Chapter 24 The digestive system Flashcards
What is the Gastrointestinal (GI) Tract?
Long tube that is open at both ends for the transit of food during processing
What are the named portions of the GI tube?
- Esophagus
- Stomach
- Small intestine
- Large intestine
- Rectum
What are accessory structures of the GI tract?
- Teeth
- Tongue
- Salivary glands
- Liver
- Gall bladder
- Pancreas
What are the function of the accessory structures of the GI tract?
Not part of the GI tract but they do contribute to food processing
What are six basic processes involved in digestion
- Ingestion
- Secretion
- Motility
- Digestion
- Absorption
- Defecation
What is the peritoneum?
Largest Serous membrane in the body
What is the mouth?
Formed by
1. Cheeks
2. Hard and soft palate
3. Tongue
What are the salivary glands?
- Lie outside the mouth
- Empty contents into ducts which delivery saliva into oral cavity
What are the functions of the salivary glands?
- Dissolve food
- Moisten food
- Enzyme release
What are the teeth?
Project into the mouth and are adapted for mechanical digestion
What is chemical digestion?
Salivary amylase converts polysaccharides to disaccharides
What is mechanical digestion?
Chewing mixes food with saliva and forms a bolus which can be easily swallowed
What do the extrinsic tongue muscles do?
- Food maneuvered for mastication
- Shaped into bolus
- Maneuvered for swallowing
What are the intrinsic tongue muscles?
Swallowing and speech
What are the taste buds?
receptors for gustation and presence of food in mouth
What are the lingual glands?
Secrete lingual lipase
What is the pharynx?
Funnel shaped tube that extends from the internal nares to the esophagus posteriorly and to the larynx anteriorly
What is the pharynx composed of?
Skeletal muscle and lined with mucous membrane
What is the esophagus?
Collapsible, muscular tube that lies posterior to the trachea and connects the pharynx to the stomach
What does the esophagus do in the upper relaxation phase?
Permits entry of bolus from laryngopharynx into the esophagus
What does the esophagus do during the deglutition (peristalsis) phase?
Pushes down esophagus
What does the esophagus do during the lower relaxation phase?
Permits entry of bolus into the stomach
What does the esophagus do during the secretion of mucus stage?
Lubricates esophagus for smooth passage
What are the functions of the stomach?
- Mixes saliva, food, and gastric juice to form chyme
- Serves as reservoir for food before release into small intestine
- Secretes gastric juice, which contains HCL, Pepsin, Intrinsic factor, and gastric lipase
- Secrets gastrin into the blood
What does the surface mucous cells do?
- Secrets mucus
- form protective barrier that prevents digestion of stomach wall
What does mucous neck cells do?
- Absorption
- Small quantity of water, ions, short chain fatty acids, and some drugs enter bloodstream
What does parietal cells do?
- Secrete intrinsic factor: Needed for absorption of VB12
- Secrete hydrochloric acid: kills microbes in food
What are chief cells?
- Secrete pepsin: breaks down proteins into peptides
- Secrete gastric lipase: splits triglycerides into fatty acids and monoglycerides
What are G cells?
Secrete gastrin: Stimulates parietal cells to secrete HCL and chief cells to secrete pepsin
What is the muscular layer of the stomach?
Mixing waves: churns and physically breaks down food and mixes it with gastric juice
What is the pyloric sphincter?
Opens to permit passage of chyme into duodenum
What is the pancreas?
- Lies posterior to stomach
- Produces enzymes that digest carbs, proteins, fats and nucleic acids
- Produces sodium bicarb which buffers stomach acid
- empties into the duodenum
What does the liver make?
Bile, which is important for the emulsification of fats
What does the gallbladder do?
Stores bile
What is the small intestine?
Majority of digestion and absorption happens here
What are the circular folds in the small intestine?
They increase the surface area for digestion and absorption in the small intestine
What are the functions of the small intestine?
- Segmentations mix chyme with digestive juices and bring food into contact with mucosa for absorption: peristalsis propels chyme through small intestine
- Completes digestion of carbohydrates, proteins, lipids; begins and completes digestion of nuclei acids
- Absorbs about 90% of nutrients and water that pass through digestive system
What does the pancreas do?
Delivers pancreatic juice into duodenum via pancreatic duct to assist in absorption
What does the intestinal glands do?
Secrete intestinal juice to assist absorption
What are absorption cells?
Digest and absorb nutrients
What does goblet cells do?
Secrete mucus
What does enteroendocrine cells do?
Secrete secretin, cholecystokinin, and glucose dependent insulin tropic peptides
What does paneth cells do?
Secrete lysozyme, and phagocytosis
What are the duodenal glands?
Secrete alkaline fluid to buffer stomach acids and mucus for protection and lubrication
What are the circular folds?
Folds of mucosa and submucosa that increase area for digestion and absorption
What are interstitial villi?
Finger like projections of mucosa that are sites of absorption of digested food and increase surface area for digestion and absorption
What are microvilli?
Microscopic, membrane covered projections of absorptive epithelial cells that contain microvillous boarder enzymes and increase surface area for digestion and absorption
What is segmentation?
Type of peristalsis; alternating contractions of circular smooth muscle fibres that produce segmentation and resegmentation of secretions of small intestines; mix chyme with digestive juices and brings food into contact with mucosa for absorption.
What are the functions of the colon?
- Haustral churning, peristalsis, and mass peristalsis
- Bacteria in colon convert proteins into amino acids, break down amino acids, and produce some B vitamins
- Absorption of some water, ions, and vitamins
- Formation of feces
- Defecation
What is Haustral churning?
Distension reaches a certain point and the walls of the haustra contract to squeeze contents onwards
What is peristalsis?
Propulsive contractions
What is mass peristalsis?
A strong peristaltic wave that begins in the transverse colon and quickly drives the contents of the colon into the rectum
What is chemical digestion in the colon?
The last stages of digestion which occurs through bacterial action
1. Substances are further broken down by bacteria
2. Some vitamins are synthesized by bacterial action
How are carbs chemically digested?
- Monosaccharides
- Salivary amylase
- Pancreatic amylase
How are proteins chemical digested?
- Amino acids
- Pepsin
- Trypsin
- Peptides
How are Lipids digested chemically?
- Triglycerides
- Biles
- Lipase
How are nucleic acids chemically digested?
- Nucleotides
- Pancreatic nucleus
- Brush border enzymes
What does the colon absorb?
- Water
- Electrolytes
- Some vitamins
What is the defecation reflex?
- Rectal walls distends and stretch receptors send sensory nerve impulses to the sacral spinal cord
- Motor impulses travel back to the descending colon, sigmoid, rectum, and anus
- Longitudinal rectal muscles contract and the internal anal sphincter opens
