new digestive

What are the main structures of the digestive tract?

Oral cavity, esophagus, stomach, small intestine, large intestine

What are the accessory organs of the digestive tract?

Salivary glands, pancreas, liver, gallbladder

What is the function of the digestive tract?

digestive, motility, secretory, and absorptive operations

What is the mucosa composed of?

Mucosal membrane, lamina propria, muscularis mucosa

What is the submucosa composed of?

Connective tissue, blood vessels, lymphatic vessels, lymphoid tissue, submucosal plexus

What is the muscularis externa composed of?

Serosa, flat mesothelial cells

What is the function of the mouth and pharynx?

Entry to the GI tract

What is the function of the salivary glands?

Release saliva

What are the parts of the salivary glands?

Parotid, submandibular, sublingual

What is the function of enzymes in saliva?

Chemical digestion

What is saliva composed of?

99.5% water; proteins like enzymes, mucus, antiviral/antibacterial proteins, electrolytes, and some solutes

What is alpha-amylase?

The principal enzyme of saliva; breaks down 1–4 bonds within starch

What are the functions of lingual lipase?

Hydrolyzes triglycerides; activity diminishes with age; most helpful in infants

What is the function of r-protein?

Enhances absorption of vitamin B12

What is the function of bicarbonate in saliva?

Neutralizes acids in consumed foods and acids produced by bacteria

Carbohydrate digestion begins in the mouth through the action of which enzyme?

Salivary amylase

What is the function of the esophagus?

Moves the bolus from the oral cavity to the stomach for muscular entry

What is swallowing?

A reflex response initiated by voluntary action and regulated by the brain

What is peristalsis?

Wave-like rhythmic contractions that propel food forward; stimulated by the nervous system

What is segmentation?

A mixing movement that moves the food mass back and forth in the GI tract

What is the role of the lower esophageal sphincter?

Relaxes to allow food into the stomach, then contracts forcefully to prevent reflux

What are the characteristics of the stomach?

When empty, volume is 50 mL; when filled, 1.5 L; pyloric sphincter located at the distal end

What are the four main regions of the stomach?

Cardia region, fundus, body, antrum (distal pyloric)

What does the stomach acid contain?

Several exocrine and endocrine glands

What facilitates digestion in the stomach?

Stomach muscles mix food with gastric juices to form chyme, which facilitates digestion

What are the three glands of the stomach?

Cardiac, oxyntic, pyloric

What do parietal oxyntic cells secrete?

HCl and intrinsic factor

What do chief (peptic or zygogenic) cells secrete?

Pepsinogen and gastric lipase

What is chyme?

The mixture of ingested material and gastric secretions

What are the four functions of stomach juice?

Denatures proteins, activates pepsin, liberates nutrients from organic complexes, destroys ingested microbes

How does the stomach empty its contents into the duodenum?

Through intense peristaltic contractions in the antrum that force small amounts of chyme through the pylorus

What happens during the "before food reaches the stomach" phase?

Acetylcholine and gastrin are released to stimulate gastric secretions and prepare the stomach for incoming food (cephalic phase)

What triggers enhanced gastric secretions once food is in the stomach, and which substances are involved?

Stomach distension enhances gastric secretions; gastrin and histamine stimulate them (gastric phase)

What happens after food has left the stomach?

Reduction in chyme volume and pH trigger release of somatostatin (intestinal phase)

What percentage of gastric acid is secreted during the cephalic, gastric, and intestinal phases?

Cephalic 30, gastric 60, intestinal 10

What are the three phases of digestion?

Cephalic, gastric, intestinal

What happens during the cephalic phase of digestion?

Food stimulates pressure sensors and chemical receptors in the mouth and nasal cavity, leading to digestive secretions

What happens during the gastric phase of digestion?

Action in the stomach triggers reflexes that increase stomach secretions and hormone release

What happens during the intestinal phase of digestion?

Mechanical and chemical events in the duodenum lead to the release of hormones like enterotoxin

What are folds of Kerckring?

increase the surface area of the small intestine wall threefold

What are enterocytes?

Villi lined with small intestine epithelial cells that have a barrier to prevent molecules and macromolecules from entering the blood; regulated by the protein zonulin

What is leaky gut?

Dysfunction in zonulin

What are the crypts of Lieberkühn?

secretion of enzymes and regulation of intestinal flora.

What are Peyer patches?

Lymphoid tissue containing T and B lymphocytes; provides a line of defense against bacteria and foreign substances

Which part of the small intestine receives secretions from the gallbladder and pancreas?

Duodenum

Where do secretions from the liver and gallbladder combine before entering the duodenum?

Common bile duct

Through which structure do bile and pancreatic secretions enter the duodenum?

Sphincter of Oddi

What is portal circulation?

Brings blood rich in nutrients from the gastrointestinal tract to the liver

What is bile composed of?

Bile acids and salts, cholesterol, phospholipids, and bile pigments in an alkaline solution

What is the main function of bile in digestion?

Acts like a detergent to emulsify fats

What is the name of the small organ that stores and concentrates bile?

The gallbladder

What hormone stimulates the gallbladder to release bile?

Cholecystokinin (CCK)

What is enterohepatic circulation?

The recirculation of bile salts from the ileum back to the liver via the portal vein

What organ is both an endocrine and exocrine gland?

The pancreas

What do the endocrine cells of the pancreas do?

Secrete hormones directly into the blood

What do the exocrine cells of the pancreas do?

Produce digestive enzymes

What are the main components of pancreatic juice?

Water, electrolytes, bicarbonate, and pancreatic digestive enzymes

What percentage of carbohydrates, proteins, and lipids are digested by pancreatic enzymes?

80-90%

What activates the other zymogens once trypsinogen reaches the duodenum?

Trypsin

What is the role of trypsin inhibitor in the pancreas?

Binds any trypsin accidentally activated in the pancreas and prevents activation of other zymogens; helps prevent pancreatitis

What are the primary stimuli for pancreatic juice secretion?

secretin and cholecystokinin (CCK), acetylcholine

What is the primary function of smooth muscle contractions in the GI tract?

To mix and propel contents

What system largely controls GI motility?

The enteric nervous system

How are longitudinal smooth muscle fibers arranged in the GI tract, and what is their effect?

They extend the length of the GI tract

How are GI muscle fibers arranged to facilitate movement?

In bundles

What is the primary function of segmentation?

To mix food in the GI tract by moving the food mass back and forth

What type of GI movement consists of wave-like rhythmic contractions that propel food forward?

Peristalsis

What is the function of the myenteric plexus?

Controls peristalsis and motility

What is the function of the submucosal plexus?

Regulates secretions and local blood flow

What is the main function of the large intestine?

Absorbs water and some electrolytes; involved in defecation

What vitamins are produced by bacteria in the colon?

Vitamin K, biotin, and short-chain fatty acids

What is the name of the condition linked to imbalances in gut microbiota?

Inflammatory bowel diseases like Crohn's disease and ulcerative colitis, colon cancer, rheumatoid arthritis, and diabetes

What is somatostatin and what does it do?

A hormone from the pancreas, stomach, and small intestine that diminishes gastric acid secretion, gastric emptying, pancreatic enzyme secretions, and inhibits gallbladder contraction

What is the most common cause of peptic ulcer disease?

Helicobacter pylori

What is pancreatitis?

A condition where zymogens become activated and digest pancreatic tissue

What are the functions of lingual lipase?

Hydrolyzes triglycerides; activity diminishes with age; most helpful in infants