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CEP > L04 - Hormone synthesis and action > Flashcards

L04 - Hormone synthesis and action Flashcards

1
Q

What is the difference between endocrine and exocrine?

A

Endocrine:
- Secretes hormones into blood directly from cells
- Ductless glands
Exocrine (not part of endocrine system):
- Duct; glands secrete directly into target site via ducts or tubes
(- Enzymes)
- Release secretions outside body

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2
Q

What is comparative endocrinology?

A

Actions of hormones similar throughout evolution

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3
Q

What is clinical endocrinology?

A

Hormones related to pathology

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4
Q

What are mixed glands?

A

A gland that secretes in endocrine and exocrine fashion

e. g.
- Pancreas produces digestive juice + insulin, glucagon and somatostatin
- Mucous and serous cells in salivary glands (two different secretory cells)

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5
Q

What is the difference in the chemical coordinator between the endocrine system and NS?

A

Endo:
- Hormones
- Many diff types affecting diff specific tissue
- Some hormones secreted from nerve endings [neuro-endocrine]
NS:
- NT
- Few types, secreted only onto target tissue

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6
Q

What is the difference in the speed of effect between the endocrine system and NS?

A

Endo:
- Generally slow
NS:
- Generally rapid

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7
Q

What is the difference in the duration of effect between the endocrine system and NS?

A

Endo:
- Generally long lasting
NS:
- Generally short-lived

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8
Q

What is the difference in the localisation of effect between the endocrine system and NS?

A

Endo:
- Secreted into blood therefore widespread
NS:
- Secreted onto target cell so effect very localisd

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9
Q

What is a hormone?

A
  • A substance secreted directly into the blood by specialised cells
  • Carried in the blood to receptors on target organs
  • Present in only minute concentrations in the blood and bind specific receptors in target cells to influence cellular reactions
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10
Q

What are the different mechanisms of chemical signalling?

A
  1. Intracrine
  2. Endocrine
  3. Paracrine
  4. Autocrine
  5. Neuroendocrine
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11
Q

What is intracrine signalling?

A

Generated by a chemical acting within the same cell

- Does not leave the cell

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12
Q

What is endocrine signalling?

A

Chemicals enter the general circulation and reach distant target cells

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13
Q

What is autocrine signalling?

A

Chemical acts on the same cell

- Leaves the cell

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14
Q

What is paracrine signalling?

A

Chemical commn between neighbouring cells within a tissue or organ
- Neighbouring cells, could be via local circ

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15
Q

What is neuroendocrine signalling?

A

Chemical released by a specialised group of cells into the circ and acting on a distant target tissue
- From neurosecretory cells to distant target cells

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16
Q

What is -ve feedback?

A

The process by which body sense change and activates mechanism to reduce it

  • The final product of an endo cascade acts to inhibit the release of hormones higher up in the cascade
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17
Q

What is +ve feedback?

A

The process by which body senses change and activates mechanism to amplify it

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18
Q

What is an endocrine axis?

A

Functional grouping of endocrine glands that stimulate each other

  • Target tissue for a hormone may be another endocrine gland
  • Faults may occur along this axis
    e. g.: Hypothalamo-pituitary adrenal (HPA) axis
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19
Q

What are the 3 main groups of hormones?

A
  1. Protein/ peptide hormones
    - E.g. Insulin
  2. Steroid hormones
    - E.g. cortisol
  3. Amine hormones
    - E.g. Tyrosine
20
Q

Describe protein/ peptide hormones

A
  • Most common type of hormone, of aa
  • Water sol (hydrophilic)
  • Preformed and stored in membrane bound vesicles ready for release by exocytosis
  • Produced on RER as large precursor molc - pre-prohormone
    Pre-prohormone –> prohormone –> hormone
21
Q

What is the benefit of a large precursor?

A

A large precursor allows structural specificity

- Cleaved via proteolysis

22
Q

Give examples of protein hormones

A
  1. Insulin
    - Pre-proinsulin –> Proinsulin –> Insulin + C-peptide
  2. ACTH
    - In the corticotroph, pre-pro-opiomelanocortin produces one ACTH (in other cells, gives diff hormones)
  3. Thyrotropin releasing hormone (TRH)
23
Q

Which proteases are involved in the formation of insulin from pre-proinsulin?

