topic 6.6 - hormones, homeostasis, and reproduction Flashcards
1
Q
function of cells in the pancreas
A
to respond to changes in blood glucose levels
2
Q
set point of blood glucose concentration
A
5 mmol/L
3
Q
what region of the pancreas secretes hormones directly into the bloodstream?
A
small regions of endocrine tissue islets of Langerhans
4
Q
alpha cells
A
synthesise and secrete glucagon if blood glucose levels fall below set point.
5
Q
function of glucagon
A
stimulates breakdown of glycogen into glucose in liver cells and its release into the blood, increasing the concentration
6
Q
beta cells
A
synthesise insulin and secrete it when the blood glucose concentration rises above the set point
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
8
Q
why must secretion of insulin be ongoing?
A
it is broken down by the cells it acts upon
9
Q
define diabetes
A
a condition where a person has consistently elevated blood glucose levels
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
11
Q
symptoms of diabetes
A
- urinate more frequently
- constantly thirsty
- feels tired
- cares sugary drinks
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
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
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
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
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
17
Q
what is thyroxin secreted by
A
thyroid gland (in neck) §
18
Q
why is thyroxin unusual?
A
- chemical structure - contains four atoms of iodine
- almost all cells in body are targets
19
Q
what prevents synthesis of thyroxin?
A
prolonged deficiency of iodine in the diet
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
21
Q
higher metabolic rate ->
A
more protein synthesis and growth and increases the generation of body heat
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
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
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
25
explain constipation in hypothyroidism
contractions of muscle in the wall of the gut slow down
26
define leptin
a protein hormone secreted by adipose cells (fat storage cells)
27
what controls the concentration of leptin in the blood?
food intake and amount of adipose tissue in the body
28
target of leptin
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.
29
if adipose tissue increases,
blood leptin concentrations rise, causing long-term appetite inhibition and reduced food intake
30
describe experiments done on obese mice
- 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
31
why did leptin injections not work as a weight loss method?
- 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
32
a very small proportion of cases of obesity in humans are due to
mutations in the genes for leptin synthesis or its various receptors on target cells
33
trials in people with such obesity have shown
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
circadian rhythms
humans are adapted to live in a 24-hour cycle and have rhythms in behaviour that fit this cycle
35
what do circadian rhythms depend on?
two groups of cells in the hypothalamus - suprachiasmatic nuclei (SCN).
36
function of SCN
control secretion of melatonin (hormone) by pineal gland.
37
describe melatonin secretion
increases in the evening and drops to a low level at dawn
38
why do blood concentrations of melatonin rise and fall rapidly in response to changes in secretion?
the hormone is rapidly removed from the blood by the liver
39
state three effects of melatonin
- 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
describe how melatonin secretion is regulated
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
how does jet lag come about?
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
initially, the development of the embryo is
the same in all embryos and embryonic gonads develop that could either become ovaries or testes
43
what does the developmental pathway of the embryonic gonads and thereby the whole baby depend on?
the presence or absence of one gene
44
if the gene SRY is present
the embryonic gonads develop into testes.
45
what does SRY do?
it codes for a DNA binding protein called TDF (testis determining factor(, which stimulates the expression of other genes that cause testis development
46
where is SRY located?
on the Y chromosome
47
when would embryonic gonads develop as ovaries?
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
when do the testes develop from the embryonic gonads?
in about the eighth week of pregnancy
49
the testes develop 1, 2, 3, at an early stage and these produce 4 which causes male genitalia to develop
testosterone-secreting cells
testosterone
50
what happens at puberty in males?
the secretion of testosterone increases
51
effects of increased testosterone secretion
- 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
describe female hormone secretion
- 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
effects of increased oestrogen and progesterone secretion during puberty
- female secondary secondary sexual characteristics: enlargement of the breasts, growth of pubic and underarm hair
54
draw a labelled diagram of the female and male reproductive systems
55
testis
produce sperm and testosterone
56
scrotum
hold testes at lower than core body temperature
57
epididymis
store sperm until ejaculation
58
seminal vesicle and prostate gland
secrete fluid containing alkali, proteins and fructose that is added to sperm to make semen
59
urethra
transfer seen during ejaculation and urine during urination
60
penis
penetrates the vagina for ejaculation of semen near the cervix
61
ovary
produce eggs, oestrogen, and progesterone
62
oviduct
collect eggs at ovulation, provide a site for fertilisation then move the embryo to the uterus
63
uterus
provide the needs of the embryo and then foetus during pregnancy
64
cervix
protect the foetus during pregnancy and then dilate to provide a birth canal
65
vagina
stimulate the penis to cause ejaculation and provide a birth canal
66
vulva
protect internal parts of the female reproductive system
67
what is the menstrual cycle controlled by?
negative and positive feedback mechanisms involving ovarian and pituitary hormones
68
state the two phases of the menstrual cycle
follicular phase
luteal phase
69
follicular phase
- 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
luteal phase
- 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
FSH and LH
protein hormones produced by the pituitary gland that bind to FSH and LH receptors in the membranes of follicle cells
72
estrogen and progesterone
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
FSH function
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
Estrogen function
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
LH function
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
progesterone function
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
draw a diagram showing the various stages of the menstrual cycle and hormones
p337
78
describe ivf
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
