CHAPTER 23 CIRCULATION. OPEN AND CLOSED CIRCULATORY SYSTEMS Among the unicellular protists, oxygen...
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Transcript of CHAPTER 23 CIRCULATION. OPEN AND CLOSED CIRCULATORY SYSTEMS Among the unicellular protists, oxygen...
CHAPTER 23
CIRCULATION
OPEN AND CLOSED CIRCULATORY SYSTEMS
• Among the unicellular protists, oxygen and nutrients are obtained directly by simple diffusion.
• Cnidarians and flatworms have cells that are directly exposed to either the external environment or to a body cavity that functions in digestion, the gastrovascular cavity.
Gastrovascular cavity
MouthPharynx
Planaria: gastrovascular cavity
OPEN AND CLOSED CIRCULATORY SYSTEMS
• Large animals have tissues that are several cell layers thick so that many cells are too far away for surface exchange.• Instead, oxygen and nutrients are transported
from the environment and digestive cavity to the body cells by an internal fluid within a circulatory system.• There are two main types of circulatory
systems:• Open circulatory system• Closed circulatory system
OPEN AND CLOSED CIRCULATORY SYSTEMS
• In open circulatory systems, there is no distinction between the circulating fluid (blood) and the extracellular fluid of the body tissues (interstitial fluid or lymph).• This fluid is called hemolymph.• Insects have a muscular tube that serves as a
heart to pump the hemolymph through a network of open-ended channels.
Insect: open circulation
Tubular heart
OPEN AND CLOSED CIRCULATORY SYSTEMS
• In a closed circulatory system, the circulating fluid (blood) is always enclosed within blood vessels that transport blood away from and back to a heart.• Annelids and all vertebrates have a closed
circulatory system.Dorsal blood vessel
Lateralhearts Ventral blood
vessel
Earthworm: closed circulation
OPEN AND CLOSED CIRCULATORY SYSTEMS
• Arteries carry blood away from the heart, and veins return blood to the heart; blood passes from the arterial system to the venous system in capillaries.
• The pressure of the blood forces some fluid out of the capillary walls.
OPEN AND CLOSED CIRCULATORY SYSTEMS
• The pressure of the blood forces some fluid out of the capillary walls.• This fluid is called interstitial fluid.
• Some of it will return to the blood but some becomes lymph and travels through the lymph vessels.
OPEN AND CLOSED CIRCULATORY SYSTEMS
• The functions of the circulatory system can be divided into three areas:• Transportation
• Substances essential for cellular functions are transported by the circulatory system.
Cold blood VeinsArtery
Capillarybed
5º CTemperature
of environment
Core bodytemperature
36º C Warm blood
VeinsArtery
OPEN AND CLOSED CIRCULATORY SYSTEMS
• Regulation• The cardiovascular
system participates in temperature regulation, such as by countercurrent heat exchange.
OPEN AND CLOSED CIRCULATORY SYSTEMS
• Protection• The circulatory system protects against injury
and foreign microbes or toxins introduced into the body.
ARCHITECTURE OF THE VERTEBRATE CIRCULATORY
SYSTEM• The vertebrate circulatory system (also
known as the cardiovascular system) is made up of three elements.• Heart—a muscular pump that pushes blood
through the body.• Blood vessels—a network of tubes through
which the blood moves.• Blood—fluid that circulates through the
vessels.
ARCHITECTURE OF THE VERTEBRATE CIRCULATORY
SYSTEM• Blood moves through the body in a cycle, from
the heart, through a system of vessels.• Blood leaves the heart in arteries.• From the arteries, blood passes into smaller arterioles.• Tiny vessels called capillaries connect arterioles to
venules, or small veins.• Venules and then veins carry blood back to the heart.
Heart
Veins
Venules
Capillaries
Arterioles
Arteries
ARCHITECTURE OF THE VERTEBRATE CIRCULATORY
SYSTEM• Although each capillary is very narrow, there are
so many of them that the capillaries have the greatest total cross-sectional area of any other type of blood vessel.
ARCHITECTURE OF THE VERTEBRATE CIRCULATORY
SYSTEM• Capillary beds can be opened or closed based on
the physiological needs of the tissues.• Precapillary sphincters can contract or relax
and affect whether blood flows into a capillary bed for exchange of gases and metabolites.
1
2
3Precapillarysphincters open
Through-flowchannel
Precapillarysphincters closed
Arteriole VenuleCapillaries
(a) Blood flows through capillary network (b) Blood flow in capillary network is limited
ARCHITECTURE OF THE VERTEBRATE CIRCULATORY
SYSTEM• An artery is more
than a simple pipe.• It needs to be able
to expand with and be strong against the pressure caused by contraction of the heart.
• For this reason, arteries have both elastic and smooth muscle layers.
Connectivetissue
Smooth muscle
Elasticlayer
Endothelialcells
(a) Artery
ARCHITECTURE OF THE VERTEBRATE CIRCULATORY
SYSTEM• Arterioles differ from arteries in that they
are smaller in diameter and respond to nervous and hormonal stimulation.• They can constrict or expand to affect blood
flow during periods of stress or body activity.
