- The _____, a group of heart cells in the right atrium, sends out signals that make the heart muscle contract. The pacemaker adjusts the heart rate according to the body's oxygen needs. When the body needs more oxygen, the heart beats faster.
- _____ carry blood away from the heart and into the capillaries.
- After leaving the heart, blood travels through ____ kinds of blood vessels.
- The heart has a right side and a left side. The right side of the heart is completely separated from the left side by a wall of tissue called the ______
- In addition, blood contains cells that fight ______
- The cardiovascular system carries needed substances to cells and carries _____ products away from cells.
- The _____ system, or circulatory system, consists of the heart, blood vessels, and blood.
- what wall thickens in preparation of possible implantation
- The flagellum enables what of the sperm
- which male organ is responsible for making testosterone
- In the Ovulation stage Estrogen levels do what
- the fusion of two cells creates how many organisms
- what completes its development within the mothers uterus with nourishment through the placenta
- what type of fertilization do aquatic animals do
- What does an egg release to attract sperm?
- In the Menstruation stage hormone levels do what?
- In the Luteal stage the follicle becomes the
- In the Follicle stage what hormone increases
- What type of fertilization do mammals do
- when sperm touches the egg surface what happens to the membrane