The Digestive System

Digestion Process:

• Ingestion - inserting something in mouth

• Digestion - breakdown of food

• Absorption - clinging onto cells

• Excretion - also known as defecation

Each cell receives a continuous supply of nutrients, which provide energy for growth, regeneration, and repair.

Functions of the Digestive System

Digestive:

Physiologic process

• Involves intake and assimilation of nutrients and elimination of waste products

Ingestion:

Beginning of the digestive process

• Food taken in the mouth

After the food is ingested it is masticated (chewing) by the teeth and tongue to break it down.

• Then, mixed with enzymes produced by the salivary glands

• Resulting in a soft ball called a bolus'

  • Bolus is swallowed and starts journey into esophagus-peristalsis moves in rhythmic, wave-like motion to the alimentary canal

Absorption:

Process

• In which, digested nutrients are transferred from the intestines to the blood or lymph vessels by active or passive transport

Excretion:

Process

• Indigestible substances, unusable materials, and wasted products are eliminated from the body through the anus in the form of feces

• Also, known as defecation

Structure of the Digestive System

• Two major components:

  • Alimentary canal

    • Called gastrointestinal (GI) tract

    • Hollow tube begins in the mouth, extends through the body, ends at the anus

  • Accessory organs

    • Teeth

    • Tongue

    • Salivary glands

    • Pancreas

    • Liver

    • Gall bladder

Structure + Function of the Alimentary Canal-Mouth

• Mouth

  • Composed of lips (labia), cheeks, and hard and soft palates (roof of mouth) and the tongue

• Oral Cavity

  • Back of oral cavity: uvulas, as small, pendulous, fleshy structure

• Tongue

  • Accessory organ composed of skeletal muscle fibers

  • Assist in the mastication process

    • Mixing food with saliva to form a bolus

    • Initiating swallowing

  • Taste flavors of food

  • Helping to form consonants during speech

• Teeth

  • Accessory structures that assist in mastication

  • Bone-like structures are calcified connective tissue covered with enamel

• Salivary Glands

  • Located inside the mouth and provide secretions that keep the mucous membrane of the mouth moist

  • Moisten and lubricate food during chewing to aid in swallowing

    • Three pairs of salivary glands:

      • Parotids

        • In front of the ears

      • Submandibular

        • Under chin

      • Sublingual

        • Under tongue

Pharynx

• Extends from the base of the skull to the esophagus

• Posterior to the mouth and is the beginning of the tube leading to the stomach

• Functions in respiratory and digestive systems, larynx (respiratory) and esophagus (digestive)

  • Consists of three parts

    • Nasopharynx

    • Oropharynx

    • Laryngopharynx

During swallowing; entrance of the larynx of the respiratory system is covered by a flap called epiglottis

Esophagus

• 10-inch muscular, collapsible tube starts at the pharynx and ends at the stomach

• Passage of bolus of food from the pharynx to the esophagus

• Bolus carries down the esophagus to the stomach by a series of muscular contractions called peristalsis

• Esophagus ends at the stomach, where the lower esophageal sphincter (LES)-called the cardiac sphincter

• Cardiac sphincter closes to keep acidic gastric juices from squirting back up called heart burn

Stomach

• Collapsible, pouch-like structure in the upper-left part of the abdominal cavity, just below the diaphragm

• Expands or decreases in diameter due to deep folds called rugae

• Upper portion connected to the lower end of the esophagus; the lower end of the stomach connects to the small intestine

• Stomach is about 10-inches long, varies with degree of distention, depending on the amount of food consumed

Stomach has four main regions

• Cardiac region

• Fundus

• Pylorus region

  • Food substance turned into chyme

• Duodenum

Small Intestine

• Tube measures 20 feet long

• Digestion and absorption takes place in small intestine

• Longest organ of the gastrointestinal tract

Three major divisions

• Duodenum

  • 10-inches long

• Jejunum

  • 8-feet long

• Ileum

  • 12-feet long

  • Joins the large intestine called ileocecal valve

Functions:

• Completiting food digestion

• Absorbing food molecules through the wall of the small intestine into circulatory system

• Secreting hormones that help control secretion of bile pancreatic juice, and intestinal juice

Large Intestine

• Larger tube extending from the ileocecal valve (where it meets the small intestine) to the anus

• Functions in digestive process are to absorb most of the remaining water from indigestible food residues, to store the residues temporarily, and to eliminate the wastes from the body as semisolid feces

• Known as colon, composed of:

  • Cecum

    • 3-inch small

  • Appendix

    • 3-inches in length

  • Ascending colon

    • 10-inches long

  • Transverse colon

    • 17-inches long

  • Descending colon

    • 6 inches long

  • Sigmoid colon

    • S-shape

  • Rectum

    • 5 to 6 inches long

  • Anal canal

    • Last inch of the rectum

The Salivary Glands

• Exocrine glands

  • Secrete amylase

    • An enzyme that breaks down starch into maltose

The Liver

• Plays a major role in metabolism

  • Glycogen (sugar) storage

• Plasma protein

• Detoxifies the things that enter the body

The Gallbladder

• Small organ that aids digestions and stores bile produced by the liver

The Pancreas

Endocrine gland : secrets only into the blood

• Creates Insulin, Glycogen