mod 10 digest Flashcards
four layered arrangement of tissue that makes up GI from lower esophagus to anal canal:
mucosa, submucosa, muscularis, and serosa
mucosa layer
inner lining of GI; epithelium that is in direct contact with contents of GI tract; also a layer of areolar connective tissue and layer of smooth muscle tissue; folds increase SA for digestion and absorption
submucosa
aoerlar CT that binds to mucosa and muscularis; contains blood and lymphatic vessels; network of neurons regulated by ANS–>control secretions
Muscularis layer
thick layer of muscle in mouth, pharynx and upper esophagus; consists in part of skeletal muscle that aids in swallowing; in rest of GI it is composed of smooth muscle for involuntary contractions that permit food breakdown
Serosa
outermost layer around organs of GI below diaphragm; simple squamous epithelium and aerolar CT; secretes fluid allowing tract to glide over other organs
Peritoneium
largest serous membrane of body; parietal portion lines wall of abdominal cavity, visceral portion line organs in cavity
lingual frenulum
fold of mucous membrane in midline undersurface of tongue; limits posterior movement of tongue
Saliva
99.5% water and 0.5% solutes (salivary amylase, mucus, lysozyme)
crown of tooth
visible portion above level of gums
root of tooth
consists of one to three projections embedded in socket
neck of tooth
junction line of the crown and root; near gum line
salivary amylase in mouth produces;
breaks down glucose into disaccharide maltose, trisaccharide maltrotriose, and larger dextrin fragments
food in the larynx
food bypasses nasopharynx (respiration) and goes through oropharynx and laryngopharynx before passing into esophagus; move via muscular contractions
three stages of swallowing:
voluntary stage (bolus forced to back of mouth into oropharynx)
Pharyngeal stage: (involuntary; uvula seals of nasopharynx, epiglottis seals of larynx vocal chords come together)
Esophageal phase: (food pushed through esophagus via peristalsis)
Peristalsis
muscle fibers around bottom of bolus contract, shortening section of esophagus below bolus and pushing walls outward; once bolus moves into new section, muscles above bolus contract and cycle repeats
four main regions of stomach
cardia (superior opening of stomach)
fundus (superior and left of cardia)
body (large central portion)
pyloric part: narrow most inferior
4 layers of tissue; the difference btw them in the stomach vs elsewhere in GI
mucosa: nonciliated simple columnar epithelial cells
gastric glands formed from mucosa
gastric glands secrete 3 types of exocrine cells;
mucous neck cells, chief cells and parietal cells (gastric juices)
neck cells
secrete mucous
chief cells
secrete inactive gastric enzymes (pepsinogen)
parietal cells
produce HCL; kills microbes and converts pepsinogen to pepsin and secretes intrinsic factors (for B12)
greater omentum
large fold of visceral peritoneum (Serosa) that hangs down from stomach
what stimulates digestion in stomach
stretching of stomach wall, and change of pH (increased); this causes gastric juices to flow and initiates mixing waves
gastric emptying
each mixing wave forces small amount of chyme through partially closed pyloric sphincter into duodenum
Gastrin
found in G cells of gastric glands; stimulated by peptides in lumen of stomach; causes secretion of HCL from parietal cells
secretin
secreted by duodenum (S cells); in response to low pH in duodenum and by increased protein products in SI; regulates the secretion of stomach and pancreas; regulats pH of duodenum
CCK
synthesized by I cells in SI due to the presence of fatty acids in chyme entering duodenum; stimulates digestion of fat and protein; causes release of bile from pancreas and gallbladder
Acini
makes up external portion of pancreas and secrete pancreatic juices
pancreatic islets/langerhans
endocrine portion of pancreas; secrete glucagon, insulin, somatostatin and pancreatic polypeptide
pancreatic juices
consists of water, salt, sodium bicarbonate, and enzymes; slightly alkaline which inactivates pepsin
pancreatic enzymes include:
pancreatic amylase
trypsin/chymotrypsin/carboxypeptidase
pancreatic lipase
ribonuclease and deoxyribonuclease
hepatocytes
major functinoal cell of liver; performs metabolic, secretory and endocrine functions; also produces bile
bile caniculli
