1. 6.6 Hormones, homeostasis, and reproduction
Essential idea: Hormones are used when signals need to be widely distributed

2. 6.6 Hormones, homeostasis, and reproduction
Nature of science: Developments in scientific research follow improvements in apparatus—William Harvey was hampered in his observational research into reproduction by lack of equipment. The microscope was invented 17 years after his death. (1.8)
Understandings
Insulin and glucagon are secreted by β and α cells of the pancreas respectively to control blood glucose concentration
Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature
Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite
Melatonin is secreted by the pineal gland to control circadian rhythms
A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone
Testosterone causes pre-natal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty
Estrogen and progesterone cause pre-natal development of female reproductive organs and female secondary sexual characteristics during puberty
The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones

3. 6.6 Hormones, homeostasis, and reproduction
Applications and skills
Application: Causes and treatment of Type I and Type II diabetes
Application: Testing of leptin on patients with clinical obesity and reasons for the failure to control the disease
Application: Causes of jet lag and use of melatonin to alleviate it
Application: The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish pregnancy
Application: William Harvey’s investigation of sexual reproduction in deer
Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

4. U6.6.1 Insulin and glucagon are secreted by β and α cells of the pancreas respectively to control blood glucose concentration
If glucose concentration changes from a set point of 5 mmol/L insulin and glucagon are initiated
Where are β and α cells located in the pancreas?
Islets of Langerhans
What cells secrete glucagon and what does it do?
Secreted by α cells, if glucose levels fall it is secreted, stimulates breakdown of glycogen into glucose in liver cells
What cells secrete insulin and what does it do?
Secreted by β cells, secreted when glucose levels rise, stimulates uptake of glucose thus to convert it to glycogen

5. A 6.6.1 Causes and treatment of Type I and Type II diabetes
What is the cause of type I diabetes?
Type I – early onset
Inability to produce sufficient quantities of insulin
Autoimmune disease arising from the destruction of beta cells in islets of Langerhans by the body’s own immune system
May have viral trigger, also a genetic component to risk (HLA type)
Treatment?
Frequent testing of blood and injections of insulin. Some implantable insulin pumps.

6. A 6.6.1 What is type II diabetes? Type II – late onset
Inability to process or respond to insulin because of a deficiency of insulin receptors on target cells
Onset is slow. Main risk factors are sugary, fatty diets, prolonged obesity due to habitual overeating and lack of exercise, together with genetic factors that affect energy metabolism
Treatment?
Weight loss, exercise, dietary adjustments to reduce foods with high sugar content and starches that break down quickly
Drugs that stimulate pancreas to produce more insulin; injected insulin if needed

7. U Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature
Where is thyroxin secreted?
Thyroid gland is a butterfly shaped gland located in your neck. The major hormone produced, thyroxin, is formed from the amino acid, tyrosine, and iodine
How many atoms of iodine does thyroxin contain? 4
Thyroxin leads to an increase in metabolism by targeting all cells but mainly liver, muscles, and brain
Thyroxin also helps to regulate internal body temperature
An increase in metabolic rate produces more heat from the increased chemical reactions. So an increase in thyroxin will lead to an increase in body temperature and vice-versa

8. U 6.6.2
Hyperthyroidism
Over production of thyroid hormones leads to high body temperature, profuse sweating, weight loss, irritability, and high blood pressure. Graves’ disease is leading cause
Hypothyroidism
Under production of thyroid hormone which can lead to lethargy and weight gain, forgetfulness and depression, feeling cold all of the time, constipation. Can be caused by an inadequate supply of iodine, or an autoimmune disease that attacks the thyroid (Hashimoto’s thyroiditis)

9. U 6.6.3 Leptin What cells secrete leptin?
Adipose cells/tissue or fat cells
What does leptin do?
Suppresses hunger, makes you feel full
As levels of adipose tissue increase, leptin suppresses appetite
When body fat decreases, leptin levels fall, and appetite increases
Helps to regulate body weight
Explain how this system was demonstrated in research with mice
ob+ allele produces the satiety factor, now understood to be the hormone, leptin, in fat cells
ob+ allele encodes the leptin receptor in membranes of cells in the hypothalamus
When ob/ob mice injected with leptin, appetite declined, energy expenditure increased and body mass dropped by 30% in a month

10. A Testing of leptin on patients with clinical obesity and reasons for the failure to control the disease
Moved to clinical trials of 73 obese volunteers, only 47 of which finished the trial.
Double blind study (neither researchers nor volunteers knew what the subjects were injecting)
Results in humans showed varied results although on average, humans on highest dose lost the greatest amount of weight…which quickly found them again when the trial was over
Only small fraction of human obesity due to lack of leptin. Most due to lack of response by target cells. So, increasing leptin levels have no effect on levels of obesity
Route of administration: injections. These were not well tolerated by the subjects (35% drop out rate)

11. U 6.6.4 Melatonin Where is melatonin secreted? Pineal gland
What does melatonin do?
It is a modified amino acid, helps control your sleep and wake cycles
What are circadian rhythms?
Rhythms of behavior/ biochemistry that fit a 24 hour cycle
Sequence of events leading to release:
Ganglion cells in the retina detect whether it is light or dark and send impulses to the supra-chiasmatic nuclei (SCN) in the hypothalamus
Supra-chiasmatic nucleus functions as a biological clock
Neurons in the SCN control secretion of melatonin by the pineal gland
Regulates functions related to light and to seasons marked by changes in day length
Primary functions relates to biological rhythms associated with reproduction

12. A 6.6.3 Causes of jet lag and use of melatonin to alleviate it
Melatonin secretion decreases with age which explains how sleep patterns become more irregular as we grow older
Circadian rhythms are disrupted by travelling rapidly between time zones. Symptoms include: sleep disturbance, fatigue, headaches, irritability. This pattern = jet lag.
SCN and pineal set rhythm to the timing of day and night at point of departure. Only lasts a few days. Exposure to light at destination resynchronizes circadian rhythm.
Melatonin can be used to prevent or reduce jet lag.
Taken orally at the time when sleep should ideally start. Works best when travelling East, crossing 5 or more time zones.

