ASCI 220 Exam 2 Study Guide: Key Concepts and Definitions

parts of human GIT

esophagus, liver, gallbladder, pancreas, stomach, small intestine, large intestine, cecum, rectum

GIT Absorptions & Secretions

large intestine is composed of

cecum, COLON, (rectum)

accessory organs

pancreas, liver, gallbladder

(connect at duodenum)

accessory organs provide __________

secretions

an animal's GIT is reflective of what?

the diet that the animal lives on

the macronutrients of the diets of animals include:

1. proteins

2. lipids

3. CHOs

which macronutrient largely determines the structure of the GIT?

CHO (ex. large cecums in herbivores)

non-structural CHO example

starch

structural CHO example

cellulose

digestibility of proteins

generally easily digestible by animal's enzymes

peptides are formed by

amino acids

what 2 enzymes cleave peptide bonds?

proteases and peptidases

proteins are broken down into peptides by which enzyme

protease

peptides are broken down into AAs by which enzyme

peptidase

digestibility of lipids

generally easily digestible by animal's enzymes

what cleaves ester bonds?

lipase

difference between triglyceride and monoglyceride

triglycerides are 3 fatty acids attached to a glycerol

monoglycerides are 1 fatty acid attached to a glycerol

which enzyme breaks triglycerides down into monoglycerides

lipase

starch

a polymer of a-1,4 glucose molecule

easily digested by an animal's enzymes

which enzyme digests starch into smaller molecules?

amylase

cellulose is an example of a ________

fiber

cellulose is a polymer of...

b-1,4 glucose molecules

digestibility of cellulose

not digestible by animal's enzymes, requires microbial fermentation

why do fermentation chambers of animals GIT arise?

cellulose is not digestible and requires microbial fermentation

speed of fiber digestion

SLOW

animals with what type of diet consume cellulose?

herbivores and some omnivores

cellulose is broken down into smaller molecules by...

cellulolytic bacteria

- cellulase

starch: 1-4 linkage of a glucose monomers

vs

cellulose: 1-4 linkage of B glucose monomers

summarize the differences, and explain the reasons why those differences exist, between the GIT of a carnivore and a herbivore

form fits the function

carnivore

- consumes less CHO

- no need for a sizeable large intestine because consumes less cellulose

herbivore

- consumes more CHO (fiber and cellulose) through plants

- has large microbial fermentation section to digest cellulose

which diet classification of animals is fibrous?

herbivores

pre-gastric fermenters

type of herbivore that conducts fermentation BEFORE gastric digestion

(eg. ruminants)

which diet classification of animals is starchy?

omnivores

post-gastric fermenters

type of herbivore that conducts fermentation AFTER gastric digestion

(eg. horses, rabbits)

size of CHO fermentation chamber in omnivores

omnivores do NOT need a big CHO fermentation chamber

omnivores mainly consume which type of macromolecules?

protein and TG

gastric

- "stomach"

- NO ABSORPTION

- acid (HCl) and pepsin digestion

- protein digestion

- low pH

pre-gastric fermenters have an (aerobic/anaerobic) microbial fermentation chamber

ANAEROBIC

aerobic

requires oxygen

anaerobic

without oxygen

the 4 chambered stomach parts

1. rumen (largest)

2. reticulum

3. omasum

4. abomasum (true stomach)

low fiber diet means a relatively small _____ _________

large intestine

true or false: we would expect the stomach to have a morphology supporting extensive surface area

FALSE

- because there is NO absorption in the stomach

primary interest of gastric digestion: gross anatomy

gastric pit

secretions enter the duodenum from where

pancreas, gallbladder, and liver

gastric digestion: gastric pits sequence

1. chief cell

2. HCl from parietal cell aids in turning pepsinogen to pepsin

3. back to HCl into pepsin

what does the inactive zymogen pepsinogen have that the active enzyme pepsin lacks?

there is a masking sequence that is dropped when pepsinogen becomes pepsin, and this exposes an active site on pepsin

why don't we want pepsin in the gastric pit?

we dont want to digest our own stomach

three stages of gastric digestion

1. physical (mechanical) digestion

- squeezing and mixing

- NOT cleaving bonds

2. chemical digestion

- HCl (also kills many bacteria)

3. enzymatic digestion

- pepsin (proteins → polypeptides)

*NO fat or CHO digestion

*NO absorption

digestion sequence

true or false: we would expect the small intestine to have a morphology supporting extensive surface area

