Digestion Flashcards
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6 basic processes
- Ingestion: taking in food and liquid
- Secretion: of water, acid, buffers, and enzymes
- Mixing and propulsion: alternating contractions and relaxation of smooth mm
- Digestion: mechanical and chemical processes to break down ingested food into small molecules
- Absorption: entrance of ingested and secreted fluids, ions, and products of digestion into epithelial cells lining the lumen of the GI tract
- Defecation: push it out shove it out
Organs of GI
- Upper:
- mouth - pharynx - esophagus - stomach - Lower:
- small - large intestines - Accessory:
- salivary glands (parotid, submadibular, sublingual) - tongue - teeth - liver - gallbladder - pancreas - vermiform appendix
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Lips
Keep food in the mouth while being chewed
- help to sense temperature and texture of food before it enters the mouth
- needs to form many speech sounds
Cheeks
- lateral boundaries of the oral cavity (keeps food between the teeth)
- lined by mucous membrane
- contain mucous-secreting glands
Hard and soft palate
The roof of the mouth
- Hard palate: 2 maxillae and 2 palatines
- Soft palate: mm arranged in arch
- uvula: hangs down form the soft palate arch in the midline; it rises during swallowing to close off the nasopharynx from the food
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Tongue
Taste buds
- also includes lingual glads that secret lipase
1. Extrinsic: - tongue muscles
- important in deglución/swallowing and speech
2. Intrinsic mm - alter the shape and size of the tongue
Lipase
Breaks down triglycerides into fatty acids and diglycerides
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Salivary glands
Saliva is the first of the digestive juices to contact food
- parotid glands: near the ear underlying the masseter muscle
- submadibular glands: on the floor of the mouth just under the mandibles
- sublingual glands: on the floor of the mouth; ducts enter beneath the tongue
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Teeth
- Pulp: soft, fibrous connective tissue with vessels and nerves (in the core)
- Dentin: hard, mineralized connective tissue similar to bone (forms the body of the tooth)
- Cementum: hard, mineralized connective tissue similar to bone (coat around the root of the tooth and helps connect to the jawbone)
- Enamel: hard, mineralized connective tissue; harder than bone (covering exposed tooth surface)
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Pharynx
- Deglutition: act of swallowing
- Bolus: rounded mass of food
- only the terminal part of the pharynx is involved in digestion
- bolus enters the oropharynx then into the esophagus
Esophagus
- collapsible muscular tube about 25 cm long
- begins at the inferior aspect of the neck and enters the mediastinum anterior to the vertebral column
- pierces the diaphragm through an opening called the esophageal hiatus
- upper eso sphincter: skeletal mm
- lower eso sphincter: smooth mm
Hiatal hernia
The stomach protrudes up thought the esophageal hiatus above the diaphragm
Stomach
Lies just below the liver and the diaphragm
- distensión after meals, food processed slowly
- usually holds up to 1-1.5L
1. Fundus: enlarged main upper portion
2. Body: large middle portion
3. Pylorus: lower part
Pyloric sphincter
- regulate passage of material at both stomach openings
- controls outlet of pyloric portion into duodenum
GERD
Gastroesophageal disease
- the backward flow of stomach acid up through the lower esophageal sphincter and into the lower part of the esophagus
- can cause heartburn
Stomach wall (mucosa)
4 layers:
- Mucosa: thick layer of simple columnar epithelium lining the stomach cavity
- designed for the production of digestive acids and enzymes
- epithelial lining has rugged marked by gastive pits (deep clefts that increase the stomachs surface area)
- gastic glands: found in the gastric pits, secrete most of the gastric juices
- chief cells: secrete the enzymes of juice
- parietal cells: secrete hydrochloride acid and produce intrinsic factor neede for vitamin B12 absorption in small intestine
- endocrine cells: secrete gherkin (hormone to increase appetite - hypothalamus) and gastrin ( influences digestive functions)
Stomach wall (submucosa)
- comprised of fibrous connective tissue to support the mucosal layer
Stomach wall (muscularis)
3 layers of smooth muscle arranged in crisscross pattern (longitudinal, circular, oblique)
- allows the stomach to contract at many angles
- along with rugae (folds) on the stomach’s interior provide grinding and mixing motion
Stomach wall (serosa)
Outer covering of the stomach
- secretes serous fluid
- contains blood vessels and nerve endings
Lesser and greater curvature of stomach
- Upper right curve (lesser)
2. Lower left curve (greater)
Functions of stomach
Food reservoir
- secretes gastive juices
- churns the food
- secretes intrinsic factor
- performs limited amount of absorption (drugs, water, alcohol, and som escort chain fatty acids)
- produces gastrin and gherlin
Small intestine
Small bowel
- 1 in diameter and 6-8 meters long
- fills most of abdominal cavity
- responsible for the major absorption of nutrients and water
- small intestine consists of 3 divisions, beginning at pylorus and ending at ileocecal valve
1. Duodenum
2. Jejunum
3. Ileum
Duodenum
(12 fingerbreadths) short length, uppermost division, attaches to pyloric en of stomach
Jejunum
Second part (empty) 8 ft long
Ileum
(Twisted) third part, 12 ft long
Wall of small intestine
The intestinal lining has circular plicae (folds) that have many tiny projections called villi
- villi are fingerlike projections of mucosa
- villus contain an arterioles, venule, and lymph vessel
- presence of villi increases the surface area of the small insteine, making it the main site of digestion and absorption
Large intestine
Colon
- 5-6 ft and 2.5 in diameter
- large intestine is designed only for absorption of water
- extends from the cecum to rectum
1. Cecum
2. Colon
3. Rectum
Cecum
First 5-8c of large intestine
- blind pouch in lower right quadrant of abdomen
- receives chyme from the terminal ileum
- guarded by a fold of mucosa called the ileocecal valve preventing fecal backflow into the small intestine
- verifrom appendix is attached to the tip
Colon
4 divisions
- Ascending: veritical position on right side of abdomen. Extends from cecum hepatic flexure
- Transvers colon: passes horizontally above the small intestine. Extends from hepatic flexure (contacts liver) to the scenic flexure ( contacts spleen)
- Descending colon: vertical position on left side of abdomen. From splenic flexure to sigmoid colon
- Sigmoid colon: joins the descending colon to the rectum. Sigmoid means s-shaped
Rectum
Last 7-8 in of instinal tube
- terminal inch is the anal canal with opening called anus
- guarded by anal sphincter, which prevents incontinence.
