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Endo > Endocrine glands in detail > Flashcards

Endocrine glands in detail Flashcards

1
Q

Describe the location of the hypothalamus

A
  • Diencephalon
  • Below thalamus
  • Floor of third ventricle
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2
Q

Outline the embryology of the anterior pituitary and intermediate lobe

A
  • Evagination of oral ectodermal cells
  • Rathke’s pouch
  • True endocrine organ
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3
Q

Outline the embryology of the posterior pituitary

A
  • Neural crest cells neuroectoderm
  • Downward evagination of third ventricle
  • Part of nervous system (storage function)
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4
Q

Which nuclei of the hypothalamus are linked to the posterior pituitary gland?

A
  • Supraoptic

- Paraventricular

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5
Q

What is produced by the paraventricular nucleus in the hypothalamus?

A
  • Oxytocin
  • ADH
  • TRH
  • CRH
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6
Q

What is produced by the supraoptic nucleus in the hypothalamus?

A

Oxytocin and ADH

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7
Q

What is the function of the suprachiasmatic nucleus in the hypothalamus?

A

Biological clock/circadian rhythm

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8
Q

What is the function of the lateral nucleus of the hypothalamus?

A
  • Arousal

- Hunger

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9
Q

What is the function of the arcuate nucleus of the hypothalamus?

A
  • Energy status
  • GnRH
  • GHRH
  • NP-Y
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10
Q

What is the function of the mammillary nucleus of the hypothalamus?

A

Wakefulness

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11
Q

What are the 3 types of input into the hypothalamus?

A
  • Direct sensing by receptors
  • Indirect humoural sensing (via blood) by receptors for circulating hormones
  • Indirect neural sensing (via nerves) by visceral and somatic sensory nerves, limbic system (emotions) and reticular activating system
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12
Q

Give examples of direct sensing by the hypothalamus

A
  • Thermoreceptors

- Osmoreceptors

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13
Q

Describe the role of the hypothalamus in thermoregulation

A
  • Neurons in anterior hypothalamus respond to heat, initiate cooling centre, respond with peripheral vasodilation adn sweating
  • Neurons in posterior hypothalamus respond to cold, initiate heating centre, respond with peripheral vasoconstriction, piloerection and shivering
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14
Q

Describe the role of the hypothalamus in osmoregulation

A
  • Respond to increase blood osmolarity
  • If dehydrated release ADH from SON, secreted via post. pit
  • Kidneys retain water
  • Stimualte neurons in thirst centre of lateral hypothalamus to find something to drink
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15
Q

Describe the role of the hypothalamus in energy balance

A
  • Neurons in arcuate nucleus
  • Sense blood glucose and hormones
  • Leptin causes anorexigenic
  • Ghrelin orexigenic
  • Satiety centre responds to elevated glucose and inhibits eating
  • Appetite centre responds to low glucose and stimulates eating
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16
Q

What are the outputs of the hypothalamus?

A
  • Neurosecretory output to the posterior pituitary

- Inhibitory and stimulatory hormones to the anterior pituitary

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17
Q

Describe the neurosecretory output of the hypothalamus

A
  • To posterior pituitary
  • ADH and oxytocin
  • Cell bodies in nuclei of hypothalamus
  • Axons descend into posterior pituitary
  • Nerves terminate on blood vessels and release hormone directly into circulation
  • Simulates release of hypothalamic hormones ADH adn oxytocin stored in post pit into general circulation
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18
Q

Describe the inhibitory and stimualtory hormone output from the hypothalamus

A
  • To anterior pituitary
  • Secreted into blood
  • Blood circulates from hypothalamus to anterior pituitary gland via pituitary portal circulation
  • Control release of other hormones from anterior pituitary
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19
Q

Compare tonic and episodic secretion from hypothalamus

A
  • Normal vs emergency
  • Tonic: constant, some fluctuations e.g. CRH
  • Episodic: when corrective response required, large release of hormone e.g. ADH, oxytocin
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20
Q

Give an example of how neuroendocrine hormones can act as hormones and neurotransmitters