A
  1. Endoprotease
  2. PC2 and PC3
  3. Carboxypeptidase
  • Cleavage of signal peptide and covalent S-S bonds
24
Q

Which hormones have a common a subunit?

A
  1. TSH
  2. LH
  3. hCG
  4. FSH
  • Common a subunit
  • Unique beta subunit
  • Confers specificity
  • Each subunit starts off as a larger molc
25
Q

Describe steroid hormones?

A
  • All made from cholesterol
  • Lipid soluble (lipophilic)
  • Hormones from adrenal cortex and sex hormones (gonads)
  • Synthesised as req and diffuse out of the cell (no exocytosis)
  • Synthesised in SER from cholesterol derived from diet or from acetate
26
Q

What is the rate limiting step of steroid hormone prod?

A 
The first (and rate limiting step) is conversion of cholesterol to pregnenolone
- Pregnenolone formed in mitochondrion but moves to ER for processing into hormones
27
Q

Describe the production of steroid hormones

A
  1. In the nucleus - hydrolysis of esters and release of cholesterol
  2. In mitochondrion - cholesterol to pregnenolone
  3. In SER - processing of pregnenolone
    - Leave by diff or facilitated
28
Q

What is the movement of cholesterol to the mitochondria regulated by?

A

Movement of cholesterol to the mitochondrion is regulated by steroid acute regulatory protein (StAR)
- ACTH (via cAMP) regulates StAR activity and processing of cholesterol

29
Q

Describe the secretion of steroid hormones

A
  • Newly synthesised steroid hormones are rapidly secreted from the cell, with little if any storage
  • Increases in secretion reflect accelerated rates of synthesis
30
Q

Describe the excretion of steroid hormones

A
  • Steroid hormones are eliminated by inactivating metabolic transformations and excretion in urine or bile`
31
Q

Describe amine hormones

A
  • Tyrosine derivatives bound together
  • Small, non-polar molcs
  • Soluble in plasma membranes
  • Lipid soluble (lipophilic)
32
Q

Describe the transport in blood for steroid and thyroid hormones

A

Need to be transported in blood by carrier protein to:

  • Inc solubility in blood
  • Inc half-life (inc sol = inc half life)
  • Create readily accessible reserve in blood
  • Not water soluble, therefore need carrier
  • Specific binding proteins, e.g. Thyroid BG (TBG) and cortisol binding globulin (CBG)
  • Non specific binding proteins, e.g. albumin - loose binding (aldosterone binds to albumin)
33
Q

Describe the transport in blood for peptide hormones

A

Freely water soluble

34
Q

What is the relationship between free and bound hormones?

A

Free and bound hormones are in equilibrium

35
Q

Where is the site of action for peptide hormones?

A

Cell surface receptors

  • GPCR (2nd messenger; intrinsic hormone)
  • Hormone binding activates second messenger cascade
  • Ultimately, there is a phosphorylation of proteins within the cell and the activated proteins bring about a change in cellular function
36
Q

Where is the site of action for steroid/ thyroid hormones?

A

Intracellular receptors

  • Receptors within the cytoplasm (or nucleus e.g. THR) of target cell
  • Steroid/ thyroid hormone receptor superfamily)
37
Q

What are ligand-inducible transcription factors

A

Hormone-receptor complex binds to specific ‘hormone response elements (HRE’s)’ in the promoter region of specific genes.

  • This results in modification of gene transcription and protein synthesis
  • These receptors are there described as ligand-inducible transcription factors
38
Q

Where are water soluble proteins synthesised/ stored in?

A

ER and golgi

39
Q

Where are lipid soluble proteins synthesised/ stored in?

A

Cytosol

40
Q

How are water soluble proteins transported?

A

Free hormone

41
Q

How are lipid soluble proteins transported?

A

Lipoprotein

42
Q

How are water soluble proteins secreted?

A

Exocytosis

43
Q

How are lipid soluble proteins secreted?

A

Diffusion

44
Q

Where is the site of action for water soluble proteins?

A

Plasma membrane

45
Q

Where is the site of action for lipid soluble proteins?

A

Genome

CEP (16 decks)

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