DIGESTIVE SYSTEM
ORAL CAVITY - bounded by the teeth, tongue, hard palate, and soft palate.
Structures of the Oral Cavity Are Responsible for the First Step of Digestion: Ingestion.
1. Mechanical digestion begins when the teeth break down ingested food.
The movement of the jaw enables the teeth to grind food into small fragments.
Mandible/jawbone - is the only bone in the head that moves.
The points where the temporal bones connect to the mandible make up the only two movable joints
in the head.
Mastication - the official name for chewing.
This is the first step in mechanical digestion.
2. Saliva Moistens Food and Begins the Process of Chemical Digestion.
Saliva secreted by salivary glands aids the mechanical and chemical process of digestion.
99% water and not only moistens food but cleanses the mouth, dissolves food chemicals so they can
be tasted, and contains enzymes that start the chemical breakdown of starchy foods.
There are three pairs of salivary glands: parotid, sublingual, and submandibular (also called the
submaxillary gland).
3. The Tongue Creates a Bolus so It Can Travel Down the Pharynx and Esophagus.
The tongue manipulates the chewed food into a small mass called a bolus, then moves it to the
oropharynx.
The next steps are involuntary: the bolus passes through the pharynx, the epiglottis closes off the
trachea and directs the bolus down the esophagus, and peristaltic waves move the bolus into the
stomach.
ALIMENTARY CANAL - a single continuous tube that includes the oral cavity, pharynx, esophagus,
stomach, small intestine, and large intestine.
Peristalsis Creates Propulsion: How Food Moves Through the Alimentary Canal.
1. The Epiglottis Directs Swallowed Foodstuffs Down the Esophagus.
The respiratory and digestive systems share structures in the back of the oral cavity that connect
with both the trachea (of the respiratory system) and the esophagus (of the digestive system).
With each swallow a structure called the epiglottis closes over respiratory structures. The
swallowed bolus stays on course and is directed toward the esophagus. One peristaltic wave can be
enough to move a bolus down the esophagus and into the stomach.
2. Peristalsis Is the Contraction of Muscle Tissue That Helps Move and Break Down Foodstuffs.
The walls of the alimentary canal include layers of smooth muscle controlled by the autonomic
nervous system. Alternating contraction and relaxation of these muscles is called peristalsis.
Peristaltic waves push the swallowed bolus down the esophagus.
In the stomach, peristalsis churns swallowed food, mixing it with gastric juices. These mechanical
and chemical actions further break down food into a substance called chyme. It takes about a
minute to chew a piece of food into a bolus and a few seconds to swallow it. Once in the stomach
foodstuffs take a few hours to become chyme.
3. Peristaltic Waves Move Nutrients and Waste Through the Intestines.
Most nutrient absorption from the foods we eat occurs in the small intestine. When chyme passes
from the stomach into the small intestine, peristaltic waves shift it back and forth and mix it with
digestive enzymes and fluids. Nutrients from the chyme are absorbed into the bloodstream through
the intestinal walls Peristaltic waves in the small intestine are smaller and more regular, pushing the
chyme for 3 to 6 hours before passing it to the large intestine where any final absorption takes place.
Peristaltic waves help compact and move waste and indigestible foodstuffs through the large
intestine for elimination.
, Accessory Organs: Glands and Organs That Facilitate the Process of Digestion.
1. Saliva Moistens Food and Begins the Chemical Digestion Process.
Six salivary glands, located around the oral cavity, secrete saliva. This substance moves out of the
glands into the oral cavity through ducts.
Saliva is 99% water, but also contains enzymes and proteins that lubricate the oral cavity and begin
chemical digestion of food. There are three pairs of salivary glands (parotid, submandibular, and
sublingual glands) and two ducts (Stensen’s and salivary ducts) on either side of the oral cavity.
2. The Liver Secretes Bile to Emulsify Fats in the Small Intestine.
Liver - one of the largest organs in the body and it is continuously producing bile.
This yellowish-brown fluid aids chemical digestion by emulsifying fats in the duodenum. Bile flows
out of the liver into the right and left hepatic ducts, into the common hepatic ducts, and toward the
small intestine to help with digestion and the absorption of fats.
