Lecture 1: Endocrine Background

Question 1

Nervous System vs Endocrine System

Answer 1

The nervous system produces short-term, very specific responses

The endocrine system: many times it produces long-term, general responses

Question 2

Role of endocrine system

Answer 2

The role of theendocrine systemis to maintain the body in balance through the release ofhormones(chemical signals) directly into the bloodstream.

Question 3

Role of Hormone

Answer 3

Hormones transfer information and instructions from one set of cells to another.

Question 4

What are hormones? Process of hormones

Answer 4

Hormones are chemical substances that affect the activity of another part of the body (target site).

Hormones serve as messengers, controlling and coordinating activities throughout the body.

Upon reaching a target site, a hormone binds to a receptor, much like a key fits into a lock.

Once the hormone locks into its receptor, it transmits a message that causes the target site to take a specific action.

Hormone receptors may be within the nucleus or on the surface of the cell.

Question 5

Major Endocrine Gland Examples

Answer 5

Pituitary gland 
Hypothalamus 
Thyroid gland 
Thymus gland 
Suprarenal glands 
Pineal gland 
Parathyroid glands 
Pancreas 
Reproductive glands

Question 6

Examples of functional hormones

Answer 6

Endocrine Hormones – Travel through the blood to act at a site distant from the secreting cell or gland

Paracrine Hormones – Act on cells near the secreting cell

Autocrine Hormones – Act on the secreting cell

Neurocrine Hormones – Secreted by neural cells
neurotransmitters
neurohormones

Question 7

Types of chemical hormones

Answer 7

Protein and polypeptide
Amine
Steroid

Question 8

Tropic vs non-tropic

Answer 8

Non-tropic hormonesare hormones that directly stimulate target cells to induce effects.

For example, aldosterone acts directly on the kidney (non-endocrine gland) to promote reabsorption of sodium, which causes an increase in blood pressure.

Tropic hormones, which act on other endocrine glands to stimulate (or inhibit) release of a second hormone.

For example, thyroid-stimulating hormone is responsible for stimulating the release for thyroid hormone by acting on the thyroid gland.

Question 9

Describe the overall process of functional hormones

Answer 9

1. endocrine gland releases hormone into blood
2. Travels in blood to target cells (cells with the appropriate receptor)
3. Hormones binds and promotes a response in the target cell

Question 10

neurotransmitter vs neurohormone

Answer 10

neurohormone: are chemicals released by neurons into the bloodstream to travel to the target cell

Neurotransmitter:
chemicals released by neurons that diffuse across a small gap to the target cell

Question 11

Chemical Hormones grouped on..

What are the 2 groups and features

Answer 11

Grouped according to chemical structure.

Steroid hormones are fat-soluble molecules made from cholesterol.

Non- steroidal
Protein and Amino acid derivatives, such as epinephrine, are water-soluble molecules

Question 12

Water vs fat soluable hormones

Answer 12

Water soluable
Like the amino acid derivatives and peptides, can travel freely in the blood because they “like” water.
However, they are repelled by lipid or fatty structures such as the membranes that surround the cell and nucleus. Because of this, these hormones generally bind to receptor sites on the outside of the cell and signal from there.

Fat soluable
Like the sex hormone steroids estrogens and androgens, are fat soluble and water repellent.
That is, they “like” lipid or fatty structures such as those surrounding cells but are generally repelled by watery areas.
Steroids generally travel to their target cells attached to a special carrier protein that “likes” water
The hormones detach before passing into the cell where they bind to receptors.

Question 13

Chemical Hormones:

Protein and polypeptide Hormones: 


Characteristics
Synthesis and Secretion pathways

Answer 13

• Products of translation
• vary considerably in size
• synthesized as prohormones, then proteolytically clipped to generate their mature form.

secreted by one of two pathways:
Regulated secretion:The cell stores hormone in secretory granules and releases them in “bursts” when stimulated. This is the most commonly used pathway and allows cells to secrete a large amount of hormone over a short period of time.

Constitutive secretion:The cell does not store hormone but secretes it from secretory vesicles as it is synthesized.

Question 14

Protein hormone action digram and labelled

Answer 14

1. lipid soluable hormone enters the cell membrane to the cytoplasma
2. Binds to cytoplasm receptor forming a hormone-receptor complex
3. This complex enters the nucleus and prompts geen transcription
4. The transcribed mRNA is taken to the cytoplasm and undergoes translation to form an active protein that alters cell activity.

Question 15

Chemical Hormones:

Amine Hormones synthesised from what?

