Introduction to Endocrinology

Question 1

What is the endocrine system?

Answer 1

The endocrine system is essentially the ‘hormone system’ and is just communication between cells. It influences metabolic activity by means of hormones.

Question 2

How is the endocrine system different to the nervous system?

Answer 2

Endocrine system initiates responses slowly (NS is rapid); ES is via hormones released into the blood (NS is via action potentials and neurotransmitters); ES can target anywhere blood reaches (NS is at specific locations determined by axon pathways); ES has hormones that act over long distances (Neurotransmitters act over very short distances)

Question 3

What is the hypothalamus?

Answer 3

Hypothalamus is a part of the brain that controls the release of hormones from the pituitary gland in 2 ways

Question 4

What are the 2 ways that the hypothalamus controls the release of hormones from the pituitary gland?

Answer 4

Posterior pituitary: action potentials travel down the axons of hypothalamic neurones, causing release from their axon terminals in the posterior pituitary
Anterior pituitary: Communicates via hormones released into a system of blood vessels

Question 5

What is an endocrine gland?

Answer 5

Glands which secrete hormones directly into the bloodstream through which they travel to affect distal organs

Question 6

What is a hormone?

Answer 6

Regulatory substance produced by the endocrine gland and transported in tissue fluid to stimulate specific target tissues into action

Question 7

What is a paracrine?

Answer 7

A hormone which has effect only in the vicinity of the gland secreting it (cells near where it is released- same tissue)

Question 8

What is an autocrine?

Answer 8

A cell produced substance that has an effect only on the cell in which it is secreted

Question 9

What are the different ways that hormones are categorised?

Answer 9

Amino acid based (can be amines- amino acid with modified R group, peptides- short amino acid sequence or proteins- long amino acid sequence). Amino acid based hormones are usually water soluble and cannot cross the plasma membrane so receptors are on the cell surface membrane.
Steroid hormones- Made from cholesterol. Lipid based so can cross the plasma membrane so receptors are within the cell.
Eicosanoid- Made from Omega 3 or 6 and essential fatty acids.

Question 10

What is a Juxtacrine?

Answer 10

Direct cellular communication often through binding cell surface receptors

Question 11

What is oxytocin and ADH?

Answer 11

Oxytocin- strong stimulant of uterine contraction (tightening and shortening of uterine muscles
ADH- Secreted into blood to prevent dehydration as more water is reabsorbed from the urine so therefore less urine is produced.

Question 12

What happens when GHRH and GHIH are released by the hypothalamus?

Answer 12

GHRH- Growth hormone releasing hormone- stimulates GH release
GHIH- Growth hormone inhibiting hormone (also called somatostatin)- inhibits GH release

Question 13

What are trophic hormones?

Answer 13

Hormones secreted by the anterior pituitary gland

Question 14

What is humoral Stimuli?

Answer 14

When hormones are released when the level of a molecule changes to outside homeostatic ‘normal’. (e.g. pancreas releases insulin when glucose level increases in the blood)

Question 15

What is neural stimuli?

Answer 15

Hormone release when nerves in the endocrine gland provide the signal

Question 16

What is hormonal Stimuli?

Answer 16

Hormone release when another hormone stimulates the gland.

Question 16

If the posterior pituitary is removed, why are the effects of the hormonal symptoms go away?

Answer 16

Hormones can still be released from the neurones (they are made in the hypothalamus not the posterior pituitary) and a new capillary bed will be made (to distribute the hormones)