6.6 - cells and micro-organisms

Question 1

how is blood glucose levels controlled?

Answer 1

• regulated by negative feedback mechanisms and involves two hormones: insulin and glucagon.
• monitored in small regions of endocrine tissue called the islets
  of Langerhans throughout the pancreas

Question 2

what are the islets of Langerhans?

Answer 2

• two types of cells needed to secrete the two hormones: a and b cells
• monitor blood glucose levels

Question 3

what is homeostasis?

Answer 3

• involves negative feedback loops
  that act to counteract the change that was applied to the system.
• the body’s tendency to resist change to maintain a stable and relatively constant internal environment around “set points”.

Question 4

what happens when glucose is low?

Answer 4

• a cells synthesise and secrete glucagon into the bloodstream
• Glucagon stimulates the breakdown of glycogen stored in the liver and muscle to form glucose that is released into blood
• Consequently, raising blood glucose levels and returning them to normal.

Question 5

what happens when glucose in high?

Answer 5

• b cells synthesise and secrete insulin into the bloodstream
• Insulin causes glucose to be taken up by skeletal muscles, liver and adipose cells
• Glucose is converted to glycogen and stored in the liver
• This removes excess glucose from the blood, thus lowering the blood glucose levels back to normal
• The secretion of insulin must be ongoing as it is broken down by the cells it acts upon.
• Secretion begins within minutes of eating and continues for several hours after a meal.

Question 6

what is type 1 diabetes?

Answer 6

• Early onset, usually develops in people under 20
• Inability to produce enough insulin arising from autoimmune destruction of b cells.
• Target cells remain sensitive to insulin.
• Involves genetic pre-disposition, virus, autoimmune disorder or destruction of pancreatic b cells.
• Treatments include daily injections of insulin or b cell transplant.

Question 7

what is type 2 diabetes?

Answer 7

• Adult onset, usually in over 40, and generally slow onset.
• Inability to respond to insulin due to insufficient receptors or glucose transporters on target cells.
• Target cells are less sensitive to insulin.
• Linked with dietary, lifestyle factors, increased fatty acids in the blood, prolonged obesity, lack of exercise
• Controlled by diet, strenuous exercise, weight loss or medication but not insulin injections.

Question 8

what is thyroxin?

Answer 8

• a hormone that is secreted by the thyroid gland, which is located in the neck
• a molecule contains four atoms of iodine, so deficiency of iodine in the diet, prevents the synthesis of thyroxin

Question 9

what does thyroxin do?

Answer 9

• regulates the body’s metabolic rate main targets being the liver, muscles and brain as these are the most metabolically active; but, all cells
  respond to thyroxin
• Higher metabolic rate increases protein synthesis and growth, and increases body heat to be generated
• thyroxin helps to control body temperature - more secretion

Question 10

what happens when you have hypothyroidism?

Answer 10

• thyroxin deficiency and suffer from a range of side effects such as: lack of energy, forgetfulness, weight gain, feeling cold all the time, constipation and impaired brain development in children.

Question 11

what is leptin?

Answer 11

• Leptin is a protein hormone that is secreted by adipose cells, which are fat storing cells.
• The amount of adipose cells and the food intake of an individual both control the concentration of leptin secreted into the blood.

Question 12

what does leptin do?

Answer 12

• targets and binds to receptors in a group of cells in the hypothalamus that contribute to the control of appetite.
• If adipose tissue increases, blood leptin concentrations will increase, which causes long-term appetite inhibition, thus reduce food intake.

Question 13

how is leptin linked to obesity?

Answer 13

• 1950s sudies on mice were done as fat mice had lack of leptin
• leptin injections reversed the fatness however didnt work as well on humans
• ## some fat humans had high leptin

Question 14

why might the rat study differ to the human results?

Answer 14

• The target cells in the hypothalamus may have developed resistance to leptin, so fail to respond normally.
• leptin injections would be ineffective in such a situation.
• A very small proportion of obesity in humans is due to mutations in the genes for leptin synthesis or receptors.
• Trials in these people have shown significant weight loss following leptin injections.
• However, leptin is a short-lived hormone, it must be injected several times a day and so it is an inconvenient treatment.
• Leptin may also affect the reproductive system so it is not generally used in children or
  young adults.

