Question

for each of the following please describe the journey of blood from heart to the region of the body presented and back to the heart

1.) The capillary beds of a left hand

2.) The capillary beds of the brain

Answer 1

Heart and the blood vessels are involved in the transfer of oxygenated blood to the different parts of the body and the blood vessels bring back the deoxygenated blood to the heart, which pumps the blood to the lungsfor oxygenation before circulating the blood to the body. This type of circulation is termed as double circulation as the blood flows twice through the heart before the circulation through the entire body.

The right atrium takes the deoxygenated blood fromvena cava, the largest vein of the body, which is then transferred to right ventricle which pumps the blood to the lungs to oxygenate the blood, through pulmonary artery. The oxygenated blood is brought back by the pulmonary vein to the left atrium, then to the left ventricle which pumps the blood to the entire body through the aorta, the largest artery of the body.

Aorta divides into smaller arteries which further divide into arterioles and then capillaries. The capillary beds are the actual site of exchange of the oxygen and carbon dioxide, transferring the oxygen to the body tissues and taking the carbon dioxide from the tissues. The blood gets deoxygenated and the capillaries fuse to form venules which furhter fuse to form veins. These veins arising from different part of the body combine to form the largest vein in the body, where superior and inferior vena cava meet to form the vena cava which brings the deoxygenated blood to the right atrium, completing one cycle of the double circulation of blood.

The oxygentated blood pumped by the left ventricle is taken by aorta for circulation to different body parts.

1. Capillary beds of the left hand: The aorta branches to form several arteries, One of them is a large artery called subclavian artery, which originates from the aortic arch towards the left side of the body, that circulates the oxygenated blood to the left arm. It branches to form the axillary artery (deep seated) and cephalic artery (superficial artery) that further breaks into branchial (upper arm), radial and ulnar (forearm) arteries that supply blood to the complete forearm. These arteries divide to form arterioles and then capillaries. A network of intervowen capillaries is called capillary bed which is involved in direct transfer of nutrients from the blood to the tissues and take the products generated during the metabolic activity of the tissues. Capillaries are connection between the arteioles and venules, present on the either side of the capillaries. The capillaries join to form the venules and then veins: radial and ulnar veins in the forearm which join to form the branchial vein in the upper arm, which then becomes the axillary vein when joined by a superficial vein called basilic vein, and finally the axillary vein and another upeficial vein called cephalic vein together form the subclavian vein. Subclavian then joins internal juglar vein, now called branchiocephalic vein, which supplies the deoxygenated blood fromt he left hand to the superior vena cava.

2. Capillary beds of the brain: On the right side of the body, the aorta gives rise to the brachiocephalic trunk that form the right subclavian artery and the common carotid artery, while on the left hand side the common carotid artery arise directly from the aortic arch. These arteries then bifurcate to form internal and external carotid arteries. Internal carotid arteries are responsible for the circulation in the anterior part of the brain through anterior and middle cerebral arteries. Another artery arises from the subclavian artery called the vertebral artery which moves through the cervical vertebrae (upwards from the sixth cervical vertebrae), and forms the basilar artery that supplies blood to the posterior part of the brain. The anterior circulation is formed by the interior carotid arteries which consist of the anterior cerebral artery, communicating artery and the middle cerebral artery. The posterior circulation begins from the vertebrobasilar system comprising of the vertebral, basilar, posterior cerebral and posterior communicating arteries. These arteries sub divide to form arterioles and capillaries. The capillaries form the capillary bed for direct nutrient transfer and uptake of the waste from the brain tissues. The capillaries again join to form the venules, and then the veins. The major veins are the superior and inferior, superficial middle, internal and the great cerebral veins. These take the deoxygenated blood to the dural sinus, which drains the blood into the sigmoid sinus that further joins the internal juglar veins that combines with the subclavian veins to form the brachiocephalic veins that take the deoxygenated blood to the superior vena cava.