Digestive System Overview

Digestive System Overview

• The digestive system is a complex series of organs that process food, extract nutrients, and eliminate waste.
• It is composed of two categories of organs: main digestive organs (also known as the gastrointestinal tract (GIT) or alimentary canal), and accessory digestive organs.
• The main digestive organs include the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus.
• Accessory digestive organs include the salivary glands, liver, gallbladder, and pancreas.

Oral Cavity (Mouth)

• The oral cavity is the entrance to the gastrointestinal tract (GI tract) and the initial site of digestion.
• It performs both mechanical and chemical digestion.
• Key structures in the oral cavity include the lips, teeth, hard and soft palate, tongue, tonsils, and salivary glands.

Tongue

• The tongue is an accessory digestive organ that plays a crucial role in chewing, mixing food, and swallowing.
• It manipulates and mixes food during chewing.
• Forms the bolus: a globular mass of partially digested food.
• Performs important functions in swallowing.
• Has numerous small projections (papillae) to help with food manipulation.
• The inferior surface of the tongue attaches to the floor of the oral cavity via the lingual frenulum.

Salivary Glands

• Salivary glands produce and secrete saliva, a fluid crucial for the initial stages of digestion.
• An average of 1.0 to 1.5 liters of saliva is secreted daily, with most produced during mealtimes and smaller amounts continuously to maintain oral moisture.
• There are three pairs of large salivary glands: parotid glands, submandibular glands, and sublingual glands.

Parotid Glands

• The parotid glands are the largest salivary glands.
• They are located anterior and inferior to the ear and partially overlying the masseter muscle, releasing saliva via the parotid duct to the oral cavity.
• Account for approximately 25-30% of daily saliva production.

Submandibular Glands

• The submandibular glands produce a significant portion of the saliva.
• They are situated inferior to the body of the mandible, with ducts opening into the floor of the mouth via a papilla, lateral to the lingual frenulum.

Sublingual Glands

• The sublingual glands are located inferior to the tongue, inside the oral cavity mucosa.
• They have multiple tiny ducts that open onto the inferior surface of the oral cavity posterior to the submandibular duct papilla.
• They contribute a relatively small amount of saliva.

Teeth

• Teeth, collectively known as dentition, are responsible for mastication (mechanical digestion of food).
• Each tooth comprises an exposed crown, a constricted neck, and one or more roots.
• Teeth are not living tissue and are composed of four different types of tissue: enamel (hardest material containing minerals), dentin, cementum (covers the root to hold the tooth in place), and pulp (innermost tissue with nerves and blood vessels).
• Types of teeth include incisors (cutting), canines (tearing), premolars (grinding), and molars (grinding).

Pharynx

• The pharynx is part of the throat situated behind the mouth and nasal cavity.
• It lies above the esophagus and trachea, which is its primary function.
• Has three parts: nasopharynx, oropharynx, and laryngopharynx.

Esophagus

• The esophagus is a muscular tube connecting the oropharynx to the stomach.
• It pierces the diaphragm at approximately T10.
• It joins the stomach at the cardiac orifice.
• Contains skeletal muscle in the upper third, a mixture of skeletal and smooth muscle in the middle third, and smooth muscle in the lower third.
• Approximatley 25 cm in length.
• Contains esophageal hiatus, through which it pierces the diaphragm.

Stomach

• The stomach is a J-shaped organ performing both mechanical and chemical digestion.
• Divided into five regions: cardia (first part below the esophagus), fundus (rounded area to the left of the cardia and below the diaphragm), body (the largest and main part where food is mixed and broken down), antrum (lower part of the stomach), and pylorus (the terminal part before the small intestine).
• The stomach has greater and lesser curvatures, and gastric folds (rugae) that allow the stomach to expand while providing elasticity.
• It contains specialized cell types (such as chief cells, parietal cells, mucous neck cells, and endocrine cells) for specific digestive functions.

Small Intestine

• The small intestine is the primary site of nutrient absorption.
• Consisting of three parts: duodenum (first and shortest part of the small intestine, C-shaped and retroperitoneal except for beginning), jejunum (second part, larger in diameter and has thicker walls, located mainly in the left upper quadrant), and ileum (third part, located mainly in the right lower quadrant and has thinner walls and shorter vasa recta).
• It has features like circular folds (plicae circulares) and microvilli to increase surface area for absorption.
• The epithelial cells in the small intestine are made of Enterocytes (absorptive), goblet cells (secrete mucus), Crypts of Lieberkuhn (glands), and Lacteals (lymphatic capillaries absorbing dietary fats).

Large Intestine

• The large intestine is responsible for water and electrolyte absorption, and fecal matter storage.
• It is approximately 1.5 meters in length.
• It consists of four segments: cecum (first part), colon (ascending, transverse, descending, and sigmoid colon segments), rectum, and anal canal.
• The colon, excluding the ascending and descending portions, is intraperitoneal.
• Ascending and descending colon are retroperitoneal.

Omentum

• The omentum are fused peritoneal folds that connect the stomach and duodenum with other abdominal organs.
• Consisiting of two layers.
• Are of two types: greater omentum and lesser omentum.

Mesenteries and Mesocolon

• The mesentery is a fold of membrane attaching the intestine to the abdominal wall, holding it in place and providing a conduit for vessels (nerves and lymphatics).
• Includes the mesentery-associated with parts of the small intestine, the transverse mesocolon-associated with the transverse colon, and the sigmoid mesocolon-associated with the sigmoid colon.

Liver

• The liver is a vital accessory digestive organ primarily located in the right hypochondriac region of the abdomen, beneath the diaphragm.
• It is the largest gland and internal organ in the body, weighing approximately 1500 grams and contributing to about 2.5% of adult body weight.
• Key functions include producing bile, detoxifying various substances (drugs, metabolites, and poisons), storing nutrients and vitamins, synthesizing blood plasma proteins like albumins and globulins, phagocytizing blood debris, and recycling components of aged red blood cells.
• The liver receives oxygenated blood through the hepatic artery and nutrient-rich deoxygenated blood via the hepatic portal vein. This dual circulation is a key aspect of its functions.

Gallbladder

• The gallbladder is a pear-shaped sac situated on the visceral surface of the right liver lobe.
• It has three main parts: fundus, body, and neck.
• Its crucial function is storing and concentrating bile received from the liver for later delivery to the duodenum during digestion.

Pancreas

• The pancreas is another accessory digestive organ responsible for producing both exocrine (digestive enzymes) and endocrine (hormones) secretions.
• Located mostly behind the stomach.
• It is retroperitoneal, except for a small part of its tail.
• The pancreas consists of several parts including the head, uncinate process, neck, body, and tail.
• The main pancreatic duct connects with the bile duct to empty digestive enzymes into the duodenum via a common channel.

Explore the fundamentals of the digestive system, its main and accessory organs, and their vital functions. This quiz will delve into components such as the oral cavity and the role of the tongue in digestion. Test your knowledge and learn more about how our bodies process food.