Question 15

what are cardiac rhythms?

Answer 15

• Humans live in a 24-hour cycle and have rhythms of behaviour that fit this cycle.
• rhythms are controlled internally, regardless of light or dark.
• rhythms are known as circadian rhythms.

Question 16

what is melatonin?

Answer 16

• secreted by the pineal gland in the brain is controlled by two groups of cells in the hypothalamus called the suprachiasmatic nuclei (SCN).
• SCN cells set a daily rhythm even without cues about the actual time of day.
• In the evening, melatonin secretion increases and is quickly removed from the blood by the liver and so the concentrations drops to a low level at dawn.
• the concentration of blood melatonin rapidly rises and falls according to the changes in secretion.
• so, the most evident melatonin effect is the sleep-wake cycle

Question 17

what does melatonin do?

Answer 17

• High levels cause drowsiness and promote sleep through the night
• lower levels of melatonin encourage waking in the morning.
• Experiments have shown that melatonin contributes to a drop in core body temperature experienced during the night as artificially blocking melatonin during the day causes a drop in core temperature during the day.
• Melatonin receptors are also on kidney cells suggesting that melatonin causes decreased urine production during the night.
• Further experiments shown melatonin rhythms are slightly longer that 24 hours when placed in the absence of light cues.
• However, this is adjusted by special
  ganglion cells in the retina of the eye that
  detects light and passes nervous impulses
  to the SCN for melatonin secretion
  adjustment.

Question 18

what is jet lag?

Answer 18

• commonly experienced when crossing three+ time zones in a plane
• struggle to stay awake during the day and to fall asleep at night, suffering from fatigue, irritability, headaches and indigestion

Question 19

what happens in your body because of jet lag?

Answer 19

• SCN and pineal gland attempting to set the circadian rhythm at the place of departure not the destination.
• only lasts a few days while ganglion cells in the retina detect light to help the body re-adjust
• Sometimes, melatonin is taken at the time when sleep should happen to reduce or prevent jet lag.
• Most trials have shown this to be effective when flying eastwards and crossing >5 time zones.

Question 20

Sex determination in males.

Answer 20

• Males have the sex chromosome XY
• Y chromosome is the SRY gene that causes embryonic gonads to develop into testes.
• SRY codes for a DNA-binding protein called testis determining factor (TDF), which stimulates the expression of other genes that cause testis development.
• this only happens if there is a Y chromosome

Question 21

what is the role of testosterone?

Answer 21

• during weeks 8-15 testosterone secretion causes male genitalia to develop.
• puberty testosterone secretion increases.
• This stimulates sperm production, which is the primary sexual characteristic of males.
• causes the development of secondary sexual characteristics during puberty such as growth of facial and pubic hair, enlargement of the penis, develop muscle mass,
  and deepening of the voice with the growth of the lary

Question 22

what is testosterone?

Answer 22

a hormone produced in the testes that develops in the 8th week of
pregnancy.
- The testes develop testosterone-secreting cells, which then produce testosterone until about the 15th week of pregnancy.

Question 23

Sex determination in females.

Answer 23

• absence of the SRY gene, the embryonic gonads develop into ovaries
• oestrogen and progesterone,
  secreted by the mother’s ovaries and then the placenta during pregnancy
• Female reproductive organs develop in the embryo in the presence of maternal oestrogen
  and progesterone.
• During puberty, the secretion of both hormones increases the development of secondary sexual characteristics that include: enlargement of breasts, growth of body hair.
• Oestrogen and progesterone are involved in monthly preparation of egg release following puberty (menstrual cycle).

Question 24

The male reproductive system.

Answer 24

-Testis - Produce sperm and testosterone
- Scrotum - Holds testes at lower than core body temperature
- Epididymis - Stores sperm until ejaculation
- Sperm duct - Transfer sperm during ejaculation
- Seminal vesicles and prostate
gland - Secretes fluid containing alkali, proteins and fructose that is
added to sperm to make semen
- Urethra - Transfer semen during ejaculation and urine during urination
- Penis - Penetrates vagina for ejaculation of semen near the cervix

Question 25

The female reproductive system.

