The Human Circulatory System

Introduction

Humans and other vertebrates have a closed circulatory system:

– This means that circulating blood is pumped through a system of vessels

– This system consists of the heart (pump), series of blood vessels and the blood that flows through them.

The Truth About Your Heart

The Heart

Located near the center of your chest

Hollow structure

Composed almost entirely of muscle

About the size of your clenched fist

The Heart

Enclosed in a protective sac called the pericardium

The Heart

In the walls of the heart, two layers of tissue form a sandwich around a thick layer of muscle called the myocardium.

Contractions of the myocardium pump blood through the circulatory system.

The Heart

The heart contracts about 72 times per minute

Pumps about 70mL of blood with each contraction.

The Heart

The right and left sides of the heart are separated by a septum, or wall.

The septum prevents the mixing of oxygen rich and oxygen poor blood.

The Heart

On each side of the septum are two chambers.

The upper chamber (receives blood) is the atrium.

The lower chamber (pumps blood out of heart) is the ventricle.

The Heart

The heart has a total of 4 chambers:

2 atriums 2 ventricles

Pathway of Blood

Deoxygenated blood passes from the right atrium into the right ventricle and then goes to the lungs.

From the lungs, blood moves back toward the heart into the left atrium to the left ventricle and then passes into the aorta to go to the rest of the body

Valves

As the heart contracts, blood flows into the ventricles and then out through the ventricles.

Flaps of connective tissue, called valves, are located between the atria and ventricles.

Blood moving keeps the valves open.

When the ventricles contract, the valves close which prevent blood from flowing back into the atria.

Valves

There are also valves that stop blood from re-entering the ventricles after the blood has left.

This system of valves keeps blood moving in one direction which increases the pumping efficiency of the heart.

Heart Beat

Heart muscles are composed of individual fibers

Each atrium and ventricle contracts as a unit.

Each contraction begins with a group of cardiac muscle cells in the right atrium known as the sinoatrial node (SA node)

Heart Beat

Because the SA node paces the heart it is known as the pacemaker.

The impulse spreads from the pacemaker to the rest of the atria.

From the atria, a signal is sent to the atrioventricular node and then to a bundle of fibers in the ventricle.

When the ventricle contracts, blood flows out.

Blood Vessels

As blood moves through the circulatory system it moves through 3 types of blood vessels:

Arteries Capillaries Veins

Arteries

Large vessels

Carry blood from heart to tissues of body

Carry oxygen rich blood, with the exception of pulmonary arteries.

Thick walls-need to withstand pressure produced when heart pushes blood into them.

Capillaries

Smallest blood vessels

Walls are only one cell thick and very narrow.

Important for bringing nutrients and oxygen to tissues and absorbing CO2 and other waste products.

Veins

Once blood has passed through the capillary systems it must be returned to the heart.

Done by veins

Walls contains connective tissue and smooth muscle.

Largest veins contain one way valves that keep blood flowing toward heart.

Many found near skeletal muscles. When muscles contract, blood is forced through veins.

Blood Pressure

The heart produces pressure

The force of blood on the wall of the arteries is known as blood pressure.

Blood pressure decreases as the heart relaxes, but the rest of the circulatory system is still under pressure.

Blood Pressure

When blood pressure is taken, the cuff is wrapped around the upper portion of the arm and pumped with air until blood flow in the artery is blocked.

As the pressure in the cuff is relaxed, 2 numbers are recorded.

– Systolic pressure- the first number taken, is the force felt in the arteries when the ventricles contract.

– Diastolic pressure- the second number taken, is the force of the blood on the arteries when the ventricles relax.

Disorders of Circulatory System

Atherosclerosis– Fatty deposits (plaque) in walls of arteries

– Deposits can obstruct flow of blood which can raise blood pressure

– Increases risk of blood clots

– If clot breaks free it can obstruct blood flow to tissues.

Disorders of Circulatory System

Heart Attack

– Due to atherosclerosis, coronary arteries may become blocked (blood can’t get to heart muscle)

– Heart muscle begins to die due to lack of O2

Disorders of Circulatory System

Stroke– Blood clot may break free and block a vessel leading to the

brain.

– Brain cells are starved of oxygen and nutrients

– Loss of function may occur

– Can cause paralysis, loss of ability to speak or death.

Blood

Composed of plasma and blood cells Types of Cells are:

– Red Blood Cells– White Blood Cells– Platelets

Blood

Plasma– Straw colored

– 90% water

– 10% dissolved gases, salts, nutrients, enzymes, hormones, wastes, and proteins.

Blood

Plasma proteins– 3 Types: Albumins, globulins and fibrinogen.

– Albumins and Globulins- transport substances such as fatty acids, hormones and vitamins.

– Fibrinogen- Responsible for blood’s ability to clot

Blood

Red Blood Cells– Most numerous type– Transport oxygen– Get color from

hemoglobin– Disk shaped– Made in red bone

marrow– Circulate for 120 days

Blood

White Blood Cells– Guard against infection,

fight parasites, and attack bacteria

– Number of WBC’s increases when body is fighting

– Lymphocytes produce antibodies which fight pathogens and remember them

Blood

Platelets– Aid the body in clotting

– Small fragments

– Stick to edges of broken blood cell and secrete clotting factor to help form clot.

Blood Clotting Problems

Hemophelia– Genetic disorder that disrupts clotting

– People must be very careful to avoid injury

– Can be treated by injecting extracts that contain the missing clotting factor.