lab 14 : digestive

• digestive system can be separated into two main components: the digestive tract and the various accessory organs.
• The digestive tract is a continuous tube that begins at the mouth and ends at the anus.
• The accessory digestive organs include the teeth, tongue, salivary glands, liver, gall bladder, and pancreas.
• The mouth has been specialized for ingestion and the mechanical processing of food
• The mouth is surrounded by the lips which are flexible and sensitive to touch.
• the teeth, are located in the mouth and surrounded by a delicate mucosa, the gingiva (or gums).
• The roof of the mouth is formed by the hard palate anteriorly and the soft palate posteriorly.
• Most of the mouth cavity is filled by the tongue, an accessory organ which functions in food manipulation, taste and speech
• mastication: Solid food must be reduced to small particles before it can effectively undergo chemical changes in the digestive tract.
• Chisel-shaped incisors are used for cutting and shearing food
• Canines (cuspids) have a single cusp, a high point used for tearing the food.
• Premolars (bicuspids) which have two cusps, are adapted for crushing and cracking food
• molars (tricuspids), with multiple cusps, are well adapted for grinding food into fine pieces
• Humans and all other mammals develop two sets of teeth during their lifetimes.
• The first set of teeth consists of the deciduous (primary or baby) teeth
• the second set, the permanent (secondary) teeth.
• Teeth begin to erupt in babies at about six months of age
• By the time a child is six years old, a full set of deciduous teeth (consisting of 20 teeth) is usually present.
• Canines are pointed cusps located between incisors and premolars; they are also called cuspids because they resemble the fangs of wolves.
• Incisors are cutting teeth that have sharp edges used for biting off food.
• Infant Dental Formula: I 2/2 , C 1/1 , P 0/0, M 2/2
• Adult Dental Formula: I 2/2 , C 1/1 , P 2/2 , M 3/3
• the permanent teeth are growing in the jaws beneath the deciduous teeth
• When the permanent teeth have enlarged sufficiently, they exert pressure on the roots of the deciduous teeth above
• The roots are resorbed and the deciduous teeth are shed (exfoliated).

  • This process usually begins when a child is about 6 years old and is completed by age 11 or 12.
• All of the permanent teeth do not appear until a person is 18 to 20 years of age.

  • In the adult, there are 16 teeth in each jaw, 32 teeth altogether.
• All teeth are constructed on a basic plan, consisting of two principal parts: the crown, which is the exposed portion of the tooth and the root, which is the portion of the tooth embedded in the alveolus (the bony socket) of the maxilla or mandible.
• Accessory organs that are found in association with the mouth include the three pairs of primary salivary glands: parotid, submandibular, and sublingual
• The parotid glands, the largest of the salivary glands, lie anterior to the ear. These glands have an irregular shape and overlap the large masseter muscle.
• Inferior to the parotid glands are the submandibular glands. These glands are situated along the inner surfaces of the mandible.
• The small sublingual glands are anterior and deep to the submandibular glands.
• Saliva has a variety of functions, including lubricating the mouth, moistening the food and dissolving chemicals in food so that they can be tasted.
• saliva contains the enzyme – salivary amylase that begins the digestion of carbohydrates
• From the mouth, food passes posteriorly into the pharynx.
• the three regions of the pharynx: the nasopharynx, the oropharynx and the laryngopharynx.
• The oropharynx and the laryngopharynx are common passageways for food, liquids and air
• The nasopharynx is not part of the digestive tract
• The esophagus is a muscular tube that functions in the transport of food to the stomach.
• The esophagus descends through the thoracic cavity, just posterior to the trachea, and then enters the abdominal cavity through an opening in the diaphragm.
• As food and liquids pass from the laryngopharynx into the esophagus, the opening to the larynx is closed off by the epiglottis.

  • This action ensures that food and fluids do not enter the respiratory tract