Digestive System

Overview

Motility and Mechanical Processing

Secretion & Digestion

Absorption

Elimination

Hormones

Vitamins & Minerals

Overview The whole goal of digestion

is to produce monomers (i.e. glucose) that can be used in cellular respiration.

Gastrointestinal (GI) tract is a hollow tube with accessory organs.

Lumen = inside of the tube. It is still considered outside of the body.

Overview

5 basic tasks:1. Mechanical processing

and motility

2. Secretion

3. Digestion

4. Absorption

5. Elimination

Overview

5 accessory glands:1. Wall of the GI tract

2. Salivary Glands

3. Liver

4. Gall Bladder

5. Pancreas

Overview 4 layers of the

digestive tract:1. Mucosa2. Submucosa3. Smooth muscle4. Serosa

Sphincters control rate of flow and prevent backflow.

Motility and Mechanical Processing Motility (mvmt)

Peristalsis = wavelike contractions that move food

Segmentation = slower mixing in the small intestine that allows for increased absorption

Motility and Mechanical Processing

The breakdown of food into smaller pieces by mashing and mixing.

2 main locations:Mouth:

32 teeth and tongue form a bolusSwallowing is both voluntary and involuntary

Stomach:Mixes food with chemicals ultimately making chyme.

Secretion and Digestion

Each organic macromolecule is broken down by different enzymes at different locations in the digestive system.

Often many enzymes are involved in the breakdown of one molecule.

These enzymes operate within a narrow pH range.

Secretion and Digestion Carbohydrate Digestion:

Starts in the mouth when salivary amylase, produced by the salivary glands, breaks down polysaccharides into oligosaccharides and disaccharides.

Then in the sm intestine pancreatic amylase, produced by the pancreas, breaks down polysaccharides into disaccharides and monosaccharides

Finally disaccharidases from the intestinal lining finish the breakdown into monosaccharides.

Secretion and Digestion Protein Digestion:

Starts in the stomach with pepsin & HCl being produced by the stomach lining. This breaks the proteins into protein fragments.

Trypsin and chymotrypsin are produced by the pancreas and continue the breakdown of proteins into fragments in the sm intestine.

Also produced by the pancreas, carboxypeptidase also works in the sm intestine but it breaks proteins further into amino acids.

Aminopeptidase, although produced by the intestinal lining plays the same role as carboxypeptidase.

Secretion and Digestion

Fat (Lipid) Digestion: Digestion of fat does not begin until the sm intestine

where the liver is pumping in bile. Bile can be stored in the gall bladder when not in use and it emulsifies fat so that it does not glob up.

Lipase is a pancreatic enzyme that is released into the sm intestine that finishes the breakdown of fats into fatty acids and glycerol molecules.

Secretion and Digestion

Nucleic Acid Digestion: Begins in the sm intestine where pancreatic nucleases

and intestinal nucleases break the DNA & RNA into nucleotides and ultimately into the bases and monosaccharides that make them up.

Absorption Almost all absorption

occurs in the sm intestine.

Villi Microvilli Substances are

absorbed by active transport, osmosis, and diffusion.

Elimination Large intestine (aka colon)

= absorbs essential salts

and remaining water Cecum (including the

appendix) 4 parts Feces = undigested/

unabsorbed food, water, and bacteria

Rectum

Hormones Many hormones dictate

when and how food is digested.

Ex) gastrin increases HCl production when aa.s are detected in the stomach.

Ex) cholecystokinin (CCK) increases pancreas secretions and gall bladder contraction.

Hormones Ex) secretin causes

increased bicarbonate production

Ex) glucose insulinotropic peptide (GIP) triggers release of insulin by the pancreas.

View 41Bin Campbell simulation

Vitamins & Minerals Vitamins = organic substances essential for growth and

survival. Ex) vit-D = bone growth; enhances Ca absorption Ex) vit-C = antioxidant; collagen synthesis; etc.

Minerals = inorganic substances also essential for growth and survival Ex) Ca = bone formation; neural and muscle action Ex) Fe = hemoglobin; ETC Ex) K & Na = muscle and neural function

Shortages or excesses of vitamins and minerals can have adverse effects.