6.6 Hormones, homoeostasis and reproduction Flashcards
What is the menstrual cycle controlled by?
controlled by negative and positive feedback mechanisms
What hormones are involved in the menstrual cycle?
Ovarian and pituitary hormones
What is the first half the menstrual cycle called?
Follicular phase
What occurs during the follicular phase?
a group of follicles is developing in the ovary
Which organ responds to changes in blood glucose levels?
Pancreas
What happens when blood glucose level is low?
alpha cells synthesize and secrete GLUCAGON which stimulates breakdown of glycogen (found in liver) into glucose
What happens when blood glucose level is high?
beta cells synthesize insulin which stimulates uptake of glucose by other tissues ( skeletal muscles and liver)
- stimulates conversion of glucose to glycogen
What is thyroxin?
Is a hormone secreted by thyroid gland (in neck) and regulates body’s metabolic rate and controls body temperature
What happens when thyroxin is deficient?
- lack of energy(tiredness)
- forgetfulness depression
- weight gain
- less heat generated
- constipation
What is leptin?
hormone secreted by ADIPOSE CELLS that controls appetite by targeting hypothalamus (region in the brain). It binds to receptors in the membrane of these cells.
What is melatonin?
Hormone secreted by pineal gland to control circadian rhythms (High melatonin = sleepy)
What is Type I Diabetes?
- Early onset diabetes
- Individual has inability to produce sufficient quantities of insulin
- This is an autoimmune disease of beta cells
- Symptoms are very sudden
- Inherited
What happens to most hormones when they act upon cells?
They are broken down, so secretion needs to be continuous (Insulin deficiency causes diabetes)
What is Type II Diabetes?
- Late onset diabetes
- Individual has inability to process or respond to insulin because of deficient insulin receptors/glucose transporters
- Symptoms occur slowly (may go unnoticed for years)
What are risk factors for getting Type II diabetes?
- Sugary foods/Fatty diets
- Prolonged obesity
- Unhealthy habits (no exercise/overeating)
- Some genetics may make people more vulnerable
How is type I diabetes treated?
- By testing blood glucose level regularly –> inject insulin
- Timing of injection is important because insulin molecules do not last long in the blood
- New treatments include: implanted devices for exogenous insulin
- A permanent cure may be achieved: coaxing stem cells to become fully functional replacement beta cells
How is type II diabetes treated?
Adjusting diets to reduce blood glucose
- small amount of food should be eaten frequently instead
- Food with high sugar content should be avoided
- Starchy food should be avoided (only allowed if low glycemic index)
- More high fiber foods
- Weight loss/exercise are beneficial (increase insulin uptake)
What does the chemical structure of thyroxin contain?
Iodine
What could prevent the synthesis of thyroxin?
Prolonged deficiency of iodine in the diet
Why does thyroxin target almost all cells in the body?
It regulates metabolic rate so all cells need to respond
What are the most metabolically active parts of the body?
Liver, muscle and brain
What do higher metabolic rates support?
more protein synthesis, growth and increased generation of body heat
How is concentration of leptin controlled in the blood?
food intake and amount of adipose tissues
What happens if adipose tissues increase?
Blood leptin concentrations rise, causing long-term appetite inhibition and reduced food intake
Why was the injection of leptin to increase blood leptin concentration unsuccessful in most cases?
Most obese humans already have exceptionally high blood leptin concentrations. So the target cells in the hypothalamus may be resistant to leptin, so fail to respond (even at high concentrations).
So appetite is not inhibited -> food intake is excessive
What does excessive food intake cause?
More adipose tissues develop, causing rise in blood leptin concentration but the leptin resistance prevents inhibition
In what cases was the leptin injection successful?
humans who had a mutation in genes for leptin synthesis or its various receptors on target cells
Why do most people refuse the leptin treatment when it works for them?
It’s a short-lived protein and has to be injected several times a day
What us a circadian rhythm?
Rhythms in behaviour that fit a human’s 24-hour cycle
What cells does the circadian rhythm depend on?
the suprachiasmatic nulcei (SCN) in the hypthalamus
What does SCN do?
set daily rhythm, by controlling secretion of melatonin by pineal gland
When does melatonin secretion increase?
in the evening
When is melatonin at low levels?
at dawn it is rapidly removed from blood by liver
What feelings do high melatonin levels cause?
drowsiness and promotion of sleep
What does the discovery of melatonin receptors in kidney suggest?
