block C - endo and reproduction Flashcards
why study endocrine pysiology?
because endocrine diseases are very common, examples are diabetes mellitus, thyroid disease and PCOS. drugs affecting this system are very commonly used
what is PCOS?
polycystic ovary syndrome - excess androgen
what are the two chemical ways you can distingish hromones?
peptide Vs steroid hormones
peptide hormones typically cause short- term effects and steroid hormones typically cause long-term effects
what is an example of a peptide hormone and how is its structure regulated?
insulin-its structure is regulated by disulphide bridges
what are some examples of steroid hormones?
cortisol and testosterone
what is an example of a ‘steroid-like hormone’?
thyroxine
what determines the charcteristics of a hormone?
the amino acid sequence
what are some of the characteristic actions of peptide hormones?
they have a rapid onset of action
they’ve got a rapid offset of action
they’re secreted in ‘bursts’ when required
what are the characteristic actions of steroid hormones?
slow onset of action
slow offset of action
secreted to maintain ‘constant’ plasma hormone concentration
how would you explain the differences between steroid and peptide hormone in terms of speed of on and offset?
it depends on their two different mechanisms
peptide is faster
what are peptide hormones involved in controlling in short-term regulation?
glucose
water
calcium
peptide hormones are secreted when they’re needed, when does this stop?
secretion is terminated when desired physiological correction is achieved
how does the control of blood glucose affect hormone secretion?
islets of langerhas cells are sensitive the to the glucose concentration in the blood and they will secrete insulin if its too high and glucagon if its too low
what are the cell types in islets of langerhas?
A ( or alpha) cells - glucagon
beta-cells - insulin
d-cells
why is insulin needed?
it is key to getting glucose into cells and helps to lower blood glucose levels
where is glucose stored in the body and what form does it take?
its stored in the liver as glycogen
what happens when blood glucose is low?
the A cell is a source of glucagon and this helps to mobilise glycogen from storage places like the liver and add the glucose back into the circulation
why is the one hormone to raise the glucose level and another one to lower it?
because it provides much tighter control than just one
what is the parathyroid hormone?
its a hormone produced in small glands beside the thyroid gland and it raises the calcium blood concentration
how is parathyroid hormone concentration regulated?
if theres low Ca2+ concentrations, the parathyroid cells release the hormone to elevate blood Ca2+ levels
what is the aim of the secretion of hormones with long-term regualtion?
their main aim is to maintain the concentration of hormone within certain physiological limits
what are the main parts of the brain involved in controlling long term regulation hormones?
the hypothalamus and the pituitary gland
what is the main control centre for:thyroxine; cortisol; sex hormones?
thyroxine - thyroid
cortisol- adrenal cortex
sex hormones- gonads (ovaries/testes)
where are hypothalamic hormones secreted form?
they’re secreted into the median eminence in the hypothalamus
how do hypothalamic hormones reach the anterior pituitary to control its secretion?
some of them come down from the median eminence through the long portal vessels into the anterior lobe
what does thyrotrophin releasing hormone cause?
it causes the release of thyrotropin, corticotrophin, growth hormone and gonadotrophins are all controlled in the same way
what are examples of inhibitory factors produced in the hypothalamus?
- dopamine inhibits the production of prolactin
- somatastosin inhibits the production of growth hormone
how does the system maintain the concentraition of hormones within physiological limits?
through negative feedback mechanisms
explain the negative feedback mechanism of thyrotrophin?
TRH brings about the secretion of thyrotropin, which causes the thyroid gland to produce thyroxine which then negatively feeds back
this keeps the thyroxine concentration within certain limits
what is the negative feedback mechanism of cortisol?
CRH releases corticotrophin, then the adrenal gland then releases cortisol (to deal with stress and reduce inflammation) then cortisol feedsback to CRH
what does stress do to cortisol secretion?
it causes a marked increase in cortisol secretion and bring about an essential survival response i.e. in terms of injury or to escape from a life threatening situation
what do thyroid hormones do?
they set the metabolic level of the body
what is essential for growth and development?
thyroid hormones
sex hormones
insulin
growth hormone
what is the other name of growth hormone?
somatrotrophin
what is growth hormone needed for?
- it promotes growth, especially in young people
- in late adult life, lack of growth hormone is associated with immune secretion
- its important in Ca2+ and phosphate retention
- increased protein synthesis
- increase in blood glucose
- increased circulating free fatty acids
what are effects of growth on an individual?
