Ch. 24: Digestive System Flashcards
Accessory digestive organs.
Teeth, tongue, salivary glands, liver, gallbladder, pancreas.
What are the 6 basic processes of the gastrointestinal tract?
1) Ingestion.
2) Secretion.
3) Motility.
4) Digestion.
5) Absorption.
6) Defecation.
Which molecules can be absorbed without digestion?
Vitamins, ions, cholesterol, water.
Mechanical digestion.
Molecules are dissolved and mixed with digestive enzymes by teeth and smooth muscles of stomach and small intestine.
Chemical digestion.
Largo CHO, lipid, protein and nucleic acid molecules are split into smaller molecules by hydrolysis, which is catalyzed by digestive enzymes produced by salivary glands, tongue, stomach, pancreas and small intestine.
Mucosa of GI tract.
Mucous membrane composed of a layer of epithelium, lamina propria, and muscularis mucosa.
Epithelium: In direct contact with GI contents. Nonkeratinized stratified squamous epithelium in mouth, pharynx, esophagus and anal canal serves a protective function. Simple columnar epithelium in stomach and intestines function in secretion and absorption. Tight junctions between columnar epithelial cells.
Lamina Propria: Areolar connective tissue. Contains blood and lymphatic vessels, which are routes for nutrients absorbed into the GI to reach other tissues. Supports the epithelium and binds to it by the muscular mucosa. Contains the majority of the cells of the MALT.
Muscular mucosa: Thin layer of smooth muscle. Creates many small folds of the mucous membrane of the stomach and small intestine. Movements from this layer ensure that all absorptive cells are fully exposed to the contents of the GI tract.
What is the rate of renewal of GI epithelial cells?
5-7 days
Exocrine cells.
Located among epithelial cells in mucosa of GI tract. Secrete mucous and fluid into GI tract.
Enteroendocrine cells.
Located among epithelial cells in mucosa of GI tract. Secrete hormones.
Submucosa of GI tract.
Areolar connective tissue. Binds the mucosa to the muscularis. Contains blood and lymphatic vessels, glands, and lymphatic tissue. Contains the submucosal plexus (neuronal network).
Muscularis of GI tract.
Muscularis of mouth, pharynx, and superior and middle parts of esophagus contains skeletal muscle that produces voluntary swallowing. Skeletal muscle also forms the external anal sphinter.
Throughout the rest of the GI tract, the muscularis consists of smooth muscle that is organized into an inner sheet of circular fibres and an outer sheet of longitudinal fibres. Involuntary contractions of smooth muscle aid in breaking down food.
What lies in between the layers of the muscularis?
Myenteric plexus.
Serosa of GI tract.
Covers parts of the GI tract suspended in the abdominal cavity. Serous membrane composed of areolar connective tissue and simple squamous epithelium.
Which part of the GI tract lacks a serosa?
Esophagus. Instead, only a single layer of areolar connective tissue forms the superficial layer, and it is called the adventitia. This structure attaches the esophagus to surrounding structures.
Neurons of the enteric nervous system are arranged in…
Myenteric plexus and submucosa plexus.
Myenteric plexus.
Located between longitudinal and circular smooth muscle layers of the muscularis. Motor neurons supply longitudinal and circular smooth muscle layers of muscularis. Controls GI tract motility, and frequency and strength of contraction of muscularis.
Submucosal plexus.
Plexus of Meissner. Located within submucosa. Motor neurons supply secretory cells of mucosal epithelium. Controls secretions of organs of GI tract.
Describe the role of interneurons and sensory neurons of the enteric nervous system.
Interneurons: interconnect neurons of myenteric and submucosal plexuses.
Sensory neurons: supply mucosal epithelium and contain receptors that detect stimuli in GI lumen.
The neurons of the ___ can function independently, but they are subject to regulation by neurons of the ___ .
ENS, ANS.
Which nerve supplies parasympathetic fibres to most of the GI tract?
Vagus nerve.
The last half of the large intestine is supplied by sacral spinal cord.
Stimulation of parasympathetic nerves…
Increases GI secretion and motility by increasing the activity of ENS neurons.
Sympathetic nerves that supply the GI tract arise from…
Thoracic and upper lumbar regions of the spinal cord.
