Human Body Pathways (Bio 11 Unit 3)

CO₂ and O₂ Pathways Through the Heart and Body

Oxygen (O₂) Pathway

• Follows oxygenated blood after O₂ enters the lungs.
• Step 1: Oxygen enters the lungs through inhalation and diffuses into pulmonary capillaries from the alveoli.
• Step 2: O₂ binds to hemoglobin in red blood cells.
• Step 3: Blood becomes oxygen-rich and moves via the pulmonary veins to the left atrium of the heart.
• Step 4: From the left atrium, blood passes through the bicuspid (mitral) valve into the left ventricle.
• Step 5: The left ventricle contracts and pumps oxygenated blood through the aortic semilunar valve into the aorta.
• Step 6: Blood is delivered to the body's tissues through systemic arteries.
• Step 7: Oxygen diffuses from the blood into cells for cellular respiration to make ATP.

Carbon Dioxide (CO₂) Pathway

• Follows deoxygenated blood carrying CO₂ waste from the body.
• Step 1: CO₂, produced as a waste product of cellular respiration, diffuses into capillaries.
• Step 2: CO₂ travels in the blood (dissolved in plasma or as bicarbonate) through veins into the superior and inferior vena cava.
• Step 3: Enters the right atrium of the heart.
• Step 4: Passes through the tricuspid valve into the right ventricle.
• Step 5: The right ventricle contracts and pumps blood through the pulmonary semilunar valve into the pulmonary arteries.
• Step 6: Blood travels to the lungs, where CO₂ diffuses into the alveoli.
• Step 7: CO₂ exits the body during exhalation.

Glucose Pathway (From Ingestion to Cell Use)

• Step 1: Ingestion: Consumption of glucose-containing substances (e.g., bread).
• Step 2: Digestion:
  • In the mouth, salivary amylase begins to break down starches into simple sugars.
  • In the small intestine, enzymes from the pancreas (like maltase) break disaccharides into glucose molecules.
• Step 3: Absorption:
  • Glucose is absorbed through the villi of the small intestine into capillaries.
• Step 4: Transport:
  • Glucose travels through the hepatic portal vein to the liver, where some is stored as glycogen.
  • The rest enters the bloodstream and is transported via systemic circulation.
• Step 5: Cellular Use:
  • Glucose is taken up by body cells (with help from insulin) and used in cellular respiration in mitochondria to make ATP (energy).

Water Pathway (From Ingestion to Elimination)

• Step 1: Ingestion: Water enters the body through drinking.
• Step 2: Digestion & Absorption:
  • Some absorption may begin in the stomach, but most water is absorbed in the small and large intestines.
• Step 3: Transport:
  • Water enters the bloodstream via capillaries in the intestinal walls.
• Step 4: Circulation:
  • Water travels through the circulatory system to maintain blood volume, hydrate cells, and regulate body temperature.
• Step 5: Homeostasis:
  • The kidneys filter the blood and regulate water levels.
  • Excess water is excreted through urine, sweat, or breath (as water vapor).

Combined CO₂ + O₂ Pathway Overview Summary

• Lungs: O₂ enters the blood, CO₂ leaves the blood.
• Heart (left side): Pumps O₂-rich blood to the body.
• Tissues: Cells use O₂, produce CO₂.
• Heart (right side): Pumps CO₂-rich blood to the lungs.
• Exhalation: CO₂ leaves the body.