Lesson 1 in science Human digestive track.

Mouth

• Entrance to the digestive system

• Teeth and tongue that digest food mechanically digest food

• Salivary glands secretions initiate chemical digestion

• Mammals generally have anatomically similar mouths

Teeth

• Adults have 32 teeth children have 20 or fewer depending on their age.

• The incisors and canines are use for cutting and tearing

• Premolars are for chewing and grinding food

• Food is broken down mixed with saliva to make chemical digestion

The crown located above the gums the neck is in between the crown and root. The root holds the teeth in place.

Tongues and salivary glands

• Rough surface because of the papillae

• Three types of papillae: vallate, foliate, and fungiform

• The taste buds are receptor cells that make the 5 tastes: bitter, salty, sour, sweet, and umami.

• the human tongue has about 2000 to 5000 taste buds

• Saliva is secreted by the salivary glands

• saliva moistens food

• The saliva is responsible in maintaining the pH level in the mouth at 6.2 and 7.6

Saliva contains a enzyme called salivary amylase, which helps in digestion of starch, a complex carbohydrate, by breaking it down into maltose, a simple carbohydrate

pairs of the salivary glands

• The parotid

• sublingual

• submandibular glands

Pulp cavity

Pulp cavity contains blood vessels located at the center of the tooth when its inflamed it causes a tooth ache

Parts of the Pulp cavity:

Dentin is the hard bony substance surrounding the pulp cavity

Enamel layer of calcium phosphate covers the dentin enables teeth to chew hard food

• Pharynx

• 12 to 14 cm tube

• Larynx, the passageway for air

• Esophagus: passageway for food

• The epiglottis, a flap of tissue that covers the front of the larynx, closes so food doesn’t enter.

Esophagus

• 25 cm tube

• Peristalsis: propels food to the stomach.

• Mucous glands: secrete mucus that lubricates food for easier passage.

• Upper esophageal sphincter: prevents air from entering the esophagus and stops food from coming back.

• Sphincter: controls the opening to the stomach

Stomach

• 20 m long

• expandable organ

• Rugea: Increases stomach surface.

• Lower esophageal sphincter: Prevents the reflux of food and acid into the esophagus

• Four regions: the cardia, fundus, body, and pylorus

• Stomach glands: makes gastric juices to aid in digestion and mucus to protect the stomach wall

• Gastric juices are composed of hydrochloric acid and the digestive enzymes pepsin and lipase.

• Hydrochloric acid softens fibrous foods and kill most of the microorganisms in the food.

• pH level of 1 and 2

• Pepsin breaks down proteins.

• The stomach of an adult can accommodate 1 to 1.5 liters of food and empty after 3 to 4 hours.

• When food and gastric juices mix, they will form chyme.

Small Intestine.

• The chyme moves down to the smaller intestine

• Peristalsis propels food along the small intestine.

• 5 to 7 meters long and 2.5 cm in diameter

• Parts: The duodenum (25 to 30 cm), jejunum (2.5 m), and ileum (3 m)

• The pyloric sphincter controls the amount of chyme that enters the small intestine.

• Main site of chemical digestion/absorption

• Finger-like projections called the villi

• At the center of each villus are tiny blood cells called capillaries and tiny lymph vessel called the lacteal.

• Capillaries transport the carbohydrates and proteins.

• Lacteals transport liquids.

Large intestine.

• 2 meters long and 7 cm in diameter. ⁣

• Only absorbs water and salts.

• The efficiency of digestion depends on if there are digestive enzymes

• Most fibers/undigested food just go to the rectum.

• Rectum: Storage chamber.

• Undigested food/feces comes out of the body through the anus in a process called egestion or defecation.

• A vestigial organ means it lost its function during evolution. Ex: appendix.

Pancreas

• secretes enzymes that help break down fats (lipase), starch (amylase), and protein (protease).⁣