CHAPTER 23Circulation

Overview:-Circulatory System-Cardiovascular System-Heart-Blood vessels-Circadian Cycle & ECG-Blood pressure-Blood components

Circulatory Systems & Functions

• Most animals have a circulatory system – It transports O2 and nutrients to cells

– It takes away CO2 and other wastes

• Every organism must exchange materials with its environment

– The purpose of the circulatory system is to facilitate this exchange

• Capillaries are microscopic blood vessels – They form an intricate network among the tissue

cells

The circulatory system associates intimately with all body tissues

• In jelly and flatworms, the gastrovascular cavity functions in both – digestion – internal transport

Several types of internal transport have evolved in animals

MECHANISMS OF INTERNAL TRANSPORT

• All but the simplest animals have circulatory systems with three main components

– A central pump– A vascular system– The circulating fluid

• Most animals have a separate circulatory system, either open or closed

• Open circulatory system

– The heart pumps blood into large open-ended vessels

– Blood circulates freely among cells

– Many invertebrates, such as mollusks, have open circulatory systems

• Closed circulatory system

– Blood is confined to vessels

– It is distinct from the interstitial fluid

– Earthworms, octopuses, and vertebrates have closed circulatory systems

• The closed circulatory system in vertebrates is called a cardiovascular system

– This system includes the heart and blood vessels

Cardiovascular System

• In the human cardiovascular system

THE HUMAN CARDIOVASCULAR SYSTEM

– The central pump is your heart– The vascular system is your blood vessels– The circulating fluid is your blood

• In humans and other vertebrates, the three components of the cardiovascular system are organized into a double circulation system

The Path of Blood

– There are two distinct circuits of blood flow

• The pulmonary circuit carries blood between the heart and the lungs

• The systemic circuit carries blood between the heart and the rest of the body

Heart- Structure & Function

• The human heart is a muscular organ about the size of a fist

How the Heart Works

– It is located under the breastbone– It has four chambers

• The mammalian heart has two thin-walled atria that pump blood into the ventricles– The thick-walled ventricles pump blood to all other

body organs

Blood vessels – Types & Functions

• If the heart is the body’s “pump,” then the “plumbing” is the system of arteries, veins, and capillaries

Blood Vessels

– Arteries carry blood away from the heart– Veins carry blood toward the heart– Capillaries allow for exchange between the

bloodstream and tissue cells

• All vessels are lined by a thin, smooth epithelium– Structural differences in the walls of the different kinds of

blood vessels correlate with their different functions

• Arteries and veins have smooth muscle and connective tissue– Valves in veins prevent the backflow of blood

• The walls of capillaries are thin and leaky

– As blood enters a capillary at the arterial end, blood pressure pushes fluid rich in oxygen, nutrients, and other substances into the interstitial fluid

– At the venous end of the capillary, CO2 and other wastes diffuse from tissue cells and into the capillary bloodstream

• The transfer of materials between the blood and interstitial fluid can occur by

– leakage through clefts in the capillary walls– diffusion through the wall– blood pressure– osmotic pressure

• After chemicals are exchanged between the blood and body cells, blood returns to the heart via the veins

Blood Return Through Veins

– By the time blood exits the capillaries and enters the veins, the pressure originating from the heart has dropped to near zero

Circadian Cycle & ECG

• The heart relaxes and contracts regularlyThe Cardiac Cycle

– Diastole is the relaxation phase of the heart cycle – Systole is the contraction phase

• Heart valves prevent backflow

• Cardiac output – The amount of blood pumped into the aorta by the

left ventricle per minute

• The pacemaker, or SA (sinoatrial) node, sets the tempo of the heartbeat

The Pacemaker and the Control of Heart Rate

• The pacemaker is composed of specialized muscle tissue in the wall of the right atrium

• The impulses sent by the pacemaker produce electrical currents that can be detected by electrodes placed on the skin– These are recorded in an electrocardiogram (ECG or

EKG)– Control centers in the brain adjust heart rate to body

needs

• In certain kinds of heart disease, the heart’s electrical control fails to maintain a normal rhythm– The remedy is an artificial pacemaker

• A heart attack is damage that occurs when a coronary feeding the heart is blocked

Connection: What is a heart attack?

• How can you avoid becoming a heart disease victim?

– Don’t smoke– Exercise– Eat a heart-healthy diet

• Every year, smoking kills about 430,000 Americans– Many smokers die from lung cancer– Smoking can also cause emphysema

Blood pressure

• The force that blood exerts against the walls of your blood vessels is called blood pressure

Blood Flow Through Arteries

– Blood pressure is the main force driving the blood from the heart to the capillary beds

– A pulse is the rhythmic stretching of the arteries caused by the pressure of blood forced into the arteries during systole

• Blood pressure depends on– cardiac output– resistance of vessels

• Normal blood pressure for adults is below 120 systolic and below 80 diastolic

• High blood pressure is persistent systolic blood pressure higher than 140 and/or diastolic blood pressure higher than 90

– It is also called hypertension

• Pressure is highest in the arteries– It drops to

zero by the time the blood reaches the veins

• Three factors keep blood moving back to the heart– muscle contractions– breathing– one-way valves

• Blood pressure is measured as systolic and diastolic pressures

Connection: Measuring blood pressure can reveal cardiovascular problems

• Muscular constriction of arterioles and precapillary sphincters controls the flow through capillaries

Smooth muscle controls the distribution of blood

Blood

• The circulatory system of an adult human has about 5 L (11 pints) of blood

Blood

– Just over half of this volume is plasma– Suspended within the plasma are several types of

cellular elements

Red blood cells transport oxygen

• Red blood cells contain hemoglobin – Hemoglobin enables the

transport of O2

• Red blood cells are by far the most numerous type of blood cell– They are also called

erythrocytes

• Each red blood cell contains large amounts of the protein hemoglobin

– Hemoglobin contains iron and transports oxygen throughout the body

– Anemia is an abnormally low amount of hemoglobin or a low amount of red blood cells

White blood cells help defend the body

• White blood cells function both inside and outside the circulatory system – They fight infections and cancer– They are also called leukocytes– There are about 1,000 times fewer white blood cells than red

blood cells

Blood clots plug leaks when blood vessels are injured

• When a blood vessel is damaged, platelets respond– They help trigger the

formation of an insoluble fibrin clot that plugs the leak

• Blood contains two components that aid in clotting– Platelets (thrombocytes) are bits of cytoplasm

pinched off from larger cells in the bone marrow– Fibrinogen is a membrane-wrapped protein found in

plasma

Connection: Stem cells offer a potential cure for leukemia and other blood cell diseases

• All blood cells develop from stem cells in bone marrow– Such cells may prove

valuable for treating certain blood disorders

• New blood cells are continually formed from unspecialized stem cells found in red bone marrow

Stem Cells and the Treatment of Leukemia

– Stem cells differentiate into red and white blood cells and the cells that produce platelets

– Bone marrow stem cells can be isolated and used to treat leukemia

• Leukemia is cancer of the leukocytes

– A person with leukemia has an abnormally high number of leukocytes

– Leukemia is usually fatal unless treated– Not all cases respond to treatment