Unit 8 Digestive System

Digestive system

Breaks down food into nutrients and absorbs them for energy, growth, and repair

Alimentary canal (digestive tract)

Tube food travels through from mouth to anus

Accessory organs

Organs that help digestion but food does not pass through (liver, gallbladder, pancreas, teeth, tongue)

Digestive pathway

Mouth → Pharynx → Esophagus → Stomach → Small intestine → Large intestine → Rectum → Anus

Ingestion

Taking food into the body

Propulsion

Moving food through the digestive tract

Egestion

Elimination of waste

Mechanical digestion

Physical breakdown of food (chewing, churning)

Chemical digestion

Breakdown of food using enzymes at the molecular level

Peristalsis

Involuntary, wave-like contractions that push food forward

Segmentation

Mixing movement in the small intestine that slows food for absorption

Bolus

Chewed food mixed with saliva

Chyme

Thick, soupy mixture of partially digested food in the stomach

Stomach

Muscular sac that performs mechanical and chemical digestion and forms chyme

Rugae

Folds in the stomach lining that allow it to expand

Maceration

Churning of food in the stomach

Why the stomach has 3 muscle layers

Allows stronger mixing and better mechanical digestion

What are the 3 layers of the stomach?

Longitudinal muscle layer, circular muscle layer, and oblique muscle layer

Mucous cells

Secrete mucus to protect the stomach lining

Chief cells

Produce protein-digesting enzymes

Parietal cells

Produce hydrochloric acid (HCl)

Sphincter

Ring of muscle that controls movement between digestive organs

Cardiac sphincter

Controls food entering the stomach from the esophagus

Pyloric sphincter

Controls food leaving the stomach into the small intestine

Small intestine

Where most digestion and nutrient absorption occur

Duodenum

First section of the small intestine where enzymes and bile act

Villi

Finger-like projections that increase surface area for absorption

Why villi are important

More surface area allows more nutrients to enter the bloodstream

Large intestine

Absorbs water and forms waste

Colon

Main section of the large intestine

Rectum

Stores feces before elimination

Bacteria (large intestine)

Produce vitamins B and K

Liver

Produces bile

Gallbladder

Stores and concentrates bile

Pancreas

Releases digestive enzymes and bicarbonate

Bile

Breaks fats into smaller droplets (emulsification)

Why bile is needed

Fats do not mix with water and are hard to digest

Bicarbonate

Neutralizes stomach acid to protect the small intestine

Carbohydrates

Main source of quick energy

Lipids (fats)

Long-term energy storage; hard to digest

Why lipids are harder to digest

They are insoluble in water

Proteins

Used for body structures and enzymes

Metabolism

All chemical reactions in the body

Catabolism

Breaking down molecules to release energy

Anabolism

Building complex molecules using energy

Why villi increase absorption

Increase surface area

Why bile helps fat digestion

Emulsifies fats into smaller droplets

Why segmentation is important

Slows food so nutrients can be absorbed