endocrine system Flashcards
what is the endocrine system? what does it consist of?
- one of the major communication system
- consists of glands and organs that secrete hormones
how many hormones can a single gland secrete?
- multiple
what are hormones?
- chemical messengers carried by blood to target cells
why are hormones released?
- released by glands to elicit a response
- enhance/ inhibit cellular reactions
what concentration are hormones present at?
- low concentrations
what cell does a hormone effect?
- only affects specific target cells even though a given hormone travels throughout the body in blood
what do hormones help regulate? (5)
- chemical composition and volume of internal environment e.g. interstitial fluid
- metabolism and energy balance
- contraction of smooth and cardiac muscle fibres
- glandular secretions
- some immune system activities
what do hormones control?
- growth and development
what are the other two roles of hormones?
- regulate operation of reproductive system
- helps establish circadian rhythm
what is the difference between endocrine system and nervous system?
- endocrine involves chemical messengers whereas nervous system involves electrical conduit system
what is the time of action and the effects of endocrine system?
- acts relatively more slow
- often longer lasting effects
what is the time of action and the effects of nervous system?
- instantaneous action (within Ms)
- short lived effect = briefer
what are the mediator molecules and site of action of endocrine system?
- hormones delivered to tissues throughout body by blood
- site is far from site of release ; binds to receptors/ target cells
what are the mediator molecules and site of action of nervous system?
- neurotransmitters released locally in response to nerve impulses
- close to site of release; at synapse it binds to receptors in postsynaptic
what are the target cells of endocrine system?
- cells throughout body
what are the target cells of the nervous system?
- muscles (smooth, cardiac or skeletal), cells, glands, other neurons
what are the three structural classes of hormones?
- amines, peptides/ proteins and steroids
what are amines derived from and secreted by?
- derivatives of amino acid tyrosine
- secreted by adrenal medulla/ hypothalamus
what are examples of amines?
- thyroid hormones, dopamine, catecholamines
what are peptide hormones, are they common?
- polypeptides are most common
- many peptide hormones are synthesised as large, inactive molecules that are cleaved into active fragments
what is an example of a peptide hormone?
- insulin
what are steroids produced by and where from?
- produced from cholesterol by adrenal cortex and gonads
what are examples of steroids?
- aldosterone, cortisol, androgens e.g. testosterone, oestrogens
what are peptide and all catecholamine hormones? how do they circulate?
- water soluble
- circulate dissolved in plasma
what do some peptide hormones bind to?
- plasma proteins
how long does it take peptide hormones and catecholamines to be removed from blood?
- rapid
where are receptors for water soluble peptide hormones and catecholamines?
- on plasma membrane
what do peptide hormones and catecholamine exert in terms of actions?
- rapid (nongenomic) and slower (gene transcription) on same target cell
how long does it take steroid and thyroid hormones to be removed from blood?
- removed more slowly
- as they circulate bound to plasma proteins
how do steroid and thyroid hormones circulate?
- mainly bound to plasma proteins
where are majority of receptors for lipid soluble steroid and thyroid hormones? what do they affect?
- inside target cells
- affect cell function by altering gene expression
what are the major organs involved in removing hormones from plasma? how do they do this?
- liver and kidney
- metabolise or excretes them
describe what liver is used for
- major organ responsible for metabolic inactivation (called metabolism or biotransformation)
describe what kidneys are used for
- filter blood, remove waste products including hormones+ their metabolites
what are some hormones metabolised into?
- more active molecules in their target cells or organs
what does responsiveness of a target cell to a hormone depend on? (3)
- hormone’s concentration in blood
- abundance of target cell’s hormone receptors
- influences exerted by other hormones
what is permissive action? give examples
- action of one hormone enhances the responsiveness or activity of another hormone
e.g. epinephrine and thyroid hormones stimulation of lipolysis
what is synergistic action? what is an example
- effect of two hormones acting together is greater or more extensive than one hormone acting on its own
e.g. follicle- stimulating hormone and estrogens
what is antagonistic action? give an example
- one hormone opposes the actions of another hormone
e.g. insulin, glucagon
what regulates the secretion of many hormones?
- negative feedback systems
what are the inputs that control hormone secretion?
- plasma concentration of an ion or nutrient that the hormone regulates
- neural input to endocrine cells
- other hormones
what is an example of plasma concentration of an ion/ nutrient that the hormone regulates?
- insulin secretion
describe neural input to endocrine cells ; ANS
- autonomic nervous system controls hormone secretion via adrenal medulla and other endocrine glands
what can also secrete hormones?
- neurons in hypothalamus
what is a tropic hormone? give an example
- hormone that stimulates the secretion of another hormone
e.g. thyroid- stimulating hormone or follicle- stimulating hormone
what are the two types of glands in the body?
- exocrine and endocrine
what are exocrine glands?
- secrete their products into duct e.g. sweat and intestines
what are endocrine glands?
- ductless and release hormones into blood
why do disorders of endocrine system vary considerably?
- wide variety of hormones and endocrine glands
what is too little hormones referred to as? give an example
- hyposecretion
e.g. type 1 diabetes
what is too much hormone referred to as? give an example
- hypersecretion
e.g. gigantism
what is the decreased resposiveness of target cells to hormone know as? what is an example?
- hyporesponsiveness
type 2 diabetes
what is an increased responsiveness of the target cells to hormone called?
give an example
- hyperresponsiveness
e.g. elevated heart rate due to increased circulating levels of thyroid hormone
what can hormones be used for?
- pharmalogical administration of hormones for medical purposes
what can hormones result in?
- supraphysiological concentrations and effects not typically observed with at physiological concentrations
what is an example of a medicine containing cortisol?
