Introduction to Hormones

Question 1

The Endocrine System (Basics)

Answer 1

• Integrates and coordinates cellular activity through the body
• Consists of multiple organs that release hormones

Question 2

What are the main organs of the endocrine system?

Answer 2

• Hypothalamus
• Pituitary Gland
• Thyroid Gland
• Parathyroid Glands
• Adrenal Glands
• Pancreas
• Gonades (Ovaries/Testes)
• Placenta

Question 3

Hormones

Answer 3

• Chemical messengers produced by an organ
• Exert effect over short or long distances

Question 4

Autocrine

Answer 4

• Hormone effects the same cell that released the hormone

Question 5

Paracrine

Answer 5

• Hormone effects neighboring cells

Question 6

Endocrine

Answer 6

• Hormone is relesaed into bloodstream to act on distant organ

Question 7

What are the three main classes of hormones?

Answer 7

• Protein/Peptide
• Steroid
• Catecholamines (amino acid-derived)

Question 8

Protein/Peptide Hormones

Answer 8

• Undergo post-translational processing
• Stored in secretory granules and released by exocytosis
• Examples: Inuslin, glucagon, adrenocorticotropic hormone (ACTH)

Question 9

Where are steroid hormones synthesized?

Answer 9

• Synthesized in adrenal cortex, gonads, and placenta

Question 10

Steroid Hormone Properties

Answer 10

• Derived from cholesterol; are lipid soluble
• Leave cell easily, therefore not stored

Question 11

How are steroid hormones regulated?

Answer 11

• Regulated by cholesterol availability and enzymatic processing

Question 12

What are the 5 subcategories of steroid hormones?

Answer 12

• Progestins
• Glucocorticoids
• Androgens
• Mineralocorticoids
• Estrogens

Question 13

Peripheral conversion of steroid hormones

Answer 13

Enzymatic conversion of some active steroids to other forms

Question 14

Where are catecholamines synthesized?

Answer 14

• Adrenal medulla
• Neurons

Question 15

Catecholamine properties

Answer 15

• Catecholamines are enyzmatic modifications of tyrosine
• Stored in secretory vesicles and released through regulated secretory pathway
• Do not cross cell membrane easily
• Have a short half-life (less than 3 minutes)
• Examples: norepinephrine, epinephrine, and dopamine

Question 16

Which hormones circulate freely (unbound to carrier/transport proteins) in the blood?

Answer 16

• Protein/Peptides
• Catecholamines

Question 17

Which hormones bind to receptors located on the cell surface?

Answer 17

• Protein/Peptides
• Catecholamines

Question 18

• What type of hormone is biologically active in the blood, free or bound hormones?
• What does this mean in terms of regulation?

Answer 18

• Free hormone is biologically active
• Transport binding also acts as a level of regulation
  
  • Concentration of bound hormone, free hormone, and transport protein are in equilibrium

Question 19

What type of hormones are bound to transport proteins when circulating in blood?

Answer 19

• Steroids as they are lipid soluble and hydrophobic

Question 20

How much hormone-receptor occupancy is required for biological effect?

Answer 20

• Often very little hormone-receptor binding is required to cause a biological effect
• This is signficant as there is usually very low concentrations of circulating hormones

Question 21

What are some causes of abnormal endocrine function?

Answer 21

• Excess or deficiency of hormone
• Decrease of hormone receptor numbers
• Decrease of hormone receptor function

Question 22

Hormone Antagonists

Answer 22

Bind receptors and blocks biological effects

Question 23

Hormone Agonists

Answer 23

Bind to receptors and stimulate downstream effects

Question 24

What type of receptors do steroid hormones bind?

Answer 24

Intracellular receptors

Question 25

What type of receptors do protein/peptide and catecholamine hormones bind to?

Answer 25

Cell membrane receptors, which include:

• G protein-coupled receptors (GPCRs)
• Enzyme-linked receptors

Question 26

G Protein-Coupled Receptors (GPCRs)

Answer 26

• 7-pass transmembrane proteins coupled to heterotrimeric guanine-binding proteins (AKA G-Proteins)
• Intracellular targets can be ion channels or effector proteins
• Intracellular signaling cascade can be propagated by another molecule called a second-messanger system

Question 27

What are 3 common second messenger systems?

Answer 27

• Adenylate cyclase/cAMP
• Membrane phospholipids
• Calcium/calmodulin

Question 28

Enzyme-linked receptors

Answer 28

Have intrinsic enzyme activity or are closely associated with enzymes

Question 29

Intracellular (aka Nuclear) receptors

Answer 29

• Reside in the cytoplasm or nucleus
• Bind hydrophibic hormones (steroid hormones)
• Can act as transcription factors when activated and increase or decrease transcription

Question 30

Timing of cellular response to hormones

Answer 30

• Activation or inhibition of existing proteins is a rapid process (milliseconds to seconds)
• Changes in gene expression and synthesis of new proteins is slower (minutes, hours, or sometimes days)

Question 31

Feedback control of hormone action

Two main types of negative feedback mechanisms

Answer 31

• Hormones are tightly controlled on multiple levels
• Two main types of hormone negative feedback mechanisms:
  
  • Physiological response-driven feedback loop
  • Endocrine axis-driven negative feedback loop

Question 32

Physiological response-driven feedback loop

Answer 32

• Result of physiological effects provided by hormone cause negative feedback
• Example, insulin: high blood glucose –> triggers pancrease to release insulin –> cells take up glucose –> decreased blood glucose –> triggers pancrease to stop releasing insulin

Question 33

Endocrine axis-driven feedback loop

Answer 33

• The hormone itself provides negative feedback to prevent further release of the same hormone