Download Circulatory, chap. 32

Circulation
Chapter 32
Pages 617-639
Major Features and Functions of
Circulatory Systems
• Circulatory systems evolved to bring the outside world to
each cell in a multicellular organism
– The earliest cells were nurtured by the primordial sea in
which they evolved
– In complex organisms, individual cells are farther away
from the outside world, but require diffusion for adequate
nutrients and to ensure they aren’t poisoned by their own
waste
– With the evolution of the circulatory system, a sort of
“internal sea” was created, which transports food and
oxygen close to each cell and carries away wastes
All circulatory systems have three
major parts
– A pump, the heart, that circulating
– Blood – liquid that serves as a medium of
transport
– A system of tubes, blood vessels, to conduct the
blood throughout the body
Two types of circulatory systems
• Open circulatory systems - invertebrates, including
arthropods and mollusks
– One or more simple hearts, network of vessels, and
series of interconnected spaces within the body
called a hemocoel
– Tissues and organs in the hemocoel are directly
bathed by hemolymph - acts as both blood and the
extracellular fluid that bathes all cells
Insect Example
• Heart is a modified blood vessel
with a series of contracting
chambers
• When chambers contract, valves
in the heart are pressed shut,
forcing the hemolymph out
through vessels and into
hemocoel spaces throughout the
body
• When the chambers relax, blood
is drawn back into them from the
hemocoel
Closed Circulatory Systems
• Invertebrates - earthworm and
active mollusks (squid and
octopuses) and all vertebrates
– Blood is confined to heart and
blood vessels, which branch
throughout the organs and
tissues of the body
• more rapid blood flow
• more efficient transport of
dissolved substances
• higher blood pressure than in
open systems
Functions of Vertebrate Circulatory
System
• Transport O2 from lungs or gills to tissues
• Transport CO2 from tissues to lungs or gills
• Distribution of nutrients from the digestive system to
body cells
• Transport of wastes and toxic substances to the liver,
where they are detoxified, and to the kidneys for
excretion
• Distribution of hormones from the glands and organs
to the tissues
• Regulation of body temperature by adjustments in
blood flow
• Wound healing and blood clotting to prevent blood
loss
• Protection against disease by circulating white blood
cells and antibodies
Vertebrate Heart
• The vertebrate heart consists of muscular
chambers capable of strong contractions
– Chambers called atria collect blood
– Atrial contractions send blood into ventricles,
chambers whose contractions circulate blood
through the lungs and to the rest of the body
Evolution of the Vertebrate Heart
• Increasingly complex and efficient hearts
– The heart has become increasingly complex
– Separation of oxygenated and deoxygenated blood
– Fish (first vertebrates to evolve) has two chambers:
a single atrium that empties into a single ventricle
• Blood from the ventricle passes first through the gills,
where it picks up O2 and gives off CO2
• Blood then travels from the gills through the rest of the
body, picking up CO2 and returning it to the single atrium
Fish Heart
gill capillaries
ventricle
atrium
body capillaries
(a) Fish
Three Chambered Hearts
• Fish gave rise to amphibians and amphibians to reptiles
• Three-chambered hearts consist of two atria and one
ventricle
• Amphibians, snakes, lizards, and turtles
• Deoxygenated blood from the body is delivered to the right
atrium, blood from the lungs enters the left atrium
• Both atria empty into the single ventricle
• Although some mixing occurs, deoxygenated blood remains in
the right portion of the ventricle and is pumped into vessels
that lead to the lungs, while most of the oxygenated blood
remains in the left portion of the ventricle and is pumped to
the rest of the body
Three Chambered Heart
lung capillaries
atria
ventricle
body capillaries
(b) Amphibians and some
reptiles
Four Chambered Hearts
• Some reptiles - crocodiles, birds, and mammals have
separate right and left ventricles
• Completely isolate oxygenated and deoxygenated
blood
Four Chambered Heart
lung capillaries
atria
ventricles
body capillaries
(c) Mammals, crocodiles,
and birds
Four Chambers – Two Pumps
• An atrium collects the blood before passing it to a ventricle
which propels it into the body
• One pump, the right atrium and ventricle, deals with
deoxygenated blood
– Oxygen-depleted blood enters the right atrium through
two large veins - the superior and inferior vena cava
– After filling with blood, the right atrium contracts, forcing
blood into the right ventricle
– Contraction of the right ventricle sends the oxygendepleted blood to the lungs through the pulmonary
arteries
Two Pumps, part II
• The second pump, the left atrium and ventricle,
deals with oxygenated blood
– Oxygen-rich blood from the lungs enters the left atrium
