Exam 4 - Digestive System 4 Flashcards
Where does nearly all chemical digestion and nutrient absorption occur?
in small intestine
Small intestine must have…
- large surface area exposed to chyme
It is the longest part of digestive tract
“small” refers to diameter not length
Location of small intestine
retroperitoneal along w/ pancreas (posterior to stomach)
Jejunum
- found primarily in “umbilical region”
- MOST DIGESTION AND NUTRIENT ABSORPTION OCCURS HERE
Ileum
Has PEYER’S PATCHES - clusters of lymphatic nodules
- ends at ileocecal junction w/ large intestine
- HAS SPHINCTER KNOWN AS THE ILEOCECAL VALVE THAT REGULATES THE PASSAGE OF FOOD RESIDUE INTO THE LARGE INTESTINE (division from small intestine and large intestine)
What doe the jejunum and ileum have in common?
they are both intraperitoneal - are covered w/ serosa
Circular folds
involve only mucosa and submucosa (SLOWS CHYME AND PROMOTES MIXING AND ABSORPTION)
Villi
- most nutrients absorbed by blood CAPILLARY
- most fat absorbed by LACTEAL
Microvilli
- is the “brush border” on cells
- BRUSH BORDER ENZYMES USED FOR FINAL STAGES OF DIGESTION
Crypts
pores opening between villi (inverse villi that go into the mucosa)
What are crypts comprised of?
Goblet cells (secrete mucus) Paneth cells (provide antibacterial secretions such as lysozyme, phospholipase, and defensins) Absorptive cells
cover it
destroy the bad stuff
absorb what’s left
Submucosa
(underneath the muscularis layer)
BRUNNER’S (duodenal) GLANDS in submucosa SECRETE BICARBONATE MUCUS
Peyer Patches
populations of lymphocytes to fight pathogens (not absorptive since it’s in the submucosa)
Segmentation
purpose is to MIX AND CHURN, not to move material along
Peristalsis
gradual MOVEMENT of contents towards colon
Chemical digestion of carbohydrates summary (what we’ve done so far)
mouth - salivary amylase
esophagus and stomach - N/A (pH is too low_
duodenum - pancreatic amylase
What acts on DISACCHARIDES to make them monosaccharides?
brush border enzymes:
Maltase
Lactase
Sucrase
Lactose intolerance
exists when lactase is ABSENT and bacteria ferment undigested sugar; leads to excessive intestinal gas and diarrhea
What should you tell someone who has had a diarrhea episode?
Tell them to avoid dairy until the gut has healed itself; BRAT diet, bananas, rice, apple sauce, toast
What is in cotransport w/ Na?
SODIUM-GLUCOSE TRANSPORT PROTEINS (SGLT) in membrane help absorb GLUCOSE and GALACTOSE
How is FRUCTOSE absorbed?
by FACILITATED DIFFUSION then converted to glucose inside the cell
Digestion of proteins in the stomach
- HCl denatures or unfolds proteins
- pepsin turns proteins into peptides
Digestion of proteins in the small intestine
Trypsin and Chymotrypsin “take over” protein digestion by breaking polypeptides into OLIGOPEPTIDES (small chunks)
What breaks down oligopeptides one amino acid at a time?
Carboxypeptidase
Aminopeptidase
Dipeptidase
from pancreas; removes amino acids from -COOH end
Carboxypeptidase
from brush border; removes amino acids from -NH2 end
Aminopeptidase
from brush border; splits dipeptides in middle
Dipeptidase
Absorption of proteins
amino acid cotransporters (active transport w/ Na or H ions / symporters) move into epithelial cells and facilitated diffusion moves amino acids out into blood stream
How do infants absorb proteins?
by pinocytosis; which allows for absorption of protective maternal IgA (allows for passive immunity)
Why do lipids have more complex digestion and absorption?
because they’re hydrophobic
What increase surface area of exposure for lipases?
Lecithin and bile salts (emulsification droplets)
Types of lipases
- lingual lipase activated by stomach acid
- pancreatic lipase
Fat hydrolysis
emulsification droplets acted upon by pancreatic lipase, which hydrolyzes the 1st and 3rd fatty acids from triglycerides, usually leaving the middle fatty acid
role of Micelles
micelles in the bile pass to the small intestine and pick up several types of dietary and semidigested lipids
Important note about micelles
micelles start in the bile as ONLY collection of bile acids; they ACQUIRE the lipid core later as they travel down the intestine
What are micelles?
minute droplets of bile that wrap above products
first step of lipid absorption
lipids move to surface of intestinal absorptive cells where they leave the micelles and diffuse into cells
Chylomicron
within the intestinal cells triglycerides are reformed and covered w/ cholesterol “coat” and protein; chylomicron is moved into secretory vesicles and released into core of villus
What takes up chylomicrons?
chylomicrons are generally too big to enter capillaries so they are taken up by LYMPHATIC LACTEAL
Where do chylomicrons travel from lacteal?
they travel in lymph system through CISTERNA CHYLI and THORACIC DUCT into LEFT SUBCLAVIAN VEIN
Percentage of cholesterol in our bodies
15% - ingested
85% - manufactured in LIVER and INTESTINAL MUCOSA
Extremely low density; enter lymph
Chylomicrons
FORM IN WHICH LIPIDS LEAVE THE LIVER; converted to LDL
VLDL
Where do triglycerides removed from VLDL go to?
stored in adipose cells
TRANPORTS CHOLESTEROL TO CELLS
LDL; cells have LDL receptors; # of LDL receptors become less once cell’s lipid/cholesterol needs are met (if you have excess it will deposit in other areas of the body)
TRANSPORTS EXCESS CHOLESTEROL FROM CELLS TO LIVER
HDL; gets ride of cholesterol in the body, allows for excretion
