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LCRS-RDT- Endocrinology > Introduction to Endocrinology > Flashcards

Introduction to Endocrinology Flashcards

1
Q

What is an endocrine gland?

A

A group of cells which secrete messenger molecules directly into the bloodstream

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2
Q

What is endocrinology?

A

Study of endocrine glands and their secretions

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3
Q

What is a hormone?

A

The bioactive messenger molecule secreted by endocrine gland into the blood (not just metabolite or energy substrate- it effects change)

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4
Q

What are the three types of secretion?

A
  • Endocrine
  • Paracrine
  • Autocrine
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5
Q

What is endocrine secretion?

A

relates to hormone’s action on target cells at a distance from source- travelling in the blood stream.

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6
Q

What is paracrine secretion?

A

relates to homone’s action on nearby (adjacent) target cells - e.g. in the immediate area

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7
Q

What is autocrine secretion?

A

relates to hormones action on its own immediate source- acts on itself

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8
Q

What are the differences between endocrine and nervous systems?

A

Endocrine:

Chemical (hormone) messenger into the bloodstream

Has effect on many target cells

The effect will take place over a relatively long time (seconds to days)

Nervous:

Chemical (neurotransmitter) across the synapse

the effect will be restricted to those target cells that it was destined to go to

The effect generated is milliseconds

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9
Q

Name some endocrine glands

A

Pituitary

Parathyroids

Thyroid

Adrenals

Pancreas

GI tract

Gonads

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10
Q

What are the three types of hormonal classification?

A
  1. Protein/polypeptide
  2. Steroid
  3. Miscellaneous
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11
Q

How is a protein/ polypeptide hormone produced?

A

They are produced as precursors (pro-hormones).

The pro hormones are a lot longer than the final product. It is cleaved to produce the active hormone.

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12
Q

Give an example of a pro-hormone and its peptide hormone

A

POMC- pro-opiomelanocortin

The peptide hormone produced is called ACTH (produced by the nterior pituitary gland)

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13
Q

What is the difference between a polypeptide and a protein?

A

Polypeptide- straight chain of amino acids

Protein- the chain of amino acids folds up and becomes a globulin

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14
Q

What are steroid hormones derived from?

A

They all start with a cholesterol backbone- cholesterol is the precursor.

All steroid hormones (produced from cholesterol) are structurally similar to cholesterol

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15
Q

Protein hormone synthesis?

A
  • Amino acids (the builidng blocks of protein) are in the bloodstream (supplied from diet) and are transferred into cells by specific amino acid transporters
  • The chosen pro-hormone is transcribed from the DNA (a signal is needed to initiate this)
  • The mRNA produced travels into the cytoplasm and binds to the RER
  • The pro-horomone is produced
  • The pro-hormone travels to the golgi and the golgi adds enzymes into the vesicles containing the pro-hormone to cleave it
  • Cleavage activates the hormone
  • Vesicles of the active hormone accumulate near the cell surface and when the appropriate signal is given, the active hormone will exocytose
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16
Q

Where are pituitary hormones secreted?

A

Pituitary capillary

17
Q

What is a corticotroph?

A

An endocrine cell

18
Q

How are steroid hormones synthesised?

A
  • Cholesterol is delivered to the cell in the form of LDLs
  • The cholesterol is stored in the cell as fatty acid esters and appear as fat droplets
  • When hormones are synthesised, these esters are broken down by esterases
  • The hormones are made in the mitochondria
  • Cholesterol gets into the mitochondrion via stAR proteins (steroidogenic acute regulatory protein)- this is a rate limiting step in synthesis
  • There are lots of enzymes in the mitochondria for the stepwise conversion of cholesterol into hormone
  • The enzymes present in certain cells determines the final steroid hormone

product

  • Once the hormone has been produced, it will diffuse across the plasma membrane and out into the bloodstream. They are not stored in the cell.
19
Q

Which glands produce the most steroid hormones?

A

Adrenal glands

Gonads

20
Q

How are steroid hormones transported?

A

They are stored in the blood and they bind to plasma proteins. Albumin is present in big concentration in the blood and can weakly bind/ mop up most steroid hormones.

There are also more specific binding proteins for the hormones too and they bind to each other with a high affinity.

There is a small pool of free hormone in the blood and they are active and can move to the blood to cause an effect.

21
Q

Explain this dynamic equilibrium

A

If there are changes in the plasma protein or free hormone, there will be a SHIFT to OPPOSE the change. For instance, if the hormone demand is high from the cell, the free pool decreases, there will be less protein bound hormones to maintain the free pool

22
Q

What happens when plasma protein increases wrt steroid hormones?

(N.B in pregnancy there is an increase in CBG levels (this is a plasma protein))

A

There will be greater synthesis and release of hormones to ensure that the free pool is constantly maintained.

23
Q

How are peptide hormones transported?

A

They are stored within cells and once secreted, their actions are short lived. They diffuse by the blood and have action on target organ.

They are broken down very quickly and are secreted when required.

24
Q

Describe hormone signalling for protein hormones

A

There are specific receptors on target cells. The receptors are g coupled proteins. The binding of the ligand to the receptor activates adenyl cyclase which increases cAMP production.

increase in cAMP leads to activation of PKA (protein kinase A)

The activation of PKA leads to activation of the stAR protein and the phosphorylation of the esterase enzyme to liberate cholesterol.

THEREFORE, steroid hormone production is stimulated as teh cholesterol can move into the mitochondrion by the stAR protein.

25
Q

Describe cell signalling for steroid hormones

A

Receptors are intracellular.

Hormone binds and the complex translocates to the nucleus.

Steroid hormones are powerful agents but they are slow acting because they have huge effects

26
Q

what is hormone feedback?

A

Negative feedback- the hormone switches off its own production. once the stimulation for hormone production has stopped, the hormone production must stop too- acth example below:

  • Anterior pituitary is stimulated by stress
  • ACTH is released
  • ACTH acts on adrenal gland to increase cortisol production
  • Cortisol enters the bloodstream and does its function to decrease stress
  • Cortisol returns to the anterior pituitary and switches ACTH off (end consequence is that Cortisol production is also switched off)
27
Q

Which hormones act by positive feedback?

A

Lh and oestrogen

LCRS-RDT- Endocrinology (10 decks)

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