Gastrointestinal Motilities Overview

Gastrointestinal Motilities

• Mastication (Chewing): Chewing breaks down food into smaller particles. This process is triggered by smell and taste, and is initially voluntary but progresses to a reflex. Jaw movement is stimulated by muscle stretching. Mixing of food with saliva occurs alongside the chewing action.

• Deglutition (Swallowing): A two-stage process involving voluntary and involuntary actions. The voluntary stage involves the tongue pushing food upwards and backwards against the soft palate. The involuntary stage starts with the pharynx contracting (as food enters). Esophageal peristalsis occurs, moving the bolus along the esophagus. Swallowing receptors in the pharynx, and swallowing centers in the brain, are involved.

Pharyngeal Stage

• Duration: Approximately 2 seconds.
• Key Events: Respiration is halted, the soft palate closes the posterior nares, the larynx moves upward, the epiglottis closes, the upper esophageal sphincter relaxes, and the esophageal opening expands. These actions propel the bolus into the esophagus.

Esophageal Stage

• Function: Conducts the bolus to the stomach.
• Types of Contractions: Primary peristaltic contractions and secondary peristalsis. Primary contractions begin in the pharynx and continue through the esophagus (8-10 seconds). Secondary contractions are triggered by esophageal distension (retained food) or failure of the primary reflex.

Gastric Motilities

• Primary Function: Food storage. The stomach can dilate from 50ml to 1000ml. Receptive relaxation reduces muscular tone to accommodate food entry.
• Gastric Secretions and Mixing: Secretions and ingested food are mixed to form chyme. Peristaltic constrictive waves mix secretions with food and push chyme toward the duodenum. Waves occur at a frequency of 3/min in the mid-stomach moving toward the antrum.

Constrictive Rings

• Description: As contractions approach the antrum they become more intense and form constrictive rings at the pylorus in the stomach. Retropulsion mixes food.

Gastric Emptying

• Small Chyme Passage: Only small amounts of fluid-consistency chyme are passed.
• Pyloric Pump: This process controls gastric emptying. The pylorus is a small opening and is guarded by a smooth muscle sphincter.

Neural and Hormonal Control of Gastric Emptying

• Stimulation: Filling the stomach activates enteric reflexes, which increase pyloric pump activity and reduce sphincter tone. Gastrin stimulates peristaltic activity.
• Inhibition: Entero-gastric reflexes are triggered by chyme entering the duodenum. This decreases pH and stimulates reflex responses. ENS; Prevertebral Ganglia; Vago-Vagal reflexes decrease antral propulsive contractions and increase sphincter tone. Hormonal feedback from the duodenum through cholecystokinin (CCK) and gastric inhibitory peptide (GIP) inhibit gastric emptying.

Intestinal Movements

• Propulsive (Peristalsis) Movements: Chyme is propelled toward the anus at an appropriate rate.
• Mixing (Segmentation) Movements: Food is mixed with gastrointestinal (GI) secretions to aid in digestion and absorption.

Neural Control of Peristalsis

• Role of Enteric Nervous System: The ENS controls GI movements and chyme movement (the rate of movement). Excitatory neurons extend upward in the Orad Extension and inhibitory neurons extend downward in the Caudad Extension.
• Mucosal Stimulation: Peristaltic contractions can also be triggered by mucosal stimulation.
• Parasympathetic Nervous System: Modulates peristaltic activity by influencing neural networks and smooth muscle function.

Hormonal Control of GI Motility

• Hormones Affecting Motility: Hormones affect intestinal motility during food processing: Gastrin, CCK, and Serotonin enhance motility. Secretin and Glucagon inhibit motility.

Mixing Movements

• Mechanism of Mixing: Circular smooth muscle contractions create segmentations, mixing chyme and secretions.

Frequency of Segmentations

• Determination: Determined by the Basic Electrical Rhythm (BER) or slow waves of smooth muscle cells. The maximum frequency is 12/minute in the upper intestine (duodenum and jejunum), and 8/minute in the terminal ileum.

Other Types of Intestinal Contractions

• Peristaltic Rush: Powerful and rapid peristaltic contractions are triggered by mucosal irritation or intestinal distension.
• Migrating Motor Complex (MMC): Sweep intestinal contents between meals. It starts in the distal stomach, continuing along the entire small intestine.

Movements Caused by Muscularis Mucosa

• Function: Responsible for shortening and elongating the mucosal folds and aiding the absorptive process. The activity is influenced by the enteric nervous system

Movements of the Colon

• **Description of Haustrations:**Similar to segmentation, this rhythmic contraction and relaxation of the circular layer of colonic smooth muscle spans 2.5 cm and lasts 30-60 seconds. Longitudinal muscle strips (teniae coli) cause the haustral appearance.
• Haustral Functions Spread colonic contents over the mucosa to aid water and electrolyte absorption; and move fecal material slowly from the cecum and ascending colon to the transverse colon.
• Propulsive Movements (Mass Contractions): A series of powerful contractions (1-3 times a day, lasting 10-30 minutes), typically occurring in the first hour after breakfast. Begins with constrictive rings at the transverse colon and moves approximately 20cm or more distally before relaxing for 2-3 minutes. Factors contributing to contractions are the gastrocolic and duodenocolic reflexes (autonomic nervous system influences); colon irritation can also promote mass movements

Reflexes Preceding Defecation

• Intrinsic Reflexes: Triggered by rectal distension. Increased contractions of the descending colon, sigmoid, and rectum. Insufficient for defecation alone.
• Extrinsic Reflexes (Parasympathetic): Rectal andsigmoid distension triggers increased signals, resulting in stronger contractions of these areas, relaxation of the internal anal sphincter; these are involuntary.

Explore the key processes involved in gastrointestinal motilities, including mastication and deglutition. Understand the roles of the tongue, pharynx, and esophagus in the swallowing process. This quiz covers the physiological actions critical to food movement through the digestive system.