Module 1 Section 1 (Principles of Endocrinology)

Question 1

Describe the general functions of the endocrine system. (6)

Answer 1

It’s a major regulatory system of the body which uses hormones to produce homeostatic adjustments.

1. Maintain constant internal environment via regulation of metabolism and H2O/electrolyte balance
2. Adaptive stress response
3. Growth and development
4. Reproduction
5. Red blood cell production
6. Integrating with the autonomic nervous system in regulating both the circulation and digestive
   functions

Question 2

Define a hormone and describe what makes hormones different from other secretions.

Answer 2

Hormones are chemical substances that’re secreted directly into the blood at low quantities, and exert a physiological effect at a distant target tissue.

Question 3

Compare and contrast the different types of hormones.

Answer 3

Hydrophilic (water-loving)
- highly water soluble
- low lipid solubility
- can be found unbound to carrier molecules within the plasma
- Most are either peptides (short chains of amino acids) or proteins (longer chains of amino acids) = peptide hormones
- Other major groups = amines
• catecholamines (norepinephrine and epinephrine) and thyroid hormones (not hydrophilic)

Lipophilic

• highly soluble in lipds
• poorly soluble in water
• require a carrier molecule for transport throughout the body
• includes the amine thyroid hormones and the steroid hormones

Question 4

Define stress

Answer 4

Describes any condition that overwhelms the body’s ability to maintain homeostasis and can be
physical (trauma, intense heat or cold), chemical (reduced oxygen supply), physiological (exercise,
pain), infectious (bacterial invasion), or emotional (anxiety, fear).

Question 5

What’s unique about catecholamines?

Answer 5

They are found both free

and bound to carrier molecules.

Question 6

Describe the 4 steps of hormone synthesis of peptide hormones.

Answer 6

1) Synthesis: Large precursor proteins called preprohormones are synthesized by endoplasmic reticulum (ER) ribosomes.
2) Packaging: As they travel through the E R and Golgi complex, these preprohormones are processed into active hormones and packaged into secretory vesicles.
3) Storage: These hormone-containing secretory vesicles can be stored until the cell receives the appropriate signal.
4) Secretion: The appropriate signal initiates exocytosis of the vesicles and the hormones are released into the blood.

Question 7

Describe the 4 steps of hormone synthesis for peptide hormones.

Answer 7

1) Synthesis: Large precursor proteins called preprohormones are synthesized by ER ribosomes.

2) Packaging: As they travel through the ER and Golgi complex, these preprohormones are processed
into active hormones and packaged into secretory vesicles.

3) Storage: These hormone-containing secretory vesicles can be stored until the cell receives the
appropriate signal.

4) Secretion: The appropriate signal initiates exocytosis of the vesicles and the hormones are released
into the blood.

Question 8

Discuss the hormone synthesis for lipophilic hormones.

Answer 8

Which steroid hormone is produced by a particular tissue depends on the specific enzymes within the cells of that tissue.
- Ex: the key enzyme that leads to cortisol synthesis is found only in the
adrenal cortex, so only this organ can make cortisol.

Steroid hormones are not stored b/c they are so lipophilic. They release as they are synthesized. Thus, to regulate the hormone, you need to regulate its synthesis.

Question 9

Match the hormone to the mechanism:

• Thyroid hormones
• Peptide hormones
• Catecholamines
• Steroid hormones

Dissolves in plasma = ___

Bound to carrier molecules or proteins = ___ and ___

Both = ___

Answer 9

Dissolves in plasma = peptide hormones

Bound to carrier molecules or proteins = thyroid hormones and steroid hormones

Both = catecholamines

Question 10

What is important to occur for hormones to achieve their desired effect?

Answer 10

It’s important that only free, unbound hormone can interact w/ a receptor at its target cell.
- not an issue for hydrophilic hormones and
catecholamines

Question 11

How do lipophilic hormones achieve their desired effect?

Answer 11

Lipophilic hormones
require carrier molecules.

Essentially what this means is that at any given time, not 100% of a steroid hormone in the blood is
bound to its carrier molecules. Instead, the hormones are dynamically unbinding and rebinding, which
results in a small fraction of hormone that is unbound at any given time. It is this unbound hormone
that is active and able to act on target cells.

Question 12

How do lipophilic hormones achieve their desired effect?

Answer 12

Lipophilic hormones
require carrier molecules.

The hormones are dynamically unbinding and rebinding, which
results in a small fraction of hormone that is unbound at any given time. It is this unbound hormone
that is active and able to act on target cells.

Lipophilic hormones, such as steroid hormones, must be unbound from their carrier protein in order to enter
their target cell and interact with their receptor.

