21 Hormonal Control of Growth, Development and Reproduction Flashcards
what is growth hormone (GH)
protein hormone secreted by somatotropin cells
where is GH released from
somatotropic cells in the anterior pituitary
what does an increase in cAMP via growth hormone releasing hormone (GHRH)
enhanced secretion of GH
what is the main stimulus for somatic growth
GH
what promotes synthesis and secretion of IGF-1
GH
where is IGF-1 released from
the liver and other tissues
what are most effects of GH on growth mediated by
IFG-1 action
is release of GH pulsatile
yes
does secretion of GH occur in discrete but irregular pulses
yes
are GH levels detectable between pulses
they can be UNdetectable
when is the amplitude of the secretory pulses at its max
at night, particularly after the onset of deep sleep
what age group is GH secretion highest
in children, maximal during puberty
what is height determined by
bone growth
what does growth involve
cell division and protein synthesis throughout the body
how does growth of bones work
new bone tissue is added at a region called the epiphyseal growth plate
what happens once the epiphyseal growth plate closes
no more bone growth can occur
what do cartilage-producing chondrocytes do
they play an important role in bone growth
also involved osteoclasts/osteoblasts
what do chondrocytes do
add new cartilage at the epiphyseal plate, pushing the bone up
what do osteoblasts do
convert cartilage to bone at the epiphyseal plate
what does GH stimulate differentiation of
precursor cells in the epiphyseal plate into chondrocytes
what do differentiated chondrocytes secrete
IGF-1 and become responsive to IGF-1
what manner does IGF-1 act in
a paracrine/autocrine manner (with IGF-1 from blood) to stimulate chondrocyte cell division
what stimulates protein synthesis in muscle and other cell types
GH / IFG-1
what increases levels of circulating energy sources
GH / IGF-1
is IGF-1 a mitogen
yes, so promotes cell growth and division throughout body
what does thyroid hormone stimulate
synthesis of GH
what does thyroid hormone increase the effects of
GH and IGF-1 on bone growth
what does thyroid hormone promote the differentiation of
chondrocytes
what are the primary reproductive organs in males and females
gonads (testes and ovaries)
what do gonads produce
gametes
what do gonads secrete
(steroid hormones)
- testosterone (highest in M)
- dihydrotesterone (highest in M)
- oestrogen’s (highest in F)
- progesterone (highest in F)
how is sex hormone secretion regulated by gonadotrophins
- the hypothalamus released gonadotropin-releasing hormone (GnRH)
- this acts on the anterior pituitary to release FSH and LH
- this causes ovaries/testes to release sex hormones
what is a common sign of the onset of puberty
an increase in pulsatile GnRH
what is kisspeptin important for
the onset of puberty
it triggers GnRH (Gonadotropin-Releasing Hormone) release from GnRH neurons in the hypothalamus
what does LH produce
testosterone release which causes development of secondary sexual characteristics and accessory structures
what cells does LH act on to release testosterone
leydig cells
what does FSH cause
- spermatogenesis
- release of inhibin
what cells does FSH act on to cause spermatogenesis and inhibin
Sertoli cells
what can testosterone be converted to
dihydrotestosterone (DHT) and estradiol, which can also have important functions in male development
are the receptors for T/DHT and E2 intra or extra cellular
intracellular
what does binding to T/DHT and E2 ligand lead to
translocation from cytoplasm to nucleus and gene transcription changes
what are the main effects of testosterone on growth
- stimulate secretion of GH
- stimulate protein synthesis in many tissues
what do sex steroids (E2) eventually promote
closure of epiphyseal plate
what is E2
estradiol
what does FSH act on to release oestrogen and cause ovulation
the growing follicle
what does LH act on to release progesterone and some oestrogen
the corpus luteum
what does increased oestrogen at the midcycle stimulate
LH secretion from pituitary
what does increases in progesterone and oestrogen after ovulation inhibit
FSH and LH secretion
what do female sex hormones do
- increase bone growth
- stimulate sexual development
- stimulate development of female body
when do levels of pituitary and ovarian hormones fluctuate in women
during the menstrual cycle
what must happen for reproduction to be successful
there must be coordination of egg development and release with preparation of the uterus
what does the ovarian cycle describe
changes occurring in the follicles of the ovary
what do follicles contain
a single oocyte (immature ovum)
what does the uterine cycle describe
the changes that occur in the endometrial lining of the uterus
what regulates the uterine cycle
estrogen/progesterone released by the ovaries
what stimulates oestrogen release from follicles
FSH and LH
does one follicle become dominant
yes and it secretes high levels of oestrogen
what happens when the dominant follicle secretes high levels of oestrogen
it exerts positive feedback which leads to a surge in LH and FSH
what does a surge in LH trigger
ovulation
what does the corpus lutes form and secrete
high amounts of oestrogen and progesterone
what does negative feedback by the combination of oestrogen and progesterone lead to
low FSH and LH levels
what happens if pregnancy doesn’t occur
the corpus luteum degrades, leads to a fall in oestrogen and progesterone
as a result FSH and LH starts to rise
effects of oestrogen and progesterone on the endometrium
it causes thickening and development in preparation for possible pregnancy
what happens as the corpus luteum degenerates
the hormone levels fall which leads to degeneration of the endometrium and menstruation
what does progesterone do in pregnancy
inhibit contractility of uterus
what does oestrogen do in pregnancy
stimulate growth of uterine muscle mass
what is HCG
a pregnancy hormone released from the conceptusw
what does HCG prevent
degeneration of the corpus luteum
does the corpus luteum degenerate in pregnancy
yes after around 3 months — after which oestrogen/progesterone is secreted from placenta
what is menopause
when menstrual cycle ends (around age 50)
what causes menopause
the failure of the ovaries to respond to gonadotropins
concentration of plasma oestrogen is too low to maintain tissues that are dependent on this hormone
why may osteoporosis occur
as oestrogen is a bone protective hormone
does oestrogen cause cardiovascular protective effects
yes
what does HRT involve
administering oestrogen/progesterone
what is a must for fertilisation
coordination of egg fertilisation with the development of the endometrial lining of the uterus
cycle of a follicle
in each menstrual cycle one follicle becomes mature and then at midpoint of cycle it releases an egg
follicle then turns into corpus luteum
what happens when oestrogen and progesterone are released together
NEGATIVE feedback and so a decrease in their levels
what produces HCG
a fertilised egg
what do pregnancy tests detect
HCG levels
what do fertility tests detect
LH levels
