15 - GI: Intestines Flashcards
Divisions of the intestines
small intestine:
- duodenum
- jejunum
- ileum
large intestine:
- caecum
- colon (4 subsections)
- rectum
- anal canal
Colon subsections
- ascending (R)
- transverse (horizontal)
- descending (L)
- sigmoid (L)
Blood supply to intestines
quiz with GN
compare to GN
- celiac:
- duodenum
- superior mesenteric:
- most of small intestine
- proximal 1/3 of large intestine
- inferior mesenteric:
- distal 2/3 of large intestine
opposite drainage proportions from veins
Venous drainage of intestines
quiz with GN diagram (in L14 notes)
compare to diagram
- superior mesenteric:
- small intestine
- proximal 2/3 of large intestine
- inferior mesenteric:
- distal 1/3 of large intestine
opposite drainage proportions from arteries
Layers of small intestine
how it differs from the general layers of the GI tract (GN)
Mucosa: increase surface area
- plicae circularis
- villi
- microvilli
- simple columnar epithelium
no other changes
Villus histology
key differentiating features
- many capillaries
- lacteals (special lymphatic vessels)
what is absorbed in lacteals?
chylomicrons
(breakdown products of fats combined with proteins)
Features of the duodenum
comparisons GN
name: duode- 12”
nutrient absorption: major site of Ca2+ and Fe absorption
plicae circularis: most dense
lumen: largest of the small intestines
- submucosal/brunner’s glands in first 10cm
- hepatopancreatic ampulla connects at 10cm
Brunner’s Glands role
secretes bicarb-rich mucus in the first 10cm of the duodenum
(stops at hepatopancreatic duct because pancreas will provide bicarb-rich mucus from there)
submucosal glands
Features of the jejunum
comparisons GN
name: means ‘empty’
nutrient absorption: glucose, amino acids, water
plicae circularis: prominent (less than duodenum)
lumen: smaller than duodenum
- 40% of small intestine
- long vasa recta
Features of the ileum
comparisons GN
name: means ‘twisted’
nutrient absorption: Vitamin B12 and fats
plicae circularis: fewest, less pronounced
lumen: smallest of small intestine
-
Payer’s patches (lymphoid nodules)
- protect against bacteria that leaks in from large I.
- most prominent lacteals
- ends at ileocaecal valve
- short vasa recta
Gastroileal reflex
stomach signals ileum to increase peristalsis and push food through the ileocaecal valve to the large intestine
Regulation of digestion in intestines
neural & hormonal GN
- cephalic & gastric
- vagus n.: release pancreatic juice
- chyme in duodenum
- enteroendocrine cells: release secretin & CCK
- hormones reach pancreas
- CCK: enzyme rich secretions
- secretin: bicarbonate rich secretions
Intestinal contraction patterns
GN
Fed pattern (segmentation):
- mass of food enters intestine
- irregular, random contractions mix food with juices
Fasting pattern (!MMC):
- peristalsis begins at duodenum
- propels residual material into colon
- helps prevent bacterial growth
!migrating motor complex
Carbohydrate Digestion
GN
enzyme source locations are most important
Enzymes from:
- salivary glands (parotid & submandibular)
- pancreas
- intenstinal absorbative cells
breaks into:
- starch & disaccharides
- disaccharides & oligosaccharides
- lactose, maltose, sucrose
- galactose, glucose, fructose
end products in italic
Fat Digestion
GN
Protein Digestion
GN
Enzymes from:
- stomach
- pancreas
- intenstinal absorbative cells
breaks into:
- large polypeptides
- small polypeptides & peptides
- amino acids
Nucleic acids: digestive enzymes
GN
Enzymes from:
- pancreas
- intenstinal absorbative cells
breaks into:
- pentose sugars, N-containing bases, phosphate ions
Pancreatic proteases
names, facts
releases inactive enzymes that digest proteins (so it doesn’t digest itself)
activated by trypsin
- trypsinogen
- membrane bound enteropeptidase reacts to produce
- trypsin
- chymotrypsinogen, precarboxypeptidase… activated by trypsin
Fat digestion
steps, mechanisms GN
Primarily in small intestines (mostly absorbed in ileum)
- fat globule
- duodenum: emulsified (physically broken down) by bile salts (from liver)
- digestion by lipase (from pancreas) to produce fatty acids and monoglycerides
- micelles formed from FA and MG and bile salts
- transported to intestinal mucosa
- FA and MG leave micelles, difuse into epithelial cells
- repackaged with proteins to form chylomicrons
- extruded by exocytosis and enter the lacteals (carried by lymph)
- …left thoracic duct to liver
Absorption in the small intestine
name of types
active transport: use ATP
secondary active transport: use ATP and another ion to facilitate
facilitated diffusion: through protein channel
diffusion: lipid soluble- through bilayer
all through absorptive intestinal epithelial cells
Absorption in small intestine
glucose, amino acids, fats
glucose: secondary active transport, facilitated diffusion, blood
- uses Na+ gradient, 2Na and glucose enter epithelial cell
amino acids: secondary (or not) active transport, diffusion, blood
- uses Na+ gradient, Na and AA enter epithelial cell
- will use active transport if necessary
short chain fatty acid: diffusion, diffusion, blood
long chain FA or monoglyceride: pathway on another card
Absorption in small intestine
vitamin absorption
fat soluble (vit A, D, E, K): absorbed via micelles
water soluble: diffusion, diffusion, blood