A
  • Dopamine
  • Catecholamine that acts at heart via adrenergic receptors to stimulate heart and blood vessles
  • Also inhibitory hypothalamic hormone
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21
Q

Define ultradian rhythm

A

Occuring more frequently than every 24 hours

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22
Q

Define infradian rhythm

A

At intervals longer than 24 hours

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23
Q

Define circadian rhythm

A

Biological process with 24 hour endogenous rhythmicity matching the rotation of the earth

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24
Q

Describe the biological clock of the hypothalamus

A
  • Light sensed by retina
  • Transmitted via nerve pathways to hypothalamus
  • To suprachiasmatic nucleus
  • Stimulation of pineal gland to produce melatonin
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25
Q

How are the hypothalamus and anterior pituitary connected?

A

Hypothalamic pituitary portal system

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26
Q

How are the hypothalamus and the posterior pituitary connected?

A
  • Axons from SON and PVN of hypothalamus to posterior pituitary
  • Release hormones into circulation
  • Posterior pituitary is storage site
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27
Q

Describe the hypothalamic pituitary portal system

A
  • Hypothalamic neurons terminate on primary plexus capillaries within hypothalamus
  • Hypophyseal portal veins connect hypothalamus to anterior pituitary
  • Secondary plexus within anterior pituitary
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28
Q

List the hypothalamic releasing hormones

A
  • CRH (corticotropin-releasing hormone)
  • TRH (thyrotropin-releasing hormone)
  • GHRH (growth hormone/somatotropinn releasing hormone)
  • GnRH (gonadotrophin releasing hormone)
  • PRL-RH (prolactin releasing hormone)
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29
Q

List the inhibitory hormones of the hypothalamus

A
  • GHIH/somatostatin (growth hormone inhibitory hormone)
  • GnIH (gonadotrophin inhibitory hormone)
  • Dopamine
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30
Q

What is the function of dopamine?

A

Inhibits prolactin and other hormones

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31
Q

Desribe the tonic inhibition of prolactin

A
  • Held in inhibited state until release needed
  • Inhibition maintained by dopamine
  • PVN of hypothalamus
  • Remains inhibited until stimulated by TRH, GnRH, PRL-RH, and nervous stimualtion from nursing/suckling
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32
Q

Describe the process of dopamine repression of PRL (prolactin)

A
  • Dopamin secreted by PVN, travels in plexus
  • Binds to G-protein coupled receptor on pit. cell
  • Binding induces DAG/Ca2+, PKA intracellular signalling
  • Switches off prolactin gene and blocks secretion of prolactin already in cell
  • Blocks PRL production at every event within cell
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33
Q

Name the cell types found in the pars distalis of the anterior pituitary

A
  • Thyrotropes
  • Corticotropes
  • Gonadotropes
  • Somatotropes
  • Lactotropes
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34
Q

Name the cell type found in the pars intemedia

A

Melanotropes

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35
Q

What is produced by the thyrotropes and where does it exert its action?

A

TSH, targets thyroid

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36
Q

What is produced by the corticotropes and where does it exert its action?

A

ACTH, targets adrenal cortex

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37
Q

What is produced by the gonadotropes and where does it exert its action?

A

FSH and LH, target gonads

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38
Q

What is produced by the somatotropes and where does it exert its action?

A

GH, targets liver, tissues etc

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39
Q

What is produced by the lactotropes and where does it exert its action?

A

Prolactin, targets mammary glands

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40
Q

What is produced by the melanotropes?

A

MSH (melanocyte stimulating hormone)

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41
Q

Describe the anterior pituitary cell types that can be defined by staining

A
  • Chromophobes: stain poorly
  • Chromophils: stain well and can be split into acidophils and basophils
  • Acidophis: take up acid dyes (eosin, red)
  • Basophils: take up basic dyes (haematoxylin, blue)
42
Q

What anterior pituitary cells are acidophils?

A
  • Somatotropes (GH)

- Lactotropes (PRL) (only when PRL in cytoplasm)

43
Q

What anterior pituitary cells are basophils?

