Download CHAPTER 23 Circulation

CHAPTER 23
Circulation
Overview:
-Circulatory System
-Cardiovascular System
-Heart
-Blood vessels
-Circadian Cycle & ECG
-Blood pressure
-Blood components
Circulatory Systems & Functions
• Every organism must exchange materials with its
environment
– The purpose of the circulatory system is to facilitate
this exchange
• Most animals have a circulatory system
– It transports O2 and nutrients to cells
– It takes away CO2 and other wastes
The circulatory system associates intimately with all body
tissues
• Capillaries are microscopic blood vessels
– They form an intricate network among the tissue
cells
MECHANISMS OF INTERNAL TRANSPORT
Several types of internal transport have evolved in animals
• In jelly and flatworms, the
gastrovascular cavity
functions in both
– digestion
– internal transport
• All but the simplest animals have circulatory
systems with three main components
– A central pump
– A vascular system
– The circulating fluid
• Most animals have a separate circulatory system,
either open or closed
• Open circulatory system
– The heart pumps
blood into large
open-ended vessels
– Blood circulates
freely among cells
– Many invertebrates,
such as mollusks,
have open
circulatory systems
• Closed circulatory system
– Blood is confined to
vessels
– It is distinct from the
interstitial fluid
– Earthworms,
octopuses, and
vertebrates have
closed circulatory
systems
• The closed circulatory system in vertebrates is
called a cardiovascular system
– This system includes the heart and blood vessels
Cardiovascular System
THE HUMAN CARDIOVASCULAR SYSTEM
• In the human cardiovascular system
– The central pump is your heart
– The vascular system is your blood vessels
– The circulating fluid is your blood
The Path of Blood
• In humans and other vertebrates, the three
components of the cardiovascular system are
organized into a double circulation system
– There are two distinct circuits of blood flow
• The pulmonary
circuit carries
blood between
the heart and
the lungs
• The systemic circuit
carries blood between
the heart and the rest
of the body
Heart- Structure & Function
How the Heart Works
• The human heart is a muscular organ about the
size of a fist
– It is located under the breastbone
– It has four chambers
• The mammalian heart has two thin-walled atria
that pump blood into the ventricles
– The thick-walled ventricles pump blood to all other
body organs
Blood vessels –
Types & Functions
Blood Vessels
• If the heart is the body’s “pump,” then the
“plumbing” is the system of arteries, veins, and
capillaries
– Arteries carry blood away from the heart
– Veins carry blood toward the heart
– Capillaries allow for exchange between the
bloodstream and tissue cells
• All vessels are lined by a thin, smooth epithelium
– Structural differences in the walls of the different kinds of
blood vessels correlate with their different functions
• Arteries and veins have smooth muscle and connective tissue
– Valves in veins prevent the backflow of blood
• The walls of capillaries are thin and leaky
– As blood enters a capillary at the arterial end, blood pressure
pushes fluid rich in oxygen, nutrients, and other substances
into the interstitial fluid
– At the venous end of the capillary, CO2 and other wastes
diffuse from tissue cells and into the capillary bloodstream
• The transfer of materials between the blood and
interstitial fluid can occur by
–
–
–
–
leakage through clefts in the capillary walls
diffusion through the wall
blood pressure
osmotic pressure
Blood Return Through Veins
• After chemicals are exchanged between the
blood and body cells, blood returns to the heart
via the veins
– By the time blood exits the capillaries and enters the
veins, the pressure originating from the heart has
dropped to near zero
Circadian Cycle & ECG
The Cardiac Cycle
• The heart relaxes and contracts regularly
– Diastole is the relaxation phase of the heart cycle
– Systole is the contraction phase
• Heart valves prevent backflow
• Cardiac output
– The amount of blood pumped into the aorta by the
left ventricle per minute
The Pacemaker and the Control of Heart Rate
• The pacemaker, or SA (sinoatrial) node, sets the
tempo of the heartbeat
• The pacemaker is composed of specialized
muscle tissue in the wall of the right atrium
• The impulses sent by the pacemaker produce
electrical currents that can be detected by
electrodes placed on the skin
– These are recorded in an electrocardiogram (ECG or
EKG)
– Control centers in the brain adjust heart rate to body
needs
• In certain kinds of heart disease, the heart’s
electrical control fails to maintain a normal
rhythm
– The remedy is an artificial pacemaker
Connection: What is a heart attack?
• A heart attack is damage that occurs when a
coronary feeding the heart is blocked
• How can you avoid becoming a heart disease
victim?
– Don’t smoke
– Exercise
– Eat a heart-healthy diet
• Every year, smoking kills about 430,000
Americans
– Many smokers die from lung cancer
– Smoking can also cause emphysema
Blood pressure
Blood Flow Through Arteries
• The force that blood exerts against the walls of
your blood vessels is called blood pressure
– Blood pressure is the main force driving the blood
from the heart to the capillary beds
– A pulse is the rhythmic stretching of the arteries
caused by the pressure of blood forced into the
arteries during systole
• Blood pressure depends on
– cardiac output
– resistance of vessels
• Normal blood pressure for adults is below 120
systolic and below 80 diastolic
• High blood pressure is persistent systolic blood
pressure higher than 140 and/or diastolic blood
pressure higher than 90
– It is also called hypertension
• Pressure is
highest in the
arteries
– It drops to
zero by the
time the
blood reaches
the veins
• Three factors keep blood moving back to the
heart
– muscle contractions
– breathing
– one-way valves
Connection: Measuring blood pressure can reveal
cardiovascular problems
• Blood pressure is measured as systolic and
diastolic pressures
Smooth muscle controls the distribution of blood
• Muscular constriction of arterioles and
precapillary sphincters controls the flow
through capillaries
Blood
Blood
• The circulatory system of an adult human has
about 5 L (11 pints) of blood
– Just over half of this volume is plasma
– Suspended within the plasma are several types of
cellular elements
Red blood cells transport oxygen
• Red blood cells contain
hemoglobin
– Hemoglobin enables the
transport of O2
• Red blood cells are
by far the most
numerous type of
blood cell
– They are also called
erythrocytes
• Each red blood cell contains large amounts of the
protein hemoglobin
– Hemoglobin contains iron and transports oxygen
throughout the body
– Anemia is an abnormally low amount of hemoglobin
or a low amount of red blood cells
White blood cells help defend the body
• White blood cells function both inside and
outside the circulatory system
– They fight infections and cancer
– They are also called leukocytes
– There are about 1,000 times fewer white blood cells than red
blood cells
Blood clots plug leaks when blood vessels are injured
• When a blood vessel
is damaged, platelets
respond
– They help trigger the
formation of an
insoluble fibrin clot
that plugs the leak
• Blood contains two components that aid in
clotting
– Platelets (thrombocytes) are bits of cytoplasm
pinched off from larger cells in the bone marrow
– Fibrinogen is a membrane-wrapped protein found in
plasma
Connection: Stem cells offer a potential cure for leukemia and other
blood cell diseases
• All blood cells develop
from stem cells in bone
marrow
– Such cells may prove
valuable for treating
certain blood disorders
Stem Cells and the Treatment of Leukemia
• New blood cells are continually formed from
unspecialized stem cells found in red bone
marrow
– Stem cells differentiate into red and white blood cells
and the cells that produce platelets
– Bone marrow stem cells can be isolated and used to
treat leukemia
• Leukemia is cancer of the leukocytes
– A person with leukemia has an abnormally high
number of leukocytes
– Leukemia is usually fatal unless treated
– Not all cases respond to treatment