The Circulatory system

Objectives

1. To learn the role and structure of the heart

2. To understand the double circulatory system of humans

3. To learn the key features of the three main types of blood vessels.

4. To know what can go wrong and why.

Human circulatory system

Key features

1. It is double

2. The heart pumps blood around it

3. It carries materials around the body

4. Systemic system takes oxygenated blood round the body and returns deoxygenated blood to the heart

5. Pulmonary system takes deoxygenated blood to the lungs and returns oxygenated blood to the heart

Blood vessels

1. Chemicals exchange into and out of the blood in capillaries

2. Arteries lead away from the heart

3. Veins lead to the heart

What the blood carries

O

C

G

A

F

M

V

C

The Heart

The journey of blood

Blood flows along pulmonary artery to lungs

(Back flow prevented by tricuspid valve)

Right ventricle contracts and blood pushed into pulmonary artery

Right atrium contracts and blood pushed to right ventricle

Deoxygenated blood enters heart in right atrium from vena cava.

Journey of blood contd.

(Backflow prevented by bicuspid valve)

Left ventricle contracts and blood enters the aorta to travel to the rest of the body

Left atrium contracts blood flows to left ventricle

Blood enters left atrium

Oxygenated blood flows from lungs to heart in pulmonary vein

Gas exchange in the capillaries of the alveoli

Structures of the heart• Left and right side separated by

solid septum to prevent mixture of oxygenated and deoxygenated blood

• Left wall much thicker as it has to pump blood all round body. (right wall only pumps to lungs)

• In baby septum, is open because it gets oxygen from placenta not lungs. Septum closes at birth

• Failure to do so leads to hole in the heart or blue baby.-

Additional features

Valves held in place by tendons called Heartstrings

Semi lunar valves prevent blood from arteries flowing back into ventricles.

Heart muscle supplied with food and oxygen by cardiac artery

Blockage of cardiac artery leads to cell death and heart attacks.

Heart beat

This travels to the atrio-ventricular (AV) node which stimulates the contraction of the ventricle

Atrium contraction led by sino-atrial (SA) node – also called the cardiac pacemaker

Stimulated by nodes

Cardiac muscle is the only muscle that can initiate its own contractions

Rhythmic contraction of heart muscle

Heart beats

• Volume and speed can vary dependent upon need. Regulated by the nervous system.

• On average about 5.25L pumped per minute – approximately your total body volume.

An electrocardiogram showing the impulses of a normal heart beat.P shows the initiation of the contraction from the SA nodeR shows the initiation of ventricular contraction

Cardiac cycleTime Atria Ventricles

0.15 secs Systole Diastole

0.3 secs Diastole Systole

0.4 secs Diastole Diastole

Systole refers the period of contraction- High pressure

Diastole refers to the period when the chambers of the heart are relaxed – low pressure

Blood vessels

Arteries

Take blood from the heart

Oxygenated blood (pink)in systemic system

Deoxygenated blood (brown) in pulmonary system

Thick muscular walls with elastin layer

Narrow lumen

Have pulse

Blood at high pressure

Arterioles have less elastic tissue but proportionally more muscular tissues to allow for vaso-constriction.

This can control flow to skin surface and thus control heat loss/conservation

Veins

Valves prevent backflow.

Blood at low pressure

No pulse

Much larger lumen

Elastin layer in walls

Thinner muscle layer in walls

Deoxygenated in the systemic system and oxygenated in the pulmonary system

Take blood to the heart

Capillaries

1. Walls one cell thick

2. Cells in wall can pull apart making them leaky

3. Site of movement of chemicals into and out of the blood and cells.

4. Lumen diameter wide enough to allow one rbc to pass through

Our major vessels

These are not correct!

• Blood flows down one leg and up the other;

• Three kinds of blood vessels are arteries, vanes and caterpillars

What can go wrong

1. With time our arteries become blocked with plaques

2. These are a build up of fatty deposits.

3. They restrict blood flow raising blood pressure.

4. This is known as hardening of the arteries or atherosclerosis

5. Eventually lead to blockages.

Blockages (Thrombus)

Prevent oxygen and food reaching body cells.

Leads to cell death.

In heart muscle leads to heart attack

In brain leads to stroke

Elsewhere in body just referred to as an infarction.

Risk factors

Aging

High levels of LDL Low

density blood cholesterol

Fatty diets

Obesity

Smoking

Diabetes

Inactivity

Use of steroids

Possibly the pill

Genetic predisposition

Preventative measures

Vegetarian food

Onions, garlic and a little red wine

Fruit, vegetables and a high fibre diet

At least 20 minutes aerobic exercise regularly

Avoid transfats

Plenary questions

Which blood vessels lead from the heart?

Which blood vessels have strong muscular walls?

In which part of the system do the veins carry oxygenated blood?

The contraction of which part of the heart raises our blood pressure to its maximum?

Describe what happens during a heart attack.