1. The Digestive Tract

2. Root Words

3. The GI tract (gastrointestinal tract)
The muscular alimentary canal
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
The accessory digestive organs
Supply secretions contributing to the breakdown of food
Teeth & tongue
Salivary glands
Gallbladder
Liver
Pancreas

4. The Digestive Process
Ingestion
Taking in food through the mouth

5. The Digestive Process Ingestion Propulsion (movement of food)
Taking in food through the mouth
Propulsion (movement of food)
Swallowing
Peristalsis – propulsion by alternate contraction &relaxation

6. The Digestive Process Ingestion Propulsion (movement of food)
Taking in food through the mouth
Propulsion (movement of food)
Swallowing
Peristalsis – propulsion by alternate contraction &relaxation
Mechanical digestion
Chewing
Churning in stomach
Mixing by segmentation

7. The Digestive Process Ingestion Propulsion (movement of food)
Taking in food through the mouth
Propulsion (movement of food)
Swallowing
Peristalsis – propulsion by alternate contraction &relaxation
Mechanical digestion
Chewing
Churning in stomach
Mixing by segmentation
Chemical digestion
By secreted enzymes: see later

8. The Digestive Process Ingestion Propulsion (movement of food)
Taking in food through the mouth
Propulsion (movement of food)
Swallowing
Peristalsis – propulsion by alternate contraction &relaxation
Mechanical digestion
Chewing
Churning in stomach
Mixing by segmentation
Chemical digestion
By secreted enzymes: see later
Absorption
Transport of digested end products into blood and lymph in wall of canal

9. The Digestive Process Ingestion Propulsion (movement of food)
Taking in food through the mouth
Propulsion (movement of food)
Swallowing
Peristalsis – propulsion by alternate contraction &relaxation
Mechanical digestion
Chewing
Churning in stomach
Mixing by segmentation
Chemical digestion
By secreted enzymes: see later
Absorption
Transport of digested end products into blood and lymph in wall of canal
Defecation
Elimination of indigestible substances from body as feces

10. Chemical digestion
Complex food molecules broken down into chemical building blocks
Carried out by enzymes secreted by digestive glands into alimentary canal

11. Histology of alimentary canal wall Same four layers from esophagus to anal canal
Mucosa
Submucosa
Muscularis externa
Serosa
from lumen (inside) out

12. Inner layer: the mucosa* (mucous membrane)
Has folds called Lumens, which help increase absorption area. *

13. Second layer: the submucosa*
Connective tissue containing major blood vessels and Nerves
Nourishes surrounding tissue *

14. Muscular Layer
Two layers of smooth muscle responsible for movement of material
Inner circular layer
Squeezes
Outer longitudinal layer:
shortens gut *

15. Serosa
Protect underlying tissue and secretes fluid which lubricates outer surface
Allows abdominal cavity to slide freely *

16. Omentum: Flap of tissue that hangs from stomach for insulation, protection, and wound isolation

18. The Mouth Mouth = oral cavity Lips- orbicularis oris muscle
Lining: thick stratified squamous epithelium
Lips- orbicularis oris muscle
Cheeks – buccinator muscle
Teeth

19. Tongue Mostly muscles Grip and reposition food
Forms “bolus” of food (lump)
Help in swallowing
Speech – help form some consonants

20. Teeth Called “dentition”
Teeth live in sockets (alveoli) in the gum-covered margins of the mandible and maxilla
Chewing: raising and lowering the mandible and moving it from side to side while tongue positions food between teeth

21. Salivary glands (tuboalveolar glands)
Parotid
Largest of salivary glands
Between skin of cheek
Submandibular
Located in the floor of lower jaw
Sublingual
Smallest salivary gland
Floor of jaw, inferior to tongue
Saliva: mixture of water, ions, mucus, enzymes
keep mouth moist
dissolves food so can be tasted
moistens food
starts enzymatic digestion
buffers acid
antibacterial and antiviral

22. Pharynx Muscular walls allows for swallowing * * * ___oropharynx
___laryngopharynx * * *

23. Esophagus * Passage from pharynx to stomach
Contains muscles to move food downward
Esophagus___________ *

24. Contains all 4 layers (see right)
Microscopic anatomy of esophagus
Contains all 4 layers (see right)
Epithelium: nonkeratinized stratified squamous epithelium
At GE junction – thin simple columnar epithelium
Mucus glands in wall
Muscle (muscularis externa) changes as it goes down
Superior 1/3 of esophagus: skeletal muscle (like pharynx)
Middle 1/3 mixture of skeletal and smooth muscle
Inferior 1/3 smooth muscle (as in stomach and intestines)
When empty, mucosa and submucosa lie in longitudinal folds

25. Esophagus histology

26. Stomach Temporary storage and mixing – 4 hours Starts food breakdown
Into “chyme”
Starts food breakdown
Pepsin
HCl (hydrochloric acid) helps kill bacteria
Most nutrients wait until get to small intestine to be absorbed; exceptions are:
Water, electrolytes, some drugs like aspirin and alcohol (absorbed through stomach)

28. Small intestine Longest part of alimentary canal (2.7-5 m)
Most enzymatic digestion occurs here
Most enzymes secreted by pancreas, not small intestine
3-6 hour process
Small intestine___________

29. Small intestine designed for absorption
Villi (fingerlike projections) 1 mm high – simple columnar epithelium: velvety
Absorptivie cell with microvilli to increase surface area & many mitochondria: nutrient uptake is energy-demanding *
Lacteal*: network of blood and lymph capillaries
-Carbs and proteins into blood to liver via hepatic portal vein
-Fat into lymph: fat-soluble toxins e.g. pesticides circulate systemically before going to liver for detoxification

30. * Intestinal flora – the permanent normal bacteria
Manufacture some vitamins, e.g. K, which get absorbed
-have many mitochondria: nutrient uptake is energy-demanding
Duodenal glands* *
Mucus to counteract acidity from stomach
Hormones:
Cholecystokinin (stimulates GB to release stored bile, also pancreas)
Secretin (stimulates pancreatic ducts to release acid neutralizer) *
-produce mucus

31. General histology of digestive tract

34. Large intestine Digested residue reaches it
Main function: to absorb water and electrolytes

35. Rectum * * * In pelvis No teniae Strong longitudinal muscle layer
Has valves * * *

36. Defecation
Triggered by stretching of wall, mediated by spinal cord parasympathetic reflex

37. Histology – large intestine
No villi
Fewer nutrients absorbed
A lot of goblet cells for mucus
Lubricates stool

38. The Liver Largest gland in the body (about 3 pounds)
Over 500 functions
Main job is to filter blood coming from digestive tract

39. posterior
anterior

41. Just some of the liver’s repertoire
Produces bile
Picks up glucose from blood
Stores glucose as glycogen
Processes fats and amino acids
Stores some vitamins
Detoxifies poisons and drugs
Makes the blood proteins

42. Gallbladder* Bile is produced in the liver
Bile is stored in the gallbladder
Bile is excreted into the small intestine when needed to dissolve fat and cholesterol *

44. Pancreatic endocrine function (hormones released into blood)
Islets of Langerhans (AKA “islet cells”) are the hormone secreting cells
Insulin (from beta cells)
Lowers blood glucose (sugar)
Glucagon (from from alpha cells)
Raises blood glucose (sugar)
(more later)

45. Endocrine cells: