1. 38–2 The Process of Digestion
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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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Digestion
The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum & anus.
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Digestion
Other structures add secretions to the digestive system, and aid in digestion. They are called accessory organs. These include the salivary glands, pancreas, and liver. Food does not actually pass through them.
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5. 38–2 The Process of Digestion
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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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 and grind the food and the 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.
Chemical digestion = chemically changing the food / breaking it down into its building blocks (ex. protein amino acids)
Saliva contains an enzyme called salivary amylase that breaks the chemical bonds in starches and releases sugars.
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The Pharynx
Food is swallowed into the pharynx
The epiglottis blocks the trachea so food doesn’t go “down the wrong pipe”
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The Esophagus
The Esophagus
From the pharynx, the chewed food, or bolus, passes through the esophagus into the stomach.
Food is moved along by contractions of smooth muscle (peristalsis) which 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 Stomach
The Stomach
Food from the esophagus empties into the stomach.
The stomach continues mechanical and chemical digestion.
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The stomach
- It is separated from the esophagus by the cardiac sphincter
The stomach wall secretes gastric juices, pepsin (a hormone) and HCl.
a thick lining of mucus protects the walls of the stomach from the acidic gastric juices
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Functions of the stomach:
Storage – many folds, can hold 2-4 liters
Mixing – food + gastric juices = chyme
Physical digestion – grinds food into smaller pieces, HCl kills pathogens
Chemical digestion – pepsin catalyses the breakdown of proteins into large peptides
Controlled release – chyme leaves via the pyloric sphincter
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The Small Intestine
The Small Intestine
Most chemical digestion and absorption of food occurs in the small intestine.
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16. Absorption in the Small Intestine
The folded surfaces of the small intestine are covered with fingerlike projections called villi. Villi are covered with microvilli which provides an enormous surface area for the absorption of nutrient molecules.
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17. 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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18. Absorption in the Small Intestine
actions of the small intestine:
- food continues to be digested chemically
- bile is released from gallbladder to emulsify fat (break fat into smaller droplets) here
- enzymes are secreted from the pancreas to digest starch, proteins, & lipids here
- nutrient absorption –now that the macromolecules are smaller, they are absorbed into the bloodstream
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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. During digestion, the pancreas produces digestive enzymes and it produces a base that neutralizes stomach acid so that these enzymes can be effective. It also produces blood sugar regulating hormones like insulin.
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The Small Intestine
Assisting the pancreas is the liver, which produces bile. Bile emulsifies fat into smaller droplets. Bile is stored in the gallbladder.
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The Large Intestine
The Large Intestine
When chyme leaves the small intestine, it enters the large intestine, or colon.
The large intestine removes water from the chyme.
It also absorbs vitamin K & B formed by bacteria in a symbiotic relationship with us
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Water is absorbed quickly, leaving undigested materials behind & forming feces.
Concentrated waste material passes through the rectum and is eliminated via the anus.
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24. 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
Food is moved through the esophagus into the stomach by
air pressure.
muscle contractions.
gravity.
swallowing.
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38–2
The enzyme in saliva that begins the digestion of starch is
amylase.
pepsin.
lysozyme.
peptidase.
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38–2
Stomach muscles contract to churn and mix stomach fluids and food, producing a mixture known as
chyme.
amylase.
bile.
acid.
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38–2
Absorption of vitamins, minerals, and digested food molecules takes place in the
stomach.
small intestine.
large intestine.
duodenum.
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