3. The Gall Bladder Stores Bile.
If bile is not immediately needed for digestion, it flows up the cystic duct to the gall bladder. The
gall bladder is a green, pear-shaped sac about 10 cm or 4 in. long that stores and concentrates excess
bile secreted by the liver. Bile is released by the gall bladder as needed into the small intestine.
4. Pancreatic Juice Breaks Down Protein, Fats, and Carbohydrates
The pancreas secretes pancreatic juice, a mix of digestive enzymes, water, buffers (bicarbonates),
and electrolytes produced by acinar and epithelial cells. Pancreatic juice drains through the main
pancreatic duct (duct of Wirsung) into the common bile duct and then into the small intestine. There
it buffers stomach acids and breaks down protein, fats, and carbohydrates.
Nutrients In, Waste Out: How the Human Body Absorbs Nutrients and Eliminates Waste
1. Villi That Line the Walls of the Small Intestine Absorb Nutrients
Villi that line the walls of the small intestine absorb nutrients into capillaries of the circulatory
system and lacteals of the lymphatic system. Villi contain capillary beds, as well as lymphatic
vessels called lacteals. Fatty acids absorbed from broken-down chyme pass into the lacteals. Other
absorbed nutrients enter the bloodstream through the capillary beds and are taken directly to the
liver, via the hepatic vein, for processing.
2. The Large Intestine Completes Absorption and Compacts Waste
Chyme passes from the small intestine through the ileocecal valve and into the cecum of the large
intestine. Any remaining nutrients and some water are absorbed as peristaltic waves move the
chyme into the ascending and transverse colons. This dehydration, combined with peristaltic waves,
helps compact the chyme. The solid waste formed is called feces. It continues to move through the
descending and sigmoid colons. The large intestine temporarily stores the feces prior to elimination.
3. Defecation Eliminates Waste From the Body
The body expels waste products from digestion through the rectum and anus. This process, called
defecation, involves contraction of rectal muscles, relaxation of the internal anal sphincter, and an
initial contraction of the skeletal muscle of the external anal sphincter. The defecation reflex is
mostly involuntary, under the command of the autonomic nervous system. But the somatic nervous
system also plays a role to control the timing of elimination.
RESPIRATORY SYSTEM
Top 5 Functions of the Respiratory System: A Look Inside Key Respiratory Activities
ORAL CAVITY - bounded by the teeth, tongue, hard palate, and soft palate.
Structures of the Oral Cavity Are Responsible for the First Step of Digestion: Ingestion.
1. Mechanical digestion begins when the teeth break down ingested food.
The movement of the jaw enables the teeth to grind food into small fragments.
Mandible/jawbone - is the only bone in the head that moves.
The points where the temporal bones connect to the mandible make up the only two movable joints
in the head.
Mastication - the official name for chewing.
This is the first step in mechanical digestion.
2. Saliva Moistens Food and Begins the Process of Chemical Digestion.
Saliva secreted by salivary glands aids the mechanical and chemical process of digestion.
99% water and not only moistens food but cleanses the mouth, dissolves food chemicals so they can
be tasted, and contains enzymes that start the chemical breakdown of starchy foods.
There are three pairs of salivary glands: parotid, sublingual, and submandibular (also called the
submaxillary gland).
3. The Tongue Creates a Bolus so It Can Travel Down the Pharynx and Esophagus.
The tongue manipulates the chewed food into a small mass called a bolus, then moves it to the
oropharynx.
The next steps are involuntary: the bolus passes through the pharynx, the epiglottis closes off the
trachea and directs the bolus down the esophagus, and peristaltic waves move the bolus into the
stomach.
ALIMENTARY CANAL - a single continuous tube that includes the oral cavity, pharynx, esophagus,
stomach, small intestine, and large intestine.
Peristalsis Creates Propulsion: How Food Moves Through the Alimentary Canal.
1. The Epiglottis Directs Swallowed Foodstuffs Down the Esophagus.
The respiratory and digestive systems share structures in the back of the oral cavity that connect
with both the trachea (of the respiratory system) and the esophagus (of the digestive system).
With each swallow a structure called the epiglottis closes over respiratory structures. The
swallowed bolus stays on course and is directed toward the esophagus. One peristaltic wave can be
enough to move a bolus down the esophagus and into the stomach.
2. Peristalsis Is the Contraction of Muscle Tissue That Helps Move and Break Down Foodstuffs.
The walls of the alimentary canal include layers of smooth muscle controlled by the autonomic
nervous system. Alternating contraction and relaxation of these muscles is called peristalsis.
