HCS 1060 – Digestive System Functions Medical Studies 20 SLO 2.4

The Mouth or Oral Cavity Functions: Receives food – ingestion Breaks food into small portions mainly done by the teeth (mastication) – mechanical digestion Tongue, cheeks and lips also aid in the process Mixes food with saliva produced by salivary glands (lubricates food and begins chemical digestion of starches with the digestive enzyme amylase)

Tongue and Pharynx Function: In swallowing, the tongue pushes a bolus (small portion of chewed food mixed with saliva), into the pharynx (throat) With the swallowing reflex, the soft palate and the uvula raise, preventing food and liquid from entering the nasal cavity

Epiglottis Function: The leaf shaped cartilage covers the opening to the larynx during swallowing keeping food out of the airway or trachea. Food is directed instead to the esophagus.

Esophagus Function: A muscular tube about 10 inches long, where food is lubricated by mucus and moved by muscular contractions known as peristalsis into the stomach No additional digestion of food occurs here The esophagus travels through a hole in the diaphragm called the esophageal hiatus and a weakness in this part of the diaphragm could lead to parts of the stomach protruding through causing a condition known as a hiatal hernia

Peristalsis

Stomach Function: A J-Shaped organ with three layers of muscles that help to grind food and mix it with digestive juices (mechanical and chemical digestion) It also serves as a storage pouch for food and it can expand to hold up to several litres of food due to the many folds in the lining known as rugae.

Stomach (Continued) Special cells in the lining of the stomach secrete: - mucus to protect the lining of the stomach from the acidic gastric juices - hydrochloric acid (HCl) – a strong acid that helps break down protein and destroy foreign organisms - pepsin – a protein digesting enzyme produced in an inactive form and activated only when food enters the stomach and HCl is produced

Stomach

Sphincters Function: Sphincters are muscular rings that regulate the size of an opening The sphincter between the esophagus and the stomach is known as the lower esophageal sphincter (LES) or sometimes called the cardiac sphincter. When digestive juices get pushed back up into the esophagus this is called “heart burn”

Sphincters (Continued) The sphincter at the end of the stomach leading to the small intestine is known as the pyloric sphincter This regulates how rapidly food moves into the small intestine.

Small Intestine Function: First portion of the small intestine – the duodenum contains glands that produce a large amount of mucus to protect the small intestine from the strongly acidic chyme (kime) – a semi-liquid mixture of gastric juices and food that leaves the stomach. Mucosal cells of the small intestine also secrete enzymes that digest proteins and carbohydrates

Small Intestine (Continued) Digestive juices from the liver and pancreas enter the small intestine through small openings in the duodenum Most digestion takes place in the small intestine under the effects of these juices

Small Intestine , Liver and Pancreas

Absorption in the Small Intestine Another important function of the small intestine is absorption of food, water and minerals through the walls of the small intestine. Surface area in the walls of the small intestine is increased by villi – millions of tiny, finger-like projections and further by micro-villi of the villi plasma membrane.

Villi Each villus has blood vessels through which most digestion products are absorbed into the blood.

Large Intestine Structures: There are 3 main components of the large intestine – the ascending colon, the transverse colon and the descending colon The descending colon connects to the sigmoid colon which empties into the rectum and to the anus where waste is eliminated from the body.

Large Intestine (Continued) Function: Secretes a large amount of mucus but no enzymes Food is not digested in the large intestine Water is reabsorbed and undigested food is stored forming waste material known as feces Feces or stool is eliminated from the body through the anus where there is an anal sphincter to control defecation