The Human Circulatory System

The circulatory system is the system that transports materials around the body to and from the cells.

Question? Why do humans need a circulatory system whereas bacteria and simple organisms do not?

Answer:

Humans have a closed circulatory system: This means that the blood is always contained in tubes and vessels.

Parts of the Circulatory System

The human circulatory system is composed of the following:

1. Blood vessels2. Heart3. Blood

Blood Vessels

Humans have three types of blood vessels. They are:

a. Arteries Structure:

o Thick, elastico Smallest arteries are called arterioleso Do not contain valves

Function: Transport blood AWAY from the heart to the organs and tissues of the body.

b. Veins Structure:

o Thin and slightly elastico Smallest veins are called venuleso Contain valves – to help blood flow back to the heart against the force of

gravity. Lower pressure than arteries.

Function: To RETURN blood from the body tissues to the heart.

c. Capillaries Structure:

o Microscopic blood vessels that connect arterioles and venuleso Thin walled and narrowo Blood cells pass through them in single file

Function: Allows material and gas and gas exchange between the body cells and the blood.

The Heart

Structure: o A four chambered muscular organ located in the chest cavity of a human. o Made of cardiac muscle. o It is covered by a pericardium that protects it.

Pericardium: A tough membrane that surrounds the heart.

Function: Pump blood around the body supplying the cells with nutrients and removing wastes (CO2) from the cells.

Functions of Heart Structures Term DefinitionInferior/Superior Vena Cava Returns deoxygenated blood to the right atrium from the

body.

Right Atrium Thin walled chamber of the heart that receives deoxygenated blood from the body.

Tricuspid valve Controls the flow of blood entering the right ventricle from the right atrium.

Right Ventricle Muscular chamber that pumps blood TO the lungs.

Semilunar Valves Valves that control the flow of blood out of the heart.

Pulmonary Arteries Arteries that carry blood TO the lungs.

Pulmonary Veins Veins that bring blood to the heart from the lungs.

Left Atrium Thin walled chamber that receives oxygenated blood from the lungs.

Bicuspid Valve A valve that controls the flow of blood from the left atrium to the left ventricle.

Left Ventricle Thick walled chamber that pumps blood out of the heart and to the body.

Aorta Large artery that carries blood away from the heart and to all parts of the body.

Septum A wall of muscle that separates the left side of the heart from the right side. This prevents the mixing of oxygenated and deoxygenated blood.

Chordae Tendonae(heart strings)

Control the opening and closing of the Tricuspid andBicuspid (Mitral) valves.

Blood Flow through the Heart

Deoxygenated blood from the body enters the right atrium via the superior and inferior vena cava. Here the blood is passed through the tricuspid to the right ventricle. The right ventricle contracts and forces blood up through the semilunar valves and out through the left and right pulmonary arteries. This brings blood to the lungs to be oxygenated. Oxygenated blood from the lungs returns to the heart via the left and right pulmonary veins to the left atrium. The blood is passed to the left ventricle through the bicuspid valve. The left ventricle contracts and pushes blood through the semilunar valves and out through the aorta to the body.

THE HEARTBEAT CYCLE

A single beat of the heart consists of contractions of the atria followed by contractions on the ventricles and then a period of relaxation of all four chambers of the heart. Contractions are called systoles, and relaxations are called diastoles.

Sequence of Events:

The “LubDub” Sound of the Heartbeat

The “LubDub” sound of the heartbeat is caused by the closing of the heart’s valves. Lub Sound - caused by the closing of the A-V valves (tricuspid, bicuspid). Dub Sound - caused by the closing of the semilunar valves.

CONTROL OF THE HEARTBEAT

The heart is caused to beat regularly by a structure called the sinoatrial node (S - A node) or the pacemaker. How it happens An electrical impulse from the brain is received by the S-A node (pacemaker) in the right atrium. The impulse spreads quickly over both atria causing atria muscles to contract. The impulse reaches the A-V node (atrioventricular node) in the right ventricle. The impulse is transmitted by the AV node down a nerve bundle (bundle of His). The impulse branches to both ventricles causing contraction from the bottom up.

The pacemaker controls the heartbeat for a human from the time they are born until they die or the pacemaker gives out. Q. What happens if the pacemaker gives out?

A person whose pacemaker gives out can get an artificial one inserted into their chest.

CONTROL OF THE HEART RATE

The heart rate (speed) at which the heart beats is controlled by two nerves. Cardioaccelerator nerve in the medulla oblongata: Nerve in the brain that causes the heart to speed up when needed. Vagus nerve: Nerve in the brain that causes the heart to slow down when needed. The medulla sends a message to the SA node to cause an impulse to be sent to the AV node causing the heart to contract more or less in an attempt to set the heart rate.