small ducts btw hepatocytes that collect bile, then bile enters ducts eventually merging and forming common hepatic duct
Common hepatic duct into…
common hepatic duct–>common bile duct–>hepatopancreatic duct–>duodenum
hepatic sinusoids
permeable blood capillaries; receive O2 rich blood from hepatic artery and O2 poor blood from hepatic vein; delivers blood to central vein then hepatic vein and into vena cava
Kupfer cells
phagocytes present in sinusoids that destory worn-out WBCs bacter and other forgein matter
Bile
aids in emulsification (break down large lipid globules) ; aids in absoprtion of lipids
Bilirubin
bile pigment made from heme; secreted in presence of broken down RBCs
Functions of liver (9)
- secrete bile
- phagocytosis by kupffer cells
- carb metabolism (breaks down glycogen, converts amino acids to glucose)
- Lipid metabolism (cholestrol to make bile)
- Protein metabolism (and synthesis of plasma proteins)
- Process drugs/hormones
- Excrete bilirubin
- Stores vitamins and minerals (A,D,E,K, Iron, Copper)
- activates Vitamin D
3 portions of SI
duodenum (shortest)
Jejunum; 1m long
Ileum; 2m long
Mucosa of SI contains:
absorptive cells that release enzymes to digest food, contain microvilli to absorb nutrients
Goblet cells: secrete mucus
Intestinal glands: secrete juices
Intestinal Glands contain:
goblet cells and absorptive cells endocrine cells (CCK cells (CKK), S cells (secretin), K cells (GIP))
submucosa of SI
contains duodenal glands that secrete alkaline mucus to neutralize acidic chyme
microvilli of SI
tiny projections that greatly increase SA of plasma membrane allowing large amounts of digested nutrients to diffuse into absorptive cells; form brush border
where does absoprtion in SI occur:
most digestion of enzymes of SI occur in/on the surface of absorptive cells
Segmentation
localized contraction that mixes chyme in SI; food particles are brought into contact with mucosa for absorption; stops once most of meal is absorbed and persistalsis take over from stomach to bring more food into SI
pancreatic amylase
breaks down starches and dextrins to maltose
maltase
splits maltose into two mlcs of glucose
sucrase
breaks sucrose into a mlc of glucose and mlc of fructose
lactase
digests lactose into a mlc of glucose and mlc of galactose
peptidase
completes protein digestion; produced by absoprtive cells that line villi
Lipid digestion
occur mostly in SI; bile salts emulsify lg globules; pancreatic lipase breaks down triglycerides; end product is fatty acids and mooglyceride
absorption of monosacharides
all carbs absorbed as monosaccharides;
active transport: glucose and galactose via absoprtive cells
faciliatated diffusion: fructose
monosaccharides are carried to liver via hepatic portal vein then through heart and gen circ
absoprtion of amino acids
mainly in duodenum/jejunum
1/2 proteins come from digeted food, other 1/2 from digestive juices, and dead cells
enter absoprtive cells of villa via active transport
carried into hepatic portal vein
absorption of bile salts/lipids
short chain fatty acids: simple diffusion into absorptive cells of villi
bile salts emulsify lipids and form MICELLES which diffuse into absorptive cells and packaged into CHYLOMICRONS which enter lymphatic fluid within a lacteal; bypass hepatic portal system and empties into subclavian vein
benefits of fats (3)
delay gastric emptying
enhance satiation with secretion of CCK
necessary for absorption of fat soluble vitamins
fat soluble vitamin absorption
with lipids in micelles and absorbed via simple diffusion
water soluble vitamins absoprtion
simple diffusion (B12 combined with intrinsic factor via active transport in ileum)
four regions of LI
cecum (appendix)
colon (longest; ascending, descending, transverse, sigmoid)
rectum
anus (smooth muscle sphincter and skeletal muscle sphincter)
mass peristalsis
strong waves that begin in middle of colon and drive contents to rectum; stimulated by food in stomach
defecation reflex
mass peristalsis pushes fecal material from sigmoid colon to rectum
distension in rectal wall stimulates stretch receptors that initiate emptying reflex
pressure increases in rectum to do ANS stimulation shortening rectal muscles
Pressure+ANS stimulation opens internal sphincter; external sphincter opens voluntarily (Skeletal muscle)
Motility
ability of GI tract to mix and move material along its length