A
  • Corticotropes (ACTH)
  • Thyrotropes (TSH)
  • Gonadotropes (FSH and LH)
44
Q

Give the prevalence of each cell type in the pars distalis of the anterior pituitary

A
  • Somatotrope 50%
  • Lactotrope 15-20%
  • Corticotrope 15-20%
  • Gonadotrope 15-20%
  • Thyrotrope 5%
45
Q

What hormones regulate GH secretion?

A
  • GH-releasing hormone (GHRH)
  • Somatostatin (GHIH)
  • Ghrelin
46
Q

Describe the products of the corticotropes

A
  • Produce prohomeone proopiomelanocortin (POMC)
  • Cleaved to produce ACTH, MSH, beta-lipotrophic hormone, beta-endorphin, enkephalin and corticotropin-like intermediate lobe peptide (CLIP)
47
Q

Describe the cleavage of POMC

A
  • First POMC cleaved to ACTH using prohormone convertase-1
  • Only in pars distalis and pars intermedia
  • Then ACTH cleaved using prohormone convertase 2 in pars intermedia to give alpha-MSH and CLIP
48
Q

What are the actions of growth hormone?

A
  • Stimulates IGF-1 secretion from liver
  • Stimulates protein synthesis
  • Stimulates lipolysis
  • Inhibits glucose utilisation by inhibiting insulin
49
Q

Describe lactotrope regulation

A
  • Tonic inhibition by dopamine
  • Stimulated by TRH
  • Hypertropy during pregnancy in preparation for lactation
  • Placenta will signal back to mother to prepare for birth
50
Q

Describe corticotrope regulation

A
  • Stimulated by corticotropin releasing hormone (CRH)

- Negative feedback from ACTH

51
Q

Describe thyrotrope stimulation

A
  • Tonic stimulation

- TRH from hypothalamus

52
Q

Describe the concept of negative feedback

A
  • Something that is produced goes back up stream to turn off or reduce production of the negative feeback signal
  • Closed, short and long feedback loops
53
Q

Describe closed feedback loops

A

Target cells secrete hormones that affect their own secretion
- Usually negative

54
Q

Describe open loops

A
  • No direct feedback
  • Stopped by removal of stimulus or depletion of biochemicals
  • e.g. stimulation of milk let down
55
Q

Describe short feedback loops (give an example)

A
  • Feedback to the stimulating organ directly “above”

- e.g. ACTH from pituitary back to hypothalamus to reduce secretion of CRH

56
Q

Describe long feedback loops (give an example)

A
  • Feedback to further up the chain
  • i.e. hormone from ultimate effector gland to initial stimulating gland
  • e.g. cortisol from adrenal to hypothalamus to reduce secretion of CRH to reduce ACTH
57
Q

Describe positive feedback loops

A
  • Rare
  • Secretion of hormone increases in response to feedback from that organ
  • Amplification
  • E.g. oxytocin in parturtition
58
Q

What is meant by independent systems? Give examples

A
  • Systems that do not depend on hypothalamus or pituitary gland
  • Glucose regulation (insulin, glucagon, epinephrine)
  • Calcium regulation PTH, calcitonin, active vit D)
  • Sodium and potassium regulation
  • Gastrointestinal enzyme secretion
59
Q

Give examples of pituitary disorders

A
  • PPID in horses
  • Pituitary neoplasms
  • Giantism
  • Acromegaly
  • Pituitary dwarfism
  • Deletion of POMC gene in some labradors
60
Q

What are the potential causes of hormone deficiency?

A
  • Less functional tissue to produce hormone
  • Interference with hormone synthesis such as dietary deficiencies
  • Reduced stimulation from higher pathways
61
Q

Outline pituitary dwarfism

A
  • Most common in GS
  • Cysts instead of adenohypophysis
  • No GH = small dog
  • No ACTH = hypoadrenocorticism
  • No TSH = hypothyroidism
  • Small, abnormal coat, metabolism non-functional
  • Most die stillborn, some live up to 5 years
  • In utero exploit maternal hormones
62
Q

What may cause hormone excess?

