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Organs of the Digestive System (Oral cavity: (Salivary glands: (Parotid…
Organs of the Digestive System
Oral cavity:
Function: Initiates digestion by mechanical means when chewing food, creating a bolus which is a wet mass of partially digested food
Salivary glands:
Parotid salivary glands (25-30% of saliva)
Submandibular salivary glands (60-70%)
Sublingual salivary glands (3-5%)
Function:
Begins chemical digestion of food by secreting saliva
Saliva contains the enzyme salivary amylase, which begins to break down starch
Aids in formation of the bolus
The enzyme salivary amylase breaks down carbohydrates mainly in the mouth
Pharynx:
Function:
Contains 3 skeletal muscle layers called the superior, middle, and inferior pharyngeal constrictors
Propels food to the esophagus
Is lined with nonkeratinized stratified squamous epithelium that protects against abrasion
Esophagus:
Consists of two sphincters:
Superior esophageal sphincter - closes during air inhalation so that air enters the larynx & trachea
Inferior esophageal sphincter - aids the diaphragm in contracting the muscles around esophageal opening
Function:
Contains elastic fibers that allows the esophagus to distend while swallowing
Contains many mucous glands to provide lubrication
Ensures that food passes quickly out of the pharynx into the esophagus before taking the next breath
The esophageal stage is involuntary and propels the bolus to the stomach
Stomach:
Digestive Process of the Stomach
Gastric mixing occurs which is mechanical digestion of the bolus to form chyme
Peristaltic waves pressure contents of the stomach toward the pyloric sphincter
Pyloric sphincter temporarily opens and allows a small amount of chyme into the duodenum
- The enzyme pepsin denatures proteins in the stomach
Small intestine:
Receives chyme from the stomach
3 sections of the small intestine:
Duodenum
Jejunum
Ileum
Absorbs most nutrients in the small intestine
Majority of triglyceride digestion occurs in the small intestine
Pancreatic lipase aids the digestion of triglycerides
Protein digestion continues in the small intestine:
The pancreas releases inactive enzymes trypsinogen, chymotrypisnogen, procarboxypeptidase
The enzyme enteropeptidase activates the inactive enzymes to form trypsin, chymotrypsin & carboxypeptidase
These enzymes break proteins into amino acids
Dipeptidase & amino peptidase break the final bonds of amino acids
Amino acids are absorbed in the small intestine
Lipids are absorbed in the small intestine
Nucleic acid digestion occurs in the small intestine
Deoxyribonuclease & ribonuclease begin digestion of nucleic acids
Enzymes phosphatase & nucleosidase continue to break down nucleic acids
All nucleic acids are absorbed across the epithelium of the small intestine directly into the blood
Carbohydrate breakdown continues in the small intestine:
The enzymes pancreatic amylase breaks carbohydrates into glucose
Glucose is broken down further by the enzymes dextrinase & glucoamylase
Lactase digests lactose to glucose
Sucrase digests sucrose to glucose
Large intestine:
Cecum
Ascending colon
Transverse colon
Descending colon
Rectum
Bacteria of the large intestine continue to break down complex carbohydrates, lipids, & proteins that remain the the chyme
Water is reabsorbed in the large intestine
Liver:
Secrets bile
Bile is an alkaline fluid composed of water & bicarbonate
Bile salts aid in the digestion of lipids to triglycerides
Gallbladder:
Stores, concentrates, & releases bile
Pancreas:
Secretes pancreatic juice, which contains:
Pancreatic amylase to digest starch
Pancreatic lipase for the digestion of triglycerides
Inactive enzymes that digest proteins
Nucleases for the digestion of nucleic acids
Tunics of the GI Tract:
Mucosa: Simple columnar epithelium
Epithelium in contact with the lumen, absorption occurs as substances are moved through the epithelium
Lamina propia has areolar connective tissue and substances are absorbed into blood vessels or lymphatic capillaries
Muscularis mucose facilitates the release of secretions into the lumen
Submucosa: Areolar & dense connective tissue
Contains many large blood vessels, lymph vessels, nerves, & glands
Submucosal nerve plexus
Muscularis: 2 layers of smooth muscle
Inner circular layer
Myenteric. nerve plexus
Outer longitudinal layer
Function: to mix and propel contents of the GI
Peristalsis- alternating contractions of the inner circular & outer longitudinal layers to propel contents
Mixing - kneading motion that occurs in order to blend ingested items
Serosa: areolar connective tissue, collagen, & elastic fibers
Covered by serous membrane called visceral peritoneum