Digestive System Flashcards
function of the digestion system
to break down ingested food to particles small enough to be absorbed into the blood
metabolism
produces cellular energy (ATP) and accounts for all constructive and degradative cellular activities
types of organs of the digestive system
1) alimentary canal (gastrointestinal tract)
- food digestion/absorption
- mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
2) accessory digestive organs
- assist digestion
- salivary glands, tongue, liver, GALLBLADDER, pancreas, teeth
functional processes of the digestive system
ingestion, propulsion, food breakdown (mechanical and chemical digestion), absorption, defecation
stimuli
stretching of the GI tract wall by food in the lumen, osmolarity, pH of lumen contents, presence of substrates and end products of digestion
response
1) activate or inhibit glands that secrete digestive juices into the lumen or hormones into the blood, 2) mix lumen contents and move them along the length of the tract by stimulating the smooth muscle of the GI tract walls
intrinsic
a product of “in-house” nerve plexuses or local hormone-producing cells
Sublayers of alimentary canal
- Mucosa
- Submucosa
- Muscularis Externa
nerve plexuses
extend entire length of alimentary canal and influence each other both in the same and in different digestive organs
Stomach & amp; small intestine also contain hormone producing cells
Which via endocrine pathways target cells in the same or different digestion tract organs.
What are the functions of the mucosa?
- Secretion (mucus, digestive enzymes, hormones)
- Absorption of end products of digestion into blood
- Protection against disease
Epithelium in mucosa
- Simple columnar epithelium rich in mucus-secreting goblet cells
- Forms inner or luminal boundary of the tract
- Stomach and small I. cells that secrete enzymes and hormone
- Absorb digested products
Lamina propria
- Loose connective tissue layer
- Blood and lymph vessels
a) Capillaries nourish epithelium & absorb digested nutrients
b) isolated lymph nodules (highest concentration tonsils in the pharynx and appendix0
Muscularis mucosae
- Smooth muscle cells that moves the mucosa, including dislodging food
- Creates folds in small i. increasing surface area to aid digestion and absorption
Submucosa
- Moderately dense connective tissue
- Contains blood vessel and lymph vessels, lymph nodules and nerve fibers
- Elastic fibers
Muscularis externa
- Responsible for segmentation and peristalsis
- Also forms sphincters
Serosa
- Connective tissue covered by single layer of squamous epithelial cells
- Protection
What are the different glands in the gastric pits?
- Mucous neck cells
- Parietal cells
- Chief cells
- Enteroendocrine cells
Mucous neck cells
acidic mucuous secretion
Parietal cells
Secrete HCl and intrinsic factor, acid pH of stomach (1.5-3.5), activation of pepsin, kill many ingested bacteria, intrinsic factor for vitamin B12 absorption
Chief cells
- Pepsinogen a
- Activated to pepsin by HCl
Enteroendocrine cells
Produce hormones (gastrin, histamine, endorphines, seotonin, cholecystokinin, somatostatin)
Mucosal barrier
1) Thick coating of bicarbonate-rich mucus in stomach wall
2) Epithelial cells of mucosa form tight junctions to keep gastric juices from underlying tissues
3) In gastric glands, where alkaline mucus absent
- External face of cell plasma membrane is impermeable to HCl
4) Damaged epithelial mucosal cells are shed and replaced
- Stomach mucosal surface replaced every 3-6 days
What does the mouth break down? How?
starch, with salivary amylase
What do the small intestines break down? How?
- carbohydrates (lactose, starch, sucrose), large polypeptides of proteins, unemulsified fats
- segmentation by smooth muscles which mixes food & propel slowly
- digestive enzymes from pancreas and villi membranes
What does the stomach break down?
- proteins with pepsin (gastric glands) in presence of HCl
- propel to duodenum
What does the large intestine break down? How?
- nothing, just absorb, propulsion toward rectum, defecation
- remaining food residues digested by bacteria
How does the portal triad work?
- Heptatic artery: branches carry oxygenated blood to hepatocytes
- Portal vein: branches carry blood with nutrients from small intestine
- Bile duct: carries bile products from hepatocytes to larger ducts & gall bladder
Hepatocyte
liver cell
3 phases in digestive activity
- Cephalic, gastric, intestinal
How are fats digested and absorbed?
