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Levels of Organization
Chemical, Cellular, Tissue, Organ, Organ System, Organismal
Chemicals produced by one set of cells that ravel trough the body to change the metabolic activity (up or down) of a different set of cells which are called the target cells. Amino acids bases: derived from the AAs themselves, a short chain of AAs called a "peptide" or a long chain of specificaly arranged AAs called a "protein". Water soluble. Generally faster acting by binding with a surface receptor (exception thyroxin)
Chemicals produced by a cell that in turn affects that same cell's metabolic activity.
Chemicals produced by a cell that in turns effects neigh boring cell population chemical structure of hormones (chemical types).
Assembled using cholesterol component (lipids can penetrate cell membranes). Slower acting by binding to internal cell receptor and activating genes (regions of the DNA).
Non-steroid lipids which signal nearby cells to action (localized reactions)
While hormones will circulate throughout the body, only cells with the appropriate internal or external receptor for the specific hormone will be "targeted" for effect.
- Muscle: contract up or down
- Epithelial: secretion of certain product up or down
Target cell responses to specific hormones
- Opens/closes ion channels which may up or down plasma membrane potential or permeability
- Stimulates synthesis or activity of proteins or regulatory molecules like enzymes within cell
- Stimulates mitosis
AA hormones work
Plasma membrane receptors and second-messenger systems
Summary of the second messenger signaling mechanisms
- Hormone (the first messenger) binds to external receptor
- Engaged external receptor Activates internal G proteins which trigger secondary messengers eventually producing intracellular changes in metabolic activities.
- Quick on & off: repeated surface receptor stimulation needed to prolong a response
AA hormones- Quick on & off
Repeated surface receptor stimulation needed to prolong a response
Cyclic AMP (cAMP)
Common intracellular secondary messengers. cAMP signaling mechanism -> actiates protein kinases -> which trigger cells internal responses (may turn on or off activity)
Common intracellular secondary messengers. PIP2-Calcium signaling mechanism -> utilizes Ca++ to triger cells internal responses.
How steroids hormone work?
Intracellular receptors and direct gene activation.
Transcription -> mRNA -> translation -> protein synthesis
hormone complex then enters nucleus and activates "recipes" stored on the DNA molecules as "genes"
Being lipid soluble, steroid hormones diffuse through the plasma membrane and bind to internal receptors. (so does the AA based thyroxine hormone... an exception to the rule)
Target cell specificity
- What receptors a cell has determines whether or not a hormone will bind to & activate it.
- Some receptors are expressed by most body cells (e.g. thyroxine) but receptors for other hormones are found in fewer more specific body locations.
Target cell hormone interaction dependent upon 3 things
- Circulating blood levels of a hormone.
- Number of receptors on or in target cells available for binding.
- Affinity:strength of binding between hormone and the receptor.
Strength of binding between hormone and the receptor.
Response by a cell to produce more receptors for a certain hormone so its response increases. (A positive reaction)
Response by a cell to down# of receptors for a certain hormone leads to a down response. (A negative reaction)