Introduction to Hormones Flashcards
Types of cell-to-cell communication
- Direct
- indirect
Direct cell-to-cell communication
- Achieved via gap junctions which allow small molecules to move from cell to cell via connexon
- Send out and relay messages and receive messages to do something with it such as filing it or performing the instructions.
- Need to maintain homeostasis
Indirect cell-to-cell communication
- indirect via second chemical messenger
- Secretory cell sends out a message → Chemical compound traverse distance and hones in on target cell with a specific receptor for it
Types of chemical messenger signalling
- paracrines
- neurotransmitters
- hormones
paracrines signalling
- A chemical messenger sent out by a secretory cell that acts on a neighboring target cell and message ER can identify its target since the receptor is expressed on the outside of the target cell.
- Travel only a short distance
nuerotransmitters signalling
The nervous system → Secretory cell would be the presynaptic cell - it sends out the message. Secreted out of the axon terminal and travels the synapse
- Message = Neurotransmitters
- Travels in: Synapse
- Target: Neurons, muscles and glands
hormones signalling
Endocrine system → Secretory cell is the endocrine cell and message goes to target cell which has the hormone receptor expressed
- Message = Hormones
- Travels in: Bloodstream
- Target: Most cell types
What are the two systems of the endocrine system?
- Communication system
- Coordination system
What are the main cells that make up the endocrine system?
- Endocrine cells: Synthesize and secrete hormones
- Target cells: Have receptors for the hormone, responsible for hormone function
Cells that release hormones
- grouped into endocrine glands
- scattered in different organs
primary endocrine organs
primary function is secretion of hormones
- pineal gland
- hypothalamus
- pituitary gland
- thyroid gland
- parathyroid gland
- thymus
- adrenal gland
- pancreas
- ovaries and testes
- placenta (pregnant female only)
secondary endocrine organs
Primary function which is not endocrine in nature
- heart
- stomach
- liver
- kidney
- small intestine
- skin
What regulates hormone secretion?
Endocrine cells are affected by various things. How efficient a cell receives a message, how fast etc. can either stimulate or inhibit a specific hormone.
- neurotransmitters
- other hormones
- metabolites
- ions
functions of the endocrine system
- Metabolism
- Growth and development
- Reproduction
- Responses to stress
- Water and electrolyte balance
- also modulates activities of the digestive and circulatory systems
Who discovered Insulin?
Charles Best and Frederich Banting and James Collip (?) in 1921
Hydrophobic hormone synthesis
- To initiate the synthesis of hormones a signal triggers the secretory cell which is another hormone (H) that triggers its receptor to trigger a cascade to stimulate enzymatic conversions of cholesterol into the hormone of interest. It is lipid-soluble in nature so can freely cross the membrane and diffuse into the bloodstream
- Do not have vesicles because of the lipid-soluble layer the hormones can freely diffuse and vesicles would not be a good system for keeping them inside.
Hydrophobic signaling steps
- Hormone diffuses into cell
- Hormone binds to receptor
- Hormone/ receptor complex binds to the DNA to form HRE
- Binding activates gene and mRNA coding for specific protein is made and moves to cytosol
- mRNA is translated to make specific protein in cytosol which will exert fnal effect on target cell
Hydrophillic hormone synthesis
- Peptide hormones like insulin. Synthesis occurs in the nucleus and cytoplasm of cells and includes gene transcription post transcription modification, translation of mature mRNA, and post-translational and co-translational modification of the hormone peptide.
- A unique feature is that they are made as preprohormones and then package and cleaved again into hormone and then store in secretory vesicles so ready to be released when the secretory cell is triggered
- Being stored in vesicles allows for the rapid increase in levels of a particular hormone since they are ready for release when prompted. Secondly, it prevents intercellular degradation of the peptides.
Hydrophilic signaling steps
- Hormone binds to receptor on plasma membrane
- G-protein is activated and alpha subunit dissociates from complex causing conformation change of GDP to GTP and allows binding to adenylate subunit
- Activity of adenlylate cyclase increases and amplification may occur
- second messenger cAMP is synthesized
- Protein Kinase A is activated via cAMP which catalyzes transfer of phosphate group from ATP to protein
- Cellular proteins are phosphorylated changing their activity (stimulate or inhibit)
