Digestive Systems & Nutrition Overview

Digestive Systems & Nutrition

• Digestive systems encompass all organs, tissues, and cells involved in ingesting and breaking down food.
• Digestive tracts are categorized into incomplete and complete.
• Incomplete tracts have a single opening (e.g., planarian), while complete tracts have two (e.g., earthworm).
• Complete tracts exhibit specialized parts, unlike incomplete tracts.
• Continuous feeders (e.g., clams) constantly filter water, while discontinuous feeders (e.g., squid) capture prey.
• Dentition (teeth) varies among mammals based on dietary needs (omnivores, herbivores, carnivores).
• The human digestive tract is a complete tube-within-a-tube system, starting at the mouth and ending at the anus.
• Digestion is primarily extracellular, occurring outside cells. Digestive enzymes break down food molecules.

Human Digestive Tract (System)

• The mouth contains salivary glands that release saliva, containing amylase, initiating starch digestion.
• The tongue mixes chewed food with saliva, forming a bolus.
• The pharynx is a passageway for food during swallowing.
• The esophagus uses peristalsis (rhythmic contractions) to propel food to the stomach.
• The stomach secretes gastric juices, containing hydrochloric acid and pepsin, to break down proteins.

Stomach

• Food mixing with gastric juices forms chyme.
• The sphincter controls the junction between the stomach and small intestine.
• A small quantity of chyme enters the small intestine when the sphincter relaxes.

Small Intestine

• The first segment is the duodenum, where chyme interacts with secretions from the liver and pancreas.
• The liver produces bile which breaks down fats.
• The small intestine absorbs nutrient molecules and water.
• The intestinal villi and microvilli increase the surface area for absorption.

Large Intestine

• Includes cecum, colon, rectum, and anal canal, absorbing water and salts and forming feces.

Accessory Organs

• Pancreas: Endocrine function regulates blood glucose levels via insulin and glucagon. Exocrine function produces pancreatic juice with digestive enzymes.
• Liver: Largest gland, detoxifies blood, stores nutrients, produces bile for fat emulsification.

Digestive Enzymes

• Salivary amylase digests starch to maltose.
• Pepsin digests proteins to peptides.
• Pancreatic amylase digests starch to maltose.
• Peptidases break down peptides into amino acids.
• Lipase digests fat into fatty acids.

Nutrition and Human Health

• Carbohydrates are sugars, starches, and fibers found in fruits, vegetables, milk, and honey.
• Glucose is the main energy source, stored as glycogen in animals and starch in plants.
• Proteins consist of 20 different amino acids, crucial for tissue formation.
• Adequate protein intake includes animal sources (complete) and plant sources (incomplete), which can be combined for optimal nutrition.

Liver, Gallbladder, and Pancreas

• Gallbladder stores bile produced by the liver.
• Gallstones can form from cholesterol crystallization in bile.

Vitamins and Minerals

• Vitamins are organic compounds the body can't make, obtained from diet, crucial for metabolic functions.
• Minerals are also essential elements for bodily functions and are obtained from diet.
• Vitamin D is crucial for calcium absorption and metabolism.

Dietary Considerations

• Diet and obesity: Too many calories from any source contribute to body fat, increasing the risk for Type 2 diabetes and cardiovascular disease.
• Fiber is indigestible carbohydrates in plant-based foods that aid in digestion
• Lipids (fats, oils, cholesterol) are crucial for energy and structure, but excessive intake can be detrimental.