chapter 25.txt

Layers—GI tract is made of four layers of tissues: mucosa, submucosa, muscularis, and serosa.

covered externally by skin and internally by mucous membrane; are the junction between skin and mucous membrane is highly sensitive; when lips are closed, line of contact is oral fissure

lateral boundaries of oral cavity, continuous with lips and lined by mucous membrane; formed in large part by buccinator muscle covered by adipose tissue; contain mucus-secreting glands

Hard palate consists of portions of four bones: two maxillae and two palatines

forms partition between the mouth and the nasopharynx and is made of muscle arranged in an arch. Suspended from midpoint of posterior border of the arch is the uvula (it helps prevent liquid & food from entering nasal cavity)

• solid mass of skeletal muscle covered by a mucous membrane; extremely maneuverable (Figure 25-4)
• •Important for mastication and deglutition
• •Has three parts: root, tip, and body
• •Papillae located on dorsal surface of tongue (roughness of the dorsal surface of the tongue is due to filiform Papillae)
• •Lingual frenulum anchors tongue to floor of mouth

• three pairs of compound tubuloalveolar glands (Figure 25-6) secrete approximately 1 liter of saliva each day; buccal glands contribute less than 5% of total salivary volume but provide for hygiene and comfort of oral tissues
• –Parotid glands —largest of the paired salivary glands; produce watery saliva containing enzymes
• –Submandibular glands —compound glands that contain enzyme and mucus-producing elements
• –Sublingual glands —smallest of the salivary glands; produce a mucous type of saliva

—exposed portion of a tooth, covered by enamel; ideally suited to withstand abrasion during mastication

narrow portion that joins the crown to the root; surrounded by the gingivae

fits into socket of alveolar process and is suspended by fibrous periodontal membrane

• -Dentin makes up the greatest portion of the tooth shell; at crown, covered by enamel, and at neck and root, covered by cementum
• –Pulp cavity—located in dentin, contains connective tissue, blood, and lymphatic vessels and sensory nerves

• - Deciduous teeth —20 baby teeth, which appear early in life
• - Permanent teeth —32 teeth, which replace the deciduous teeth

Tube through which a bolus passes when moved from the mouth to the esophagus by the process of deglutition

• •Tube that extends from the pharynx to the stomach
• •First segment of digestive tube

junction between the esophagus and the stomach

enlarged portion to the left and above the opening of the esophagus into the stomach

central portion of the stomach

lower part of the stomach

upper right curve of stomach

lower left curve of stomach

• circular muscle fibers arranged so that there is an opening in the center when relaxed and no opening when contracted
• -lower esophageal sphincter (LES) or cardiac sphincter controls opening of esophagus into stomach
• - pyloric sphincter controls outlet of pyloric portion of stomach into duodenum

• •Epithelial lining has rugae marked by gastric pits (Figures 25-11 and 25-12)
• •Gastric glands —found below level of the pits; secrete most of gastric juice

secretory cells found in gastric glands; secrete the enzymes of gastric juice (pepsinogen)

secretory cells found in gastric glands; secrete Gastric acid (hydrochloric acid); thought to produce intrinsic factor needed for vitamin B12 absorption

secrete gastrin and ghrelin

thick layer of muscle with three distinct sublayers of smooth muscle tissue arranged in a crisscrossing pattern; this pattern allows stomach to contract strongly at many angles

• –Reservoir for food until it is partially digested and moved further along GI tract
• –Secretes gastric juice to aid in digestion of food
• –Breaks food into small particles and mixes them with gastric juice
• –Secretes intrinsic factor
• –Limited absorption
• –Produces gastrin and ghrelin
• –Helps protect body from pathogenic bacteria swallowed with food

Size and position of the small intestine—tube approximately 2.5 cm in diameter and 6 m in length; coiled loops fill most of abdominal cavity

• –Duodenum —uppermost division; approximately 25 cm long, shaped roughly like the letter C
• –Jejunum —approximately 2.5 m long
• –Ileum —approximately 3.5 m long

• –Intestinal lining has plicae with villi
• –Villi—important modifications of mucosal layer
• •Each villus contains an arteriole, venule, and lacteal
• •Covered by a brush border made up of 1,700 ultrafine microvilli per cell
• •Villi and microvilli increase surface area of small intestine hundreds of times for absorption

• Cecum
• Colon

first 5 to 8 cm of large intestine, blind pouch located in lower right quadrant of abdomen

• •Ascending colon —vertical position on right side of abdomen; ileocecal valve prevents material passing from large intestine into ileum
• •Transverse colon passes horizontally across abdomen, above small intestine; extends from hepatic flexure to splenic flexure
• •Descending colon —vertical position on left side of abdomen
• •Sigmoid colon joins descending colon to rectum
• •Rectum —last 7 or 8 inches of intestinal tube; terminal inch is anal canal with opening called the anus (Figure 25-17)

Accessory organ of digestive system; 8 to 10cm in length; communicates with cecum

• •Large, continuous sheet of serous membrane (Figure 25-20)
• •Made up of parietal and visceral layers

—extension of peritoneum that supports transverse colon

A fan-shaped projection of parietal peritoneum; allows free movement of each coil of the intestine and helps prevent strangulation of the long tube (Figure 25-21)

• Location and size of the liver (Figure 25-22)— largest gland in body, weighs approximately 1.5 kg; lies under diaphragm; occupies most of right hypochondrium and part of epigastrium
• •Liver lobes and lobules—two lobes separated by falciform ligament

forms about 1/6 of of liver

forms about 5/6 of liver; divides into right proper, caudate lobe, and quadrate lobe

—anatomical units of liver; small branch of hepatic vein extends through the center of each lobule (Figure 25-23) Slide

Right and left hepatic ducts immediately join to form one hepatic duct

Common hepatic duct merges with cystic duct to form common bile duct, which opens into 2nd part of the duodenum (greater doudenal papilla)

• Detoxification by liver cells—ingested toxic substances and toxic substances formed in intestines may be changed to nontoxic substances
• –Bile secretion by liver—bile salts are formed in liver from cholesterol and are the most essential part of bile; liver cells secrete approximately 1 pint of bile per day
• –Liver metabolism carries out numerous important steps in the metabolizing of proteins, fats, and carbohydrates
• –Storage of substances such as iron and some vitamins
• –Production of important plasma proteins

• Size and location of the gallbladder—pear-shaped sac from 7 to 10 cm long and 3 cm wide at its broadest point; holds 30 to 50 ml of bile; lies on undersurface of liver
• •Structure of gallbladder—serous, muscular, and mucous layers compose the gallbladder wall; mucosal lining has rugae

• –Storage of bile
• –Concentration of bile fivefold to tenfold
• –Ejection of the concentrated bile into duodenum

• •Size and location of the pancreas—grayish pink–colored gland; 12 to 15 cm long; weighs approximately 60 g; runs from duodenum and behind stomach to spleen
• •Structure of the pancreas (Figure 25-27) —composed of endocrine and exocrine glandular tissue
• –Exocrine portion makes up majority of pancreas; has a compound acinar arrangement; tiny ducts unite to form main pancreatic duct, which empties into duodenum
• –Endocrine portion—embedded between exocrine units; called pancreatic islets; constitute only 2% of total mass of pancreas; made up of alpha cells and beta cells; pass secretions into capillaries

• •As an exocrine gland:
• –Acinar units secrete digestive enzymes
• •As an endocrine gland:
• –Beta cells secrete insulin (it ↓ blood glucose level)
• –Alpha cells secrete glucagon (it ↑ blood glucose level)