Human Digestive System Anatomy and Pulmonary Circulation

The Role of Nutrition and Digestion

The role of nutrition: food digests (breaks it down into nutrients and undigested residues (feces)) and absorbs nutrients (from the digestive tract into the blood).

Functions of the Mouth

The mouth prevents food from falling out during chewing and allows us to suckle. The palate separates the mouth from the nasal passages and allows us to breathe while eating. It consists of the hard palate (anterior, formed by bone) and the soft palate (posterior, a membranous muscle formed by the uvula or 'bell' ending).

The tongue is a muscle on whose surface gustatory papillae are located. It detects the taste of food and moves food during chewing and swallowing.

The Small Intestine

The small intestine is a long tube that begins in the stomach and ends in the large intestine. At the connection between the small and large intestine, there is a slim ileocecal valve (sphincter). There are three parts: the duodenum, jejunum, and ileum. The duodenum receives secretions from the liver and pancreas.

Functions of the Small Intestine

• Chemical digestion: performed by digestive juices that are secreted by the small intestine, the pancreas, and the liver.
• Absorption of nutrients.

The Large Intestine

The large intestine consists of the cecum, colon (the longest part, which absorbs water), and rectum. The cecum (blind pouch) is so called because it has no input except from the colon and an exit. It connects with the colon and has a valve called the ileocecal valve. In this area is the appendix.

The rectum follows a straight trajectory. It measures some 15 cm, begins at the end of the colon, and ends at the anus (a sphincter-type valve that is the only one we can control).

Mechanical and Chemical Digestion

• Mechanical digestion: breaks down food without altering its chemical composition. It involves the crushing and movement of food in the digestive tract.
• Chemical digestion: alters the components of the food through the action of digestive juices.

The Process of Chewing and Swallowing

Chewing-insalivation: food is crushed with grinding and mixed with saliva; the food is mixed and becomes the bolus.

The Swallowing Process

Swallowing is the process by which the bolus is swallowed and passed from the mouth to the stomach:

1. The tongue pushes the bolus toward the pharynx.
2. The soft palate closes the choanae (nasal passages).
3. The bolus falls into the pharynx, and the walls contract, pushing it down.
4. The epiglottis closes the path to the trachea so that food passes through the esophagus.
5. The walls of the esophagus contract, making the bolus move to the stomach.
6. The cardia opens, and the bolus enters the stomach.

Common Digestive Disorders

Gastritis: the walls of the stomach become inflamed. It is managed with a soft diet and gastric protectants.

Biliary colic: occurs when gallstones are expelled into the canal, irritating the system. When these are very frequent, the gallbladder is removed.

Pulmonary Circulation (Minor Circuit)

Pulmonary circulation (Circuit less): Heart → Pulmonary artery → Lungs → Pulmonary veins → Heart (Right and Left sides).