A
  • Increased synthesis of hormone by affected tissue
  • Loss of negative feedback control due to:
  • Hormone was never under -ve feedback control
  • Tissue continues secretion regardless of stimulating hormone
  • Unable to send signal, or upstream tissue unable to receive/respond to signal
63
Q

Outline adenomas of pars distalis

A
  • Overproduction of ACTH and GH

- Non-function

64
Q

Outline GH-secreting pars distalis tumours

A
  • Affects acidophils within pars distalis
  • very rare
  • Excess GH and IGF-1 from liver
  • Alters growth, and affects energy metabolism
  • Differential diagnosis for diabetes mellitus
65
Q

Outline giantism

A
  • Hyperactivity or neoplasia before adolescence
  • All tissues grow rapidly incl bones
  • Hyperglycaemia as GH antagonises insulin
  • Pancreatic failure due to overwork
  • Diabetes mellitus
  • Eventually pan-hypopituitarism due to negative feedback loop
66
Q

Outline acromegaly

A
  • Pituitary disorders after adolescence
  • Epiphyses of bones fused
  • Only bones of extremities grow (paws)
  • Membranous bones of face grow
  • Mandible continue to grow leading to prognathism
  • Eventual organ enlargement
  • Kyphosis of vertebrae (hunchback)
67
Q

What is the function of ADH?

A

Acts on renal tubules to retain water

68
Q

Outline the detection of dehydration by osmoreceptors

A
  • Within hypothalamus
  • Respond to an increase in osmolarity of ECF
  • More ADH released
  • More water conserved and behaviour to find a drink
69
Q

OUtline the detection of dehydration by stretch receptors

A
  • Volume receptors in atria and veins
  • Respond to large changes (10%
    decrease)
  • Decrease in distension detected
  • nervous impulses to hypothalamus, more ADH released = water conservation
70
Q

Outline the integration of signals from osmoreceptors in hypothalamus and stretch receptors

A
  • Osmoreceptors most sensitive

- Stretch receptors triggered as emergency response where there is a large decrease in volume

71
Q

Where does ADH act?

A

Distal tubule and colleccting duct

72
Q

Where are aquaporins always present?

A
  • In proximal ubule on all membranes

- In distal tubule and collecting duct always on baso-lateral membranes

73
Q

Where are aquaporins inserted under the influence of ADH?

A

Apical membranes

74
Q

Explain how ADH inreases aquaporin density on tubule surfaces

A
  • ADH binds to receptors
  • Activates adenyl cyclase
  • Produce cAMP
  • Vesicles containing AQP-2 move to cell surface
  • Inserted via exoctysosi
  • Proportional to plasma ADH concentration
75
Q

What is diabetes insipidus?

A

Increased urine output caused by ADH dysregulation

76
Q

What are the 2 types of diabetes insipidus?

A
  • Neurogenic

- Nephrogenic

77
Q

Describe neurogenic diabetes insipidus

A
  • Inadequate ADH released from pituitary

- Must be this if injection of exogenous ADH leads to concentrated urine

78
Q

Describe nephrogenic diabetes insipidus

A
  • Inadequate response to ADH within the kidney

- Will not respond to exogenous ADH

79
Q

What is congenital diaebtes insipidus caused by?

A

AQP-2 deficiency (nephrogenic)

80
Q

Describe the role of prolactin in milk synthesis

A
  • mRNA for milk protein synthesis

- alpha-lactalbumin (aLA) for lactose production

81
Q

What is the role of lactose in milk?

A
  • Draws water into gland

- Easily digestible so ideal for neonate

82
Q

Describe the role of alpha-lactalbumin

A
  • Lactose productioin
  • Is a whey protein produced by mammary epithelial cells, forms complex with galactosyl transferase to form lactose synthase
83
Q

What is the role of oxytocin?

