1. Digestive System

2. Digestive System – Fig. 15-1, Table 15-1
Digestion – process of changing food substances into forms that can be absorbed; digestive system consists of an alimentary canal & several accessory organs
Digestive structures are adapted for mechanical and chemical digestion; enzyme secretion, and absorption
(overview of digestive system)

3. Digestive System – Fig. 15-1, Table 15-1
General Characteristics of the Alimentary Canal – various regions are specialized to perform specific functions
Structure of the wall – 4 layers – Fig. 15-2
Mucous membrane – inner most layer; function to protect, absorption, secretion
Submucosa – functions to nourish surrounding tissues, tranports absorbed materials
Muscular layer (muscularis) – functions in the movement of the tube and its contents; smooth muscle fibers are arranged in circular & longitudinal groups
Serous (serosa) – composed of visceral peritoneum; functions to protect and lubricate

4. Wall of Digestive Tract

5. Digestive System Movements of the tube – Fig. 15-3
Motor functions include mixing and propelling movements
Mixing – small segments of smooth muscle contraction
Movement by peristalsis – tube undergoes receptive relaxation just ahead of a peristaltic wave

6. Peristalsis

7. Digestive System Innervation of the tube
Innervated by branches of sympathetic and parasympathetic divisions of the autonomic nervous system
Parasympathetic impulses generally cause an increase in digestive activities; sympathetic impulses generally inhibit digestive activities

8. Mouth – adapted to receive food and begin preparing it for digestion
Mouth – adapted to receive food and begin preparing it for digestion. It also serves as an organ of speech & sensory reception. Fig. 15-4

9. Mouth Cheeks & lips Tongue Cheeks form the lateral walls of the mouth
Lips – highly mobile & possess a variety of sensory receptors useful in judging the characteristics of food
Tongue
Thick, muscular organ that aids in the mastication of food with saliva and moving it toward the pharynx
Rough surface (papillae) aids in handling food & contains taste buds
Lingual tonsils (lymphatic tissue) are located on the root of the tongue

10. Mouth
Palate
Comprises the roof the mouth and includes hard & soft palates
Soft palate closes the opening to the nasal cavity during swallowing
Palatine tonsils (lymphatic tissue) are located on either side of the tongue in the back of the mouth
Pharyngeal tonsils (adenoids) are located on the posterior wall of the pharynx above the border of the soft palate

11. Mouth
Teeth
Two sets of teeth develop in sockets of the mandibular & maxillary bones
20 primary (deciduous) & 32 secondary teeth - Fig. 15-6
Break food into smaller pieces to increase surface area for digestive enzymes to act upon
Teeth are adapted to handle food in different ways
Incisors – biting
Canines (cuspids) – grasping
Molars - grinding

12. Mouth
Teeth
Anatomy – Fig – tooth is divided into crown, neck, root, and is attached/anchored by periodontal membrane (ligament)
Enamel – protects
Dentin – makes up the bulk of the tooth

14. Salivary Glands
Salivary glands – secrete saliva, moistens food, binds food particles together, begins digestion of carbohydrates, makes taste possible, helps cleanse the mouth, & regulates pH in the mouth (pH 6.5 – 7.5) – Fig. 15-7
Salivary secretions – glands include
Serous cells that secrete digestive enzymes (amylase) that are more liquid/watery
Mucous cells that secrete mucus that is more viscous

15. Major salivary glands Parotid – largest; secretion rich in amylase
Submandibular – secretes combinations of enzymes and mucus
Sublingual – secretes mucus

16. Pharynx & Esophagus – serve as passageways
Pharynx – throat, passage for air & food
Swallowing mechanism – 3 stages
food is mixed with saliva & forces into pharynx
Involuntary reflex actions move the food into esophagus
Esophagus to stomach by peristalsis

17. Pharynx & Esophagus – serve as passageways
Passes through mediastinum & penetrates diaphragm
Cardiac sphincter – circular ring of muscle that prevents regurgitation
Hiatal hernia – weak diaphragm, some part of stomach, large intestine or other abdominal organ protrudes into thoracic cavity
Heart burn – gastric juice enters esophagus & causes mucosa to become inflamed

20. Stomach
Mixes food with gastric juices carries on a limited amount of absorption; & moves food to small intestine – Fig. 15-8
Parts of stomach
Cardiac, fundic body & pyloric regions
Pyloric sphincter – serves as a valve between stomach & small intestine; regulates how much “chyme enters
Gastric glands secrete pepsin (breaks down proteins), HCl (kills bacteria, and keeps stomach at pH of about 2 which is optimal for action of pepsin), and lipase (breaks down lipids)

21. Stomach
Stomach not well adapted for absorption, however it can absorb some water, lipid soluble drugs, and alcohol
Mixing & Emptying Actions
as stomach fills the walls stretch – internal pressure remains unchanged
Mixing movements (3 directions of smooth muscle) aid in producing chyme; peristaltic waves move chyme to pyloric region
Muscular wall of pyloric region pumps chyme into the small intestine
Rate of emptying depends on fluidity of chyme & the type of food present

23. Pancreas (accessory organ) – Fig. 15-10
Pancreatic juice digests all food types
Has a high HCO3- (bicarbonate) content that helps to neutralize chyme & causes intestinal contents to be alkaline
Pancreatic duct merges with bile duct & enters small intestine at duodenum

24. Accessory Organs of Digestive Tract

25. Liver/Gall Bladder – Accessory Organs
Functions of the liver
Metabolism of fats, sugars, & proteins
Filters blood
Storage of substances – glycogen, iron, vitamins
Detoxifies – converts ammonia to urea
Secretes bile – emulsifies lipids
Structure
Located in upper R. & central portion of abdominal cavity
Highly vascular & divided into lobes
Functional unit – hepatile lobule

26. Liver/Gall Bladder – Accessory Organs
Function of the Gall Bladder – Fig
Store bile between meals
Release of bile form the common bile duct is controlled by sphincter muscle
Gallstones – cholesterol that has crystallized (pg. 405)
Release of bile is stimulated by cholescystokinin from the small intestine which causes the gall bladder to contract

27. Small Intestine – extends from pyloric sphincter to the large intestine Fig. 15-9
Functions
Complete digestion of all nutrients
Absorbs nutrients which then enter blood stream
Transports residues to the large intestine
Secrete digestive enzymes
Parts
Duodenum, jejunum, & ileum
Suspended from the posterior abdominal wall by mesentery (extension of peritoneum)

28. Small Intestine Structure (circular folds – plica{e})
Lined with villi that increase surface area & aid in mixing & absorbing
Microvilli on the free ends of epithelial cells increase surface area even more
Regulation/absorption/movements
Secretion of intestinal enzymes are enhanced by the presence of gastric juice & chime and distension of small intestinal wall
Villi absorb water & nutrients
Movements include mixing by segmentation & peristalsis
Ileocecal valve controls movements of contents from small to large intestine

29. Small Intestine

30. Villi of Small Intestine

31. Large Intestine
Reabsorbs water & electrolytes and forms 7 stores feces – Fig , 15-13
Parts divided into cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal
Functions
Little or no digestive function; secretes mucus 
Absorption of H2O, electrolytes, & vitamins (produced by bacteria that inhabit large intestine) 
 Movements – similar to those of small intestine
Feces – stored in rectum and eliminated through anus

32. Large Intestine

33. Large Intestine
(colonoscopy)
(colonoscopy showing rectal cancer)