1. The Process of Digestion
Photo Credit: © Fred Hossler/Visuals Unlimited
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What are the organs of the digestive system?
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The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
Other structures add secretions to the digestive system, and aid in digestion. These include the salivary glands, pancreas, and liver.
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The Digestive System
Mouth
Pharynx
Salivary glands
Esophagus
Liver
Stomach
The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Because the pancreas and most of the gallbladder are behind other organs, their locations are indicated by dotted lines.
Pancreas
Gallbladder
Large intestine
Small intestine
Rectum
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FUN ANIMATION!!!
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The Mouth
What is the function of the digestive system?
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The Mouth
The function of the digestive system is to help convert foods into simpler molecules that can be absorbed and used by the cells of the body.
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The Mouth
The Mouth
Chewing begins mechanical digestion, which is the physical breakdown of large pieces of food into smaller pieces.
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The Mouth
The teeth cut, tear, and crush food into small fragments.
As the teeth cut and grind the food, salivary glands secrete saliva, which moistens food and makes it easier to chew.
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The Mouth
Saliva helps ease the passage of food through the digestive system and also begins the process of chemical digestion.
Saliva contains amylase, an enzyme that breaks the chemical bonds in starches and releases sugars.
Saliva also contains lysozyme, an enzyme that fights infection.
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The Esophagus
The Esophagus
From the throat, the chewed food passes through the esophagus, or food tube, into the stomach.
Food is moved along by contractions of smooth muscle.
These contractions, known as peristalsis, squeeze the food through the esophagus into the stomach.
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The Esophagus
Esophagus
Bolus
Peristalsis
Muscles contracted
Stomach
Muscles in the walls of the esophagus contract in waves. Each wave pushes the chewed clump of food, or bolus, in front of it. Eventually, the bolus is pushed into the stomach.
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The Esophagus
The cardiac sphincter closes the esophagus after food has passed into the stomach.
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The Stomach
The Stomach
Food from the esophagus empties into the stomach.
The stomach continues mechanical and chemical digestion.
Alternating contractions of three smooth muscle layers churn food.
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The Stomach
Chemical Digestion
The stomach lining has millions of gastric glands that release substances into the stomach.
Some glands produce mucus, which lubricates and protects the stomach wall.
Other glands produce hydrochloric acid, which makes the stomach contents very acidic.
Other glands produce pepsin, an enzyme that digests protein.
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The Stomach
Pepsin and hydrochloric acid begin protein digestion.
Pepsin breaks proteins into smaller polypeptide fragments.
Other enzymes are denatured by stomach acid.
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Question of the Day #1
Q: What is the “hangy ball” thing in the back of the throat?
A: Uvula
Functions helps close off nasal cavity during swallowing, involved with gag reflex, may cause snoring…
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The Stomach
Digestive enzymes break down foods and make nutrients available to the body.
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The Stomach
Mechanical Digestion 
The stomach contracts to churn fluids and food, gradually producing a mixture known as chyme.
After 1–2 hours, the pyloric valve between the stomach and small intestine opens and chyme flows into the small intestine.
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The Small Intestine
The Small Intestine
As chyme is pushed through the pyloric valve, it enters the duodenum.
The duodenum is the first of three parts of the small intestine, and is where most digestive enzymes enter the intestine.
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The Small Intestine
Most chemical digestion and absorption of food occurs in the small intestine.
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The Small Intestine
Accessory Structures of Digestion
Liver
Bile duct
Pancreas
Gallbladder
Pancreatic duct
Duodenum
Accessory structures, including the liver and pancreas, add secretions to the digestive system. The pancreas secretes enzymes that help break down carbohydrates, proteins, and fats.
To rest of small intestine
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The Small Intestine
Accessory Structures of Digestion
Just behind the stomach is the pancreas.
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The Small Intestine
During digestion, the pancreas:
produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids.
produces sodium bicarbonate, a base that neutralizes stomach acid so that these enzymes can be effective.
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The Small Intestine
Assisting the pancreas is the liver, which produces bile.
Bile dissolves and disperses droplets of fat in fatty foods. This enables enzymes to break down smaller fat molecules.
Bile is stored in the gallbladder.
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26. Absorption in the Small Intestine
The small intestine is adapted for the absorption of nutrients.
The folded surfaces of the small intestine are covered with fingerlike projections called villi.
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27. Absorption in the Small Intestine
Villus
Small intestine
Circular folds
Epithelial cells
Villi
Capillaries
Lymph vessel
The lining of the small intestine consists of folds that are covered with tiny projections called villi. Within each villus there is a network of blood capillaries and lymph vessels that absorb and carry away nutrients. 
Vein
Artery
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28. Absorption in the Small Intestine
Cell surfaces of villi have more projections called microvilli.
These provide an enormous surface area for the absorption of nutrient molecules.
Slow, wavelike contractions of smooth muscles move the chyme along this surface.
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29. Absorption in the Small Intestine
Nutrient molecules are absorbed into the cells lining the small intestine.
Most products of carbohydrate and protein digestion are absorbed into the capillaries in the villi.
Molecules of undigested fat are absorbed by lymph vessels.
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The Large Intestine
The Large Intestine
When the chyme leaves the small intestine, it enters the large intestine, or colon.
The large intestine removes water from the chyme.
Water is absorbed quickly, leaving undigested materials behind.
Concentrated waste material passes through the rectum and is eliminated from the body.
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Q.O.T.D.
Q: What is Ulcerative Colitis?
A: -Inflammation of the colon
-Believed to be caused by the Immune System reacting abnormally to bacteria in the gut
-Symptoms are: abdominal pain, cramping, irregular bowl movements, bleeding, nausea, vomiting and weight loss
-Goes through phases  active / remission
-Can be treated with medication or possibly surgery to remove the colon
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32. Digestive System Disorders
Stomach acids sometimes damage the organ’s own lining, producing a hole in the stomach wall known as a peptic ulcer. Most peptic ulcers are caused by the bacterium H. pylori.
Other digestive disorders include diarrhea and constipation.
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38–2
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Food is moved through the esophagus into the stomach by
air pressure.
muscle contractions.
gravity.
swallowing.
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A gland that has both endocrine and exocrine functions is the
liver.
spleen.
pancreas.
gallbladder.
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The enzyme in saliva that begins the digestion of starch is
amylase.
pepsin.
lysozyme.
peptidase.
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Stomach muscles contract to churn and mix stomach fluids and food, producing a mixture known as
chyme.
amylase.
bile.
acid.
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Absorption of vitamins, minerals, and digested food molecules takes place in the
stomach.
small intestine.
large intestine.
duodenum.
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