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ap104
digestive system LARGE SMALL INTESTINE
32
Anatomy
Undergraduate 1
02/16/2021

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Term
stomach functions
Definition
-mixing chamber and holding reservoir
-continuation of starch digestion
-digestion of proteins and triglycerides
-bolus converted to liquid
-certain substances absorbed
Term
4 district regions of the stomach
Definition
1. mucosa
-simple columnar / lamina propria / mm muscosa / gastric glands (mucous neck, parietal, chief cells) / gastric juices (2000-3000ml/per day) / enteroendocrine (G cells)

2. submucosa: areolar connective tissue

3. muscularis: 3 layers of smooth mm / outer-longitudinal; middle-circular; inner-oblique

4.serosa: simple squamous epithelium (mesothelium) / areolar connective tissue / portion of visceral peritoneum
Term
how does mechanical digestion work
Definition
-peristaltic movements: mixing waves; creates chyme (liquid material)
- less movement; greater movement (fundus / body / pylorus / gastric emptying: 3 ml of chyme from pylorus into duodenum / remaining chyme returns into the body of the stomach-continued mixing
Term
how does chemical digestion work
Definition
-salivary amylase still effective if food that is not mixed with gastric acid remains in the fundus

-gastric (inactive salivary amylase / actives lingual lipase; digestion of triglycerides into FA and diglycerides)

-parietal cells: secretes H+ and Cl = HCI

-proton pumps (H+/K+ ATPase) transports H+ into lumen while K+ into cells / Cl and K+ diffuse out into the lumen through Cl and K+ channels in the apical membrane

-formation of H2CO3 (carbonic acid): carbonic anhydrase H20C02 / HCO3 exchanges for Cl

- HCI secretion can be stimulated by several sources: EACh release by Ps neurons / Gastrin secretion by G cells / histamine secretion by mast cells

-receptors for all 3 substances present in the plasma membrane of parietal cells

-pepsin-secreted by chief cells: only proteolytic enzyme in stomach / most effective in acidic environments (pH2) / inactive with higher pH

-Pepsinogen (inactive form in pH 5-6)

-gastric lipase: splits triglycerides into FA and MG / limited role/active in ph 5-6
Term
small intestine function and size
Definition
-function: digestion and absorption of nutrients
-size: diameter 2.5cm length 3m
Term
circular folds (plica circulares) location and significance
Definition
location: duodenum (proximal) - ileum (midpoint)

significance: enhance absorption
Term
villi location and significance
Definition
location: surrounding epithelium; core lamina propria

significance: contains arterioles, venues, capillaries, lacteals
increase SA of epithelium for absorption and digestion
Term
microvilli location and significance
Definition
location: brush border w/ enzymes extends into the lumen

significance: projections of absorbtive cells
Term
intestinal juice: amount per day / what it contains & function
Definition
-1-2L per day

-contains water and mucus - slightly alkaline

-function: provides medium to aid the absorption of chyme and works with pancreatic juices
Term
what is brush border enzymes & what types of enzymes does is contain
Definition
- its a the plasma membrane of absorptive cells

-4 carb digesting enzymes
-2 protein digesting enzymes
-2nucleotide digesting enzymes
Term
Small I mechanical digestion segmentation
Definition
Localized, mixing contractions

Mix chyme with digestive juices and allows it to contact with
the mucosa for absorption

Duodenum (12 times/min)

Ileum (8 times/min)
Term
Small I mechanical digestion migrating motility complex (MMC)
Definition
Slow peristalsis

Begins in stomach (lower portion)

Reaches ileum within 90-120 min
Term
Small I chemical digestion (what does it digest)
Definition
carbs / proteins / lipids / nucleic acids
Term
how are carbs digested in the Small I
Definition
Salivary amylase: inactive in stomach (acidic pH)

Pancreatic amylase: breaks down maltose, maltotriose, and
α-dextrins

No effect on cellulose

α-dextrinase (BBE)

Sucrase, lactase, maltase (BBE)

Digests the disaccharides into monosaccharides

Digestion of carbohydrates ends with the production of
monosaccharides
Term
how are proteins digested in the Small I
Definition
Pepsin

Pancreatic enzymes: trypsin, chymotrypsin,
carboxypeptidase, and elastase

Each splits peptide bonds bw different amino acids

Brush-border enzymes: Aminopeptidase and Dipeptidase

Each splits dipeptides into single amino acids
Term
how are lipids digested in the Small I
Definition
Lipases – enzymes that split triglycerides and
phospholipids

