Principles of endocrinology

Question 1

Define endocrine gland

Answer 1

Group of cells that secrete hormones to the bloodstream.

Question 2

Define endocrinology

Answer 2

The study of endocrine glands and secretions.

Question 3

Define hormone

Answer 3

Bioactive messengers secreted by endocrine glands into blood.
(Not simple metabolite or energy substrate)

Question 4

Define neurotransmitter

Answer 4

Endogenous chemicals that enable one neurone to transfer a signal from itself to a target cell.

Question 5

Define neurosecretion

Answer 5

Secretion of chemical messengers from neurones

Question 6

What distinguishes endocrine from paracrine and autocrine systems?

Answer 6

Action of the hormones secreted:

• Endocrine - action on target cells at a distance from a source
• Paracrine - action on nearby target cells
• Autocrine - action on self

Question 7

What are the 3 main differences between the endocrine and nervous systems?

Answer 7

• Release of chemical hormones vs chemical neurotransmitter
• Effect spread across many target cells throughout body vs restricted to localised target cells that are innervated
• Effect can take place over a long time span vs generated in milliseconds

Question 8

Name the 6 classic endocrine glands

Answer 8

1) Pituitary
2) Parathyroids
3) Thyroid
4) Adrenals
5) Pancreas
6) Gonads (and GI tract)

Question 9

How are hormones classified?

Answer 9

1) protein/polypeptide hormones
- protein derived
2) Steroid hormones
- derived from cholesterol
- Intact or broken steroid nucleus
3) Misc.
- amines

Question 10

How are protein hormones synthesised?

Answer 10

1) Transcription
2) mRNA to RER
3) Translation of pre-prohormone
4) Cleavage of pre-prohormone by proteolytic enzymes in RER to prohormone
5) Prohormone packed into golgi vesicle
6) Prohormone broken down into hormone
7) Secretion via exocytosis

Question 11

How are steroid hormones synthesised?

Answer 11

1) Derived from cholesterol
2) LDL carries cholesterol to cell for storage as fatty acid esters
3) Cholesterol esterase liberates cholesterol
4) Cholesterol taken to mitochondria by Steroidogenic Acute Regulatory protein (StAR)
5) Hormone produced in mitochondria and SER
6) Lipid soluble steroid diffuses out of cell immediately
7) Steroid binds to protein in blood

Question 12

How are hormones transported?

Answer 12

Most hormones secreted into systemic circulation
hypothalamus releases into→hypophyseal portal system
Water soluble → bloodstream
Insoluble steroids and thyroid hormones →
bound to plasma proteins or transport proteins

Question 13

Name the 6 more recently identified endocrine glands

Answer 13

Kidneys
Heart/blood
Liver
Brain
Adipose tissue
Placenta

Question 14

What is the purpose of hormones bound to transport proteins?

Answer 14

Act as a reservoir so that bound hormone in dynamic equilibrium with small amount of free hormone
Protects against rapid changes on hormone concentration

Question 15

What is the main receptor for peptide hormones and where is it located?

Answer 15

G-Protein Coupled Receptors

Plasma membrane of target cells

Question 16

What is the mechanism of action of a G protein receptor in the case of ACTH?

Answer 16

1) Hormone binds to receptor
2) G-protein dissociates from receptor
3) G protein activates enzyme adenylate cyclase
4) AC converts ATP to cAMP
5) cAMP activates protein kinase A (PKA)
6) PKA acts as 2nd messenger producing an effect

Question 17

How does PKA upregulate cortisol synthesis?

Answer 17

Protein Kinase A phosphorylates StAR protein, upregulating cortisol synthesis

Question 18

What is the main receptor for steroid and thyroid hormones?

Answer 18

Intracellular receptors inside the target cells

Steroids are lipid soluble and can penetrate plasma membranes via diffusion

Question 19

What is the mechanism of action of steroid hormones?

Answer 19

Act in nucleus as transcription factors to increase or decrease the rate of gene transcription

Question 20

Define positive feedback

Answer 20

When end products of an action cause more of that action to occur in a feedback loop

Question 21

Define negative feedback

Answer 21

When a deviation from the normal levels induces a response to correct the change and restore the normal state

Question 22

How are hormone systems controlled?

Answer 22

Most often closed loop feedback systems - predominantly negative feedback
Via interaction between hypothalamus and pituitary and target organs
Peripheral hormones from target organs feed back to HP system ∴ regulating target hormone production