structure of the heart

what is the heart?

a hollow, double pump organ made of cardiac muscle located in the chest cavity

it is divided into four chambers, the top two are atria and the bottom two are ventricles  

name the structures of the heart

1) superior vena cava
2) pulmonary veins
3) right atriun
4) tricuspid valve
5) right ventricle
6) inferior vena cava
7) left ventricle
8) semilunar valves
9) bicuspid valve
10) left atrium
11) pulmonary veins
12) pulmonary artery
13) aorta

what are the five types of blood vessels?

arteries, arterioles, veins, venules, capillaries 

what are the features that all blood vessels have in common?

the endothelium, a one cell thick smooth inner layer 

three main layers that form the walls of the blood vessles; the tunica intima (endothelium), tunica media (smooth muscle + elastic fibres), tunica externa/adventita  (connective tissue + elastic fibres)

what is the function of arteries?

arteries transport blood away from the heart at a high pressure to the tissues

what are features of the endothelium in arteries?

very smooth and reduces friction for free blood flow

a highly folded to enable expansion under high pressure 

what are features of the tunica media in arteries?

thick tunica media strengthens the arteries so they can withstand high pressure

contraction of muscle causes constriction of lumen

elastic tissue stretches and recoils to maintain blood pressure

what are features of the tunica adventitia in arteries?

contains collagen which protects arteries from damage by over-stretching 

what is a feature of the lumen in arteries?

narrow lumen helps to maintain a high blood pressure

what are arterioles?

they are blood vessels that branch off the artery and transport blood to the capillaries, and have a similar structure to arteries but with much smaller and thinner muscular walls + elastic layers

what is the function of veins?

veins transport blood to the heart at low pressure

what is a feature of the tunica media in veins?

it is much thinner than in the arteries as veins do not have to withstand high pressure 

what is a feature of the lumen in veins?

it is much wider to ensure that blood returns to the heart at an adequate speed
it also reduces friction between the blood and the endothelium of the vein so a high volume of blood can be delivered to the heart

what vital feature do veins have which aid in blood flow?

they have valves which prevent backflow of blood

what are venules?

smaller version of veins but lack valves
they transport blood from the capillaries to the veins

what are capillaries?

microscopic blood vessels that carry blood to the cells where substances leave the blood to reach the body’s tissues

how do capillaries aid in diffusion?

wall of capillary is a single layer of endothelial cells only one cell thick which reduces the diffusion distance for fast exchange of substances
can form capillary beds which are important exchange surfaces
large number of capillaries branch between cells which reduces diffusion distance

what is a feature of the lumen in capillaries?

very narrow lumen which forces blood to travel slowly so there is more time for diffusion 

how do components of blood interact with capillaries?

pores which allow blood plasma to leak out and form tissue fluid + white blood cells to squeeze through to fight infections