Introduction to Endocrine

Question 1

What is the 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 are paracrine chemicals?

Answer 2

Chemicals that act local to the site of synthesis, do not travel to distant sites e.g. histamine

Question 3

What are autocrine chemicals?

Answer 3

Chemicals that act on/in the same cell that synthesises the hormone e.g. cytokines

Question 4

What are exocrine chemicals?

Answer 4

Exocrine chemicals are released from exocrine glands via ducts to the external environment including the GI tract e.g. saliva, sweat and bile

Question 5

Define endocrine communication in regards to the endocrine system

Answer 5

Endocrine communication is hormones that travel in the blood to their target organs/tissues - only works on cells with specific receptor to hormone

Question 6

Define neural communication in regards to the endocrine system

Answer 6

Neurotransmitters released from presynaptic neurons travel across the synaptic cleft to the postsynaptic cell to influence its activity. Neurotransmitter is the chemical released by the neuron but, in contrast to hormonses, acts locally within the synaptic cleft.

Question 7

Define neuroendocrine communication in regards to the endocrine system

Answer 7

Neuroendocrine communication is where the endocrine and nervous systems combine. Nerves release hormones which enter blood and travel to their target cells e.g. hypothalamic - posterior pituitary axis

Question 8

What are the six features of an endocrine hormone?

Answer 8

1. Produced by a cell or 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
5. Act by binding to receptors on target tissues
6. Have their actions terminated, often via negative feedback loops

Question 9

What are the three classifications of endocrine hormones?

Answer 9

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

Question 10

Where are peptide hormones stored prior to release?

Answer 10

Peptide hormones are stored in vesicles

Question 11

What is the initial form of a peptide hormone when it is first produced?

Answer 11

Peptide hormones are initially produced in large inactive preprohormones and contain one or more copies of the active hormone

Question 12

What role does the RER have in peptide hormone synthesis?

Answer 12

Preprohormones are cleaved into smaller units in the RER to leave smaller but still inactive proteins called prohormones

Question 13

What role does the golgi apparatus have in peptide hormone synthesis?

Answer 13

Prohormones are packaged into vesicles in the golgi apparatus, along with proteolytic enzymes which break the prohormones down into active hormone and other fragments

Question 14

What are C-peptides?

Answer 14

C-peptide is the inactive fragment cleaved from the insulin prohormone. levels of C-peptide in plasma or urine are often measured to indicate endogenous insulin produced from the pancreas (produced in equal amounts).

Question 15

How do peptide hormones reach target cells?

Answer 15

Peptide hormones reach the target cell by travelling through the blood

Question 16

How do peptide hormones affect target cells?

Answer 16

Peptide hormones are water soluble so cannot pass the cell membrane so bind to membrane bound receptors on target cells

Question 17

What is the difference between steroid hormones and all other types of hormones?

Answer 17

Steroid hormones are synthesised directly as need instead of stored and released

Question 18

Why are steroid hormones synthesised as they are needed?

Answer 18

Steroid hormones are synthesised at the site of action because they are lipid soluble so cannot be contained in vacuoles

Question 19

What carrier protein binds to steroid hormone in the blood?

Answer 19

Albumin binds to steroid hormone as it is poorly soluble in blood

Question 20

What are he four sites of steroid hormone production?

Answer 20

Steroid hormones are produced in 
Gonads (testes and ovaries) - sex steroids 
Placenta - hCG and steroids 
Kidney - Vitamin D3
Adrenal cortex - Corticosteroids

Question 21

What mlocule are all steroids derived from?

Answer 21

Steroids are all derived from cholesterol