Chapter 22: The Digestive System

Stimulation of salivary glands comes from

Facial and glossopharyngeal nerves

Villi

Fingerlike projections in the mucosal layer of the small intestine.

Pharyngeal Phase

Food bolus stimulates afferent nerves (trigeminal and glossopharyngeal) to send information to the medulla. Medulla sends motor information to elevate the soft palate. Passageway between nasopharynx and oropharynx is closed.

General Tissue Organization of the Digestive System (the layers)

Four Tunics: serosa, muscularis externa, submucosa, mucosa.

What connects smooth muscle cells in the stomach?

Gap Junctions

What does stomach distention stimulate?

Gastrin release

GERD

Gastroesophageal reflux disease: back flow of acid contents of stomach into the esophagus. The lower esophageal spinster fails to close.

Esophageal Phase

In the esophagus, the bolus is moved toward the stomach by peristalsis.

Functions of Small (6)

Mix liver and pancreatic secretion with chyme, continue digestion, absorb nutrients, move chyme to large intestine, produce regulatory hormones and produce immune cells in large numbers.

Muscularis Externa

Mostly muscle tissue, contains myenteric plexus, and regulates secretion.

Absorption

Movement of substances from the lumen to the cells.

Secretion from Small intestine to lumen

Mucous, electrolytes, and water.

Mucosa Composition

Muscularis mucosae (smooth muscle), laminae propria (connective tissue) and epithelial tissue.

Layers of Muscle in the Muscularis externa

Outer layer of longitudinal smooth muscle (controlling length and inner layer of circular smooth muscle (controlling radius). The myenteric plexus lies between them.

Surosa

Outermost layer, continuous with mesenteries that anchor the digestive tract to the abdominal wall; innervated,vascular and has lymphatic vessels.

Secretions from Accessory Organs into SI

Pancreas supplies digestive enzymes and alkaline broth to neutralize acid from stomach. Liver and gallbladder supply bile salts for lipid digestion.

What results in the failure to utilize or produce intrinsic factor?

Pernicious Anemia

Which teeth crush and grind food?

Premolars and molars

Endocrine Cells

Produce hormones

Goblet Cells

Produce mucous

Uvula

Projection of the soft palate

Plicae

Projections formed by the submucosal and mucosal layers in the small intestine.

Function of the Oral cavity

Protection afafsint physical and chemical abrasions, increasing surface area of foos, coating food with saliva, and initiating the process of swallowing.

Mixing Waves

Push chyme in the body of the stomach to pyloric sphincter. 80% of gastric contractions are mixing waves.

Lower Esophogeal Sphincter

Relaxes to allow food to enter stomach from esophagus. Contracts to prevent backsplash.

Small Intestine

Responsible for 90%of digestion and a major site of absorption.

Active transport in Parietal Cells

Secrete H+ into the stomach lumen via the H+/K+-ATPase ("proton pump"), Cl- ions are transported into lumen via conductance channels, HCl is form int he lumen.

Parietal Cells

Secrete HCl into stomach lumen with active transport, secrete bicarbonate to bilateral side, maintains pH of .8, secrete intrinsic factor.

Chief Cells

Secrete Pepsinogen, and contain hormone receptors that stimulate pepsin release.

G cells

Secrete gastrin hormone in response to food in the lumen, bind to receptors on basolateral side of partial to stimulate HCl realism, stimulate pepsin ad histamine release.

D cells

Secrete somatostatin, inhibit gastrin and histamine secretion.

Function of the Stomach

Short term shortage, mixing HCl and pepsin with contents, construing chemical digestion particularly of proteins, move chyme to small intestine.

Mucosa cells in Large Intestine

Simple columnar epithelium without folds or villi like the small intestine.

Segmentation

Simultaneous contraction of circular smooth muscle in front of and behind the bolus to mix it with digestive enzymes.

Peristalic Waves

Stimulated by gastrin; release the pyloric sphincter to create a path for the chyme into the duodenum.

Phasic Contractions of the Stomach

Stimulated by nervous system, hormones, or food.

pH of saliva

6.5-7.5

How much of chyme is reabsorbed?

90%

What is a gastric ulcer?

A break in the normal tissue lining of the stomach or small intestine.

Regions of the large intestine

Cecum, Colon, and rectum

Mastication

Chewing: breaks up food into smaller particles, mixes food with saliva, controlled by the medulla oblongata.

Types of Cells in Gastric Pits

Chief cells, enterochromaffin cells, D cells, parietal cells and G cells.

Cardiac Region of Stomach

Connects the esphagus to stomach at the cardia.

Peristalsis

Creates wavelike movements with circular muscle contractions behind a bolus and relaxations in front of the bolus as well as longitudinal muscle contractions.

Structural Differences in the Jejunum and Ilieum

Decreases in wall diameter and thickness as well as a decrease in the number of place and villi.

Submucosal Layer

Deep to muscularis externa, composed of connective tissue and nervous tissue (submucosal plexus), contains small blood and lymph vessels.

Pylorus

Distal region of the stomach, opening to the duodenum of the small intestine.

Motility

Due to smooth muscle contraction, occurs in the digestive tract, carries food bolus from esophagus to rectum.

