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Regulatory Mechanisms and Salivary Gland Function

Kapitel i bok
Författare Jörgen Ekström
Nina Khosravani
Publicerad i Salivary Gland Disorders: Diagnosis and Management
Sidor 10-18
Förlag Georg Thieme Verlag
Förlagsort Stuttgart, Germany
Publiceringsår 2011
Publicerad vid Institutionen för neurovetenskap och fysiologi, sektionen för farmakologi
Sidor 10-18
Språk en
Ämneskategorier Fysiologi, Fysiologi

Sammanfattning

* Acinar cells secrete water and proteins.The isotonic saliva is modified by duct cells and becomes hypotonic. Immunoglobulin A from plasma cells is transported across the epithelial cells into the saliva.Contraction of myoepithelial cells increases luminal pressure and expels saliva. * The volume of saliva secreted and its protein composition varies between various types of gland.Minor glands continously secrete a protective mucin-rich film of saliva, while submandibular and parotid glands secrete their reflexly elicited watery saliva mainly during a meal. * Stimulation of various receptors (mechanoreceptors,gustatory receptors,thermoreceptors,olfactory receptors and noiceptors) triggers reflex secretion. * Salivary nuclei in the central nervous system are influenced by higher brain regions:sleep,fever and fear reduce or inhibit the outflow of impulses for secretion. * Parasympathetic innervation evokes secretion of proteins and large volumes of fluid, while sympathetic innervation of any of the secretory elements evokes secretion of proteins and small volumes of fluid. In reflex conditions, sympathetic activity occurs during ongoing parasympathetic activity and the two sets of nerves interact synergistically. * In acinar cells,Ca2+ causes mainly fluid secretion, while cAMP causes mainly protein secretion. The two pathways interact positively. The parasympathetic nerve uses different transmitters to activate the two pathways (acetylcholine for Ca2+ and vasoactive intestinal peptide for cAMP), while the sympathetic nerve activates the two pathways through the action of norepinephrine on α1(Ca2+) and β1(cAMP) adrenoreceptors. Agonists using cAMP also generate nitric oxid as an intracellular messenger, which contributes to the protein secretion. * Concomitant with secretion, gland blood flow increases due to parasympathetically induced vasodilation involving both cholinergic and vasoactive intestinal peptide transmission mechanisms. Sympathetic vasoconstrictor fibers are not activated during reflex secretion, but in response to a severe drop in mean arterial blood pressure. * Recent studies have drawn attention to the role of gastrointestinal hormones (gastrin,cholecystokinin and melatonin) in protein secretion and synthesis, engaging nitric oxide intracellularly. * Sensory nerves, using substance P and calcitonin gene-related peptide as transmitters, innervate ducts and blood vessels and may evoke pain,glandular swelling and glandular inflammation. * Both nerves and hormones such as estrogen and testosterone have long-term trophic effects on glandular metabolism and gland weight. Parasympathetic nonadrenergic,noncholinergic transmission mechanisms are particularly important for maintaining gland weight. * Neural regulation of the receptor sensitivity of the secretory cells to stimulating agents is a further example of trophic effects. Loss of the nerve supply is followed by denervation supersensitivity. * Xerogenic drugs act centrally or peripherally, or at both levels. Antipsychotic agents are well-known xerogenic drugs, but clozapine causes sialorrhea. Local activation of the minor glands may be an advantageous approach to the treatment of dry mouth.

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