- external sphincter is voluntary, internal is not
Wall of large intestine
No villi as in small intestine
- intestinal mucous glands produce lubricating mucus that coats feces as its formed
Veriform appendix
Tubular organ
- 3-4 inches in length
- found just behind cecum
- functions are not fully understood
- breeding ground for intestinal bacteria that aid digestion
Peritoneum
Large continuous sheet of serous membrane
- lines the walls of the entire abdominal cavity and forms the serous outer coat of the organs
- forms the mes enter y
- includes greater and lesser omentum
Liver
- largest gland in the body
- weighs 3-4 lbs
- lies immediately under the diaphragm
- consists of two lobes (right and left)
Hepatic lobules
Tiny hexagonal or pentagonal cylinders (anatomical units of the liver)
Functions of liver
- detoxicification of certain substances
- breaks down and removes old red blood cells, recycling iron from hemaglobin
- secretes about one pint of bile per day
- important role in metabolism of proteins, fats, and carbs
- storage of iron, vit A, vit B12, adn vit D
- produces important plasma proteins and serves a sa site for blood cell production during fetal development
Gallbladder
A pear shaped sac 3-4 inches long
- lies undersurface of liver stores bile that enters by way fo hepatic and cystic ducts
- concentrates bile. (5-10x)
- during digestion, the gallbladder contracts and elects bile into duodenum
- gallstones may form causing inflammation of the gallbladder (cholecystitis)
- cholecystectomy: surgical removal
Pancreas
Grayish pink glad 6-9 in
- located in C shaped curve of duodenum
- composed of two different types of glándula tissue (exo and endocrine)
- between exocrine units lie cluster of endocrine cells (pancreative islets)
Functions of pancreas
Secretes digestive enzymes
- beta cells secrete insulin, a hormone that exerts a major control over carbohydrate metabolism
- alpha cells secrete glucagon
Deglutition
Swallowing
- facilitated by saliva
- involves the mouth, pharynx, and esophagus
1. Oral stages
2. Pharyngeal stage (oropharynx to esophagus)
3. Esophageal stage (esophagus to stomach)
Digestive functions
To bring essential nutrients into internal environment so nutrients are available to each cell fo the body
- Ingestion
- Digestion
- Motility of GI wall
- Absorption
- Regulation
- Elimination
Ingestion
Taking in of complex food
Digestion
Breakdown of complex nutrients into simple nutrients
- facilitates absorption
- mechanical and chemical digestion
Mechanical digestion
Change ingested food from large particles into minute particles, facilitating chemical digestion
- churn contents of GI lumen to mix with digestive juices and come into contact with surface fo the intestinal mucosa, faciliatiating absorption
- propel food along the alimentary tract, ultimately eliminating digestive waster from body
- aided by mastication, deglutition, peristalsis and segmentation (two main types of motility produced by the smooth mm of GI tract, can occur together, in an alternating fashion
Peristalsis
Wavelike ripple of mm layer of hollow organ, progressive motility that produces forward movement of matter along the GI tract
Segmentation
Mixing movement
- digestive reflexes cause a forwar-and-backward movement with a single segment of the GI tract
Gastric motility
Emptying the stomach takes 2-6 hours
- chyme is ejected about every 20 sec into duodenum
Intestinal motility
Includes both peristalsis and segmentation
- mixes chyme with digestive juices from pancreas, liver, and internal mucosa
- chyme takes about 5-6 hrs to pass through small intestine
Chemical digestion
Changes in chemical composition of food as it travels though the digestive tract
- hydrolysis: a chemical process in which a compound unites with water and then splits into simpler compounds
- numerous enzymes in the various digestive juices catalyze they hydrolysis of food
Resides if digestion
Certain compounds of food resist digestion and are eleiminated from the intestines in feces
- these substances remain undigested due to lack of enzymes required to hydrolysis them
- feces: undigested compounds, bacteria, pigment, water, and mucus
Digestive tract
Functionally an extension of the external environment
- material does not truly enter the body until it is absorbed into the internal environment
