5.4.1: Endocrine communication

Question 1

What is the endocrine system?

Answer 1

A communication system using hormones as signalling molecules.

Question 2

What are hormones?

Answer 2

• molecules (proteins or steroids) that are released by endocrine glands directly into the blood.
• They act as messengers, carrying a signal from the endocrine gland to a specific target organ or tissue.

Question 3

What are the two types of hormones?

Answer 3

• Protein and peptide hormones, and derivatives of amino acids (e.g. adrenaline, insulin, glucagon)
• Steroid hormones (e.g. oestrogen and testosterone)

Question 4

Proteins are not soluble in the phospholipid membrane, what does this mean for their signalling?

Answer 4

• Protein hormones do not enter the cell.

- They need to bind to the cell surface membrane and release a second messenger inside the cell.

Question 5

Why do steroid hormones not need a second messenger?

Answer 5

-They can pass through the membrane and enter the cell and the nucleus, to have a direct effect on the DNA in the nucleus.

Question 6

Where are hormones released from?

Answer 6

Hormones are released directly into the blood from the endocrine glands.

Question 7

What are endocrine glands and what do they consist of?

Answer 7

-Endocrine glands are ductless glands that consist of groups of cells that manufacture and release the hormone directly into the blood capillaries, running through the gland.

Question 8

What do endocrine glands consist of?

Answer 8

-Groups of cells with associated capillaries but no visible ducts.

Question 9

Name the major endocrine organs in the human body.

Answer 9

• Pituitary gland
• Thyroid gland
• Thymus
• Adrenal glands
• Pancreas
• Ovaries (in females)
• Testes (in males)

Question 10

What are the cells receiving an endocrine signal called?

Answer 10

-Target cells.

Question 11

What are the two different arrangements of target tissue that can e found?

Answer 11

• grouped together in a target tissue such as the epithelium of the collecting ducts.
• more widely dispersed in a number of tissues, such as receptors for adrenaline found in the central nervous system and the tissues enervated by the peripheral nervous system including the heart, smooth muscle and skeletal muscle.

Question 12

What must the target cell possess if the hormone a non-steroid hormone?

Answer 12

• A specific receptor on their plasma membrane that is a complementary shape to the shape of the signalling molecule (hormone).
• The hormone can then bind to this receptor and initiate changes in the cell.

Question 13

How can hormones be carried in the blood without affecting the wrong cells?

Answer 13

• Each hormone is different.
• The hormones can be carried in the blood without affecting cells that do not possess the correct specific receptor.
• Only the specific target cells that possess the correct receptor will respond to the hormone.

Question 14

What are non-steroid hormones known as and why?

Answer 14

• First messengers.
• They usually cause the release of another signalling molecule in the cell which is called the second messenger.
• The second messenger is what stimulates the change in the activity of the cell.

Question 15

What do many non-steroid hormones activate when the hormone binds to the receptor on the membrane?

Answer 15

• Many non-steroid hormones act via a G protein in the

- The G protein is activated when the hormone binds to the receptor.

Question 16

How is the second messenger activated?

Answer 16

• The G protein activates an effector molecule.
• In many cells, the effector molecule is the enzyme adenyl cyclase, which converts ATP into cyclic AMP (cAMP).
• cAMP the second messenger.

Question 17

What does the second messenger do to affect the activity of the cell?

Answer 17

• This second messenger may act directly on another protein (such as an ion channel), or…
• It may initiate a cascade of enzyme controlled reactions that affect the activity of the cell.

Question 18

What is an effector molecule?

Answer 18

-This is usually an enzyme that converts an inactive molecule into the active second messenger.