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The Digestive System

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Major Functions

• Digestion- Break down food into the nutrients the body can absorb.

• Absorption- Take out nutrients out of the food we eat and deliver it to the cells in our body.

• Eliminate solid wastes that is not needed by the body.

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Digestion

• Processing of food• Types

– Mechanical (physical)• Chew• Tear• Grind• Mash• Mix

– Chemical- uses catabolic reactions and enzymes to break down food

• Saliva• Stomach Acids• Bile used to break down fats

Examples of Mechanical Digestion

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Digestion

• Phases– Ingestion– Movement– Digestion– Absorption– Further digestion

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Digestive System Organization

• Gastrointestinal (Gl) tract– Tube within a tube– Direct link/path between organs– Major Organs:MouthPharynx Esophagus Stomach Small Intestines

Large Intestines Rectum

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Digestive System Organization

• Accessory Organs– Not in tube path

– Organs• Teeth

• Tongue

• Salivary glands

• Liver

• Gall bladder

• Pancreas

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Mouth- where digestion beginsTeeth- Mechanical Digestion

Salivary Glands- Chemical digestion of compounds such as starch

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Teeth- Mechanical Digestion

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Surface of the Tongue

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The Major Salivary Glands

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Deglutition (swallowing)

• Sequence– A. Voluntary stage

• Push food to back of mouth

– B. Pharyngeal stage• Raise pallate

- C. Esophageal stage- Contract pharyngeal muscles, open esophagus, start peristalsis

Peristalsis__________________

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Esophagus

• Usually collapsed (closed)

• Functions– Secrete mucous

– Transport food to the stomach

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PeristalsisContractions of smooth muscles that push food down the digestive tract

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Esophagus

• Sphincters– Upper

– Lower

• Abnormalities– Achalasia

– Atresia

– Hernia

– Barret’s esophagus

– Esophageal varices

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Stomach

• Usually “J” shaped• Mucous membrane

– G cells – make gastrin

– Goblet cells – make mucous

– Gastric pit – Oxyntic gland – Parietal cells – Make HCl

– Chief cells – Zymogenic cells• Pepsin

• Gastric lipase

Very Acidic, but the cells are produced faster than they die

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Anatomy of the Stomach

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Stomach

• Functions1. Mix food- Mechanically

2. Reservoir- Store food

3. Start chemical digestion of• Protein

• Nucleic acids

• Fats

4. Destroy some bacteria

5. Absorbs• Alcohol

• Water

• Lipophilic acid

• B 12

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Stomach

Function- To mix, break down (chemically and mechanically), and store food.

• Inner surface thrown into folds – Rugae

• Contains enzymes that work best at pH 1-2 (VERY ACIDIC)

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Stomach

• Food leaves the stomach as a soupy mixture called chyme

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Small Intestine

• Function- Major site of chemical digestion and absorption.

• Movements– Peristalsis

• Absorbs– 80% ingested water– Vitamins– Minerals– Carbonates– Proteins

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Structure of the Villi in the Small Intestine

Villi- Increase surface area for absorption.

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Small Intestine- Accessory Organs

• Liver- Creates bile that is used to break down fats.

• Gal bladder- Stores bile and releases it into the small intestines

• Pancreas- Creates pancreatic juices that neutralize the chyme.

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Anatomy of the Large Intestine

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Large Intestine

Function- To reabsorb water from digested wastes to make solid wastes.

- No villi– No permanent circular folds– Smooth muscle

•Chyme dehydrated to form feces

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Feces Formation and Defecation“whats in it?”

• Chyme dehydrated to form feces

• Feces composition– Water– Inorganic salts– Epithelial cells– Bacteria– Byproducts of digestion

Defecation– Peristalsis pushes feces into

rectum– Rectal walls stretch until full

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Anatomy of the Large Intestine

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The Organs and Positions in the Abdominal Cavity

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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html

Video of the digestion of food- The whole picture

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Digestive Disorders

Chrone’s Disease (inflammatory bowel syndrome)- Inflammation of the intestines

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Digestive disorders

Blind loop syndrome-Blind loop syndrome occurs when part of the intestine becomes bypassed, so that digested food slows or stops moving through the intestines. This causes bacteria to grow too much in the intestines and leads to problems in absorbing nutrients.

Diarrhea- increased frequency of watery feces. Causing dehydration and abdominal pain.

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Digestive DisordersPhenylketonuria (PKU)- is a rare condition in which a baby is born without the ability to properly break down an essential amino acid called phenylalanine.

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Symptoms

•Lighter skin and hair color

•Delayed mental and social skills

•Bad breath and odor from skin and urine.

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PKU is a recessive trait and therefore both parents must carry the allele to pass the trait.

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Mouth Salivary gland

Esophagus

LiverStomach

PancreasLarge Intestines

Gal Bladder

Small Intestines

RectumAnus