What are the tyrosine derivatives and where are they located and function.

Answer 15

Amine hormones are synthesised from the amino acids tryptophan (derivative makes melatonin) or tyrosine.

Tyrosine derivatives include the metabolism-regulating thyroid hormones, as well as the catecholamines, such as epinephrine, norepinephrine, and dopamine.

Epinephrine and norepinephrine are secreted by the adrenal medulla and play a role in the fight-or-flight response

Dopamine is secreted by the hypothalamus and inhibits the release of certain anterior pituitary hormones.

Question 16

Steroid Hormones: Characteristics and examples

Answer 16

Are made from cholesterol, are lipophilic & can enter target cell

Are immediately released from cell after synthesis

Interact with cytoplasmic or nuclear receptors

Activate DNA for protein synthesis

Are slower acting and have longer half-life than peptide hormones

Examples: cortisol, estrogen & testosterone

Question 17

Steroid Hormones process +diagram

Answer 17

1. Most hydrophobic steroids are bound to a plasma carrier protein and once they reach the target site will deattach and diffuse out of the blood.
2. Steroid hormones bind to receptors in the cytoplasm or the nucleus forming a hormones-receptor complex
3. The complex binds to the DNA and can either activate or suppress one or more genes
4. Activated genes create new mRNA that moves to the cytoplasm
5. Translation of mRNA creates new proteins
6. Some steroid hormones bind to membrane receptors and use second messenger systems to create a rapid cellular response

DIAGRAM ON SLIDE

Question 18

Hypothalamus-pitutary and endocrine regulation

What feedback loop is used?
Diagram and explanation

Answer 18

Negative

Lecture slide for diagram

When the level of hormone made by the endocrine gland is sufficent, negative signals are sent to the anterior pitrarty and hypothalamus to stop signalling to create more hormones. Increasing levels of these hormones in the blood then give feedback to the hypothalamus and anterior pituitary to inhibit further signalling to the endocrine gland.

Question 19

Purpose of feedback loops

Answer 19

Feedback loops govern the initiation and maintenance of most hormone secretion in response to various stimuli.

Question 20

Define Negative feedback loop

Answer 20

Characterised by the inhibition of further secretion of a hormone in response to adequate levels of that hormone.

Question 21

Thyroid negative feedback example process

Answer 21

Hypothalamus releases thyrotropin releasing hormone to anterior pituraty gland. This releases thyroid stimulating hormones to thyroid gland which releases thyroid hormones T3 and T4)

Question 22

Define Positive Feedback and example

Answer 22

Positive feedbackoccurs when a product feeds back to increase its own production. This causes conditions to become increasingly extreme.

The release of oxytocin from the posterior pituitary gland during labour is an example of positive feedback mechanism.

Oxytocin stimulates the muscle contractions that push the baby through the birth canal.

The release of oxytocin result in stronger or augmented contractions during labour.
The contractions intensify and increase until the baby is outside the birth canal. When the stimulus to the pressure receptors ends, oxytocin production stops

Question 23

What is involved in clinical endocrinology investigation

Answer 23

Hypofunction of a gland
Hyperfunction of a gland
Receptor defect
Second messenger defect

Question 24

Endocrine disorders primary, secondary, tertiary

Answer 24

Primary (1o) excess (T3/T4): low trophic hormone (TSH)
Primary (1o) deficiency (T3/T4): high trophic hormone (TSH)
(issue at endocrine gland)

Secondary (2o) excess (T3/T4): high trophic hormone (TSH) and hormones of target gland
Secondary (2o) deficiency (T3/T4): low trophic hormone (TSH) and hormones of the target gland
(issue at pituitary gland)

Tertiary (3o) deficiency (T3/T4): low trophic hormone (TSH) and hormones of the target gland
(issue at hypothalamus)

Question 25

When an endocrine issue us suspected, what test is ordered and why

Explain the test

Answer 25

Sometimes, however, endocrine glands do not respond properly to feedback mechanisms.
A gland might produce too much of a hormone, or it might produce too little.
Or, a receptor might not respond to a hormone as expected. Either way, some reactions do not occur at a normal rate.

Dynamic function tests (DFTs) involve either stimulating or suppressing a particular hormonal axis and observing the appropriate hormonal response.

In general,

if a deficiency is suspected (hypofunction of gland causing not enough tropic hormone produced), a stimulation test should be used

if excess is suspected (hyperfunction of gland causing too much tropic hormone produced), a suppression test is used.