Venules collect blood from the capillaries and the blood channels known as sinusoids and unite to form progressively larger veins that terminate as the great veins, or venae cavae. In the extremities there are superficial and deep veins; the superficial lie just under the skin and drain the skin and superficial fasciae (sheets of fibrous tissue), while the deep veins accompany the principal arteries of the extremities and are similarly named. Interconnections between the superficial and the deep veins are frequent.
Venous blood enters the right atrium from three sources: the heart muscle by way of the coronary sinus; the upper body by way of the superior vena cava; and the lower body by way of the inferior vena cava.
Veins are blue they have thin walls and are like tubes they are sort of like spaghetti. And they have three layers one outer layer of tissue one middle layer of muscle and one layer smooth inner layer of epithelial cells. Blood with little oxygen is a bright red and blood with lots of oxygen is a dark red. There are more veins then arteries also veins are thicker than arteries.
Types of Veins
There are 6 types of veins but there are three main veins and they are:
The Pulmonary Veins contain arterial blood, which they return from the lungs to the left atrium of the heart.
The Systemic Veins return the venous blood from the body to the right atrium of the heart.
The Portal Vein is found in abdominal cavity, and returns the venous blood from the spleen to the liver. It forms a small network of capillary-like vessels, from which the blood is carried.