The Processing of an Ingested MealCephalic PhaseOral PhaseGeneral Properties of Secretions of the GI tractSlide 5Slide 6Slide 7The Major Salivary GlandsControl of Salivary SecretionSlide 10Slide 11Salivary Gland SecretionsSlide 13Secretion vs. AbsorptionGeneral Characteristics of trans-Epithelial TransportIon Transport by Salivary GlandSlide 17The Processing of an Ingested Meal•Cephalic, Oral, and Esophageal Phases•Gastric Phase•Intestinal Phase•Colonic PhaseCephalic Phase•Activation of the GI tract to receive a meal•Anticipation or thinking about a meal•Visual and olfactory stimuli•Conditioned reflex: auditory•Increased excitatory parasympathetic outflow to the gutOral Phase•Many of the responses are identical to the Cephalic response.•Physical presence of food generates specific signals sensed by:•Mechanoreceptors•Chemoreceptors•Gustatory receptors•Nociceptors•Chewing•Mechanical disruption•Mixes food particles with salivary secretionsGeneral Properties of Secretions of the GI tract•Salivary glands, pancreas, liver, glands of the gut wall, and from intestinal mucosa•Exact nature of the secretory product varies with functional region•Common characteristics:•Water•Electrolytes•Proteins•Signaling molecules (hormones)Daily Secretion of GI JuicesSecretion Daily Volume (ml)pHSaliva 1000 6.0-7.0Gastric 1500 1.0-3.5Pancreatic 1000 8.0-8.3Bile 1000 7.8Small Intestine 1800 7.5-8.0Brunner’s gland 200 8.0-8.9Large Intestine 200 7.5-8.0Total 6700Exocrine Gland SecretionTubuloalveolar Glandtypical of salivary gland and the exocrine pancreasThe Major Salivary GlandsSecretion of SalivaThree pairs of major salivary glands1. Parotid2. Submandibular3. SublingualMany small buccal glandsControl of Salivary Secretion•Exclusively neural•Stimulated by both parasympathetic and sympathetic branches of autonomic nervous system•Parasympathetic innervation is most dominantSalivary Reflex SecretionSalivary Gland Secretions•Large flow rate•Hypotonic•Na+, K+, HCO3-, Ca+2, Mg+2, Cl-•Mucin•Amylase•Lipase•Lysozyme•Salivary flow rate up to 1 ml/min/g salivary gland•Composition changes as flow rate increases (see fig 27-2)Composition of Saliva Changes as a Function of Flow RateSecretion vs. Absorption•Direction of movement; not a specific molecular mechanism•Absorption: from outside  to inside body •Secretion: generally from inside  to outside body (exception are hormonal and paracrine secretions)General Characteristics of trans-Epithelial TransportIon Transport by Salivary GlandAcinar Cells Duct CellsImportant Points to Consider1. Describe the major phases of digestion in the GI tract.2. How does the cephalic phase differ from the oral phase?3. What are the basic properties of GI secretions? Saliva?4. What is the difference between an endocrine and an exocrine secretion?5. How are the salivary glands controlled?6. What are the basic characteristics of epithelial