Digestive System Overview

Digestive System Overview

• The digestive system is a complete system, containing specialized regions.
• The length of the digestive tract varies based on diet. Herbivores and omnivores have longer digestive tracts than carnivores due to cellulose being harder to digest.
• The human digestive system is 7-9 meters long when stretched.

The Mouth

• The mouth is the site of both mechanical and chemical digestion.
• Key structures include teeth, tongue, hard and soft palate, and salivary glands.
• Saliva, produced by salivary glands, lubricates food and contains amylase, an enzyme that begins the breakdown of starches.

Swallowing

• The tongue shapes food into a bolus.
• The soft palate rises to prevent food from entering the nasal passages during swallowing.
• The epiglottis covers the trachea to prevent food from entering the lungs.

The Esophagus

• Swallowed food travels down the esophagus.
• The esophagus is made of smooth muscle and epithelial tissue.
• Peristalsis, a wave-like muscle contraction, moves food through the esophagus.

The Stomach

• The stomach is a J-shaped sac made of smooth muscle and epithelial tissue.
• It aids in both physical and chemical digestion.
• A mucous lining protects the stomach from the acidic gastric juices within it.
• Gastrin, a hormone, stimulates the release of gastric juices.
• Gastric juices have a pH of 2.0-3.0 and begin protein digestion by converting pepsinogen to pepsin.

The Small Intestine

• The small intestine breaks down food particles so nutrients can be absorbed.
• It receives enzymes from the liver and pancreas to aid in digestion.
• The inner lining of the small intestine is folded with finger-like projections called villi, which increase the surface area for absorption significantly (up to 500X).
• Each epithelial cell covering the villi is covered in microvilli.
• Digested fats are absorbed via lacteals into the lymphatic system, whereas other nutrients enter the bloodstream through capillaries.

The Duodenum

• The duodenum is the first part of the small intestine (25 cm long).
• Chyme, partially digested food, is released into the duodenum from the stomach.
• Enzymes from the pancreas and liver are added in the duodenum.

The Jejunum

• The jejunum is the second part of the small intestine (2-2.5m long).
• It's thicker and redder than the duodenum, continuing digestion and absorption.

The Ileum

• The ileum is the third and longest section of the small intestine (3.5m).
• It plays a critical role in nutrient absorption.

The Large Intestine

• The large intestine, also known as the colon, converts liquid chyme into semi-solid feces.
• Significant water absorption occurs in the large intestine (approx. 20 liters).
• The large intestine contains "good" bacteria that help digest cellulose and create vitamins K and B.

The Rectum

• The rectum's function is elimination, the opposite of ingestion.
• Cellulose and fiber contribute bulk and maintain water to facilitate egestion.
• Peristaltic waves expel feces during defecation.

Accessory Organs

• These organs assist in digestion but aren't part of the continuous digestive tract.
• The accessory organs include the pancreas, liver, gallbladder, and salivary glands.

The Pancreas

• The pancreas is a 6-inch long (pink/gray) leaf-shaped organ.
• It produces enzymes for breaking down proteins, lipids, and carbohydrates.
• It neutralizes the acidic chyme.
• The enzymes from the pancreas are released into the duodenum.

The Liver

• Nutrient-rich blood from the intestine filters through the liver.
• The liver performs 250+ vital functions, including:
  • Storing and releasing glucose for energy.
  • Processing vitamins and minerals.
  • Breaking down toxins into less harmful substances.
  • Recycling old blood cells.

Liver and Gallbladder

• The liver produces bile (1 liter daily).
• Bile aids in the emulsification of fats into micelles.
• Bile is stored and concentrated in the gallbladder.
• Bile is released into the duodenum.

Enzymes

• Enzymes are specialized proteins coded for by DNA.
• They accelerate chemical reactions by breaking or forming bonds.
• They are specific to their substrates (they only work with certain substrates).

Hydrolysis

• Hydrolysis is the chemical process of digestion, using water in the presence of enzymes, to break down food.
• The process involves: ingestion, digestion, absorption, assimilation, and elimination.

Chemical Digestion

• Chemical digestion breaks down macronutrients into monomers that the body can absorb and utilize.
• Examples of enzymes and their macronutrient targets:
  • Carbohydrates: amylase, disaccharidases
  • Proteins: pepsin, trypsin, erepsin
  • Fats: lipases
  • Nucleic acids: nucleases

Explore the fascinating functions and regions of the digestive system in this quiz. Learn about the roles of the mouth, esophagus, and the process of swallowing. Discover how diet influences the length of the digestive tract across different species.