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Comparative animal physiology > endocrine system > Flashcards

endocrine system Flashcards

1
Q

exocrine glands

A
  • specialised epthithelial cells secrete products into ducts that carry them outside the body (including into lumens like the GI tract)
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2
Q

endocrine glands

A
  • specialised epithelial cells that secrete hormones into instertial fluid surrounding secretory cells
  • the hormones then diffuse into circulatory systems and target cells with specialised receptors
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3
Q

peptide hormones

A
  • water soluble
  • synthesised within organelles (rough ER)
  • packed into vesicles and stored
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4
Q

steroid hormones

A
  • lipid soluble
  • synthesised from precursors e.g. cholesterol using enzymes
  • not stored, product immediately diffuses across cell membrane
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5
Q

amine hormones

A
  • catecholamines are water soluble
  • thyroid hormones are lipid soluble
  • synthesised from tyrosine (amino acid)
  • stored until secreted
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6
Q

transport of hormones

A
  • hydrophilic hormones mostly dissolved in blood plasma
  • lipophilic hormones bind to plasma proteins (inactivates them)
  • catecholamines transported using both methods (50:50)
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7
Q

action of hormones

A
  • lipophilic and thyroid hormones can cross cell membranes, so bind to internal receptors (sometimes in nuclei - often transcription factors)
  • hydrophilic and catecholamine hormones cannot cross cell membrane, so bind to cell surface receptors, activating ion channels or second messenger systems (activating enzymes or protein synthesis)
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8
Q

permissiveness

A
  • one hormone permits another hormone’s effect
  • e.g. thyroid hormone increases sensitivity to adrenaline
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9
Q

synergism

A
  • effects of two hormones greater than sum of parts
  • e.g. FSH and testosterone both required for sperm production
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10
Q

antagonism

A
  • one hormone reduces effectiveness of another
  • e.g. progesterone decreases uterine responsiveness to oestrogen
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11
Q

paracrine system

A

targets local neighbouring cells

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12
Q

autocrine system

A

affects cell that secreted them

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13
Q

control of blood glucose, Pancreatic islets of Langerhans

A

-alpha cells produce glucagon
- beta cells produce insulin
- glucagon and insulin have antagonistic effects
- delta cells produce stomatostatin
-F cells produce pancreatic polypeptides

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14
Q

control of blood glucose, hypoglycaemia

A
  1. alpha cells secrete glucagon
  2. stimulates hepatocytes to increase glycogenolysis (glycogen-> glucose) and gluconeogenesis (glucose production from amino acids and glycerols)
    3, blood sugar levels rise, hyperglycaemia inhibits glucagon secretion
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15
Q

hyperglycaemia

A
  1. beta cells secrete insulin
  2. hepatocytes increase glycogenesis (glucose into glycogen) and decrease glycogenolysis and gluconeogenesis, body cells increase diffusion of glucose into cells
  3. blood glucose levels decrease, hypoglycaemia inhibits insulin secretion
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16
Q

diabetes mellitus

A
  • t1 destroys beta cells
  • t2 reduced responsiveness of target cells
  • opens closed feedback loop, cells can’t take up glucose when blood sugar rises
  • fat becomes main substrate for respiration, acidic metabolites produced decreases blood pH
  • excessive glucose overwhelms kidneys, increasing water and sugar in kidney
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17
Q

positive feedback loops e.g. oxytocin

A
  • relative unusual as amplifies stimulus, systems generally aim for homeostasis
  • oxytocin secreted by neurosecretory glands in posterior pituitary, important in milk ejection and uterine contraction in labour
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18
Q

oxytocin; milk ejection in mammals

A
  • neonatal mammals cannot suckle milk, needs to be ejected by contraction of myoepithelial cells
    1. suckling stimulates mechanoreceptors in nipple
    2. action potential transmitted through NS to hypothalamus, which contains the cell bodies of the neurosecretory cells
    3. oxytocin secreted by posterior pituitary
    4. triggers contraction of myoepithelial cells, increasing suckling
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19
Q

neuroendocrine control of moulting and metamorphosis in insects

A
  1. PTTH initiates secretion of ecdysone
  2. ecdysone initiates moulting
  3. JH indicated ‘quality’ of moult, a decrease in JH concentration means more adult characteristics after moult
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20
Q

prothoracicotropic hormone (PTTH)

