The chemical bond holding large food molecules together are broken down by specific enzymes. Generally polymers are reduced to their component monomers.

Proteins-->component amino acids

Carbohydrates-->simple sugars

Fats-->fatty acids

Nucleic acids (RNA, DNA)-->nucleotides

salivary glands

liver

gall bladder

pancreas

Carries out mechanical and chemical digestion.

Mechanical: Chewing

Chemical: Two enzymes

• Salivary Amylase starts breaking starches (long chains of glucose) into simple sugars.
• Lysozyme: Antibacterial function

1-1.5 Liters/day of saliva is secreted by the savitory glands, made up of 99% water.

Three Stages

1. Oral Phase: voluntary

2. Pharyngeal Phase: Food passes through the throat

3. Esophageal Phase: Peristaltic waves propel food to the stomach.

Regulates food entry in to the stomach.

If it doesn't close all the way, acid from the stomach can come up into the esophagus causing acid reflux, or heart burn.

Secretions of the stomach.

• HCl: Acidifies food to sterilizes it. Also, activate the digestive enzyme pepsin. pH of 1.5 or 2
• Pepsinogin: inactive form of the enzyme pepsinogen activated by low Ph in the stomach. Pepsin breaks down proteins.
• Mucus: further moistens food and protects the lining of the stomach from acid and pepsin.

• Cephalic Phase: Parasympathetic nerve stimulate gastric juice secretion, in response to the sight, smell, taste or thought of food.
• Gastric Phase: Food in stomach causes stretch receptors to stimulate gastrin secretion. Gastrin is a hormone that stimulates smooth muscle activity and gastric juice secretion. 
• Intestinal Phase: Once acid chyme enters the duodenum, the decreased Ph and the presence of protiens, carbs, and lipids triggers the release of hormones from the duodenum: Secretin, Cholecystokinin (CCK), and gastric inhibitory petide. All work to inhibit stomach activity

Hormones released from the duodenum (in response to the low pH and the presence of lipids, proteins and carbs) that inhibit stomach activity.

low pH-secretin

lipids/proteins-cck

fats/carbs-GIP

Secretin and CCK stimulate pancreatic and liver secretion.

GIP stimulates insulin secretion.

Assessory organ that produces and secrets two crucial substances

• Digestive Enzymes: For chemical digestion
• Alkaline solution (rich in bicarbonate): To neutalize high pH material that enters the small intestine.
• These secretions enter the Small Intestine through a duct. 

• Secretes bile (which is stored in the gall bladder).
• Bile emulsifies fats (making more surface area for the digestive enzymes to attack).
• Bile enters Small Intestine through a duct
• Nutrients in the GI tract are absorbed by the blood and the blood goes directly to the liver. Liver absorbs and stores the nutrents and vitamins and captures any toxins before the blood goes to the rest of the body. 

Also known as the Cecum (immune system outpost), Colon, and Rectum. Specialized in water absorbtion and waste elimination.

Most materials passing from the Small Intestine are indigestibles (wastes) and these wastes are concentrated and solidified into feces.

When feces enters the recutum, peristalsis encourages defecation.

Smooth muscles will voluntarily relax when feces enters the rectum, skeletal muscle is under voluntary control.

6 feet, 8 cm in diameter

Hypothalamus contains a feeding center that is always 'on,' telling the body to eat.

Also contains a satiety center which, when activated, inhibits the feeding center.

Glucostatic theory: Increase blood sugar causes increase in insulin, which activates satiety center

Ghrelin: Hormone secreted from the stomach and duodenum which inhibits satiety center.

Leptin: A hormone secreted into the blood by adipose cells that inhibits appetite.

Open wound caused by the erosion of the mucosa, and other tissue. Acid and pepsin chew through the layers of the stomach.

A bleeding ulcer is when it is so deep that you are bleeding into your stomach

A perforating ulcer is when the contents of the GI tract get out into the abdominal cavity and cause an infection.

Aspirin and Stress inhibit mucosa production.

Heliobacter pylori: bacteria that loves low pH of stomach and causes ulcers.

Lipases: break down lipids

Proteases: break down proteins (pepsin)

Carbohydrase: break down carbs

During prolonged excersize, your body may run out of glycerol so you have to break down triglycerides into glycerol and fatty acid.

the fatty acids go to the muscles

The glycerol goes to the liver. The liver takes two glycerols and jams them together to make glucose to feed the central nervous system. Neurons only eat glucose.

Bacteria that feeds on indigestible material (2 pounds of bacteria, more bacteria cells than any other in the body). As a byproduct, they produce vitamins that are absorbed in the water (b,k).

2 liters enter, and only 200 ml leave. This means lots of recycling.

Infection or inflammation decrease ion transport, and the large intestine doesn't remove as much water.

Can be deadly, especially for children.

Cause by slow peristalsis. Feces in large intesine too much can cause too much water to be absorbed.

Eating laxatives and veggies and drinking lots of water can help.

Incoming nutrients can by used by the cell either

1. As fuel for the generation of ATP

2. As building materials (cellular repair, maintanence and growth)

• Glucose is coverted to pyruvate in ten steps
• The enzymes that carry out glycolosis are in the cytosol
• Glucose, six carbon sugar is converted into two pyruvates with 3 carbons each
• Glycolosis does not require oxygen
• A little bit of ATP is produced

A series of steps converts pyruvate and degrades it, carbon by carbon.

The enzymes that carry out the TCA cycle are located in the mitochondria

As carbons are liberated, they bind with oxygen to produce C02. This C02 diffuses out of the mitochondria, out of the cell and into the blood, eventually we breath it out.

Yes, fatty acids and amino acids can enter too.

Fatty acids-can enter certain steps of glycolosis and the TCA cycle

Amino acids can be turned into piruvate and some can enter the TCA cycle.

As the TCA cycle breaks down pyruvate, carbon by carbon, the electron that was holding the carbons together is set free. This electron possesses a lot of energy. There high energy electrons are transported to the Electron Transport Chain.

This is a series of proteins and organic molecules present in the mitochondrial membrane that pass the electron from one to another.

The final electron acceptor is oxygen and water is produced.

As it passes an electron along, the Electron Transport Chain moves protons (H+) across the mitochondrial membrane. These protons accumulate outside the membrane creating a concentration gradient.

The proton gradient represents a potential source for energy, as the protons will want to go down the gradient, but can't pass through the membrane.

ATP Synthase is an enzyme in the mitochondrial membrane that acts like a protein channel and allows protons to pass through. ADP and phosphate are present in the mitochondria.As Protons flow down the gradient, the ATP synthase uses the energy to combine the phosphate and the ADP, producing ATP.