BMS Section 2 - Endocrine System Pt. I

Exchange of ions and molecules of adjacent cells

Across gap junctions with the same cells

Transfer of information from cell to cell

Chemical signals within a single tissue

Hormones are transported to target cells

Through the bloodstream

Hormone

Any chemical that controls and regulates the activity of certain cells or organs 

Types of cellular communication

Autocrine, Paracrine, Endocrine, Direct

Autocrine

Cell releases a signaling molecule that binds to receptors on its own surface, influencing its own behavior

• Ex. positive self talk, someone is influencing their self only

Paracrine

Cell releases chemical messenger molecules that diffuse short distances to act on neighboring cells, influencing their behavior and function

• Ex. Coach talking to players in a huddle, coach is only influencing the players near him

Direct

Cells to communicate through physical contact to transfer small molecules, or by the binding of surface proteins on adjacent cells

• Ex. Someone shaking you awake, only making sure you are awake

Endocrine

When specialized cells, or endocrine glands, release chemical messengers called hormones into the bloodstream

• Ex. Making a phone call, can be short distance or long distance to specific cells 

Glandular Epithelium

Make up endocrine and exocrine glands, specialized epithelial tissue that secretes substances

Exocrine glands

release contents through a duct that leads to epithelial surface

Merocrine

Part - release by exocytosis

• sweat and salivary glands

Apocrine

Away - release by exocytosis, part of the cell is pinched off

• mammary and odorous sweat glands

Holocrine

Whole - release by entire cell rupturing

• sebaceous glands

Classes of hormones

Amino acid derivatives, peptide hormones, lipid derivatives 

Amino acid derivatives

Derived from amino acids

• Tryptophan (→ melatonin) and 

• Tyrosine (→ thyroid hormones) (hydrophobic) vs catecholamines (epinephrine and norepinephrine) (hydrophilic)

Peptide hormones

Derived from amino acids, linked by peptide bonds

• Peptides (2-50 amino acids) vs protein hormones (<50 amino acids)

Lipid derivatives

Derived from fatty acid molecules

• steroid hormones → derived from cholesterol

Mechanisms of catecholamine and peptide hormones

Not lipid soluble, cannot penetrate plasma membrane. Binds to receptor proteins on outer surface of plasma membrane (extracellular receptors)

Mechanisms of steroid and thyroid hormones

Lipid soluble, diffuses across plasma membrane. Binds to receptors inside the cell (intracellular receptors)

Mechanisms of G protein coupled receptors

Hormones uses an intracellular intermediary to bring affects. Once activated, these proteins increase cyclic AMP levels, acting as a second messenger within the cell 

Effects of the secondary messengers

How G protein activation impacts metabolic activity of a cell

G protein activation increases

Accelerate the activity of the cell

• Epinephrine, norepinephrine, calcitonin, parathyroid hormone, ADH, ACTH, FSH, LH, TSH

• Activating enzymes, opening ion channels

G protein activation decreases

Decrease cAMP levels in the cytoplasm resulting in an inhibitory effect on the cell

• Epinephrine and norepinephrine

Transport of hormones

Can circulate freely or be bound to special carrier proteins.

Bloodstream contains a substantial reserve of bound hormones

Free hormone activation

Remain functional for less than an hour and proceed to be inactivated when

1. diffuse out of bloodstream and bind to receptors on target cells

2. are absorbed and broken down by liver or kidneys

3. are broken down in blood or intestinal fluids

Thyroid and steroid hormones functionality

Remain functional for much longer

Geonomic effects of hormones and intracellular receptors

Steroid hormones can alter rate of DNA transcription in nucleus, Alterations in synthesis of enzymes of structural proteins

• can directly affect activity and structure of target cell

Non-geonomic effects of hormones and intracellular receptors 

Thyroid hormones bind to receptors within nucleus and on mitochondria

• activates genes or change rate of transcription, increases rate of ATP production

Down-regulation of hormone action

Presence of a hormone triggers a decrease in the number of hormone receptors 

• When levels of a particular hormone are high, cells become less sensitive to it

Up-regulation of hormone action

Abscence of a hormone triggers an increase in the number of hormone receptors

• when levels of a particular hormone is low, cells are more sensitive to it

Hormones release triggers

• Hormonal stimuli

• Humoral stimuli 

• Neural stimuli

Hormonal stimuli

Arrival or removal of a hormone

Humoral stimuli

Change in extracellular fluid

Neural stimuli

Neurotransmitters