Digestion and Nutrition Digestion Digestion mechanical AND chemical

Digestion and Nutrition Digestion: Digestion mechanical AND chemical breakdown of foods into… Nutrients: Nutrients food substances necessary to survive

Digestive System • Alimentary canal: from your mouth to your anus (your butthole, not the planet) – 9 meters long • Wall of the alimentary canal – Mucosa: innermost epithelial layer • Forms many folds to increase absorption – Submucosa: loose connective tissue with many glands and blood vessels—nourishes – Muscular layer: smooth muscle fibers are in circular fibers or longitudinal fibers – Serosa: secrete serous fluid so things move freely

Movements in the canal • Two basic movements: mixing movements and propelling movements • Peristalsis: Peristalsis wavelike motion • See Figure 15. 4

MOUTH • Receives food and begins digestion • Cheeks are the outer layers of skin with fat and muscles of facial expression • Lips are mobile structures that can close the mouth • Tongue fills oral cavity – Frenulum connects midline of tongue to the floor of the mouth – Papillae contain taste buds – Lingual tonsils at the root

MOUTH cont. • Palate forms the roof of the oral cavity and consists of the hard palate and soft palate • Uvula is a projection of soft palate that closes the opening between the nasal cavity and pharynx • Palatine tonsils in back of mouth • Pharyngeal tonsils (adenoids) on posterior walls of pharynx • Teeth: Teeth see table 15. 1

Salivary Glands • Secrete saliva which moistens food particles and begins the chemical digestion of carbohydrates • Amylase: Amylase enzyme that digests carbohydrates • Parotid glands: largest; found in front of ear; secrete watery fluid rich with amylase • Submandibular glands: in floor of mouth secrete a viscous fluid • Sublingual glands: smallest; secrete thick, stringy mucus

Pharynx • Cavity behind mouth • Nasopharynx: Nasopharynx passageway for breathing found behind/below nasal cavity • Oropharynx: Oropharynx opens behind the soft palate; passageway for food and air • Laryngopharynx: Laryngopharynx passageway to esophagus below oropharynx

Esophagus • Straight tube that provides passageway from pharynx to stomach • Goes through diaphragm (esophogeal hiatus) • Lower esophageal sphincter (cardiac sphincter) opens to stomach

Swallowing Mechanism • Three stages: – Food is chewed and mixed with saliva; the tongue rolls this mixture into a bolus and forces it into pharynx – Swallowing reflex • Soft palate prevents food from going up nose • Hyoid bone and larynx are elevated and epiglottis closes off trachea so you don’t choke • Tongue seals off oral cavity • Pharynx is pulled upward • Esophagus opens • Peristaltic wave begins to force food into esophagus – Peristalsis transports food in the esophagus to stomach