through the pulmonary veins and is squeezed into the left
ventricle
– Contraction of the left ventricle sends the oxygenated
blood through the aorta to the rest of the body
Heart Valves
• Maintain the direction of blood flow
– When the ventricles contract, blood must be prevented from
flowing back into the atria
• Blood entering the arteries must also be prevented
from flowing back into the ventricles as the heart
relaxes
– Pressure in one direction opens valves easily, but reverse
pressure forces valves closed
• Atrioventricular valves blood flows from atria into the
ventricles
• Semilunar valves blood enters the pulmonary artery
and aorta when ventricles contract, but prevent blood
from returning as the ventricles relax
Cardiac Muscle Cells
• Cardiac muscle cells are small, branched, and striated
– Linked to one another via intercalated discs, appear as
bands between the cells
– Adjacent cell membranes are attached to one another by
desmosomes, prevent heart contractions from pulling
muscle cells apart
– Intercalated discs also contain gap junctions to allow the
electrical signals that trigger contractions to spread from
one muscle cell to another, producing synchronous heart
muscle contractions
Cardiac Cycle
• The coordinated contractions of atria and
ventricles produce the cardiac cycle
– The heart beats in a coordinated fashion
• Both atria contract and pump blood into the ventricles
• Both ventricles contract and pump blood into the
arteries that exit the heart
• All chambers relax briefly before the cycle repeats
– This cardiac cycle lasts less than 1 second
Cardiac Cycle
The Cardiac Cycle
Oxygenated blood
is pumped to the
body
Deoxygenated
blood from the
body enters the
right ventricle
Deoxygenated blood is
pumped to the lungs
Oxygenated blood from the
lungs enters the left ventricle
1 Atria contract, forcing
blood into the ventricles
2 Then the ventricles
contract, forcing blood
through the arteries to
the lungs and the rest
of the body
Blood fills the
atria and begins
to flow passively
into the ventricles
3 The cycle ends as
the heart relaxes
Blood Pressure
• The cardiac cycle generates the forces that are
measured when blood pressure is taken
• Systolic pressure, the higher of the two readings, is
measured during ventricular contraction
• Diastolic pressure is the minimum pressure in the
arteries as the heart rests between contractions
– A BP reading of less than 120/80 is healthy; higher
than 140/90 is defined as high
– High blood pressure, or hypertension, is caused
by the constriction of small arteries, which causes
resistance to blood flow and strain on the heart
Electrical Impulses Coordinate the
Contractions
• The contraction of the heart is initiated and coordinated by a pacemaker,
a cluster of specialized muscle cells that produce spontaneous electrical
signals at a regular rate
• The heart’s pacemaker is the sinoatrial (SA) node, located in the upper
wall of the right atrium
• Electrical signals from the SA node pass freely into the connecting cardiac
muscle cells and then throughout the atria
• The electrical signal then passes from the right atrium to a specialized
group of muscle cells between the right atrium and right ventricle called
the atrioventricular (AV) node
• The signal to contract spreads
along specialized tracts of rapidly
conducting muscle fibers called
the atrioventricular bundle,
which sends branches to the
lower portion of both ventricles
• Here, the bundles branch
further, forming Purkinje
fibers that transmit the
electrical signal throughout
the ventricle
The Pacemaker and Its Connections
1 An electrical signal
from the sinoatrial (SA)
node starts atrial
contraction
2 The electrical
signal spreads
through the atria,
causing them to
contract
3 The signal enters
the atrioventricular
(AV) node, which
transmits it to the
AV bundle with a
slight delay
4 The signal travels
through the AV bundle
branches to the base
of the ventricles
5 Purkinje fibers transmit
the signal to ventricular
cardiac muscle cells,
causing contraction from
the base upwards
SA node
AV node
Inexcitable tissue
separates the atria
and ventricles
AV bundle
AV bundle
branches
Purkinje
fibers
Disorders
– When the pacemaker fails, rapid, uncoordinated,
weak contractions called fibrillation may occur
• Treated with a defibrillating machine, which applies a
jolt of electricity, synchronizing the contractions of the
ventricular muscle cells, and the pacemaker resumes its
normal coordinating function
Heart Rate
• Influenced by nervous system and hormones
– On its own, the SA node pacemaker maintains a heart rate
of 100 beats per minute
– Nerve impulses and hormones alter the heart rate
• At rest, the parasympathetic nervous system slows the
heart rate to about 70 beats per minute
• During exercise and stress, the sympathetic nervous
system increases the heart rate to meet the demand for
greater blood flow to the muscles
What Is Blood?