Question 13

Using what you’ve learned about hydrophilic and hydrophobic hormones, predict where the
receptors of peptide hormones, steroid hormones, catecholamines, and thyroid hormones are
located in the cell.

Answer 13

Peptide hormones and catecholamines bind to specific receptors on the outer surface of the plasma
membrane of their target cells and they are hydrophilic, and thus unable to freely cross the lipid bilayer of
the plasma membrane.

On the other hand, steroid hormones and thyroid hormones are lipophilic and can
easily slip through the plasma membrane and bind to specific receptors inside their target cells.

Question 14

How do peptide hormones and catecholamines exert their effects on their target cell?

Answer 14

Binding of these hormones on the surface receptors results in the activation of second messenger systems
- They amplify the OG signal, as low conc of hormones trigger pronounced cell responses.

Question 15

Using the word bank, match the correct word with the correct location in the paragraph provided:

• adenylyl cyclase
• cAMP
• G protein,
• messenger
• phosphorylate
• target proteins

First, an extracellular __ binds to a receptor, activating a ___ which shuttles to and activates several ___ enzymes. Next, these activated proteins convert many molecules of ATP to ___, which then activate protein kinase A. The activated protein kinase A enzymes then ___, and activate ___, which can then bring about the desired result.

Answer 15

First, an extracellular messenger binds to a receptor, activating a __G protein__ which shuttles to and activates several __adenylyl cyclase__ molecules. Next, these activated proteins convert many molecules of ATP to __cAMP__, which then activate protein kinase A. The activated protein kinase A enzymes then
__phosphorylate__, and activate __target proteins__, which can then bring about the desired result.

Question 16

Using the word bank, match the correct word with the correct location in the paragraph provided:

• C a2+
• G protein
• PIP2
• phospholipase C
• protein kinase
• target proteins

First, an extracellular messenger binds to a receptor, activating a ___________, which shuttles to activate
several ___________ enzymes. These proteins convert ____________ to IP3 and DAG. I P3 mobilizes
intracellular ___________, which activates calmodulin. The C a 2+ -calmodulin complexes then activate Ca 2+ -calmodulin-dependent _________ (CaM kinase), which phosphorylate and activate, ___________ bringing about the desired response.

Answer 16

First, an extracellular messenger binds to a receptor, activating a __G protein__, which shuttles to activate
several __phospholipase C__ enzymes. These proteins convert __PIP2__ to I P3 and DAG. I P3 mobilizes
intracellular __Ca2+__, which activates calmodulin. The Ca 2+
-calmodulin complexes then activate Ca2+ -calmodulin-dependent __protein kinase__ (CaM kinase), which phosphorylate and activate __target
protein__, bringing about the desired response.

Question 17

How do steroid and thyroid hormones exert their effects on their target cell?

Answer 17

They pass through both the plasma and nuclear membranes of the cell. The binding of these hormones to their receptors in the target cells produces effects by regulating gene transcription and protein synthesis.

Question 18

How do lipophilic hormones exert their effects on their target cell? What are the 6 steps?

Answer 18

They exert their effects on cells by regulating protein synthesis.

1) Free lipophilic hormone diffuse across the plasma membrane and/or the nuclear membrane to
interact with intracellular receptors.

2) The hormone-receptor complex (H-R) binds to the hormone response element (HRE) within the DNA.
3) DNA binding activates specific genes and produces messenger RNA (mRNA).
4) The mRNA leaves the nucleus.
5) The mRNA binds to a ribosome and proteins are synthesized.
6. These newly synthesized proteins ultimately lead to the cellular response of the hormone.

Question 19

Using what you have learned about hormones and their function within the endocrine system,
list the key differences between hormones and neurotransmitters.

Answer 19

1) Neurotransmitters belong to the nervous system, and hormones are a central component of the
endocrine system.

2) Neurotransmitters are transmitted across a synaptic cleft. Hormones are transported by the
blood.

3) Hormones are produced by endocrine glands, while neurotransmitters are produced by neurons.

4) Neurotransmitters must travel a short distance to their target, while hormones may travel a great
distance

Question 20

Select the following statements that are functions of the endocrine system.

1. Regulation of metabolism, and H2O/electrolyte balance
2. Circulation and digestion
3. Breathing
4. Growth and development
5. Reproduction
6. Immune system activation
7. Red blood cell production
8. Adaptive stress response

Answer 20

1) Regulation of metabolism, and H2O/electrolyte balance ✔
2) Circulation and digestion ✔
3) Breathing ✘
4) Growth and development ✔
5) Reproduction ✔
6) Immune system activation ✘
7) Red blood cell production ✔
8) Adaptive stress response ✔