Chapter 23 A&P II

What is the digestive process in the stomach?

1. Physical digestion 2. Denaturation of proteins 3. Enzymatic digestion of Pepsion 4. Chyme delivered to Small intestine 5. Secretes intrinsic factor glycoprotein for vit b12 absorption

Describe the regulation of defecation

Rectum is usually empty, mass movements force feces into rectum, distension of rectum initiates spinal defection reflex and parasympathetic signals.

flow from mouth to anus

mouth, pharynx, esophagus, stomach, duodenum, jejunum, ileum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus

Identify and describe the structural modifications of the wall of the small intestine that enhance the digestive

* the mucousa and submucousa are modified to reflect the intestines functions in the digestive pathway * epithelium= simple columnar absorptive cells bound by tight junctions (responsible for nutrient and electrolyte absorption) * intestinal crypts= secretory cells the secrete intestinal juice (serve as a carrier fluid for absorbing nutrients from chyme)

State the role of bile in digestion and describe how its entry into the small intestine is regulated.

Bile is a fat emulsifier. Bile does not usually enter the small intestine until the gallbladder contracts when stimulated by cholecystokinin.

. List the major functions of the large intestine.

Chemical Digestion, Absorption (most remaining water, vitamins and electrolytes), Propulsion of feces toward the rectum and storage of feces

Describe the process of vitamin absorption of breakdown products of foodstuffs that occurs in the small intestine.

Large fat globules are emulsified via bile salts Lipase breaks down the fatty acids which can then be ferried by the bile

Describe the role of the gallbladder

The gallbladder stores and concentrates bile that is not needed immediately for digestion.

Describe the histologic anatomy of the liver.

The liver is composed of sesame seed-sized structural and functional units called liver lobules. Each lobule is a roughly hexagonal (six-sided) structure consisting of plates of liver cells, or hepatocytes, organized like bricks in a garden wall. The hepatocyte plates radiate outward from a central vein running in the longitudinal axis of the lobule.

Describe the location and function of the peritoneum.

• The visceral peritoneum covers the external surfaces of most the digestive organs, and the parietal peritoneum lines the body wall of the abdominopelvic cavity. • The peritoneal cavity is located between the visceral and parietal peritoneum and is filled with serous fluid

State the role of pancreatic juice in digestion.

•Pancreatic juice consists mainly of water and contains enzymes that break down all categories of foodstuffs and electrolytes.

Describe the tissue composition and the general function of each of the four layers of the alimentary canal

1. Mucosa: the innermost, moist, epithelial membrane that lines the entire digestive tract. The mucosa consists of an epithelium, underlying lamina propria [areolar CT] and a thin muscularis mucosae [smooth muscle]. • It secretes mucus, digestive enzymes, and hormones • Absorbs digestive end products into the blood • Protects against infectious disease 2. Submucosa: a moderately dense connective tissue layer [areolar and dense irregular CT] containing: • Blood and lymphatic vessels • Lymphoid follicles • Nerve fibers [submucosal nerve plexus or Meissner] The lamina propria of the mucosa and the submucosa house MALT [Mucosa-Associated Lymphatic Tissue]; in the ileum [lasy section of the small intestine] the MALT is known as Peyer patches. 3. Muscularis externa: typically consists of smooth muscle and is responsible for peristalsis and segmentation. It consists of an: • Inner circular layer • Outer longitudinal layer These muscular layers are controlled by the myenteric [Auerbach] plexus. 4. Serosa [adventitia]: the protective outer layer of the intraperitoneal organs, is the visceral peritoneum.

Describe the function of the digestive system, and differentiate between organs of the alimentary canal and accessory digestive organs.

Digestive organs fall into two main groups: the alimentary canal and the accessory organs. • The alimentary canal, or GI tract, is the continuous muscular digestive tube that winds through the body digesting and absorbing foodstuff; its organs include: the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. • Accessory digestive organs or structures aid digestion physically and produce secretions that break down foodstuff in the GI tract; the organs involved are the teeth, tongue, gallbladder, salivary glands, liver and pancreas.

