Endocrine System Flashcards
functions
regulates long term processes:
growth, development + reproduction
consists of hormones (chemical messengers) + glands
organs of ES
hypothalamus
pineal gland
pituitary gland
parthyroid glands
thyroid gland
adrenal gland
pancreatic islets
endocrine communication
through the bloodstream, using hormones, target cells are primarily in other tissues and organs + must have appropriate receptors
endocrine glands
ductless glands comprised of endocrine cells
have good blood supply
secrete hormones directly into the bloodstream
hormones
organic chemical messengers produced and secreted by endocrine cells into the bloodstream
bind to receptors (binding sites) in target cells (cells with receptors)
stimulates gene expression/ protein synthesis to regulate, integrate and control a wide range of physiological functions
if there is no binding site that is correct/ complementary then there will be no response from that cell/ organ
types of hormones
amino acid derivatives- small molecules, structurally similar to amino acids (water soluble)
peptide hormones- chains of amino acids- largest class of hormones (water soluble)
lipid derivatives- 2 classes of lipid based hormones- streoid and eicosanoids (lipid soluble)
steroid hormones
anabolic steroids have receptors in muscle that stimulate muscle protein production
not all steroid hormones build muscle
hormones have specific effects
risks of anabolic steroids:
teenagers- early skeletal and sexual maturation (stunted growth)
damage to liver + cardiovascular systems
males- reduced sperm count
females- facial hair
hormone receptor locations
on cell membrane- includes receptors for non-lipid soluble hormones inc epinephrine + norepinephrine, adrenaline, peptide hromones and eicosanoids
trigger signalling cascaded inside cell involving: G proteins + second messengers
inside cell- includes receptor for all steroid hormones and thyroid hormones
active of cAMP
extracellular
- activation of G protein activates enzyme adenylate cyclase
- adenylate cyclase converts ATP to cAMP
- cAMP activates kinase enzymes
- activated kinases affect target cell
different efffects
same hormone can have different effects in different cells with different receptors
same hormone can activate different reponses in different target cells
eg adrenaline- binding to B receptors increases cAMP
adrenaline binding to a recpetors stimulates cAMP breakdown
intracellular recptors
steroid hormones
1. diffusion through membrane lipids
2. bind to cytoplasmic or nuclear receptors
3. binding of hormone receptor complex to DNA
4. gene activation
5. trancription and mRNA production
6. translation and protein synthesis
alteration of cellular structure or activtity > target cell response
thyroid hormones
bind to receptors in mitochondria + in nucleus, increasing ATP production
1. transport across cell membrane
2. binding to receptors at mitochondria and nucleus
same as steroid hormones 3-6
after secretion
free hormones- remain functional for less than 1 hour, bind to target cell receptors or broken down in liver, kidney or by enzymes in plasma
thyroid and steroid hormones- remain in circulation much longer as most are bound, emeter bloodstream
more than 99% become attached to special transport proteins, bloodstrema contains substantial reserves of bound hormones
regulation of endocrine system
controlled by hypothalamus + negative feedback
hypothalamus- interface between nervous and endocrine systems
regulatory hormones affect pituitary function
pituitary- anterior pituitary - hormones that control other endocrine organs
posterior pituitary- oxytocin and ADH release
hypothalamus activity
- production of ADH and oxytocin
- secretion of regulatory hormones to control activity of the anterior lobe of pituitary gland
- control of sympathetic output to adrenal medullae
hypophyseal portal system
neurosecretory neurons at median eminence secrete regulatory factors
enter fenestrated capillaries in capillary bed in hypothalamus
into portal veins
into capillary beds in anterior pituitary
feedback control of endocrine secretion
prolactin regulation- hypothlamus produces releasing factor (PRF) and inhibiting hormone (PIH)
growth hormone regulation- hypothalamus produces releasing hormone (GH-RH) and inhibiting hormone (GH-IH)
anterior pituitary hormone
effects of growth hormone
acts on liver to promote release of somatomedins eg insulin growth factors (IGFs)
IGFs stimulate tissue gorwth and increase amino acid uptake/ protein synthesis
growth hormone acts directly on tissues to:
stimulate cell division in epithelial and connective tissue
stimulate triglyceride breakdown in adipocytes
stimulate liver glycogen breakdown
posterior pituitary hormones
ADH- in kidneys, water reabsoprtion - elevation of blood volume and pressure
OXT- males - smooth muscles in ductus deferens and prostate gland
females- uterine smooth muslce (labour contractions) and mamary glands (lactation)
pineal gland
contains
neurons - collaterals from visual pathways
pinealocytes secrete melatonin- lowest production during daylight
functions of melatonin- influences circadian rhythms + antioxidant
thyroid gland
anterior to thyroid cartilage of larynx
two lobes connected by narrow isthmus
stores and secretes thyroid hormones- thyroxine + triiodothyronine
thyroid hormones increase sodium pottassium ATPase production
effects of thyroid hormones
increase oxygen and energy consumption
increase HR
increase sensitivity to sympathetic stimulation
stimulates red blood cell formation
affects activity of other endocrine tissues
increases bone turnover
thyroid follicles
hollow spheres lined by cuboidal epithelium, surrounded by capillaries
contain colloid (protein rich fluid)
follicle cells synthesise tyrosine rich thryoglobulin
iodine incorporated to form thyroxine and triiodothryonine
C cells
produce calcitonin
important in calcium homeostasis
reduces serum calcium- deposition in bone, increased excretion by kidney
