Digestive System Overview and Functions

Digestive System Overview

• The digestive system functions as a disassembly line, breaking down nutrients into usable forms for the body.
• It absorbs these usable nutrients, distributing them to body tissues.
• Most ingested foods need to be broken down into smaller components (like amino acids & monosaccharides) for use.

Digestive System Functions

• Ingestion: The selective intake of food
• Digestion: Mechanical and chemical breakdown of food into usable forms
• Absorption: The uptake of nutrients into the bloodstream and lymphatic system
• Compaction: Absorbing water and consolidating indigestible material into feces
• Defecation: The elimination of feces

The Mouth (Oral Cavity)

• Also known as the buccal cavity
• Includes teeth, tongue, palate, and cheeks
• Function in ingestion, taste, chewing, speech, and respiration
• Mechanical digestion begins with teeth chewing food – mechanical digestive
• Chemical digestion starts with saliva and amylase in the mouth

Salivary Glands

• Three major pairs: parotid, submandibular, and sublingual
• Secrete saliva at a fairly constant rate, keeping the mouth moist and preventing bacterial growth.
• Intrinsic salivary glands are numerous small glands scattered throughout other oral tissues (like the tongue, lips, and cheeks)

Pharynx

• A funnel-shaped tube connecting the oral and nasal cavities to the esophagus and larynx.
• Acts as a passageway for both air and food.
• Swallowing involves the tongue and soft palate, pushing food into the esophagus.

Esophagus

• A muscular tube connecting the pharynx to the stomach.
• Transports food from the mouth to the stomach.
• Peristaltic contractions propel food downward.

Stomach

• A muscular sac-like organ in the upper left abdominal cavity, inferior to the diaphragm.
• Functions as a food storage site
• Mechanically breaks down food, mixing it with digestive juices (HCl and enzymes). This produces chyme.
• Begins the chemical digestion of proteins and fats.

Small Intestine

• A long, coiled tube extending from the stomach to the large intestine.
• Divided into three segments: duodenum, jejunum, and ileum
• The primary site of nutrient absorption – digestion and nutrient absorption occurs
• Long length and extensively folded surface area maximize absorption efficiency
• Receives secretions from the liver (bile) and the pancreas (pancreatic juice) for further digestion.

Large Intestine

• A shorter, wider tube that receives indigestible food residue.
• Absorbs water and salts from the residue, compacting it into feces.
• Four parts: cecum, colon, rectum, and anal canal
• Houses gut bacteria that aid in waste breakdown.
• Eliminates feces through defecation.

Liver

• The body's largest gland, located below the diaphragm.
• Involved in bile production, secretion, and excretion (for fat digestion)
• Detoxifies blood.
• Makes numerous substances the body needs

Pancreas

• Endocrine function (release hormones like insulin and glucagon)
• Exocrine function (release pancreatic juice containing digestive enzymes that help complete the digestive breakdown of all food types.
• Secrete pancreatic juice (containing digestive enzymes) into the duodenum, further breaking down food.

Accessory Structures

• Teeth
• Tongue
• Salivary glands
• Liver
• Gallbladder
• Pancreas