Digestive System I: Overview and Early Structures

Flashcards covering the overview of the digestive system, its functional processes, anatomical layers, and the initial stages of the GI tract including the mouth, pharynx, and esophagus.

Alimentary Canal

Also known as the gastrointestinal (GI) tract or gut tube, this is the continuous tube through which food passes during digestive activity.

Accessory digestive organs

Organs that provide chewing, enzymes, and buffers, such as teeth and salivary glands, that assist in the mechanical and chemical breakdown of food.

Ingestion

The process of taking in food and water via the mouth.

Propulsion

The movement of food/water by swallowing (voluntary) or peristalsis (involuntary alternating waves of smooth muscle contraction).

Mechanical breakdown

Processes that increase the surface area of food to prepare for chemical digestion, including chewing, churning in the stomach, and segmentation.

Segmentation

The back and forth movement of food in the small intestine that facilitates mixing and mechanical breakdown.

Digestion

A catabolic process where enzymes secreted into the lumen break food down into its chemical building blocks.

Absorption

The movement of nutrients from the lumen of the alimentary canal into the blood or lymph.

Defecation

The elimination of solid waste (feces), including indigestible substances and metabolic wastes.

Aboral

The direction of motility moving from the mouth toward the anus.

Peritoneum

A slippery, continuous serous membrane sac made of two layers: the parietal peritoneum and the visceral peritoneum.

Parietal peritoneum

The layer of the peritoneum that lines the inner surface of the body wall.

Visceral peritoneum

The layer of the peritoneum that lines the surface of the digestive organs.

Peritoneal cavity

The fluid-filled potential sterile space located between the parietal and visceral peritoneal layers.

Mesenteries

Folds of peritoneum that suspend organs in the abdomen, provide routes for vessels and nerves, and store fat.

Mucosa

The innermost layer of the alimentary canal made of epithelium, lamina propria, and muscularis mucosa; it functions in secretion, absorption, and protection.

Submucosa

Areolar connective tissue containing blood vessels, lymphatic vessels, lymphoid follicles, and the submucosal plexus.

Muscularis Externa

The major smooth muscle layer of the GI tract, usually consisting of an inner circular layer and an outer longitudinal layer.

Serosa

The outermost layer of the alimentary canal, also known as the visceral peritoneum, consisting of areolar connective tissue and mesothelium.

Enteric Nervous System (ENS)

The 'Third Division' of the autonomic nervous system consisting of neurons in the walls of the gut that control local reflexes.

Myenteric Plexus

A nerve plexus located between the muscle layers of the muscularis externa that controls GI muscle function.

Submucosal Plexus

A nerve plexus located in the submucosa layer that controls glandular secretions.

Interstitial cells of Cajal

Modified smooth muscle cells that act as pacemakers for the digestive system.

Short reflexes

Local gut reflexes mediated entirely by the enteric nervous system (ENS) in response to stimuli within the GI tract.

Long reflexes

Digestive reflexes involving extrinsic autonomic nervous system (ANS) controls and central nervous system (CNS) regulation.

Enteroendocrine cells

Hormone-producing cells within the gut wall that release products into the interstitial fluid to affect secretion or contraction.

Saliva

A fluid consisting of $97\,\%$ to $99\,\%$ water, electrolytes, amylase, lipase, and proteins like mucin and IgA; output is roughly $1.5\,dm^3$ per day.

Deglutition

The medical term for swallowing, consisting of a voluntary oral phase and an involuntary pharyngeal-esophageal phase.

GERD

Gastroesophageal reflux disease, which occurs when acid reflux from the stomach inflames the esophagus wall.

Achalasia

A condition characterized by difficulty opening the lower esophageal sphincter (LES) or a failure of peristalsis coordination.

Dysphagia

Difficulty swallowing, which may be caused by nervous system or muscular system issues.