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• 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• 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 Digestion

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

Chemical Digestion

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

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.

MOUTH• 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)

FAUCES

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

MOUTH

• 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

• 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.

• 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.

• 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

• 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.

• 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

• Two curved folds of mucous membrane extending laterally & downward from soft palate

- palatoglossal arch- palatopharyngeal arch

• 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.

• 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.

BABIES:

20 TEETH

10 ON EACH JAW

ADULTS:

32 PERMANENT

16 ON EACH JAW

EACH JAW HOLDS:

4 CUTTING TEETH (INSCISORS)

2 CANINES

4 PREMOLARS

SIX MOLARS

THIRD MOLARS (WISDOM TEETH)B/W AGES 17-21, NO BABY TOOTH BEFORE.

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.

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.

EYETEETH

•Why are canine teeth called “eyeteeth”?

Tongue

• 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

• Composed of skeletal muscle

• Covered by smooth mucous membrane on underside

• Dorsal surface contains papillae (taste buds)

• Mucous membrane is divided in two

• The oral part, anterior two-thirds

• Pharyngeal part, posterior third

• Delineated by the V-shaped sulcus terminalis

• 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

Three types of papillae

The Pharynx

The Esophagus

•3 parts:

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

•Nasopharynx- superior to soft palate

•Oropharynx- soft palate to the epiglottis

•Laryngopharynx- posterior to the epiglottis, joins the espophagus

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

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.

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

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

3. 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.

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

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

3. 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.

*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.

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

*1.5L of gastric juice is secreted daily.

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.

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.

1. 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.

•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

•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.

SPHINCTER

• 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

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.

-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.

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

-cecum

-veriform appendix

-rectum

• 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

• 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.

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.