- elongation of the bones
- the epiphysis is a cartilage plate in the bone and the growth occurs until teenage years
- the epiphyseal plate is where cartilage forms and actively proliferating cartilage tissue (chondrocytes)
- as the chondrocytes move further down the bine, the cartilage is converted into bone by osteoblasts at the shaft end of the plate
- finally the ephyseal plate then becomes converted into bone and no more growth of the bone can take place
how can growth hormone affect the growth of bones?
it can promote the conversion of cartilage to bone at shaft edge of the plate and in general promote cartilage to bone production
how does growth hormone affcect the growth of muscle?
it promotes the transfer from the liver of glucose from glycogen and lipids, helping to grow muscle
how does growth hormone affet adipose tissue growth?
it accelarates lipolysis in the adipose tissue, which leads to increased circulating free fatty acids.
then reduced tissue glucose uptake
how does growth hormone work indirectly?
it goes to the liver, then insulin like growth factor-1 (IGF-1) to promote growth
how is growth hormone regulated?
its secreted from the pituitary, its production is promoted by the availability of amino acids, low blood glucose, exercise and stress (chronic stress inhibits growth hormone though)
what hormones allow and inhibit the production of growth hormone?
growth hormone releasing hormone and somatostatin (growth hormone release inhibitory hormone)
IGF-1 also gives negative feedback on the production of growth hormone
grehlin has a complex role in glucose production
what are the conceqences of growth hormone deficiency?
if growth hormone deficiency comes before epiphyseal closure= dwarfism
IGF-1 deficiency= dwarfism
what is IGF-1?
it stands for insulin-like growth hormone
when does epiphyseal closure happen?
in your mid teens
what happens the longer your living without growth hormone?
the greater the effect the longer your living without growth hormone
what are some of the different syndromes of growth hormone deficiency?
- problems with producing growth hormone (deficient GH secretion)
- problems responding to growth hormone (deficient GH action)
- problems producing IGF-1 (deficient IGF-1 production)
what are the consequences of growth hormone excess before growth cessation?
gigantism- people growing really tall
what is the concequence of excess growth hormone after growth cessation?
acromegaly - has effects of the general economy of the body and affects the immune system
what does the thyroid secrete?
thyroxine and triiodothyronine
where is the thyroid?
its in between the larynx and the trachea in the throat
what is thyroglobulin?
its a storage form of thyroid hormone and can be mobilised if needed
what is the enzyme deiodinase important for?
its important for taking the thyroxine into triiodothyronine (this is more potent on endocrinological speak)
what is the action of the thyroid hormone?
- influence activity of almost every body system
what are thyroid hormones required for?
the synthesis of various key enzymes involved in cellular functions like Na-K ATPase, glyceraldehyde 3-phosphate dehydrogenase and beta-adenoceptors and enzymes involved in fatty acid synthesis and cardiac sarcoplasmic Ca2+-ATPase
what os TSH?
thyroid stimulating hormone
what is a control mechanism for the thyroid?
thyroxine extemsively bound to plasma proteins
what are the consequences of thyroid hormone deficiency?
reduced function of most organs
marked reduction in metabolic rate of tissues
what happens if there’s a thyroid hormone deficiency in a newborn?
congenital hypothyroidism (cretinism)
- impaired growth and development and mental retardation
what are the effects of hypothyroidism in adulthood?
severe mental retardation
dwarfism
impaired sexual reproduction
what are the concequences of excess thyroid hormone?
- increased function of most organ systems and a marked increase in metabolic rate of tissues
how do we define the sex of an individual?
genetics (determined by XX or XY chromosomal make up)
gonadal- ovaries/ testes
phenotypic
genital- male/ female external genitalia
behavioural
this is a pathway but i cant show it on this flashcard
what is inside the testes?
interstatial cells (leydig cells)
seminiferous epithelium
seminiferous tubules
what are the functions of testes?
gametogenisis - spermatozoa
endrocrine - androgens
- oestrogens
- inhibin
what are the steps of spermatozoa formation? (spermiogenesis)
- spermatogonia
- primary spermatocyte
- secondary spermatocyte
- spermatid
- spermatozoa
what are the functions of sertoli cells?
-nourish sperm
endocrine function- inhibin; oestrogens; MIF (AMF- anti-mullerian factor)
barrier function- blood/ seminiferous epithelium
phagocytosis of defective sperm
paracrine function- growth factors; androgen binding protein
what are the requirements of spermatogenesis?
optimal temp ~34 degrees (below body temp)
action of various hormones
how is the temp for spermatogenisis kept below body etmperature?
large surface area - scrotum
abundant sweat glands
muscles - cremaster and dartos (to raise and lower the testes)
what blood vessels supply blood to the testes?
pampiniform plexus allows heat exchange
where do the testes develop?
they develop intra-abdominally and then descend into scrotum before birth
what happens if the testes fail to decend?
cryptorchidism occurs and the temp cant be regulated which means the individual will be sterile
what are the hormonal requirements for spermatogenisis?
follicle stimulating hormone (FSH)
luteinising hormone (LH)
testosterone
what are the actions of androgens?
