Digestion II Study Guide Flashcards
term for a bolus of food after it is undergoing digestion in the stomach
chyme
how tunics are modified in stomach
- Muscularis - added internal, oblique layer to allow increased mixing and churning – more intense mechanical breakdown
- Mucosa - contains simple columnar epithelium made entirely of mucous cells – produces a cloudy, protective double layer of alkaline mucus
- Dotted with millions of deep gastric pits
- Gastric pits lead into the gastric glands responsible for producing gastric juice
secretory cells in gastric glands
Mucus neck cells, parietal cells, chief cells, Eneteroendocrine cells
mucus neck cells
produce thin, soluble mucus
Parietal cells
produce HCL (pH 1.5-3.5, required to activate pepsin (breakdown proteins in stomach?)) and secrete intrinsic factor (required to absorb B12)
Chief cells
secrete pepsinogen (inactive pepsin) and lipases
Eneteroendocrine cells
secrete chemical messengers into lamina propria as well as gastrin
Mucosal barrier
produced to protect the stomach
- A thick coating of bicarbonate-rich mucus
- Tight junctions between epithelial cells
- Quick replacement of damaged mucosal cells by stem cells
Gastritis
Inflammation of the stomach in response to breaches of the mucosal barrier
peptic/gastric ulcers
- Erosions of the stomach-wall – cause gnawing, epigastric pain
- Pain typically appears 1-3 hours after eating and resolves with eating again, ulcers are linked to peritonitis and h. Pylori; a type of acid resistant bacteria
different functions completed in the stomach
Propulsion
Mechanical breakdown
Digestion
Absorption
Secretion of intrinsic factor
propulsion
peristalsis
Mechanical breakdown
churning
Absorption
only lipid soluble substances – alcohol and aspirin
Digestion
breakdown of proteins by HCl and pepsin (rennin in infants)
Secretion of intrinsic factor
essential for B12 absorption and maturation of RBCs
Gastrin
hormonal mechanism of regulation of gastric secretion
- Stimulates secretion of hcl by the stomach
- Stimulates secretion of gastrin antagonists by the SI
branch of the ANS that increases gastric secretions
parasympathetic
3 phases of gastric secretions
cephalic/reflex phase, gastric phase, intestinal phase
cephalic/reflex phase
triggered by smell, taste, and sight; act via the vagus nerve
Gastric phase
triggered by stretch receptors and/or chemical stimuli – partially digested protein, caffeine, rising pH
- Activates G cells (enteroendocrine cells) to secrete gastrin
- Gastrin initiates release of HCl
- Low pH (between meals) or firing of the SNS will inhibit gastrin
Intestinal phase
Partially digested food enters the SI and triggers the release of intestinal gastrin
- Distension of the SI and or the presence of acidic, fatty, or hypertonic chyme will inhibit gastric secretions – protects the SI from excess acidity and being overwhelmed * enterogastric reflex and enterogastrones
Enterogastric reflex
short reflexes by the enteric nervous system and long reflexes by the sympathetic and vagus nerves inhibit acid secretion
Enterogastrones
duodenal enteroendocrine cells release secretin or cholecystokinin (CCK) to inhibit gastric secretions
digestive function of liver
Production of bile
About 900ml per day
(additional functions: processed bloodborne nutrients, stores fat-soluble vitamins, and performs detoxification)
bile
fat emulsifier
Livers functional unit
liver lobules (hexagonal) composed of plates of hepatocytes
- Central vein: located in the longitudinal axis
Hepatocyte
specialized liver cells that filter and process nutrient-rich blood
- Have increased numbers of rER, sER, golgi complexes, peroxisomes, and mitochondria
Portal triad
located in each corner of the lobule
Hepatic artery
Hepatic portal vein
Bile duct
Hepatic artery
supplies oxygen to the liver
hepatic portal vein
brings nutrient rich blood from the intestines
Bile duct
receives bile from the bile canaliculi
function of hepatic macrophages
Exist in the liver sinusoids to remove debris and old RBCs
portion of the SI that reabsorbs bile salts for recycling
ileum during enterohepatic circulation
Bile salts
cholesterol derivatives that function in fat emulsification/absorption
Bilirubin
yellow pigment formed from heme during breakdown of RBCs
- Metabolized by bacteria in the SI to stercobilin which gives feces a brown color
pathway for bile moving out of the liver
- Leaves liver via r and l hepatic ducts
- R and l hepatic ducts fuse into common hepatic duct
- Common hepatic ducts joins with cystic duct from gallbladder and forms the common bile duct
Hepatitis
inflammation of the liver
- Typically, viral infection, but can be caused by alcohol, drug toxicity, or wild mushrooms
- Six viruses: a-f; 2 transmitted through food, remainder via blood
Cirrhosis
progressive, chronic inflammation from hepatitis or alcoholism
- Liver activity is depressed
- Liver becomes fatty and fibrous
- Portal hypertension: flow of blood through the liver is obstructed
gall bladder
Store and concentrate bile
- Muscular contractions release bile via the cystic duct – flows into the common bile duct
gallstone
- Caused by excess cholesterol or too few biles salts (cholesterol crystallized into stones)
- Can obstruct the flow of bile from the gallbladder (painful when the gallbladder contracts against sharp crystals)
Obstructive jaundice
blockage causes bile salts and pigments to build up in blood – results in yellowed skin
Exocrine function of pancreas
production of pancreatic juice
endocrine function of pancreas
secretion of insulin and glucagon via the pancreatic islet cells
pancreatic juice
contains enzymes needed to break down all categories of foodstuffs (multiple ducts secrete into the duodenum via the main pancreatic duct)
- Contains electrolytes (primarily HCO3-)
- Watery, alkaline solution (pH 8) used to neutralize acidic chyme from stomach
4 macromolecules digested by the digestive tract and the enzyme responsible for its digestion
Proteases – for proteins; secreted in inactive form to prevent self digestion
Amylase – for carbohydrates
Lipase – for lipids
Nucleases – for nucleic acids
