THE DIGESTIVE SYSTEM

THE MAIN FUNCTIONS OF THE DIGESTIVE SYSTEM• Ingestion: The in take of food into the digestive tract through the mouth

• Mechanical Processing: The physical manipulation of solid foods into materials that are easier to propel through the digestive tract. Also increases the solid foods surface area which makes them more susceptible to enzyme activity and easier to absorb.

• Digestion: The chemical breakdown of food into organic compounds that can be absorbed by the rest of the digestive system.

• Secretion: The release of water, acids, enzymes, and buffers by the digestive system to aid in digestion and absorption.

• Absorption: The movement of small organic molecules, vitamins etc. across the digestive epithelium and into the interstitial fluid of the digestive tract ( the absorption of materials from the digestive tract and into the body for use)

• Excretion: The removal of waste products from bodily fluid ( These products are compacted into feces and discharged via the defecation process).

THE DIGESTIVE TRACT

• The digestive system has the job of breaking down and processing food materials to convert them into a usable for of energy that all of the body’s cells can use as a source of food as well as removing waste products from our food supply.

• The digestive system consists of a muscular tube called the digestive tract (gastrointestinal tract GI, alimentary canal) and several accessory structures.

• The digestive tract begins at the oral cavity(mouth) and continues through the esophagus, stomach, small intestines, larges intestines ending at the rectum and anus.

• The mucosa is the inner lining or membrane of the digestive tract, it consists of epithelia and loose connective tissue.

ANATOMICAL & ACCESSORY STRUCTURES OF THE DIGESTIVE SYSTEM

ANATOMICAL STRUCTURES & ACCESSORY STRUCTURES OF THE DIGESTIVE SYSTEM• Oral Cavity ( Teeth & Tounge): Mechanical function.

• Liver: secretion, storage, various other functions.

• Gallbladder: storage of bile.

• Pancreas: Secretion of enzymes and hormones.

• Large Intestine: Dehydration, compaction, and preparation of waste products for elimination.

• Salivary Glands: Secretion of enzymes.

• Pharynx: Muscular propulsion of materials to the esophagus.

• Esophagus: Transportation of materials to the stomach.

• Stomach: Chemical breakdown of materials using enzymes and muscular contraction.

• Small Intestine: Digestion and absorption of materials.

PHYSIOLOGICAL ROLES OF THE STRUCTURES OF THE DIGESTIVE TRACT• Lining of the digestive tract:

• Mucosa- Provides for an increased surface area that allows for absorption and expansion, forms the villi structures of the small intestine

• Submucosa- Controls and coordinates muscle contraction and secretion for digestion.

• Muscularis Externa- Smooth muscle layer that is used in combination and propulsion of materials along the digestive tract.

• Serosa-Provides a pathway for blood vessels, nerves, and lymphatic vessels to service the digestive tract.

• Villi- Structure of the mucosa that increase surface are and further facilitate absorption.

• Movement in the digestive tract:

• Peristalsis- Waves of muscle contraction carried out by the Muscularis Externa that propels food the length of the digestive tract.

• Segmentation-Movements of smooth muscle contraction the churn and fragment digestive materials.

ANATOMY & PHYSIOLOGY OF THE ORAL CAVITY

• The oral cavity receives food that enters the digestive system (ingestion).

• Roles of the oral cavity

• Sense & Analyze ingested material

• Mechanically Process food (use; teeth, tongue, palate)

• Lubricate & Mix food with mucus and saliva

• Begin Digestion with salivary enzymes

• Tongue: Mechanically Process, Manipulate & Assist Chewing, Sensory Analysis

• Salivary Glands: Three pairs of glands (Parotid, Sublingual, Submandibular), secrete saliva

• Saliva: contains water, buffers, ions, metabolites, and enzymes (99.4% water)

• Teeth: Performs chewing (mastication), Four types ( Incisors, Cuspids, Bicuspids, Molars)

ORAL CAVITY

ANATOMY & PHYSIOLOGY OF THE PHARYNX & ESOPHAGUS• Pharynx: Common connection or passageway of the digestive and respiratory tracts. Muscular

contractions here force food material into the esophagus. ( Has three main divisions; Nasopharynx, Oropharynx, Laryngopharynx)

• Esophagus: Muscular tube about 10in. Long that coveys solid food and liquid to the stomach, prevents the backflow of food from the stomach. (upper & lower esophageal sphincters)

• Swallowing (Deglutition): Complex voluntary process that has four specific steps. Swallowing begins after the teeth and saliva have molded and compacted food into a bolus (small mass of food material) that is approved by taste receptors and is ready to be digested. (about 9 secs.)

• Oral Phase: The bolus is compressed against the palate and forced into the pharynx.(only consciously controlled step)

• Pharyngeal Phase: sensory receptors of the pharynx initiate swallowing reflex(involuntary) that directs the bolus past the closed glottis and into the esophagus.

• Esophageal Phase: The bolus now in the esophagus is pushed toward the stomach through a series of peristaltic contractions that also stimulate the lower esophageal sphincter to open.(involuntary)

• Bolus Enters Stomach: Passing the lower esophageal sphincter the bolus enters the stomach for digestion.

STEPS OF SWALLOWING

ANATOMY AND PHYSIOLOGY OF THE STOMACH• The stomach is a j-shaped organ (made of smooth muscle) that receives food from the

esophagus and carries out four primary functions.

• Storage of ingested food.

• Mechanical breakdown of ingested food.

