6.2: BLOOD SYSTEM

WILLIAM HARVEY (1578 – 1657)English physicianFirst known person to completely describe the detail for the circulatory system and the properties of blood.

HIS WORK…

- Demonstrated that blood flows in one direction in larger blood vessel's (unidirectional) and these vessels contain valves to prevent back flow.

- Also demonstrated that the heart pumps blood out in arteries, and blood returns in the veins ready to be ‘recycled’ by the body

- He predicted the existence of capillaries (no microscopes yet)

- Blood was seen flowing in capillaries in 1660, after his death.

HARVEY DISPROVED THEORIES BY GALEN

Galen was an ancient Greek philosopher.

Galen’s theories included the ‘vital spirit’ (for details see page 290). Harvey would never have been able to disprove Galen’s theories without evidence from systematic scientific investigations.

“Diligent observation is therefore requisite in every science, and the senses are frequently to be appealed to. We are, I say, to strive after personal experience, not to rely on the experience of others, without which no one can properly become a student of any branch of natural science” Harvey, W., 1651. On the Generation of Animals.

• Thick muscular, elastic walls

• Blood away from heart

• Blood at v. high pressures

• No valves (except aorta & pulmonary artery)

• Blood flow is rapid in pulses (pulsatile)

ARTERIES

ARTERIES AND PRESSURE…

Systolic pressure: highest pressure lumen widens, and the elastic stretches storing potential energy.

Diastolic pressure: at the end of the heart beat, pressure falls. Stretched elastic fibers, squeeze blood in the lumen.

Vasoconstriction: circular muscles in arteries contract, lumen narrows. Blood pressure increases. Controlled through hormones/nervous system – when might this happen?

Vasodilation: opposite of vasoconstriction.

• Blood back to heart

• Blood at lower pressure

• Thinner walls than arteries

• Can dilate and be flattened

• Contain valves

• Moderate speed blood flow

VEINS

VEINS AND VALVES

Prevent backflow

A valve is described as a three cup-shaped flap of tissue (pocket valve)

Ensure blood circulates in the correct direction.

ARTERY OR VEIN?

• Microscopic

• Form network throughout body

• Blood at moderate pressure but low speed

• V. thin, permeable walls (10µm), materials easily exchange

• No valves

CAPILLARIES

SKILL: IDENTIFYING BLOOD VESSELS

Table 1, page 294.

Use this table to make sure you are able to distinguish between and correctly identify the different blood vessels.

THE HEART

Double circulatory

system

Pulmonary

circulationBlood flowing to and from

the lungs

SYSTEMIC CIRCULATION

Blood flowing to and from all other organs in the body. Including, heart

muscles.

STRUCTURE OF THE HEART

Draw and label a diagram of the heart. Include the following labels:

AortaSemi lunar (aortic) valveLeft ventricleAtrioventricular (mitral) valveLeft atriumPulmonary veinVena cavaRight atriumAtrioventricular (tricuspid) valveRight ventricleSemi lunar (pulmonary) valvePulmonary arterySeptum

ATHEROSCLEROSIS

Control of heart rate

Cardiac muscle contracts and relaxes spontaneously – myogenic muscle contraction

Sinoatrial node (SA) in the right atrium. Natural pacemaker, ‘sends out’ electrical signals every 0.8 sec. Contracts both atria.

Atrioventricular node (AV) also in the right atrium. Receives signal, sends a second signal 0.1 sec. later. Contracts ventricles.

The medulla area in the brainstem, sends signals to the SA, via the cranial nerve to alter the heart rate depending on body conditions. E.g. exercise.