• Blood has two major components
– A liquid or plasma, 55% of total volume
– The cellular portion, 40–45% of total volume
• Red blood cells
• White blood cells
• Platelets
Plasma
• Primarily water with proteins, salts, nutrients, and wastes
– 90% water, it contains > 100 different molecules, including
hormones, nutrients, cellular wastes, ions
– Proteins are the most abundant dissolved molecules by
weight and include:
• Albumin, helps maintain the blood’s osmotic strength
• Globulins, antibodies that play an important part in
immune response
• Fibrinogen, important in blood clotting
Cellular Components of Blood
• Formed in bone marrow
– Of the 3 cell-based components - only the white blood
cells are complete, functional cells
• Mature RBCs are not cells because they lack a nucleus,
which is lost during development
• Platelets are small fragments of cells
– All 3 components originate from blood stem cells which
reside in the bone marrow
• Stem cells are unspecialized cells that can divide to
produce offspring capable of maturing into one or more
types of specialized cells
• Megakaryocyte
Red Blood Cells
• Carry oxygen from the lungs to the tissues
– 99% of all blood cells, and 45% of the total volume
– Oxygen-carrying red blood cells or erythrocytes
– The red color of erythrocytes is caused by the
protein hemoglobin, each hemoglobin binds 4 oxygen
molecules, one on each iron-containing heme group
• Oxygenated hemoglobin is bright cherry-red color
• Hemoglobin becomes bluish as it releases O2 and picks
up CO2 at tissues
Hemoglobin
Red Blood Cells
– Life span of 4 months,
replaced by new cells from
the bone marrow
– Macrophages (white blood
cells) in spleen and liver
engulf and break down
dead red blood cells
– Iron from erythrocytes is
returned to the bone
marrow and recycled into
new red blood cells
Regulated by Negative Feedback
• Red blood cell count is maintained by a negative
feedback system that involves the hormone
erythropoietin
– Erythropoietin is produced by the kidneys and released
into the blood in response to oxygen deficiency
• Stimulates rapid production of new red blood cells by
the bone marrow
• When the oxygen level is restored, erythropoietin
production declines and the rate of red blood cell
production returns to normal
Red Blood Cell Regulation
Oxygen deficiency
stimulates
Erythropoietin
production
by the kidneys
stimulates
inhibits
Red blood
cell production
in the bone marrow
Restored oxygen
level
causes
White Blood Cells
• Defend the body against disease
– Five types of white blood cells or leukocytes
•
•
•
•
•
Neutrophils
Eosinophils
Basophils
Lymphocytes
Monocytes
WBC Details
• Cell life spans range from
hours to years
• <1% of the cellular portion
of blood
• All WBC help to protect the
body against disease
• Monocytes, enter tissues
and transform into
macrophages that engulf
bacteria and cellular debris
Platelets
• Cell fragments that aid in blood clotting
– Pieces of megakaryocytes, reside in bone marrow
• Megakaryocytes pinch off membrane-enclosed pieces
of cytoplasm to form platelets, which enter the blood
and play a role in blood clotting
• Platelets survive for about 10 days
Blood Clotting
• Blood clotting plugs damaged blood vessels
• Complex process that plugs damaged blood vessels
and protects excessive blood loss
How it works…
– Clotting begins following a break in a blood vessel wall,
exposing collagen fibers that attract platelets, which form
a platelet plug
– The platelets and ruptured cells release chemicals that
initiate a series of reactions, producing the enzyme
thrombin from its inactive form, prothrombin
– Clotting begins following a break in a blood vessel wall,
exposing collagen fibers that attract platelets, which form
a platelet plug
– The platelets and ruptured cells release chemicals that
initiate a series of reactions, producing the enzyme
thrombin from its inactive form, prothrombin
Blood Clotting
