1. Cellular Secretions
1. For communication (8-1)
1. Autocrine - when the secretion affects the cell itself (NE released from a nerve prevents further NE release)
2. Paracrine - secretion affects neighboring cells (histamine release causes local vasodilation)
3. Endocrine - secretion into the bloodstream which affects different tissues (aldosterone, cortisol, estrogen, testosterone)
4. Exocrine - secretion onto the surface of an animal (including the GI tract, or other internalized structures) - (pheremones communicating between animals)
5. A secretion can have autocrine, paracrine and endocrine effects
6. Autocrine and paracrine secreting cells can be formed into groups, but they don't have to be; endocrine and exocrine are almost always in groups
2. Cell Coat and Mucus - surface secretions
1. Glycocalyx (cell coat)
1. Made of glycoproteins and polysaccharides
2. Protects, alters filtration and diffusion, aids in identification
2. Mucus
1. Made of mucoproteins
2. Secreted by the goblet cells
3. Protects
3. Packaging and transport of secretions
1. Synthesis and packaging usually occur in a different place in the cell than secretion
1. Secretory vessicles - similar to synaptic vessicles - are released by exocytosis
2. Steroid hormones aren't packaged - membrane diffusable
2. Polymer gels (mucus)
1. Packaged and stored in secretory vessicles
2. Stored in a condensed phase - low pH in vessicles neutralizes the neg charge on proteins, and favors the condensed phase
3. Once released, the expanded hydrated phase is entered, causing the gel to "explode" from the vessicle due to repulsion of negative charges
3. Secretory and membrane proteins
1. Synthesized in the rough endoplasmic reticulum (ER)
2. Modifications to the protein occur in the Golgi
3. Membrane proteins are incorporated into vessicle walls; join cell membrane during exocytosis
4. Membrane proteins can direct where a secretory vessicle goes in the cell
4. Storage - secretions stay in vessicles due to
1. Size
2. Being bound to other proteins
3. Some don't stay/ aren't packaged: lipid soluble (steroids)
5. Secretory Mechanisms
1. Apocrine - apical portion is sloughed off and cell reseals at the apex
2. Merocrine - apical portion pinches off and bursts in lumen of the gland
3. Halocrine - whole cell is released and bursts in lumen of the gland
4. Ca²⁺ changes in the cytosol stimulate these secretory mechanisms to occur
2. Glandular Secretions
1. Endocrine Glands
1. Often found in nonendocrine organs
2. Identification of endocrine glands (steps)
1. Ablation / removal of tissue - deficiency symptoms should occur - be careful that the symptoms aren't due to damage caused by the surgery to the surrounding tissues
2. Replacement / reimplantation - reversal of the deficiency symptoms should occur
3. Hormone replacement by injection - relieve symptoms, not as good as replacement of the gland because delivery is in a bolus, not steady and small release
4. Purify and synthesize biological molecule (hormone) - test for potency (does it work like the hormone)
5. Create Antibodies - use in immunohistochemistry to determine the location of hormone synthesis and release
6. RIA's (radioimmunoassays) - Determines the amount of hormone in the blood via competition between labeled and unlabeled hormone.
3. Mammalian adrenal medulla / chromaffin cells
1. synthesis
1. Synthesizes catecholamines (8-13) - epinephrine (E), norepinephrine (NE)
2. Enzymes for all stages of synthesis are in the cytoplasm except for dopamine to norepinephrine (located in the granule)
3. Blood travels from the cortex to the medulla, carrying glucocorticoids which promote production of epinephrine to norepinephrine
2. Release
1. Stimulation of sympathetic pre-ganglions ® ­ ACh ® ­ Ca²⁺ ® ­ NE and E release (NE mostly from nerves, E mostly from the adrenal medulla)
2. Norepinephrine and Epinephrine ® ­ blood flow ® ­ NE and E release
3. Hypoxia ® ­ NE and E release
4. ATP in vessicles breaks down ® ­ Adenosine ® ¯ Ca²⁺ ® ¯ NE and E release
5. NE release ® ¯ NE release from the same nerve terminal (autocrine negative feedback)
3. Removal
1. Reuptake ® storage in vessicles for reuse or destruction by monoamine oxidase (MAO)
2. Catabolism by Catecholamine-O-methyltransferase
4. Effects and Regulation
1. Different receptors lead to different effects
2. Alpha adrenoreceptors
1. Mediate smooth muscle contractions (except in intestines)
2. Generally inhibit cellular secretions
3. Cholinergic receptors in these same tissues cause relaxation (opposes alpha receptor effects)
3. Beta adrenoreceptors
1. Mediate smooth muscle relaxation (except cardiac)
2. Stimulate cellular secretion
3. Cholinergic receptors in these same tissues cause contraction
4. Up-regulation - increases the number of receptors (makes the system more sensitive)
5. Down-regulation - decreases the number of receptors (makes the system less sensitive)
2. Exocrine Glands
1. Structure
1. Duct for secretions
2. Secretory cells line a cavity (acinus)
3. Modification of secretions occurs in secretory duct
2. Vertebrate Salivary Gland
1. Function and flow
1. Lubricates mouth; aids in taste
2. Controls bacteria - kills some and promotes growth of others
3. Begins digestion of starch
2. Formation
1. NaCl (Na following Cl) is secreted, followed by water
2. Aminoacids, proteins, glycoproteins, and amylase are added via exocytosis
3. Potassium bicarbonate is added in the duct, while some Na is reabsorbed
3. Spider silk gland
1. Spider silk is now being looked at by the military for bullet proof vests because of its great strength and light weight
3. Energy Cost
1. Lactation - very costly to the mother
2. Mother mouse feeding 8 pups (just before weaning) will consume 4X amount of nutrition; 75% will go to synthesizing milk for pups