1. Chapter 14 – Part 4 The Digestive System

2. Accessory Digestive Organs
Salivary glands
Teeth
Pancreas
Liver
Gall bladder

3. Salivary Glands
Salivary Glands – empty their secretions (saliva) into the mouth
Three Pairs:
Parotid glands – located anterior to ears
Submandibular and Sublingual glands – Empty secretions into the floor of the mouth through tiny ducts

4. Saliva Mixture of mucus and serous fluids
Moistens and helps to bind food together into a mass called a bolus
Contains the enzyme salivary amylase, which begins starch digestion in the mouth
Dissolves food chemicals so they can be tasted

5. Teeth The role is to masticate (chew) food
The teeth tear and grind the food, breaking it down into smaller fragments
Humans have two sets of teeth
Deciduous (baby) teeth
Permanent teeth

6. Teeth Deciduous (baby) teeth Permanent teeth
Begin to erupt around 6 months
Full set (20 teeth) by the age of 2 years
Permanent teeth
Replace deciduous teeth beginning between the ages of 6 to 12
A full set is 32 teeth, but some people do not have wisdom teeth

7. Classification of Teeth
Incisors – chisel-shaped; adapted for cuttin
Canines – Fanglike; adapted for tearing or piercing
Premolars (bicuspids) and Molars – broad crowns with rounded cusps (tips); best suited for grinding

8. Regions of a Tooth: Crown
Crown – exposed part of the tooth above the gum
Covered with enamel, the hardest substance in the body
Enamel is heavily mineralized with calcium salts

9. Regions of a Tooth: Crown
Dentin - A bonelike material that underlies the enamel and forms the bulk of the tooth
Pulp cavity – Cavity that contains blood vessels and nerves and that is surrounded by dentin
Supplies nutrients and provides for tooth sensation

10. Regions of a Tooth: Root
Root – Portion of the tooth embedded in the jawbone
Periodontal membrane (ligament) holds the tooth in place in the bony jaw
The root canal carries the blood vessels and nerves

11. Regions of a Tooth: Neck
Neck – Connects the crown to the root
Region in contact with the gum

12. Impacted Teeth
Impacted teeth – when teeth remain embedded in the jawbone
Exert pressure and cause a good deal of pain and must be removed

13. Pancreas
Produces a wide spectrum of digestive enzymes that break down all categories of food
Enzymes are secreted into the duodenum
Enzymes are secreted in an alkaline fluid, which neutralizes the acidic chyme coming in from the stomach
The pancreas also has an endocrine function. It produces the following hormones:
Insulin
Glucagons

14. Liver Largest gland in the body
Located on the right side of the body under the diaphragm; Overlies and almost completely covers the stomach
Consists of four lobes and is suspended from the diaphragm
Many functions; However, its digestive function is to produce bile

15. Bile Produced by cells in the liver
Bile leaves the liver through the common hepatic duct and enters the duodenum through the bile duct
Function: Its bile salts emulsify fats by physically breaking large fat globules into smaller ones
Provides more surface area for the fat-digesting enzymes to work on
Does not contain enzymes

16. Composition of Bile Yellow-to-green watery solution containing:
Bile salts
Bile pigments
Cholesterol
Phospholipids
Electrolytes

17. Gall Bladder
Small, thin-walled green sac found in a shallow fossa in the inferior surface of the liver
Function: Store bile from the liver
When food digestion is not occurring: Bile backs up the cystic duct and enters the gallbladder to be stored
When food digestion is occurring: Stored bile is spurt out into the duodenum in the presence of fatty food

18. Gallstones
Gallstones – The crystallization of cholesterol found in bile
Occurs when bile is stored for too long in the gallbladder or when too much water is removed
Tend to be quite sharp; Agonizing pain may occur

19. Jaundice
Jaundice - The yellowing of the body tissues caused by bile pigments circulating through the body
Bile salts and bile pigments begin to enter the bloodstream
Can be caused by:
Blockage of the common hepatic or bile ducts (example: wedged gallstones)
Liver problems such as hepatitis or cirrhosis

20. Liver Problems Hepatitis - Inflammation of the liver
Most often due to viral infections resulting from drinking contaminated water or transmitted in blood via transfusion or contaminated needles
Cirrhosis - Chronic, inflammatory condition in which the liver is severely damaged and becomes hard and fibrous
Almost guaranteed when one drinks alcoholic beverages in excess for many years
Is a common consequence of severe hepatitis

21. Processes of the Digestive System
The essential activities of the GI tract include the following six processes:
Ingestion
Propulsion
Food breakdown: mechanical digestion
Food breakdown: chemical digestion
Absorption
Defecation

22. Processes of the Digestive System
Ingestion – Getting food into the mouth
Active, voluntary process

23. Processes of the Digestive System
Propulsion – Moving foods from one region of the digestive system to another
Peristalsis – Involuntary alternating waves of contraction and relaxation; Net effect is to squeeze the food along the tract
Segmentation – Moving food back and forth across the internal wall of the organ; Aids in mixing it with digestive juices

24. Processes of the Digestive System
Food Breakdown: Mechanical digestion
Prepares food for further degradation by enzymes
Examples include:
Mixing of food in the mouth by the tongue
Churning of food in the stomach
Segmentation in the small intestine

25. Processes of the Digestive System
Food Breakdown: Chemical Digestion
Enzymes break down food molecules into their building blocks
Each major food group uses different enzymes:
Carbohydrates are broken down into simple sugars
Proteins are broken down into amino acids
Fats are broken down to fatty acids and glycerol (an alcohol)

26. Processes of the Digestive System
Absorption
End products of digestion are absorbed in the blood or lymph
The small intestine is the major site of absorption
Defecation
Elimination of indigestible substances from the body via the anus in the form of feces

27. Processes of the Digestive System

28. Control of Digestive Activity
The body must maintain a constant internal environment, especially in the blood, since it comes into contact with all body cells
The digestive system is mostly controlled by reflexes via the parasympathetic division of the autonomic nervous system
Chemical and mechanical receptors are located in organ walls that trigger reflexes

29. Control of Digestive Activity
The sensors involved in these reflexes respond to a number of stimuli:
Stretch of the organ by food in its lumen
pH of the contents
Presence of certain breakdown products of digestion
Reflexes include:
Activation or inhibition of glandular secretions (digestive juices or hormones)
Smooth muscle activity (mixing or propagation of food)