(b) Capillary
Endothelialcells
Endothelium
ARCHITECTURE OF THE VERTEBRATE CIRCULATORY
SYSTEM• Capillaries are where
O2 and food molecules are transferred from the blood to the body’s cells and waste CO2 is picked up.• Capillaries are narrow
and have thin walls for exchange.
• Almost all cells of the vertebrate body are no more than 100 micrometers from a capillary.
• The blood pressure is actually far lower in the capillaries than in the arteries.
ARCHITECTURE OF THE VERTEBRATE CIRCULATORY
SYSTEM
• Veins are vessels that return blood to the heart.• The walls of veins
are thinner because the blood pressure is not great.
(c) Vein
Connective tissue
Smooth muscle
Elastic layer
Endothelium
Blood flowstoward heart
Openvalve
Vein
Contractingskeletalmuscles
Valveclosed
ARCHITECTURE OF THE VERTEBRATE CIRCULATORY
SYSTEM• Veins have
unidirectional valves that prevent the flow of blood backwards.
THE LYMPHATIC SYSTEM: RECOVERING LOST FLUID
• The cardiovascular system is very leaky.• From capillary exchange, the
body loses about 4 liters of fluid each day.
• To collect and recycle this fluid, the body uses a second circulatory system called the lymphatic system.• The lymphatic system is
also a network of vessels filled with a fluid called lymph.
• Ultimately the lymph reenters the bloodstream through veins in the neck .
Lymph nodes
Lymphatic vessels
Thymus
Spleen
LYMPHATIC CAPILLARIES RECLAIM FLUID FROM INTERSTITIAL FLUID
Lymphaticcapillary
Blood pressurecauses net filtration
Excess interstitial fluidbecomes lymph
Osmosis due to plasmaproteins causes netabsorption
Interstitialfluid
Capillary
VenuleArteriole
Bloodflow
THE LYMPHATIC SYSTEM: RECOVERING LOST FLUID
• The lymphatic system has 3 important functions:• It returns proteins to circulation.
• If this protein remains in the tissues, it would cause swelling or edema.
• It transports fats absorbed from the intestine.• It aids in the body’s defense.
• Swellings along lymph vessels called lymph nodes and a lymph organ called the spleen are where bacteria and dead blood cells are destroyed.
• The thymus produces white blood cells.
BLOOD
• Blood plasma is a complex solution of water with three kind of substances dissolved in it:• Metabolites and wastes
• Glucose, vitamins, hormones, wastes.• Salts and ions
• Sodium, chloride, and bicarbonate.• Proteins
• Proteins help keep water in the plasma.• Serum albumin functions in maintaining
osmotic balance.
THREADS OF FIBRIN
• Other proteins found in blood include: antibodies, globulins, and fibrinogen.• Fibrinogen
(which converts into fibrin) is required for blood clotting.
BLOOD
• Nearly half the volume of blood is occupied by cells.• The three principal cell types are:
• Erythrocytes (red blood cells)• The blood’s hematocrit is the fraction of the
total volume of the blood that is occupied by red blood cells.
• In humans, the hematocrit is usually about 45%.
• Leukocytes (white blood cells)• Platelets (cell fragments)
BLOOD
• Erythrocytes resemble flat disks with a central depression on both sides.• Almost the entire interior is packed with
hemoglobin, which carries oxygen.• Because these cells have no nucleus they are
short-lived and must be replaced by new cells synthesized in the bone marrow.
BLOOD
• Leukocytes contain no hemoglobin and are essentially colorless.• There are several different kinds, all of which
help defend the body against invading microorganisms and other foreign substances.
BLOOD
• Platelets are cell fragments, pinched from large cells in the bone marrow, called megakaryocytes, that play a key role in clotting.
FISH CIRCULATION
• The chordates that were ancestral to the vertebrates have simple tubular hearts.
• The evolution of gills by fishes required a more efficient pump, a true chamber-pump heart.
A V
VA
Sinusvenosus Atrium Ventricle Conus
arteriosus
SV CA
Systemiccapillaries
Respiratorycapillaries
GillsBody
SV CA
(a)
FISH CIRCULATION
• The fish heart is essentially a tube with four chambers arrayed one after another.• The sinus venosus (SV) and
atrium (A) are collecting chambers, and the ventricle (V) and conus arteriosus (CA) are pumping chambers.• The SV and CA chambers are
reduced in higher vertebrates.• The chambers contract in a
peristaltic sequence.• The blood that is pumped to the
body is fully oxygenated because it passes through the gills first, but it has less pressure.
AMPHIBIAN AND REPTILE CIRCULATION
• The advent of lungs involved a major change in the pattern of circulation.• After blood is pumped by the heart to the lungs,
it does not go directly to the tissues of the body but instead returns to the heart.• Pulmonary circulation goes to and from the
heart and lungs.• Systemic circulation goes to and from the
heart and the rest of the body.
AMPHIBIAN AND REPTILE CIRCULATION
• The amphibian heart has structural features to prevent the mixing of deoxygenated blood from the body with oxygenated blood from the lungs.
