gastrointestinal system (digestive system)
-system of organs that breaks down foods into nutrients that the body can use
-ALSO known as digestive system
... [Show More] or the GI system
-accomplished by the processes of digestion and absorption
-controlled by the autonomic nervous system and regulated by series of hormonal feedback loops
-smooth muscle is effected by emotions
-sympathetic nervous system slows digestion and can cause the bowels to empty in preparation of dealing w/ a threat
-the parasympathetic nervous system increases blood flow to the stomach and intestine
-components: oral cavity, mouth, pharynx, esophagus, stomach, liver, gall bladder, duodenum, pancreas, jejunum, colon, ileum, cecum, vermiform appendix, rectum, and anus
digestion
chemical and mechanical breakdown of foods into smaller compounds that can be utilized by the body
absorption
-movement of a substance such as nutrients from the intestine to the bloodstream
-after foods have been digested, their nutrients are absorbed
alimentary canal
-pathway through the body that food travels while being digested and absorbed, as well as the accessory organs that release secretions necessary for digestion to occur
-food enters the canal through the mouth
salivary glands
release digestive enzymes that mix w/ the food to begin chemical digestion and lubricate the mouth
bolus
-chewed food
-to be swallowed, first must be sensed by the pharynx
-bolus passes through the esophagus and then into the stomach
pharynx
dividing point b/t the trachea and esophagus, where the throat senses the presence of food and triggers swallowing
esophagus
portion of the alimentary canal b/t the pharynx and the stomach
peristalsis
wavelike contraction of smooth muscle that moves digested material along the digestive tract
swallowing
triggered when the chewed food (bolus) is sensed by the pharynx
stomach
-both mechanical and chemical digestion continue in the stomach
-hollow organ separated from the esophagus by the esophageal sphincter and from the small intestine by the pyloric sphincter
-the pH of the stomach is maintained b/t 1 and 2 by the release of gastric juice, which contains hydrochloric acid (HCl) as well as enzymes that begin the chemical digestion of protein
esophageal sphincter
ring-shaped muscle that tightens to separate the stomach and esophagus
pyloric sphincter
ring-shaped muscle that tightens to separate the stomach from the small intestine
gastric juice
-liquid in the stomach containing hydrochloric acid and enzymes that begin the chemical digestion of protein
-maintains the pH of the stomach b/t 1 and 2
chyme
-when chyme enters the intestine, it signals the pancreas and gallbladder to release their digestive secretions into the duodenum
small intestine
-part of the alimentary canal below the stomach in which digestion is completed and absorption of nutrients into the bloodstream occurs
-where digestion is completed and absorption begins
-3 sections: duodenum, jejunum, and ileum
duodenum
-first part of the small intestine
-digestion of protein, carbs, and fats occurs here
-when chyme enters the intestine, it signals the pancreas and gallbladder to release their digestive secretions into the duodenum
bile
-created in the liver and stored in the gallbladder
-emulsifies fats
-origin: liver
-helps neutralize the acidic chyme as it enters the small intestine; aids in fat digestion and absorption by emulsifying lipid particles
common bile duct
tube that conveys bile from the gallbladder to the duodenum
cecum
-pouch at the junction of the small and large intestines
-digested material from ileum passes through here
villi
-line small intestine
-finger like folds in the lining of the intestine that increase surface area to aid absorption
microvilli
-line small intestine
-finger like folds in the lining of the intestine that increase surface area to aid absorption
jejunum
-approximately 90% of nutrients will be absorbed here, w/ the exception of vitamin B12 (only absorbed in ileum)
-middle part of small intestine where most absorption occurs
ileum
-terminal part of the small intestine
-vitamin B12 absorbed here
-bile salts and acids are also absorbed here
colon
-water, salts, and vitamin K are absorbed here
-proximal part of the large intestine
rectum
-remaining waste from digestion collects in rectum
-terminal section of large intestine
anus
-terminal end/final portion of the alimentary canal and site of solid waste excretion
-remaining waste is expelled through the anus
-regulated by action of the anal sphincter
anal sphincter
ring-shaped muscle that tightens to control the excretion of solid waste from the digestive tract
mechanical digestion
-involves the physical breakdown of food into smaller pieces
-chewing, the churning of the stomach, and muscular action of peristalsis physically mash food apart, creating a greater surface area for chemical digestion to occur
chemical digestion
involves enzymes or acids that break down food at the molecular level
zygomen
...