Decreased urine production at night
What does the development pathway of the embryonic gonads depend on?
The presence or absence of the SRY gene
What happens if the SRY gene is present in the embryonic gonad?
Embryonic gonad develops into testes. It codes for DNA binding protein called TDF which stimulates expression of other genes (that caus testes development)
Where is the SRY gene located if present?
Y chromosome
What do testes develop until around the 15th week of pregnancy?
testerone secreting cells that cause male genitalia to develop
What happens to males at puberty?
secretion of testerone increases, and stimulates production if sperm (primary sexual characteristic of males)
- development of secondary sexual characteristics occurs during puberty (enlarged penis, growth of pubic hair and deeper voice)
What does testosterone cause?
Prenatal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty
What causes prenatal development of female reproductive organs and female secondary sexual characteristics during puberty?
Estrogen and progesterone which are always present in pregnancy
What causes the development of female secondary sexual characteristics?
Puberty, as it increases the secretion of estrogen and progesterone. (cause enlargement of breast and growth of pubic/underarm hair)
Annotate a diagram of the male reproductive system
Testis, scrotum, epididymis, sperm duct, seminal vescicle and prostate gland, urethra and penis
Annotate a diagram of the female reproductive system
Ovary, oviduct, uterus, cervix, vagina, vulva
Annotate a diagram of the female reproductive system
Ovary, oviduct, uterus, cervix, vagina, vulva
What is the first half of the menstrual cycle called?
follicular phase
What occurs during the follicular phase?
group of follicles develop in the ovary. In each follicle an egg is stimulated to grow.
At the same time the lining of the uterus (endometrium) is repaired and starts to thicken.
What happens when the follicle breaks
It releases egg into the overduct. The other follicles degenerate
What is the second half of the cycle called?
Luteal phase
What occurs during the luteal phase?
wall of the follicle (after it has released an egg) becomes a corpus luteum
What happens if egg is not fertilized?
Corpus luteum in ovary breaks down, and the thickening of the endometrium in the uterus breaks down and sheds during menstruation
Which hormones are produced by the pituitary gland?
FSH and LH
What are ovarian hormones?
Estrogen and progesterone
Where are ovarian hormones produced?
wall of follicle and corpus luteum
What do ovarian hormones affect?
Gene expression and development
What is the order of the hormones in the menstrual cycle?
FSH Estrogen LH progesterone
When doe FSH peak?
End of menstrual cycle
What does FSH stimulate?
Development of follicles (containing oocyte and follicular fluid). Also stimulates secretion of ESTROGEN
When does estrogen peak?
End of follicular phase
What does estrogen stimulate?
repair and thickening of endometrium AFTER menstruation.
It also creates a positive feedback loop by increasing FSH receptors.
At high levels, it stimulates LH secretion
When does LH peak?
End of follicular phase
What does LH stimulate?
completion of meiosis in oocyte and partial digestion of follicle wall (so it can burst).
Stimulates follicle wall to develop into corpus luteum. (secretes estrogen/progesterone)
When do progesterone levels peak?
Start of Luteal Phase
What does progesterone promote?
thickening and maintance of the endometrium (inhibits FSH and LH secretes)
What is it called when fertilization occurs outside the body?
In vitro fertilization (IVF)
What is the procedure for IVF?
- Woman takes drugs to stop natural hormone production of pituitary gland so that doctors control timing and amount of egg production
- Intramuscular injections of FSH and LH are given to stimulate follicles to develop (IVF has much more than normal) –> called superovulation
- injection of HCG stimulates follicles to mature
- eggs are harvested from woman’s ovaries
- sperm donor needed
- sperm is washed before use
- eggs are mixed with sperm on petridish
- 2-3 embryos are planted into uterus
- Pregnancy test to check whether implantation was successful
What did William Harvey investigate in deer?
He slaughtered and dissected female deer during mating season to see whether eggs were developing in the uterus immediately after mating. But signs of development only arised two or more months after mating season
