Hormone Structure and Action

Question 1

LIVING CHEMICAL COMMUNICATIONS

Answer 1

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

Question 2

HORMONES

Answer 2

• 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

Question 3

PROTEIN HORMONES

Answer 3

• 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

Question 4

AMINE HORMONES

Answer 4

• modified single amino acid (monoamine hormones)
• smaller/simpler than protein hormones; include:
  METABOLISM/BODY FUNCTION
• adrenaline (epinephrine)
• noradrenaline (norepinephrine)
• thyroid hormones
• melatonin

Question 5

PROTEIN/AMINE HORMONE ACTION PROCESS

Answer 5

• 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

Question 6

PROTEIN/AMINE HORMONES

Answer 6

• 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

Question 7

STEROID HORMONES

Answer 7

• derived from cholesterol
• made from 4 interconnected carbon rings
• soluble in lipids; include:
  SEX HORMONES
• oestrogen
• progestins
• androgens (ie. testosterone)
  STRESS HORMONES
• glucocorticoids

Question 8

STEROID HORMONE ACTION PROCESS

Answer 8

• 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

Question 9

ENDOCRINE GLANDS/ORGANS

Answer 9

• follicular cells secrete hormones into lumen
• hormone transported into thin-walled capillary; flows into bloodstream
• ductless = no ducts leading to bloodstream

Question 10

EXOCRINE VS ENDOCRINE GLANDS

Answer 10

EXOCRINE
- duct
- secretory product 
- exocrine cell
ENDOCRINE
- endocrine cell
- blood flow
- blood vessel

Question 11

ENDOCRINE SYSTEM SUBDIVISIONS

Answer 11

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

Question 12

HYPOTHALAMUS

Answer 12

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

Question 13

ANTERIOR PITUITARY GLAND

Answer 13

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

Question 14

PANCREAS

Answer 14

POLYPEPTIDES

• insulin = decreases blood glucose
• glucagon = increases blood glucose

Question 15

OVARIES (F)

Answer 15

STEROIDS

• estradiol = regulates development/maintenance of secondary female sex characteristics; other effects
• progesterone = prepares uterus for pregnancy

Question 16

TESTES (M)

Answer 16

STEROIDS

- testosterone = regulates development/maintenance of male secondary characteristics; other effects

Question 17

KIDNEYS

Answer 17

POLYPEPTIDES
- EPO (erythropoietin) = increases red blood cell synthesis
STEROIDS
- vitamin D = decreases blood Ca^2+

Question 18

ADRENAL GLANDS

Answer 18

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

Question 19

THYROID GLAND

Answer 19

AMINO ACID DERATIVES

- thyroxine = increases metabolic/heart rate; promotes growth

Question 20

PARATHYROID GLANDS

Answer 20

POLYPEPTIDES

- PTH (parathyroid hormone) = increases blood Ca^2+

Question 21

HORMONE PRODUCTION CONTROL

Answer 21

• 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

Question 22

AUTOCRINE FEEDBACK

Answer 22

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

Question 23

TARGET CELL FEEDBACK

Answer 23

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

Question 24

BRAIN REGULATION

Answer 24

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

Question 25

BRAIN/PITUITARY REGULATION

Answer 25

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

Question 26

PITUITARY GLAND

Answer 26

- includes 2 parts doing different things: 1. ANTERIOR PITUITARY/ADENOHYPOPHYSIS - synthesises/secretes hormones 2. POSTERIOR PITUITARY/NEUROHYPOPHYSIS - stores/secretes only (no synthesis)

Question 27

PITUITARY HORMONE TARGETS

Answer 27

- 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

Question 28

HORMONE EFFECTS

Answer 28

SHORT-TERM (ie. oxytocin's milk let-down reflex) | LONG-TERM (ie. growth hormone's bone growth); some can be reversed (ie. psychosocial dwarfism)

Question 29

SHORT-TERM EFFECTS

Answer 29

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

Question 30

LONG-TERM EFFECTS

Answer 30

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

Question 31

SUMMARY

Answer 31

- 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