The Circulatory System

The Circulatory System• The function of a circulatory system is to

carry blood or hemolymph into close contact with every cell in the body.

• The most sophisticated circulatory systems consist of:– one or more pumps called hearts– arteries (tough, thick-walled tubes)

that carry blood away from the heart under high pressure;

– small vessels called capillaries whose walls are just one cell thick, allows the exchange of gases and other molecules with tissues in networks called capillary beds; and

– vessels called veins that return blood to the heart under low pressure

Functions of the Circulatory System

• Transport oxygen to cells

• Transport nutrients from the digestive system to body cells

• Transport hormones to body cells

• Transport waste from body cells to excretory organs

• Distribute body heat

•Blood : connective tissue that consists of cells in a watery extracellular matrix called plasma •Remainder of the blood is made up of formed elements: platelets, red blood cells, and several types of white blood cells:•Platelets : Cell fragments that minimize blood loss from ruptured blood vessels by releasing material that assists in the formation of clots •White blood cells: which are part of the immune system fight infections

How Are Oxygen and Carbon Dioxide Transported in Blood?

RBCs

• Red blood cells (RBCs):– transport oxygen from the lungs

to tissues throughout the body– critical role in transporting

carbon dioxide from tissues to lungs •In humans, red blood cells

make up 99.9% of the formed elements.

– contain an oxygen-carrying molecule called hemoglobin

CirculationPulmonary Circuit

Systemic Circuit

How Does the Heart Work?

• In animals with closed circulatory systems, the heart contains at least two chambers.

• the atrium receives blood returning from

circulation• the ventricle generates force to propel

the blood through the system.

• Atria are separated from ventricles by atrioventricular valves.

• The number of distinct heart chambers has increased as vertebrates diversified.

How Does the Heart Work?

• Vertebrates evolved two separate pumping circuits: – The pulmonary circulation

is a lower-pressure circuit to the lungs.

– The systemic circulation is a higher-pressure circuit to the rest of the body.

Components of the Human Circulatory

System

The HeartBlood Vessels

BloodLymphatic Vessels

Lymph

Types of Blood Vessels• Capillaries:

– smallest vessels – the site where gases, nutrients, and

wastes are exchanged between the blood and other tissues

• The smallest veins are venules; – carry blood back to the heart after it

passes through the capillaries – veins have much thinner walls and

much larger interior diameters than arteries

Location of Heart

Pericardial Cavity

Layers of Cardiac Tissue

Visceral pericardium • Outer protective layer

composed of a serous membrane

• Includes blood capillaries, lymph capillaries, and nerve fibers.

Myocardium • Relatively thick. • Consists largely of cardiac

muscle tissue responsible for forcing blood out of the heart chambers.

• Muscle fibers are arranged in planes, separated by connective tissues that are richly supplied with blood capillaries, and nerve fibers.

• Endocardium • Consists of epithelial and

connective tissue that contains many elastic and collagenous fibers.

• Connective tissue also contains blood vessels and some specialized cardiac muscle fibers called Purkinje fibers.

• Lines all of the heart chambers and covers heart valves.

Heart Anatomy

The Human Heart• The human circulatory system returns

oxygen-depleted blood from the body to the right atrium of the heart through two large veins– the inferior and superior venae cavae.

• When the right atrium contracts:– deoxygenated blood is sent to the right

ventricle – it contracts and sends blood out to the

lungs via the pulmonary artery • One-way valves ensure that blood follows

only this path. After blood has circulated through the capillary beds in the lung’s alveoli:

• it becomes oxygenated – returns to the heart through the

pulmonary veins

The Human Heart

• The oxygenated blood enters the left atrium:– it contracts and pushes the blood

into the left ventricle • The contraction of the left ventricle

sends oxygenated blood at high pressure out the aorta and into:– the arteries – capillaries – veins

•forms the systemic circulation

Heart Anatomy

Heart Anatomy

VALVES

bicuspid valve

aortic

semilunar valve

tricuspid valve

pulmonary

semilunar valve

Heart valvesHeart valves

The Cardiac Cycle

• The contraction phase of the atria and the ventricles:– called systole

• is coordinated with their relaxation phase – called diastole

• A cardiac cycle:– consists of one complete

systole and one complete diastole

• systolic blood pressure :– blood pressure measured in

the systemic arterial circulation at the peak of ventricular ejection into the aorta

• diastolic blood pressure:– blood pressure measured

just prior to ventricular ejection

Contraction cycle of the heart

Contraction Contraction Cycle of the Cycle of the

HeartHeart

Contraction Cycle of the Heart

Excitation of the Heart

Depolarization of the atria

Excitation of the Heart

Depolarization of the ventricles

Excitation of the Heart

Excitation of the Heart

Circulatory System -Gross and Cool Facts!

•The body of an adult contains over 60,000 miles of blood vessels! •An adult's heart pumps nearly 4000 gallons of blood each day! •Your heart beats some 30 million times a year! •The average three-year-old has two pints of blood in their body; the average adult at least five times more! •A "heartbeat" is really the sound of the valves in the heart closing as they push blood through its chambers.