Hormone Structure and Action Flashcards
LIVING CHEMICAL COMMUNICATIONS
AUTOCRINE COMMUNICATION
- chemical released by cell affects its own activity
NEUROCRINE/SYNAPTIC COMMUNICATION
- chemical released neuron diffuses across synaptic cleft; affects postsynaptic membrane
PARACRINE COMMUNICATION
- chemical released into extracellular environment; affects nearby target cells
ENDOCRINE/HORMONE COMMUNICATION
- chemical released into bloodstream; selectively affects distant organs
PHEREMONE COMMUNICATION
- chemical released into external environment; affects conspecifics
ALLOMONE COMMUNICATION
- chemical released into external environment; affects heterospecifics
HORMONES
- bioregulators of endocrine system
- secreted via specialised cells directly into blood; transported via it too
- selectively act on target cells (usually far)
- chemical messengers produced in endocrine cells
- 3 main types:
1. PROTEIN/PEPTIDE
2. AMINE
3. STEROID
PROTEIN HORMONES
- have short chains (ie. amino acids); include:
- GH (growth hormone)
- TSH (thyroid-stimulating hormone)
RELEASING HORMONES - CRH (corticotropin-releasing hormone)
- GnRH (gonadotropin-releasing hormone)
REPRODUCTION - FSH (follicle-stimulating hormone)
- LH (luteinising hormone)
SOCIAL BONDING/PARENTAL CARE - oxytocin
- vasopressin
- prolactin
METABOLISM - insulin
- glucagon
AMINE HORMONES
- modified single amino acid (monoamine hormones)
- smaller/simpler than protein hormones; include:
METABOLISM/BODY FUNCTION - adrenaline (epinephrine)
- noradrenaline (norepinephrine)
- thyroid hormones
- melatonin
PROTEIN/AMINE HORMONE ACTION PROCESS
- receptor specific to hormone type between cell inside/outside
- hormones attach; receptor shape alters
- receptor sends secondary messengers inside cell
- secondary messengers alter cell function/trigger multiple bio effects
PROTEIN/AMINE HORMONES
- bind to specific receptors outside cells
- act rapidly (s/m)
- can have prolonged effects
- sensitivity can be altered via increasing/upregulating OR decreasing/downregulating receptor numbers on cell
- stored in vesicles; secreted on demand
STEROID HORMONES
- derived from cholesterol
- made from 4 interconnected carbon rings
- soluble in lipids; include:
SEX HORMONES - oestrogen
- progestins
- androgens (ie. testosterone)
STRESS HORMONES - glucocorticoids
STEROID HORMONE ACTION PROCESS
- hormones passively diffuse into cells
- specifically bind to/act on steroid receptor inside cell
- steroid-receptor complex binds to DNA altering protein production
- act slowly (hours)
- long-lasting effects via DNA transcription
- sensitivity can be altered by presence/absence of co-factors necessary for cell response
- cannot be stored; must be synthesised on demand
ENDOCRINE GLANDS/ORGANS
- follicular cells secrete hormones into lumen
- hormone transported into thin-walled capillary; flows into bloodstream
- ductless = no ducts leading to bloodstream
EXOCRINE VS ENDOCRINE GLANDS
EXOCRINE - duct - secretory product - exocrine cell ENDOCRINE - endocrine cell - blood flow - blood vessel
ENDOCRINE SYSTEM SUBDIVISIONS
NORRIS & CARR (2013)
1. ENDOCRINE (ONLY)
- typically respond to chemical levels in blood; not directly controlled by nervous system
2. NEUROENDOCRINE
hypothalamus -> pituitary -> endocrine glands -> target organs -> effect OR…
hypothalamus -> pituitary -> target organs (via nonapeptide hormones) -> effect
HYPOTHALAMUS
POLYPEPTIDES
- growth-hormone-releasing hormone = stimulates GH release from pituitary gland
- CRH (corticotropin-releasing hormone) = stimulates ACTH release from pituitary gland
- thyroid-releasing hormone = stimulates TSH release from thyroid gland
- GnRH (gonadotropin-releasing hormone) = stimulates FSH/LH release from pituitary gland
- ADH (antidiuretic hormone) = promotes H2O reabsorption by kidneys
- oxytocin = induces labour/milk release from mammary glands in females
ANTERIOR PITUITARY GLAND
POLYPEPTIDES
- GH (growth hormone) = stimulates growth
- ACTH (adrenocorticotropic hormone) = stimulates adrenal glands to secrete glucocorticoids (ie. cortisol)
- TSH (thyroid-stimulating hormone) = stimulates thyroid gland to secrete thyroxine
- FSH (follicle-stimulating hormone)/LH (luteinising hormone) = involved in sex hormone production; regulate female menstrual cycles
- PRL (prolactin) = stimulates female mammary gland growth/milk production
PANCREAS
POLYPEPTIDES
- insulin = decreases blood glucose
- glucagon = increases blood glucose
OVARIES (F)
STEROIDS
- estradiol = regulates development/maintenance of secondary female sex characteristics; other effects
- progesterone = prepares uterus for pregnancy
TESTES (M)