Stimulation of sympathetic nerves…
Decreases GI secretion and motility by inhibiting ENS neurons. Emotions like anger, fear and anxiety may slow digestion because they stimulate the sympathetic nerves.
Gastrointestinal reflex pathways.
Regulate GI secretion and motility in response to stimuli in the GI lumen.
Peritoenum.
Largest serous membrane of the body. Consists of a layer of simple squamous epithelium with an underlying supporting layer of areolar connective tissue. Divided into the parietal peritoneum and visceral peritoneum.
Parietal peritoneum.
Lines abdominal cavity.
Visceral peritoneum.
Covers some organs in the abdominal cavity and is their serosa.
Peritoneal cavity.
Slim space containing lubricating serous fluid that is between the parietal and visceral layers.
Ascites.
When the peritoneal cavity becomes distended by the accumulation of fluid. Occurs in some diseases.
Retroperitoneal organs.
Lie on the posterior abdominal wall. Covered by peritoneum only on their anterior surfaces. Kidneys, ascending and descending colons, duodenum.
Describe the peritoneal folds.
Peritoneum contains large folds that weave between the viscera, and bind the organs to one another and to the walls of the abdominal cavity. These folds also contain blood vessels, lymphatic vessels, and nerves that supply the abdominal organs.
What are the 5 major peritoneal folds?
1) Greater omentum.
2) Falciform ligament.
3) Lesser omentum.
4) Mesentery.
5) Mesocolon.
Greater omentum.
Longest fold. Drapes over transverse colon and small intestinal coils, and folds back on itself to give it a total of 4 layers. Contains adipose tissue and lymph nodes, which contribute macrophages and antibody-producing plasma cells that fight against GI infections.
Falciform ligament.
Attaches the liver to the anterior abdominal wall and diaphragm.
Which is the only digestive organ attached to the anterior abdominal wall?
Liver.
Lesser omentum.
Arises as an anterior fold in the serosa of the stomach and duodenum. Connects stomach and duodenum to liver. Pathway for blood vessels entering the liver. Contains hepatic portal vein, common hepatic artery, common bile duct, and lymph nodes.
Mesentery.
Largest fold. Fan-shaped. Binds jejunum and ileum of small intestine to posterior abdominal wall. Contributes to large abdominal in obese individuals as it is laden with fat. Extends from posterior abdominal wall to wrap around small intestine and return to its origin to form a double-layered structure. Between the 2 layers are blood vessels, lymphatic vessels and lymph nodes.
Mesocolon.
2 separate folds (transverse mesocolon, sigmoid mesocolon).
Bind transverse colon and sigmoid colon of large intestine to posterior abdominal wall. Carries blood and lymphatic vessels to intestines.
How do the mesentery and mesocolon folds work together?
They hold intestines loosely in place to allow movements of muscular contractions.
Mouth.
Oral cavity. Cheeks, hard palate, soft palate, tongue.
What lies in between the skin and mucous membrane of the cheeks?
Buccinator muscles and connective tissue.
Labial frenulum.
A midline fold of mucous membrane that attaches the inner surface of the lips to the gingiva.
Oral vestibule.
The space bounded externally by the cheeks and lips and internally by the gums and teeth.
Oral cavity proper.
The space that extends from gums and teeth to the fauces.
Fauces.
Openings between the oral cavity and oropharynx.
Palate.
Wall/septum that separates the oral cavity from the nasal cavity. Forms the roof of the mouth.
Hard palate: Anterior roof of the mouth. Formed by maxillae and palatine bones. Covered by mucous membrane.
Soft palate: Posterior roof of the mouth. Arch-shaped muscular partition between the oropharynx and nasopharynx. Covered by mucous membrane.
Uvula.
Muscular structure. Hangs from free border of soft palate.
Lateral to the base of the uvula, there are 2 muscular folds that run down the lateral sides of the soft palate.
Palatoglossal arch: Anterior. Extends to the side of the base of the tongue.
Palatopharyngeal arch: Posterior. Extends to the side of the pharynx.
Palatine tonsils are located between these arches.
Lingual tonsils are located at the base of the tongue.
What are the salivary glands in the mouth and tongue?
