end show slide 1 of 36 copyright pearson prentice hall 38–2 the process of digestion
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38–2 The Process of Digestion
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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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38–2 The Process of Digestion
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38–2 The Process of Digestion
Mouth
Salivary glands
Stomach
Pancreas
Large intestine
Small intestine
Pharynx
Esophagus
Liver
Gallbladder
Rectum
The Digestive System
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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
Peristalsis
Esophagus
Bolus
Stomach
Muscles contracted
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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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Absorption in the Small Intestine
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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The Small Intestine
Small intestine
Circular folds
Villi
Villus
Epithelial cells
Capillaries
Lymph vesselVein Artery
Absorption in the Small Intestine
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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
Absorption in the Small Intestine
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The Small Intestine
Accessory Structures of Digestion
Liver
Gallbladder
Duodenum
Bile duct
Pancreas
Pancreatic duct
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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Digestive System Disorders
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
a. air pressure.
b. muscle contractions.
c. gravity.
d. swallowing.
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38–2
The enzyme in saliva that begins the digestion of starch is
a. amylase.
b. pepsin.
c. lysozyme.
d. peptidase.
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38–2
Stomach muscles contract to churn and mix stomach fluids and food, producing a mixture known as
a. chyme.
b. amylase.
c. bile.
d. acid.
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38–2
Absorption of vitamins, minerals, and digested food molecules takes place in the
a. stomach.
b. small intestine.
c. large intestine.
d. duodenum.