Introduction to endocrinology

Question 1

Define endocrinology

Answer 1

The study of endocrine glands (tissues) and the substances they secrete

Question 2

Define endocrine gland

Answer 2

A gland that makes and secretes hormones into the bloodstream, through which they travel to affect distant targets

Question 3

Define hormone

Answer 3

A chemical substance produced by cells and released especially into the blood and having a specific effect on cells or organs usually at a distance from the place of origin

Question 4

Define exocrine gland

Answer 4

A gland that secretes its products through ducts opening onto an epithelium rather than directly into the blood.

Question 5

What is endocrine secretion?

Answer 5

Secretion of a hormone into the bloodstream to act on a distant target

Question 6

Define paracrine

Answer 6

of, relating to, promoted by, or being a substance secreted by a cell and acting on adjacent cells.

Question 7

Define autocrine

Answer 7

of, relating to, promoted by, or being a substance secreted by a cell and acting on surface receptors of the same cell.

Question 8

What are the 4 types of chemical messengers?

Answer 8

1) Neurotransmitters (act like paracrine)
2) Neuroendocrine messengers
3) Hormones (ie. endocrine messengers)
4) Cytokines (peptides with autocrine, paracrine or endocrine functions)

Question 9

List the main endocrine organs

Answer 9

• Hypothalamus
• Pituitary (anterior and posterior)
• Thyroid
• Thymus
• Adrenal
• Pancreas
• Kidney
• Testes
• Ovary
• Uterus

Question 10

List the main hormones

Answer 10

• Glucocorticoids
• Insulin, glucagon
• Thyroid hormones
• Gastric hormones
• Intestinal hormones
• ADH, RAAS

Question 11

What are the major molecular types of hormones?

Answer 11

• Modified single amino acids eg. catecholamines (adrenaline, noradrenaline, dopamine and serotonin).
• Peptides eg. Thyrotropin Releasing Hormone, Antidiuretic hormone, Somatostatin, Insulin, PTH, gonadotrophs (FSH, TSH, LH)
• Steroids (derives from cholesterol) eg. cortisol, sex steroids (eg. testosterone), vitamin D

Question 12

Describe the characteristics of amino acids and peptides

Answer 12

• water soluble
• rapid changes in [plasma]
• Short (sec-to-min) plasma half life
• cell membrane receptor
• mechanism: activate preformed enzymes, secretory granules, constitutive + bursts
• rapid (sec-to-min) speed of effect

Question 13

Describe the characteristics of steroids and thyroid hormones

Answer 13

• lipid soluble
• slow fluctuations in [plasma]
• long (min-to-days) plasma half life
• intracellular receptor
• mechanism: stimulate protein synthesis, direct rapid passage, related to secretion rate
• Slow (hrs-to-days) speed of effect

Question 14

Describe how catecholamines, peptides and proteins are transported in the blood

Answer 14

Water-soluble hormones are carried in free form in the blood. Dissolve in blood

Question 15

Describe how steroids and thyroid hormones are transported in the blood

Answer 15

Hydrophobic (fat-soluble) hormones.

• Transported bound to plasma binding proteins. Binding affinity is important
• The hormone is:
  1) Considered inactive
  2) Protected from degradation
  3) Acts as a reservoir

Question 16

What are the signalling mechanisms of water-soluble hormones?

Answer 16

Are large and hydrophilic (water-soluble)
Cannot pass through membranes
Bind to cell surface receptors, e.g. G protein-coupled receptors (GPCR) –> Adenylyl cyclase or phospholipase C; tyrosine kinase receptors

Question 17

What are the signalling mechanisms of hydrophobic hormones?

Answer 17

Are large and hydrophobic (lipid soluble) can diffuse across the plasma membrane
Bind to intracellular and cell surface receptors

Question 18

What is negative feedback?

Answer 18

Output reduces the original stimulus

Question 19

What is positive feedback?

Answer 19

Output enhances the original stimulus

Question 20

What is the difference between a tropic hormone and a trophic hormone?

Answer 20

A tropic hormone affects other endocrine glands.

A trophic hormone affects growth and development directly

Question 21

What is primary endocrine dysfunction?

Answer 21

Too much of effector hormone from endocrine organ

Question 22

What is secondary endocrine dysfunction?

Answer 22

Overstimulation of the effector endocrine organ by excessive tropic hormone

Question 23

What effects does cortisol (a glucocorticoid) have on the body?

Answer 23

1) Decrease bone function, increase bone resorption
2) Decrease connective tissue
3) Inhibit inflammatory and immune response
4) Maintain cardiac output, decrease endothelial permeability, increase arteriolar tone
5) Facilitate maturation of the foetus
6) Increase glomerular filtration and water clearance
7) Modulate emotional tone, wakefulness
8) Maintain muscle function, decrease muscle mass

Question 24

What is Cushing’s syndrome?

Answer 24

Glucocorticoid excess

Symptoms:

• Central weight gain
• Change in appearance – moon face
• Depression
• Psychosis
• Insomnia
• Amenorrhoea
• Poor libido
• Thin skin
• Bruising
• Growth arrest
• Back pain
• Polyuria/polydipsia

Treatment is surgery to remove tumour or drugs to inhibit cortisol production

Question 25

What is Addison’s syndrome?

Answer 25

Hypoadrenalism - reduced glucocorticoids and mineralocorticoids

Symptoms:

• Weight loss
• Anorexia
• Weakness
• Fever
• Depression
• Impotence/amenorrhoea
• Nausea/vomiting
• Diarrhoea/constipation
• Confusion
• Abdominal pain
• Back pain

Causes:

• Destruction of adrenal cortex
• Reduced glucocorticoid, mineralocorticoid and sex steroid production