BIO 103NSI

Biology ILecture 13

The Human Digestive SystemAnatomy

Digestive systemStructural Regions

DigestionWhy chemical digestion is needed?How Does Chemical Digestion Occur?Digestion in different stages

Digestive SystemDigestive system consists of series of connected

organs whose purpose is to break down, or digest, the food we eat.

Food ( large complex molecules)simple and smallest parts absorbed in bloodstream

Digestion generally involves 2 stages:

Mechanical Digestion

Chemical Digestion

Why is Chemical Digestion Needed?Chewing, chopping and mixing with saliva can only split

up the food into small pieces. Foods need to be separated into small simple molecules to

be effective.Nutrients are absorbed by blood through the cell

membrane and blood transport them to different parts of the body.

Fats and Carbohydrates are water insoluble. They are converted to a soluble product before they are absorbed.

Finally, Carbohydrate, Fat and Protein that we eat are not the same as our own Carbohydrate, Fat and Protein. Digestive system converts those “animal/plant” products to “Human products”.

How Does Chemical Digestion Occur?Most chemical digestion in your body uses a water

molecule to break the bonds between the parts of the large molecules. This process is called hydrolysis.

Specific enzymes may speed up the hydrolysis of the large molecules by positioning the water molecule in just the right place for the chemical reaction to occur.

For example, proteinases or proteases help hydrolyze proteins, lipases help hydrolyze lipids or fats, and carbohydrases help hydrolyze carbohydrates.

AnatomyAnatomy

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6. Anal RegionAnal Region

Accessory Digestive Organs1. Salivary Glands2. Pancreas3. Liver4. Gallbladder

The Mouth Region

Mechanical and Chemical DigestionGlands in cheek secrets saliva (digestive enzymes).Make the food chopped, moist and smooth for easy

swallowing.Food enters in pharynx (food and air passageway). Epiglottis covers the trachea(windpipe) when food

is swallowed. Sense receptors in mouth can characterize the food

texture, temperature and taste.Amylase; an starch/carbohydrate digesting enzyme

is secreted from mouth.

The Mouth Region

Your mouth produces up to 1.5 liters of liquid every day

Saliva is produced when food being tasted or chewed

Saliva is a solution of three main substances:

Water: for moisten and taste

Amylase: Breakdown of starch/Carbohydrates.

Mucin: Lubricant the food

The Esophagus

•The esophagus is a muscular tube about 25 cm (10 inches) and 2.5 cm (1 inch) across long,

passes behind the trachea (windpipe) and heart and penetrates the diaphragm (muscular wall between the chest and abdomen) before reaching the stomach within two to three seconds.

•Digestion by rhythmic muscle contractions (tightening) known as peristalsis.

•No chemical digestion.

The Stomach

located in the upper abdomen just below the diaphragmsac-like structure with strong, muscular wallsThe stomach can expand significantly to store all the

food from a mealboth mechanical and chemical processingcontracts about three times per minute, churning the

food and mixing it with gastric juice.thousands of gastric glands (2 liters of gastric

juice/day )in the lining of the stomach, consists of water, hydrochloric acid(HCl), an enzyme called pepsin, and mucin (the main component of mucus)

The StomachComposition of Gastric Juice: Water

food moisten and dissolves any soluble nutrients HCl (Hydrochloric Acid)

It helps dissolve insoluble minerals. It kills many bacteria taken in with the food. It aids in the digestion of starch. It provides the acidity needed to keep the pepsin enzyme working.

Pepsin Pepsin, a protease enzyme, Hydrolysis of a protein by pepsin produces several shorter chains of amino acids.

Mucin coats the stomach, protecting it from the effects of the acid and pepsin

About 4 hours after each meal, small portion of processed food is passed through “pyloric sphincter” to duodenum (first part of small Intestine).

The Small Intestine•Most digestion, as well as absorption of digested food, occurs in the small intestine.•This narrow, twisting tube, about 2.5 cm (1 in) in diameter, fills most of the lower abdomen, extending about 6 meters (20 feet) in length.• Three parts:•Duodenum•Jejunum•Ilium

•Chemical digestion takes place in small intestine by digestive juices from 3 different sources:•Liver•The Pancreas•Intestinal Lining

The Small IntestineLiver:

makes complex mineral salts in a solution called bilestored and concentrated unit needed in the gall gladder.Bile salts break up large drops of fat into many smaller droplets.Bile salts also prevent the small droplets from going back together again.It stores glucose in the form of starch-like molecules called glycogen.

Pancreas: produces 3 enzymes:Protease, which hydrolyze protein.Amylase, which hydrolyze starch, andLipase, which hydrolyze fat or oil

Intestinal Lining: Produces enzymes to make the small chains of

foods(proteins/carbohydrates) into smallest parts.Mucin lubricates and protects the wall of Intestine.

The Large Intestine•A watery residue of indigestible food and digestive juices remains unabsorbed•They leaves the ileum of the small intestine and moves by peristalsis into the large intestine, where it spends 12 to 24 hours•The large intestine is 1.5 to 1.8 meters (5 to 6 feet) long and about 6 cm (2.5 inch) in diameter.•Function:

•It absorbs water—about 6 liters (1.6 gallons) daily•Absorbs dissolved salts.•bacteria in the large intestine promote the breakdown of undigested materials •Bacteria make several vitamins, notably vitamin K, which the body needs for blood clotting.•large intestine moves its remaining contents toward the rectum, which makes up the final 15 to 20 cm (6 to 8 in) of the alimentary canal•The rectum stores the feces—waste material that consists largely of undigested food, digestive juices, bacteria, and mucus—until elimination.

The Large IntestineSources of water used in digestion________________________________________________________________________RegionSecretion Daily Volume of Water________________________________________________________________________Mouth Saliva 1.5 litersStomach Gastric juice 1.5 litersLiver Bile 0.8 literPancreas Pancreatinc juice 0.8 literSmall intestine Intestinal juice 1.0 liter________________________________________________________________________Total Volume of secretion 5.6 liters________________________________________________________________________

0.2 Liter is not absorbed

AnatomyAnatomy

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3.

4.

5.

6. Anal RegionAnal Region

Accessory Digestive Organs1. Salivary Glands2. Pancreas3. Liver4. Gallbladder

Summary Food Type Major Digestion

areaMajor Digestive Enzyme

End products

Carbohydrates Mouth Amylase Glucose

Protein Stomach Pepsin Amino acids

Fats Small Intestine Lipase Small lipid molecules

Thank you Handout + Slide