7: Endocrine System Flashcards
what is the endocrine system
regulates long term processes: growth, development reproduction
consists of: hormones, glands
hormones = chemical messengers to relay information and instruction between cells
endocrine communication = through the blood stream, targets cells in other tissues and organs, cells must have appropriate receptors
endocrine glands
ductless glands comprised of endocrine cells
good blood supply
secrete hormones directly into blood stream
hormones
organic chemical messengers produced and secrete by endocrine cells into the blood stream
bind to receptors (binding sites) in target cells
this stimulates gene expression/protein synthesis to regulate, integrate and control a wide range of physiologic functions
growth hormone regulates cell growth by binding to growth hormone receptors on target cells
hormone types
amino acid derivates: small molecules, structurally similar to amino acids
peptide hormones: consist of chains of amino acids, largest class of hormones
lipid derivatives: 2 classes of lipid based hormones - steroids and eicosanoids
only thyroid hormones (type of amino acid derivative) and steroid hormones lipid soluble
anabolic steroid receptors
some steroids (anabolic) have receptors in muscle that stimulate muscle protein production
not all steroid hormones build muscle
lipid soluble
testosterone is a steroid hormone that can activate genes to increase muscle protein synthesis
hormones have specific risks:
- teenagers have early skeleton and sexual maturation so stunted growth can occur
- damage to liver, CV system and increased cholesterol
- males: reduced sperm count, infertility, baldness, prostate cancer
- females: facial hair, baldness, cessation of menstrual cycles
- receptors may be present in many tissues, with different effects in each one
hormone receptor locations
2 locations of hormone receptors: on cell membrane or inside the cell
on the cell membrane: includes receptors for non-lipid soluble hormones, triggers signalling cascades inside the cell involving G proteins and second messengers
inside the cell: includes receptors for all steroid and thyroid hormones because they can travel through cell membrane
cell membrane receptors: activation of cAMP
hormone binds to receptor o cell membrane, receptor is also bound to G protein
activated G protein from hormone binding activates enzyme adenylate
adenylate cyclase converts ATP to cAMP
cAMP acts as a second messenger to carry message through inside of cell
cAMP activates kinase enzymes
activated kinases affect target cell by altering enzyme activating e.g. opening ion channels
the same hormone can have different effects in different cells due to different receptors
the same hormone can activate different responses in different target cells e.g.
adrenaline binding to beta receptors increased cAMP
adrenaline binding to alpha receptors stimulates cAMP breakdown
inside cell receptors
diffusion of hormone through membrane lipids
hormone binds to cytoplasmic or nuclear receptors
hormone-receptor complex binds to DNA
gene activation
transcription and mRNA production
translation and protein synthesis
alteration of cellular structure or activity leads to target cell response
for thyroid hormones, they bind to receptors on mitochondria as well to increase mitochondrial activity and therefore ATP production
hormones after secretion
free hormones remain functional for less than 1 hour
they bind to target cell receptors or are broken down in liver, kidney or by enzymes in plasma
thyroid and steroid hormones remain in circulation much longer because they are bound to carrier proteins
once they enter blood, more than 99% become attached to special transport proteins, blood stream contains substantial reserve of bound hormones
regulation of endocrine system
hypothalamus is the interface between the nervous and endocrine systems
it produces regulatory hormones that control other endocrine organs
the pituitary is spilt in anterior (produces hormones that control other endocrine organs) and posterior (oxytocin and ADH release)
hypothalamus has 3 different mechanisms to control activity of endocrine system
- some cells directly produce ADH and oxytocin in hypothalamus but axons extend to posterior where they’re released into general circulation
- some regions secrete regulatory hormones that control activity of anterior pituitary - this stimulates release of other hormones from pituitary to control endocrine glands (main mechanism)
- some neurons that travel by the Vagus nerve directly to the adrenal medulla (the centre of the adrenal glands) can cause rapid secretion of adrenaline and catecholamines
pituitary
posterior lobe: made of lots of neuron tissue
pars intermedia: middle section, secrete a different hormone called melanocyte stimulating hormone
anterior lobe: lots of endocrine tissue, lots of blood vessels
hypophyseal portal system: controls anterior lobe hormones
neurosecretory neurons at median eminence secrete regulatory factors
regulatory factors then enter fenestrated capillaries in capillary bed in hypothalamus
regulatory factors travel through portal veins
another capillary bed in anterior pituitary delivers the regulatory factors to the endocrine cells in the anterior pituitary to stimulate the activity of the anterior pituitary cells to produce their hormones which will then be delivered into blood stream
negative feedback control
hypothalamus produces releasing hormone, anterior pituitary then produces hormone 1 which acts on an endocrine organ to produce hormone 2 to reach target cells
if hormone 2 is too high, levels of releasing hormone are reduced
