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Digestive System. Digestive System. Also called the gastrointestinal tract Major components Mouth Pharynx Esophagus Stomach Intestine Rectum Anus. Digestion. The mechanical and chemical processes that breaks down large food molecules into smaller ones. Absorption.

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Digestive System

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Digestive system

Digestive System

Digestive system1

Digestive System

  • Also called the gastrointestinal tract

  • Major components

    • Mouth

    • Pharynx

    • Esophagus

    • Stomach

    • Intestine

    • Rectum

    • Anus



  • The mechanical and chemical processes that breaks down large food molecules into smaller ones.



  • When the small food molecules pass through the cells of the small intestine into the blood stream and lymphatic system. Water, minerals (salts), and some vitamins enter the blood stream via the large intestine.

Activities of digestion

Activities of Digestion

  • Ingestion, or eating

  • Peristalsis, or involuntary, sequential contractions that move ingested nutrients along the digestive tract.

  • Digestion, or the conversion of large nutrient molecules into small molecules.

  • Absorption, or the passage of usable nutrients into the blood stream and lymphatic system

Activities of digestion1

Activities of Digestion

  • Defecation- the elimination from the body of undigested and unabsorbed material as solid waste.

Chemical digestion

Chemical Digestion

  • Breaks down food particles through a series of metabolic reactions involving enzymes.

Mechanical digestion

Mechanical Digestion

  • Physical processes such as chewing, peristalsis, and the churning movement of the stomach and small intestine of mix the food with enzymes and digestive juices.



  • Also known as the ORAL CAVITY

  • Includes: Outer vestibule or Buccal cavity

    • Lips, cheeks, teeth and gums

  • Oral cavity proper

    • Opening (cavity),

    • fauces (L. throat)



A sensory nerve ending that triggers the involuntary phase of swallowing. Also stimulates the gag reflex.



  • 1 to 2 liters of saliva each day

  • 1st food breaks apart by chewing

  • Chemical digestion starts with starch being broken down.

  • Chewing mixes the food with saliva

  • Saliva is mostly water

  • Mixture (lubricated ball is called BOLUS

Digestive system

Lips & Cheeks

Lips consists mainly of fibroelastic connective tissue and skeletal muscle covered by epithelium.

Orbicularis oris muscle makes the lips capable of movement.

Lips are sensitive and abundantly supplied with blood vessels, lymphatic vessels, and sensory nerve endings coming from the trigeminal nerve.

Digestive system

Lips & Cheeks

  • labial frenulum- fold of mucous membrane that connects each lip to the gum.

  • lingual frenulum- limits backward movement of tongue.

  • red free margin- lips are covered by thin translucent epidermis that allows capillaries underneath to show, to give lips a reddish color.

Digestive system


  • Lips place food in mouth to keep food in proper position.

  • Contain sensory receptors to identify specific textures of food.

  • Moist mucous membrane of inner surface of lips leads to mucous membrane of inner surface of cheeks.



  • Cheeks- fleshy part of either side of face, below eyes and between nose and ear.

  • The mucous membrane lining the lips and cheeks is a thick squamous epithelium.

  • When surface cells are worn away, they are replaced by rapid dividing cells underneath.

  • Muscle of cheeks contribute to chewing process, and help hold food in position.

Digestive system


  • Roof of mouth

  • 2 Sections - hard palate (anterior)formed by part of palatine bones & maxillae - soft palate (posterior)posterior border of hard palate, extends b/w the oral & naval parts of pharynx

  • The small, fleshy, hard cone in center is called the uvula- keeps food from entering nasal passages when swallowing

Digestive system



  • Two curved folds of mucous membrane extending laterally & downward from soft palate- palatoglossal arch- palatopharyngeal arch

  • The hard palate is covered with a firm mucous membrane, the soft palate composed of interlacing skeletal muscles allowing it to move up & down over the nasopharynx.

  • The palatine tonsils lie b/w the arches.

  • When food is chewed & moistened by saliva, the tongue pushes it up against the surface of the hard palate, crushing & softening it.

Digestive system














Digestive system


Root-embedded in a socket in alveolar process of a jaw bone.

Crown- projecting upward from the gum.

Neck- b/w root and crown, which is surrounded by the gum.

Digestive system

Composition of Teeth and Gums

Dentine- is extremely sensitive yellowish portion surrounding the pulp cavity. (bulk end of tooth)

Enamel-is the insensitive white covering of the crown. (hardest substance in the body)

Cement- bonelike covering of neck and root

Pulp- soft core of connective tissue; contains the nerves and blood vessels of the tooth.

Gum- firm connective tissue. Covered with mucous membrane.



  • Why are canine teeth called “eyeteeth”?



  • Tip of tongue functions in chewing

  • Base of tongue helps move food from the mouth to the pharynx

  • Important for speech

  • Helps to taste food

Digestive system

  • Composed of skeletal muscle

  • Covered by smooth mucous membrane on underside

  • Dorsal surface contains papillae (taste buds)

Digestive system

  • Mucous membrane is divided in two

  • The oral part, anterior two-thirds

  • Pharyngeal part, posterior third

  • Delineated by the V-shaped sulcus terminalis

Digestive system

Three types of papillae

  • Filiform papillae, appear whitish and contain no taste buds

  • Fungiform papillae, located on the tip of the tongue, contain taste buds

  • Circumvallate papillae, in shape of a V on posterior of oral part of tongue, contain taste buds

Digestive system

The Pharynx

The Esophagus

Digestive system

Pharynx and Esophagus

Involuntary Phase

  • Pharynx

  • Air passage way during breathing & a food passage during swallowing.

