CHAPTER 23 Circulation 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 O 2 and nutrients to cells –It takes away CO 2 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, CO 2 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 regularly The 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 O 2 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