Deoxygenated blood enters the heart through 3 vessels (1) ( and ( it then enters a chamber called the ( and passes through the (5) the blood then enters a chamber called the ( and passes up through the ( and ( the area splits into the right and left ( blood then enters the right and left ( where oxygen is picked up. the oxygenated blood then reenters the heart through the right and left ( it enters a chamber called the ( and passes through the ( the blood then enters a chamber called the ( and pushes up through the ( blood will then enter the ( if it is going to move to the upper part of the body, blood will exit through the ( ( or the ( if it is going to the lower part of the body, blood will go through the (

1-3. Deoxygenated blood enters the heart through 3 vessels the superior vena cava, the inferior vena cave and the coronary sinus.

(The superior vena cava carries blood from the upper limbs, head and the upper torso. The inferior vena cava carries blood from the lower limbs, the pelvis and the abdomen. The coronary sinus on the other hand carries blood from the coronary circulation, which is the circulation that nourishes the heart wall.)

4. It then enters a chamber called the Right Atrium.

(The right atrium is small and has thin muscle lining. It is one of the two receiving chambers of the heart. It is, as the name suggests, on the right side on the upper area of the heart.)

5. and passes through the tricuspid valve.

(It is also known as the right atrioventricular valve. Its main function is to prevent back flow of blood. It is made up of 3 valves, which look like flaps.) 

6. The blood then enters a chamber called the right ventricle.

(One of the two pumping chambers of the heart. The muscles are thicker than those you would find on the atria.  It is the right lower chamber of the heart)

7. and passes up through the pulmonary semilunar valve.

(It was named as such because this is the valve that opens into the pulmonary circuit. It is sometimes referred to as the pulmonic valve. It also has three cusps. This valve opens during ventricular systole.)  

8. and Pulmonary trunk.

(This is considered as the first vessel of the pulmonary circuit because it is at this point where the blood makes its way to the lungs to be oxygenated. It is also known as the main pulmonary artery. It is one of the major vessels of the human heart.)

9. The area splits into the right and left pulmonary artery.

(The pulmonary arteries are the only arteries in the body that carry unoxygenated blood or deoxygenated blood. They are considered arteries despite this because they carry blood away from the heart.)

10.  Blood then enters the right and left lung where oxygen is picked up.

(As the blood picks up oxygen, it releases carbon dioxide during respiration. The arteries are divided further into really small capillaries, which have extremely thin walls.)

11. The oxygenated blood then reenters the heart through the right and left pulmonary veins.

(Like pulmonary arteries, pulmonary veins are unique because they are the only veins in the body that carry oxygenated blood. They are considered as veins because they carry blood towards the heart.)

12. It enters a chamber called the left atrium.

(The right atrium is the second of the two receiving chambers. It differs from the left because on this side of the heart, it receives oxygenated blood which come from the pulmonary veins.)

13. and passes through the bicuspid valve.

(Named as such because it has two cusps. It is also known as the bicuspid aortic valve, the mitral valve or the left atrioventricular valve. This valve opens during diastole and closes during systole.)

14. The blood then enters a chamber called the left ventricle.

(The left ventricle is the second of the two pumping chambers. It has thicker muscles than the right ventricle because it has to pump blood all around the body. The right ventricle only has to pump blood into the lungs.)

15. and pushes up through the aortic semilunar valve.

(Also known simply as the aortic valve, it has 3 cusps. It opens as the pressure builds up in the left ventricle. As the pressure decreases when systole ends, the aortic valve will close. The opening and closing of the aortic valve makes the second heart sound.)

 16. Blood will then enter the Aorta.

(The aorta is the largest artery in the human body. It has four sections; ascending aorta, aortic arch, descending aorta and abdominal aorta. )

17. If it is going to move to the upper part of the body, blood will exit through the Brachiocephalic trunk,

(The brachiocephalic trunk is the first and the biggest branch of the aortic arch. It splits into smaller arteries called the right common carotid artery and the right subclavian artery. It supplies blood to the right side of the head, neck and right upper limb.)  

18. Left common carotid artery.

(This artery is one of the two carotid arteries. It supplies blood to the left side of the head and the neck. Unlike the right common carotid artery, it stems directly from the aortic arch.)

19. Left subclavian artery.

(The left subclavian artery supplies blood to the upper limbs on the left side of the body. It also stems directly from the aortic arch, unlike its counterpart the right subclavian arteries.

20.  If it is going to the lower part of the body, blood will go through the descending aorta.

(The descending aorta is also called the thoracic aorta. It continues from the aortic arch. It supplies blood to lower half of the body. As it leaves the thorax, it becomes the abdominal aorta)

relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

hope this .. .