Describe the composition and functions of saliva, and explain how salivation is regulated.

Salivary glands produce saliva, which cleanses the mouth, dissolves food chemicals for taste, moistens food, and contains chemicals that begin the breakdown of starches. Saliva Composition: 1.0-1.5 liters/day, 97- 99.5% water, but also IgA, lysozyme, defensins, mucins and salivary amylase; production of a bolus. Regulation: Parasympathetic [watery saliva] and sympathetic [more viscous saliva] stimulation.

Describe stimuli and controls of digestive activity (basic functional concepts).

• Digestive activities within the GI tract are triggered by mechanical and chemical stimuli [e.g., stretching of organ by food, osmolarity, pH, etc.] and are detected by mechanoreceptors and chemoreceptors. • Controls of digestive activity are both intrinsic ["in-house"] and extrinsic. a. Neural mechanisms [Enteric Nervous System (ENS)]: the ENS has roughly as many neurons as the spinal cord, and as many neurotransmitters as the brain, but whose functions remain largely unknown... ❊ Short [myenteric] reflexes control smooth muscle contraction and glandular secretion as relatively localized activities involving small segments of the digestive tract; this mechanism is usually considered parasympathetic, but the plexus also contains sensory neurons, motor neurons and interneurons for local reflexes whose internal workings operate entirely outside the control of the CNS. ❊ Long reflexes involve interneurons and motor neurons in the CNS and provide a higher level of control over digestive and glandular activities. b. Hormonal mechanisms involve as many as 18 hormones, affecting almost every aspect of digestive function. c. Local mechanisms involve prostaglandins, histamines and other chemicals released into the interstitial fluid and affecting adjacent cells...

List and define the major processes occurring digestive system activity.

• Ingestion: the simple act of putting food into the mouth • Propulsion or Motility: moves food through the alimentary canal and includes both swallowing and peristalsis. • Mechanical Breakdown or Digestion: the physical process of preparing the food for chemical digestion and involves chewing, mixing, churning and segmentation. • Chemical Digestion: a series of catabolic steps in which complex food molecules are broken down to their chemical building blocks by the secretion of enzymes and various secretions (acid, bile, etc...) • Absorption: the passage of digested end products from the lumen of the GI tract through the mucosal cells into the blood or lymph. • Defecation or Elimination: eliminates indigestibles substances from the body via the anus as feces. ❊ Segmentation: rhythmic local constrictions of the small intestine. Segmentation mixes food with digestive juices and makes absorption more efficient by repeatedly moving different parts of the food mass over the intestinal wall.

Describe the mechanisms of chewing and swallowing.

•Mastication, or chewing, begins the mechanical breakdown of food and mixes the food with saliva (p. 866). •Deglutition, or swallowing, is a complicated process that involves two major phases (p. 866; Fig. 23.13). 1.The buccal phase is voluntary and occurs in the mouth where the bolus is forced into the oropharynx. 2.The pharyngeal-esophageal phase is involuntary and occurs when food is squeezed through the pharynx and into the esophagus.

Describe the gross and microscopic anatomy and the basic functions of the mouth, pharynx, and esophagus.

•Mouth is a stratified squamous epithelial mucosa-lined cavity with boundaries of the lips, cheeks, palate, and tongue oThe lips and cheeks have a core of skeletal muscle covered externally by skin that helps to keep food between the teeth when we chew and plays a small role in speech. oThe palate forms the roof of the mouth and has two parts: the hard palate anteriorly and the soft palate posteriorly. oThe tongue is made of interlacing bundles of skeletal muscle and is used to reposition food when chewing, mix food with saliva, initiate swallowing, and help form consonants for speech. oSalivary glands produce saliva, which cleanses the mouth, dissolves food chemicals for taste, moistens food, and contains chemicals that begin the breakdown of starches. oThe teeth tear and grind food, breaking it into smaller pieces. •Pharynx - oropharynx and laryngopharynx provides a common passageway for food, fluids, and air (p. 864). •Esophagus - provides a passageway for food and fluids from the laryngopharynx to the stomach where it joins at the cardiac orifice