  • 3 parts:

  • Nasopharynx- superior to soft palate

  • Oropharynx- soft palate to the epiglottis

  • Laryngopharynx- posterior to the epiglottis, joins the espophagus

Digestive system

Pharynx and Esophagus

Involuntary Phase

  • Esophagus

  • Muscular, membranous tube( about 25 cm long), which food passes from the pharynx into the stomach

  • Located in front of the vertebral column and behind the trachea

  • Each end closed by sphincter muscle-rest & collapsed

  • Irritation in lining of esophagus-heartburn

  • Epiglottis-goes to stomach or lungs-moves so that you can swallow food

Digestive system


The stomach is the most expandable part of the digestive tract. It stores, mixes, and digests ingested nutrients.

*Food enters the stomach through the lower esophageal orifice.

*Partially digested nutrients leave the stomach and enter the opening at the other end of the stomach called the pyloric orifice.

Digestive system

Stomach Functions

  • The stomach stores ingested nutrients until they can be released into the small intestine.

  • The stomach churns ingested nutrients, breaks them up into small particles, and mixes them with gastric juices to form a liquid called chyme.

  • The stomach secretes hydrochloric acid and enzymes that initiate the digestion of proteins and kill most of the bacteria that enter the stomach in food.

Digestive system

Digestived Movemets within the Stomach

  • After food enters the stomach slow peristaltic mixing waves start in the fundus and body. Basic Electrical Rhythm (BER).

  • After the pyloric region fills, peristaltic waves chop the chyme and push it toward the pyloric canal toward the pyloric orifice.

  • As the stomach empties, peristaltic waves ,move farther up the body of the stomach, so that all the chyme is pushed into the pyloric region.

Digestive system

Regulation of Gastric Emptying

*Gastric emptying is regulated by both neural and hormonal mechanisms.

*Gastric emptying in inhibited by the presence of fat, acid, hypertenosity, or distension in the duodenum.

*A neural response is mediated by the enterogastric reflex, which decreases stomach motility and gastric secretion.

*The hormonal response inhibits gastric motility by releasing hormones collectively known as enterogastrones.

Digestive system

Secretion of Gastric Juices...

***Gastric juice is a clear, colorless fluid secreted by the stomach mucosa in response to food.

*1.5L of gastric juice is secreted daily.

Digestive system

Secretion of Gastric Juices...

Gastric juice is composed of hydrochloric acid, mucus, and several enzymes. That enzymes being pepsinogen.

Small amounts of gastric lipase are secreted in the stomach, and the digestion of fats begins there, though only minimally.

Digestive system

Gastric juice also contains an intinsic factor that combines with Vitamin B12 from digested food to form an antianemic factor necessary for the formation of red blood cells.

***Pepsin, assisted by hydrochloric acid, breaks down large protein molecules into smaller molecule peptones,proteoses, and amino acids.

Digestive system

The Control of Gastric Juice Secretion

3 Overlapping Phases

  • Cephalic (“head”) phase.- When food is seen, smelled, tasted, chewed, or swallowed, the stomach is stimulated by activity of the vagus nerve, gastric juice is secreted before the food is swallowed.

Digestive system

Small Intestine

  • Chyme moves into the small intestine after 1 to 3 hrs.

  • Takes 1 to 6 hrs to move through the 6-m (20ft) intestine.

  • Absorbs almost all the digested molecules of food into the blood and

  • lymph.

  • Lies within the abdominopelvic cavity

  • Separated into three parts the duodenum, jejunum, and ileum

Digestive system

Small Intestine

  • Duodenum- is the C-shaped initial segment and is about 25cm long the

  • Shortest of the three

  • Jejunum is about 2.5 m (8ft) long. Ileum extends from the jejunum to the

  • cecum. Both are suspended from the posterior abdominal wall by the

  • Mesentery.

  • A sphincter that ordinarily remains constricted, regulating the entrance

  • Of chyme into the large intesine and preventing the contents of the cecum

  • From flowing back into the ileum.



  • A sphincter that ordinarily remains

    constricted, regulating the entrance

    of chyme into the large intestine and

    preventing the contents of the cecum

    from flowing back into the ileum

Digestive system

Mucosa has three distinctive features that enhance the digestion and absorption processes known as plicae circulares, and villi and glands that secrete intestinal juice.

Plicae circulares- are circular folds that increase the surface area available for absorption and cause the chme to spiral rather than move in a straight line; the spiraling motion enhances absorption.

Digestive system

-The large intestine’s primary functions are to reabsorb any remaining water and some salts, and the accumulation and movement(excretion) of undigested substances like feces.

Digestive system

Large Intestine

-The part of the digestive tract between the ileocecal orifice and the anus.

-7 parts of the Large Intestine

-Ascending colon

-Transverse colon

-Descending colon

-Sigmund colon


-veriform appendix


Digestive system

  • Muscles are arranged so it can move side to side, up and down, and in and out.

  • Three bilateral pairs of extrinsic muscles

    • Hypoglossus

    • Genioglossus

    • Styloglossus

Digestive system

  • Four pairs of intinsic muscles

    • Longitudinalis superior

    • Longitudinalis inferior

    • Transversus lingual

    • Verticalis lingual

  • The extrinsic muscles move food within the mouth to form it into a round mass, or bolus, and the intrinsic muscles assist in swallowing

  • Uvula


    • Hanging down from the center of upper soft palate.

    • Helps keep food from entering the nasal passages during swallowing.

    Digestive system

    Large Intestine

    -The part of the digestive tract between the ileocecal orifice and the anus.

    -4 parts of the Large Intestine

    -Ascending colon

    -Transverse colon

    -Descending colon

    -Sigmund colon

    -The large intestine’s primary functions are to reabsorb any remaining water and some salts, and the accumulation and movement(excretion) of undigested substances like feces.

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