Digestive System part 3

Question 1

what is the absorbable unit of carbs in the small intestine?

Answer 1

monosaccharides: glucose, fructose, galactose

Question 2

what is the absorbable unit of lipids in the small intestine?

Answer 2

free fatty acids, glycerol and monoglycerides

Question 3

what is the absorbable unit of proteins in the small intestine?

Answer 3

primarily single amino acids, dipeptides and tripeptides

Question 4

glucose and galactose absorption in the small intestine

Answer 4

• pass through apical surface by secondary active transport using Na+ conc. gradient
• glucose and galactose compete for the same protein channel
• cross basolateral surface by way of facilitated diffusion

Question 5

fructose absorption in the small intestine

Answer 5

passes through apical and basolateral surfaces via facilitated diffusion

Question 6

amino acid absorption in the small intestine

Answer 6

• pass through apical surface via active transport or secondary active transport with Na+
• pass through basolateral surface via simple diffusion

Question 7

dipeptide and tripeptide absorption in the small intestine

Answer 7

• pass through apical surface by way of secondary active transport with H+
• pass through basolateral surface via simple diffusion

Question 8

small short chain FAs (10-12C) absorption in the small intestine

Answer 8

• simply diffuse through apical and basolateral surfaces

Question 9

long chain fatty acids (>12C) and monoglycerides

Answer 9

• bile salts surround long chain FAs and form a micelle which picks up and drops off into other side of apical cell surface by simple diffusion
• TG are surrounded by chylomicrons (proteins that are too big to enter capillaries) so they enter the lymphatic system through a lacteal of a villus
• then travel through thoracic duct (central lymphatic vessel) to junction of left internal jugular and subclavian veins

Question 10

where do absorbed nutrients go once past basolateral surface of intestinal cells? (all nutrients but lipids)

Answer 10

they are taken up by a villus blood capillary
to hepatic portal vein
to the liver

Question 11

fluid ingested/secreted into GI system/day

Answer 11

9.3 L

Question 12

fluid absorbed by GI system/day

Answer 12

8.3 L

Question 13

fluid excreted in feces

Answer 13

100ml

Question 14

large intestine

Answer 14

1.5 m long, 6.5 cm wide
4 major regions
ascending and descending colon are retroperitoneal

Question 15

ileocecal sphincter

Answer 15

valve that controls movement of chyme into LI

Question 16

cecum

Answer 16

where SI opens into LI, like a pocket for contents from SI

Question 17

veriform appendix

Answer 17

• don’t know exact function, contains lymphatic tissue so thought to have some immune function
• also may aid in microbe formation: repopulation of env’t of colon after a change

Question 18

4 regions of the colon

Answer 18

from start to end:
ascending
transverse
descending
sigmoid

Question 19

sigmoid colon

Answer 19

S shaped, brings chyme back to midline region of the body

Question 20

right colic flexure

Answer 20

located just below liver

ascending colon turns to transverse colon

Question 21

left colic flexure

Answer 21

located just below spleen

transverse colon turns to descending colon

Question 22

omental appendices

Answer 22

small lipid filled pouches that attach to teniae coli

Question 23

rectum

Answer 23

15cm long
thicker muscle layer here than the rest of the GI tract
contains simple columnar epithelium

Question 24

anal canal

Answer 24

final 2-3 cm of GI tract
thickened muscle walls form sphincters
contains stratified squamous epithelium for protection

Question 25

internal vs external anal sphincters

Answer 25

internal: made of smooth muscle so involuntary external: skeletal muscle, allows it to be voluntary

Question 26

anal columns

Answer 26

folds in mucous membrane of anal canal where arteries and veins are found - hemorrhoids are a result of swollen, enlarged, or inflamed veins here

Question 27

types of cells found in large intestine (in glands)

Answer 27

absorptive cells | goblet cells

Question 28

absorptive cells in LI

Answer 28

take up water primarily, some ions, some cells have microvilli surface

Question 29

goblet cells in LI

Answer 29

secrete mucous, also help move chyme here

Question 30

muscular layer in LI

Answer 30

- internal circular layer found everywhere | - outer layer of thickened longitudinal muscle found in 3 bands known as the teniae coli

Question 31

teniae coli

Answer 31

when it contracts, it forms pockets called haustra | - it's always slightly contracted

Question 32

gastroileal reflex

Answer 32

when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make room

Question 33

haustral churning

Answer 33

hasutrum fills and once distended, contracts to move contents to the next haustrum -- fills cecum and initiates contraction from one haustrum to another

Question 34

peristaltic waves in LI

Answer 34

3-12 contractions/min | alternating circular and longitudinal muscle contractions

Question 35

mass peristalsis

Answer 35

in LI, strong peristaltic wave from transverse colon (initiated by gastrocolic reflex) pushes contents into rectum

Question 36

gastrocolic reflex

Answer 36

when stomach fills, mass peristalsis moves contents of transverse colon into rectum

Question 37

chemical digestion in LI

Answer 37

- no enzymes secreted, only mucous - bacteria ferment things - bacteria also produce vitamins K and B in colon which get absorbed with water and ions in LI

Question 38

what do bacteria ferment in LI

Answer 38

- undigested carbohydrates produce hydrogen, CO2, methane gases - digestion of AAs; indoles and skatoles give odor to feces - decomposition of bilirubin to stercobilin which makes feces brown

Question 39

feces

Answer 39

produced after 3-10 hours in LI from chyme when 90% of water is reabsorbed - composed of dead epithelial cells, metabolic byproducts, undigested food (ex. cellulose), bacteria (live and dead; makes up 30% of dry feces weight)

Question 40

defecation reflex

Answer 40

- gastrocolic reflex caused by filling of stomach moves feces into rectum which initiates defecation reflex - stretch receptors signal sacral spinal cord - parasympathetic nerves contract longitudinal muscles of descending/sigmoid colon, rectum and internal anal sphincters relax - external anal sphincter is voluntarily controlled

Question 41

phases of digestion

Answer 41

describe regulation of movement through GI system 1. cephalic phase 2. gastric phase 3. intestinal phase

Question 42

cephalic phase

Answer 42

preps mouth and stomach for food before or just as our food is eaten: preps mouth and stomach for food, initiated by sight, smell, thought and taste - neural centres use facial & glossopharyngeal nerves to stim. salivation and vagus nerve to stimulate gastric juice release in stomach

Question 43

gastric phase

Answer 43

once bolus reaches stomach causes an increase in both gastric secretion and motility - receives both neural (feedback loop via parasympathetic and ENS) and hormonal regulation (gastrin), promotes gastric emptying

Question 44

intestinal phase

Answer 44

once chyme enters SI, inhibits gastric emptying to promote digestion of our food - neural (feedback loop: enterogastric reflex) and hormonal regulation (secretions of secretin and cholecystokinin aka CCK)

Question 45

secretin

Answer 45

release is stimulated by acidic chyme entering SI - stim release of pancreatic juice and decreases gastric secretions - all in an effort to reduce acid coming into SI

Question 46

cholecystokinin (CCK)

Answer 46

release is stimulated by AA and fat in chyme entering SI - stm secretion of pancreatic juice, contraction of gallbladder to release bile and then relaxes hepatopancreatic ampulla so secretions can enter SI - decreases gastric emptying by contraction of pyloric sphincter - stimulates hypothalamus so the brain has feelings of satiety and we feel full