Unit 6.6- Homeostasis and Sexual Reproduction

Question 1

Response to high blood glucose

Answer 1

Insulin secreted by beta cells - stimulates the liver and muscle cells to absorb glucose and convert it to glycogen - granules of glycogen are stores in these cells and other cells are stimulated to absorb glucose and use it in cell resp instead of fat.

Question 1

Blood glucose concentration

Answer 1

usually kept between 4 and 8 millimoles per dm*3 of blood. Cells in the pancreas monitor the concentration and secrete the hormone insulin and glucagon when levels are high or low.

Question 2

Responses to low blood glucose levels

Answer 2

Glucagon is secreted by alpha cells - stimulated the liver to breakdown glycogen into glucose and release the glucose raising blood levels

Question 3

Diabetes

Answer 3

in some people the control of glucose does not work affectively and the concentration can rise or fall beyond the normal limits - diabetes mellitus

Question 4

Type 1 diabetes

Answer 4

onset is usually during childhood, immune system destroys beta cells in the pancreas so the amount of insulin secreted becomes insufficient. Blood glucose levels have to be measured regularly and insulin injections are used to control levels. Diet cannot by itself control this type of diabetes

Question 5

Type 2 diabetes

Answer 5

onset usually after childhood, target cells become insensitive to insulin so insulin injections are not effective treatment. Low carb diets can control the condition, various risk factors increase the rate particularly diets rich in fat and low in fibre

Question 6

Thyroxin

Answer 6

secreted by the thyroid gland in the neck (unusual structure as thyroxin molecule contains four atoms of iodine. Prolonged deficiency of iodine in the diet therefore prevents synthesis of thyroxin. Hormones also unusual as almost all cells in body are target cells as thyroxin regulates body’s metabolic rate so all cells need to respond but most metabolically active (liver muscle and brain) main targets - higher metabolic rate supports more protein synthesis and growth and increases generation of body heat.

Question 7

Role of thyroxin in heat generation

Answer 7

implicated in heat generation by shivering and by uncoupled cell resp in brown adipose tissue - in person with normal physiology , cooling triggers increase thyroxin secretion by the thyroid gland which stimulated heat production - thyroxin can constriction of vessels that carry blood for the core to skin

Question 8

Leptin and Obesity

Answer 8

strain of mice was discovered in the 1950’s that feed ravenously. becoming inactive and gain mass through adipose tissue - breeding experiments showed that the obese mice had two copies of a recessive allele. In early 1990’s it was discovered that the wild-type allele of this gene supported the synthesis of a new hormone (leptin)

Question 9

Leptin

Answer 9

Leptin is protein secreted by adipose cells - if amount of adipose tissue increases the concentration of leptin also increases - target of the hormone is groups of cells in hypothalamus of the brain that contributes to the control of appetite. Leptin binds to receptors in membrane causing long term appetite inhibition and reduced food intake

Question 10

mice experiment for leptin

Answer 10

ob mice were injected with leptin and their appetite declined, energy expenditure increased and body mass decreased by 30% in a month. Trials were therefore done to see if leptin would control obesity in humans. mass was lost in those using leptin but was quickly regained afterwards.

Question 11

Melatonin and Jet lag

Answer 11

humans are adapted to live in a 24hour cycle and have circadian rhythms in behaviour that fit this cycle - ganglion cells in the retina detect whether it is light or dark and send impulses to the supra-chiasmatic nuclei in the hypothalamus- Neurons in the SCN control secretion of the hormone melatonin by the pineal gland. Melatonin secretion increases in the evening and drops to a low level at dawn.

Question 12

Graph of melatonin

Answer 12

melatonin secretion declines with age helping to explain how sleep patters become more irregular as we grow older

Question 13

Jet Lag symptoms

Answer 13

circadian rhythms are disrupted by travelling rapidly between time zones - symptoms : sleep disturbance, headaches, fatigue, irritability -
caused by the pineal gland continuing to set a circadian rhythm to suit the timing of day and night at the point of departure rather than the destination. This only lasts for a few days, during which time impulses sent by the ganglion cells to the SCN when they detect light help the body to adjust to the new regime

Question 14

Use of Melatonin

Answer 14

sometimes used to try to prevent or reduce jet lag- It is taken orally at the time when sleep should ideally by commencing - most trials of melatonin have shown that it is effective at promoting sleep and helping reduce jet lag

Question 15

Female reproductive systems

Answer 15

ovary (produces eggs estrogen and progesterone), oviduct (collects eggs at ovulation, provides a site for fertilisation then moves the embryo to the uterus) , cervix, (protects the fetus during pregnancy and then dilates to provide a birth canal), uterus (provides protection, food, oxygen and removal of waste products for the fetus during pregnancy), bladder , urethra, vulva (protects internal parts of the female reproductive systems), large intestine, vagina (stimulates penis to cause ejaculation and birth canal)

Question 16

Sex determination

Answer 16

human reproduction involves the fusion of a sperm and an egg - embryos all initially develop in a similar way. Embryonic gonads are formed that could become either ovaries or testes. Presence of absence of a single gene decides which development pathway is formed. this gene codes for TDF, a gene regulation protein. By binding to specific DNA sites TDF stimulates the expression of gene for testis development.

