Chapter 14 Part 4 The Digestive System Accessory

Chapter 14 – Part 4 The Digestive System

Accessory Digestive Organs · Salivary glands · Teeth · Pancreas · Liver · Gall bladder

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

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

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 1. Deciduous (baby) teeth 2. Permanent teeth

Teeth · 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 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: 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: 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: 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: Neck · Neck – Connects the crown to the root · Region in contact with the gum

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

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: 1. Insulin 2. Glucagons

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

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 fatdigesting enzymes to work on · Does not contain enzymes

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

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

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

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: 1. Blockage of the common hepatic or bile ducts (example: wedged gallstones) 2. Liver problems such as hepatitis or cirrhosis

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

Processes 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 System · Ingestion – Getting food into the mouth · Active, voluntary process

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

Processes of the Digestive System · Food Breakdown: Mechanical digestion · Prepares 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 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 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 System

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

Control 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. p. H 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)