Lingual lipase, gastric lipase – digestion in stomach

Pancreatic lipase – digestion in small intestine

Emulsification – large lipid globule is broken down into
several small lipid globules

Bile salts are amphipathic – allows for emulsification of large
lipid globule
Term
how are nucleic acids digested in the Small I
Definition
Pancreatic juices

Ribonuclease: digests RNA

Deoxyribonuclease: digests DNA

Brush-border enzymes: Nucleosidases and phosphatase

Nucleotides digested into pentoses, phosphates, and
nitrogenous bases
Term
ratio of digestion Small/large I
Definition
small 90% large 10%
Term
Small I absorption (monosaccharides) process
Definition
Abundant levels of monosaccharide absorption

Most dietary carbohydrates digested are absorbed

120 grams/hr

Only cellulose and fibers are indigestible

Absorbed via facilitated diffusion or active transport from
the lumen through the apical membrane in absorptive cells

From absorptive cells --> capillaries of the villi
Term
how are nutrients absorbed
Definition
diffusion, facilitated diffusion, osmosis, and active
transport
Term
small I absorption (protein) process
Definition
½ of absorbed a.a found in food

½ of absorbed a.a found in body

95% of proteins present in small intestine is digested and
absorbed

Absorbed via active transport into absorptive cells

Duodenum and jejunum

From absorptive cells, aa go through simple diffusion into
capillaries of the villi
Term
small I absorption (lipids) process
Definition
95% of lipids in small intestine is digested/absorbed

Emulsification and digestion: triglycerides
Term
small I (electrolyte) absorption process
Definition
-from GI secretions of food
-Na+ reclaimed by active transport
-other ions also absorbed by active transport
Term
small I (vitamin) absorption process
Definition
-fat soluble vitamins (a,d,e,k): simple diffusion and transported with lipids in micelles
-most water soluble vitamins also absorbed by simple diffusion
Term
(water) absorption process
Definition
-9.3l comes from ingestion (2.3l) and Gi secretions (7l)
-absorbtion: SI: 8.3L LI:0.9L
all water absorption by osmosis
Term
large intestine size and function
Definition
size: diameter: 6.5cm length: 1.5 meters

completion of absorption, production. of certain vitamins, formation and expulsion of faces from the body
Term
what are the 4 major regions of the large intestine
Definition
-cecum

-colon

-rectum

-anal canal
Term
large intestine histology mucosa
Definition
1. Muscosa (Simple columnar epithelium)
-Absorptive cells: Water absorption
-Goblet cells: Secretes mucus – lubricates passageway
-Lamina propria (areolar connective tissue): Solitary lymphatic nodules
-Muscularis mucosae (smooth muscle)
-No structural adaptations that increase SA

2. Submucosa
-Areolar connective tissue

3. Muscularis
-Smooth muscle (longitudinal and circular)
-Teniae coli – 3 longitudinal bands
-Haustra – series of pouches formed by contractions of
the teniae coli

4. Serosa
-Omental (fatty) appendices (viseral peritoneum)
Term
what is gastroileal reflex
Definition
-passage of chyme from ileum to cecum
-ileocecal sphincter (gastrin-relaxant)
Term
large intestine mechanical digestion process
Definition
1. Gastroileal reflex
-Passage of chyme from ileum to cecum
-Ileocecal sphincter (gastrin – relaxant)

2. Hautral churning
-Haustra relaxed until filled (contraction starts)

3.Peristalsis
-Slow rate (3-12 contraction per min)

4. Mass Peristalsis
-Forces colon contacts (quickly) toward rectum
Term
large intestine chemical digestion process
Definition
1. Final Stage: Digestion through bacterial action

2. Occur in the colon

3. Mucus is secreted, but no enzymes

4. Fermentation of remaining carbohydrates
- Release H+, CO2, methane gases (flatulence)
- Produce Vitamin B and K

5. Absorption: water w/ ions and some vitamins

6. Feces: chyme remaining for 3-10 hrs
-Water, inorganic salts, epithelial cells from mucosa of GI, bacteria, unabsorbed digested materials, indigestible food
Term
process of the defecation reflex in large intestine
Definition
1. Emptying the rectum.

2. Distension in rectal wall / sensory nerve impulses to
sacral spinal cord / motor responses back to the colon
/ contractions in rectal muscles & voluntary
contractions of diaphragm and abdominal muscles /
opens anal sphincter.

3. Diarrhea
- Increase in frequency , volume, and fluid content

4. Constipation
- Infrequent or difficult defecation
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