Introduction to the endocrine system

Question 1

What is the simplest form of intercellular communication is for cell A to…

Answer 1

…release a chemical substance into the extracellular fluid. Some of the chemical will arrive at cell B and will influence the activity of that cell, hence the message will have been transmitted.

Question 2

The major problems with the simplest form of intercellular communication is that…

Answer 2

… it is non-specific, as many other cells may also receive the chemical message and that a large amount of transmitter substance must be released in order to ensure that the desired cell receives the message.

Question 3

What will happen is cell A and cell B are further apart?

Answer 3

The greater the distance between the cells are, the amount of transmitter substance that must be secreted increases, hence there are greater problems of NON-SPECIFICITY of action, that is, a greater number of cells receive the message that is only intended for cell B.

Question 4

How is non specificity overcome?

Answer 4

By the development of outgrowths from cell A towards the target cell. The cell may then become further specialised by only releasing transmitter from one area of its surface. This specialisation is the beginning of a nerve cell.

Question 5

What is a drawback of neuronal form of intercellular communication?

Answer 5

Each cell can only communicate directly with a limited number of other cells. The organism therefore requires a method by which a single cell can communicate with a large number of widely distributed cells.

Question 6

What is the nervous system?

Answer 6

The nervous system responds to stimuli by sending electrical action potentials along neurons, which in turn transmit these action potentials to their target cells using neurotransmitters, the chemical messenger of the nervous system. This response to stimuli is near instantaneous.

Question 7

The nervous system allows very

Answer 7

rapid, focussed, precise communication between INDIVIDUAL cells.

Question 8

The endocrine system allows very

Answer 8

slow, sustained communication between GROUPS of cells.

Question 9

The nervous and endocrine systems both work together to maintain __________

Answer 9

homeostasis.

Question 10

The signal is ________ BETWEEN neurones and _____ within neurones.

Answer 10

chemical

electrical

Question 11

Why does chemical transmission take longer than electrical transmission?

Answer 11

This process takes significantly longer, as hormones must first be synthesized, transported to their target cell, and enter or signal the cell. Then, the target cell must go through the process of transcription, translation, and protein synthesis before the intended action of the hormone is seen.

Question 12

Define the endocrine system.

Answer 12

A system in which a group of secretory cells (a gland) secretes a potent chemical transmitter substance (hormone) into the blood. The transmitter is then carried by the blood to the target cells where a response is elicited. Endocrine glands are ductless glands and their hormone transmitters are always secreted into the blood.

Question 13

What are two functions of the pineal gland?

Answer 13

It controls the onset of menstrual cycle and puberty.

It controls melatonin levels.

Question 14

Name the endocrine glands from top (head) to bottom (toe)

Answer 14

Hypothalamus
Pineal
Pituitary
Parathyroid
Thyroid
Thymus
Adrenal
Kidney
Pancreas
Ovary
Testes

Question 15

What is the function of thymus?

Answer 15

Increase cell proliferation

Question 16

The pituitary gland is located where and is sometimes called what gland?

Answer 16

below the brain. encased in skull. It is sometimes called the ‘master gland’

Question 17

Where are the thyroid and parathyroid glands situated? Expand on each gland.

Answer 17

Situated in the neck.
Thyroid responsible for metabolism and growth.
Parathyroid responsible for calcium homeostasis and phopshate homeostasis (maintenance and regulation)

Question 18

Excess calcium can cause _________. This is caused by malfunction of the ________ gland.

Answer 18

kidney stones

parathyroid

Question 19

Give examples of glands that are both endocrine and exocrine glands?

Answer 19

Pancreas

Liver - growth hormone into blood (endo)/ bile into small intestines (exocrine)

Question 20

Why is pancreas both an exocrine and endocrine gland?

Answer 20

The pancreas secretes digestive enzymes directly into the GI tract (exocrine function). It also secretes the hormone insulin directly into the blood (endocrine function). Insulin regulates blood glucose concentration and glucose utilisation.

Question 21

The pancreas has lots of ____ cells. State what the majority of the cells are and what each cell secretes.

Answer 21

islet
beta - insulin
alpha - glucagon
delta - somatostatin

Question 22

Where do the adrenal glands lie? Expand on the divisions

Answer 22

above the kidneys
outer cortex involved in stress, sodium and glucose homeostasis
inner medulla involved in stress response

Question 23

What are the gonads and what are they responsible for?

Answer 23

ovaries and testes.
secrete the female and male reproductive hormones respectively. These are responsible for the development of secondary sexual characteristics and reproduction.

