Digestive System Overview

Digestive System Overview

• The digestive system is a disassembly line, breaking down nutrients into absorbable forms.
• It absorbs nutrients and distributes them to tissues.
• Most food cannot be directly used as is; it needs breakdown.
• Nutrients are broken down into simpler forms (e.g., amino acids, monosaccharides) universal to all species.

Digestive System Functions

• Ingestion: Selective intake of food.
• Digestion: Mechanical and chemical breakdown of food.
• Absorption: Uptake of nutrients into the blood and lymph.
• Compaction: Absorbing water and consolidating indigestible material into feces.
• Defecation: Elimination of feces.

Digestive Tract

• The digestive tract (or alimentary canal) extends from mouth to anus.
• It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
• The stomach and intestines together form the gastrointestinal (GI) tract.
• Teeth, tongue, salivary glands, liver, gallbladder, and pancreas are accessory organs.

The Mouth (Oral Cavity)

• Also known as the buccal cavity.
• Function: Ingestion, taste, chewing (mastication), speech, and respiration.
• Enclosed by cheeks, lips, and tongue.
• Mechanical digestion begins with teeth.

Salivary Glands

• Three major pairs: parotid, submandibular, and sublingual.
• Secrete saliva to moisten and aid in digestion.
• Saliva keeps the mouth moist and inhibits bacterial growth.
• Salivary glands include intrinsic glands (small glands inside oral tissues) and extrinsic glands (three major pairs).

The Pharynx

• Muscular funnel connecting oral cavity to esophagus and nasal cavity to larynx.
• Critical point where digestive and respiratory tracts intersect.
• Swallowing involves the tongue and palate moving food toward the pharynx.

The Esophagus

• Muscular tube about 25-30 cm long.
• Connects pharynx to stomach.
• Carries food from pharynx to stomach.
• Swallowing propels food from the pharynx to the esophagus.
• Food transport is via waves of muscular contraction.

The Stomach

• Located in the upper left abdominal cavity.
• Functions as a food storage organ.
• Mechanically breaks down food, liquefies it, and begins protein and fat digestion.
• Produces chyme (a soupy mixture of partially digested food).

The Pylorus

• The end of the stomach.
• Surrounded by the pyloric sphincter (a thick ring of smooth muscle).
• The pyloric sphincter regulates the passage of chyme to the duodenum.

The Small Intestine

• Long, coiled tube in the lower abdomen.
• Divided into duodenum, jejunum, and ileum.
• Function: Absorbs nutrients.
• Large surface area for absorption due to folds and villi.
• Nearly all chemical digestion and nutrient absorption happen here.

The Ileum

• The last part of the small intestine.
• Joins the large intestine at the ileocecal junction.
• Thickened muscular region called the ileocecal valve.
• Regulates food residue passage from small to large intestines.

The Large Intestine

• Receives indigestible food residue from small intestine.
• Resorbs water and electrolytes.
• Eliminates waste as feces.
• Four regions: cecum, colon (ascending, transverse, descending, sigmoid), rectum, and anal canal.

The Liver

• Largest gland, reddish-brown.
• Located beneath the diaphragm.
• Produces bile (emulsifies fats).
• Detoxifies blood and synthesizes various substances.
• Has several important functions including the detoxification of blood and the production of bile.

The Pancreas

• Spongy digestive gland posterior to the greater curvature of the stomach.
• Has both endocrine and exocrine functions.
• Endocrine: secretes hormones like insulin and glucagon.
• Exocrine: secretes pancreatic juice (alkaline, digestive enzymes like amylase, lipase, and proteases) to the duodenum.