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IB biology > topic 6.6 - hormones, homeostasis, and reproduction > Flashcards

topic 6.6 - hormones, homeostasis, and reproduction Flashcards

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1
Q

function of cells in the pancreas

A

to respond to changes in blood glucose levels

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2
Q

set point of blood glucose concentration

A

5 mmol/L

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3
Q

what region of the pancreas secretes hormones directly into the bloodstream?

A

small regions of endocrine tissue islets of Langerhans

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4
Q

alpha cells

A

synthesise and secrete glucagon if blood glucose levels fall below set point.

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5
Q

function of glucagon

A

stimulates breakdown of glycogen into glucose in liver cells and its release into the blood, increasing the concentration

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6
Q

beta cells

A

synthesise insulin and secrete it when the blood glucose concentration rises above the set point

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7
Q

function of insulin

A

stimulates uptake of glucose by various tissues, particularly skeletal muscle and liver, in which it also stimulates conversion of glucose to glycogen, reducing blood glucose concentration

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8
Q

why must secretion of insulin be ongoing?

A

it is broken down by the cells it acts upon

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9
Q

define diabetes

A

a condition where a person has consistently elevated blood glucose levels

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10
Q

effects of continuously elevated glucose

A
  • damages tissues, particularly their proteins
  • impairs water reabsorption from urine while it is forming in the kidney, resulting in an increase in the volume of urine and body dehydration
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11
Q

symptoms of diabetes

A
  • urinate more frequently
  • constantly thirsty
  • feels tired
  • cares sugary drinks
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12
Q

type 1 diabetes (early onset diabetes)

A
  • characterised by an inability to produce sufficient quantities of insulin
  • autoimmune disease arising from the destruction of beta cells in the islets of Langerhans by the body’s own immune system
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13
Q

type 2 diabetes (late onset diabetes)

A
  • characterised by an inability to process or respond to insulin because of a deficiency of insulin receptors or glucose transporters on target cells
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14
Q

main risk factors of type 2 diabetes

A
  • sugary, fatty diets
  • prolonged obesity due to habitual obesity and lack of exercise
  • genetic factors that affect energy metabolism
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15
Q

treatment of type 1 diabetes

A
  • testing blood glucose concentration regularly and injecting insulin when it is too high or likely to become too high
  • injections often done before a meal to prevent peak of blood glucose as the food is digested/absorbed
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16
Q

treatment of type 2 diabetes

A
  • adjusting diet to reduce peaks and troughs of blood glucose.
  • small amounts of food eaten frequently rather than infrequent large meals
  • foods with high sugar content avoided; starchy foods only allowed if low glycemic index (digested slowly); high-fibre foods included to slow digestion of other foods
  • strenuous exercise and weight loss
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17
Q

what is thyroxin secreted by

A

thyroid gland (in neck) §

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18
Q

why is thyroxin unusual?

A
  • chemical structure - contains four atoms of iodine
  • almost all cells in body are targets
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19
Q

what prevents synthesis of thyroxin?

A

prolonged deficiency of iodine in the diet

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20
Q

function of thyroxin

A
  • regulates body’s metabolic rate, so all cells need to respond
  • main targets are most metabolically active such as liver, muscle and brain
  • control of body temperature
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21
Q

higher metabolic rate ->

A

more protein synthesis and growth and increases the generation of body heat

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22
Q

in a person with normal physiology, cooling triggers…

A

increased thyroxin secretion by the thyroid gland, which stimulates heat production so body temperature rises

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23
Q

effects of hypothyroidism

A

thyroxin deficiency:
- lack of energy/persistent tiredness
- forgetfulness and depression
- weight gain
- persistent feeling cold
- constipation
- impaired brain development

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24
Q

explain weight gain despite of loss of appetite in hypothyroidism

A

less glucose and fat are being broken down to release energy by cell respiration

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25
Q

explain constipation in hypothyroidism

A

contractions of muscle in the wall of the gut slow down

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26
Q

define leptin

A

a protein hormone secreted by adipose cells (fat storage cells)

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27
Q

what controls the concentration of leptin in the blood?

A

food intake and amount of adipose tissue in the body

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28
Q

target of leptin

A

group of cells in the hypothalamus of the brain that contribute to the control of appetite - leptin binds to receptors in the membrane of these cells.

