digestive system Flashcards
what are the parts of the alimentary canal?
GI tract: mouth–> pharynx–> esophagus–> stomach–> small intestine –> large intestine
what are the 6 accessory glands?
-teeth
-tongue
-gallbladder
-liver
-pancreas
what are the 6 essential activities in digestion?
ingestion–> propulsion–> mechanical digestion–> chemical digestion (secretion) –> absorption –> defacation
what are the 4 major tissue layers of the digestive tract?
- mucosa (INNERMOST, secretions, absorption)
- SUBmucosa (blood/nerve supply)
- muscularis external (motility)
- serosa (outer CT layer)
what are the GI tract sensory receptors?
-mechanoreceptors (stretch from food passing)
-chemoreceptors (osmolarity and pH changes, digestive substrate/end products)
extrinsic vs intrinsic controls and what do they effect?
-extrinsic= from outside of digestive tract
-intrinsic = from inside of digestive tract
-both affect motility and secretion of enzyme/homrones
what are the 3 GI tract regulatory mechanisms?
-short reflexes: nerve plexuses (gut-brain) respond to GI tract stimuli
-hormones: stomach to small intestine and stimulate target cells in organs
-long reflexes: response to stimuli in/out of the GI tract, autonomic control/CNS system
What are the 4 digestive processes?
motility
secretion
absorption
digestion
what is motility and the 2 types?
motility is muscular contractions that mix/move contents of digestive tract forward
1) peristalsis (propulsive)
2) segmentation (mixing for digestion and absorption)
where do digestive enzymes and mucus come from?
-mouth
-stomach
-small intestine
what structures help in absorption?
villi and microvilli increase surface area for absorption
what are the 2 parts of digestion?
-mechanical digestion by chewing
-chemical breakdown by enzymes
how are carbohydrates digested?
starch –> maltose–> glucose
-amylase from salivary glands and pancreas act in the mouth and SI
-lactase and maltase from the SI wall act in the SI
-glucose is directly absorbed into the blood
what are examples of di- and monosaccarides?
-disaccarides=ducrose, lactose
-monosaccarides=glucose
how are complex carbohydrates digested? examples?
complex carbs. such as fiber, is digested in the large intestine
humans lack the enzyme glactosidase to digest them so it moves to the large intestine where it is digested by E.coli
-fermentation; gas production
how are proteins digested?
protein –> polypeptide–> dipeptide–> amino acids
-pepsin from the stomach
-trypsin/chymotrypsin, carboxypeptidase, and aminopeptidase are from the pancreas but act in the SI
-dipeptidases are from the SI
-many different enzymes are needed to break the bonds between different amino acids
-amino acids are directly absorbed into the blood
how are fats digested? what is needed>?
fat–> smaller fat globules–> glycerol (lymph to blood) and fatty acids (directly into blood)
-non-polar
-emulsifier is needed in the form of bile
-the enzyme lipase is from the pancreas and acts in the small intestine
how does lipase act?
-acts on emulsified droplets
-gets monoglycerides and fatty acids that can enter absorbative cells or form micells
-within cell, they form chylomicrons whch are absorbed into lymph
how are nucleic acids and vitamins digested?
-digested by nucleases that are from the pancreas and act in the SI
-SI enzymes
-vitamins are absorbed as whole from the carriers
what does the mouth add to digestion?
-chewing increases surface area and decreases choking
-secretion of mucus for lubrication and salivary amylase for starch digestion
what is the swallowing reflex?
it is triggered by food in the pharynx and coordinated contractions from the medulla
how is the esophagus separated from the stomach?
-gastroesophageal (cardiac) sphincter and valve
what are the 3 sections of the stomach? sphincters? rugae?
sections: fundus, body, antrum
sphincters: gastroesophageal, pylorus
rugae: deep folds that allow for expansion
what are the 4 functions of the stomach?
storage, mixing, absorption, secretion
what is secreted by the stomach?
-acid (activates pepsin from parietal cells)
-mucus (acid protection
-pepsin (protein digestion, chief cells)
-intrinsic factors (absorption of B12 in SI)
what do chief and parietal cells do?
-chief cells/pepsinogen are the inactive form
-parietal cells convert pepsin to HCl
what are the functions of hydrochloric acid in the stomach?
