203 - Puberty & Adolescence Flashcards
What is thelarche?
the onset of breast development after 8 years old caused by oestrogen
What is adrenarche?
the onset of increased androgen secretion by the adrenal cortex at 6-8 years old that is not controlled by the HPG axis
what is menarche?
the onset of menstruation at an average age of 13
what is gonadarche?
the onset of and increase in nocturnal secretion of GnRH (start of puberty)
Describe how the hypothalamic-pituitary-gonadal axis works.
*Hypothalamus produces Gonadotrophin Releasing hormone (GnRH), Growth-hormone releasing facto (GRF) and somatostatin.
*In the pituitary:
GnRH stimulates release of Follicle stimulating hormone (FSH) and Luteinising Hormone (LH) which act on the gonads to produce ova/sperm and release testosterone/oestrogen respectively.
GRF stimulates release of Growth Hormone (GH) and somatostatin inhibits the production.
*GH stimulates liver to produce IGF-1 (mediates effects of GH)
what does LH stimulate in females?
proliferation of follicular cells (produce eggs) and thecal cells (production of androstenedione and therefore oestradiol)
what does FSH stimulate in females?
proliferation of granulosa cells (develop oocytes) and incr. expression of LSH receptors
what do LH and FSH together cause in females?
stimulation of oestrogen and progestogen production and stimulate ovulation
what does LH stimulate in males?
acts on leydig cells to stimulate testosterone production
what does FSH stimulate in males?
acts on sertolli cells to stimulate androgen binding protein and inhibin B
what do LH and FSH cause together in males?
stimulate secondary sexual characteristic developments and testosterone production causes -ve feedback on hypothalamus and pituitary
what is virilisation?
the development of sex differences between males and females caused by androgens
what factors initiate puberty
- genetic factors (when did parents start)
- nutritional status - need a BMI of at least 17kg/m2 and 17% fat mass (22% for menarche)
- too much exercise delays it
- chronic inflammatory conditions delay it eg crohn’s
- poor environment delays it
what is consonant pubertal development in girls?
- breast budding at 10-11 as growth spurt begins
- peak growth at 12
- menarche at 13 as growth spurt slows
breast development occurs before pubic and axillary hair development
what is consonant pubertal development in boys?
- testicular growth at 12 with an incr. of >4mls in vol
- peak growth at 14 (longer pre-pubertal growth than girls - 13cm taller)
testicular growth and genital development occurs before pubic & axillary hair development
what test results would you expect in non consonant puberty?
low FSH and LH but high adrenal or gonadal hormones. hair growth before testicular/breast growth
what are the consequences of sexual precocity?
- Initial incr. in stature but a low stature in adulthood due to fusing of epiphyseal plates by oestrogen early.
- early risky behaviour and low attainment in education and work
- impact on time of fertility
what is true central precocious puberty?
- consonant pattern -early normal puberty caused by early activation of HPG axis (Gonadotrophin dependent)
- common is girls but rare in boys (pathological)
- causes: idiopathic in girls, cranial irradiation, tumour, neurological disorder, head trauma, sexual abuse, adoption
what investigations and management is necessary for suspected true central precocious puberty?
investigations - hormone assays LH, FSH sex hormones and MRI of head to exclude tumour. Bone age x-ray and USS to see development. Also parents ages of puberty important
management - GnRH analogue to inhibit LH and FSH secretion which is stopped at 11-12 years old
what is peripheral precocious puberty (pseudopuberty)?
