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 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.
Evolution of the CS
• In water, single-celled and multicellular organisms of
only 2 cell layers do not need a circulatory system.
– Oxygen and nutrients diffuse in, wastes diffuse
out. Ex. diatom, sponge
• Multicellular organisms of 3 cell layers or more require
a circulatory system to bring the mesoderm (middle
layer) in contact with oxygen and nutrients.
Types of Circulatory Systems
• Open circulatory system: cells are directly bathed
in blood. Blood is pumped into cavities in the body
by one or two hearts.
– Ex. Snails, insects and crustaceans
Types of Circulatory Systems
• Closed circulatory systems: Blood is contained in
blood vessels and is separated from the fluid between
the cells (interstitial fluid)
– Ex. earthworms, squids, octopus, and vertebrates
Evolution of Closed CS
Mammalian Circulatory System
• Have evolved circulatory systems
that meet their high metabolic
needs.
• They have a circulatory system
that keeps oxygen-rich
and
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oxygen-poor blood separate
from
one another.
– Blood that flows to the body
carries as much oxygen as
possible.
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
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
• This initiates the almost
simultaneous contraction
of all cells of the right and
left ventricles.
Cardiac Output Calculations
• To calculate the cardiac ouput we use
the following:
CO = Cardiac Output (should be in L/min)
SV = Stroke Volume (how many mL of blood
pushed out of heart each beat)
HR = Heart Rate (beats per min or bpm)
CO = SV x HR
THE END
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 iron molecules (heme) and 1 globin
(protein)
– High affinity for oxygen
– Hemoglobin + oxygen
= oxy-hemoglobin
• 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 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)
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
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.
• Systolic Pressure: pressure on the
wall of the aorta as the ventricles
Contrac
of the heart _____________
(systole) – 120 t
• Diastolic Pressure: pressure on the
wall of the aorta as the heart
Relax
or fills (diastole) - 80
_____________
Heart Rate: number of
beats (contractions) per
minute (bpm)
Stroke Volume: volume
of blood leaving heart (L)
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
Fluid Exchange
Two forces regulate the movement of fluid
• Fluid Pressure: the force that blood exerts on the wall of the
capillary pushes water outward.
– Pushes water OUT (absorption into tissues)
• Osmotic Pressure: the force pushing water from hypotonic to
hypertonic concentrations (more concentration of solutes)
– Pushes water IN
Fluid Exchange
• Your body tries to maintain this balance, but...
• Osmotic pressure can change with:
– Fluid intake / loss (perspiration, vomiting, diarrhea),
which changes concentration
– Inflammation (decreases pressure)
• Fluid Pressure can change with:
– Hemorrhage