Labial glands in lips.
Buccal glands in cheeks.
Palatal glands in palate.
Lingual glands in tongue.
3 pairs of major salivary glands.
Parotid: Inferior and anterior to ears. Between the skin and masseter muscle. Secrete saliva into oral cavity via a parotid duct.
Submandibular: In the floor of the mouth medial and inferior to the mandible. Submandibular ducts run under the mucosa on either side of the midline of the floor of the mouth and enter the oral cavity proper lateral to the lingual frenulum.
Sublingual: Beneath the tongue. Superior to the submandibular glands. Lesser sublingual ducts open into the floor of the mouth in the oral cavity proper.
Saliva.
99.5% water, 0.5% solutes.
Describe the liquids secreted by parotid, submandibular and sublingual glands.
Parotid: Watery. Contains salivary amylase.
Submandibular: Thickened with mucus. Contains salivary amylase.
Sublingual: Much thicker. Contains a small amount of salivary amylase.
Describe water in saliva.
Provides a medium for dissolving fluids, so that they can be tasted by gustatory receptors.
Describe Cl- ions in saliva.
Activate salivary amylase.
Salivary amylase.
Enzyme that starts the breakdown of starch to maltose, maltotriose, and alpha-dextrin. Inactivated by stomach acids.
Describe HCO3- and phosphate ions in saliva.
Buffer acidic foods.
Describe IgA in saliva.
Prevents attachment of microbes so they cannot penetrate the epithelium.
Describe how salivation is controlled by the ANS.
Parasympathetic stimulation promotes continuous secretion of a moderate amount of saliva, which keeps the mucous membrane moist and lubricates the movements of the tongue and lips during speech. Saliva is then swallowed and helps moisten the esophagus.
Sympathetic stimulation causes dryness of the mouth. Also, if you are dehydrated, the salivary glands will stop secreting saliva to conserve water.
How much saliva is release per day?
1,000 to 1,500 mL
Describe how salivation is controlled by food.
Chemicals in food stimulate receptors in taste buds on tongue –> impulses are conveyed to superior and inferior salivary nuclei in brainstem –> returning parasympathetic impulses in fibres of facial and glossopharyngeal nerves stimulate salivation.
Tongue.
Skeletal muscle covered in mucous membrane. Divided into lateral halves by a median septum. Attached inferiorly to the hyoid bone, styloid process of temporal bone, and mandible. Each half of the tongue consists of an identical arrangement of extrinsic and intrinsic muscles.
Extrinsic muscles of the tongue.
Originate outside the tongue. Insert into connective tissues in the tongue. Move the tongue from side to side, and in and out. Form the floor of the mouth. Hold the tongue in position.
Intrinsic muscles of the tongue.
Originate inside the tongue. Insert into connective tissue within the tongue. Alter the shape and size of the tongue for speech and swallowing.
Lingual frenulum.
Fold of mucous membrane in the midline of the undersurface of the tongue. Attached to the floor of the mouth. Limits the posterior movements of the tongue.
Papillae of tongue.
Projections of lamina propria covered with stratified squamous epithelium. Located on the dorsum and lateral surfaces of the tongue. May contain taste buds or touch receptors. Increase friction between tongue and food.
Lingual lipase.
Acts on 30% of dietary triglycerides and converts them to simpler FAs and diglycerides. Secreted by lingual glands in lamina propria of tongue. Becomes activated in the acidic environment of the stomach.
Where are teeth located?
Located in sockets of the alveolar processes of the mandible and maxillae. The sockets are lined by the periodontal ligament, which consists of dense fibrous connective tissue that anchors the teeth to the socket walls and acts as a shock absorber during chewing.
Dentin.
Forms the majority of the tooth. Consists of a calcified connective tissue that gives the tooth its basic shape and rigidity. Harder than bone because of its higher content of hydroxyapatite.
Enamel.
The dentin of the crown is covered in enamel. Consists of calcium phosphate and calcium carbonate. Harder than bone because of its even higher content of hydroxyapatite. Hardest substance in the body. Protects the tooth from wear and tear, and from acids.
Cementum.
The dentin of the root is covered in cementum. Attaches the root to the periodontal ligament.
Pulp cavity.
