BIO 222 Lecture7.DigestiveSystem.Digestion&Absorption Review

BIO 222 Anatomy & Physiology 2

In mouth.

In stomach.

In small intestine (recall digested material is chyme at this point).

digestion

In mouth.

(Starch) Polysaccharides → oligosaccharides [di-s, tri-s].

salivary amylase

Very little action by salivary amylase (HCl usually inactivates it)

in stomach

In small intestine

pancreatic amylase

lactase

maltase

sucrase

Remaining polysaccharides → oligosaccharides.

**No effect on cellulose**.

pancreatic amylase

(Brush border enzymes) complete the digestion.

**The digestive system absorbs the monosaccharides & sends them to the bloodstream**.

lactase

maltase

sucrase

Dissaccharide → monosaccharides (glucose & galactose)

lactase

Disaccharide → monosaccharides (glucose)

maltase

Disaccharide → monosaccharides (glucose, fructose)

sucrase

Remaining oligosaccharides from amylase activity → monosaccharides

dextrinase

Glucose and galactose absorbed via

Na⁺/glucose transporter

Fructose absorbed via

facilitated diffusion

Hepatocytes convert galactose & fructose to

glucose

Glucose used for:

cell respiration

glycogenesis

lipogenesis

amino acid synthesis

~50% of glucose in a meal used for ATP

cell respiration

Glucose converted into glycogen.

Glycogen.

Stored in liver & skeletal muscle if not immediately needed for cell respiration.

Can store ~500g (most in skeletal muscle).

~10% of glucose in a meal stored as glycogen.

glycogenesis

Polysaccharide; storage form of carbohydrate in human body

glycogen

Glucose (& some aas) converted into fatty acids to make triglycerides.

~40% converted to triglycerides.

lipogenesis

11 of the 20 amino acids can be synthesized in the human body (Considered “non-essential”).

9 of the 11 can be made from glucose.

The aa’s are used to make proteins.

amino acid synthesis

Protein → smaller polypeptides, oligopeptides, (pepsin responsible for ~10% of protein digestion)

pepsin

Brush border enzymes.

Pancreatic enzymes (released as inactive precursors).

digestion of proteins in small intestine

Brush border enzymes.

(Aminopeptidase & dipeptidase): peptides → aa’s.

peptidases

Pancreatic enzymes (released as inactive precursors)

trypsin

chymotrypsin

carboxypeptidase

elastase

Trypsinogen becomes

trypsin

catalyzes the activation of the other inactive pancreatic enzyme precursors

trypsin

proteins → small peptides & aa’s

chymotrypsin

carboxypeptidase

elastase

Proelastase becomes

elastase

Procarboxy-peptidase becomes

carbaxy-peptidase

Chymotrypsinogen becomes

chymotrypsin

Transport from lumen into enterocyte.

Transport from cell to ECF.

aa’s then go to liver for processing.

absorption of proteins

Transport from lumen into enterocyte.

Transported via a cotransporter or actively by themselves.

Within cell, the oligopeptides are broken down in to aa’s.

oligopeptides

aa’s

Transport from cell to ECF

aa’s cross via facilitated diffusion

The amine group converted into ammonia and the ammonia to

urea

nucleic acids → nucleotides

pancreatic nucleases

Brush border enzymes

nucleosidases

phosphatases

Break apart the nucleotide

nucleosidases

Break apart the nucleotide

phosphatases

Absorbed via primary & secondary active transport mechanisms into the enterocytes.

Ultimately transported to liver for metabolism.

absorption of nucleic acids

Majority of ingested lipids

triglycerides

glycerol + 3 fatty acids

triglyceride

Mouth.

Acts on triglycerides (once it hits the stomach).

lingual lipase

Stomach

churning

gastric lipase

Breaks up globules

churning

Acts on triglycerides

gastric lipase

Small Intestine (most of the digestion occurs here)

bile salts
pancreatic lipase
micelles

Emulsification = break apart the globules into smaller pieces.

The bile salts do not chemically digest.

bile salts

Acts on triglycerides

pancreatic lipase

After lipase action ....Bile salts + digested lipids (monoglycerides + free fatty acids).

Escort the lipids to the enterocyte.

micelles

The lipid components diffuse across membrane

simple diffusion

Lipids are reassembled & packaged into.

A type of lipoprotein.

chylomicrons

Salivary amylase.

Pancreatic amylase.

Maltase, sucrase, lactase, dextrinase (aka dissacharidases).

carbohydrates

Pepsin (precursor = pepsinogen).

Trypsin.

Chymotrypsin.

Carboxypeptidase.

Peptidases.

proteins

Gastric lipase.

Pancreatic lipase.

lipids

Nucleases (ribonuclease & deoxyribonuclease phosphateses.

nucleic acids

Water enters small intestine each day (via ingestion or secretion).

Absorption occurs by OSMOSIS.

Idea behind laxatives.

absorption of water

Put excess solute in the lumen = less water in lumen = water doesn’t diffuse out of lumen = softer feces

laxatives

Mg⁺, Iron, Phosphate

active transport mechanisms

Most absorbed in small intestine by diffusion.

Vitamin B-12.

water-soluble vitamins

Requires help of intrinsic factor to cross (active transport).

aka gastric intrinsic factor (GIF).

A glycoprotein produced by the parietal cells of the stomach.

vitamin B-12

Packaged into micelles w/ glycerides and absorbed with them by diffusion.

Examples: Vitamin A, D, E, and K.

fat-soluble vitamins