1 Damaged cells expose
collagen, which activates
platelets, causing them to
stick and form a plug
2 Both damaged cells
and activated platelets
release chemicals that
convert prothrombin
into the enzyme thrombin
collagen
fibers
blood
vessel
fibrin
platelet
plug
platelets
red
blood
cells
3 Thrombin catalyzes the
conversion of fibrinogen
into protein fibers called
fibrin, which forms a
meshwork around the
platelets and traps red
blood cells
thrombin
prothrombin
thrombin
fibrinogen
Functions of Blood Vessels
• Arteries to arterioles to capillaries, then into
venules, to veins, blood returns to the heart
– Except for capillaries, blood vessels have three
cellular layers
• Lined with endothelial cells
• The second layer is smooth muscle cells
• The outermost layer is connective tissue
Structures of Blood Vessels
capillary network
within body tissues
precapillary
sphincter
arteriole
venule
capillary
artery
valve
endothelium
smooth muscle
connective tissue
from heart
to heart
vein
The Human Circulatory System
jugular vein
aorta
superior
vena cava
carotid artery
pulmonary artery
lung capillaries
heart
liver
inferior
vena cava
intestine
femoral artery
kidney
femoral vein
Types and Functions of Blood Vessels
• Arteries and arterioles carry blood away from
the heart
– The walls are thicker and more elastic than those
of veins
– With each heart beat, the arteries expand slightly,
like thick-walled balloons
– Arteries branch into smaller diameter vessels
called arterioles, which play a major role in
determining how blood is distributed in the body
Arteries and Arterioles
• Arteries and arterioles carry blood away from
the heart
– The walls are thicker and more elastic than veins
– With each heart beat, the arteries expand slightly,
like thick-walled balloons
– Arteries branch into smaller diameter vessels
called arterioles, which play a major role in
determining how blood is distributed in the body
Capillaries
• Exchange of nutrients and wastes
– Arterioles conduct blood into networks of capillaries,
microscopically thin vessels
– Capillaries allow individual body cells to exchange
nutrients and wastes with the blood by diffusion
• So numerous that most of the body’s cells are no more
than 100 μm from a capillary, close enough for diffusion
• Capillaries are so narrow that red blood cells pass
through them single file
Leaky Blood Vessels
– Blood pressure within capillaries causes fluid to leak into
the space surrounding the capillaries
– Resulting in extracellular fluid, resembles plasma without
the proteins
• Primarily water containing dissolved nutrients,
hormones, gases, cellular waste, and WBC
• This fluid provides body cells with nutrients and accepts
their wastes
How to Diffuse thru Capillaries
– Gases, water, lipid-soluble hormones and fatty
acids diffuse through the endothelial cell
membranes
– Small water-soluble nutrients, (salts, glucose, and
amino acids) enter the extracellular fluid through
narrow spaces between adjacent capillary cells
– Some proteins are carried across the endothelial
cell membrane as vesicles
Osmotic Pressure and Capillaries
– Pressure within the capillaries drops as blood travels
toward the venules, and the high osmotic pressure of the
blood that remains inside the capillaries draws water back
into the vessels by osmosis as blood approaches the
venous side of the capillaries
– As water enters the capillaries (diluting the blood),
dissolved substances in the extracellular fluid tend to
diffuse back into the capillaries
– Thus, most of the extracellular fluid is restored to the
blood through the capillary walls on the venous side of the
capillary network
Veins and Venules
• Carry blood to the heart
• After picking up CO2 and wastes from cells, capillary
blood drains into larger vessels, called venules,
which empty into larger veins
– Walls of veins are thinner, less muscular, and more
expandable than arteries
