2 weeks.
123
Step 1b of IVR
- FSH and LH are injected at a higher dose than normal for around 12 days to stimulate the production of a number of ova (egg cells), called superovulation.
- The clinic monitors progress throughout the drug treatment through vaginal ultrasound scans and, possibly, blood tests.
124
Step 2 of IVF
- Between 34 and 38 hours before the eggs are due to be collected, the woman will be given a hormone injection to help the eggs mature (this is likely to be human chorionic gonadotropin).
- Eggs are then usually collected from the ovaries by using ultrasound guidance while the person is sedated.
- A hollow needle is attached to the ultrasound probe and is used to collect the eggs from the follicles in each ovary.
125
Step 3 of IVF
A sperm sample is collected from the woman's partner and checked for viability.
126
Step 4 of IVF
- The eggs are mixed with the partner's or the donor's sperm and cultured in the laboratory for 16–20 hours after which they are checked for signs of fertilization.
- (Sperm can also be injected directly into the egg.)
- Eggs that are fertilized (now called embryos) are grown in the laboratory incubator for up to 6 days.
- The embryologist will monitor the development of the embryos and the best will then be chosen for transfer.
- The remaining embryos of suitable quality are frozen for future use.
127
Step 5 of IVF
- If the woman is under the age of 40, one or two embryos are implanted in the uterus at the appropriate time in her menstrual cycle.
- But, if she is older than 40 years, a maximum of three may be used.
- The number of embryos transferred is restricted because of the risks associated with multiple births.
128
Arguments in favor of IVF
- Infertile families can have a baby
- Embryos can be screened for genetic anomalies and other disorders
- Increases understanding of human reproduction
129
Arguments against IVF
- Not all embryos are used, and some are destroyed
- IVF often results in multiple births, which may be an increased risk for the mother and babies
- IVF is not considered 'natural', so it is not condoned by some religious groups
- Women may be at risk because of hormonal injections
130
Who was William Harvey?
William Harvey, the same person who developed theories about the circulatory system, was also the personal physician of Charles I, the King of England in the 17th century.
131
Why did Harvey's theory about fertilization not agree with the thinking of that time?
Philosophers and physicians in Harvey's day believed in the theory put forward by Aristotle, where the man produces a seed which develops into an egg, which then further develops into an embryo with the help of menstrual blood.
132
Describe Harvey's approach
- Harvey used a scientific approach, observing and dissecting female deer during the mating season to ascertain if small embryos could be found immediately after fertilization.
- He theorized that the 'seed and soil' theory put forward by Aristotle could not be true, because he found no small embryos in the uterus of female deer after fertilization.
133
What did Harvey not fully understand from his method and what limitations did he have?
- He could not fully explain how development occurred, as he was unable to see any embryo until many weeks after fertilization; the instruments at his disposal at that time were not sophisticated enough to allow him to see gametes and the early stages of embryos.
- Harvey used only a magnifying glass: compound microscopes were not invented until after his death.
134
What evidence allowed Harvey to conclude that Aristotle's theory was incorrect?
Lack of proper embryos in female deer that had recently mated.
Although Harvey did not have access to microscopes, he could not find any embryos that should have been present from the start according to Aristotle's theory.
135
What does William Harvey's investigation into reproduction of deer indicate about the nature of science?
Improvements in equipment can allow research that was previously not possible.
136
Thyroxin
- Thyroxin is a hormone secreted by the thyroid gland in response to signals initially derived from the hypothalamus
- Thyroxin acts on nearly every tissue in the body and is essential to the proper development and differentiation of cells
- The primary role of thyroxin is to increase the basal metabolic rate (the amount of energy the body uses at rest)
- This can be achieved by stimulating carbohydrate and lipid metabolism via the oxidation of glucose and fatty acids
- A consequence of increased metabolic activity is the production of heat – hence thyroxin helps to control body temperature
- Thyroxin is released in response to a decrease in body temperature in order to stimulate heat production
- Thyroxin is partially composed of iodine and hence a deficiency of iodine in the diet will lead to decreased production of thyroxin
- Iodine deficiency will cause the thyroid gland to become enlarged, resulting in a disease known as goitre