A
  • secreted by neurosecretory cells in brain when excited
  • tropic hormone, controls the secretion of ecdysone
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21
Q

ecdysone

A
  • steroid hormone secreted by prothoracic gland
  • stimulates moulting and metamorphosis
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22
Q

juvenile hormone (JH)

A
  • secreted by corpora allata, regulated by cerebral neuropeptides (allostatin inhibits, allotropin stimulates)
  • functions include maintenance of juvenile characteristics
  • concentration regulated by JH binding protein (JHBP) and JH esterase (JHE)
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23
Q

what happens when the corpora allata of an insect is surgically removed

A

early laval moult into adult at first moult as no JH

24
Q

procenes (JH)

A
  • chemical defence molecule released by some plants
  • blocks JH production in insects that feed on plant
  • insects moult straight into adult, adult will no longer feed on plant
25
Q

suprachiasmatic nucleus (SCN)

A
  • cluster of neurons in hypothalamus
  • receives sensory information about light intensity from eyes
  • acts as a pacemaker for circadian rhythm
26
Q

pineal gland

A
  • secretes melatonin under control of the SCN
  • melatonin concentration increases as light decreases, influences 24hr cycle and seasonal behaviour (short day and long day breeders)
27
Q

posterior pititary gland (neurohypophysis)

A
  • extension of hypothalamus
  • axons and terminals of hypothalamic neurosecretory cells
  • secreted oxytocin and ADH (increases water reabsorption from urine in response to dehydration)
28
Q

anterior pituitary gland (adenohypophesis)

A

-endocrine tissue controlled by hypothalamus (neurosecretory cells secrete releasing and inhibiting hormones into hypophyseal portal system)

29
Q

hormones secreted by anterior pituitary gland with tropic effects

A
  • follicle stimulating hormone (FSH)
  • lutenising hormone (LH)
  • thyroid stimulating hormone (TSH)
  • adrenocorticotropic hormone (ACTH)
30
Q

hormones secreted by anterior pituitary gland with nontropic effect

A
  • prolactin (PRL)
  • MSH
31
Q

hormones secreted by anterior pituitary gland with tropic and nontropic effects

A
  • human growth hormone (hGH)
32
Q

FSH and LH

A
  • tropic hormones secreted by anterior pituitary
  • stimulated by gonadotropin releasing hormone (GnRH)
  • FSH influences sperm or follicle development
  • LH influences testosterone secretion or ovulation and CL production
33
Q

TSH

A
  • stimulated by thyrotropin releasing hormone (TRH)
  • controls thyroid gland (secretes T3 and T4 hormones which regulate metabolism)
34
Q

ACTH

A
  • stimulated by corticotropin releasing hormone (CRH)
  • controls adrenocortex (secretes cortisol as a part of stress response)
35
Q

PRL

A
  • regulated by PIH and PRH
  • initiates and maintains milk secretion in mammary glands
  • example of an ancient hormone, has other specialised uses in other taxonomic groups
36
Q

MSH

A
  • inhibited by dopamine
  • alpha-MSH controls skin colouration by the dispersion of melanin granules in melanocytes
  • small amounts in humans regulated food intake and excitability of nervous system
37
Q

hGH

A
  • regulated by GHRH and GHIH
  • controls liver metabolism and influences it to release insulin like growth factors (IGFs) that control skeletal growth
38
Q

intermediate lobe of pituitary gland

A
  • present in jawless fish, amphibians, reptiles and most mammals
  • absent in birds, cetaceans and rudimentary in humans after birth
  • secretes MSHs
39
Q

adrenal glands in mammals

A
  • on top of each kidney
  • adrenal cortex on outside
  • adrenal medulla on inside
40
Q

adrenal glands in non-mammals

A

two tissue types but not segregated into cortex and medulla

41
Q

control of adrenal cortex

A
  • not directly controlled by neurons of the autonomic nervous system
  • controlled by the hypothalamus, secreting corticotropin releasing hormone (CRH) which stimulates anterior pituitary to secrete adrenocorticotropic hormone (ACTH), which stimulates the adrenal cortex
42
Q