- can be non consonant - caused by abnormal secretions of sex hormones independent of HPG axis (gonadotrophin independent)
- causes - adrenal or gonadal tumour, McCune Allbright Syndrome (cafe-au-lait markings, bone fractures & endocrine dysfunction), Congenital adrenal Hyperplasia (overproduction of testosterone), severe hypothyroidism, Iatrogenic (drugs)
what investigations and management should be carried out in suspected peripheral precocious puberty?
investigations - urine (detectable oestradiol), bone age advance by 2 years or more, bloods (low FSH/LH but high test/oest), tumour markers, pelvic USS, abdo CT or MRI
management - surgery for tumours, GnRH analogues for continuous stimulation, sex steroid restriction
define delayed puberty?
the absence of secondary sexual characteristics by 13.5 in girls and 15 in boys. Or >3 years since thelarche and still no menarche
What causes Constitutional Delay in Growth and Puberty (CDGP)?
idiopathic not pathological.
most common cause
what are the central causes of delayed puberty (intact HPG axis and imparired HPG axis)?
- intact HPG axis - chronic disease/anorexia such as crohns, psychosocial deprivation, steroids, hypothyroidism
- impaired HPG axis - tumours (disruption of hypothalamic/pituitary control), kallmans syndrome (deficiency of GnRH & abnormality of hypothalamus), Prader-Willi syndrome
what are the gonadal causes of delayed puberty?
- bilateral testicular damage eg cryptorchidism, torsion
- Turner’s syndrome - delayed puberty, amennorrhoea, infertility, incr. FSH and LH
- Noonan’s syndrome - male turners cryptorchidism common
- Prader-Willi syndrom - undescended testes or premature adrenarche
- Androgen insensitivity disorder - inability to form androgen receptor
- kleinfelters - lack of gonadal response to gonadotrophins
what are some treatment options for delayed puberty?
- maturation delay -give boys testosterone to cause virilisation until gonadotrophin secretion starts
- gonadal problem eg turners - sex steroid replacement
- treat the systemic disease
what makes up the urogential ridge?
- nephrogenic cord/ridge (lateral) - gives rise to mesonephros (urinary system)
- gonadal ridge (medial) - gives rise to gonads
what 3 cell types make up the urogenital ridge?
- intermediate mesoderm - makes up ridge
- mesothelium - covers surface of ridge along posterior wall
- primordial germ cells - migrate to ridge and developing gonads from yolk sac
indifferent gonads develop by week 7 but what is their structure made from?
- external cortex - from epithelium containing germ cells
* internal medulla - from intermediate mesoderm with primitive sex cords (derived from epithelium) penetrating in
what causes differentiation into a male?
SRY (sex determining region on the Y chromosome) and testosterone
SRY codes for production of Testis determining factor (TDF) which leads to development of medullary cords and primitive testes which produce testosterone and lead to further testicular development
what dominates testicular development?
The medulla -sex cords enlarge & penetrate medulla taking germ cells with them.
- The outer parts (medullary cords) will form the seminiferous tubulues containing : *sertolli cells make up the tubule walls and are stimulated by FSH to support spermatocytes *leydig cells make up space between tubules stimulated by LH to secrete testosterone *germs cells develop into spermatogonia
- The inner part become the rete testis formed by the cords in the medulla linking up
the sex cords connect with the mesonephric duct (wolffian) to form what?
- tubules linking mesonephric duct to rete testis become efferent tubules
- the mesonephric duct becomes the epididymis, ductus deferens and ejaculatory duct
what does the cortex develop into in males?
tunica albiguinea
what dominates in the development of ovaries?
The cortex
- germ cells remain in the cortex to form oocytes
- outer sex cords form cortical cords & inner sex cords degenerate
- thecal and follicular cells formed, produce oestrogen and mesonephric cord degenerates
That causes the male genital duct to develop from mesonephric (wolffian) duct?
testosterone and anti mullerian hormone (from sertolli cells)
what does the urogential sinus develop into?
- upper portion - bladder
* lower portion - urethrea from endoderm
what causes the female genital tract to develop from the paramesonephric (mullerian) duct?
absence of testosterone and anti mullerian hormone
what does initial gonad formation depend upon?
presence of Y chromosome (and SRY)
what does completion of normal gonadal development depend upon?
on the number of X chromosomes
