Introduction to Hormones Flashcards
The Endocrine System (Basics)
- Integrates and coordinates cellular activity through the body
- Consists of multiple organs that release hormones
What are the main organs of the endocrine system?
- Hypothalamus
- Pituitary Gland
- Thyroid Gland
- Parathyroid Glands
- Adrenal Glands
- Pancreas
- Gonades (Ovaries/Testes)
- Placenta
Hormones
- Chemical messengers produced by an organ
- Exert effect over short or long distances
Autocrine
- Hormone effects the same cell that released the hormone
Paracrine
- Hormone effects neighboring cells
Endocrine
- Hormone is relesaed into bloodstream to act on distant organ
What are the three main classes of hormones?
- Protein/Peptide
- Steroid
- Catecholamines (amino acid-derived)
Protein/Peptide Hormones
- Undergo post-translational processing
- Stored in secretory granules and released by exocytosis
- Examples: Inuslin, glucagon, adrenocorticotropic hormone (ACTH)
Where are steroid hormones synthesized?
- Synthesized in adrenal cortex, gonads, and placenta
Steroid Hormone Properties
- Derived from cholesterol; are lipid soluble
- Leave cell easily, therefore not stored
How are steroid hormones regulated?
- Regulated by cholesterol availability and enzymatic processing
What are the 5 subcategories of steroid hormones?
- Progestins
- Glucocorticoids
- Androgens
- Mineralocorticoids
- Estrogens
Peripheral conversion of steroid hormones
Enzymatic conversion of some active steroids to other forms
Where are catecholamines synthesized?
- Adrenal medulla
- Neurons
Catecholamine properties
- 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
Which hormones circulate freely (unbound to carrier/transport proteins) in the blood?
- Protein/Peptides
- Catecholamines
Which hormones bind to receptors located on the cell surface?
- Protein/Peptides
- Catecholamines
- What type of hormone is biologically active in the blood, free or bound hormones?
- What does this mean in terms of regulation?
- 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
What type of hormones are bound to transport proteins when circulating in blood?
- Steroids as they are lipid soluble and hydrophobic
How much hormone-receptor occupancy is required for biological effect?
- 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
What are some causes of abnormal endocrine function?
- Excess or deficiency of hormone
- Decrease of hormone receptor numbers
- Decrease of hormone receptor function
Hormone Antagonists
Bind receptors and blocks biological effects
Hormone Agonists
Bind to receptors and stimulate downstream effects
What type of receptors do steroid hormones bind?
Intracellular receptors
What type of receptors do protein/peptide and catecholamine hormones bind to?
Cell membrane receptors, which include:
- G protein-coupled receptors (GPCRs)
- Enzyme-linked receptors
G Protein-Coupled Receptors (GPCRs)
- 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
What are 3 common second messenger systems?
- Adenylate cyclase/cAMP
- Membrane phospholipids
- Calcium/calmodulin
Enzyme-linked receptors
Have intrinsic enzyme activity or are closely associated with enzymes
Intracellular (aka Nuclear) receptors
- Reside in the cytoplasm or nucleus
- Bind hydrophibic hormones (steroid hormones)
- Can act as transcription factors when activated and increase or decrease transcription
Timing of cellular response to hormones
- 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)
Feedback control of hormone action
Two main types of negative feedback mechanisms
- 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
Physiological response-driven feedback loop
- 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
Endocrine axis-driven feedback loop
- The hormone itself provides negative feedback to prevent further release of the same hormone
