Ingegneria delle tecnologie per la salute Fondamenti di anatomia e istologia aa. 2016-17 Digestive System (b) Salivary Glands = many small salivary glands housed within mucous membranes of mouth and tongue, constantly secreting saliva, either directly into oral cavity or indirectly through ducts (1-1.5 lts/day): usually just enough saliva is present to moisten mouth and teeth, but increases when eating, because it is essential to moisten food and initiate chemical digestion of carbohydrates Major Salivary Glands =outside oral mucosa 3 pairs of glands, secreting majority of saliva into ducts opening into mouth: • submandibular glands = in floor of mouth, secreting through submandibular ducts. • sublingual glands = below tongue, using lesser sublingual ducts to secrete into oral cavity. • parotid glands = between skin and masseter muscle (near ears), secreting through parotid duct (located near second upper molar tooth). Salivary Glands Salivary Glands Salivary Glands Salivary Glands Salivary Glands Salivary Glands Salivary Glands Saliva = essentially (95.5 %) water + 4.5 % [=complex mixture of ions, glycoproteins, enzymes, growth factors, and waste products] salivary amylase = perhaps most important ingredient in saliva initiating breakdown of carbohydrates (not enough time in mouth to allow all carbohydrates break down, but salivary amylase continues acting until inactivated by stomach acids) Bicarbonate + phosphate ions = chemical buffers, maintaining saliva at a pH 6.35-6.85. Salivary mucus = lubricate food, facilitating movement in mouth, bolus formation, and swallowing. immunoglobulin A + lysozyme = antimicrobial Regulation of Salivation • autonomic nervous system regulates salivation (secretion of saliva): parasympathetic stimulate - sympathetic reduce salivation • chemicals stimulating taste receptors on tongue impulses to sup and inf salivatory nuclei in brain stem parasympathetic impulses through fibers in glossopharyngeal and facial nerves, stimulating salivation Teeth = organs similar to bones used to tear, grind, and otherwise mechanically break down food. Types of Teeth 2 sets of teeth (= dentition): 20 deciduous teeth, or baby teeth, first appearing at about 6 mos of age; between approximately age 6 and 12, replaced by 32 permanent teeth, moving from center of mouth toward side: • 8 incisors, 4 top + 4 bottom • 4 canines • 8 premolars (or bicuspids) • 12 molars Teeth: Anatomy of a Tooth = secured in alveolar processes (sockets) of maxilla and mandible by connective tissue called periodontal ligament gingivae (gums) = soft tissues that line alveolar processes and surround necks of teeth. 2 main parts of a tooth: 1. crown (= portion projecting above gum line, 2. root (embedded in maxilla+mandible), both containing inner pulp cavity with loose connective tissue inside through which run nerves and blood vessels [root canal = pulp cavity that runs through root of tooth]; surrounding pulp cavity is dentin (=bone-like tissue) covered in root by an even harder bone-like layer called cementum and in crown by an outer layer of enamel (hardest substance in body) Teeth Pharynx = (involved in both digestion and respiration, when food enters pharynx, involuntary muscle contractions close off air passageways) short tube of skeletal muscle lined with mucous membrane, running from posterior oral and nasal cavities to opening of esophagus and larynx; 3 subdivisions: sup, nasopharynx, involved only in breathing and speech, other 2 subdivisions, oropharynx and laryngopharynx, used for both breathing and digestion: oropharynx begins inf to nasopharynx and continue below with laryngopharynx, connecting to esophagus, whereas ant portion connects to larynx, allowing air to flow into bronchial tree; histologically, wall of oropharynx is similar to that of oral cavity, with mucosa of stratified squamous epithelium endowing with mucus-producing glands. During swallowing, elevator skeletal muscles of pharynx contract, raising and expanding pharynx to receive bolus of food, then relax and constrictor muscles of pharynx contract, forcing bolus into esophagus and initiating peristalsis, meanwhile soft palate and uvula rise reflexively to close off entrance to nasopharynx and larynx is pulled superiorly with cartilaginous epiglottis folding inferiorly to cover glottis Esophagus = muscular tube connecting pharynx to stomach (running a mainly straight route through mediastinum of thorax, but to enter abdomen penetrates diaphragm through an opening = esophageal hiatus), approximately 25 cm in length, located post to trachea, and remaining collapsed when not engaged in swallowing Esophagus Passage of Food through Esophagus upper esophageal sphincter (continuous with inferior pharyngeal constrictor) = controls movement of food