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Endocrine physiology > Hormones, receptors & hormone signalling > Flashcards

Hormones, receptors & hormone signalling Flashcards

1
Q

What is the definition of hormones?

A
  • chemical messangers carried in the blood stream from the site of synthesis (ie endocrine gland) to the site of action (target tissue)
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2
Q

What are the 3 major hormone classes?

A
  • Peptide hormones
  • Amine hormones
  • Steroid hormone
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3
Q

What are examples of amine hormones?

A
  • catecholmines eg NA and Adr
  • Thyroid hormones
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4
Q

What are examples of steroid hormones?

A
  • androgens/ estrogens/ progestagens
  • corticosteroids
  • Vit D
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5
Q

**Describe **peptide hormones

A
  • most abudant class
  • water soluble - therefore easily transported in the blood but DO NOT cross cell membranes readily
  • synthesised on the rough ER
  • stored in secretory vesicles
  • hormone is** processed intracellularly and extracellularly**
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6
Q

What is an example of a peptide hormone processing?

A

preproglucagon
* this is a precursor of glucagon
* generated in the alpha cells of the pancreas and the L cells of the intestine

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7
Q

What substance are all the hormones in the class amines derived from?

A

the amino acid -** tyrosine**

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8
Q

Where is noradrenaline produced & what cells is it produced by?

A
  • in the** medulla** of the adrenal gland
  • synthesised by the chromaffin like cells
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9
Q

is noradrenaline water soluble?

A
  • yes noradrenaline is water soluble - therefore is readily soluble and easily transported in blood
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10
Q

where is thyroid hormone stored?

A

the colloids

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11
Q

Which** three plasma proteins** function to transport thyroid hormones & which has the highest affinity?

A
  • thryroxine binding globulin (TBG)
  • Transthyretin
  • Albumin

however TBG has highest afinity

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12
Q

which thyroid hormone is more biologically active?

A

T3
* T4 is converted to T3 - which is the biologically active hormone that regulates your bodies metabolism

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13
Q

What are all steroid hormones derived from?

A
  • cholesterol
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14
Q

are steroid hormones stored?

A

No they are not stored but they are immediately released from cell after synthesis

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15
Q

are steroid hormones water soluble?

A

NO
* they are extremely hydrophobic (ie not water soluble)
* they can freely diffuse across plasma membrane at site of synthesis and site of action
* require plasma transport proteins to reach target cell

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16
Q

Do steroid hormones have a longer half life than peptide hormones?

A

yes - longer half life and slower acting

17
Q

How do receptors bind to hormones?

A
  • they bind with** high specificity & affinity**
  • the interaction is reversable
18
Q

What is the binding affinity of the receptor known as?

A
  • equilibrium constant called **Kd or the dissociation constant **
19
Q

what does a **low vs high dissociation constant **mean for the affinity of the receptor?

A
  • the lower the Kd, the greater the hormone binding affinity
20
Q

Compare upregulation vs downregulation of receptors

A
  • Upregulation involves the increase in the number of receptors due to external stimulation
    * downregulation involves the decrease in the number of receptors eg when receptors have been chronically exposed to an excessive amount of hormones
21
Q

Describe the **steps of the mechanism of action **of a steroid hormone

A
  • lipid soluble hormones passes freely through cell membrane
  • hormone binds to receptor in the cytoplasm- forming a receptor -hormone complex
  • receptor hormone complex enters the nucleus and binds to another receptor on the chromatin
  • transcribed mRNA is translated into proteins that alter cell activity
22
Q

Describe the** mechanism of action** of the thyroid hormone and it’s receptor

A
  • the thyroid hormone receptor is a transcription factor (ie it regulates the expression of genes)
  • without the thyroid hormone, the receptor forms a homodimer with another thyroid hormone receptor
  • thyroid hormones enter the cell through certain receptors and T4 converted into T3
  • T3 enters the nucleus and binds to the receptor
  • co repressor is released and co activator binds to this complex and activates gene transcription
23
Q

Describe the structure of G protein coupled receptors?

A
  • 7 transmembrane domains
  • 3 subunits - G alpha, beta and gamma
  • Galpha binds to GDPin inactive state and becomes activated by exchange of GDP for GTP
24
Q

Describe how G proteins work

A
  • binding of the hormone induces a conformational change in the receptor
  • the activated receptor **binds to the Ga subunit **
  • activated receptor causes conformational change in Ga, triggering dissociation of GDP
  • **binding of GTP to Ga **triggers dissociation of of Ga from the receptor and Gby
  • hormone dissociates from G receptor , Ga binds to effector and activates it
  • hydrolysis of GTP to GDP causes Ga to dissociate from effector and reassociate with GBy
25
Q

What are** tyrosine kinase receptors**?

A
  • receptors that contain tyrosine kinase enzyme - an enzyme that adds a phosphate group to a tyrosine residue of a substrate protein
  • most must dimerise before they become functional
26
Q

Describe** JAK-STAT signalling** (tyrosine kinase)

A
  • 2 cytokine receptors are associated with 2 JAK proteins
  • when a ligand binds to cytokine receptor, it changes the conformation of the receptor and brings close together
  • one JAK protein phosphorlyates the other
  • the phosphorlyated JAK proteins phosphorlyate the tyrosine cytokine receptors
  • the phosphorlyated receptor DOCKS to stats protein
  • the Stat proteins dimerise and translocate to the nucleus, bind to DNA and activate gene transcription
27
Q

what are 3 main examples of second messangers?

A
  • cAMP
  • Ca2+
  • phospholipids ( IP3 and DAG)
28
Q

What is the function of protein kinases (A & C)?

A
  • they are enzymes that add a phosphate group to another protein
  • they are activated by 2nd messangers
29
Q

what does PKC require for maximal activity?

A
  • requires Ca2+ and DAG
30
Q

what does PKC require for maximal activity?

A
  • requires Ca2+ and DAG

Endocrine physiology (19 decks)

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