In the circuit of Figure 10.11, assume that the currents and charges are all zero prior to the switch being closed at time 0. Find the loop currents for time t > 0. 50 103 F 10 H i2
A&P Chapter 24 The Digestive System Gastrointestinal (GI) Tract Long tube that is open at both ends for the transit of food during processing. Parts of this tube are: esophagus, stomach, small intestine, large intestine, and rectum. Accessory Structures Are not part of the GI tract, but they do contribute to food processing. This includes: teeth, tounge, salivary glands, liver, gall bladder, and pancreas. Digestive Process There are 6 processes involved in digestion: Ingestion: taking food into mouth. Secretion: release of water, acid, buffers, and enzymes into lumen of GI tract. Mixing and propulsion: churning and movement of food through GI tract. Digestion: mechanical and chemical breakdown of food. Absorption: passage of digested products from GI tract into blood and lymph. Defecation: elimination of feces from GI tract. Neural Innervation of the Gut Enteric Nervous System- Submucosal Plexus & Myenteric Plexus. Autonomic Nervous System- Parasympathetic & Sympathetic. GI Reflex Pathways GI reflex pathways regulate GI secretion and motility in response to stimuli within the GI tract. Peritoneum the largest serous membrane in the body. 5 major folds: Greater Omentum (fatty apron), Lesser Omentum, Mesentery, Mesocolon, & Falciform Ligament. Mouth the mouth is formed by cheeks, hard and soft palates, and tongue. Salivary Glands Salivary glands lie outside the mouth and empty their contents into ducts which deliver saliva into the oral cavity. 3 pairs: Parotid, Submandibular, & Sublingual. Tongue The tongue, together with associated muscle, forms the floor of the oral cavity. Composed of skeletal muscle covered with mucous membrane. Participates in chewing, swallowing, and speech. The upper and lateral surfaces of the tongue are covered with papillae, some of which contain taste buds. Teeth The teeth project into the mouth and are adapted for mechanical digestion. Enamal is the hardest thing in the body. Harder than bone. Mechanical and Chemical Digestion in the Mouth Mechanical- chewing mixes food with saliva and forms a bolus which can be easily swallowed. Chemical- Salivary amylase converts polysaccharides to disaccharides. Pharynx The pharynx is a funnel shaped tube that extends from the internal nares to the esophagus posteriorly and the larynx anteriorly. a funnel shaped tube that is composed of skeletal muscle and lined with mucous membrane. Esophagus The esophagus is a collapsible, muscular tube that lies posterior to the trachea and connects the pharynx to the stomach. About 10 inches. Deglutition 3 stages: 1- tongue shapes food and moves into back of mouth cavity. 2- uvula and palate seal off the nasal cavity. Epiglottis covers the larynx. 3- esophageal sphincter contracts and relaxes to move food to stomach. Stomach Is a J-shaped enlargement of the GI tract. Functions: Mixes saliva, food, gastric juice to form chime, Serves as reservoir for food before release into small intestine, secretes gastric juice which contains HCI( kills bacteria and denatures proteins) ,pepsin, intrinsic factor, and gastric lipase, & Secretes gastrin into blood. Pancreas Is a gland that lies posterior to the stomach Produces enzymes that digest carbohydrates, proteins, fats, and nucleic acids Produces sodium bicarbonate which buffers stomach acid Empties its contents into the duodenum Liver & Gallbladder The liver makes bile, important in the emulsification of fats The gallbladder stores bile until it is needed The liver is composed of hepatocytes, bile canaliculi, and hepatic sinusoids Functions: Carbohydrate, lipid, and protein metabolism, Processing of drugs and hormones, Bilirubin excretion, Bile salt synthesis, Storage, Phagocytosis, & Vitamin D activation. Small Intestines (SI) The majority of digestion and absorption occur in the small intestines. Circular folds increase the surface area for digestion and absorption in the small intestine Intestinal juice provides a vehicle for absorption of substances from chyme as they come in contact with the villi Brush border enzymes, found on the surfaces of the microvilli of absorptive cells, break down food products Segmentation- localized contractions. Peristalsis- Propulsive contractions. Digestion of: Cabs, Proteins, Lipids, & Nucleic Acids. Functions of the Colon Haustral churning, peristalsis, and mass peristalsis drive contents of colon into rectum. Bacteria in large intestine convert proteins to amino acids, break down amino acids, and produce some B vitamins and vitamin K. Absorption of some water, ions, and vitamins. Formation of feces. Defecation (emptying rectum) Haustral Churning- Distension reaches a certain point and the walls of the haustra contract to squeeze contents onward. Mass Peristalsis- A strong peristaltic wave that begins in the transverse colon and quickly drives the contents of the colon into the rectum. The last stages of digestion occur through bacterial action: Substances are further broken down by bacteria & Some vitamins are synthesized by bacterial action. Absorption and Feces Formation Absorption- The colon absorbs water, electrolytes, and some vitamins. Feces- Consist of water, inorganic salts, sloughed-off epithelial cells, bacteria, products of bacterial decomposition, and undigested portions of food. Defecation Reflex Rectal wall distends Stretch receptors send sensory nerve impulses to the sacral spinal cord. Motor impulses travel back to the descending colon, sigmoid colon, rectum, and anus. Longitudinal rectal muscles contract and the internal anal sphincter opens. If the external anal sphincter is voluntarily relaxed, defecation occurs and the feces are expelled. Phases of Digestion Cephalic phase- stimulates gastric secretion and motility. Gastric phase- neural and hormonal mechanisms. Intestinal phase- neural and hormonal mechanisms.