-activates pepsin
-breaks down connective tissue and muscle
-kills pathogens
-stomach protects itself with mucus, tight junctions, and cell replacements
what causes gastric emptying and mixing?
antral peristaltic contractions
what is gastrin?
a hormone that increases HCl secretion, pepsinogen,and motility
-it is stimulated by proteins, distension and smell
what is heart burn?
leaky valve between the esophagus and the stomach leading to acid reflux
what is a gastric/peptic ulcer?
it is a hole caused by inflammation and necrosis in the stomach
-caused in part by pepsin and helicobacter pylori
-affects the stomach and duodenum
what are symptoms and treatment of an ulcer?
pain and bleeding
-treated by reduction of contributory factors, antacids, and surgery in severe cases
what occurs in the small intestine?
it is the site of digestion, secretion, and absorption
-alternates between segmentation and peristalsis
what does the gallbladder secrete?
bile
what does the pancreas secrete and into where?
amylase
trypsin/chymotrypsin
pepsidases
lipase
nucleases
bicarbonate/neutralizer
-these secretions are dumped into and act onto the duodenum
what is CCK?
cholecystokinin
it is triggered by a small bolus of food entering the SI
-acts on the pancreas and gallbladder to increase release of enzymes and bile
when would CCK be released?
-released if the duodenum is distended or if fat content in SI increases
what is gastric inhibition?
the distention of duodenum inhibits gastric emptying
-this allows time for digestion and absorption in the SI
what is secretin and when is it released?
it is a hormone that causes the pancreas to release bicarbonate (neutralize acids). it increases bile formation in liver and inhibits gastric motility
-it will be released if the SI is too acidic
what is motilin?
hormone that promotes motility in the SI
how are amino acids and sugar absorbed in the SI?
into villi capillaries
how are fatty acids absorbed in the SI?
into the lacteals of lymph vessles then into blood
via carriers
how are carbohydrates absorbed in the SI?
they are quickly absorbed in the first half of the jejunum
takes 2-3 hours to empty stomach
how long does it take for fats and proteins to be absorbed in the SI?
slower to digest
takes 8-10 hours
how are vitamins absorbed in the SI?
fat soluble=with micelles
water soluble=by carriers
water reabsorption is by osmosis and follows solutes
how is calcium absorption regulated?
regulated by vitamin D and PTH
what are the features of the large intestne?
haustral contraction (slow)
-Na+ and water reabsorption
-E.coli digestion of fiber (incomplete)
what is the defecation reflex?
-the distension of rectum
-PARAsympathetic response; relaxes the sphincter and contracts rectal walls
-it can override the higher brain centers
what is a hemorrhoid?
varicose veins in the rectum that can be internal or external
-can be caused by pressure in the anal area, and constipation. prolonged, standing, or childbirth/pregnancy
what are the 3 types of cells in the pancreas and their secretions?
exocrine/endocrine functions
-duct cells - secrete bicarbonate
-acinar cells - secrete bile
-endocrine cells - secrete insulin and glucagon
how does the liver receive blood?
-hepatic artery
-hepatic portal vein (gut)
what are hepatocytes?
the cells of the liver that are arranged in sinusoids
what does the liver excrete and store?
stores: glycogen, fats, iron, copper, vitamins
excretes: cholesterol and bilirubin
-synthesizes plasma proteins
how is bile formed?
cholesterol based and is stored in the gallbladder between meals
-bilirubin gives bile the yellow colour
-cholesterol, lecithin
what are bile salts for?
important in fat digestion and derived from cholesterol
-they are recycled within the gut
how does the gallbladder contract
with CCK
what is liver cirrhosis?
-chronic, irreversible, degenerative damage from alcohol, toxins, or disease
-loss of normal liver cells
-no organization and scar tissue
what are ascites?
a symptom of liver cirrhosis that causes high abdominal venous pressure
-organs swell and bleed
what are gallstones?
consists of cholesterol, bilirubin, calcium
-it can block ducts (if small, gravel)
what are the 5 risk factors for gallstones?
female
fair complexion
fat
fertile
forty or older
what is Crohn’s disease?
InflammatoryBowelDisease
-often in the SI
