Digestive System 1

• Break down nutrients into a form that the body can use
• Absorb nutrients into bloodstream
• Eliminate parts of food that can't be digested

Materials enter digestive tract

• Mechanical: Materials are crushed, sheared, and churned to allow them to fit through digestive tract and to increase surface area
• Chemical Break down food

Nutrients, vitamins, electrolytes move into the interstitial fluid of the digestive tract, then into the blood

Water and indigestible residue consolidated into feces

Feces is eliminated

• Digestive tract (alimentary canal): mouth, pharynx, esophagus, stomach, small intestine, large intestine and GI tract includes stomach and intestines
• Accessory Organs: include teeth, tongue, salivary glands, live, gallbladder, pancreas

Lines the lumen and consists of inner epithelium, lamina propia (loose connective tissue), and Muscularis mucosa (thin layer of smooth muscle)

• Thicker layer of loose connective tissue
• Contains blood vessels, lymphatic vessels, nerves, and mucous glands

• Two layers of muscle
• Inner circular layer: sometimes thickens to form valves
• Outer longitudinal layer: responsible for moving food through tract

Thin layer of tissue between end of esophagus and beginning of rectum

Fibrous connective tissue in pharynx, esophagus, and rectum

• Fluid-filled sac
• Visceral peritoneum: serosa layer of GI tract
• Parietal peritoneum: lines inner surface of the body cavity
• Membrane secrete fluid for lubrication
• Intraperitoneal organs are enclosed by mesentery (stomach, liver, parts of small intestine and colon)
• Retroperitoneal organs lie against posterior body wall and are only covered by mesentery on anterior side (duodenum, pancreas, parts of colon)

• Connective tissue sheets that suspend the stomach and intestines from the parietal peritoneum
• Allows freedom of movement while still holding abdominal viscera in proper place
• Prevents tangling (twisting) of intestines
• Holds blood vessels and nerves in contact with GI tract

• Mesentery that extends from the liver to the stomach
• Stabilizes the stomach
• Provides route for blood vessels entering and leaving the liver

• Pouch of adipose tissue that hangs from the stomach and over the small intestine
• Provides protection and insulation

Provides support for the small intestine

• Mesentery fused to posterior body wall
• Provides support for the colon

• Nervous system network in the esophagus, stomach, and intestines
• Regulates tract motility, secretion, and blood flow
• Can function independently of the CNS, but influenced by it

• In submucosa
• Controls secretion from glands in mucosa
• Controls movement of muscularis mucosa

• Parasympathetic fibers between layers of muscularis externa
• Controls contractions of these muscles

Monitor tension in gut wall

Stretch or chemical stimulation activates contractions in nearby muscularis externa

Parasympathetic activation regulates digestive motility and secretion

Gastrin and secretin regulate digestion

Chemical messengers produced by digestive tract diffuse to nearby target cells

• Senses taste of food
• Mechanically processes food
• Lubricates food with saliva
• Begins chemical digestion of carbohydrates and lipids

• Hold food in mouth and push it between teeth
• Essential for sucking and blowing
• Consist of subcutaneous fat, buccinator muscle of cheek, and orbicularis oris of lips

Colored like rest of face, has hair follicles and sebaceous glands

• Red, hairless region where lips meet
• Blood vessels very close to epidermal surface

Inner surface of lips

Fold that connects lip of gum

• Manipulates food between teeth
• Covered in nonkeratinized stratified squamous epithelium
• Body: anterior 2/3 in oral cavity
• Root: posterior 1/3 in oropharynx

Row of papillae marking boundary between body and root

Groove behind vallate papillae

Fold that attaches tongue to floor of mouth

Contained in the root of the tongue

• Entirely within tongue
• Produced subtle tongue movements

• Insert into tongue
• Produce strong tongue movements

• Serous and mucous glands among extrinsic muscles
• Secrete some saliva

Separates oral cavity from nasal cavity

Anterior part supported by maxillae and palatine bones

Ridges that help tongue hold food

• Posterior part composed of muscle and glands
• Contains uvula, which keeps food in the mouth until swallowing occurs and prevents food from entering nasal cavity

• Masticate food into smaller pieces
• Makes it easier to swallow
• Increases surface area for enzymes to digest it

• 32 adult teeth, 20 deciduous (baby) teeth
• 16 in mandible, 16 in maxilla
• From midline to rear-
• 2 incisors to bite food
• 1 canine to puncture/shred
• 2 premolars and 3 molars to crush and grind

• Teeth develop beneath gums to erupt in predictable order
• Erupt from 6-30 months
• Replaced by permanent teeth from ages 6-25
• Root of baby teeth dissolves as permanent tooth develops
• Wisdom teeth (3rd molars) can be crowded against neighbors so that they can't erupt (impacted)

Tooth socket in the bone

Anchors tooth in alveolus

Covers alveolar bone

Portion above gum

Portion below gum

Where crown, root, and gum meet

Groove between tooth and gum

Hard, yellow tissue

Hard covering for crown formed before tooth erupts

• Hard covering for root
• Dentin and cementum can regenerate but enamel can't

Tube for nerves and blood vessels to reach pulp cavity in crown

Plaques of sugars and bacteria left on the teeth can erode enamel and dentin to for caries (cavities)

• Endodontic Therapy required if cavity extends into pulp
• Pulp is removed and replaced with new material

• Moistens mouth
• Begins digestion of starch and fat
• Cleanses teeth
• Inhibits bacterial growth
• Dissolves tastants to stimulate taste buds
• Moistens and binds food for swallowing

Mostly water

begins starch digestion

activated by stomach acid and digests fat after food is swallowed

binds and lubricates food

kill bacteria

inhibits bacterial growth

Small glands that constantly secrete saliva

Large glands with ducts

Anterior to earlobe

Along Mandible

Along tongue

• Mucous cells secrete mucous
• Serous cells secrete thin fluid full of amalyse and electrolytes
• The fluids combine to salivary ducts
• Salivatory nuclei in medulla and pons regulate saliva production

• Three pharyngeal constrictors force food downward during swallowing
• When not swallowing, inferior constrictor remains closed to prevent air from entering esophagus

• Extends from pharynx to cardiac orifice of stomach
• Passes through esophageal hiatus in diaphragm
• Lower esophageal sphincter prevents stomach contents from entering esophagus and prevents stomach acid from eroding esophagus (heartburn)

• Bolus of food pushed down through mouth, pharynx, and esophagus
• Swallowing center in medulla coordinates muscles of pharynx and esophagus through trigeminal, facial, glossopharyngeal and hypoglossal nerves

• Under voluntary control
• Tongue collects flood, forms bolus, pushes it posteriorly
• Food accumulates in oropharynx, epiglottis moves, and bolus enters laryngopharynx
• Bolus activates tactile receptors that trigger phase 2

• Involuntary
• Tongue, soft palate, and epiglottis/larynx block food from mouth, nasal cavity, and larynx
• Food driven downward by pharyngeal constrictors
• Bolus triggers peristalsis once it enters esophagus
• Lower esophageal sphincter relaxes to let bolus enter stomach