6.6 Hormones, homeostasis and reproduction Flashcards
how is blood glucose concentration controlled
insulin and glucagon are secreted by alpha and beta cells in the pancrease to control blood glucose concentration
if the blood glucose conc deviates by 5mmol per liter then homeostasis is triggered
pancrease is two galnds in one organ - exocrine which means it releases digestive enzymes and endocrine which means it releases hormones into the blood
the islets of langerhans are this endocrine tissue - to type alpha and beta
what are alpha cells in teh islet of langerhans
these syntheizise and secrete glucagon if teh blood sugar level falls below a point, so glycogen is broken down into glucose in teh liver cells and released into the blood
what are beta cells in the islet of langerhans
these synthesize and secret insulin if the blood glucose conc is too high, uptake of glucose by e.g. skeletal, muscle and liver tissue and glucose is converted to glycogen
what is type 1 diabetes
consistently elevated blood glucose levels that present at childhood due to an inability to produce insuline, thought to be autoimmune as white blood cells destroy beta cells
presence of glucose in urine
continually elevated glucose damages tissues , their proteins, and impairs water reabsorption, increase volume of urine and dehydration
symptons
- constant thirst
- tired
- need to urinate more
- craves sugary drinks
- test for glucose in urine
treatment
- testing blood glucose levels regularly
- injecting insulin when it is too high or at risk of being too high
- timing is important as insulin does not last long in the blood so often just before a meal
- in the future implantable devices that can release exogenous indulin into the blood when necessary
- mayb ecoaxing stem cell to replace beta cells
what is type 2 diabetes
late onset diabetes caused by a bad lifestyle means that the person in not responsive to insulin as the receptors of insulin are deficient or glucose transporters on target cells are deficient
mainly over 50-65s
risk factors
- sugay
- fatty diety
- obesity
- lack of exercise
treatment
- adjust diet
- small amounts of food often
- not high sugar content
- low glycemic index for starchy food
- high fibre foods to slow digestion
- strenuous exercise and weight loss are beneficial
what is thyroxin
it is secreted by the thyroid gland in the neck to regulate metabolic rate and control body temp
has 4 atoms of iodine - so iodine deficiency leads to less of this
targets all cell s(metabolic rate) but esecailly liver, muscle and brain
higher metabolic rate –> more protein synthesis and growth nad icnrease body heat –>cooling triggers increased thryoxin secretion so body heat rises
what are the effects hypothyroidism
- lack of energy and feeling tired
- forgetfulness and depression
- weight gain despite loss of appetite - less glucose and fat is broken down
- feeling cold - less heat created
- impaired brain development in kids
- constipation as contractions of muscle in teh wall of the gut slow down
what is leptin
a protein hormone secreted by adipose tissue which acts on the hypothalamus of hte brain to inhibit appetite
concentration of leptin is controlled by food intake and the amount of adipose tissue - more of these and leptin conc decreases
leptin binds to receptors in the membrane of cells
how does obesity affect leptin?
discovery on obese mice that injection of leptin caused a reduction in body mass by 30%
tested leptin on obese people to see if this resulted in a decrease of appetite - double blind - used placebos
any body mass lost during the trial was later regained - humans too different to mice
most obese humans have exeptional high leptin levels but the target cells in the hypothalamus have become resistant to leptin so do not respond - appetite is not inhibited - more adipose tissue - rise in blood leptin conc but this has no effect anymore
if people have a mutatation that prevents them from producing leptin then leptin is an effect way of reducing obesity but needs to be injected several times daily and has side effects
what is the role of melatonin?
melatonin is secreted by the pineal gland to control circadian rhythms (24 hour rhythm of sleep and be awake)
the rhythm is set by superchiasmatic nuclei (SCN) cells which control the secretion of melatonin
aslo photoreceptors (special type of ganglion cells in teh retina of the eye) detect light and send nerve impulses to the hippothalamus. this helps the scn adjust as it would usually maintain a rhythm slighly longer than 24 hours
Melatonin is inhibited by light exposure (so melatonin increases in the dark). High levels of melatonin promote sleep in diurnal animals (not nocturnal)
melatonin also casues a drop in core temperature
also potentially causes a decrease in urine production
melatonin and jet lag
SCN and pinneal gland are adjusted to a circadian rhythm at the depature destination not the current place
impulses sent from the ganglion to the retina help the body to adjust to the new regime
melatonin helps as it is effective at promoting sleep
understanding of reproduction before william harvey and after
before - the seed and soil theoruy - a male seed mixes with menstrual blood of female to form an egg into a foetus - aristotle
harvey killed female deer during mating season and found that eggs only developed 2 or more months after mating
so concluded that menstrual blood does not contribute to the development of a foetus but he could not detect teh true mechanism (saif foetus does not result from sexual intercourse)
how are males determined for?
a gene on the y chormosome causes embryonic gonads to develop as testes and secrete testosterone
y chromosome has SRY gene which codes for TDF (testes determining factor)
in women no SRY gene so no TDF so tested develop from gonads into ovaries
male hormones
testosterone causes prenatal development of male genitalia and both sperm production and development of male secondary sexual characterstics during puberty
testes develop from gonad in 8th week of pregnancy - these develop testosterone secreting cells at an early stage which product testosterone
testosterone causes primary sexual characteristics such as male genitalia and secondary such as enlargement of penis, growth of pubic hair, deepening of voice due to growth of larynx
female hormones
estrogen and progesterone casue prenatal development of female reproductive organs and female secondary sexual characteristics during puberty
no sry present so gonads develop into ovaries , oestrogen and progesterone are always present at pregnancy, at first secreted by mother’s ovaries and then placenta - mother’s hormones cause development of female characteristics
during puberty oestrogen and progesterone increase cause enalrgement of breasts, growth of pubic and underarm hair, maintenance of menstrual cycle
male reproductive system front view
the prostate releases alkaline fluids which contain proteins and fructose
epididymis holds sperm until ejaculation
male reproductive system side view
female reproductive system frontal view
vulva is outside the vagina and protects teh female reproductive system
female reprodcutive system side view
what are the role of anterior pituitary and ovarian hormones in the mesnstural cycle?
anterior pituitary hormones -
FSH - act on ovaries to stimulate growth of follicle and stimulates estrogen secretion from follicles
LH - acts on ovaries to trigger ovulation which results in a corpus luteum which produces progesterone
ovarian
estrogen and progesterone prommotes developement of thickening of the endometrium and stimulate FSH and LH secretion in the follicular phase and inhibit FSH and LH in the luteal phase
