GI Physiology - Digestion and Absorption (Dr. Sun)

The epithelial cells lining the intestine (___________) express enzymes that facilitate the digestive process and transport nutrients out of the GI tract.

enterocytes

The bulk of digestion depends on pancreatic enzymes and the final aspects of digestion occur at the _________ membrane

plasma

Define the following:

Dissolving and breaking down process of food into small molecules that can be taken up by the body

Digestion

The main organ of digestion and absorption:

small intestine

The three fundamental processes that take place in digestion are:

- secretion

- absorption

- motility

Define the following:

Delivery of enzymes, mucus, ions into the digestive tract, and hormones into blood

secretion

Define the following:

Transport of water, ions and nutrients from the digestive tract, across the epithelium and into the body

absorption

Define the following:

Contractions of smooth muscle in the wall of the tube that crush, mix, and propel its contents

Motility

hormonal messengers stimulate the pancreas to release _______________

pancreatic juice

hormonal messengers stimulate the gallbladder to release __________ from the liver

bile

_________ emulsifies fats and pancreatic enzymes digest them

Bile

About __ liters of fluid pass through the GI system each day

9

how much fluid is added to the body from food and water?

2000 mL

how much fluid is added to the GI tract from secretions (exocrine glands, the salivary glands, the pancreas and the liver and epithelial cells)?

7000 mL

how much fluid is eliminated each day in stool?

100 mL

the small intestine reabsorbs ___ liters

8

large intestine reabsorbs ____ of that last liter

90%

absorption of water occurs via _______ through cell wall into vascular capillaries

osmosis

_____________ have apical cell membrane bound peptidases (cleave peptides to amino acids) and disaccharidases (cleave disaccharides to glucose) so they can be transported into the cell

enterocytes

_____________ are projections into the lumen covered predominantly with mature, absorptive enterocytes, along with occasional mucus-secreting goblet cells. These cells live only for a few days, die and are shed into the lumen

villi

_____________ are invaginations of the epithelium between the villi, and are lined largely with younger epithelial cells

crypts

Which small intestine epithelial cell absorbs:

- amino acids

- glucose

- monoglycerides

- membrane enzymes

enterocyte

Which small intestine epithelial cell is associated with

mucin

goblet cell

Which small intestine epithelial cell is associated with

gastrin, CCK, secretin

enteric endocrine cell

Which small intestine epithelial cell is associated with

cell renewal

stem/progenitor cell

Which small intestine epithelial cell is lysozyme associated with?

paneth cell

what intestinal feature increases surface area 1x fold?

cylinder shape

what intestinal feature increases surface area 3x fold?

intestinal folds

what intestinal feature increases surface area 10x fold?

villi

what intestinal feature increases surface area 20x fold?

microvilli

What are the 3 major mechanisms employed by the small intestine to increase surface area?

- intestinal folds

- villi

- microvilli

This short first section of the small intestine is where partially digested food from the stomach (chyme) is mixed with bile and pancreatic enzymes

duodenum

The middle section of the small intestine. Here the chyme undergoes the largest amount of digestion with significant amount of nutrient absorption

jejunum

This last section is the longest part of your small intestine. It is where large amounts of nutrients are absorbed before emptying into the large intestine.

ileum

____________ is mainly involved with the absorption of water and salts from the material that has not been digested.Most digestion and nutrient absorption has already taken place

colon

carbohydrates are 1st digested in the _____

mouth

T/F: Iron, vitamin B12, and bile acids have specific absorption areas where transporter mechanisms are expressed to facilitate absorption

true

Where is there a high absorption of bile salts?

Proximal ileum

what vitamin is needed for RBCs to form and grow?

vitamin B12

Intrinsic factor binds to B12 in the duodenum escorts it to the _____ where the complex binds to its receptor allowing vitamin B12 to be absorbed into portal blood

distal ileum

T/F: The digestive system is set up to maximize absorption; there is no regulation in the amount of substances absorbed into the body.

True

Define the following:

The random motion of particles from a higher to lower concentration.

Diffusion

Define the following:

Needs specific protein channels for the particles to go through. These particles are moving down their electrochemical gradient.

Facilitated diffusion

what enzyme begin digestion of carbohydrates in the mouth?

amylase

carbohydrates are digested into _____

disaccharides

disaccharides are digested into simple sugars (monosaccharides) by ______

disaccharidases

lactose is what type of sugar?

disaccharide

sucrose is what type of sugar?

disaccharide

maltose is what type of sugar?

disaccharide

glucose is what type of sugar?

simple sugar

fructose is what type of sugar?

simple sugar

galactose is what type of sugar?

simple sugar

What is the most abundant monosaccharide?

Glucose

Sugars are absorbed in the ______ and carried to the liver

capillaries

which sugars require Na+ co-transportation into the cell during absorption?

glucose and lactose

which sugars require non Na+ dependent transporter into the cell during absorption?

fructose

trypsinogens cleavage to trypsin by _______, which allows them to activate all pancreatic proteases

entrokinase

__________ cleaves a peptide bond at basic amino acids

trypsin

__________ leaves a peptide bond at aromatic amino acids

chymotrypsin

__________ cleaves a peptide bond at glycine, alanine, or serine

elastase

__________ cleaves a peptide bond at the carboxy-terminal (C-terminal) end of a protein or peptide

carboxypeptidase

__________ provide the small peptides that are cleaved to amino acids by membrane bound peptidases

pancreatic enzymes

What type of transporters transport most amino acids into the enterocytes?

Na+ dependent co-transporters

The ________ enable the fatty acids and cholesterol to come in contact with the brush border, where they easily cross the fat-soluble cell membrane

micelles

triglycerides must be broken down into _______ to be transported across the cell via micelles

monoglycerides

The triglycerides enter the smooth endoplasmic reticulum where they are repackaged into ________ that are made-up of proteins and lipids

chylomicrons

Chylomicrons contain many of the components found in micelle except for _________

bile acids

Chylomicrons are secreted from the cell by exocytosis into the _______

lymphatics

In the absence of bile salts very few fatty acids make it through this layer and much of the fat will pass through the gut undigested and unabsorbed causing ___________

steatorrhea (fatty stool).

Fats are digested by Lipases which hydrolyze the glycerol-fatty acid bonds. Of particular importance in fat digestion and absorption are _____________ which emulsify the fats allowing for their solution as micelles in chyme, and _____________ the surface area on which the pancreatic lipases can operate

bile salts, increasing

Where are lipases found?

- Mouth

- Stomach

- Pancreas

About how many mL of fluid leave the small intestine and enter the colon each day?

1500mL

t/f: the surface area of the colon is 2000x smaller than the total surface area of small intestine

true

Of all the digestive enzymes, which kind of proteases need to be activated?

stomach and pancreatic proteases

Micelles are able to effectively allow the fats to act like water soluble particles and penetrate the unstirred layer adjacent to the small intestinal epithelium and be absorbed due to its ___________

Hydrophilicity

Amino acids and simple sugars are absorbed through ___________ or transporters while fatty acids and glycerol are absorbed ___________

membrane channels, directly