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29
Q

if adipose tissue increases,

A

blood leptin concentrations rise, causing long-term appetite inhibition and reduced food intake

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30
Q

describe experiments done on obese mice

A
  • they had two copies of recessive allele, ob, causing their adipose cells to be unable to produce leptin
  • feed ravenously, become inactive and gain body weight, mainly through increased adipose tissue
  • when these mice were injected with leptin their appetite declined, energy expenditure increased, and body mass dropped
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31
Q

why did leptin injections not work as a weight loss method?

A
  • in contrast to ob/ob mice, most obese humans have exceptionally high blood leptin concentrations
  • target cells in hypothalamus have become resistant to leptin so fail to respond to it, even at high concentrations
  • appetite not inhibited and food intake is excessive
  • more adipose tissue develops, causing a rise in blood leptin concentration but leptin resistance prevents inhibition of appetite
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32
Q

a very small proportion of cases of obesity in humans are due to

A

mutations in the genes for leptin synthesis or its various receptors on target cells

33
Q

trials in people with such obesity have shown

A

significant weight loss while the leptin injections are continuing; however, leptin is a short lived protein and has to be injected several times a day. also affects the development and functioning of the reproductive system, so is not suitable to children and YAs

34
Q

circadian rhythms

A

humans are adapted to live in a 24-hour cycle and have rhythms in behaviour that fit this cycle

35
Q

what do circadian rhythms depend on?

A

two groups of cells in the hypothalamus - suprachiasmatic nuclei (SCN).

36
Q

function of SCN

A

control secretion of melatonin (hormone) by pineal gland.

37
Q

describe melatonin secretion

A

increases in the evening and drops to a low level at dawn

38
Q

why do blood concentrations of melatonin rise and fall rapidly in response to changes in secretion?

A

the hormone is rapidly removed from the blood by the liver

39
Q

state three effects of melatonin

A
  • the sleep-wake cycle: high levels of melatonin cause drowsiness and promote sleep through the night. falling levels encourage waking at the end of the night
  • night-time drop in core body temperature
  • decreased urine production at night: melatonin receptors have been discovered in the kidney
40
Q

describe how melatonin secretion is regulated

A

a special type of ganglion cell in the retina of the eye detects light of wavelength 460-480nm and passes impulses to cells in the SCN. This indicates to the SCN the timing of dusk and dawn and allows it to adjust melatonin secretion so that it corresponds to the day-night cycle.

41
Q

how does jet lag come about?

A

the SCN and pineal gland are continuing to set a circadian rhythm to suit the timing of day and night at the point of departure rather than destination.

42
Q

initially, the development of the embryo is

A

the same in all embryos and embryonic gonads develop that could either become ovaries or testes

43
Q

what does the developmental pathway of the embryonic gonads and thereby the whole baby depend on?

A

the presence or absence of one gene

44
Q

if the gene SRY is present

A

the embryonic gonads develop into testes.

45
Q

what does SRY do?

A

it codes for a DNA binding protein called TDF (testis determining factor(, which stimulates the expression of other genes that cause testis development

46
Q

where is SRY located?

A

on the Y chromosome

47
Q

when would embryonic gonads develop as ovaries?

A

when embryos have 2 X chromosomes and so do not have a copy of the SRY gene. TDF is not produced and the embryonic gonads develop as ovaries

48
Q

when do the testes develop from the embryonic gonads?

A

in about the eighth week of pregnancy

49
Q

the testes develop 1, 2, 3, at an early stage and these produce 4 which causes male genitalia to develop

A

testosterone-secreting cells
testosterone

50
Q

what happens at puberty in males?

A

the secretion of testosterone increases

51
Q

effects of increased testosterone secretion

A
  • sperm production in the testes (primary sexual characteristic of males)
  • secondary sexual characteristics: enlargement of the penis, growth of pubic hair, deepening of voice due to growth of the larynx
52
Q

describe female hormone secretion

A
  • estrogen and progesterone are always present in pregnancy
  • at first they are secreted by the mother’s ovaries and later by the placenta
  • in the absence of fetal testosterone and the presence of maternal oestrogen and progesterone, female reproductive organs develop
53
Q

effects of increased oestrogen and progesterone secretion during puberty

A
  • female secondary secondary sexual characteristics: enlargement of the breasts, growth of pubic and underarm hair
54
Q

draw a labelled diagram of the female and male reproductive systems

A
55
Q

testis

A

produce sperm and testosterone

56
Q

scrotum

A

hold testes at lower than core body temperature

57
Q

epididymis

A

store sperm until ejaculation

58
Q

seminal vesicle and prostate gland

A

secrete fluid containing alkali, proteins and fructose that is added to sperm to make semen