adrenal cortex

A
  • contains steroidogenic hormones which secrete mineralocorticoids, glucocorticoids and weak androgens and estrogens
43
Q

mineralocorticoids

A
  • secreted by steroidogenic cells i the adrenal cortex
  • mainly aldosterone
  • regulates homeostasis of Na+ and K+
  • helps increase/maintain blood pressure and volume
44
Q

glucocorticoids

A
  • secreted by steroidogenic cells in the adrenal cortex
  • mainly cortisol and corticosterone
  • regulates metabolism, freeing up resources by
  • stimulation gluconeogenesis
  • inhibiting glucose uptake by tissues (not including brain)
  • stimulating protein degradation
  • stimulating lipolysis
45
Q

weak androgens and estrogens

A
  • no masculinising/feminising effects due to relatively low importance vs gonads
  • Dehydroepianrosterone (DHEA) is a weak androgen that is unimportant in males but important in female libido and hair growth
46
Q

control of adrenal medulla

A
  • directly controlled by sympathetic division of the autonomic nervous system, as the medulla is a modified ganglion
  • the chromaffin cells of the adrenal medulla are modified postganglionic neurons, but do not have axons that extend to targets, instead have an endocrine function
47
Q

adrenal medulla

A
  • chromaffin cells are modified postganglioic neurons that secrete adrenaline and noradrenaline, which are catecholamines, into circulation to influence target systems
48
Q

adrenergic receptor types

A
  • alpha receptors have a greater sensitivity to noradrenaline
  • alpha1 receptors usually cause an excitatory response e.g. contraction of smooth muscle in blood vessel walls
  • alpha2 receptors usually have an inhibitory response e.g. inhibition of smooth muscle in GI tract
  • beta1 receptors bind to adrenaline and noradrenaline equally and are excitatory and mainly in heart (increase rate and force of contraction)
  • beta2 receptors have greater affinity for adrenaline and are usually inhibitory e.g. bronchiolar dilation
49
Q

stressor

A
  • any disturbance to the body such as an attack, predator presence, competition, change in environmental conditions
50
Q

general adaptation syndrome

A
  • all stressors elicit the same response across all vertebrates
  • controlled by hypothalamus
  • three stages
    1. fight or flight
    2. resistance reaction
    3. exhaustion
  • if any of these stages removes stressor, the response ceases
51
Q

fight-or-flight response

A
  • immediate short term rapid response
  • hypothalamus activates sympathetic division of autonomic nervous systen
  • inhibits non-essential bodily functions to allows maximum physical and mental exertion
  • mobilises resources for immediate activity by direct innervation of organs and activation of adrenal medulla (secretion or adrenaline and noradrenaline)
52
Q

resistance reaction

A
  • longer term response is fight-or-flight is unsuccessful
  • triggered more slowly
  • mobilises resources and converts them into energy for a continued response to the stressor
  • hypothalamus (CRH) stimulate anterior pituitary (ACTH) which stimulates adrenal cortex
  • ACTH suppresses GH, TSH and gonadotropins, suppressing growth, metabolism and reproduction
  • ACTH storage vesicles in pituitary contains beta-endorphin which may exert analgesic effect
  • adrenal cortex secretes cortisol and corticosterone which break down lipids and proteins and stimulates glucose production
53
Q

exhaustion

A
  • long term stress response is not possible
  • prolonged cortisol levels causes muscle wastage and immune suppression
  • resistance reaction ends one body’s reserves have run out
54
Q

octopamine in insects

A
  • insects don’t have adrenaline and noradrenaline
  • octopamine is a biogenic amine that can acts as a neurotransmitter, a neuromodulator and a neurohormone
55
Q

octopamine as a neuromodulator

A
  • can prevent habituation, keeping neurons responsive to threats
  • seen in locust visual neurons and spider sensory hair neurons
  • PM4 neurons release octopamine when under threat
56
Q

octopamine as a neurohormone

A
  • acts on fat body of locust, increasing lipid levels to power flight for an escape response
  • mediates aggression in crickets as a response to competition

Comparative animal physiology (8 decks)

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