The Digestive System

Flashcards relating to key vocabulary terms about the digestive system.

What is the primary function of the digestive system?

• to take food into the body and break it down into its component nutrients so they can be used by body cells.

• critical role in fluid, electrolyte, and acid-base homeostasis.

Name the organs that make up the alimentary canal (also known as the GI tract or digestive tract).

oral cavity (mouth), pharynx, esophagus, stomach, small intestine, and large intestine.

Name the accessory digestive organs.

the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. They are located around the alimentary canal and assist in digestion.

List the seven basic processes the digestive system must perform.

(1) ingestion, (2) secretion, (3) propulsion, (4) peristalsis, (5) digestion (both mechanical and chemical), (6) absorption, and (7) defecation.

Define peristalsis.

a type of propulsion; It involves waves of smooth muscle contraction to move material through the alimentary canal.

Explain the difference between mechanical digestion and chemical digestion.

Mechanical digestion physically breaks food into smaller parts. Chemical digestion breaks the chemical bonds between food molecules, often catalyzed by enzymes via hydrolysis reactions.

List the four main tissue layers of the alimentary canal wall, from the innermost layer facing the lumen to the outermost layer.

Mucosa, Submucosa, Muscularis externa, and Serosa (or Adventitia).

What are the main functions of the muscularis externa layer?

contains two layers of smooth muscle (inner circular, outer longitudinal) and is responsible for motility. Motility in the muscularis externa is regulated by the myenteric plexus (Auerbach's plexus).

What is the role of the enteric nervous system (ENS)?

specifically regulates motility of the alimentary canal and also regulates secretion and blood flow in the submucosa. It includes the submucosal plexus and myenteric plexus.

How do the sympathetic and parasympathetic divisions of the autonomic nervous system generally affect digestive processes?

Sympathetic activity generally inhibits digestive processes, while parasympathetic activity generally stimulates them.

What is mastication?

the process of chewing, which is a form of mechanical digestion that occurs in the oral cavity.

How many permanent teeth are typically found in an adult mouth, and what are the types?

There are typically 32 permanent teeth. The types are incisors, canines (cuspids), premolars, and molars.

What are the primary components and functions of saliva?

fluid containing water, enzymes, mucus, and other solutes. Its functions include moistening, lubricating, and cleansing the oral mucosa.

Which parts of the pharynx are considered part of the alimentary canal?

Only the oropharynx and laryngopharynx are part of the alimentary canal. The nasopharynx is not.

What is the main function of the esophagus?

propulsion, transporting a bolus from the pharynx to the stomach. It also secretes a small amount of mucus.

Name and briefly describe the three phases of swallowing (deglutition).

(1) Voluntary phase: The tongue pushes the bolus posteriorly toward the oropharynx. (2) Pharyngeal phase: The bolus enters the oropharynx; the soft palate seals off the nasopharynx, and the epiglottis seals off the larynx. (3) Esophageal phase: Peristaltic waves move the bolus down the esophagus to the stomach.

What is chyme?

Chyme is the liquid mixture created when the stomach pummels the incoming bolus.

What are rugae in the stomach?

folds in the interior of the stomach that allow it to expand considerably.

Name the four main cell types found in gastric glands and state what each secretes.

Enteroendocrine cells secrete hormones (like G cells secreting gastrin). Chief cells secrete pepsinogen. Parietal cells secrete hydrochloric acid (HCl) and intrinsic factor. Mucous neck cells secrete acidic mucus.

Which cell type secretes HCl in the stomach, and what are the functions of this acid?

Parietal cells secrete HCl. HCl's functions include activating pepsinogen, destroying disease-causing organisms, and stimulating parietal cell production of intrinsic factor.

How is pepsinogen activated, and what is the role of active pepsin?

Pepsinogen, secreted by chief cells, becomes active pepsin when it encounters an acidic pH(around 2). Pepsin begins protein digestion in the stomach, breaking proteins into smaller polypeptides, oligopeptides, and some free amino acids.

List the three divisions of the small intestine in order from proximal to distal.

The three divisions are the duodenum, jejunum, and ileum.

Name the three types of folds/projections that increase surface area in the small intestine for absorption.

The three types are circular folds (plicae circulars), villi, and microvilli. These increase the surface area about 400 to 600 times.

What are brush border enzymes and where are they located?

digestive enzymes produced and secreted by enterocytes. They are found in the microvilli (which give the cell the appearance of a "brush border"). They catalyze reactions to break down disaccharides and peptides.

Describe segmentation in the small intestine.

type of motility that occurs during eating. It is a churning motion that mixes the chyme with digestive juices and exposes it to the enterocytes for absorption. Unlike peristalsis, it doesn't primarily move material forward.

What are the primary roles of the large intestine?

The large intestine receives material that was not digested or absorbed in the small intestine. It is active in absorbing water and electrolytes (critical for fluid, electrolyte, and acid-base homeostasis), secreting mucus, and propelling fecal material towards the anal canal for defecation.

What are taeniae coli and haustra?

Taeniae coli are three bands of muscle that represent the unique arrangement of the longitudinal layer of the muscularis externa in the large intestine. Their constant tension bunches the colon into pockets called haustra.

Describe the defecation reflex.

initiated when mass movements force fecal material into the rectum, causing it to distend. Stretch receptors transmit the sensation to the spinal cord. Parasympathetic neuronscause smooth muscle in the sigmoid colon and rectum to contract and the internal anal sphincter to relax. Impulses from the cerebral cortex trigger relaxation of the external anal sphincter.

What is pancreatic juice composed of, and what are its main digestive functions?

consists of water, multiple digestive enzymes, other proteins, and bicarbonate ions. The enzymes are crucial for digesting carbohydrates, proteins, lipids, and nucleic acids in the small intestine. The bicarbonate ions are alkaline and help neutralize the acidic chyme entering the duodenum from the stomach.

What is the main digestive function of the liver, particularly regarding bile production?

produce bile. Bile is required for the digestion and absorption of lipids, specifically through the process of emulsification. Bile also serves as a mechanism for the liver to excrete wastes.