Question 24

Like drugs, hormones produce their effects by interaction with receptors which may be ________ or ________-_____. What are the major types of receptor involved?

Answer 24

intracellular
membrane bound
Steroid hormone receptors, G-protein coupled receptors and Tyrosine Kinase receptors

Question 25

How do steroid hormone receptors work?

Answer 25

The hormone (very lipid soluble) crosses the cell membrane and binds to a receptor which may either be cytoplasmic or nuclear (either way it is intracellular receptor). The hormone receptor complex binds to the hormone - response element of the DNA to influence gene transcription. The receptor may be constitutively active.

Question 26

Why can steroid hormones cross the cell membrane but not peptide hormones?

Answer 26

Steroid hormones are very lipid soluble whereas peptide hormones are water soluble and therefore will not be able to diffuse through.

Question 27

How do G-protein coupled receptors work?

Answer 27

The hormone binds to the 7TM receptor to cause the synthesis of a secondary messenger, e.g. inositol trisphosphate or cyclic AMP. Secondary messengers phosphorylate intracellular, regulatory proteins to influence cellular activity e.g. smooth muscle contraction.

Question 28

How do tyrosine kinase receptors work?

Answer 28

They are membrane bound enzymes which is a single strand of protein. Often, two receptors must be present for hormone action (dimerised receptor). One hormone must bind to each receptor, the receptor then acts as an enzyme to phosphorylate ‘tyrosine’ components of the intracellular regulatory proteins.

Question 29

Examples of tyrosine kinase receptor hormones?

Answer 29

Insulin

Proline

Question 30

Example of G protein coupled receptor/ hormone?

Answer 30

M3 - muscarinic acetylcholine receptor.

Question 31

What is hormone receptor removal?

Answer 31

Once a hormone binds to a membrane-bound receptor:

• The hormone receptor complex is internalised within a vesicle
• Within these vesicles (Clathrin-coated pits) the hormone may be removed from the receptor
• Once in the vesicle, arrestin, may replace the hormone on the receptor and prevent the receptor interacting with its G protein
• Overall effect : internalised receptors are inactive,some are broken down and/or some are recycled.

Question 32

What are the two classes of hormones and its examples?

Answer 32

1. Steroid hormones (+ thyroid hormone) - lipid soluble e.g. oestrogen
2. Peptide hormone (comprised of amino acids) - water soluble e.g. insulin

Question 33

10 points about peptide hormones

Answer 33

1. highly water soluble
2. cannot cross cell membrane without a carrier protein
3. made up of amino acids
4. susceptible to protease attack
5. act on membrane bound receptors
6. not orally active
7. rapid onset of action (minutes to hours)
8. short plasma half life
9. short duration of action
10. synthesised and stored as inactive precursor
    THIS IS WHY INSULIN CANNOT BE TAKEN ORALLY BECAUSE IT WILL BE INACTIVATED BY THE ENZYMES IN THE STOMACH

Question 34

10 points about steroid/ thyroid hormones

Answer 34

1. highly lipid soluble/ poorly water soluble
2. can cross the cell membrane
3. act on intracellular receptors
4. must be transported in blood bound to plasma protein
5. only unbound hormone is biologically active
6. orally active
7. long duration of action
8. synthesised on demand (made within days)
9. slow onset of action
10. long plasma half life

• ALL STEROID HORMONES ARE MADE FROM CHOLESTEROL
• YOU NEED IODINE TO MAKE THYROID

Question 35

What is a common consequence of negative feedback in hormone concentration?

Answer 35

cyclical variation.

Question 36

Typically, but not in all cases, the secretion of a hormone by a given gland is controlled by the ______ ______ ____. This secretes _________ or ( t____ hormones).

Answer 36

anterior pituitary gland
stimulating
trophic

Question 37

Name the Releasing hormones the hypothalamus secretes to stimulate the anterior pituitary gland to produce stimulating hormones for:
Throxine
Cortisol
Oestrogens
Growth hormone

Answer 37

Thyrotrophin Releasing Hormone (TRH)
Corticotrophin Releasing Hormone (CRH)
Gonadotrophin Releasing Hormone (GnHR)
Growth Hormone Releasing Hormone

Question 38

Name the Stimulating hormones the anterior adrenal gland secretes to act on the following glands and this stimulate the secretion of:
Thyroid - Thyroxine
Adrenal Cortex - Cortisol
Ovary - Oestrogen
Ovary - Progesterone

Answer 38

Thyroid Stimulating Hormone (TSH)
Adrenocorticotrophic Hormone (ACTH)
Follicle Stimulating Hormone (FSH)
Luteinising Hormone (LH)