The three parts of the small intestine and their respective lengths

Duodenum (4%) , jejunum (40%) and ileum (56%).

Enterochromaffin cells

ECL cells; secrete histamine, bind H2 receptors on partial cells to stimulate HCL secretion.

Haustram

Each pucker/pouch in the large intestine.

What begins in the stomach?

Enzymatic digestion of food converting the bolus into chyme.

Epiglottis Bends

Epiglottis covers the opening to larynx. Upper esophageal spinster relaxes involuntarily. Food moves into esophagus.

Nervous control of esophagus

Stretch receptors are stimulated and signal through the enteric nervous plexus to smooth muscle stimulating their contraction and peristalsis. Efferent neurons further stimulate peristalsis with contraction of smooth muscle in the esophagus.

Deglutition

Swallowing; connects oral cavity to the stomach

Lacteal

The blood and lymphatic capillary inferior to each villus.

Teniae Coli

The incomplete longitudinal layer of smooth muscle in the large intestine which forms three bands giving it a segmented appearance.

Pepsins

The major proteases active in the stomach synthesized in the gastric pits.

Secretion

The movement of substances into the lumen from the cells.

What glands secrete salvia into the oral cavity?

The partid gland, the submandibular gland and the sublingual gland.

How does the medulla control chewing?

The presence of food int he oral cavity stimulates sensory cells to the medulla that stimulate the jaw to relax and open. This action stimulation a reflexive contraction and the process repeats.

Digestion

The process of breaking down food molecules that can be mechanical or chemical.

What happens when food enters the stomach to present an increase in pressure?

The stomach walls expand

Difference in the Anatomy of the esophagus

The upper esophagus has an inner circular layer of skeletal muscle rather than smooth muscle even though it is involuntarily contracted during the swallowing process.

What regulates how long chyme is stored in the stomach?

The volume and composition of it.

Fundus

Top of the stomach

Pharnyx

Tube connecting inner ear, oral cavity and larynx. A passageway for food, air and liquid into esophagus or trachea.

Intestinal Crypts

Tubular invaginations of the mucosal layer at the base of each villus where stem cells division occurs.

Rugae

folds in the stomach that allow for it to stretch

Phases of Deglutition

pharyngeal, epiglottis bends, and esophageal

Type of cells on the epithelium in the small intestine

simple columnar epithelium

How many teeth do humans have?

32

Brush Border

Microvilli that increase the surface area by 600-fold for nutrient digestion.

Parts of the colon

ascending, transverse, descending, sigmoid

Intrinsic Factor

A glycoprotein secreted by parietal cells which plays a role in the absorption of vitamin B12.

Function of the Large Intestine

Absorption of water from chyme, secretion of protective mochas, movement of non-digested food, site of bacterial colonization for specific nutrient digestion, and site of immune cell production.

Unique Epithelial Cell types in the small intestine

Absorptive, Goblet Cells, Granular, Endocrine

Chyme

An acidic fluid containing partially digested food.

Pepsinogen

An inactive signal peptide which is activated by the acidic conditions of the stomach lumen and becomes active pepsin.

Membrane Bound Enzymes in the small intestine

Attached to microvilli: Disaccharidases, peptidases, and nucleases.

Why is the stomach resistant to adage from gastric acid and pepsin?

Because of a mucous layer formed by mucous secreting epithelium.

Chemical Digestion

Begins in oral cavity but peaks in stomach and small intestine, carried out by enzymes that break down chemical bonds.

Mechanical Digestion

Begins in the oral cavity, doesn't break chemical bonds, and increases surface area for chemical digestion.

Enterogasterones

Hormones that inhibit gastric motility and secretion including CCK, GIP, and secretin.

What causes a gastric ulcer?

Imbalance between acid/pepsin secretion and mucosal lining defenses.

Granular Cells

Immune protection

Body of Stomach

Interior and medial to the cardiac region, largest part of the stomach.

Cajal Cells

Interstitial cells in modified smooth muscle tissue that generate slow waves of membrane depolarization.

Anatomical distinction of the Stomach

It includes a inner oblique smooth muscle layer to increase strength of contractions. It also contains specialized gastric pits in the mucosal layer.

How long is a typical meal stored in the stomach?

It would typically leave the stomach within four hours.

Absorptive cells

Lots of microvilli and produce digestive enzymes

Peyer's Patches

Lymph nodes that are numerous in the ileum's mucosal and submucosal layers.

What does the strength of contractions depend on?

Magnitude of Ca2+ influx into cells.

Components of Saliva (9)

Water, electrolytes, mucous, leukocytes, epithelial cells, glycoproteins, enzymes, IgA, and lysozyme.

Ileocecal Sphincter

Where chyme moves into the large intestine

Hepatopancreatic Ampulla

Where the common bile duct and the pancreatic duct join.

Tonic Contractions of the Stomach

Without outside stimulation.

Which teeth cut and tear food?

incisors and canines

Types of teeth

incisors, canines, premolars, molars

Function of Saliva

moistens epithelia and liquifies food, begins carbohydrate breakdown with amylase enzyme, provides immunity.