AMPHIBIAN AND REPTILE CIRCULATION
• The atrium is divided by a septum that separates the blood coming from the body and from the lungs.
• There is a single, common ventricle, but little mixing of blood occurs because• Some species of
amphibians have folds in the ventricle that direct the flow of blood from the atria
• The conus arteriosus is branched
AMPHIBIAN AND REPTILE CIRCULATION
• Amphibians in water supplement the oxygenation of their blood by obtaining additional oxygen by diffusion across their skin.• This is called cutaneous respiration.
AMPHIBIAN AND REPTILE CIRCULATION
• The reptilian heart is additionally specialized. • There is a partial septum in the ventricle.• The conus arteriosus has become incorporated
into the large arteries leaving the heart.
MAMMALIAN AND BIRD CIRCULATION
• Mammals, birds, and crocodiles have a four-chambered heart with two complete pumping circuits.• This increased efficiency of the double
circulation in mammals and birds may have been important in the evolution of endothermy.• More efficient circulation is necessary to
support the high metabolic rate required.
MAMMALIAN AND BIRD CIRCULATION
• In the mammalian heart,• Oxygen-rich blood
returns from the lungs through pulmonary veins to the left atrium of the heart and flows through the mitral valve into the left ventricle.
• The thick-walled left ventricle contracts, sending oxygenated blood through a large artery called the aorta and out to the body.• Backflow of blood from
the aorta is prevented by the aortic semilunar valve.
Superiorvena cava
Aorticsemilunarvalve
Pulmonarysemilunar valve
Right atrium
Tricuspid valve
Inferiorvena cava Right ventricle
Left ventricle
Bicuspid(mitral) valve
Left atrium
Pulmonaryveins
Pulmonaryartery
Aorta
MAMMALIAN AND BIRD CIRCULATION
• Blood travels through the body and returns to the heart via the vena cavae, which drain into the right atrium.
• Blood flows from the right atrium through the tricuspid valve to the right ventricle.
• The right ventricle contracts, pushing blood through the pulmonary valve into pulmonary arteries that lead to the lungs.
Superiorvena cava
Aorticsemilunarvalve
Pulmonarysemilunar valve
Right atrium
Tricuspid valve
Inferiorvena cava Right ventricle
Left ventricle
Bicuspid(mitral) valve
Left atrium
Pulmonaryveins
Pulmonaryartery
Aorta
http://youtu.be/gn6QmETEm8s
THE HEART AND CIRCULATION OF MAMMALS AND BIRDS
Superiorvena cava
Carotid artery
Jugular vein
Aorta
Pulmonaryartery
Heart
Inferiorvenacava
Aorta
Femoralarteryandvein
Femoralvein
Greatsaphenousvein
Brachialartery
Hepaticportalsystem
Radialartery
Femoralartery
MAMMALIAN AND BIRD CIRCULATION
• The simplest way to monitor heartbeat is to listen using a stethoscope.– “Lub” is the sound made by the closing
of the bicuspid and tricuspid valves at the start of ventricular contraction.
– “Dub” is the sound made by the closing of the pulmonary and aortic valves at the end of ventricular contraction.
• A heart murmur is heard due to turbulence created by the valves not closing fully.
MAMMALIAN AND BIRD CIRCULATION
• Another way to examine the events of the heartbeat is to monitor the blood pressure.– A device called a sphygmomanometer is
used to measure the blood pressure in the brachial artery of the arm.
– Diastolic pressure is the low pressure when the atria are filling.
– Systolic pressure is the high pressure associated with the ventricles contracting.
0 0
321 Bloodpressuregauge
150
200
2500
50
100150
200
100
50
250
Cuff pressure: 75Sound stops:Diastolic pressure
Cuff pressure: 120Pulse sound:Systolic pressure
Cuff pressure: 150No sound:artery closed
Cuff
100 150
50 200
250
Stethoscope
MEASURING BLOOD PRESSURE
MAMMALIAN AND BIRD CIRCULATION
• The contraction of the heart consists of a carefully orchestrated series of muscle contractions.• First the atria contract, followed by the
ventricles.• The sinoatrial (SA) node is the pacemaker of
the heart and determines the rhythm of the heart’s beating.
MAMMALIAN AND BIRD CIRCULATION
• Contraction of the atria is initiated by the SA node.
• The wave of depolarization does not immediately spread to the ventricles because it must pass first through cardiac muscle called the atrioventricular (AV) node.• This delays the signal for about 0.1 sec until the
atria have finished contracting.
MAMMALIAN AND BIRD CIRCULATION
• The ventricles finally contract after the signal passes from the AV node to an atrioventricular bundle of muscle called the bundle of His.
• Bundle branches divide into fast-conducting Purkinje fibers which initiate the almost simultaneous contraction of the right and left ventricles.
• The electrical activity of the heart can be measured by a recording called an electrocardiogram (ECG or EKG).
HOW THE MAMMALIAN HEART CONTRACTS
1 2 3 4
P T
R R
Q S
P wave in ECG QRS wave in ECG
Purkinje fibers
AV nodeSA node
Bundle of His
1 sec
QRS wave
RV
RA
LA
LV
ECG