TRUE

- because extensive nutrient absorption in the SI

small intestinal digestion is initiated by enzymes originating from the __________

pancreas

- in luminal phase of digestion

- enzymes: protease, lipids, starches

key aspect of small intestinal morphology

nutrient absorption

3 main parts of small intestinal morphology

mucosal folds, villi, microvilli (brush border)

enterocyte

absorptive cell of the small intestine

microvilli

- location

- relation to digestion and absorption

projections that confer surface area of enterocyte

- mucosal phase of digestion and absorption

brush border

composed of microvilli that greatly increase the surface area

mucosal region is made up of ___________

enterocytes

intestinal villi are (projections/indentations)

projections into the lumen

intestinal crypts are (projections/indentations)

indentations

what is absorbed from the large intestine?

water and VFA

(1) luminal phase of intestinal enzymatic digestion

- pancreatic enzymes begin hydrolysis in the 'bulk phase' of the digesta

- pancreatic enzymes and bile (ONLY lipids- TGs) are active

- digestion, but NOT absorption

(2) mucosal (brush border) phase of intestinal enzymatic digestion

end-products of pancreatic digestion are often substrates for brush border enzymes; these end-products are then absorbed

- true for proteins and starch

pancreatic enzymes in luminal phase (3)

proteases

protein digestion:

- polypetides (substrates) → smaller peptides (products)

amylase

starch digestion:

- starch → maltose (disaccharide)

lipase

lipid digestion:

- TG → FA + B-MG

liver function

- bile synthesis

- many metobolic functions

gallbladder function

- bile storage and secretion

- role in fat emulsification

pancreas function

secretes enzymes and sodium bicarbonate (NaCHO3)

maltase

- intestinal enzyme

- never moves

- involved with proteins

glucose transporter

- cell membrane associated

- never moves

fat digestion sequence

1. emulsification (amphipathic)

2. hydrolysis

3. re-esterification

4. lymph → blood

amphipathic

having both a hydrophilic region and a hydrophobic region

emulsification

physical process of breaking up large fat globules into smaller globules, increasing surface area that enzymes use to digest fat

micelles

lipid molecules

what kind of diffusion and transport do micelles use?

- passive diffusion to absorb

- active transport

re-esterification

process of reattaching a fatty acid to glycerol that has lost a fatty acid

explain what happens when a fatty acid and a monoglyceride enter an enterocyte

chylomicrons are formed, then are transported to the lymph, then bypass the liver and enter the thoracic duct

Fat Digestion, Emulsification, & Absorption in SI

fat digestion

there is NO mucosal phase of fat digestion

- the end products (FA & MG) of luminal digestion are absorbed directly

- the FA & MG are then re-esterified into TG

the TG are then packaged into chylomicrons and enter the lymph

- chylomicrons are like lipoprotein particles

serosa

outermost layer of GI tract

mucosal phase is in the area of the _________

microvilli

which enzymes are active in the mucosal phase?

S.I. enzymes

in the mucosal phase, digestion and absorption are ____________.

expand.

coupled.

- maltose → glucose

- small peptides → AA, dipeptides...

- MG & free FA: no further digestion

only part of GIT where active S.I. enzymes (maltose, small peptides, MG, and FFA) are absorbed

mucosal phase

what is needed to absorb the S.I. enzymes active in the mucosal phase (maltose, small peptides, MG, and FFA)

transporters needed for absorption

- glucose or AA

why are transporters needed to absorb amino acids and sugars?

AA and glucose are very polar so they need active transport across the nonpolar region of the enterocyte cell membrane

small intestinal absorption at the villus

- absorbed AA and glucose directly into bloodstream

- absorbed FA and B-MG (which are now present as TG in chylomicrons) DO NOT - they enter the lymph system

- lipids enter the lymph as chylomicrons

size of chylomicrons

relatively huge

lacteal is another word for __________

lymph

how are FA and MG metabolized?

absorption

- passive diffusion and via transporters

intracellular metabolism

- re-esterification

- packaged into chylomicrons (lipoprotein particles)

two stages of large intestinal digestion

1. water absorption

(stool formation)

2. some fiber digestion

- cellulolytic microbes

- VFA produced and absorbed

major structural difference of small v large intestines

the large intestine has no villi

why are there lots of goblet cells in the colon?

they secrete mucin (mucus) to make surfaces slippery (lubricant)

digestion by microbial fermentation in L.I.

- bacterial fiber digestion

- production and absorption of VFA

absorption of water in L.I.

- the digesta becomes drier

- secretion of mucus from goblet cells, making digesta slippery

cecum

- blind pouch

- small in humans

colon

- water re-absorption

- leads to the rectum and outside the body

rectum

storage and removal of feces

the absorption of amino acids, fatty acids, and glucose into the bloodstream occurs in the...

small intestine

what makes up the fore-stomach in ruminants?

rumen, reticulum, omasum

what is the true stomach?

abomasum