The human digestive organs can be divided into those of the alimentary canal and the accessory digestive organs.
The gastrointestinal tract is composed of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus.
The accessory organs are the teeth, tongue, gallbladder, salivary glands, liver and pancreas.
See module –review all figures and diagrams
a. Opening = Lips
b. Floor = Tongue
c. Walls = Cheeks
d. Roof = Hard/soft palates
The tongue is attached to the hyoid bone and the mandible and the membranous lingual frenulum.
There are thirty-two teeth in the human mouth. Together they work to tear, crush and grind food to mechanically digest food.
The teeth are composed of two chisel-shaped incisors for biting; one pointed canine for tearing; two fairly flat pre-molars for grinding; and three flat molars for crushing.
Food is mixed and moistened with saliva (from the salivary glands) containing enzymes that begin the process of chemical digestion by breaking down starches.
Taste buds are found primarily on the tongue but also on the surface of the mouth and the wall of the pharynx.
The tongue grips the food, constantly repositions it between the teeth and forms it into a compact mass which is pushed back to the pharynx to begin the process of swallowing.
A bolus is the compact mass of food formed by the combination of chewing by the teeth and repositioning by the tongue.
The pharynx is made up of three parts: the nasopharynx, the oropharynx, and the laryngopharynx.
Air enters the nose, continues through the nasopharynx, oropharynx and the laryngopharynx. Air then enters the trachea on its way to the lungs. Food and liquid enter the mouth, continue through the oropharynx and the laryngopharynx but then continue into the esophagus.
Food is prevented from entering the larynx by the epiglottis, a flap of elastic cartilage which covers the larynx when swallowing food or liquid.
The pharynx has two types of skeletal muscles; a circumferential outer layer and an inner longitudinal layer which contract alternatively squeezing food into the esophagus.
The esophagus contains 4 layers of tissue: the innermost layer is the mucosa which secretes mucus into the interior the gastrointestinal tract, the second layer is the submucosa which contains blood and lymph vessels, lymph nodes, nerves, and mucous glands, the third layer is the muscularis externa which is made of two layers of muscle: the outer longitudinal fibers and inner circumferential fibers and the outermost layer is the serosa which is made up of cells that make serous fluid.
Peristalsis is the squeezing of food through the GI tract by the alternating contraction of the sets of longitudinal and circumferential muscles.
Each tooth is made of three main parts: the crown, the neck and the root
There are three types of papillae which help to grip food on the tongue: circumvallate, fungiform and filiform. Circumvallate and fungiform papillae both contain taste buds.
See module –review all figures and diagrams
The stomach is a backward C shaped organ that is located along the left side of the abdomen below the diaphragm.
Food enters the stomach from the esophagus via the cardioesophageal sphincter and exits the stomach via the pyloric sphincter into the small intestine.
The stomach has two curvatures: the concave lesser curvature which extends inward on the shorter side of the stomach and the convex greater curvature which extends outward on the longer side of the stomach.