genetic and endocrine regulation Flashcards
endocrine regulation
branch of biological sciences concerned with hormones, the glands that secrete. them and their actions
hormone structure
amino acid derivatives- small molecules eg thyroid molecules
peptide hormones-= chains of amino acids
lipid derivatives- steroids derived from cholesteral form gonads and adrenal glands
hormone structure
maintain an optimal internal environment for biochemical process
responsible for a smooth, sequential integration of growth and development
respond to external environment changes eg starvation, infection and trauma
contribute to sexual reproduction through gametogenesis, coitus, fertilisation + foetal development
hormone mode of action
few processes under hormonal control are regulated by only one hormone and few only have one role
additive- net result is greater than each would produce acting along
antagonistic- opposing effects, net results depends on the balance between the 2 hormones
permissive- first hormone is needed for 2nd one to have an effect
integrative- hormones produce different but complementary effects
forebrain
region of the developing vertebrate brain- includes tencephalon + diencephalon which contains thalamus, hypothalamus, epithalamus and subthalamus
pituitary gland- attached to hypothalamus by stalk of neuronal axons + influences almost evry part of the body- regulates functions such as growht
axes
most axes start with the hypothalamus releasing a peptide which causes the pituitary gland to release a hormone which will affect growth via a gland
positive feedback
as more hormone is released, increases the amount of hormone released at hypothalamus
negative feedback
as more hormone is released, leads to less hormone released by hypothalamus
HPG axis
central feature of puberty is reactivation of HPG axis followung quiscence of childhood
active during infancy, inactive during childhood, reactivation of HPG axis is the first sign of puberty
drives the adolescent growth spurt and development of secondary sexual characteristics
operates via testis in boys and ovaries in girls
HPG axis- differences in males + females
negative feedback during most of menstrual cycle + positive feedback between days 12-14 of menstrual cycle
causes a rapid rise in production of estrogen leading to ovulation
rise in estradiol (oestorgen) combined with increases in FSH and LH
negative feedback causes hormones to come back dowon
gonadal steroids induce bone growth and epiphyseal closure- active agent for this indiction in males may be oestrogen
HPG axis also drives development of secondary sexual characteristics
HPS axis
hypothalamic pituitary somatic (somatotropic) axis
hypothalmus- anterior pituitary- liver- IGF-1- bone and muscle growth
IGF-1- insulin like growth factor produced by liver
GHRH- growth horomone releaseing hormone released by hypothalamus
GH released by AP
HPS axis
Gh alone can directly affect muscle, adipose tissue and growth plates
somatostatin- cycle peptide known for its strong regulatory effects through the body (known as growth hormone inhibiting hormone)
stomach is affected by stress, amino acids + hypoglycaemia - releases ghrelin
HPA axis
hypothalamic pituitary adrenal axis
corticotropin releasing hormone (CRH) released by hypothalamus
adrenocorticotropic hormone (ACTH) released by AP
cortisol is a stress hormone; excess cortisol inhibits growth but normal levels are part of the mix that ensures normal growth- if cortisol regulation is not optimal can have negative effects
children exposed to stress early in life show abnormal cortisol levels later on in life
hypothalamic pituiary thyroid (HPT) axis
thyrotropin releasing hormone (TRH) released by hypothalamus
thyroid stimularing hormone released by pitutiary
hypothryoidism
hypo- not producing- dont produce thyroid hormone
can affect child growth and puberty
short stature or slow growtj, rough dry skin, cold intolerence, fatigue, bruising easily, delayed puberty
can also cause excess weight gain
when axes are important
HPG= adolesence/puberty
HPS= during puberty
genetics
growth= genetics x environment
phenotypic variation= genetic variation + environmental variation
σ2P = σ2G + σ2E
variation in any phenotype is due to a combination of genetic variation and environmental variation
heritability
h2 = σ2G / σ2P
statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population
heritability= genetic variation/ phenotypic variation
heritability is always changiing- known as gene by age interaction
birth weight heritability
estimates of the influence of foetal genes, maternal genes, non-genetic maternal factors, environmental effects vary across studies because of unique foetal environment and interaction with mother
estimating heritability
twin studies- often used to assess genetic variation in a trait
identical twins- arise from the splitting of a fertilised egg (genetically identical)
fraternal twins- arise from 2 fertilised eggs (half genes identical)
similarity measured by correlation
all of the additive genetic effects contribute to the MZ similarity- as do the environmetnal affects
half of the genetic effects contribute to DZ similarity, as do all of the shared environmental effects
differences between MZ and DZ twins correaltions correspond to half of the additive genetic effects
H2 = 2x (MZ correlation – DZ correlation)
GWAS
can use genome wide association studies to estimate heritability
can look at every genetic variant and see how it is associated
variants are significantly associated with the outcome fall above the dotted line in a graph
once you know SNPs that cause a phenotype- you can estimate how much variabiloty in the phenotype is explained by those variants
there is missing heritability in these studies- may be as it doesnt consider gene x environment interactions
epigenetics
genes arent changing but the way the body reads the gene changes- explains why heritabiloty studies and genetic twin study results differ
study of how behaviours and environments can cause changes that affect the way your genes work
unlike genetic changes, epigenetic changes are reversible and do not change DNA sequence
epigenome is not stable across your life and epigenetics can help to explain gene by age interaction
partitioning variance
heritability is all about partitioning variance
can do this by using twin studies, nuclear families, extended pedigrees and GWAS
heritability and genetic effects are not constant over age/ time and in all environments- due to epigenetics
