The New Childrens Encyclopedia

THE HUMAN BODY

What goes into blood? Blood is made up of red blood cells, white blood cells, platelets, and plasma. Plasma is mostly water but also carries dissolved proteins, glucose, minerals, hormones, and carbon dioxide.

BLOOD FLOW

TAKE A LOOK: BLOOD VESSELS



ARTERIES

carry oxygen-rich blood away from your heart. They have thicker walls than veins or capillaries.



CAPILLARIES

are microscopic, with walls just one cell thick. They link your arteries to your veins.



VEINS

carry

oxygen-poor blood to your heart. Many veins have valves to stop the blood from running backward.

There are three types of blood vessel: arteries, veins, and capillaries. Blood begins its journey around the body in a large artery, called the aorta. Arteries have thicker walls than other vessels because the blood flow is at higher pressure.

O

Beats per day

Approx 100,000

O

Average weight

Male: 10

1 ⁄^2

oz

(300 g) Female: 9 oz (200 g)O

Length

5 in (12 cm)

O

Width

3½ in (9 cm)

Your heart and how it works The muscular human heart is about the size of a fist. It pumps blood around your body that takes oxygen to the cells and removes waste. A heart has four chambers: two lower ventricles, and two upper atria. If your heart stops, no other part of your body can work.

Superior vena cava Aorta Pulmonary arteryRight atriumRight ventricle

Pulmonary valve

Thick cardiac muscle

BODY

CIRCULATION Stretched out, your blood vessels would reach 93,000 miles

(150,000 km).

That’s about four

times around Earth.

Blood clots If you fall over and cut your knee, the cut area scabs over and heals. This happens in a series of steps, as shown below.

Plasma (about 50-55%)

White blood

cells and platelets

(about 1-2%)Red blood cells

(about 40-45%)

This is the body’s

longest vein. Blaood flows

through it from

the foot and

lower leg on its

journey back to the heart.

1 INJURY

When skin is

cut, it bleeds because of damage to the blood vessels. 3 PLUGGING

The clot

forms a plug that stops blood from leaking out.

Blood clot

ScabScar

2 CLOTTING

Platelets

stick together and a blood clot begins to form. 4 SCABBING

The plug hardens

to form a protective scab, which eventually falls off.

Injury site Severed vessel Plug of tissueNew tissue