• Breakdown chemical bonds of food using acids and enzymes (gastric juices) produces by gastric glands (Parietal and Chief) to produce chyme (digested food).

• Production of intrinsic factor (vitamin B absorption compound)

• The stomach is divided into four main regions.

• Cardia (portion that connects with esophagus)

• Fundus (buldge superior to cardia)

• Body (portion between the fundus and the j-curve)

• Pylorous (distal part of the j-curve that connects the stomach to the small intestines)

REGULATION OF GASTRIC ACTIVITIES & STOMACH DIGESTION• The production of acids and enzymes used in digestion is regulated by the central

nervous system and hormones via three overlapping phases.

• Cephalic Phase: Initiated by the sight, smell, or taste of food this phase accelerates the rate of gastric secretion (500ml per hour) and prepares the stomach for food only lasts a few minuets before the gastric phase commences.

• Gastric Phase: Begins with the arrival of food in the stomach. Stomach muscle is stimulated to stretch and initiate mixing waves of muscle contraction as well as the stimulation of gastric glands to increase production and release the hormone gastrin. Gastrin stimulates further muscle contractions in churning and twisting motions creating small amounts of chyme.

• Intestinal Phase: Begins when chyme first inters the small intestines. To ensure that maximum digestion and absorption occur the enterogastric reflex is initiated during this phase.

THE HUMAN STOMACH

ANATOMY AND PHYSIOLOGY OF THE SMALL INTESTINES• The small intestine’s role in the digestive system is the digestion and absorption of nutrients.

• 90% of absorption occurs in the small intestine.

• The small intestine is about 20ft. long and has a diameter of between 1in.(larges intestine)-1.6ins.(stomach).

• The intestinal lining has many of folds called plicae circulares and is composed of many villi. Both of these characteristics facilitate nutrient absorption.

• The small intestine is divided into three segments

• Duodenum: Segment closest to the stomach(~10in.) receives the chyme form the stomach and the digestive juices from the pancreas and liver. Is known as the “mixing bowl”

• Jejunum: Middle segment (~8ft.) the bulk of chemical digestion and nutrient absorption occur here.

• Ileum: Last segment (~12ft.) regulates the flow of material into the large intestine via the ileocecal valve.

ANATOMY OF THE SMALL INTESTINE

ANATOMY AND PHYSIOLOGY OF THE PANCREAS, LIVER, & GALLBLADDER• Pancreas: Elongated pinkish-gray organ that is about 6 inches long and has a weight of about 3oz. It

provides digestive enzymes as well as buffers that help the digestive system neutralize chyme.

• The pancreas also produces the hormone insulin and secretes it into the bloodstream in order to regulate the body's glucose or sugar level.

• Liver: A firm reddish-brown organ (largest visceral organ, 2 nd largest overall) that has a weight of about 3.3lbs. The liver accounts for about 2.5% of total body weight. It secrets bile that is stored in the gallbladder into the small intestines where it is used for the digestion and absorption of lipids. The liver does several other function for the digestive and metabolic systems of the body as well as various other functions for the body.

• Other functions of the liver

• Detoxifies the blood to rid it of harmful substances such as alcohol and drugs

• Stores some vitamins and iron

• Stores the simple sugar glucose

• Converts stored sugar to usable sugar when the body’s sugar (glucose) levels fall below normal.

• Breaks down hemoglobin as well as insulin and other hormones

• Converts ammonia to urea, which is vital in metabolism

• Destroys old red blood cells

• Gallbladder: A hollow, muscular, pear-shaped organ that stores and concentrates bile for the small intestines.

PANCREAS, LIVER, GALLBLADDER

ANATOMY AND PHYSIOLOGY OF THE LARGE INTESTINES• Horseshoe shaped organ that runs from the ileum of the small intestine to the anus.

• Also known as the large bowel.

• The large intestine has three main functions.

• The reabsorption of water and the compaction of the intestinal contents into feces.

• Absorption of important vitamins (Vitamin K, Biotin, Vitamin B5).

• Storage of fecal material prior to defecation

• The large intestine is divided into three parts.

• Cecum: The primary function of the cecum is the compaction of intestinal material. The appendix is attached to the cecum.

• Colon: The colon removes water, salt, and some other nutrients from intestinal material. It is also responsible from the propulsion of intestinal material along to the rest of the intestine. The colon is loaded with bacteria (probiotic) that help the digestive system.

• Rectum: the remaining section of the large intestine which is used for the temporary storage of feces.

THE ANATOMY OF THE LARGE INTESTINE

THE DIGESTIVE SYSTEM AND THE OTHER SYSTEMS OF THE HUMAN BODY

• The digestive system is functionally linked to all other systems, and it has extensive anatomical connections to several specific systems like the nervous, cardiovascular, endocrine, and lymphatic systems.

• See Hand-out for further explanation of these relationships.

• Liver Disease

• Colorectal Cancer

• Diverticulosis

• Diverticulitis

• Pancreatic Cancer

• Lactose Intolerance

• Malabsorption Syndromes

• Liver Cancer

• Acid Reflux

• Colitis

• Ascites

• Mumps

• Esophagitis

• Diaphragmatic Hernias

• Gastritis

• Peptic Ulcers

• Stomach Cancer

• Vomiting

• Pancreatitis

• Esophageal Cancer

DISEASES, DISORDERS, & CONDITIONS OF THE DIGESTIVE SYSTEM

Can range from chronic to acute Can range in severity and treatability