Question 17

SRY

Answer 17

present in an embryo if the sex chromosomes are XY the embryonic gonads therefore develop into testes and the fetus becomes male.

Question 18

SRY

Answer 18

abesnt in an embryo if the sex chromosomes are XX. TDF is therefore not produced so the embryonic gonads develop as ovaries and the fetus becomes female

Question 19

The Male reproductive system

Answer 19

bladder, seminal vesicle (secretes an alkaline fluid at the end of ejaculation containing proteins that make semen sticky), sperm duct (transfers sperm during ejaculation), erectile tissue, penis (has erectile tissue that becomes enlarged and hard allowing penetration of the vagina, urethra (transfers semen during ejaculation and urine during urination), foreskin, testis (produces sperm and testosterone), scrotum (holds testes at lower than core body temperature), epididymis (stores sperm until ejaculation), prostate gland (secretes an alkaline fluid that is added to sperm at the start of ejaculation and helps sperm to swim)

Question 20

Steroid Hormones

Answer 20

Testosterone, estrogen and progesterone are all steroids.

Question 21

Testosterone

Answer 21

produced by developing testes in the fetus, it causes pre-natal development of male genitalia, including the penis, sperm duct and prostate gland. During puberty testosterone production increases. It stimulates development of male secondary characteristics during puberty, including growth of the testes, penis and pubis hair. Testosterone also stimulates sperm production from puberty onwards.

Question 22

Estrogen

Answer 22

causes pre-natal development of female reproductive organs if testosterone is not present, These organs include the oviduct, uterus and vagina. Raised levels of estrogen during puberty cause development of female secondary characteristics including growth of breasts and pubic hair

Question 23

Progesterone

Answer 23

prepares the uterus during the menstrual cycle for the implantation of an embryo and has important roles in supporting a pregnancy

Question 24

The menstrual cycle

Answer 24

Between puberty and the menopause, women who are not pregnant follow a cycle called the menstrual cycle.

Question 25

Role of FSH and LH

Answer 25

menstrual cycle controlled by hormones produced by the pituitary gland (FSH and LH) and estrogen and progesterone produced by the ovary

Question 26

Positive and Negative feedback loops

Answer 26

Both positive and negative feedback loops control is used in the menstrual cycle
Negative = stablizing effect because of a change in levels always cause the opposite change. A rise leads to a decrease and reduce level a decrease leads to an increase in production.
Positive = tends to lead to sudden rises and falls because a rise causes further rises and a fall causes further falls.

Question 27

Stages of the menstrual cycle

Answer 27

1) FSH rises to a peak and stimulates the development of follicles, each containing an oocyte and follicular fluid. FSH also stimulates secretion of estrogen by the follicle wall
2) Estrogen stimulates an increase in FSH receptors in the follicles, making them more receptive to FSH which boosts estrogen production (positive feedback)
3) Estrogen stimulates the repair and thickening of the endometrium (uterus lining) after menstruation
4) When it reaches high levels estrogen stimulates LH secretion and also inhibits secretion of FSH by the pituitary gland leading to a fall in estrogen secretion
5) LH rises to a sudden and sharp peak towards the end of the follicular phase. It stimulates the completion of meiosis in the oocyte and partial digestion of the follicle wall allowing it to burst open
6) LH also promotes the development of the wall of the follicle after ovulation into the corpus luteum which secretes estrogen and progesterone
7) Progesterone levels rise in the days after ovulation, promoting the thickening and maintenance of the endometirum
8) High progesterone and estrogen levels inhibits FSH and LH secretion. This is negative feedback because FSH and LH stimulated estrogen and progesterone secretion
9) progesterone and estrogen levels fall if no embryo has been formed eventually levels are low enough to allow FSH secretion
10)FSH levels rise again starting the next cycle

Question 28

In Vitro Fertilisation

Answer 28

pioneering research in the second half of the 20th century led to develpoment of IVF

Question 29

Down Regulation

Answer 29

women takes a drug each day, usually as nasal spray to stop her pituitary gland secretion FSH or LH - allows doctors to control the timing and amount of egg production in womens ovaries

Question 30

Artificial Doses of hormones

Answer 30

Intramuscular injections of FSH and LH are then given for about ten days to stimulate the follicles to develop. FSH injections give a much higher conc than normal - many more follicles develop = superovulation

Question 31

Egg retrieval and fertilisation

Answer 31

when the follicles are 18mm in diameter they are stimulated to mature by an injection of hCG - hormone usually secreted by the embryo. Micropipette mounted on an ultrasound scanner and passed through the uterus wall to wash out the follicles - each egg mixed with 50,000 to 100,000 sperm cells in sterile conditions in a shallow dish, which is then incubated at 37 degrees until the next day

Question 32

Establishing a pregnancy

Answer 32

If fertilization is successful then one or more embryos are places in the uterus when they are about 48 hours old - if the embryos implant and continue to grow then pregnancy follow as usual

Question 33

William Harvey

Answer 33

He tested william harvery tested aristotole’s theory using a natural experiment. Deer are seasonal breeders and only become sexually active during autumn, he examined the mating season by slaughtering and dissecting them. He expected to fins eggs developing immediately but only found them after two / three months = he regarded his experiments with deer as proof that Aristotle’s theory of reproduction was false.

Question 34

Why challenge did Harvey encounter

Answer 34

effective microscopes were not available when he was working