Review of Endocrinology Flashcards

1
Q

what is a hormone

A

are signalling molecules that modulate the activity of a target tissue

are synthesized by particular endocrine glands and then are secreted in the bloodstream to be carried to a target tissue some distance away

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2
Q

Mechanisms of Hormone Delivery

A
  1. Classical Endocrine Signalling = endo cell –> blood –> target cell
  2. neuroendocrine signalling = neuro-endo cell –> blood –> target cell
  3. autocrine regulation= hormone –> diffuses through interstitial fluid –> target cell nearby
  4. paracrine regulation = hormone from cell A –> diffuses through interstitial fluid –> hormone reaches cell B
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3
Q

Synthesis of Peptides

A

Peptides: short sequence of amino acids that are joined by peptide bonds

substrate: amino acids

Sequence of Events

  1. transcription of peptide gene – > peptide mRNA
  2. translation of peptide mRNA –> peptide
  3. post-translational modifications
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4
Q

Synthesis of Glycoproteins

A

Glycoproteins: polypeptides containing carbohydrate moieties covalently bonded to the alpha and beta subunits

substrate: amino acids, carbohydrates

sequence of events

  1. transcription of polypeptide genes
  2. translation of polypeptide mRNAs
  3. post-translational modifications –> glycosylation

2 subunits:

  • alpha is common among hormones
  • beta is unique for each hormone
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5
Q

Synthesis of steroids

A

steroids: lipids, derived form cholesterol, contain common molecular nucleus: cyclopentanoperhydrophenanthrene
substrate: cholesterol

Sequence of Events
cholesterol–> pregnenolone –> progesterone –> testosterone –> estradiol

cell machinery needed

  • enzymes
  • transcription
  • translation
  • post-translational modifications
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6
Q

Synthesis of Eicosanoids

A

Eicosanoids: lipids, derived from arachidonic acid

Substrate: arachidonic acids (PUFA)

Sequence of Events
membrane phospholipids –> tissue specific isomerases –> end product

cell machinery needed

  • enzymes
  • transcription
  • translation
  • post-translational modifications
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7
Q

Secretion: pattern and duration

A

Episodic: hormone released in bursts, varying in duration and quantity , when predictable, it is also called pulsatile secretion

Basal: hormone remains low and fluctuates with amplitude

sustained: steady secretion for extended time

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8
Q

regulation by feedback

A

affect synthesis or secretion of hormones

represents a fine-tuned control of hormone secretion

feedback is the communication between different tissue/cells

there are positive and negative feedbacks
- positive –> induces greater secretion

  • negative –> inhibits secretion

there are interactions between feedback loops of different hormones
- progesterone levels have a dominant effect over estradiol on GnRH stimulation

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9
Q

transport to the target tissue- what needs a carrier in plasma and what doesn’t ?

A

glycoproteins and peptides are soluble in plasma

steroids and eicosanoids need carrier proteins for transport

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10
Q

Cell Membrane Receptor

A

hormone specific extracellular domain –> trans membrane domain changes shape after binding the ligand –> activated G-proteins create downstream signaling that affects protein synthesis or activity of existing proteins and the biology of the cell

fast response
- protein hormones, steroid hormones, eicosanoids

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11
Q

Nuclear Receptor

A

lipophilic steroid hormones can cross the membrane and go to nucleus
hormone-receptor complex acts as transcription factor
complex binds to a consensus sequence - response element

slow response

  • steroid hormones
  • eicosanoids
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12
Q

receptor density

A

varies with expression of the gene and protein

  • cell type and presence of stimulators or repressors
  • it can be up and or down regulated by (hormone) or duration of exposure
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13
Q

receptor hormone affinity

A

increase interactions between H and R –> increase receptor affinity –> increase biological response

agonists or analogs: similar structure and action as native hormone
- bind receptors with similar or greater biological activity

Antagonists: interferes with native hormone action

  • bind to receptor with greater affinity than native hormone
  • promotes weaker biological activity than the native hormone
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14
Q

Clearance: hormone half-life

A

rate of hormone clearance determines the hormone half-life
- binding proteins (protection)
- glycosylation (protection)
- metabolism
longer half-life –> increase biological activity for a longer time
rapid hormone turnover is often essential for biological action

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15
Q

protein hormone metabolism

A

De-glycosylation or Denaturation
- deglycosylated hormones bind to liver cells then are internalized and degraded in the cytoplasm
- amino acids are recycled
denatured in plasma and lose activity

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16
Q

Eicosanoid Metabolism

A

rapidly degraded in blood
almost all prostaglandins are degraded after one pass through pulmonary circulation

liver deactivates steroids
- double bonds saturated
- sulfate or glucuronide residue attached
excreted in urine