What are the 6 processes related to digestive function?
Ingestion
Mechanical Processing
Digestion
Secretion
Absorption
Excretion
What is ingestion?
Occur when foods enter the digestive tract
What is the mechanical processing of food?
Physical manipulation of food by mouth and digestive tract ( swirling and mixing)
Describe digestion.
Chemical breakdown of food into organic fragments that can be absorbed by the digestive epitheleum
Describe secretion.
Release of water, acids, enzymes and buffers by digestive tract and digestive organs
Describe absorption.
Movement of small organic molecules, electrolytes, vitamins and water across the digestive epithelium & into interstitial fluid of the digestive tract
Describe excretion.
Removal of waste products from body fluids
Describe the defensive role of the digestive tract.
Protects surrounding tissues fr corrosive effects of digestive acids & enzymes and fr bacteria swallowed w food or that resides in the there
Four major layers of the digestive tract are. . . . .
Mucosa
Submucosa
Muscularis Externa
Serosa
The mucosa is . . . .
Inner lining of digestive tract consisting of mucosal epithalium and the lamina propria, an underlying layer of loose connective tissua
The submucosa is . . . . .
Second layer of loose connective tissue containing lg blood vessels, lmyphatic vessels, nerve fibers, sensory neurons and parasympathetic motor neurons
What is the submucosal plexus?
Controls & coordinates contractions of smooth muscle layers and regulating secretion of digestive glands
The muscularis externa is. . . .
Band of smooth muscle cells arranged in an inner circular layer and an outer longitudinal layer. Contractions both agitate materials & propel them along the digestive tract
What is the Serosa?
Serous membrane that covers muscularis externa along most porttions of the digestive tract within the peritoneal cavity
Pacesetter cells do what?
Trigger waves of motion within the smooth muscle of the digestive tract resulting in rhythmic cycles of activity
What is Peristalsis?
Waves of muscular contraction that move along digestive tract propelling digestive contents
What happens to dead areas in digestive tissue? 27 minutes digestive part 1
They often must be removed b/c w/o movement of that muscle they could become necrotic fr something sitting in there and rotting
What are four activities of the oral cavity?
Sensing & analyzing material b/f it is swallowed
Mechanically processing material thru actions of teeth, tongue & surfaces of palate
Lubricates material by mixing it w/ mucus & salivary secretions
Begins digestion w/ salivary enzymes
The oral cavity is aka?
Buccal Cavity
What does the tongue do?
Mechanical processing by compression, abrasion & distortion
Manipulation to assist in chewing & to prepare material for swallowing
Sensory analysis by touch, temp & taste
What do salivary glands produce?
1.0 - 1.5 liters of saliva/day consisting of 99.4% water plus mucins & assorted ions, buffers, waste products, metabolites & enzymes
What does the pharynx do for digestion?
Pharyngeal muscles cooperate w/ oral muscles & esophagus to initiate process of swallowing
The esophagus is. . . .
muscular tube that conveys food & liquids to stomach. Begins @ pharynx, passes thru mediastinum & enters peritoneal cavity thru the esophageal hiatus (opening in the diaphragm) before emptying into the stomach
The stomach is located where?
Within L upper quadrant of the abdominopelvic cavity
What are the four primary functions of the stomach?
Temporary storage of ingested food
Mechanical breakdown of ingested food
Breakdown of chemical bonds in food using acids and enzymes
Production of intrinsic factor, compound necessary for absorption of vitamin B12
What is intrinsic factor?
Compound produced in the stomach that is necessary for the absorption of Vitamin B12
What is chyme?
Viscous, acidic, soupy mixture of ingested materials & secretions of the glands of the stomach
What is the cardia?
Smallest part of the stomach where the esophagus connects
The fundus is . . .
The bulge of the stomach superior to the cardia
Where is the body of the stomach located?
Lg area between the fundus and the curve of the J
The pylorus . . . .
is the distal part of the J and connects the stomach w/ the small intestine thru the pyloric sphincter
Rugae are . . . .
Folds or ridges within the mucosa of the stomach when it is empty
What are gastric pits?
Openings onto the gastric surface containing gastric glands that actively divide and replace superficial cells of the mucus epithelium shed into chyme
Each day the cells of the gastric glands secrete about ____ mL of ____ ____.
1500 mL of gastric juice
What do parietal cells do?
Secrete intrinsic factor and hydrochloric acid
Chief Cells. . . .
Secrete protein called pepsinogen into stomach lumen.
What happens when pepsinogen meets hydrochloric fr parietal cells?
It is converted to pepsin which is a proteolytic (protein digesting) enzyme
What are renin and gastric lipase used for in newborns?
Renin coagulates milk slowing passage thru stomach & allowing more time for digestion
Gastric lipase initiates digestion of milk fats
What are the three phases gastric secretion & where do they begin?
Cephalic Phase - Begins w/ senses fr your brain
Gastric Phase - Begins in stomach
Intestinal Phase - Begins when chyme starts to enter the small intestine
Describe the cephalic phase.
Begins in ur head
Under ctrl of vagus nerves, parasympathetic fibers innervate mucous, parietal, chief & endocrine cells of stomach
Lasts only a few minutes
Describe the gastric phase.
Begins in the stomach w/ arrival of food
Gastrin stimulates stomach contractions which begin to swirl & churn stomach contents creating chyme
Describe the Intestinal Phase
Begins when chyme enters the sm intestine
Inhibitory function that controls rate of gastric emptying to ensure secretory, digestive & absorptive functions proceed efficiently.
