Anatomy and Function of the Alimentary Canal: From Mouth to Stomach, Study notes of Physiology

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The Digestive System

Chapter 14 Lecture

Digestion

‡ Digestion Ȃ mechanical and chemical breakdown of

foods

± Breakdown allows for absorption of nutrient molecules

‡ The digestive system consists of:

1) Alimentary canal

‡ Tube that runs from the mouth to the anus

2) Accessory organs

‡ Salivary glands, liver, gallbladder, and pancreas ‡ Food does NOT travel through the accessory organs!!

The Alimentary Canal

‡ Alimentary Canal

± Tube is ~8M in length

± Runs through the thoracic

& abdominopelvic cavities

The Alimentary Canal

‡ Structure

± Outermost layer = serosa (serous layer; composed of

visceral peritoneum)

‡ Secretes serous fluid ± Protects underlying tissues ± Lubrication of the tube prevents friction with organs in the abdominal cavity

± Middle layer = Muscle (two layers of smooth muscle)

‡ Moves food through the tube ± Contraction of circular fibers Ȃ decreases diameter ± Contraction of longitudinal fibers Ȃ shortens tube

The Alimentary Canal

‡ Movements of the tube

± Mixing movements

‡ Smooth muscles contract rhythmically in small sections of the tube

± Propelling movements

‡ Peristalsis Ȃ wavelike motion

‡ Waves of contraction and relaxation ± Contraction pushes food through the tube; relaxation allows food to move into the next segment of the tube

Mouth

‡ Mouth

± Receives food

± Both mechanical and chemical digestion occur in the

mouth:

‡ Mastication Ȃ mechanical breakdown of food ( chewing )

‡ Enzymes secreted in the saliva initiate chemical digestion

Mouth

‡ Cheeks and Lips

± Cheeks form the lateral walls of the mouth

‡ Composed of : skin, muscle, fat, and epithelium ± Do you remember the muscles that are located within the cheeks and are associated with chewing and facial expressions?

± Lips surround the mouth opening

‡ Composed of skeletal muscle ‡ Contain sensory receptors Ȃ detect food temperature and texture

Mouth

‡ Teeth

± Begin mechanical digestion Ȃ break food into smaller pieces

± Two sets of teeth:

‡ Deciduous (primary) teeth Ȃ develop between 6 months and 4 years of age ± 20 total Ȃ 10 in the maxilla and 10 in the mandible

‡ Permanent (secondary) teeth Ȃ develop between 6 years and 25 years of age ± 32 total Ȃ 16 in each jaw

Mouth

‡ Teeth

± Teeth are adapted to handle food in different ways

‡ Incisors (8) ± Bite off pieces of food ‡ Canines (4) ± Ž•‘”‡ˆ‡””‡†–‘ƒ•Dz —•’‹†•dz ± Grasp and tear food ‡ Premolars (8) ± Ž•‘”‡ˆ‡””‡†–‘ƒ•Dz„‹ —•’‹†•dz ± Grind food particles ‡ Molars (12) ± Grind food particles

*Numbers are representative of secondary teeth