A&P 2 Exam 1 - Hormones and Endocrine System

Name the 4 different types of intercellular communication

Direct communication, paracrine communication, endocrine communication, synaptic communication

Describe direct communication

• Uses gap junctions (connect cytoplasm directly), one cell to another cell.

• Small things like ions, small solutes, and lipid-soluble materials can go through (sugars, amino acids)

• Effects distributed to similar adjacent cells

• Rare, highly specialized

• Ex: cardiac myocytes (muscle cells)

Describe paracrine communication

• Release paracrine factors through extracellular fluid (in the interstitial fluid, which is between cells)

• Effects distributed to local area

• Ex: blood clotting, inflammation

Describe endocrine communication

• Hormones released by endocrine glands through the bloodstream

• Effects distributed in target cells in other tissues and organs (far away distant cell)

• Alters metabolic activities

• Ex: pancreas releases insulin to process glucose

Describe synaptic communication

• Happens across synapses

• Neurons release neurotransmitters (out of synapse) into synaptic cleft

• Effect distribution at specific areas (need appropriate receptors)

• Crisis management

• Ex: neuromuscular junction or neuron and a neuron

Name the three major classes of hormones

Monoamines, peptide hormones, and steroids

Characteristics of monoamines?

• Made from amino acids (1 aa) which are converted into hormone

  • Come from tyrosine or tryptophan

• Derivatives of tyrosine

  • Thyroid hormones (LIPID-SOLUBLE)

  • Catecholamines - epinephrine, norepinephrine, dopamine (all water-soluble)

• Derivatives of tryptophan

  • Serotonin, melatonin (water-soluble)

• Most water-soluble EXCEPT THYROID HORMONE

Characteristics of peptide hormones?

• Made from chains of amino acids linked by peptide bonds

• Synthesized through central dogma (DNA to RNA to protein) as pro-hormones (inactive to active)

• 3 types: glycoproteins, small proteins, short chain polypeptides

• ALL water-soluble

Describe the 3 types of peptide hormones?

• Glycoproteins: huge (>200 aa), carbohydrate side chains. Ex: TSH, LH, FSH

• Small proteins: 50-100 aa. Includes all hormones secreted by hypothalamus, heart, thymus, digestive tract pancreas, posterior lobe of pituitary gland. Basically most hormones. Ex: GH, PRL

• Short chain polypeptides: very short (<50 aa). Ex: ADH, OXT

• ALL water-soluble

Characteristics of steroids?

• Made from cholesterol

• Released by

  • Reproductive organs (androgens, estrogens, progestins)

  • Adrenal glands (corticosteroids)

  • Kidneys (calcitriol)

• ALL lipid-soluble

• Because they are lipid-soluble and travel in blood (plasma contains water), they bind to transport (binding) proteins, like having a protein water-soluble coat to help them travel

Characteristics of paracrine factors?

• Released into extracellular fluid (interstitial fluid) and act on nearby cells

• Coordinate local cellular activities and affect enzymatic processes in extracellular fluid (interstitial fluid)

• Ex: Histamine, nitric oxide (NO), catecholamines, eicosanoids

• Eicosanoids - derived from arachidonic acid (big molecule, 20-carbon fatty acid)

  • Ex: prostaglandins, thromboxanes, prostacyclins, leukotrienes

How do free hormones circulate and act?

• Molecules travel and freely dissolved in blood stream (plasma)

• Fast acting: easily go through the kidney or liver and are processed

• Enzymes, liver, kidneys will (easily) degrade the hormones in plasma or interstitial fluids

• Functional <1 hour (short half-life)

• Water-soluble

• Monoamines, peptide

• Since plasma membrane is a lipid barrier (water-soluble can’t get through), they use extracellular receptors (cell surface receptors)

How do bound hormones circulate and act?

• Bind to specialized transport proteins

• Enzymes can’t get to them easily, not processed very well by liver and kidney

• Remain in circulation longer >1 hour (days) (long half-life)

• Bloodstream has a reserve of these hormones

• Lipid-soluble

• Steroids and thyroid hormone

• They can leave plasma membrane easily because lipid-soluble and bind to binding proteins

• Use intracellular receptors (nuclear receptors) (in cytoplasm and nucleus), interact with DNA (gene expression)

Summarize the characteristics of water-soluble molecules

• High solubility in blood (because they can dissolve in water)

• Quickly digested by enzymes in blood

• Easily filtered by kidneys (leads to short half-life)

• Short half-life (<1 hour)

• No binding proteins

• Peptide/protein hormones, monoamines

Summarize the characteristics of lipid-soluble molecules

• Do not dissolve well in blood

• Need binding proteins which allow them to be more water-soluble, which gives them long half-life

• Long half-life (>1 hour-days)

• Binding is specific (to hormone/molecule) and reversible (be able to let it go)

• Steroids, eicosanoids (paracrine factors), thyroid hormone

Describe hormone receptors

How do extracellular (membrane-bound) receptors cause effects in a target cell?

• Use different “signaling cascades” (pathways) to cause changes in cell function

• Cyclic AMP (cAMP) Pathway

How do intracellular (nuclear) receptors cause effects in a target cell?