Space inside the crown enclosed by dentin. Filled with pulp, which is a connective tissue containing blood vessels, nerves, and lymphatic vessels.
Root canals.
Narrow extensions of the pulp cavity that run through the root of the tooth.
Apical foramen.
Opening at the base of each root canal. Blood vessels, lymphatic vessels and nerves enter into the tooth through this opening.
Describe the blood vessels, lymphatic vessels and nerves of a tooth.
Blood vessels: nourishment
Lymphatic vessels: protection
Nerves: sensation
Endodontics.
Prevention, diagnosis and treatment of diseases that affect the pulp, root, periodontal ligament, and alveolar bone.
Periodontics.
Treatment of abnormal conditions of the tissues immediately surrounding the teeth.
Describe the 2 dentitions of humans.
Deciduous: Primary teeth. Milk teeth. Begin to erupt at 6 months, and two teeth appear each month thereafter. Lost between 6 and 12 years of age. 20 teeth total.
Permanent: Erupt between age 6 and adulthood. 32 teeth total.
Incisors.
Closest to midline. Chisel-shaped. Adapted for cutting into food. Central or lateral incisors. Have 1 root each.
Canines.
Pointed surface. Tear and shred food. Have 1 root each.
First and second deciduous molars.
4 cusps each. Maxillary molars have 3 roots. Mandibular molars have 2 roots. Crush and grind food.
Which 2 substances are involved in chemical digestion?
Salivary amylase, and lingual lipase.
Pharynx.
Skeletal muscle lined with mucous membrane. Divided into 3 parts (nasopharynx, oropharynx, laryngopharynx).
Esophagus.
Collapsible muscular tube posterior to trachea.
Describe the path of the esophagus.
Begins at inferior end of laryngopharynx –> inferior part of neck –> mediastinum –> pierces diaphragm through esophageal hiatus –> superior part of stomach.
Mucosa of esophagus.
Nonkeratinized stratified squamous epithelium. Contains lamina propria and muscularis mucosa. Contains mucous glands near the stomach.
Submucosa of esophagus.
Areolar connective tissue. Blood vessels. Mucous glands.
Muscularis of esophagus.
Skeletal muscle in superior 1/3rd of esophagus. Skeletal and smooth muscle in intermediate 1/3rd of esophagus. Smooth muscle in inferior 1/3rd of esophagus.
At each end, the muscularis becomes more prominent and forms two sphincters.
Upper esophageal sphincter (UES).
Skeletal muscle. Regulates movement of food from the pharynx into the esophagus.
Lower esophageal sphincter (LES).
Smooth muscle. Near the heart. Regulates movement of food from the esophagus into the stomach.
Deglutition.
Movement of food from mouth to stomach. Involves mouth, pharynx, esophagus, and saliva and mucus.
What are the 3 stages of swallowing?
1) Voluntary stage: Bolus is forced into the back of the oral cavity via the tongue –> oropharynx.
2) Pharyngeal stage: Bolus stimulates receptors in oropharynx –> send impulses to deglutition center in medulla oblongata and lower pons –> returning impulses cause soft palate and uvula to move upward and close off nasopharynx –> epiglottis also closes off the larynx opening –> bolus moves through oropharynx –> laryngopharynx –> UES –> esophagus.
3) Esophageal stage: Esophageal circular muscle fibres contract to constrict esophageal wall –> squeeze bolus towards stomach –> longitudinal fibres inferior to bolus also contract –> bolus reaches LES –> stomach.
Peristalsis.
Progression of coordinated contractions and relaxations of circular and longitudinal layers of the muscularis.
What does the esophagus secrete?
Mucus only.
Passage of solid/semi-solid food from the mouth to the stomach takes ___ .
Passage of very soft foods/liquids from the mouth to the stomach takes ___ .
4-8 seconds, 1 second.
Stomach.
Mixing chamber and holding reservoir. Continues digestion of starch and triglycerides. Begins digestion of protein. Semisolid bolus is converted to a liquid, and certain substances are absorbed.
Stomach.
Mixing chamber and holding reservoir. Continues digestion of starch and triglycerides. Begins digestion of protein. Semisolid bolus is converted to a liquid, and certain substances are absorbed.
