Phys Lab M13

⭐ Digestive Tract Pathway

Mouth → pharynx → esophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine → rectum → anal canal → anus.

⭐ Accessory Digestive Organs

The salivary glands, liver, gallbladder, and pancreas aid digestion by producing secretions but food does not pass through them.

⭐ Small Intestine Divisions

The small intestine consists of the duodenum, jejunum, and ileum. Most digestion and nutrient absorption occur here.

⭐ Large Intestine Function

The large intestine absorbs water and electrolytes, compacts waste into feces, and stores fecal material until defecation.

⭐ Cephalic Phase of Digestion

The cephalic phase begins before food enters the stomach. The sight, smell, taste, or thought of food stimulates digestive secretions through the vagus nerve.

⭐ Vagus Nerve (CN X)

The vagus nerve is Cranial Nerve X and part of the parasympathetic nervous system. It stimulates digestive secretions during the cephalic phase.

⭐ Parasympathetic "Rest and Digest"

The parasympathetic nervous system promotes digestion by increasing digestive secretions and gastrointestinal activity.

⭐ Gastric Phase

The gastric phase begins when food enters the stomach. Stretch receptors activate gastrin release, increasing hydrochloric acid (HCl) and pepsin secretion.

⭐ Gastrin

Gastrin stimulates gastric acid production and digestive enzyme release while increasing stomach activity.

⭐ Intestinal Phase

The intestinal phase begins when chyme enters the duodenum. Secretin and CCK coordinate pancreatic secretions and bile release.

⭐ Secretin

Secretin stimulates the pancreas to release bicarbonate, which neutralizes acidic chyme entering the small intestine.

⭐ Cholecystokinin (CCK)

CCK stimulates pancreatic enzyme secretion and gallbladder contraction to release bile for fat digestion.⭐ Nutrient Absorption

⭐ Villi

Villi are finger-like projections lining the small intestine that greatly increase the surface area available for nutrient absorption.

⭐ Microvilli

Microvilli form the brush border on intestinal epithelial cells, providing even more surface area for absorption.

⭐ Carbohydrate Absorption

Carbohydrates are digested into monosaccharides (such as glucose) and absorbed into the bloodstream through active transport.

⭐ Protein Absorption

Proteins are broken down into amino acids, which are absorbed into the bloodstream by active transport.

⭐ Fat Absorption

Fats are emulsified by bile and digested by lipase into fatty acids and monoglycerides before being absorbed by intestinal cells.

⭐ Micelles

Micelles transport fatty acids and monoglycerides across the intestinal lumen to the epithelial cells for absorption.

⭐ Chylomicrons

Inside intestinal cells, fats are reassembled into triglycerides and packaged into chylomicrons, which enter the lymphatic system before reaching the bloodstream.

⭐ Fat-Soluble Vitamins

Vitamins A, D, E, and K are absorbed with dietary fats.

⭐ Water-Soluble Vitamins

Vitamins B and C are absorbed directly into the bloodstream through specific transport mechanisms.

⭐ Water Absorption

Water is absorbed by osmosis along with electrolytes to help maintain hydration and fluid balance.

⭐ Gastric Inhibitory Peptide (GIP)

GIP slows gastric emptying when the small intestine is full of chyme, preventing the stomach from emptying too quickly.

⭐ Insulin After a Meal

After carbohydrates are absorbed, increased blood glucose stimulates insulin release from the pancreas to promote glucose uptake and storage.

⭐ Esophageal Peristalsis

Peristalsis consists of wave-like contractions that move the food bolus from the esophagus to the stomach.

⭐ Stomach Propulsion

Peristaltic waves in the stomach mix food with gastric secretions to form chyme and propel it toward the pyloric sphincter.

⭐ Segmentation

Segmentation in the small intestine mixes chyme with digestive enzymes while maximizing nutrient absorption.

⭐ Large Intestine Peristalsis

Peristalsis in the large intestine moves undigested material toward the rectum for elimination.⭐ Defecation Reflex

⭐ Internal vs. External Anal Sphincters

The internal anal sphincter is composed of smooth muscle and is under involuntary control, while the external anal sphincter is skeletal muscle and is under voluntary control.

⭐ Digestive Enzymes Review

Salivary amylase begins carbohydrate digestion in the mouth, pepsin begins protein digestion in the stomach, pancreatic enzymes continue digestion in the small intestine, and lipase digests fats.

⭐ Bile Review

Bile is produced by the liver, stored in the gallbladder, and released into the duodenum where it emulsifies fats to increase the surface area available for lipase.

⭐ Pancreas Review

The pancreas releases digestive enzymes and bicarbonate into the duodenum to aid digestion and neutralize acidic chyme.

⭐ Liver Functions in Digestion

The liver produces bile and processes absorbed nutrients before they enter the general circulation.

⭐ Gallbladder Function

The gallbladder stores and concentrates bile until it is released in response to CCK after a fatty meal.

⭐ Small Intestine Review

The small intestine is the primary site of digestion and nutrient absorption because of its large surface area created by villi and microvilli.

⭐ Large Intestine Review

The large intestine primarily absorbs water and electrolytes, houses beneficial bacteria, and compacts feces for elimination.

⭐ Digestive Hormone Review

Gastrin stimulates stomach activity, Secretin stimulates bicarbonate secretion, CCK stimulates pancreatic enzymes and bile release, and GIP slows gastric emptying while promoting insulin release.

⭐ Digestive Process Summary

Food is mechanically and chemically digested, nutrients are absorbed primarily in the small intestine, water is reclaimed in the large intestine, and waste is eliminated through defecation.

⭐ Lab Practical Focus

Be able to identify digestive organs, accessory organs, digestive hormones, major digestive enzymes, and the pathway food follows through the digestive tract.