Human Body Systems: Digestive System

• All living things, including humans, consist of cells.
• Cells form tissues, tissues combine to create organs, and organs work together in organ systems.
• The main organ systems are digestive, respiratory, circulatory, and excretory.

Digestive System

• Breaks down food into nutrients that provide energy for growth and repair.
• Major organs include: mouth, esophagus, stomach, small intestine, large intestine, liver, and pancreas.
• Digestion begins in the mouth because saliva contains enzymes.
• The esophagus moves food to the stomach through peristalsis.
• The stomach uses acid and enzymes to break down food particles.
• The small intestine absorbs nutrients via villi and microvilli, which increase its surface area.
• The large intestine absorbs water and forms solid waste (feces).
• The liver produces bile to digest fats, and the pancreas secretes digestive enzymes and bicarbonate.
• Villi in the small intestine absorb nutrients.
• Enzymes break down macromolecules like carbs, proteins, and fats into simpler molecules like sugars, amino acids, and fatty acids.

Respiratory System

• Brings in oxygen and expels carbon dioxide.
• Major organs include: nose/mouth, trachea, lungs, bronchi/bronchioles, and alveoli.
• Air enters through the nose/mouth, where it is filtered, warmed, and moistened.
• The trachea (windpipe) acts as the path to the lungs.
• Lungs are the place for gas exchange, where oxygen enters and carbon dioxide exits.
• Bronchi and bronchioles are airways that lead to smaller regions in the lungs.
• Alveoli are tiny sacs in the lungs where gas exchange occurs.
• Alveoli walls are thin to allow for efficient gas exchange.
• Cilia and mucus in the airways protect against pathogens and particles.

Circulatory System

• Transports oxygen, nutrients, hormones, and waste throughout the body.
• Major organs include; heart, blood vessels (arteries, veins, capillaries), and blood.
• The heart pumps blood.
• Arteries carry oxygen-rich blood away from the heart.
• Veins carry oxygen-poor blood back to the heart.
• Capillaries are tiny vessels facilitating nutrient and waste exchange at the cellular level.
• Blood contains red blood cells (oxygen), white blood cells (immune response), platelets (clotting), and plasma (carries nutrients/waste).
• Red blood cells contain hemoglobin to transport oxygen.
• Heart valves ensure one-way blood flow.

Excretory System

• Removes waste products (urea, ammonia, excess salts) and maintains water balance.
• Major organs include: kidneys, ureters, bladder, and urethra.
• Kidneys filter blood to remove waste and produce urine.
• Ureters carry urine from the kidneys to the bladder, which stores urine.
• The urethra excretes urine.
• Nephrons in the kidneys filter blood, reabsorb necessary substances, and secrete waste.
• The glomerulus filters blood in the kidneys.
• The Loop of Henle concentrates urine and reabsorbs water and salts.

Organ Systems Working Together

• Cells are the building blocks of life, forming tissues, which create organs that work in systems.
• All systems (digestive, respiratory, circulatory, excretory) work together to maintain homeostasis (balance).
• Each system has specialized structures to perform its job efficiently.
• The digestive System breaks down food, which provides nutrients the circulatory system carries.
• The respiratory system brings oxygen into the body, which is then transported by the circulatory system to cells for energy.
• The excretory system removes excess waste and helps maintain water and salt balance, which prevents toxins from building up.
• Everything works together to keep you alive and functioning properly.

Explore the digestive system: how it breaks down food into nutrients for energy, growth, and repair. Learn about organs like the mouth, esophagus, stomach, and intestines, and their roles in digestion, absorption and waste removal.