Peristaltic waves push the swallowed bolus down the esophagus.
In the stomach, peristalsis churns swallowed food, mixing it with gastric juices. These mechanical
and chemical actions further break down food into a substance called chyme. It takes about a
minute to chew a piece of food into a bolus and a few seconds to swallow it. Once in the stomach
foodstuffs take a few hours to become chyme.
3. Peristaltic Waves Move Nutrients and Waste Through the Intestines.
Most nutrient absorption from the foods we eat occurs in the small intestine. When chyme passes
from the stomach into the small intestine, peristaltic waves shift it back and forth and mix it with
digestive enzymes and fluids. Nutrients from the chyme are absorbed into the bloodstream through
the intestinal walls Peristaltic waves in the small intestine are smaller and more regular, pushing the
chyme for 3 to 6 hours before passing it to the large intestine where any final absorption takes place.
Peristaltic waves help compact and move waste and indigestible foodstuffs through the large
intestine for elimination.
, Accessory Organs: Glands and Organs That Facilitate the Process of Digestion.
1. Saliva Moistens Food and Begins the Chemical Digestion Process.
Six salivary glands, located around the oral cavity, secrete saliva. This substance moves out of the
glands into the oral cavity through ducts.
Saliva is 99% water, but also contains enzymes and proteins that lubricate the oral cavity and begin
chemical digestion of food. There are three pairs of salivary glands (parotid, submandibular, and
sublingual glands) and two ducts (Stensen’s and salivary ducts) on either side of the oral cavity.
2. The Liver Secretes Bile to Emulsify Fats in the Small Intestine.
Liver - one of the largest organs in the body and it is continuously producing bile.
This yellowish-brown fluid aids chemical digestion by emulsifying fats in the duodenum. Bile flows
out of the liver into the right and left hepatic ducts, into the common hepatic ducts, and toward the
small intestine to help with digestion and the absorption of fats.
3. The Gall Bladder Stores Bile.
If bile is not immediately needed for digestion, it flows up the cystic duct to the gall bladder. The
gall bladder is a green, pear-shaped sac about 10 cm or 4 in. long that stores and concentrates excess
bile secreted by the liver. Bile is released by the gall bladder as needed into the small intestine.
4. Pancreatic Juice Breaks Down Protein, Fats, and Carbohydrates
The pancreas secretes pancreatic juice, a mix of digestive enzymes, water, buffers (bicarbonates),
and electrolytes produced by acinar and epithelial cells. Pancreatic juice drains through the main
pancreatic duct (duct of Wirsung) into the common bile duct and then into the small intestine. There
it buffers stomach acids and breaks down protein, fats, and carbohydrates.
Nutrients In, Waste Out: How the Human Body Absorbs Nutrients and Eliminates Waste
1. Villi That Line the Walls of the Small Intestine Absorb Nutrients
Villi that line the walls of the small intestine absorb nutrients into capillaries of the circulatory
system and lacteals of the lymphatic system. Villi contain capillary beds, as well as lymphatic
vessels called lacteals. Fatty acids absorbed from broken-down chyme pass into the lacteals. Other
absorbed nutrients enter the bloodstream through the capillary beds and are taken directly to the
liver, via the hepatic vein, for processing.
2. The Large Intestine Completes Absorption and Compacts Waste
Chyme passes from the small intestine through the ileocecal valve and into the cecum of the large
intestine. Any remaining nutrients and some water are absorbed as peristaltic waves move the
chyme into the ascending and transverse colons. This dehydration, combined with peristaltic waves,
helps compact the chyme. The solid waste formed is called feces. It continues to move through the
descending and sigmoid colons. The large intestine temporarily stores the feces prior to elimination.
3. Defecation Eliminates Waste From the Body
The body expels waste products from digestion through the rectum and anus. This process, called
defecation, involves contraction of rectal muscles, relaxation of the internal anal sphincter, and an
initial contraction of the skeletal muscle of the external anal sphincter. The defecation reflex is
mostly involuntary, under the command of the autonomic nervous system. But the somatic nervous
system also plays a role to control the timing of elimination.
RESPIRATORY SYSTEM
Top 5 Functions of the Respiratory System: A Look Inside Key Respiratory Activities
