Download Chapter 14 Notes: The Digestive System

Chapter 14 Notes: The Digestive System
The Digestive System Functions
 Ingestion—
 Digestion—
 Absorption—
 Defecation—
Organs of the Digestive System
 Two main groups


Organs of the Alimentary Canal

 Pharynx

 Stomach

 Large intestine

Mouth (Oral Cavity) Anatomy
 Lips (labia)—
 Cheeks—form the
 Hard palate—forms the
 Soft palate—forms the
 Uvula—fleshy projection of the
 Vestibule—space between
 Oral cavity proper—area contained by the
 Tongue—attached at
, and by the lingual
frenulum to the
 Tonsils


Mouth Physiology
 Mastication (
) of food
 Mixing
 Initiation of swallowing by the tongue
 Allows for the
Pharynx Anatomy
 Nasopharynx—
 Oropharynx—
 Laryngopharynx—
 Serves as a
 Food is propelled to the esophagus by two muscle layers


 Food movement is by alternating contractions of the muscle layers
(peristalsis)
Esophagus Anatomy and Physiology
 Anatomy

 Runs from
 Physiology
 Conducts food by
 Passageway for food only
Layers of Alimentary Canal Organs
 Four layers




 Mucosa
 Innermost, moist membrane consisting of

 Small amount of connective tissue
(lamina propria)

 Submucosa

 Soft connective tissue with
 Muscularis externa—


 Serosa—
 Visceral peritoneum—
 Parietal peritoneum—innermost layer that lines the
Stomach Anatomy
 Located on the
 Food enters at the
 Food empties into the small intestine at the
 Regions of the stomach
 Cardiac region—
 Fundus—
 Body—
 Pylorus—
 Rugae—
 External regions
 Lesser curvature—
 Greater curvature—
 Layers of peritoneum attached to the stomach
 Lesser omentum—
 Greater omentum—
 Contains fat to
 Has lymph nodules containing
Stomach Physiology
 Temporary storage tank for food
 Site of food breakdown
 Chemical breakdown of protein begins
 Delivers
Structure of the Stomach Mucosa
 Mucosa is
 Mucous neck cells—
 Gastric glands—
 Chief cells—
 Parietal cells—
 Enteroendocrine cells—
Small Intestine
 The body’s major digestive organ
 Site of nutrient
 Muscular tube extending from the
 Suspended from the
Subdivisions of the Small Intestine
 Duodenum


 Jejunum

 Ileum

Chemical Digestion in the Small Intestine
 Chemical digestion begins
 Enzymes are produced by


 Pancreatic ducts carry enzymes to the
 Bile, formed by the
Small Intestine Anatomy
 Three structural modifications that increase
 Microvilli—
 Villi—
 Circular folds (plicae circulares)—
Large Intestine
 Larger in diameter, but
 Frames the
Large Intestine Anatomy
 Cecum—
 Appendix
 Accumulation of lymphatic tissue that sometimes
 Hangs from
 Colon
 Ascending—
 Transverse—travels across
 Descending—
 Sigmoid—
 Rectum and anal canal—
 Anus—
 External anal sphincter—
 Internal involuntary sphincter—
 These sphincters are normally
 No
 Goblet cells produce alkaline mucus which
 Muscularis externa layer is reduced to three bands of
 These bands cause the wall to
Accessory Digestive Organs
 Teeth (we won’t focus on the details of these)
 Salivary glands
 Pancreas
 Liver
 Gallbladder
Salivary Glands
 Three pairs of salivary glands empty



Saliva
 Mixture of
 Helps to form a
 Contains salivary amylase to begin
 Dissolves chemicals so
Pancreas
 Found posterior to the
 Extends across the
 Produces a wide spectrum of digestive enzymes that break down all
categories of food
 Enzymes are
 Alkaline fluid introduced with enzymes neutralizes
 Hormones produced by the pancreas


Liver

 Located on the
 Consists of four lobes suspended from the
 Connected to the gallbladder via the
Bile
 Produced by cells in the liver
 Composition is

 Bile pigments (mostly bilirubin from the breakdown of hemoglobin)



 Function—emulsify fats by
Gallbladder
 Sac found in
 When no digestion is occurring,
 When digestion of fatty food is occurring,
 Gallstones are
Functions of the Digestive System
 Ingestion—
 Propulsion—moving foods from one region of the digestive system to
another
 Peristalsis—
 Segmentation—
 Food breakdown as
 Examples:



 Mechanical digestion prepares food for further
 Food breakdown as
 Enzymes break down food
 Each major food group uses
 Carbohydrates are broken to
 Proteins are broken to
 Fats are broken to
 Absorption
 End products of digestion are absorbed
 Food must enter mucosal cells and then into
 Defecation
 Elimination of indigestible substances
Control of Digestive Activity
 Mostly controlled by reflexes via the
 Chemical and mechanical receptors are located in organ walls that trigger
reflexes
 Stimuli include



Reflexes include


Digestive Activities of the Mouth
 Mechanical breakdown

 Chemical digestion


Activities of the Pharynx and Esophagus

 Serve as passageways
Deglutition (Swallowing)
 Buccal phase

 Occurs in the mouth
 Food is formed
 The bolus is forced into the
 Pharyngeal-esophageal phase

 All passageways
 Tongue blocks

 Epiglottis
 Pharyngeal-esophogeal phase (continued)


Food Breakdown in the Stomach
 Gastric juice is regulated by
 Presence of food or
 Gastrin causes stomach glands to produce



 Hydrochloric acid makes the stomach
 Acidic pH
 Activates pepsinogen
 Provides a hostile environment for
Digestion and Absorption in the Stomach
 Protein digestion enzymes
 Pepsin—
 Rennin—
 Alcohol and aspirin are the only items
Propulsion in the Stomach
 Food must first be
 Rippling peristalsis occurs in the
 The pylorus meters out chyme
 The stomach empties in
Digestion in the Small Intestine
 Enzymes from the brush border function to


 Pancreatic enzymes play the major digestive function


 Digest fats using
 Digest nucleic acids
 Alkaline content neutralizes
Regulation of Pancreatic Juice Secretion
 Release of pancreatic juice into the duodenum is stimulated by

 Local hormones


 Hormones travel the blood to stimulate the pancreas to release enzymeand bicarbonate-rich product
 Secretin causes the
 CCK causes the gallbladder to
 Bile is necessary for
Absorption in the Small Intestine
 Water is absorbed along the
 End products of digestion
 Most substances are absorbed

 Substances are transported to the liver
Propulsion in the Small Intestine
 Peristalsis is the major
 Segmental movements


Food Breakdown and Absorption in the Large Intestine
 No
 Resident bacteria digest remaining nutrients


 Water and vitamins
 Remaining materials are
 Feces contains




Propulsion in the Large Intestine
 Sluggish
 Mass movements

 Occur
 Presence of feces in the rectum causes a

 Defecation occurs with
Developmental Aspects of the Digestive System
 Problems of the digestive system
 Gastroenteritis—
 Appendicitis—
 Metabolism decreases with
 Middle-age digestive problems


 Activity of the digestive tract in old age


