The Digestive System Overview

The Digestive System

• The digestive system breaks down food for energy.
• Four major processes are involved: ingestion, digestion, absorption and egestion.
• Ingestion is when food enters the mouth.
• Digestion breaks down food into smaller components (mechanical and chemical).
• Absorption involves nutrients being absorbed by the bloodstream to deliver them to cells.
• Egestion is the removal of waste products.
• Enzymes are proteins that act as biological catalysts, increasing the rate of chemical reactions like metabolism in the body.
• An enzyme's active site is specialized for a specific substrate (a molecule being broken down or built up).
• Nutrients need to be broken down into smaller subunits (monomers) to be absorbed in the digestive system. Monomers for: carbohydrates are monosaccharides; proteins are amino acids; lipids are glycerol and fatty acids).
• Carbohydrates, the main source of energy, break down through chemical digestion into smaller sugar molecules such as glucose, fructose, and galactose
• Proteins are broken down to amino acids in the stomach. Enzymes such as pepsin participate in this breakdown.
• Lipids are broken down using bile and lipase.
• Mechanical digestion involves physically breaking down food into smaller pieces in the mouth and stomach; chemical digestion involves breaking down large food molecules into smaller simpler molecules that can be absorbed by the blood.
• The mouth is the start of the digestive system. Mechanical digestion starts here using teeth to break food into smaller pieces aiding digestion. Saliva contains chemical enzymes called Amylase.

Organs of the Digestive System

• Mouth: Breaks down food and aids speech
• Pharynx: Passes food to esophagus
• Esophagus: Transits food to stomach using peristalsis.
• Stomach: Stores, churns, and digests food (releases gastric juices such as HCI and pepsin) using mechanical digestion.
• Small Intestine: Site of nutrient absorption. 3 parts are the duodenum, jejunem and ileum.
• Duodenum: Chemical digestion occurs here
• Pancreas: Produces pancreatic enzymes for digesting all macronutrients. Secretes hormones insulin and glucagon to regulate blood sugar.
• Gallbladder: Stores and concentrates bile.
• Liver: Produces bile for fat emulsification.
• Large Intestine: Absorbs water and electrolytes. 3 parts are the ascending, transverse, and descending colon.
• Rectum: Stores waste.
• Anus: Eliminates waste).

Digestion in the Mouth

• Mechanical: teeth tear and grind food.
• Chemical: saliva (containing amylase) starts carbohydrate digestion.

The Epiglottis

• A flap that covers the trachea during swallowing to prevent food from entering the lungs.

The Esophagus

• Muscular tube connecting the mouth to the stomach.
• Peristalsis propels food down into the stomach.

The Stomach

• Stores, churns, and digests food.
• Has a low pH (~2) to aid in protein digestion.
• Secretes gastric juices (HCI and pepsinogen).
• Pepsinogen converts to pepsin in the low pH.
• Secretes mucus to protect from acid.
• Important for chemical digestion of proteins.
• Mechanical and churing to aid chemical digestion.

The Small Intestine

• Main site of nutrient absorption.
• Chyme is the name for partially digested food.
• Cells release enzymes such as amylase, lipase and trypsin, along with hormones like insulin and glucagon. The small intestine has three parts: duodenum, jejunum and ileum.

The Pancreas

• Produces pancreatic juices containing enzymes for digesting carbohydrate, protein and fat (amylase, lipase and trypsin) and sodium bicarbonate neutralising stomach acid.

The Liver and Gallbladder

• Liver produces bile, which helps emulsify fats.
• Gallbladder stores and concentrates bile, releasing it into the duodenum.

The Large Intestine

• Absorbs water, electrolytes and minerals preparing waste for elimination. If the large intestine absorbs too much water, constipation results; if it absorbs too little water, diarrhea results. Ascending, transverse and descending colon are the major parts.

Blood Sugar Regulation

• Insulin decreases blood sugar.
• Glucagon increases blood sugar.
• Insulin promotes glycogen formation in the liver
• Glucagon promotes glycogen breakdown in the liver.

Celiac Disease

• A disease where the immune system responds negatively to gluten, affecting the small intestine's ability to absorb nutrients.

Explore the essential functions and processes of the digestive system, including ingestion, digestion, absorption, and egestion. Understand how enzymes play a crucial role in breaking down food and facilitating nutrient absorption. This quiz will test your knowledge of the digestive processes and nutrient monomers.