– When veins are compressed, one-way valves keep blood
flowing toward the heart
Valves Direct Blood Flow in Veins
valve
open
valve
closed
muscle
contraction
compresses
vein
relaxed
muscle
valve
closed
Moving Blood thru Veins
– Pressure changes in the body caused by breathing, as well
as contractions of skeletal muscle during exercise, help
return blood to the heart by squeezing the veins and
forcing blood through them
– Prolonged sitting or standing can cause swollen ankles,
without muscle contractions to compress the veins,
venous blood pools in the lower legs
– Varicose veins may result from permanently swollen veins
in the lower leg as a result of stretched and weakened vein
valves
Controlling Blood Flow
• Arterioles carry blood to capillaries; their
muscular walls are influenced by nerves,
hormones and chemicals
• Arterioles contract and relax in response to
the needs of the tissues and organs they
supply
Examples of Arteriole Control
– In cold weather, fingers and toes can become frostbitten
because arterioles that supply blood to the extremities
constrict
• Blood is shunted to vital organs (heart and brain) which
cannot function at low temperatures
– On a hot summer day, arterioles in the skin expand to
bring more blood to the skin capillaries, so excess heat is
dissipated to the air outside
Precapillary Spincters
• Blood flow to capillaries is
further regulated by tiny rings
of smooth muscle called
precapillary sphincters
• They surround junctions
between arterioles and
capillaries
• Open and close in response to
local chemical changes that
signal the needs of nearby
tissues
The Lymphatic System
• Includes organs and a system of lymphatic vessels, feeds
into the circulatory system
– Return excess extracellular fluid to the bloodstream
– Transport fats from the small intestine to the bloodstream
– Filter old blood cells and other debris from the blood
– Defend the body by exposing bacteria and viruses to white
blood cells
The Human Lymphatic System
The thoracic duct
enters a vein that
leads to the superior
vena cava
superior
vena cava
thymus
thoracic
duct
lymph
nodes
lymph
vessels
bone
marrow
spleen
Lymphatic Vessels
• Lymphatic capillaries resemble blood capillaries that
branch throughout the body.
• Their walls are only one cell thick, but they are more
permeable than blood capillaries
• Unlike blood capillaries (form continuous
interconnected network) lymphatic capillaries “deadend” in the extracellular fluid surrounding body cells
Lymph Capillary Structure
lymph
capillary
3 Lymph is transported
into larger lymph vessels
and back to the
bloodstream
arteriole
capillary
venule
1 Pressure forces
fluid from the plasma
at the arteriole end of
the capillary network
extracellular
fluid
2 Extracellular fluid
enters lymph vessels
and the venous ends
of capillaries
Lymph
• From the lymphatic capillaries,
the lymph  lymphatic vessels
 increasingly large lymphatic
vessels
– Vessels resemble veins similar walls and one-way
valves that control the
direction of flow
– Flow of lymph is regulated by
internal pressures from
breathing and muscle
contraction
Transporting Fat from Small
Intestine
• The small intestine is supplied with lymph capillaries called
lacteals
• After absorbing digested fats, intestinal cells release fattransporting particles into the extracellular fluid
• These particles are too large to diffuse into blood capillaries,
but can move through the openings in lymphatic capillary
walls
• They are eventually released into the venous blood along with
the lymph
Defend Body and Filter Blood
• Tonsils, thymus, spleen, and hundreds of lymph nodes located
along lymphatic vessels
• Spleen, located between the stomach and diaphragm and
supplied by vessels of both the lymphatic and circulatory
systems, filters the blood
– It has a porous interior that is lined with white blood cells,
which engulf old red blood cells and platelets, fragments
of dead cells, and foreign matter