- corticosteroids are administered to suppress allergens and inflammation
what is the risk of experiencing side effects depending on? (4)
- type of steroid ( oral= act systematically so more likely)
- does
- length of treatment
- age of patient (child/ older adults)
where are hormones synthesised?
- hypothalamus
where do axons pass down and terminate?
- axons pass down infundibulum
- terminate in posterior pituitary and release hormones
what does the anterior pituitary gland secrete?
- growth hormone, thryoid- stimulating hormone, adrenocorticotropic hormone, prolactin and two gonadotropic hormones- follicle- stimulating hormone and luteinizing hormone
what is secretion of anterior pituitary gland controlled by? how are the connected?
- hypophysiotropic hormones from hypothalamus via portal vessels connecting hypothalamus and anterior pituitary gland
what does negative feedback do?
- inhibits hormonal response
where is the thyroid gland?
- sits within the neck in front of trachea
what effects do thyroid hormones have on the body? give an example
- diverse and widespread effect
e.g. protein synthesis in follicular epithelial cells, increases DNA replication and cell division
what does thyroid gland produce?
- thyroxine ( T4= 4 iodine’s) and triiodothyronine (T3)
what is the major thyroid hormone ?
- T3 as T4 converted to T3 in target tissues via enzymes
what is thyroid- stimulating hormone production controlled by?
- negative feedback action of T3 and T4 on anterior pituitary gland and to lesser extent, the hypothalamus
what does TSH cause? what can excessive exposure cause?
- hypertrophy of thyroid tissue
- excessive exposure of thyroid gland to TSH can cause goiter
what is increased T3 and T4 associated with?
- increased oxidative substrate metabolism and mitochondrial enzyme activity = increased carb and lipid metabolism
what is T3 required for? why is it important
- normal production of growth hormone from anterior pituitary gland
- important developmental hormone for NS
what is cortisol secretion mediated by?
- hypothalamus- anterior pituitary gland system
what does cortisol affect in non- stressful situations?
- responsiveness of smooth muscle cells to epinephrine and norepinephrine (permissive)
- helps maintain normal blood pressure
what does cortisol maintain and what are the other functions?
- maintains enzyme conc. involved in metabolism homeostasis to prevent plasma glucose conc. dropping
- anti- inflammatory and anti- immune functions
when is cortisol the highest?
- around 9am
how is metabolism affected in stressful situations ? (4)
- stimulation of protein catabolism in bone, lymph, muscle
- stimulation of liver uptake of amino acids- glucose (gluconeogenesis)
- maintenance of plasma glucose conc.
- stimulation of triglyceride catabolism in adipose tissue, with release of glycerol and fatty acids into blood
what does cortisol enhance in stressful situations?
- enhanced vascular reactivity
- improves cardiovascular performance
what protective effects does cortisol have?
- unidentified protective effects against damaging influences of stress
what does cortisol inhibit in stressful situations?
- inflammation and specific immune responses
- nonessential functions e.g. reproduction and growth
what do massages decrease?
- circulating cortisol levels
how do massages support recovery? (3)
- increased cortisol at rest inhibits immune system
- inhibits inflammatory response
- decreases capillary permeability in inured areas
how is the stress response a combination of endocrine system and nervous system working together?
- sympathetic nervous system is activated, triggering release of epinephrine
- at same time, endocrine system releases cortisol from adrenal glands
what effects does cortisol have on epinephrine?
- synergistic effect
what is the net result of cortisol in stressful situations? (3)
- faster breakdown of fuel stores
- larger increase in cardiac function
- bigger increase in ventilation
what four hormones are most important for human growth?
-growth hormone, insulin- like growth factors 1 and 2
- T3 (childhood/ adolescent)
- insulin (fetal life)
- testosterone and estradiol
what effects do hormones involved in growth have?
- widespread effects
what is growth hormone the major stimulus of?
- postnatal growth
what does growth hormone stimulate?
- release of IGF-1 from liver and other cells; acts locally to stimulate cell division
how else can growth hormones act?
- directly on cells to stimulate protein synthesis
when is growth hormone secretion highest?
- during adolescence
what is growth hormone secretion stimulated and inhibited by?
- stimulated by growth hormone- releasing hormone (GHRH)
- inhibited by somatostatin (SST)
where is testosterone produced in males?
- produced by testes
where are the small quantities of testosterone in women produced from?
- ovaries and adrenal cortex
- peripheral conversion of androgens
what does testosterone promote?
- muscle growth
- development of male sex characteristics
where is oestrogen and progestogen produced from in females?
- produced by ovaries
where else can oestrogens be produced from in post- menopausal females?
- produced in smaller amounts by other tissues e.g. liver, pancreas, bone, adrenal glands, skin, brain, breast
how is estrogen produced in males?
- when FSH binds to FSH receptors
what does oestrogen and progestogen promote?
- development of female sex characteristics
- regulates menstrual cycle and adipose tissue growth
what do oestrogens also promote?
- endothelia function
- protective effects
what is DHEA?
- dehydroepiandrosterone
where is DHEA and its sulfates (DHEAS) produced from?
- adrenal cortex
what are the roles of DHEAS (2)
- precursors for sex hormones e.g. testosterone
- affect various systems of body - purported to be anti- ageing
when does DHEA production peak?
- at age 20-30
- declines progressively with age
how does DHEA increase?
- following low and moderate intensity exercise
- doesn’t increase in older adults
describe oestrogen containing hormone replacement therapy benefits
- maintains muscle mass and prevents fat infiltration into muscle compartment
what are exercise and hormone replacement therapy considered?
- counteractive treatments ; age- related changes in muscle phenotype
what does testosterone containing hormone replacement therapy help?
- preserves muscle tissue
- offset age- related muscle loss rather than cause significant gains
what hormones increase post exercise and what does this promote?
- androgens and testosterone
- helps promote anabolic processes
