Chapter 14 – Part 4The Digestive System

Accessory Digestive Accessory Digestive Organs Organs

Salivary glands

Teeth

Pancreas

Liver

Gall bladder

Salivary Salivary GlandsGlands

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

SalivaSaliva 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

TeethTeeth 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

1.Deciduous (baby) teeth

2.Permanent teeth

TeethTeeth

Deciduous (baby) 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

Classification of TeethClassification 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

Regions of a Tooth: CrownRegions 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

Regions of a Tooth: CrownRegions 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

Regions of a Tooth: RootRegions 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

Regions of a Tooth: NeckRegions of a Tooth: Neck

Neck – Connects the crown to the root Region in contact

with the gum

Impacted TeethImpacted Teeth

Impacted teeth – when teeth remain embedded in the jawbone

Exert pressure and cause a good deal of pain and must be removed

PancreasPancreas 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:1. Insulin2.Glucagons

LiverLiver

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

BileBile 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

Composition of BileComposition of Bile

Yellow-to-green watery solution containing: Bile salts

Bile pigments

Cholesterol

Phospholipids

Electrolytes

Gall BladderGall 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

GallstonesGallstones

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

JaundiceJaundice 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:

1. Blockage of the common hepatic or bile ducts (example: wedged gallstones)

2. Liver problems such as hepatitis or cirrhosis

Liver ProblemsLiver 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

Processes of the Digestive SystemProcesses of the Digestive System

The essential activities of the GI tract include the following six processes:

1. Ingestion

2. Propulsion

3. Food breakdown: mechanical digestion

4. Food breakdown: chemical digestion

5. Absorption

6. Defecation

Processes of the Digestive SystemProcesses of the Digestive System

Ingestion – Getting food into the mouth

Active, voluntary process

Processes of the Digestive SystemProcesses 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

Processes of the Digestive SystemProcesses of the Digestive System

Food Breakdown: Mechanical digestionPrepares food for further degradation by

enzymes

Examples include:

1. Mixing of food in the mouth by the tongue

2. Churning of food in the stomach

3. Segmentation in the small intestine

Processes of the Digestive SystemProcesses 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)

Processes of the Digestive SystemProcesses 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

Processes of the Digestive SystemProcesses of the Digestive System

Control of Digestive ActivityControl 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

Control of Digestive ActivityControl of Digestive Activity

The sensors involved in these reflexes respond to a number of stimuli:

1. Stretch of the organ by food in its lumen

2. pH of the contents

3. Presence of certain breakdown products of digestion

Reflexes include:

1. Activation or inhibition of glandular secretions (digestive juices or hormones)

2. Smooth muscle activity (mixing or propagation of food)