week 9 Flashcards
describe the small intestine as well as its role in digestion
main functions: secretion, digestion, absorption, propulsion
divisions of the small intestine:
- duodenum
- jujunum
- ileum
accessory organs: pancreas, liver, gallbladder
describe how peristalsis and segmentation contribute to the motility of the small intestine
peristalsis propels chyme towards the large intestine and segmentation contributes to mechanical digestion and mixes the chyme with digestive juices
what do the folds in the small intestine help with
they increase the surface area for absorption
what are the roles of villi and microvilli in the small intestine
villi: each villus has a layer of enterocytes surrounding a central core of capillaries and a lymphatic vessel (lacteal)
microvilli (the brush border): final steps of digestion and all absorption here
describe the pancreas as well as its secretions
the exocrine pancreas consists of acinar cells that arrange in groups around ducts that drain into the main pancreatic duct
the secretions from the pancreas are called pancreatic juice. they are a mix of water, digestive enzymes, and HCO3-
describe two of the hormones secreted by the endocrine cells lining the duodenum (Cholecystokinin (CCK) and Secretin)
cholecystokinin (CCK): stimulates acinar cells to secrete digestive enzymes into the pancreatic duct
secretin: stimulates secretion of HCO3- into the pancreatic duct - also feeds back to inhibit acid secretion from parietal cells
what does the liver produce and what is it needed for
the liver produces bile which is needed for the digestion of lipids
what does the gallbladder store via the common bile duct and what does this duct join to
the gallbladder stores, concentrates and regulates the release of bile via the common bile duct
the common bile duct joins the main pancreatic duct and secretes product into the duodenum
what are other functions of the liver other than producing bile
- metabolism of nutrients
- detoxification/metabolism of drugs
- prep of waste products for excretion
what do cholecystokinin and secretin trigger
the contraction of the gallbladder
what do the presence of bile salts in the small intestine trigger
more bile release (positive feedback) - bile secretion continues until the duodenum empties
outline mechanical digestion
- mouth (chewing)
- stomach (mixing and churning)
- small intestine (segmentation)
outline chemical digestion
- digestive enzymes break chemical bonds through a hydrolytic reaction
- occurs in the mouth, stomach and small intestine (extent varies and depends on the nutrient)
outline the process of carb digestion
mouth: salivary amylase begins small amounts of digestion of polysaccharide chains into oligosaccharides
stomach: NO chemical digestion of carbs here
small intestine: pancreatic amylase continues digestion of polysaccharide chains into oligosaccharides
brush border enzymes finish digestion of oligosaccharides into monosaccharides
- lactase (lactose -> glucose + galactose)
- maltase (maltose -> glucose)
- sucrase (sucrose -> glucose + fructose)
where does carbohydrate absorption take place
exclusively in the small intestine where it is converted into absorbable units such as glucose, galactose and fructose
REVIEW SLIDE 14 (MAR 12)
outline the steps of protein digestion
mouth: no chemical digestion of proteins here
stomach: pepsin initiates the digestion of proteins into smaller polypeptides, oligopeptides, and some amino acids
small intestine:
- pancreatic enzymes continue digestion of all peptides into di- and tri- peptides - trypsin, chymotrypsin, carboxypeptidase
- brush border enzymes finish digestion and di- and tri- peptides into free amino acids - dipeptidase and tripeptidase
where does protein absorption take place
exclusively in the small intestine where it is converted into absorbable units such as free amino acids
REVIEW SLIDE 16 (MAR 12)
what does fat (lipid) in our diet mainly come in the form of?
triglycerides with variable amounts of cholesterol and phospholipids
outline the steps of lipid digestion
mouth: NO chemical digestion of lipids here
stomach: mixing and churning breaks up the large lipid globules and gastric lipase initiates chemical digestion of lipids
small intestine:
- bile salts are secreted from the gallbladder and coat lipid droplets - forms an emulsion
- pancreatic lipase chemically digests the lipids into monoglycerides and fatty acids - contained in micelles
- micelles contain a mix of fatty acids, cholesterol and any fat-soluble vitamins that were present in the meal (vitamin A, D, E, K)
REVIEW SLIDE 18 (MAR 12)
what happens during lipid absorption
chylomicrons contain the triglycerides, cholesterol, phospholipids and lipid-binding proteins (apoproteins)
lacteal drains into larger lymphatic vessels and then eventually into thoracic duct to join the circulation
where are most nutrients absorbed and then taken
most nutrients are absorbed from the small intestine and taken to the liver for initial processing
- capillaries of the GI tract pick up absorbed nutrients
- capillaries of the hepatic portal system present nutrients to the liver
**fats enter the lymphatic system and do not travel directly to the liver
what are the 3 divisions of the large intestine
- cecum
- colon
- ascending -> transverse -> descending -> sigmoid - rectum -> anal canal
what are the main functions of the large intestine
- absorption of water, electrolytes, and some vitamins
- secretion (mainly mucus)
- propulsion and defecation of waste
- houses many important bacteria
what is the function of bacteria in the large intestine
- produce vitamin K
- metabolize undigested materials
- deter growth of harmful bacteria
- stimulate the immune system
REVIEW SLIDE 22 (MAR 12)