A
  • Stimulates milk let down
  • Uterine muscle contraction duing parturitio
  • Induces contraction of alveoli in mammary glands
84
Q

Outline the neural transmission to stimulate oxytocin release

A
  • High density of sensory nerve fibres in teats, detects suckling or prep for milking
  • Impulses via superficial sensory pathways of spinal cord
  • Afferent sensory neurons enter lumbar segments of spinal cord
  • Ascend spinal cord sensory tracts
  • To thalamus, influence cell bodies of neuroendocrine cells
  • Stimulates secretion of oxytocin from nerve endings in posterior pituitary gland into circulation
85
Q

Describe the action of oxytocin in the mammary glands

A
  • Increases pressure within alveoli as myoepithelial cells surrounding alveoli contract
  • Reduces resistance in excretory ducts as myoepithelial cells orientated along long axis of secretory duct, so when contract duct becomes shorter and wider, causing relaxation
  • Reduces resistance in teat canal
  • Results in increased milk outflow
86
Q

Outline how oestrogen:progesterone ratio affecs oxytocin

A
  • Progesterone blocks oxytocin recetpros
  • Oestrogen increass oxytocin receptors
  • In pregnancy, ratio is lower and so inhibits oxytocin
  • In parturition is higher, stimulating oxytocin
87
Q

Describe the neuroendocrine reflex at parturition

A
  • Stimulation of sensory nerve endings in cervix
  • Afferent nerve impulses to the hypothalamus
  • Neuroendocrine cells of PVN and SON depolarise
  • Secrete oxytocin from pars nervosa
  • Enters blood circulation, acts on receptors of myometrium
  • Atrong uterin contractions
88
Q

Describe the clinical relevance of oxytocin

A
  • Can be administered to induce parutrition in horses
  • Other strategies to promote/mimic effect of oxytocin (oestrogen/oestradiol, dexamethasone, PGF2a)
  • Treatment for uterine inertia
  • Retained placenta
89
Q

Describe the HPA axis

A
  • Hypothalamic-pituitary adrenal axis
  • Hypothalamus secretes CRH, acts on ant. pit to secrete ACTH, acts on adrenal cortex to secrete corticosteroids
  • Long and short negative feedback loops
90
Q

Describe the HPT axis

A
  • Hypothalamic-pituitary thyroid axis
  • Hypothalamus secretes TRH, ant pit secretes TSH
  • Acts on thyroid gland to secrete T4 (thyroxine) and T3 (triiodothyronine)
91
Q

Describe the male HPG axis

A
  • Hypothalamic-pituitary gonadal axis
  • Hypothalamus secrete GnRH, (GnIH)
  • Ant. pit secretes FSH and LH if GnRH secreteed
  • Stimulates testes to secrete inhibin (FSH stimulated) and testosterone (LH stimulated)
92
Q

Describe the female HPG axis

A
  • Hypothalamic pituitary gonadal axis
  • Hypothalamus secretes GnRH (or GnIH if inhibiting)
  • Ant. pit secretes FSH and LH
  • In ovaries, FSH stimulates oestradiol and LH stimulates progesterone
93
Q

Outline the control of melatonin release

A
  • Pineal gland responds to light

- More melatonin when dark less when light

94
Q

What are the actions of melatonin?

A
  • Induces sleep
  • Control of moulting
  • Seasonal reproduction
95
Q

Describe melanin production

A
  • Melanocytes in skin

- Stimulated by MSH from melanocytes in pituitary gland (pars intemedia) and hypothalamic neurons (arcuat nucleus)

96
Q

Outline the link between melatonin and MSH

A
  • Seasonal haircoat colour changes
  • Seasonal haircoat shedding (horses)
  • Seaonal anoestrus (horse)
97
Q

Describe the location of the adrenal glands

A
  • On medial side of cranial pole of skidney

- Paired and asymmetrical

98
Q

What are the zones of the adrenal cortex?

A
  • Zona glomerulosa (most outer)
  • Zona fasciculata (middle)
  • Zona reticularis (most inner)
99
Q

Describe the adrenal medulla

A
  • 10-20% of gland
  • Neuroendocrine tissue
  • Secretes catecholamines
  • Acts as post-ganglionic ganglion cells (sympathetic)
100
Q

What is the embryological origin of the adrenal medulla?

A

Autonomic nervous system

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