SBI3U - The Circulatory System

Introductionand

Human Circulatory

System

Fun Facts!

• No cell in your body is further than two cells away from a blood vessel.

• If you laid all of your arteries, veins and capillaries end-to-end, they would circle the Earth twice.

• Your heart is size of a fist, weighs approximately 300g and beats an average of 100,000 times a day.

• During the average lifetime, your heart pumps enough blood to fill two large ocean tankers!

Introduction

• The circulatory (or cardiovascular) system has several functions:

1. Transportation of O2, CO2, wastes, nutrients, and hormones

2. Maintain body temperature

3. Maintain body fluid levels

Parts of the Mammalian Circulatory System

1. The Heart: a muscular organ that continuously pumps blood through the body, generating blood flow.

2. The Blood Vessels: a system of hollow tubes through which the blood moves.

3. The Blood: The fluid that transports nutrients, O2, CO2 and many other materials throughout the body.

Human Heart Anatomy• Located slightly to the left of the middle of the chest. • The walls of the heart are made of a unique type of

muscle called cardiac muscle.

Cardiac muscle cells are arranged in a network that allows the heart to contract and relax rhythmically and involuntarily without becoming fatigued.

Human Heart Anatomy

• Has four chambers– Atria: the two top

chambers that fill with blood returning from the body or the lungs (singular atrium).

– Ventricles: two bottom chambers that receive blood from the atria and pump it out to the body or the lungs.

Blood Flow in the Heart

• The vena cavae bring oxygen-poor blood from the body to the right atrium.

• The oxygen-poor blood flows from the right atrium into the right ventricle.

• The right ventricle pumps the oxygen-poor blood to the lungs through the pulmonary arteries.

Blood Flow in the Heart• The pulmonary veins bring

oxygen-rich blood from the lungs back to the heart through the left atrium.

• Oxygen-rich blood flows from the left atrium to the left ventricle.

• The left ventricle pumps the oxygen-rich blood to the body through the aorta.

Heartbeat “lub-DUB”• Valves prevent the blood

from flowing backwards. • The “lub” sound is caused

by the closing of the atrioventricular (AV) valves as blood is pumped from the atria to the ventricles.

• The “DUB” sound is caused by semilunar valves, as blood is pumped from the ventricles into the arteries

THE END

THE HEART

THE VALVES

The tricuspid valve separates the right atrium from the right ventricle.

The mitral (bicuspid) valve separates the left atrium from the left ventricle.

The pulmonary (semi-lunar) valve separates the right ventricle from the pulmonary artery.

The aortic (semi-lunar) valve separates the left ventricle from the aorta.

THE VALVES

Cardiac Cycle Control

The Cardiac Cycle

• A bundle of specialized muscle tissue, called the sinoatrial (SA) node, stimulates the muscle cells to contract and relax rhythmically.

• Also referred to as the pacemaker, because it sets the pace for cardiac activity

• Located in the wall of the right atrium.

The Cardiac Cycle

• The SA node generates an electrical signal that spreads over the two atria and makes them contract simultaneously.

• As the atria contract, the signal reaches another node, called the atrioventricular (AV) node.

The Cardiac Cycle

• The AV node transmits the electrical signal through a bundle of specialized fibers, called purkinje fibres, that run down the septum and up around the ventricles

• This initiates the almost simultaneous contraction of all cells of the right and left ventricles.

Blood Vessels: Arteries, Veins and Capillaries

Cycles• Blood vessels are organized into

three primary cycles1. Cardiac Circulation: route taken by

blood within the heart.2. Pulmonary Circulation: pathway of

the blood from the heart to the lungs and back.

3. Systemic Circulation: pathway of blood from the heart to the rest of the body, includes all blood vessels other than those associated with the lungs.