from pharynx into esophagus. upper two-thirds of esophagus = both smooth and skeletal muscle fibers, with the latter fading out in the bottom third of esophagus rhythmic waves of peristalsis, which begin in upper esophagus, propel bolus of food toward stomach, meanwhile, secretions from esophageal mucosa lubricate esophagus and food, that passes from esophagus into stomach at lower esophageal sphincter (also called gastroesophageal or cardiac sphincter), relaxing to let food pass into stomach, then contracting to prevent stomach acids from backing up into esophagus. Esophagus Histology of the Esophagus mucosa with non-keratinized, stratified squamous epithelium, with a layer of basal and parabasal cells, protecting against erosion from food particles + lamina propria containing mucus- secreting glands + muscularis layer changing according to location: in upper third muscularis = skeletal muscle, in middle third = skeletal and smooth muscle and in lower third = smooth muscle + adventitia, most superficial layer of esophagus not covered by a fold of visceral peritoneum. Esophagus Esophagus Esophagus Esophagus Esophagus Esophagus Esophagus Digestive functions Stomach [FUNCTION] = temporary holding chamber = meal can be ingested far more quickly than it can be digested and absorbed by small intestine: stomach holds food and parses only small amounts into small intestine at a time; foods not processed in order are eaten, but mixed together with digestive juices in stomach (= chyme), released into small intestine. plays several important roles in chemical digestion, including continued digestion of carbohydrates and initial digestion of proteins and triglycerides little if any nutrient absorption occurs in stomach, with exception of negligible amount of nutrients in alcohol Stomach: structure 4 main regions in stomach: 1. cardia (or cardiac region) = point where esophagus connects to stomach and through which food passes into stomach 2. Fundus = dome-shaped and located inf to diaphragm, above and left of cardia 3. Body = below fundus, main part of stomach 4. Pylorus = funnel-shaped, connecting stomach (pyloric antrum) to duodenum (=narrower end, called pyloric canal, with smooth muscle pyloric sphincter located at latter point of connection and controls stomach emptying) Stomach: structure In absence of food, stomach deflates inward, and mucosa and submucosa fall into a large fold (=ruga). greater curvature = convex lateral surface lesser curvature = concave medial border held in place by lesser omentum (extending from liver to lesser curvature) and greater omentum (running from greater curvature to posterior abdominal wall) Stomach: structure Stomach: histology wall made of same 4 layers as rest of alimentary canal, but with adaptations for unique functions of this organ to: a) Muscularis = in addition to typical circular and longitudinal smooth muscle layers, muscularis has an inner oblique (= in addition to moving food through canal, stomach can vigorously churn food, mechanically breaking it down into smaller particles) Stomach: histology b) mucosa Stomach: histology b) Mucosa = epithelial lining consists only of surface mucus cells, secreting a protective coat of alkaline mucus + vast number of gastric pits dot surface of epithelium, marking entry to each gastric gland, secreting complex digestive fluid referred to as gastric juice; Stomach: histology walls of gastric pits made up primarily of mucus cells, but gastric glands made up of different types of cells: glands of cardia and pylorus = primarily mucus-secreting cells pyloric antrum = mucus and a number of hormones, including majority of stimulatory hormone, gastrin fundus and body = (much larger glands) site of most chemical digestion, producing most of gastric secretions, due to a variety of secretory cells: Stomach: histology Stomach: histology 1. Parietal cells—located primarily in middle region of gastric glands (among the most highly differentiated of the body‘s epithelial cells) producing both hydrochloric acid (HCl, responsible for high acidity [pH 1.5 to 3.5] needed to activate protein-digesting enzyme, pepsin, and also killing much of bacteria ingested with food and helping to denature proteins, making them more available for enzymatic digestion) and intrinsic factor (glycoprotein necessary for absorption of vitamin B12 in small intestine). 2. Chief cells—located primarily in basal regions of gastric glands, secreting pepsinogen (inactive proenzyme form of pepsin, with HCl necessary for its conversion from pepsinogen) 3. Mucous neck cells— (gastric glands in upper part of stomach) secreting thin, acidic mucus that is much different from the mucus secreted by the goblet cells of the surface epithelium (role not currently known) 4. Enteroendocrine