Digestive Physiology Flashcards
What is the primary function of the digestive system?
To bring essential nutrients into the internal environment so they are available to every cell in the body
What mechanisms are used to accomplish digestion?
-ingestion
-digestion
-motility of GI wall
-secretion
Movement of nutrients through the GI mucosa into the internal environment
Absorption
Excretion of material that is not absorbed; from rectum through the anus (defecation)
Elimination
Coordination of the various functions of the digestive system (motility, secretion…)
Regulation
T/F
The digestive tract is functionally an extension of the external environment; material does not truly enter the body until it is absorbed into the internal environment
True
Movements of the digestive tract that:
-change ingested food from large to small particles
-churn contents of the GI lumen to mix with digestive juices and come in contact with the surface of intestinal mucosa for absorption
-propel food along the alimentary tract, eliminating digestive waste from the body
Mechanical digestion
-reduced size of food particles
-mixes food with saliva in preparation for swallowing
Mastication
*chewing
Process of swallowing; complex process requiring coordinated, rapid movements
Deglutition
What are the 3 stages of deglutition?
- Oral stage
- Pharyngeal stage
- Esophageal stage
-mouth to oropharynx
-voluntarily controlled
-formation of bolus in middle of tongue
-tongue presses bolus up against soft palate and food is moved into oropharynx
*soft palate and uvula are elevated by bolus to block the opening into the nasopharynx
Oral stage of deglutition
-oropharynx to esophagus
-involuntary movement
-propel bolus from pharynx to esophagus
*with swallowing, larynx moves up as bolus moves down causing epiglottis to close over trachea and bolus slips over epiglottis into laryngopharynx
Pharyngeal stage of deglutition
*contractions from pharynx and esophagus move bolus down through the esophagus
-esophagus to stomach
-involuntary movement
-contractions and gravity move bolus through esophagus and into stomach
Esophageal stage
T/F
Swallowing process must occur rapidly because inspiration is suspended for 1-3 seconds as food passes through pharynx
True
*involves respiratory system
What are the 2 main types of motility produced by smooth muscle of the GI tract?
Peristalsis
Segmentation
*can occur together in alternating fashion
Wa like ripple of muscle layer of a hollow organ; progressive motility that produces a forward movement of matter along the GI tract
Peristalsis
*bolus of food stretches the wall of the GI tract and triggers a reflex contraction in the smooth muscle
Mixing motion; digestive reflexes cause forward and backward movement within a single segment of the GI tract; helps break down food particles, mixes food and digestive juices, bring digested food in contact with intestinal mucosa for absorption
Segmentation
T/F
Emptying the stomach takes approx. 2-6 hours
True
What happens to food while it is in the stomach?
Food is churned and mixed with gastric juices to form chyme
*chyme is ejected approx. every 20 seconds into the duodenum
What is the term for chyme continually being pushed down toward the pyloric sphincter by wave of peristaltic contractions?
Propulsion
What is retropulsion?
Occurs when chyme is forced back from the pyloric sphincter, because it stays closed most of the time
T/F
Gastric emptying is controlled by hormonal and nervous mechanisms
True
Fats and other nutrients in the duodenum stimulate the release of gastric inhibitory peptide (GIP) which travels in the bloodstream to reach the stomach and decrease peristalsis of gastric muscles therefore slowing passage of chyme into duodenum
Hormonal mechanism
Enterogastric reflex; receptors in the duodenal mucosa are sensitive to presence of acid and distension; impulses over sensory and motor fibers in the vagus nerve cause a reflex inhibition of gastric peristalsis
Nervous mechanism
What does segmentation in the duodenum and upper jejunum mix chyme with?
Digestive juices from the pancreas, liver and intestinal mucosa
T/F
The rate of peristalsis picks up as chyme approaches the end of the jejunum, moving it through rest small and into large intestine
True
T/F
After leaving the stomach, chyme usually takes approx. 5 hours to pass through small intestine
True
What is peristalsis regulated and stimulated by?
Regulated by intrinsic stretch reflex:
-the receptors sense distension and peristalsis decreases
Stimulated by CCK - cholecystokinin:
-hormone in small intestinal mucosa that detects fat in chyme and slows down digestion so fat can be absorbed/digested
What are the components of chemical digestion: secretion?
Saliva
Gastric juice
Bile
-secreted by salivary glands
-mostly water with some mucus
-amylase
-sodium biocarbonate
Saliva
An enzyme in saliva that begins digestion of starches
Amylase
Secreted in saliva and increased the pH for optimal amylase function
Sodium bicarbonate
Secreted by gastric glands which have ducts that lead the gastric lumen by way of gastric pits
Gastric juice
A protease that begins the digestion of proteins
*secreted as inactive pepsinogen by chief cells
Pepsin
What do parietal cells of the stomach secrete to maintain an acidic environment in the stomach?
HCl
*releases H+ into the gastric lumen at the same time the contents of the blood become more basic when the bicarbonate ion (HCO3-) moves into the blood
-secreted by the liver; stored and concentrated in the gallbladder
-specifically contains lecithin and bile salts that emulsify fats
-sodium bicarbonate increase pH back to more basic level for optimal enzyme function and help neutralize chyme
Bile
T/F
Bile has excretions like cholesterol, products of detoxification and bile pigments called bilirubin (old RBC)
*these are waste products and are excreted by the liver and eventually eliminated in feces
True
The expulsion of feces from the digestive tract; acts of expelling feces is called defecation
Elimination
Occurs as a result of a reflex brought about by stimulation of receptors in the rectal mucosa
*when fecal matter is moved into the rectum, a reflex relaxation of the internal anal sphincter is initiated
Defecation
*external anal sphincter is voluntary
Contents of the lower part of the colon and rectum move at a slower than normal rate; extra water is absorbed from the feces, resulting in hardened stool
Constipation
Result of increased motility of the small intestine, causing decreased absorption of water and electrolytes and a watery stool
Diarrhea