spermatogenisis and external genitalia and ducts and glands
what are the ducts in the male reproductive system?
ejaculatory duct
vas deferens
urethra
epididymis
seminal vesicle
prostate
bulbourethral gland
what are other secondary sexual characteristics?
male pattern baldness
facial hair; body hair; pubic hair
aggressiveness
enlarged larynx
muscle mass
deeper voice
what determines the male sexual organs
something about the gonads
can you tell if its a male or fameal feotus in the early foetal reporductiive stage?
no, its down to hormones and genes
what are the 2 types of ducts in the early foetal reproductive system?
mullerian - female ducts (think of muller yougurt being produced by female cows)
wolffian - male ducts (think of wolves)
what chromosome has the testes determining factor?
the Y chromosome
why do the testes release MIF (AMF (anti-mullerian factor)?
because it causes mullerian duct regression
when do the testes release androgen and what does it do?
about day 65-84 and it causes male external genitalia
how do external genitalia develop along female lines?
if there’s no foetal testes then they wont produce androgen secretion
or if theres no androgen receptors
what ways can the testes be regulated?
by inhibin and testosterone (the testosterone is produced by the gonads) creating a feedback loop back to GnRH
GnRH then produces FSH and LH
where does early oogenisis occur for females?
in the foetus
what are the reproductive cycles called in lower animals, and in humans and higher primates?
lower animals- oestrous cycle
humans and higher primates- menstrual cycle
when do reproductive cycles stop?
after menopause (may continue through adulthood life in males)
what is the average length of a human menstral cycle? and whats the normal range of it in days?
average length- 28.1 days
normal range- 26-35 days
what are the phases of the menstrual cycle?
day 1 - 5 menstrual cycle
days 5-14 follicular phase
day 14- ovulation
days 14-28 luteal phase
what are ovarian events in the mentrual cycle?
folicle developemnt
ovulation
corpus luteum development
what are ovarian events and uterine events controlled by?
hormones
what is oogenisis? where and when does it occur? and how do the numbers decrease?
its the production of an ovum
occurs duting intrauterine developemnt in female foetus
at birth- 2-4 million primary oocytes - arresteed in meiosis
by puberty its only about 400,000 then the number decreases throughout your life
what are the stages to go from an oogonium to a secondary oocyte
- during intra-uterine development, the oogonium develops into a primary oocyte
- at time of ovulation it develops into a secondary oocyte
[only one cell- other material is ejected at 1st polar body]
what are the stages of primary follicle development?
primary oocyte with granuloma cells surrounding it
then the cells surrounding it thicken to produce theca
it then becomes a graafian follicle
then it becomes a cumulus oophorus
what happens after the formation of cumulus oophorus?
ovulation
what are some points about ovarian events?
- several folicles start to develop each month
- usually only one reaches maturity (this is called the dominant folicle
- the rest of the folicles undergo atresea
- in human corpus luteum seems to have pre-determined life span and atrats to degenerate about day 23 if the blastocyst doesnt implant
what happens to the uterus in the folicular phase?
- the endometrium thickens
- glands grow
- blood vessels and spiral arteries grow
what happens in the uterus in the luteal phase if fertilisation hasn’t occurred?
- the thickening of the endometrium declines
- the glands branch and secrete
what happens in the menstrual phase?
the spiral arteries constrict
the inner endometrium becomes ischaemic (reduces blood supply) and the tissue dies
then the arteries dilate to allow blood and necrotic tissue to shed via the vagina
it occurs progressively across the endometrium over several days
what are the changes in the cervix over the menstrual cycle?
think watery secretion around the time of ovulation which allows sperm penetration
what are the changes in uterine motility?
uterine peristaltic contractions occur
- movement in the follicular phase is from the cervix towards the fallopian tubes
- contractions increase as the follicular phase progresses
- contractions decrease during the luteal phase
- contractions increase during the menstrual phase
what is the hormonal control of the menstrual cycle?
follicular stage- oestrogen - helps with endometrial development, and cervical muscles and increases contractions
luteal phase- progesterone- gland development and secretion, cervical muscles and decrease in contractions
menstrual phase- reduced levels of oestrogen and progesterone - constriction of spiral arteries and endometrial shedding
what hormones peak around LH peak?
LH, FSH and oestradiol
what hormone peaks after LH peak?
progesterone
what hormone peaks after LH peak?
progesterone
what do FSH and LH influence?
ovulation
what does oestradiol promote?
GnRH, this is what gives the pulse to FSH and LH
what does oestradiol inhibin do?
it inhibits GnRH production which in turn inhibits LH and FSH
what cells do LH and FSH do?
LH- drives the production of androgens - in females, this happens in thecal cells
FSH- promotes the conversion of androgen into oestrogens in granulosa cells with the help of the enzyme aromatase