- Digested in small intestine with pancreatic lipase and emulsifier bile salts
- Absorbed in small intestine; primarily by lymph to systemic circuit, then to liver
Gastric ulcer
- Erosions of the stomach wall
- Cause pain, result in perforation of the stomach wall, peritonitis and possibly massive hemorrhage
- 90% recurrent ulcers caused by acid resistant bacteria which burrow underneath mucus and destroy the epthilelial mucosal layer
Renin
enzyme in stomach of children that breaks down milk protein (caesin); used to make cheese
Portal triad
1) portal arteriole - supplies O2 rich blood to liver
2) portal venule - carries venous blood laden with nutrients from digestive vicera
3) bile duct
- Blood from portal arteries and veins percolate, mix and drain into the central vein
- Blood and bile opposite direction flow
Kupfer cells
Hepatic macrophages
Hepatocytes
1) Produce bile
2) Process bloodborne nutrients
3) Store fat-soluble vitamins
4) Play an important role in detoxification (eg. converting blood ammonia to urea)
Hepatitis
Inflammation of liver
Cirrhosis
“orange color” chronic inflammation with scarring and loss of function in liver
Bile salts
- emulsify fats (homogenize) creating increased surface area to aid fat digesting enzymes
- facilitate fat and cholesterol absorption
- recycled - reabsorbed in ileum; returned to liver via hepatic portal blood; resecreted in newly formed bile
gall stones
too much cholesterol or too little bile salts lead to crystallizaton of cholesterol
3 stages in making energy
1) Digestion in GI tract lumen
2) Anabolism and formation of catabolic intermediates within tissue cells
3) oxidative breakdown in mitochondria of tissue cells
Goblet and other epithelial cells
Goblet secretes mucus, other cells secrete fluids
What are the 3 parts of the mucosa, from top to bottom?
(Top) Surface epithelium
(Middle) Lamina propria
(Bottom) Muscularis mucosae
Functions of GI epithelium
- Secrete substances used in digestion
- Absorption of digested products
bile
- needed for digestion and absorption of fat
- concentrated in gall bladder
exocrine pancreas
produces digestive juice that contains
- enzymes to digest major foodstuffs
- bicarbonate to neutralize acidic chyme from stomach
3 phases of control in digestive system
1) cephalic
2) gastric
3) intestinal
cephalic phase
1) Stimulatory event
- sight & thought of food
- stimulation of taste and smell receptors
Result: vagus nerve preps GI for arrival of meal
2) Inhibitory event
- loss of appetite, depression
- lack of stimulatory impulses to the parasympathetic center
gastric phase
1) Stimulatory event
- meal in stomach, distension
Result: increase in gastric motility, vagus nerve, gastrin release to blood
2) Inhibitory
- Excessive pH, emotional upset
Result: gastrin secretion declines, overrides PNS
intestinal phase
1) Stimulatory event:
- low pH and partially digested meal moves into intestine (contents and volume)
Result:
- initiate reflexes that cause secretion of bicarbonate, digestive enzymes & bile
- begin segmenting contraction in small intestine
2) Inhibitory event:
- Distension, fatty/acidic/partially digested food move into duodenum (intestine)
Result: inhibitory reflexes slow gastric emptying while intestinal contents are neutralized, absorbed and digested
Cholecystokinin in liver/gall bladder and pancreas
a) Liver/gallbladder: acidic chyme enters duodenum, cause GALLBLADDER contraction and release of gallbladder
b) Pancreas: fatty protein rich chyme enters duodenum, results in secretion of ENZYME rich juice
Secretin in liver/gall bladder and pancreas
a) Liver/gallbladder: acidic, fatty chyme entering duodenum causes, w/ bile, liver to produce more BILE
b) Pancreas: acidic chyme entering duodenum, leads to secretion of BICARBONATE rich juice
Protein digestion & absorption
a) Digestion: Begins in stomach with pepsin, occurs in small intestine w/ pancreatic enzymes + brush border enzymes
b) Absorption: in small intestine, amino acids are absorbed into capillaries and carried to the liver
Portal triad
1) Hepatic artery: branches carry oxygenated blood to hepatocytes
2) portal vein: branches carry blood with nutrients from small intestine
3) bile duct: carries bile products away from hepatocytes to larger ducts and gallbladder
Function of liver
filter blood coming from digestive tract b/f passing it to the rest of the body; detoxifies chemicals and metabolizes drugs; secrete bile to intestines; make proteins important for blood clotting and other functions
Carbohydrate absorption and digesting
a) Digestion: Begin in mouth with amylase, small intestine with pancreatic amylase and brush border enzymes
b) Absorption: in small intestine, sugars absorbed in capillaries and carried to liver
Fat digestion and absorption
a) Digestion: in small intestine with pancreatic lipase and emulsifier bile salts
b) Absorption: small intestine, primarily by lymph -> systemic circulation -> liver