STEROIDS
- testosterone = regulates development/maintenance of male secondary characteristics; other effects
KIDNEYS
POLYPEPTIDES
- EPO (erythropoietin) = increases red blood cell synthesis
STEROIDS
- vitamin D = decreases blood Ca^2+
ADRENAL GLANDS
AMINO ACID DERATIVES
- epinephrine = produces many effects related to short-term stress response
STEROIDS
- cortisol = produces many effects related to short/long term stress responses
- aldosterone = increases Na+ reabsorption via kidneys
THYROID GLAND
AMINO ACID DERATIVES
- thyroxine = increases metabolic/heart rate; promotes growth
PARATHYROID GLANDS
POLYPEPTIDES
- PTH (parathyroid hormone) = increases blood Ca^2+
HORMONE PRODUCTION CONTROL
- production requires constant management
- feedback loops play key role
- gen includes negative feedback; high hormone levels inhibit hormone production -> maintaining homeostasis
- sometimes includes positive feedback (ie. oxytocin secretion in milk let-down effect)
KEY PATHWAYS
1. autocrine feedback
2. target cell feedback
3. brain regulation
4. brain/pituitary regulation
AUTOCRINE FEEDBACK
endocrine cells -> (+negative feedback) target cells
PROSTOGLANDINS (INHIBIT ACID SECRETION)
- stomach cell walls release prostaglandin E^2 to parietal cells in stomach BUT along journey, negative feedback returns to stomach wall cells
- parietal cells release hydrochloric acid
TARGET CELL FEEDBACK
endocrine cells -> target cells -> bio response -> negative feedback to endocrine cells
INSULIN PATHWAY
- pancreas detects high circulating glucose (post meal); releases insulin to muscle/fat cells
- leads to glucose uptake which causes negative feedback to pancreas of low circulating glucose levels
BRAIN REGULATION
hypothalamus -> (via endocrine cell neural/hormonal stimulation) endocrine cells -> target cells -> bio response -> negative feedback to hypothalamus
ALARM RESPONSE
- hypothalamus detects alarming stimulus; activates adrenal medulla
- adrenaline released (ie. to heart) leads to FVF responses; negative feedback (ie. increased heart rate) back to hypothalamus
BRAIN/PITUITARY REGULATION
hypothalamus -> (via hormone release) pituitary gland -> (via tropic hormone) endocrine cells -> target cells (BUT negative feedback to hypothalamus/pituitary gland along way) -> bio response
TEMP REGULATION
- hypothalamus senses low environmental temp
- TRH (thyroid-releasing) activates pituitary gland then thyroid gland; thyroxine released to metabolism cells
- negative feedback to hypothalamus/anterior pituitary via thyroxine inhibition
- metabolism cells increase basal metabolic rate
PITUITARY GLAND
- includes 2 parts doing different things:
1. ANTERIOR PITUITARY/ADENOHYPOPHYSIS - synthesises/secretes hormones
2. POSTERIOR PITUITARY/NEUROHYPOPHYSIS - stores/secretes only (no synthesis)
PITUITARY HORMONE TARGETS
- ADH (antidiuretic hormone)/vasopressin = kidney
- oxytocin = breast
- GH = bone/soft tissues
- ACTH = adrenal gland -> adrenocorticosteroids
- TSH = thyroid gland -> thyroid hormones
- FSH/LH (ICSH) = testes -> testosterone
- FSH/LH = ovary -> estrogen (corpus luteum -> progesterone)
- prolactin = breast
HORMONE EFFECTS
SHORT-TERM (ie. oxytocin’s milk let-down reflex)
LONG-TERM (ie. growth hormone’s bone growth); some can be reversed (ie. psychosocial dwarfism)
SHORT-TERM EFFECTS
OXYTOCIN: MILK LET-DOWN REFLEX
- hypothalamus releases oxytocin neuron to posterior pituitary
- oxytocin released -> mammary glands contract to release milk
- nipple receptors sense sucking (response conditioned to crying) -> positive feedback via nerve impulses stimulating hypothalamus
- when satiated baby stops sucking/crying, stimulation/oxytocin production stops
LONG-TERM EFFECTS
GH (SOMATOTROPIN): BONE GROWTH REGULATION
- hypothalamus releases GHRH (somatocrinin) to anterior pituitary
- this releases growth hormone to influence bone growth
- SLEEP stimulates somatocrinin/GH release; -> enhances bone growth
- STRESS/STARVATION/VIGOROUS EXCERCISE inhibits somatocrinin/GH release -> retarded bone growth
SUMMARY
- endocrine glands release chemicals (hormones) into bloodstream for circulation around body
- NOT exocrine glands (ie. sweat/tear/salivary glands) which release substances onto surfaces/ducts
- released hormones act w/specialised cells oft distance from releasing glands
- protein/amine hormones bind to receptors on cell membrane surface; steroids pass through membrane and bind to receptors inside
- can be released at specific times oft regulated by negative/(rarer) positive feedback loops
- can have short-term (ie. oxytocin milk let-down reflex)/long-term (ie. GH bone growth) effects
