CH23: The Digestive System

What is the definition of Ingestion?

Is simply taking food into the digestive tract, usually via the mouth.

What are some examples and function of the sphincters?

In several places along the tract, the circular layer thickens, forming Sphincters that act as valves to control food passage from one organ to the next and prevent backflow.

List the organs of the alimentary canal, in order?

Includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus.

What is the function of Mechanical Breakdown process?

Increases the surface area of ingested food, physically preparing it for digestion by enzymes. Mechanical processes include chewing, mixing food with saliva by the tongue, churning food in the stomach, and segmentation, or rhythmic local constrictions of the small intestine.

Can you describe the Mucosa?

The Mucosa or Mucous membrane- the innermost layer- is a moist epithelial membrane that lines the alimentary canal lumen form mouth to anus. its major functions are to: Secret mucus, digestive enzymes, and hormones. Absorb the end products of digestion into the blood. Protect against infectious disease.

List the accessory digestive organs?

Are the teeth, tongue, gallbladder, and a number of large digestive glands - the salivary glands, liver, and pancreas.

What is the location of the salivary glands?

Lie outside the oral cavity and empty their secretions onto it.

Can you describe briefly the intrinsic and extrinsic controls of digestive activity?

Many of the controlling systems of the digestive tract are intrinsic "in house" - nerve plexuses and hormone-producing cells. The so-called gut brain consisting of enteric nerve plexuses spreads like chicken wire along the entire length of the GI tract and regulates digestive activity all along the tract. 2 kinds of reflex activity occur, short and long. Short reflexes are mediated entirely by the local enteric or "gut" plexuses in response to stimuli arising in the GI tract. Long reflexes are initiated by stimuli arising inside or outside the GI tract that involves CNS centers and extrinsic autonomic nerves.

Can you list all the mechanical and chemical stimuli of digestive activity?

Sensors involved in controlling GI tract activity are located in the walls of the tract organs. These sensors respond to several stimuli, most importantly stretching of the organ by food in the lumen, osmolarity and pH of the contents, and the presence of substrates and end products of digestion. When stimulated, these receptors initiate reflexes that (1) activate or inhibit glands that secrete digestive juices into the lumen or hormones into the blood or (2) stimulate smooth muscle of the GI tract walls to mix lumen contents and move them along the tract.

Can you describe briefly the muscle tissues that form the 2 layers of muscularis externa?

Surrounding the submucosa is the Muscularis Externa, also simply called the muscularis. This layer is responsible for segmentation and peristalsis. It typically has an inner circular layer and an outer longitudinal layer of smooth muscle cells.

Can you describe the Palate: Hard Palate, Soft Palate?

The palate forming the roof of the mouth, has 2 distinct parts: the hard palate anteriorly and the soft palate posteriorly. The hard palate is underlain by the palatine bones and the palatine processes of the maxillae, and it forms a rigid surface against which the tongue forces food during chewing. The Soft Palate is a mobile fold formed mostly of skeletal muscle that rises reflexively to close off the nasopharynx when we swallow.

What is the definition of Propulsion?

Which moves food through the alimentary canal, includes swallowing, which is initiated voluntarily, and peristalsis, an involuntary process.

Can you describe how the process of Peristalsis and Segmentation occur?

a) Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally. b) Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward the backward. Food mixing and slow food propulsion occur.