Gastrointestinal System - Anatomy and Physiology

Vocabulary practice flashcards covering the functional layers, vascular supply, nervous and hormonal control, motility, and upper gastrointestinal anatomy from the lecture on the gastrointestinal system.

Primary Organs of the Gastrointestinal Tract

The sequence of digestive tract organs through which food passes: mouth, pharynx, oesophagus, stomach, small and large intestines, rectum, and anal canal.

Accessory Organs of the Gastrointestinal Tract

Organs that aid in digestion but are outside the continuous digestive tube: salivary glands, pancreas, liver, and biliary tract.

Four Functional Layers of the Gastrointestinal Tract

The structural tissue layers comprising the digestive wall from outer to inner: serosa (adventitia), smooth muscle, submucosa, and mucosa.

Peritoneum

A large serous membrane composed of a parietal layer (lining the abdominal wall) and a visceral layer (covering abdominal organs), separated by peritoneal cavity fluid to provide protection and support.

Greater Omentum

A large apron-like fold of visceral peritoneum that extends downward from the stomach over the surface of the small intestine.

Coeliac Artery (Coeliac Trunk)

A major anterior branch of the abdominal aorta delivering blood at $700\,\text{mL/min}$; divides into the left gastric artery (supplying the stomach and duodenum), splenic artery (supplying the spleen), and hepatic artery (supplying the liver).

Superior Mesenteric Artery

An arterial branch of the abdominal aorta delivering blood at $700\,\text{mL/min}$ to the small intestine, caecum, ascending colon, part of the transverse colon, and most of the rectum.

Inferior Mesenteric Artery

An arterial branch of the abdominal aorta delivering blood at $400\,\text{mL/min}$ to the remaining part of the large intestine and the rest of the rectum.

Hepatic Portal Vein

A large vessel formed by gastrointestinal venous drainage that channels nutrient-rich venous blood from the stomach, spleen, pancreas, and intestines into the liver.

Hepatic Veins

Veins that drain deoxygenated and processed blood from the liver into the inferior vena cava at an approximate resting rate of $1300\,\text{mL/min}$.

Sympathetic Nervous Supply to the GIT

Autonomic innervation originating from thoracic and lumbar spinal levels that generally acts to inhibit gastrointestinal motility and secretions.

Parasympathetic Nervous Supply to the GIT

Autonomic innervation provided primarily by the vagus nerve (cranial nerve X) for upper regions and sacral nerves for lower regions that acts to stimulate gastrointestinal motility and secretions.

Cephalic Phase

The initial phase of gastric secretion initiated prior to ingestion by the sight, smell, taste, or thought of food, causing the vagus nerves to stimulate the secretion of gastric juice.

Gastric Phase

The second phase of gastric secretion triggered by food entering the stomach, which stimulates the release of gastrin into the bloodstream to promote further secretion of gastric juice.

Intestinal Phase

The regulatory phase triggered by the presence of chyme in the duodenum, causing the secretion of secretin and cholecystokinin into the blood to reduce gastric motility and inhibit gastric juice production.

Basic Electrical Rhythm (BER)

Spontaneous, self-generated rhythmic electrical slow waves produced in the stomach, small intestine, and large intestine, whose rate and contractile force are regulated by luminal distension and nervous signals.

Regional Rates of Basic Electrical Rhythm (BER)

Specific BER pacemaker frequencies across the GIT: stomach ($4/\text{min}$), duodenum ($12/\text{min}$), distal ileum ($8/\text{min}$), caecum ($2/\text{min}$), and sigmoid colon ($6/\text{min}$).

Peristalsis

A propulsive wave of muscular activity occurring in the oesophagus, stomach, and small intestine characterized by a wave of relaxation ahead of the bolus followed by a wave of contraction behind it.

Segmentation

Non-propulsive, oscillating smooth muscle contractions occurring in the stomach and small intestine that serve to churn and mix food with digestive juices.

Mass Movement

A forceful type of gastrointestinal motility unique to the large intestine that sweeps fecal material over long distances toward the rectum.

Six Overall Functions of the Gastrointestinal Tract

The six core physiological activities of the digestive system: ingestion, storage, digestion, motility, absorption, and defaecation.

Mouth

The initial digestive structure lined with mucous membrane rich in mucus-secreting glands, responsible for ingestion, physical digestion, chemical digestion of starches, and propulsive motility.

Tongue

A structure composed of striated muscle under voluntary control containing taste receptors; functions to mix food with secretions, initiate food propulsion down the oesophagus, and perceive taste.

Salivary Glands

Three pairs of exocrine glands located in the head and neck: the parotid glands, submandibular glands, and sublingual glands.

Saliva

An oral secretion produced at an average of $1.5\,\text{litres}$ per day with a pH of $6.2\text{--}7.6$, composed of $99\%$ water, mucus, salivary amylase, and antimicrobial substances.

Salivary Amylase

A digestive enzyme present in saliva that initiates chemical digestion by breaking down polysaccharides (starch and glycogen) predominantly into disaccharides in the form of maltose.

Pharynx

A muscular funnel-shaped passageway divided into the nasopharynx, oropharynx, and laryngopharynx, composed of superficial mucosa, connective tissue, and involuntary muscle layers.

Pharyngeal Swallowing

The second phase of deglutition where the mouth closes, the bolus is pushed against the hard palate, the soft palate elevates to seal the nasopharynx, and the larynx rises while the epiglottis closes to inhibit respiration.

Pharyngeal Plexus

A network formed by sympathetic and parasympathetic nerve fibers that supplies motor and sensory innervation to the tissues of the pharynx.

Oesophagus

A muscular transport tube measuring $25\,\text{cm}$ in length and $2\,\text{cm}$ in diameter lined by non-keratinised stratified squamous epithelium, consisting of striated muscle in the upper $1/3$ and smooth muscle in the lower $1/3$.

Swallowing Reflex

An involuntary reflex initiated when food enters the pharynx and activates mechanical stretch receptors, sending signals to the swallowing centre in the medulla to begin esophageal peristalsis.

Lower Oesophageal Sphincter

A physiological smooth muscle sphincter at the junction of the oesophagus and stomach that remains tonically constricted at rest to prevent acid reflux and relaxes ahead of the peristaltic wave to allow food entry.