BLOOD PRESSURE

Blood Pressure: A measure of the pressure blood exerts on the walls of blood vessels. Q. How is blood pressure measured?

It measures the pressure in an artery at its highest point (systolic pressure) and the lowest point while the heart is resting (diastolic pressure). A simple fraction is calculated using the following formula:

Blood Pressure =

For example: A person with a pressure 120/80 means that the person has a pressure of 120 while the heart is contracting and 80 when the heart is relaxing. P.S. Normal blood pressure is different for each person but is usually around 120/80. (high is over 140/90)

Divisions of Circulation

There are two types of circulation that happen in the human organism.

1. Pulmonary Circulation 2. Systemic circulation

1. PULMONARY CIRCULATION

This is circulation of blood from the heart and to the lungs and vice versa. This type of circulation adds oxygen and removes carbon dioxide from the blood. 2. SYSTEMIC CIRCULATION

This is circulation of blood between the heart and the body. This type of circulation brings blood to the cells and from the cells.

Systemic circulation has three subdivisions. They are:

A. Coronary Circulation B. Hepatic-portal circulation C. Renal circulation

A. Coronary circulation is circulation that supplies blood and nutrients directly to the heart muscle. B. Hepatic - portal circulation is circulation that carries nutrients and blood from the digestive system to the liver to maintain glucose levels in the body. C. Renal Circulation is circulation that carries blood to and from the kidneys so that nitrogenous wastes may be removed from the blood and excreted by the kidneys.

Assignment:

Summary on heart disease in North America (leading causes, preventative measures, medical interventions – treatments & surgical options, ect..)

In your answer include, what is a heart attack.

Some helpful links (don’t feel restricted to these)

https://www.heartandstroke.ca/heart

https://www.heart.org/en/about-us/heart-and-stroke-association-statistics

http://www.cdc.gov/heartdisease/facts.htm

http://www.nhlbi.nih.gov/health/health-topics/topics/heartattack

Gross Anatomy of the Heart

Coronary Artery – Supplies blood to nourish the heart muscles.

Coronary Sulcus – encircles the heart like a crown (corona = crown). The atria are found above and the ventricles are found below this blood vessel.

What happens when there is a blockage within the coronary artery?

Anterior Interventricular Sulcus – marks the front (ventral) position of the heart. This vessel follows the septum that separates the right and left ventricles.

Apex – the pointed end of the heart. Only the left ventricle forms the heart apex.

Front = VentralBack = Dorsal

Pericardium – the double-walled sac around the heart. Function: - Protects and anchors the heart- Prevents overfilling of the heart with blood- Allows for the heart to work in a relatively friction-free environment

Myocardium – cardiac muscle layer forming the bulk of the heart

Why do you think there is a thicker layer of myocardium in the ventricles compared to the atria?

In the left ventricle compared to the right ventricle?

Electrocardiogram (EKG or ECG)

If you’ve ever seen the heart test called an EKG (electrocardiogram), you’ve seen a graphical picture of the electrical activity of your heart.

P wave represents the depolarization of the atria atrial contraction PR represents the time the electrical impulse takes to go from the SA node to the ventricles QRS complex represents the depolarization of the ventricles ventricular contraction ST segment represents the time period between depolarization and repolarization of the

ventricles. T wave corresponds to the period when the lower heart chambers are relaxing and preparing

for their next muscle contraction (repolarizing)

Electrical signals within the heart can be measured and recorded by a machine called an electrocardiograph. This recording is then shown as an electrocardiogram. An EKG is a technological device that monitors the heart’s electrical activity.

The EKG is an important tool used in diagnosing abnormal heart rhythms or patterns. Each peak or valley in the EKG tracing represents a particular electrical activity that takes place during a heartbeat.

What is an arrhythmia?

An arrhythmia (also referred to as dysrhythmia) is an abnormal rhythm of the heart, which can cause the heart to pump less effectively.

Arrhythmias can cause problems with contractions of the heart chambers by:

not allowing the chambers to fill with an adequate amount of blood because the electrical signal is causing the heart to pump too fast. Termed Tachycardia

not allowing a sufficient amount of blood to be pumped out to the body because the electrical signal is causing the heart to pump too slowly or too irregularly. Termed Brachycardia

In any of these situations, the body may not receive enough blood because the heart cannot pump out an adequate amount with each beat as a result of the arrhythmia's effects on the heart rate.

Fibrillation:

Is the condition that results when the heart goes into arrest and is in a state of rapid quivering

In this situation, the pacemaker cells are sending electrical signals faster than the heart can respond.

Therefore the heart can only be restored to normal beating by means of defibrillation.

Defibrillator:

Is the delivery of an external current into the heart muscle. This “shock” stops the uncontrolled electrical activity and allows the heart’s normal pacer to take ove