13. U A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone
What is the name of this gene?
During the 6th week of embryogenesis, a gene on the Y chromosome (SRY – sex determining region of the Y) causes embryonic gonads to develop as testes and secrete testosterone
SRY gene codes for TDF (testis determining factor), a gene regulation protein which binds to specific DNA sites
TDF stimulates the expression of other genes that cause testis development

14. U Testosterone causes pre-natal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty
Testosterone is secreted from an early stage in fetal development (after the 8th week until the 15th week of pregnancy)
Testosterone causes prenatal development of male genitalia
At puberty, the secretion of testosterone increases
This stimulates sperm production (primary sex characteristic of males) and development of male secondary sexual characteristics during puberty
Secondary sex characteristics include enlargement of the penis, growth of pubic hair, deepening of the voice due to growth of the larynx

15. In the absence of SRY gene, embryonic gonads develop as ovaries
U Estrogen and progesterone cause pre-natal development of female reproductive organs and female secondary sexual characteristics during puberty
In the absence of SRY gene, embryonic gonads develop as ovaries
Estrogen and progesterone (which are always present in pregnancy first secreted by mother’s ovaries and later by the placenta) cause prenatal development of female reproductive organs
At puberty secretion of these hormones increase and female secondary sexual characteristics develop
Enlargement of breasts and growth of pubic and underarm hair
Female pattern of fat deposition

16. U The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones
What is the first half of the menstrual cycle called?
Follicular phase- group of follicles is developing in ovary, each follicle contains an egg
Lining of endometrium starts to thicken
Most developed follicle releases egg into oviduct
What is the second half called?
Luteal phase- wall of the follicle that released an egg becomes the corpus luteum
Endometrium continues to thicken
If egg is not fertilized the corpus luteum breaks down, endometrium is broken down

17. FSH rises to a peak at the end of menstrual cycle and stimulates development of follicles. Also stimulates secretion of estrogen by the cells in the follicle walls. Example of + feedback.
Estrogen peaks towards the end of the follicular phase. Stimulates repair and thickening of the endometrium after menstruation and an increase in FSH receptors, boosting estrogen production. When estrogen reaches high levels it inhibits the secretion of FSH (- feedback) and stimulates LH secretion
LH rises to a sudden and sharp peak towards end of follicular phase. Stimulates the completion of meiosis in the oocyte and partial digestion of follicle wall allowing it to burst open at ovulation. LH also promotes development of the wall of follicle after ovulation into corpus luteum which secretes estrogen (+ feedback) and progesterone
Progesterone levels rise at start of luteal phase, reach a peak and then drop back to a low level at the end of luteal phase. Promotes the thickening and maintenance of the endometrium. Inhibits FSH and LH secretion (- feedback).

19. A The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish pregnancy
Stage 1: Downregulation. Nasal spray of drug stops pituitary gland from secreting FSH and LH. Secretion of estrogen and progesterone therefore also stops.
Stage 2: Intramuscular injections of FSH in a much higher concentration and LH given daily for about 10 days, to stimulate follicles to develop. This is to mature far more follicles than usual follicles= superovulation
Stage 3: Injection of HCG to stimulate maturation when follicles are about 18 mm diameter
Stage 4: Harvesting eggs and fertilization while progesterone tablets placed in vagina to ensure that uterine lining is maintained

20. A 6.6.5 William Harvey’s investigation of sexual reproduction in deer
He was taught the “seed and the soil” theory of Aristotle, according to which the male produces a seed, which forms an egg when it mixes with menstrual blood. The egg develops into a fetus inside of the mother
Deer are seasonal breeders and only become sexually active in autumn
Harvey examined the uterus of female deer during mating season by slaughtering and dissecting them expecting to find eggs developing in the uterus immediately after mating
He only found evidence of anything happening in females 2 or more months after the start of the mating season
Led him to the belief that Aristotle’s theory was false

21. S Annotate diagrams of the male and female reproductive system to show names of structures and their functions
Male Reproduction
Be able to annotate for function:
Testis
Scrotum
Epididymis
Penis and erectile tissue
Urethra
Sperm duct
Seminal vesicle
Prostate gland
Bulbourethral gland

22. Functions: Male Reproductive System
Testis: produce sperm and testosterone
Scrotum: hold testes at lower than core body temperature
Epididymis: store sperm until ejaculation; cause sperm to become motile
Sperm duct: transfer sperm during ejaculation
Seminal vesicle: secrete fluid containing fructose and proteins
Prostate gland: secrete alkaline fluid with mineral ions
Urethra: transfer semen during ejaculation and urine during urination
Penis: penetrate the vagina for ejaculation of semen near the cervix
Bulbourethral gland: increases viscosity of ejaculate

23. Skill 6.6 Annotate diagrams of the male and female reproductive system to show names of structures and their functions
Annotations of the female reproductive system:
Ovary
Oviduct
Uterus
Cervix
Vagina
Vulva

24. Functions: Female Reproductive System
Ovary: produce eggs, estrogen, and progesterone
Oviduct (fallopian tubes): collect eggs at ovulation, provide a site for fertilization then move the embryo to the uterus
Uterus: provide for the needs of the embryo and then fetus during pregnancy. Formation of placenta
Cervix: protects the fetus during pregnancy and then dilate to provide a birth canal
Vagina: stimulate the penis to cause ejaculation and provide a birth canal
Vulva: protect internal parts of the female reproductive system