Introduction to Internal Anatomy and Digestion

This study guide covers the basics of internal anatomy and digestion, focusing on the dissection of fetal pigs as a model organism. It includes laboratory protocols, identification of major organs, and the physiological roles of digestive and associated systems.

Dissection Protocols

Laboratory Safety and Cleanup

Proper dissection technique and cleanup are essential for safety and scientific accuracy in the laboratory.

• Biohazard Disposal: All actual pig parts must be disposed of in biohazard containers; other waste goes in regular trash.

• Specimen Handling: Dissection specimens must remain in the lab room at all times.

• Cleaning: Dissection mats and utensils must be rinsed and dried after use before returning to kits.

• Pin Management: Dissection pins should be placed back into the bowl after use, not into kits or down the drain.

• Scalpel Safety: Always be aware of the blade when handling a scalpel to prevent injury.

Overview of Internal Anatomy

Major Organ Systems in the Thoracic and Abdominal Cavities

The thoracic and abdominal cavities contain vital organs involved in digestion, circulation, respiration, and excretion. Understanding their structure and function is key to studying vertebrate biology.

• Lungs: Responsible for gas exchange, supplying oxygen to the blood and removing carbon dioxide.

• Liver: Performs multiple functions including detoxification, production of bile, breakdown of erythrocytes, storage of glycogen, and synthesis of cholesterol and blood proteins such as fibrinogen (a zymogen, or inactive enzyme precursor, involved in blood clotting).

• Gallbladder: Stores and releases bile into the small intestine to aid in fat digestion; bile release is triggered by food ingestion.

• Umbilical Vein and Arteries: In fetal pigs, the umbilical vein brings oxygenated blood from the placenta, while two umbilical arteries carry deoxygenated blood from the fetus to the placenta.

• Intestines: The small intestine is the primary site for nutrient absorption and enzyme secretion; the large intestine (spiral colon) reabsorbs water and compacts waste.

• Bladder: Stores urine before excretion.

• Heart: Pumps blood throughout the body, supplying tissues with oxygen and nutrients.

• Thymus: Part of the immune system; some white blood cells (WBCs) mature here.

Digestive System

Structure and Function of Digestive Organs

The digestive system breaks down food into nutrients that can be absorbed and utilized by the body. It involves both mechanical and chemical processes.

• Mouth: Begins mechanical digestion through chewing and chemical digestion via enzymes in saliva.

• Stomach: Performs physical digestion by churning food and chemical digestion primarily of proteins via the enzyme pepsin. The stomach also serves as a short-term food storage site and has two sphincters (cardiac and pyloric) to regulate food entry and exit.

• Small Intestine: Main site for enzymatic digestion and nutrient absorption. Receives bile from the gallbladder and digestive enzymes from the pancreas.

• Large Intestine (Spiral Colon): Reabsorbs water and compacts indigestible material. Mammals cannot break down cellulose directly; instead, they rely on symbiotic bacteria in the gut.

Accessory Organs

• Liver: Produces bile, stores glycogen, breaks down old erythrocytes, and detoxifies substances.

• Gallbladder: Stores and concentrates bile, releasing it into the small intestine as needed.

• Pancreas: Has both digestive (exocrine) and endocrine functions. The exocrine pancreas secretes digestive enzymes into the small intestine. The endocrine pancreas (islets of Langerhans) releases hormones such as insulin (promotes glycogen storage) and glucagon (stimulates glycogen breakdown and glucose release).

Digestive Enzymes and Hormones

• Pepsin: Enzyme in the stomach that breaks down proteins into peptides.

• Amylase: Enzyme that breaks down starches into sugars; found in saliva and pancreatic secretions.

• Insulin: Hormone produced by beta cells in the pancreas; lowers blood glucose by promoting glycogen synthesis in the liver.

• Glucagon: Hormone produced by alpha cells in the pancreas; raises blood glucose by stimulating glycogen breakdown in the liver.

Fetal Circulation (Special Features in Fetal Pigs)

Fetal pigs have unique circulatory adaptations for life in the womb, including the umbilical vein and arteries, which facilitate nutrient and gas exchange with the placenta.

• Umbilical Vein: Delivers oxygenated, nutrient-rich blood from the placenta to the fetus.

• Umbilical Arteries: Carry deoxygenated blood from the fetus to the placenta for waste removal.

Summary Table: Major Digestive Organs and Functions

Key Terms and Definitions

• Zymogen: An inactive enzyme precursor that requires a biochemical change to become active (e.g., fibrinogen to fibrin).

• Glycogen: A polysaccharide that serves as a form of energy storage in animals, primarily in the liver and muscles.

• Cardiac Sphincter: The muscular ring at the junction of the esophagus and stomach, preventing backflow of food.

• Pyloric Sphincter: The muscular ring at the junction of the stomach and small intestine, regulating passage of food.

• Endocrine vs. Exocrine: Endocrine glands secrete hormones directly into the bloodstream; exocrine glands release substances through ducts (e.g., digestive enzymes).

Example: Digestion of Carbohydrates

• Carbohydrate digestion begins in the mouth with salivary amylase, continues in the small intestine with pancreatic amylase, and results in monosaccharides that are absorbed into the bloodstream.

• Equation for starch breakdown:

Additional info:

• Some content was inferred and expanded for academic completeness, such as the functions of specific organs and the roles of digestive enzymes and hormones.

• Details about fetal circulation and the distinction between endocrine and exocrine pancreas were added for clarity.