Arteries• Carry oxygen-rich* blood AWAY

from the heart. • Able to stretch and recoil • Thick-walled, with three layers:

• Outer: connective tissue (tissue between organs)

• Middle: muscle and elastic connective tissue

• Inner: connective tissue

*Exception: Pulmonary Arteries carry oxygen-poor blood

Arterioles• Smaller arteries• Blood flows from

large arteries into arterioles

• Middle layer: elastic fibers and smooth muscle

Capillaries

• Very narrow blood vessels. • Blood flows into capillaries from

arterioles. • Regulated by sphincters • Sphincters only open when new

blood needed. – e.g. open in brain all the

time, not always in muscle

Capillaries • Single layer of cells, no muscle

– Easily ruptured, causes bruising• Site of GAS and FLUID EXCHANGE between blood and

body cells (lose O2, pick up CO2)

Gas Exchange

Venules

• Capillaries merge to form small veins which carry the oxygen-poor blood

• Have a thin muscle layer• Venules merge to form veins

Veins• Return oxygen-poor* blood TO the heart• Lack the ability to contract. • Low blood pressure.

– Far away from heart.– Loss of fluids to tissues in the capillaries.

• Veins can prevent blood from flowing backward:– One-way (uni-directional) valves– Skeletal muscle of the surrounding area

helps push blood through veins

*Exception: Pulmonary Veins carry oxygen-rich blood

Arteries vs. Veins

Blood

Blood Introduction

• Blood is a collection of cells that have been specialized to perform a set of tasks within an organism.

• For this reason, doctors and scientists consider blood a tissue and not a fluid.

Blood consists of two distinct elements:

1. Plasma: the fluid portion of the blood (55% of blood)

2. Cells: the solid portion of blood (45% of blood)

Plasma• Fluid portion of the

blood that carries blood cells.

• Made up of 90% water, the other 10% made up of blood proteins, glucose, vitamins, minerals, dissolved gases, waste products of cell metabolism.

• Also transports CO2.

Red Blood Cells• Erythrocytes• Make up 44% of blood.• Specialized for transport of O2.

Without them plasma could only carry 2% of the oxygen that normally travels through our bodies.

• Shape: biconcave disk to increase surface area.

• No nucleus, lifespan of 120 days, constantly reproduced.

• Males ~ 5.5 billion RBC/mL blood; Females ~ 4.5 billion.

Red Blood Cells

• Packed with 280 million molecules of hemoglobin, an iron-containing molecule that binds with oxygen.

• Hemoglobin has 4 globular protein molecules (globin) and 1 iron molecule (protein)– High affinity for oxygen– Hemoglobin + oxygen =

oxy-hemoglobin

• RBC lose their nucleus when they enter the blood stream in order to carry more hemoglobin.

White Blood Cells• Make up about 1% of blood's volume. • Produced in bone marrow.• White blood cells contain nuclei and appear colourless.• They play many roles in fighting off infection and

protecting the body from pathogens.– The number of WBC may

increase by double when you are fighting off an infection.

– Pus: fragments of remaining protein of the WBC and the invader.

Leukocytes and Lymphocytes• Two of the most important disease-fighting white blood

cells are leukocytes and lymphocytes.• Leukocytes (macrophages) engulf and digest pathogens.

– Innate immune response (generalized response of the body to infection).

– Can pass through the wall of the capillaries.

Leukocytes and Lymphocytes

• Lymphocytes – Acquired immune

response (specific immune response).

– Recognize and remember specific pathogens and fend them off if they attack again.

Platelets

• Are not cells. • Fragments of larger cells

that broke apart in the bone marrow.

• They contain no nucleus and break down relatively quickly.

• They help the blood to clot and protect the body from excessive blood loss after an injury.

Blood Pressure

• Force of the blood on the walls of the arteries.

• Normal BP 120/80 mm Hg; decreases as you move away from the heart.

– Stroke Volume: volume of blood leaving heart (L)

– Heart Rate: number of beats (contractions) per minute (bpm)

Blood Pressure

Two factors determine BP:1. Cardiac Output (CO): amount of

blood pumped from the heart each minute = Heart Rate (HR) x Stroke Volume (SV)

– ⇡ CO = BP⇡– increase CO by HR or ⇡ ⇡

Stroke Volume (stronger heart)

2. Arteriolar resistance: diameter of the arteriole determines the amount of blood flow

– ⇡ diameter = BP⇣

Blood Pressure Regulation• Diameter of blood vessels

regulated by the medulla oblongata.

• Vasoconstriction: nerve impulses cause muscle to contract, reducing diameter of vessel, reduces flow to tissue, increases pressure

• Vasodilation: nerve impulses cause muscles to relax, increasing diameter of vessel, increases flow to tissue, decreases pressure