Answer 25

• Ovary - Produces eggs, oestrogen and progesterone
• Oviduct - Collects eggs during ovulation, provides site for fertilisation then moves embryo to uterus
• Uterus - Provides the needs of the embryo and then foetus during pregnancy
• Cervix - Protect the foetus during pregnancy, then dilates to provide the birth canal
• Vagina - Stimulate penis to cause ejaculation, and provides birth canal
• Vulva - Protects internal parts of female reproductive system

Question 26

what is the first half of the menstrual cycle?

Answer 26

• follicular phase, when a group of follicles develops in the ovary.
• In each follicle, an egg is stimulated to grow.
• The lining of the uterus, called the endometrium, is repaired and starts to thicken.
  The most developed follicle breaks open to release its egg into the oviduct, while the other follicles degenerate.

Question 27

what is the second part of the menstrual cycle?

Answer 27

• The second half of the cycle is called the luteal phase, when the egg-releasing follicle becomes the body called the corpus luteum.
• The endometrium continues to develop in preparation for the implantation of an embryo.
• If fertilisation does not occur, the corpus luteum in the ovary breaks down.
• The thickening of the endometrium also breaks down, and it is shed during menstruation.
• Four hormones control the menstrual cycle.

Question 28

what is the Follicle Stimulating Hormone (FSH)?

Answer 28

• FSH is produced by the pituitary gland and is secreted at the start of the menstrual cycle.
• The blood concentration rises to a peak towards the end of the cycle.
• It stimulates follicle development in the ovary and stimulates the secretion of oestrogen by the follicle wall (positive feedback, +).

Question 29

what does Oestrogen do?

Answer 29

• produced by the ovaries.
• It rises to a peak towards the end of the follicular phase.
• It stimulates repair, thickening of the endometrium, increases FSH receptors, makes the follicles more receptive to FSH, and boosts further oestrogen production (+). At high levels of oestrogen, it inhibits the secretion of FSH (negative feedback, -) but stimulates the
  secretion of LH (+).

Question 30

what does Luteinising Hormone (LH) do?

Answer 30

• produced by the pituitary gland and is secreted before ovulation.
• It rises to a sharp peak towards the end of the follicular phase.
• Causes ovulation, development of the corpus luteum, further secretion of oestrogen (+) and the secretion of progesterone (+) from the ovary.

Question 31

what does Progesterone?

Answer 31

• produced by the ovaries.
• The levels rise at the start of the luteal phase, reaches a peak, and then decreases by the end of this phase.
• Progesterone thickening and maintenance of the endometrium, preparing it for implantation.
• It inhibits the secretion of LH and FSH (-).
  Falling levels at the end of the cycle allow FSH production, and thus menstruation

Question 32

What is IVF?

Answer 32

• used to overcome fertility problems in either the male of female and so this process of fertilisation happens outside the body in carefully
  controlled laboratory conditions
• Drugs are used to suspend the normal secretion of hormones so that doctors can control the timing and amount of egg production in the ovaries

Question 33

what is the first stage of IVF?

Answer 33

• requires the woman to take a drug to stop the pituitary gland from
  secreting FSH and LH (i.n.).
• Subsequently, this prevents the secretion of oestrogen and progesterone.

Question 34

what is the second stage of IVF?

Answer 34

• The second stage is where higher than normal concentrations of FSH and LH are injected(i.m.) daily for ten days to stimulate more than normal follicles to develop (12-20). This process is called superovulation.
• The follicles are stimulated to mature with injections of HCG (i.m.), a hormone that is normally secreted by the embryo.

Question 35

what happens in IVF?

Answer 35

The eggs are washed out of the follicles with a micropipette attached to an ultrasound scanner.
- Each egg is mixed with 50,000 to 100,000 sperm cells in sterile conditions in a sterile dish, and incubated for a day at 37°C.
- If fertilisation is successful, one or more embryos are placed in the uterus at around 48 hours old.
- This is because the woman has not
undergone a normal menstrual cycle.
- Additionally, the woman is given extra progesterone tablet in the vagina to ensure the uterus lining is maintained for embryo implantation.
- If implantation is successful, normal
pregnancy continues.