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Flashcards in Intro to Endocrine Deck (19)
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1
Q

Define the endocrine system?

A

A system that integrates & controls organ function via secretion of chemicals carried in the blood to target organs where they influence the organ activity.

2
Q

What makes endocrine hormones different to paracrine, exocrine and autocrine?

A

Endocrine are carried in the blood to distant target cells whereas:

  • Autocrine act on the cell that syntehsised them e.g. cytokines
  • Paracrine act on neighbouring cells through the ECF e.g. Histamine
  • Exocrine reach the external environment through ducts e.g. sweat/bile/saliva
3
Q

What are the three major types of hormones?

A

Peptide hormones derived from amino acids
Steroid hormones derived from cholesterol
Amine hormones derived from 2 specific amino acids (tryptophan & Tyrosine)

4
Q

How are peptide hormones produced?

A

1) As preprohormones
2) Cleaved into prohormones in RER
3) Stored in vesicles with enzymes that cleave them down to active hormones
4) Released into blood when needed along with inactive fragments

5
Q

Why is it relevant that peptide hormones are released into blood along with inactive fragments of prohormones?

A

The fragments can be measured to assess hormone levels

E.g. C-peptide levels tell us about the levels of endogenous insulin production

6
Q

How do peptide hormones travel/work?

A
  • Water soluble so dissolves in blood
  • Act on membrane bound receptors
  • Have rapid effects (S or mins)
7
Q

What are the main differences between water and lipid soluble hormones?

A

Water soluble - Peptide hormones & Catecholamine hormones

Lipid Soluble - Steroid hormones & Thyroid hormones

Water soluble:
#Dissolve in blood
#Act on membrane bound receptors
#Short half life
Lipid Soluble:
#Bound to Carrier proteins
#Act on cytoplasmic/nuclear receptors
#Long half life (hours/days)
8
Q

How are steroid hormones produced?

A

They’re synthesised directly when needed (since they’re lipophilic they can’t be stored inside cells)

9
Q

How are steroid hormones transported?

A

In carrier proteins e.g. Albumin

10
Q

How do steroid hormones work?

A

They move into cells and act on internal receptors
Activate/inhibit gene function which raises/lowers protein synthesis

This is a slow process compared to peptide hormones taking hours/days and persisting for a similar time after production stops

11
Q

What are the types of amine hormone?

A

3 main types:

1) Catecholamines which are water soluble
2) Thyroid hormones which are lipid soluble
3) Melatonin, the only one derived from tryptophan

(1&2 derived from tyrosine)

12
Q

What are the types of protein carriers for lipid soluble hormones?

A

Specific e.g. CCS-binding globulin

Non-specific E.g. Albumin

13
Q

If lipid soluble hormones are carried by proteins how do they cross the cell membrane to have action?

A

There’s a constant ratio of free hormone:Complexed hormone.
The law of mass action dictates that as free hormone is taken up by cells more is released from carrier proteins.

This equilibrium ensures the prolonged activity of the hormone

14
Q

Why don’t hormones go round the blood continuously causing effects?

A

They are metabolised and excreted, mainly by the liver/kidneys.

Protein complexed hormones are protected from this hence their long half-lives.

15
Q

What mechanisms exists to control the level of hormone secretion?

A

1) Most endocrine pathways are have a trigger (E.g. low Calcium) and are then inhibited by the correction of this trigger in a -ve feedback loop
2) Some respond to neural feedback loops (Fight/flight -> Generalised symp. activation -> Adrenaline release from adrenal medulla)
3) Some (e.g. insulin) have multiple methods of control

16
Q

How are hormone receptor numbers regulated?

A

Prolonged high hormone concentrations down-regulates the receptors and vice versa.

Some hormones can up or down regulate expression of receptors for others (permissive or antagonistic)

17
Q

Example of permissive receptor regulation by another hormone?

A

Thyroid hormone increases the presentation of epinephrine receptors on adipocytes.

Thus increasing the lipolytic effect of epinephrine despite not having any lipolytic effect itself.

18
Q

Summary of Hormone Types:

A
Peptide:
# Water Soluble
# Membrane bound receptors
# Produced & Stored in cells
# Short Half lives
# Dissolves directly in blood
Steroid:
# Lipid soluble
# Cytoplasmic/nuclear receptors
# Produced when needed
# Long half lives
# Transported by carrier-proteins
Amine:
# Catecholamines are water soluble tyrosine derivatives
# Thyroid hormones are lipophilic tyrosine derivatives
# Melatonin is a tryptophan derivative
19
Q

Examples of different hormone types:

A
Peptide:
# Insulin
Steroid:
# CCS
# Sex Steroids
Catecholamine:
# Dopamine
# Epinephrine/Norepinephrine
Thyroid:
#Thyroxine