L3. Cellular Communication Pt. 1 Flashcards
What are hormones?
Chemical messengers that are produced by endocrine glands/cells
- Transported in the blood stream
- Slower signals generating longer lasting responses (compared to neuron signals which are fast)
Water soluble hormones?
- Peptide hormones: from 3 amino acids to large proteins
- Catecholamines: (adrenaline and noradrenaline)
- Some amine hormones
- Made and stored until required
- Released by exocytosis
- Most travel dissolved in blood (plasma) but some are bound to carrier protein
- Receptor on the surface of a cell
Lipid soluble hormones?
- Steroid hormones: made from cholesterol
- Thyroid hormones: T3 and T4
- Some amine hormones
- Cannot be stored EXCEPT thyroid hormones –> they are made in thyroid cells and stored until required
- Travel in the blood bound to a carrier protein
- Receptor inside target cell
Amine hormones?
Derived from tyrosine (amino acid)
Steroid hormone?
Are made from cholesterol as required and cannot be stored
Thyroid hormone?
Are made in thyroid cells and stored till required
Peptide hormones?
- Short peptide chains: ADH and vasopressin
- Long peptide chains or more than 1 joined together: insulin
- Proteins: growth hormone
Peptide hormone synthesis?
Preprohormone in ER –> cleaved to prohormone –> Golgi –> hormone (water soluble) –> secreted via exocytosis
*When they are being packaged as a prohormone to a hormone, they may have the fragments still attached and can be secreted like that via exocytosis
Steroid hormone synthesis?
Structure = 4 hydrocarbon rings
Another hormone stimulates/binds to the cell receptor to trigger a series of events that synthesize steroid hormones from cholesterol –> then when synthesized it is lipid soluble so diffuses out of the cell and is transported around the blood with a carrier
*must be carried by a carrier protein in order for it to stay in the blood long enough to make it all around the body
Adrenal steroid synthesis?
- Cortisol = stress hormone GLUCOcorticoid: mobilises glucose and other functions
- Aldosterone = blood pressure hormone
MINERALcorticoid: control of kidney reabsorption of Na+, K+, and H+ ions
Sex steroid synthesis?
All come from cholesterol to androstenedione and converted to estradiol by aromatase
Catecholamine synthesis?
Tyrosine –> dopamine –> noradrenaline (norepinephrine); some can then be stored in vesicle-like structures and the rest continues on –> adrenaline (epinephrine) –> stored in granules –> secreted out via exocytosis as they are water-soluble hormones
Thyroid synthesis?
- Thyroglobulin (TGB) protein is made in thyroid follicles and contains tyrosine (Y)
- Iodine (I) enters follicle cell from blood and reacts with tyrosine in TGB
- Thyroid hormones detach from iodised TGB as needed:
T3 = the active form
T4 = the more plentiful form - T3 and T4 travel bound to a carrier protein (thyroid-binding globulin, TBG) to target cells
Hormone-protein complex?
Free hormone + binding complex = hormone-protein complex
What are the fates of secreted hormones?
- Excreted
- Inactivated by metabolism
- Activated by metabolism
- Bind to target cells to that produce a cellular response
- All result in hormone unbinding
Receptors?
Receptors for water soluble hormones = on the surface of target cells
Receptors for lipid soluble hormones = inside the target cells
Specificity?
Different types of cells can have receptors for the same hormone
BUT
The response caused by the hormone binding to the receptor can be different for the different types of cells
Sensitivity?
The sensitivity of a target cell to any particular hormone depends on the number of receptors expressed
The more receptors for a hormone that a cell has, the greater the likelihood that hormone will bind to one of them, causing a response
Up-regulation of sensitivity?
- Synthesis > degradation
- Increases the number of receptors expressed to increase sensitivity
- Occurs when the cell is exposed to LOW levels of the hormone for a long period of time
Down-regulation of sensitivity?
- Synthesis < degradation
- Decreases the number of receptors expressed to decrease sensitivity
- Occurs when the cell is exposed to HIGH levels of the hormone for a long period of time
