Endocrinology and puberty Flashcards
Principles of endocrine signalling
Stimulus
Endocrine cells sense stimulus and secretes hormone in response to bloodstream
Change in activity in distant cells with appropriate receptors
Primary endocrine glands
Hypothalamus
Pituitary
Thyroid
Adrenal
Pancreas
Pineal
Parathyroid
Organs with secondary endocrine functions
Heart
Thymus
GI tract
Kidneys
Gonads
3 classes of hormones
Protein/peptide
Steroid
Amine
Protein/peptide hormones
Steroid hormones
Amine hormones
Peptide hormones activating target cells
Bind to cell surface receptors
Act via second messengers
Cause rapid change in biochemical activity
Release of stored compounds and alteration of gene transcription
Steroid hormones activation of target cells
Diffuse through the cell membrane
Bind cytoplasmic or nuclear receptors
Act as transcription factors
Alteration in gene expression
What regulates plasma hormone concentration
Negative feedback
How do target cells change their sensitivity or responsiveness to hormones
Change in receptor affinity for ligand or activity
Change in amount of receptor
Change in receptor affinity for ligand or activity
Via covalent modification or action of inhibitors on receptor or signalling molecule
Change in amount of receptor
Decreased number of receptors
Decreased sensitivity to stimulus
Long term exposure to constant stimulus abolishes target response to it
Cells respond to changes in stimulus rather than quantity
Internalisation of GPCR= desensitisation
Categories of primary sexual characteristics
Gonads
Internal genitalia
External genitalia
Female gonads
Ovaries
Oocytes
Follicles
Female internal genitalia
Oviducts
Uterus
Cervix
Upper vagina
External genitalia female
Labia Minorca
Labia Majorca
Clitoris
Male gonads
Testes: sertoli and leading cells
Spermatogonial stem cells
Seminiferous tubules
Male internal genitalia
Epididymis
Vas deferens
Seminal vesicles
External genitalia male
Penis
Safe
Scrotum
Glans penis
When do primary sexual characteristics develop
During foetal development
Master switching gene in primary sexual characteristics
SRY gene
On the Y chromosome
Causes somatic cells of genital ridge to become the testis
What causes the trigger of development of male internal and external genitalia
Testosterone and mullerian inhibiting
Triggers development of male internal and external development
Absence of the SRY gene
Ovaries will develop
Ovarian endocrine activity isn’t essential for development of female primary sexual features
Describe signalling process to determine male and female characteristics sexual
Androgen insensitivity syndrome
Testicular feminisation
X linked recessive
Functioning SRY gene forms testes
Produces testosterone and MIH
Inactivating genetic mutation in androgen receptor gene
Decreases testosterone signalling in target cells
Leads to female external genitalia to develop from common primordial
Absence of any internal genitalia
Congenital adrenal hyperplasia
Loss of 21-hydroxylase function
Decreased corticosteroids and increased androgens
Cortisol down regulates ACTH and CRH secretion
Via negative needback
ACTH stimulates the adrenal gland growth and activity of steroid synthesis enzymes
5 alpha reductive deficiency/ guevodoces
46 x y infant
Female looking external and pseudo aging
At puberty functional penis and male secondary characteristics develop
Mutation in 5 alpha reductive causes inability to produce dihydrotestosterone, high affinity for AR
Pseudovagina
Both gonads and internal genital organs are male
What is puberty
Sexual maturation and fertility
Physical and behavioural changes: secondary sexual features, growth
Definitive signs
Definitive signs of puberty
Menarche in girls
First ejaculaiton in boyss
How does puberty start
Hypothalamus releases gonadotrophin releasing hormone
Stimulates anterior pituitary, gonadotrophins secrete FSH and LH
To the gonads
Hypothalamus-pituitary-gonad or HPG axis
Hypothalamus activation hypothesis
Childhood: regulatory synaptic inputs to the GnRH-producing neuron will inhibit the hypothalamic GnRH secretion
Leptin is important factor involved in puberty intimidation
Leptin bins to LepR and activates Kiss1 neurons
Synapse onto GnRH secreting neurons
Increased kisspeptin signalling
Activation of GnRH secreting neurons
Increased GnRH secretion increased LH and FSH
Increased sex steroids
Mean age at menarche decreasing
High daily energy intake
Associated with higher Leptin levels
Lower age at menarche
Where do gametes originate from
Primordial germ cells
Male gamete production
LH stimulates lending celsl to make testosterone: spermatogenesis, maintains secondary sexual features, support secretory activity of accessory sex glands
FSH stimulates sertoli cells to produce estradiol,androgen-binding protein, inhibit and growth factors For spermatogenesis
Sperm production
Before puberty prospermatogonia are quiescent
At puberty they start mitotic division
Spermatogenesis takes around 64 days
female gametes maturation
LH and FSH required for maturation of a follicle and subsequent ovulation of oocyte
contribute to oestrogen and progesterone secretion
growth spurt
early: low sex steroids to hypothalamus releases GHRH to pituitary
;ate: hypothalamus GHRH to pituiatyr and secretes GH
releases IGF-1
causes increased longituidnal bone growth and epiphyseal growth plate fusion= cessation of longitudinal bone growth
secondary sexual characteristics developmetn
hypothalamus releases GnRH
to anterior pituitary
releases LH and FSH
to the adrenal crotex and gonads
releases oestrogens and androgens
female secondary characteristics
development of breast tissues, enlargement of genitalia, increase in body
fat,
male secondary charactersitics
enlargement of genitalia, deep voice, increase in lean body mass and strength, facial
effect of testosterone on behaviour
testosterone is important for the development and maintenance of male sexual behaviour but other factors are also crucial (e.g. learning, social interactions, biological)
menstrual cycle and sexual behaviour
Increase in intercourse frequency and desire around ovulation
as
↑ female libido and sexual behaviour
↑ women’s sexual attractiveness to males
BUT other factors are involved (e.g. personal motivation, past experiences, cultural & social factors) as ovarectomy does not cause loss of libido
