The route blood takes through the circulatory system starts in the heart.
1. **From the Heart:**
- The blood is pumped out of the heart through the arteries. Oxygen-rich blood is pumped out of the left side of the heart through the aorta, while oxygen-poor blood is pumped out of the right side of the heart through the pulmonary artery.
2. **To the Lungs:**
- Oxygen-poor blood travels from the heart to the lungs through the pulmonary artery, where it picks up oxygen and releases carbon dioxide.
3. **Back to the Heart:**
- Oxygen-rich blood returns from the lungs to the heart through the pulmonary veins.
4. **To the Body:**
- The oxygen-rich blood is then pumped out of the heart to the rest of the body through the aorta, supplying oxygen and nutrients to the body's cells.
5. **Returning to the Heart:**
- Oxygen-poor blood returns to the heart through the veins, entering the right atrium.
Throughout this journey, changes occur in the blood:
- **Oxygen Levels:** Blood becomes oxygenated in the lungs, where it exchanges carbon dioxide for oxygen.
- **Nutrient Levels:** Nutrients are absorbed from the digestive system into the bloodstream to be transported to cells throughout the body.
- **Waste Removal:** Blood picks up waste products like carbon dioxide and urea from the body's cells to be eliminated through the lungs, kidneys, and other organs.
- **Hormone Transport:** Blood carries hormones from endocrine glands to target organs to regulate various bodily functions.
- **Temperature Regulation:** Blood helps regulate body temperature by absorbing and releasing heat as needed.
These changes ensure that the blood delivers essential substances to cells, removes waste products, and helps maintain homeostasis within the body.
