Introduction

Question 1

What is the definition of endocrine system?

Answer 1

A system that integrates and controls organ function via the secretion of chemicals (hormones) from cells, tissues or glands which are then carried in the blood to target organs, distal from the site of hormone synthesis, where they influence the activity of that target organ.

Question 2

What is a paracrine chemical?

Answer 2

A chemical which acts local to the site of synthesis, does not travel to distant sites e.g. histamine

Question 3

What is an autocrine chemical?

Answer 3

A chemical which acts on/in the same cell that synthesises the hormone e.g. cytokines

Question 4

What is an exocrine chemical?

Answer 4

A chemical which is released from exocrine glands via ducts to the external environment including the GI tract e.g. saliva, sweat, bile

Question 5

What is neuroendocrine communication?

Answer 5

Endocrine and nervous systems combine. Nerves release hormones which enter blood and travel to their target cells e.g. hypothalamic - posterior pituitary axis

Question 6

What is the effect of insulin on skeletal muscle/adipose tissue?

Answer 6

Increased glucose uptake

Question 7

What is the effect of insulin on the liver?

Answer 7

Increased glycogenesis, decreased gluconeogenesis

Question 8

What are the 6 features of an endocrine hormone?

Answer 8

1. Produced by a cell or a group of cells
2. Secreted from those cells into the blood
3. Transported via the blood to distant targets
4. Exert their effects at very low concentrations (act in the range 10^-9 - 10^-12M)
5. Act by binding to receptors on target tissues
6. Have their action terminated, often via negative feedback loops

Question 9

What are the three different classes of endocrine hormones?

Answer 9

1. Peptide or protein hormones - composed of chains of amino acids (most common)
2. Amine hormones - all derived from one of two amino acids (tryptophan or tyrosine)
3. Steroid hormones - all derived from cholesterol

Question 10

What are peptide hormones initially synthesised as?

Answer 10

Preprohormones

Question 11

What are peptide hormones stored as?

Answer 11

Prohormones

Question 12

What is a preprohormone?

Answer 12

Large and inactive initial peptide hormone containing one or more copies of the active hormone in the amino acid sequence

Question 13

What is a prohormone?

Answer 13

Smaller units made by cleaving the preprohormone

Question 14

What happens to prohormones, and how are they secreted?

Answer 14

Packaged into vesicles in the golgi apparatus, along with proteolytic enzymes which break the prohormone down into active hormone and other fragments. Hormones and fragments are stored in vesicles in the endocrine cells until release is triggered then all vesicle contents are released into plasma (co-secretion).

Question 15

What is C-peptide?

Answer 15

The inactive fragment cleaved from the insulin prohormone.

Question 16

Why might you want to measure plasma C-peptide?

Answer 16

Levels of C-peptide in plasma or urine are often measured to indicate endogenous insulin production from the pancreas (produced in equal amounts). However, because insulin is metabolised faster, levels of C-peptide are typically about 5x higher than endogenous insulin.

Question 17

Are peptide hormones hydrophilic or lipophilic?

Answer 17

Hydrophilic

Question 18

How do peptide hormones stimulate their target cells?

Answer 18

Binding to membrane bound receptors on the target cells.

Question 19

How fast are the responses created by peptide hormones binding to receptors on target cells?

Answer 19

Relatively fast - seconds to minutes

Question 20

Which signalling pathways do peptide hormones modulate?

Answer 20

GPCR (G Protein Coupled Receptor) or tyrosine kinase linked signalling pathways