Digestive System

MoleculesDNA molecules

Atoms

Organ systems

Cells

nerve cell

Tissuesleaf tissues

cardiactissue

Organismstree human

Organs

leaf

stem

brain

heart

Cells require nutrients obtained from food and oxygen

The Digestive System will:

Disassemble large organic molecules into smaller component molecules

Transfer these to circulatory system for distribution to rest of body

Get rid of indigestible material

Functions of the Digestive System

Mechanical Digestion: Grinding large food particles into smaller clumps (reducing # molecules per clump)

Chemical Digestion: Breaking larger molecules into smaller component molecules, by means of a chemical reaction, using enzymes

Absorption: Smaller component molecules transported across wall of digestive tract and into blood vessels 

Elimination : getting rid of undigested food

Different steps of digestion

Organs involved in digestion

Two types of organs:

Digestive Tract Organs

Accessory Organs

Stomach

Oral cavity

Small intestine

Esophagus

Large intestine

Pancreas

Liver

Gall Bladder

Salivary glands Digestive tract

(Muscular tube w/ specialized segments)

Accessory glands

(secrete substances that aid with digestion)

Pharynx

Components of the digestive system

Oral Cavity: Mechanical processing- chewing

Chemical Digestion- saliva secretion: carbohydrate digestion

• Epiglottis:

“Lid” that closes over opening to trachea - Prevents food entering airway

Enzyme must bind to substrate, so enzyme must have access to these larger molecules.

Mechanical processing:

•increases surface area of food particles

•Exposes more molecules to enzymes, increases efficiency.

Why is mechanical processing important?

Swallowing:

Pharynx and Esophagus: No mechanical processing, digestion, or absorption, Merely conducts food to stomach.

If you stand on your head, will the food still move to your stomach?

YES: food moves down by muscle contractions of the esophagus (= peristalsis)

Stomach: Storage for food

Mechanical processing: churning

Chemical digestion: protein digestion - enzymes secreted from stomach wall hydrochloric acid also secreted - Lowers pH to kill pathogens (disease-causing organisms) and activate protein enzymes

Small Intestine:

Function:• Most chemical digestion

occurs in the small intestines (lipids, nucleic acids, carbohydrates, proteins)

• Absorption of nutrients

Small Intestine:

From Accessory Organs:

• Bile produced in liver stored in gall bladder

• Pancreatic juices (enzymes)

Digestion

Mechanical - Lipids not water soluble, but enzymes are - Bile will break up large groups of lipid molecules into smaller droplets so enzymes can act on them (Emulsification)

Bile enters the small intestine through the bile duct

Chemical - Carbohydrate, protein, & lipid digestion enzymes secreted from pancreas

enzymes located in the intestinal wall

Small Intestine:

Small Intestine:

Absorption - Component molecules diffuse across intestinal wall into circulatory system

Villi(fingerlike projections)

Increased surface area for absorption:

Intestinal wall - folded

Villi - Fingerlike projections of intestinal wall;

Microvilli - Projections of plasma membrane of intestinal cells

Amino acids, glucose, other water soluble nutrients absorbed into the capillaries

What are lacteals?

• Inside the villi are vessels of the lymphatic system that absorb the fatty acids and glycerol.

Large Intestine (colon): - Absorbs water; - Contains lots of bacteria (mostly E. coli), bacteria digest some remaining food, bacteria produce vitamins; - Responsible for elimination of undigested food = feces)

Blood leaving intestines is transported to the liver via the hepatic portal vein for processing [molecules modified, toxins removed]

The liver Removes• unwanted or harmful chemicals (detoxification) including chemicals produced in the body, •unwanted chemicals taken into the body (e.g. carcinogens), and medications.

•Hepatocytes - Liver cells - the liver's main functional units.

Pancreas

Pancreas

•Main enzyme producing organ of digestive system• Pancreatic duct enters the small intestine to deliver fluid (pancreatic juice) through a small hole in the wall of the second part of the duodenum•Pancreatic juice contains enzymes capable of digesting all food types - protein, fat and carbohydrates