digestive enzymes
-digestive enzymes are secreted by certain exocrine organs--including the pancreas, liver, and salivary glands and specialized cells in the lining of the stomach
-so they don't digest the cells that synthesize them, enzymes are released in the inactive zygomen form and are rendered active only in the presence of other digestive compounds
saliva
-origin: salivary glands
-lubricates the mouth; contains salivary amylase, which breaks down carbohydrates and starches; contains salivary lipase, which breaks down fats
hydrochloric acid (HCl)
-origin: parietal cells (stomach)
-sterilizes potentially harmful bacteria; causes proteins to denature; converts pepsinogen to pepsin
pepsin(ogen)
-origin: chief cells (stomach)
-digests protein by breaking bonds of amino acids
gastric lipase
-origin: chief cells (stomach)
-digests lipids and fats in the stomach
mucus
-origin: goblet cells (stomach)
-maintains the mucosal lining of the stomach; protects the stomach walls from the digestive activity of HCl and other gastric enzymes
pancreatic bicarbonate
-origin: pancreas
-neutralizes chyme as it enters the duodenum
pancreatic lipase
-origin: pancreas
-digests lipids and fats in the small intestine
trypsin(ogen) (proteases)
-origin: pancreas and small intestine
-digests proteins in the small intestine
brush order enzymes
-origin: microvilli (small intestine)
-includes lactase and other disaccharidases that break down lactose and other simple sugars; nucleases that break down nucleic acids; and peptidases that complete protein digestion and convert trypsinogen to trypsin
hepatic portal vein
-the capillary network of the digestive tract carries blood to the liver through this
-vein that carries blood from GI tract to the liver
gastrin
-stimulus for release: arrival of protein in the stomach
-released from: stomach/small intestine
-target: parietal cells of stomach
-function: stimulates gastric acid and mucosal secretion; increases motility
ghrelin
-stimulus for release: empty stomach
-released from: stomach
-target: hypothalamus
-function: induces hunger
leptin
-stimulus for release: fat in bloodstream
-released from: adipose (fat) tissue
-target: hypothalamus
-function: reduces hunger by signaling satiety
secretin
-stimulus for release: arrival of chyme in the duodenum
-released from: small intestine
-target: pancreas, stomach, liver
-function: stimulates pancreas to release bicarbonate; inhibits gastric emptying; increases bile secretion
insulin
-stimulus for release: increase in blood glucose levels
-released from: pancreas
-target: liver, muscle, and adipose tissue
-function: stimulates uptake of glucose for conversion into glycogen; decreases blood glucose levels
glucagon
-stimulus for release: low blood glucose levels
-released from: pancreas
-target: liver
-function: initiates breakdown of glycogen; increases blood glucose levels
somatostatin
-stimulus for release: acid in stomach
-released from: stomach
-target: secretory stomach cells
-function: inhibits gastric secretion and slows digestion
cholecystokinin (CCK)
-stimulus for release: fats and amino acids
-released from: small intestine
-target: gallbladder, pancreas, stomach
-function: stimulates gallbladder to release bile; stimulates the pancreas to release pancreatic enzymes; inhibits gastric emptying and acid secretion
A client undergoes a cholecystectomy, a surgery in which the gallbladder is removed and the common bile duct is connected to the hepatic duct. Which of the following measures should be taken to prevent diarrhea after surgery?
The client should eat meals low in lipids, because the release of bile into the small intestine can no longer be triggered by the presence of fats
A client has a disease that involves her gallbladder. Which of the following processes is most likely to be affected?
Digestion of fats
Which of the following is NOT a role of gastric HCl?
-Denaturing proteins
-Activating zymogens
-Sterilizing pathogens
-Buffering gastric pH
Buffering gastric pH
**HCl denatures protein bonds, converts pepsinogen (a zymogen) to pepsin, and kills harmful microorganisms. HCl lowers the pH of the stomach; bicarbonate is a buffer that stabilizes pH.
Which of the following organs transforms a bolus into chyme through the processes of digestion?
Stomach
Which of the following can be absorbed into the bloodstream without being further chemically digested?
Water, electrolytes, vitamins
In which of the following is the digestion of food completed?
Small intestine
Excess intake of acetaminophen, an over-the-counter pain reliever, can affect the functioning of the liver. Which of the following is a possible result of taking too much acetaminophen?
The body cannot effectively eliminate toxins from itself
Which of the following would be expected following the consumption of a meal high in fat?
Increase in cholecystokinin release
**Cholecystokinin induces bile release from the gall bladder and stimulates the pancreas to release digestive enzymes. Release of this hormone would be expected to increase following a fatty meal
Which of the following is a result of reverse peristalsis?
Vomiting
A client mentions that he is lactose intolerant, meaning that his body does not produce sufficient quantities of the enzyme lactase that digests lactose. Lactase is normally secreted by which of the following?
Brush order
**Recall that lactase is an example of a disaccharidase, an enzyme that breaks down carbohydrates into simple sugars. Disaccharidases are released by the brush border of the small intestine
A healthcare provider determines through a blood test that a client is deficient in several vitamins. Which of the following organs is most likely impaired?
small intestine
**This question is asking which organ, if impaired, would result in a vitamin deficiency. Recall that most vitamins are absorbed through the lining of the small intestine.
This question is asking which organ, if impaired, would result in a vitamin deficiency. Recall that most vitamins are absorbed through the lining of the small intestine.
Neutralizing bacteria ingested w/ food [Show Less]