Cardiovascular System Chapter 11 Cardiovascular System

The major function of the cardiovascular system is transportation. The blood is the transport vehicle. It carries oxygen, nutrients, cell wastes, hormones, and many other substances vital for body homeostasis to and from cells.

The force to move the blood throughout the body is provided by the beating heart.

The Cardiovascular System consists of: Blood (transport vehicle) Heart (pump) Blood vessels (network of tubes)

Location and Size of the Heart The heart is the size of a fist The heart is located between the two lungs A double sac called the pericardium surrounds the heart.

Lubricating fluid is found in between the two layers of the sac Lubricating fluid is found in between the two layers of the sac. This fluid allows the heart to beat easily in a frictionless environment.

The walls of the heart are made of 3 layers: Epicardium – outer layer Myocardium – layer that contracts Endocardium – lines the chambers and goes into the blood vessels

The heart has four chambers or cavities. The two atria are located at the superior or top of the heart and the two ventricles are located at the inferior or bottom of the heart.

Blood flow through the heart

Pulmonary Circulation Right side: pumps to lungs oxygen poor on its way to the lungs – picks up oxygen – becomes oxygen rich

The Steps: Oxygen poor blood enter the superior and inferior vena cava Blood goes into the right atrium then right ventricle Blood is them pumped to the pulmonary trunk which branches into pulmonary arteries

Blood goes to the lungs and picks up oxygen Blood leaves the lungs in the pulmonary veins and goes to the left atrium

Systemic Circulation Left side: pumps blood with oxygen to the body cells and back to the heart

The Steps: Blood enters the left atrium then goes to the left ventricle Blood is then pumped to the body cells through the aorta

3. Blood travels from the aorta to arteries, smaller arteries, capillaries (losses oxygen) then to the veins and then to the superior and inferior vena cava

Cardiac Circulation The blood in the heart does not nourish the myocardium. The blood supply that nourishes the heart is provided by the right and left coronary arteries which branch from the aorta.

Physiology of the Heart 6 quarts pushed through 1000X Heart pumps 6000 quarts a day Cardiac muscle cells can and do contract spontaneously and independently. These contractions occur in a regular and continuous way.

The muscles in the different parts of the heart have different rhythms. The heart has a unifying control system that coordinates its movement.

The Two Controlling Systems 1. The autonomic nervous system (automatic) acts like: the brakes and accelerators to increase or decrease heart rate

Intrinsic conduction system or nodal system - causes the heart to depolarize in one direction (from atria to ventricle) - enforces a contraction rate of 75 beats/min

SA node starts each heartbeat and is known as the pacemaker.

Cardiac Cycle and Heart Sounds

In a healthy heart the atria contract simultaneously Systole – heart contraction Diastole – heart relaxation

The Cardiac Cycle refers to: The events of one complete heart beat during which both atria and ventricles contract and then relax.

The average heart beats 75 beats/min. The cardiac cycle lasts for .8 sec.

Heart Sounds When using a stethoscope, you can hear 2 distinct sounds during each cardiac cycle. These heart sounds are often described as lub and dub.

The first heart sound is made when: the AV valve closes - Lub The second heart sound is made when: the semilunar valves close at the end of systole - Dub

The average heart rate is faster in females than males. Females – 72-80 beats per minute Males – 64-72 bpm

Cardiovascular System: Blood Vessels

Blood circulates inside the blood vessels which is a closed transport system, the so called vascular system.

The Path of Blood: Arteries carry blood away from the heart (oxygen) Veins carry blood to the heart (no oxygen) From the heart blood is propelled into: arteries smaller arteries  arterioles capillary beds venules  veins  great veins

Microscopic Anatomy of Blood Vessels

The walls of blood vessels have 3 coats or tunics Tunica intima decreases friction Tunica media changes diameter of blood vessels Tunica externa  function: support and protect blood vessels

The walls of arteries are usually thicker than the walls of veins Artery walls must be strong and stretchy enough to take these continuous changes in pressure

Veins have thinner walls because they do not have to take the pressure However, they are modified: to ensure the amount returning to the heart equals what is being pumped

Modifications Valves to prevent backflow Muscles milk veins and move blood to the heart Breathing also helps

Location of Arteries and Veins in the body

Arteries are generally located in deep, well protected body areas. Many veins are more superficial and some are easily seen and palpated on the body surface. Most deep veins follow the course of the major arteries.

Hepatic Portal Vein Delivers blood to the liver from the digestive organs

Fetal Circulation Since the lungs and digestive system are not yet functioning in a fetus, all nutrient, excretory and gas exchange occur through the placenta. Nutrients and oxygen move from the mother’s blood into the fetal blood and fetal wastes move in the opposite direction.

Physiology of Circulation A good indication of the efficiency of a person’s circulatory system can be obtained by taking arterial pulse and blood pressure. Vital Signs: arterial pulse, blood pressure, respiratory rate, body temperature

Arterial Pulse Pulse: alternating expansion and recoiling of an artery that occurs with each ventricular beat Average pulse is a person at rest: 70-76 BPM

Pressure Points Areas where you can feel your pulse These points can also be compressed to stop blood flow into distal tissue during hemorrhage

Blood Pressure Pressure the blood exerts against the inner wall of the blood vessels and it sis the force that keeps the blood circulation

Blood Pressure Gradient Blood flows along a pressure gradient (from high to low) If a vein is cut the blood flows evenly from the wound If an artery is cut the blood comes out in rapid spurts

Measuring Blood Pressure Because the heart alternately contracts and relaxes the off-and-on flow of blood into the arteries causes the blood pressure to rise and fall during each beat.

There are two arterial blood pressure measurements that are usually made: Systolic Pressure – pressure in the arteries at the peak of ventricular contraction (first number) Diastolic Pressure – pressure when the ventricles are relaxing (second number)

Blood pressure is reported in mmHg Millimeters of mercury Average 120/80 mmHg

Effects of Various Factors on BP

Peripheral Resistance Amount of friction encountered by the blood as it flows through blood vessels

1. Nervous System Can cause vasoconstriction (narrowing of blood vessels – pressure increases

2. Kidneys Role in blood pressure is alternating blood volume

3. Temperature Cold – vasoconstricting effect Heat vasodilating effect

4. Chemicals Epinephrine – increases heart rate and blood pressure Nicotine – increase blood pressure by vasoconstriction Alcohol and Histamine – vasodilation – decreases blood pressure

5. Diet Hypertension (high blood pressure) Prevented by a diet low in salt, saturated fat and cholesterol

Variations in Blood Pressure Normal adults systolic blood pressure varies between 110-140 mmHg Normal adults diastolic blood pressure varies between 75-80 mmHg Hypotension – low blood pressure Hypertension – high blood pressure

The End