Chapter 17 Flashcards
What does the Digestive System do?
- Breaks down food into smaller components (e.g. amino acids and monosaccharides)
- Processes food, extracts nutrients, and eliminates residue
What is Gastroenterology?
Study of digestive tract and disorders
What are the stages of Digestion?
1) Ingestion –> Selective intake of food
2) Digestion –> Breakdown of food into usable form
3) Absorption –> Uptake of nutrients into digestive tract, then into blood or lymph
4) Compaction –> Absorption of water. Consolidation of indigestible residue into feces
5) Defecation –> Elimination of feces
What is Mechanical Digestion?
The physical breakdown of food into smaller particles achieved by the cutting and grinding action of the teeth and the churning movements of the stomach and small intestine. It exposes more food surface to the action of digestive enzymes.
What Chemical Digestion?
Employs enzymes to break dietary macromolecules into their basic building blocks: Polysaccharides into monosaccharides, proteins into amino acids, fats into monoglycerides and fatty acids, and nucleic acids into nucleotides. All chemical digestion is by the process of enzymatic hydrolysis, breaking covalent bonds by adding water to them.
What nutrients are already present in usable form in the ingested food and are absorbed without being broken down by digestion?
Vitamins, Minerals, Cholesterol, and water
What is Deglutition?
- Swallowing
- Involves over 22 muscles in the mouth, Pharynx, and esophagus.
- Coordinated by the swallowing center in the medulla oblongata and occurs in 3 phases.
What are the 3 phases of Swallowing?
1) Oral Phase –> Under voluntary control. Tongue collects food, presses it against the palate to form bolus and pushes it posteriorly. When Bolus reaches a critical size, the epiglottis tips posteriorly and the bolus slides around it through a space on each side, into the laryngopharynx.
2) Pharyngeal Phase –> Involuntary and is initiated when food contacts touch receptors of the laryngopharynx. Soft palate and root of the tongue block food from enter in the nasal cavity or reentering the mouth. The Larynx is pulled up against epiglottis, which prevents food from entering the larynx and trachea. The pharyngeal constrictors contract in order from superior to inferior to drive the bolus downward into esophagus. And Breathing is suspended.
3) Esophageal Phase –> A wave of involuntary contraction (“Peristalsis”). Controlled jointly by the brainstem swallowing center and the enteric nervous system in the esophageal wall. Esophagus constrict ABOVE the Bolus and relaxes BELOW it, propelling the bolus along. As bolus reaches the lower end of esophagus, the lower esophageal sphincter relaxes to let it pass into the stomach.
What is the Stomach?
- Muscular sac in upper left abdominal cavity
- Food storage organ
- Breaks up food particles
- Liquifies food
- Begins chemical digestion of proteins and fat
- Produces semi-digested food – “Chyme”
The gastric mucosa is pocked with Depressions called _________?
Gastric Pits
What are the gland types near the esophagus and pylorus?
Cardiac Glands near the esophagus and Pyloric glands at the pylorus. Both secreting mainly mucus.
What are the cells of Gastric Glands in most of the stomach?
1) Mucous Cells –> secrete mucus
2) Regenerative Cells –> Found in base of the put and neck of the gland, divide rapidly and Produce continual supply of new cells.
3) Parietal Cells –> Found mostly in the upper half of the gland and secrete hydrochloric acid and intrinsic factor
4) Chief Cells –> Most numerous and secrete the enzymes “pepsinogen and gastric lipase.
5) Enteroendocrine Cells –> Concentrated especially in the lower end of a gland, secrete hormones and local chemical messengers that regulate digestion. Include the G cells which secretes regulatory hormone “Gastrin.”
What solutes compose Gastric Juice?
1) Hydrochloric Acid –> Produced by the parietal cells; activate enzyme pepsin; converts dietary iron to a form the body can absorb and use; breaks up connective tissue and plant cells; and destroys most ingested pathogens
2) Pepsin –> enzyme that digests proteins to shorter peptides. inactive precursor called pepsinogen secreted by chief cells.
3) Gastric Lipase –> secreted by chief cells, it
digests small percentage of dietary fat.
4) Intrinsic Factor –> glycoprotein secreted by parietal cells; needed for absorption of B12 by small intestine; needed to synthesize hemoglobin; only indispensable function of stomach
5) Hormones and Local chemical messengers –> produced by enteroendocrine cells; several also produced in central nervous system (called “gut-brain peptides” and include gastrin, serotonin, histamine, somatostatin, and others)
What happens when you begin to swallow?
Stomach signaled to relax by medulla oblongata. Allows smooth muscle to relax and stretch.
What happens during Peristalsis?
- Contractions churn food and Mix with gastric juice and promote breakup and digestion.
- Contractions governed by pacemaker cells in muscularis externa.
- Waves squeezing shut pyloric sphincter
- Squirts small amount of chyme into duodenum
- Typical meal emptied in 4 hours. less time if more liquid; longer if higher in fat
What is Vomiting?
- The forceful ejection of stomach and intestinal contents from the mouth.
- Involves multiple muscular actions, integrated by the “emetic center” of the medulla oblongata.
How is Vomiting induced?
- overstretched stomach or chemical irritants
- visceral trauma or intense pain
- repugnant sights, smells, or thoughts
What are the dangers of Chronic Vomiting?
- Can cause dangerous imbalances in fluid, electrolyte and acid-base.
- Can erode tooth enamel
- Inhalation of Acid which is destructive to the respiratory tract.
