1. Digestive System
Chapter 14

3. 14.1 Anatomy & Physiology of the Digestive System
The organs of the digestive system can be separated into two groups; those forming the alimentary canal (line of organs starting at the mouth and ending at the anus) and those that are accessory organs
The mouth is a chamber of ingestion and where chemical and mechanical digestion begin
The teeth and tongue provide the initial mechanical digestion
Saliva contains the enzyme, amylase, that begins the chemical digestion of starch (this tends to be minimal as most humans do not properly chew their food)
We say food is masticated as it is mixed with saliva

4. 14.1 Anatomy & Physiology of the Digestive System
Swallowing is initially a voluntary action, but continues as an involuntary action
The tongue moves the food to the back of the mouth, elevation of the soft palate, seals off the nasal cavity
Pressure against the pharynx triggers the autonomic, involuntary, swallowing reflex
Beneath the pharynx is the larynx, or voice box, when food is in the pharynx, it causes the larynx to rise, which causes the epiglottis to close off the trachea to keep food out of the respiratory system

6. 14.1 Anatomy & Physiology of the Digestive System
The food (called a bolus) leaving the pharynx, enters the esophagus, a long muscular tube, and is pushed down to the stomach through rhythmic contractions called peristalsis
The opening to the stomach is through a ring of muscle called the cardioesophogeal sphincter
The stomach is a holding station that contains acids that assist in chemical breakdown, denaturing of proteins and killing bacteria
It is highly convoluted which helps it change size; empty it has a volume of 50 mL, full up to 4 L
The stomach has large folds called rugae, when it is empty
Ulcers are caused by the H. pylori bacteria, but where once thought to be the result of stress or poor diet

9. 14.1 Anatomy & Physiology of the Digestive System
Partially digested food and gastric juice (called chyme) leave the stomach through the pyloric sphincter and enter the small intestine
The small intestine of a living person is 4.5 m long (6 m long is a deceased person as muscles have relaxed)
Digestive processes take time here and that is why large amounts of food should not be eaten at one time
The first 25 cm make up the duodenum
It continues digestion, receives enzymes from the liver, pancreas and gall bladder (accessory digestive organs)
Beyond the duodenum are the jejunum and the ileum
Nearly all food absorption occurs ins the small intestine

10. 14.1 Anatomy & Physiology of the Digestive System
The epithelial wall of the small intestine is covered in tiny finger like projections called villi and each villi is covered with projections called microvilli (also called brush border)
The projections greatly increase the surface area for absorption to about 3200 square feet and assist in digestion
Nutrients are absorbed into the blood or lymph

14. 14.1 Anatomy & Physiology of the Digestive System
The large intestine is much larger in diameter, but shorter in length. It is about 5 ft. long and extends from the ileocecal valve to the anus. It eliminates solid waste (feces) and conserves water. It consists of the ascending, transverse and descending colons, the cecum, appendix, rectum and anal canal.

15. 14.2 Anatomy & Physiology of the Digestive System: Accessory Organs
The liver is the largest gland in the body
Its located under the diaphragm, towards the right side of the body
It has four lobes and is suspended by the Falciform ligament
Bile is produced in the liver and transported to the gall bladder for storage through the common hepatic duct (it prepares fats for digestion)
The Pancreas is a soft, pink, triangular gland that extends across the abdomen from the spleen to the duodenum
It produces the following enzymes;
Trypsin, chymotrysin, amylase and lipase, which digest proteins, starches and fats, respectively

17. 14.2 Anatomy & Physiology of the Digestive System: Accessory Organs
Salivary glands-empty their secretions into the mouth, mostly amylase
Includes the parotid glands that are anterior to the ears, the submandibular glands which are along the jawline
Teeth-play a role in the mechanical breakdown of our food
Two types: Deciduous and permanent

19. 14.3 Homeostatic Imbalances
Gallstones: when bile is stored too long in the gall bladder or too much water is removed, cholesterol may crystalize forming gall stones. This can be quite painful!
Heart burn: occurs when the Cardioesophageal sphincter fails to close tightly and gastric juice backs up in the esophagus causing pain and even ulceration aka acid reflux
Emesis: irritation in the stomach causes the medulla to call for a reverse of peristalsis also called vomiting
Pancreatitis: rare, very serious inflammation of the pancreas that is the result of pancreatic enzymes breaking down the pancreas itself and the ducts
Diverticulitis: occurs when the diet lacks fiber; colon walls narrow and diverticula form (mucosa protrudes from the colon wall)