59
Q

urethra

A

transfer seen during ejaculation and urine during urination

60
Q

penis

A

penetrates the vagina for ejaculation of semen near the cervix

61
Q

ovary

A

produce eggs, oestrogen, and progesterone

62
Q

oviduct

A

collect eggs at ovulation, provide a site for fertilisation then move the embryo to the uterus

63
Q

uterus

A

provide the needs of the embryo and then foetus during pregnancy

64
Q

cervix

A

protect the foetus during pregnancy and then dilate to provide a birth canal

65
Q

vagina

A

stimulate the penis to cause ejaculation and provide a birth canal

66
Q

vulva

A

protect internal parts of the female reproductive system

67
Q

what is the menstrual cycle controlled by?

A

negative and positive feedback mechanisms involving ovarian and pituitary hormones

68
Q

state the two phases of the menstrual cycle

A

follicular phase
luteal phase

69
Q

follicular phase

A
  • a group of follicles is developing 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
  • the most developed follicle breaks open, releasing its eggs into the oviduct
  • the other follicles degenerate
70
Q

luteal phase

A
  • the wall of the follicle that released an egg becomes the corpus luteum
  • continued development of the endometrium prepares it for the implantation of an embryo
  • if fertilisation does not occur the corpus lute in the ovary breaks down
  • the thickening of the endometrium in the uterus also breaks down and is shed during menstruation
71
Q

FSH and LH

A

protein hormones produced by the pituitary gland that bind to FSH and LH receptors in the membranes of follicle cells

72
Q

estrogen and progesterone

A

ovarian hormones produced by the wall of the follicle and corpus lute. they are absorbed by many cells in the female body, where they influence gene expression and therefore development

73
Q

FSH function

A

rises to a peak towards the end of the menstrual cycle
- stimulates the development of follicles, each containing an oocyte and follicular fluid
- stimulates the secretion of oestrogen by the follicle wall

74
Q

Estrogen function

A

rises to a peak towards the end of the follicular phase
- stimulates repair and thickening of the endometrium after menstruation and an increase in FSH receptors that make the follicles more receptive to FSH, boosting oestrogen production (positive feedback)
- at high levels, oestrogen inhibits FSH secretion (negative feedback) and stimulates LH secretion

75
Q

LH function

A

rises to a sudden and sharp peak towards the end of the follicular phase
- stimulates the completion of meiosis in the oocyte and partial digestion of the follicle wall allowing it to burst open at ovulation
- LH promotes development of wall of follicle after ovulation into corpus luteum, which secretes oestrogen (positive feedback) and progesterone

76
Q

progesterone function

A

rise at the start of the luteal phase, reach a peak and then drop back to a low level by the end of this phase
- promotes thickening and maintenance of endometrium
- inhibits FSH and LH secretion by pituitary gland

77
Q

draw a diagram showing the various stages of the menstrual cycle and hormones

A

p337

78
Q

describe ivf

A
  1. down-regulation: woman takes a drug each day (usually nasal spray) to stop her pituitary gland secreting FSH or LH. secretion of oestrogen and progesterone therefore also stops. menstrual cycle suspended and doctors can control timing and amount of egg production in woman’s ovaries
  2. superovulation- intramuscular injections of FSH and LH given daily for ~10 days, to stimulate follicles to develop. FSH injections are of higher concentration than usual so far more follicles develop than usual.
  3. injection of HCG- stimulates follicles to mature
  4. micropipette mounted on an ultrasound scanner is passed through uterus wall to wash eggs out of the follicles
  5. each egg is mixed with 50-100,000 sperm cells in sterile conditions in a shallow dish, which is then incubated at 37’C until the next day
  6. if fertilisation occurs then one or more embryos are placed in the uterus when they are ~48 hours old
  7. extra progesterone usually given as a tablet placed inside vagina, to ensure uterus lining is maintained

IB biology (60 decks)

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