Lecture 11 VMT 2024

Chapter 6: Gut Instincts

Quote:

“True champions aren’t always the ones that win, but the ones with the most guts.” – Mia Hamm

The Digestive System

The digestive system, often referred to as the gastrointestinal (GI) system or alimentary system, is a complex network designed to process food. It is essentially a tube that runs from the mouth to the anus, facilitating a series of crucial functions.

Digestive Functions

The primary functions of the digestive system encompass:

  1. Intake and digestion of food and water: This involves the consumption of various food types and liquids essential for health.

  2. Absorption of nutrients: Nutrients derived from digested food are absorbed into the bloodstream for use by the body’s cells.

  3. Elimination of solid wastes: Indigestible substances are expelled from the body to maintain homeostasis.

Path of Digestion

The digestive process follows a specific path:

  • Prehension: This refers to the act of grasping food and bringing it into the oral cavity. This step is critical for the subsequent digestion.

  • Mastication: The mechanical breaking down of food into smaller pieces through chewing, facilitating easier digestion.

  • Deglutition: This is the process of swallowing, which transports the chewed food from the oral cavity into the pharynx and esophagus.

Digestion & Metabolism

Digestion is defined as the method by which food is broken down into nutrients that the body can utilize. It involves two metabolic processes:

  • Anabolism: The construction of body cells from simpler compounds, aiding growth and repair.

  • Catabolism: The breakdown of body cells and substances into simpler forms, releasing energy necessary for bodily functions.

Absorption

Absorption is the process of taking digested nutrients into the circulatory system. This mostly occurs in the small intestine, where nutrients are absorbed efficiently into the bloodstream. Some water and vitamins are also absorbed in the large intestine, while certain species can digest and absorb nutrients in the cecum, a pouch connected to the large intestine.

Structures of the Digestive System

Key components of the digestive system include:

  • Mouth (oral cavity): Initiates the digestive process.

  • Pharynx: Connects the mouth to the esophagus and aids in swallowing.

  • Esophagus: A muscular tube that transports food to the stomach.

  • Stomach: A sac-like organ that further digests food chemically and mechanically.

  • Small intestine: The primary site for nutrient absorption, divided into three segments.

  • Large intestine: Responsible for waste processing and water absorption.

  • Accessory organs: Includes the salivary glands, liver, gallbladder, and pancreas, which support digestive functions.

The Oral Cavity

Mouth:

The mouth, known as the oral cavity, plays a critical role in ingestion and initial digestion. Key combining forms include or/o and stomat/o.

  • Teeth: The primary tools for mastication with several combining forms such as dent/o, dent/i, and odont/o. Developmentally, there is a distinction between primary (baby) teeth and secondary (permanent) teeth.

  • Gingiva (gums): The soft tissue surrounding the teeth, protecting the roots. The combining form is gingiv/o.

  • Lips: Form the entrance to the oral cavity with combining forms cheil/o and labi/o.

Oral Cavity Continued

  • Cheeks: Form the walls of the oral cavity, supported by a combining form of bucc/o.

  • Palate: The roof of the mouth, dividing the oral and nasal cavities. The combining form is palat/o.

  • Tongue: A muscular organ that aids in manipulation of food and taste sensation, combining forms include gloss/o and lingu/o.

  • Boundaries: The mouth is bordered by the maxilla and mandible (jaw), represented by the combining form gnath/o.

Pharynx & Esophagus

  • Pharynx: This structure connects the oral cavity with the respiratory and GI systems, serving as a pathway for both food and air. The combining form is pharyng/o.

  • Esophagus: A collapsible tube essential for guiding food from the throat to the stomach, with the combining form esophag/o.

Remaining Digestive Organs

Located within the abdomen (peritoneal cavity), between the diaphragm and the pelvis. The terms abdomin/o and celi/o denote abdominal structures, while lapar/o refers to the flank or abdomen.

Stomach

  • The stomach is a sac-like organ that further breaks down food, with a combining form of gastr/o. It is classified into:

    • Monogastric: Having one true glandular stomach.

    • Ruminants: Possessing one true glandular stomach complemented by three other compartments (the foregut containing the esophagus, rumen, reticulum, omasum, and abomasum).

Small Intestine

Extending from the pylorus to the large intestine, the small intestine has key combining form enter/o, and is divided into three segments:

  • Duodenum: The proximal portion, using combining forms duoden/i or duoden/o.

  • Jejunum: The middle section, with the combining form jejun/o.

  • Ileum: The distal section, represented by combining form ile/o.

Large Intestine

The large intestine extends from the ileum to the anus and is segmented into:

  • Cecum: A pouch that varies among species, represented by the combining form cec/o.

  • Colon: The major part of the large intestine, with combining form col/o.

  • Rectum: The terminal section of the digestive tract, identified with combining form rect/o.

  • Anus: The opening of the digestive tract, represented by an/o and proct/o, encompassing both the anus and rectum together.

Large Intestine Representation

The anatomy of the large intestines varies significantly among species, exemplified by the differences observed in:

  • Pig

  • Cat/Dog

  • Ruminants

  • Horse

Accessory Organs

The accessory organs play a vital role in digestion:

  • Salivary glands: Produce saliva to aid in the initial digestion, using combining forms sial/o or sialaden/o.

  • Liver: Lies caudal to the diaphragm and is pivotal for metabolism and bile production, with the combining form hepat/o.

  • Gallbladder: Stores bile produced by the liver, represented by the combining forms chol/e (bile) and cyst/o (sac).

  • Pancreas: A crucial organ for endocrine and exocrine functions, including secretion of digestive enzymes. The combining form is pancreat/o.