Transcript SBI3U - The Circulatory System

SBI3U - The Circulatory System
Introduction
and
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 endto-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 oxygenpoor 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 cycles
1. 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 ironcontaining 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