Lesson 68- Structure and function of the stomach

By the end of this session, students will be able to:
- Describe the structure and function of the stomach in monogastric animals.
- Describe the different components of the stomach wall, including mucosa cells.
- Describe the secretions and motility patterns of the stomach in domestic animals.

Definition of Monogastric:
- Animals with a single-chambered stomach that digest food in one compartment using gastric acids and enzymes.
- Examples: Humans, pigs, dogs, cats, horses, rabbits.
Characteristics of Monogastric Animals:
1. Limited Fiber Digestion: Inability to efficiently break down fiber-rich foods (e.g., cellulose).
  - Some, like horses and rabbits, have an enlarged cecum for partial fiber digestion.
2. Enzyme-Based Digestion: Relies on enzymes like amylase (carbohydrates), pepsin (proteins), and lipase (fats).
3. Fast Digestion: Quicker than ruminants, as food does not undergo fermentation in multiple chambers.
4. Dietary Habits: Mostly omnivorous or carnivorous, requiring easily digestible nutrients.

Food Storage: Temporarily holds food for gradual digestion.
Mechanical Digestion: Muscular contractions (peristalsis) churn food with gastric juices to create chyme.
Chemical Digestion:
- Protein: Pepsin breaks proteins into peptides.
- Fat: Gastric lipase aids in fat breakdown.
- Carbohydrate: Salivary amylase continues carbohydrate action until deactivated.
Regulation: Hormone gastrin stimulates acid secretion and gastric motility; pyloric sphincter regulates chyme release into the small intestine.

Divisions:
- Fundus (Cardia)
- Body
- Pylorus (Pyloric antrum, Pyloric canal)
- Curvatures: Greater and lesser curvature;
- Notches: Angular notch (prominent in cats);
- Rugae: Folds in gastric wall that allow expansion.

Anatomy Overview:
- Located transversely between ribs 9-12.
- Left Side: Fundus and body.
- Right Side: Pylorus.

Definition: The mesentery of the stomach, includes:
- Lesser Omentum: Between liver and stomach's lesser curvature.
- Greater Omentum: Between body wall and greater curvature.
- Gastrosplenic Ligament: Part of greater omentum.
Functions:
- Fat Storage: Energy reserve.
- Immune Function: Contains macrophages for immune response.
- Infection Control: Moves to sites of injury for healing; prevents peritonitis.
- Friction Reduction: Supports blood vessels, nerves, and lymphatics.

Gastric Dilation/Bloat with Volvulus (GDV):
- Common in deep-chested dogs; emergency condition.

Arterial Supply:
- Celiac Artery: Supplies hepatic, splenic, and left gastric arteries.
- Anatomical Components: Includes short gastric, left and right gastric, left gastroepiploic, and right gastroepiploic arteries.

Hepatic Portal Vein: Major tributaries include splenic vein, left and right gastric veins, and cranial mesenteric vein.

Sympathetic Innervation: Originates from thoracic spinal cord (T5–T12); influences digestion by inhibiting gastric motility and secretion.
Parasympathetic Innervation:
- Originates from dorsal motor nucleus of vagus nerve; promotes digestive functions.

Layers of the Stomach Wall:
- Mucosa: Contains gastric pits and glands.
- Submucosa: Connective tissue supporting mucosa.
- Muscular Layer: Includes longitudinal, circular, and oblique muscle fibers.
- Serosa: Visceral peritoneal layer.

Phases of Secretion:
- Cephalic Phase: Triggered by sight, smell, or thought of food.
- Gastric Phase: Triggered by food presence; involves stretch receptors.
- Intestinal Phase: Triggered by chyme entering duodenum; hormones inhibit gastric secretion.

Unique Characteristics:
- Small, located in the dorsal part of the abdomen, flexed close to the exit.
- Cardiac sphincter thick, preventing vomiting.
- Pneumogastric function leads to unique digestive physiology.