the circulatory system
TRANSCRIPT
The circulatory system
Refer Chapter 43, Internal transport, pg 919
Circulatory system in……….
Unicellular organisms and Multicellular organisms
Trading with the Environment
• Every organism must exchange materials with its environment– And this exchange occurs at the cellular
level
• In unicellular organisms– exchanges occur directly with the environment
• In multicellular organisms– by diffusion is NOT possible, WHY?– not possible for transporting substances over
long distance in animal– The surface area to volume ratio of the organism
is small so that diffusion of materials across the body surface cannot keep pace with demand
Most complex animals have internal transport systems
That circulate fluid, providing a lifeline between the aqueous environment of living cells and the exchange organs (such as lungs) that exchange chemicals with the outside environment
Unicellular organism: in contact with the environment
Diffusion
(a) Single cell
• A single-celled protist living in water – Has a sufficient surface area of
plasma membrane to facilitates the direct exchange with the environment
(S.A.-to-Vol. R )
• Exchange with the environment occurs as substances dissolved in the aqueous medium– Nutrients and oxygen move
across the plasma membrane into the cytoplasm.
– Metabolic wastes (CO2) move out of the cell.
Contact with the environment
• The feathery gills projecting from a salmon– Are an example of a specialized exchange
system found in animals
Invertebrate circulation
(1) Gastrovascular cavities(2) Open and closed circulatory system L.O.
Compare and contrast internal transport in animals with
NO circulatory system (gastrovascular cavity)
With an open circulatory systemAnd with a closed circulatory system
• NO circulatory system– No specialized circulatory
structures– E.g. sponges, jellyfish, comb jellies,
flat worms, round worms– Cnidarians (jellyfish),
gastrovascular cavity (both circulatory and digestive organs)---animal stretches and contracts—stir up the contents of the gastrovascular cavity, distribute nutrients
– Flatworm, flattened body—effective gas exchange by diffusion, gastrovascular cavity—branched
– Others invertebrates, Fluids in a pseudocoelom act in circulation
Types of circulatory systems
Invertebrate circulation: Gastrovascular Cavities
• Simple animals/multicellular organism, (cnidarians)– body wall only two cells thick
that encloses a gastrovascular cavity
• The fluid inside the cavity is continuous with the water outside, via a single opening.
• Only the cells of the inner layer have direct access to nutrients, – but the nutrients have to diffuse
only a short distance to reach the cells of the outer layer.
Mouth
Gastrovascularcavity
Diffusion
Diffusion
(b) Two cell layers
Open and Closed Circulatory Systems
• More complex animals– Have one of two types of circulatory systems:
open or closed
• Both of these types of systems have three basic components– A circulatory fluid (blood> con. t)– A set of tubes (blood vessels, in which blood
circulates)– A muscular pump (the heart)
Invertebrate circulation:
In insects (arthropods) and most molluscs– Blood bathes the organs directly in an open circulatory
system– Heart pumps blood into vessels that have open ends
Open circulatory system
Blood and interstitial fluid are the same – hemolymph.
Spaces surrounding the organs – sinuses---make up the hemocoel (invert. blood cavity)
(a) An open circulatory systemFigure:
Heart
Hemolymph in sinusessurrounding organs
Heart
Hemolymph in sinusessurrounding organs
Anterior vessel
Tubular heartLateral vessels
Ostia
(a) An open circulatory systemFigure 42.3a
Open circulatory system
When the heart contracts,the heart pumps the hemolymph through vessels out into sinuses---where materials are exchanged between the hemolymph and cells.
When the heart relaxes, hemolymph returns to the heart through ostia, which are equipped with valves
The body movements that squeeze the sinuses help circulate the hemolymph.
The rate of hemolymph circulation increases when animal moves.
Figure 43.2: Open circulatory systems.
In mollusks and arthropods, a heart pumps the blood into arteries that end in sinuses of the hemocoel.
Hemolymph circulates through the hemocoel. In mollusks, Heart- 3 chambers (TWO atria, SINGLE ventricle)heart >sinuses of the hemocoel >gills >heart
In arthropods, heart> sinuses of the hemocoel > heart via ostia
An open circulatory system cannot provide enough oxygen to maintain the active lifestyle.—tracheal systemHemolymph--- nutrients and hormones in insects.
In some molluscs and arthropods---have hemocyanin, (copper-containing hemolymph pigment); when oxygenated, blue colour----BLUE BLOODS!!
Open circulatory system
Open circulatory system show :
(1) a lowered transport efficiency and
(2) a slower circulatory time
Closed circulatory systemIn a closed circulatory system
– Blood is confined to vessels and is distinct from the interstitial fluid Interstitia
lfluid bathing the cells
Heart
Small branch vessels in each organ
Dorsal vessel(main heart)
Ventral vesselsAuxiliary hearts
(b) A closed circulatory system
Chemical exchange occurs:
-between the blood and the interstitial fluid,
-and between interstitial fluid and body cells.
Annelids, cephalopods and echinoderms
• FIVE contractile b.v. (heart) pump blood• Dorsal vessel, 5 contractile b.v. and contraction
body wall muscle--> circulate the blood
• Earthworms, have hemoglobin– NOT contained within RBC, but
dissolved in the blood plasma
• TWO main blood vessels– dorsal and ventral vessels,
connected by lateral vessels
What is the advantage associated with……..?
Open circulatory system– Energy expenditure –Because they lack an extensive system of blood vessels-- require less energy.
Closed circulatory system-More efficient at transporting circulatory fluids >> tissues and cells.-To meet the high metabolic demands of the tissues and cells of larger and more active animals
Vertebrate Circulation
Cardiovascular system
What are the functions of the vertebrate circulatory system?
(1) Transportation of nutrients, respiratory gases, wastes and hormones
(2) Maintenance of fluid balance(3) Internal defense(4) Thermoregulation(5) Maintenance of pH
Vertebrate Circulation
• Humans and other vertebrates have a closed circulatory system– cardiovascular system
• Blood flows in a closed cardiovascular system– Consisting of blood vessels and a two- to
four-chambered heart
Evolution of the vertebrate cardiovascular
systemL.O.
Describe the evolution of the vertebrate cardiovascular system
from fish to mammal
Vertebrate circulation: Fishes
• A fish heart has two main chambers– One ventricle and one atrium
• A single circuit of blood flow – one way street!
• Blood pumped from the ventricle– Travels to the gills (gill
circulation), where it picks up O2 , disposes of CO2
– The gill capillaries converge into a vessel that carries O2 rich blood to capillary beds, all other parts of the body (systemic circulation).
Note: In a fish, blood must pass through two capillary beds during each circuit.
FISHES
Systemic capillaries
Gill capillaries
SystemiccirculationVein
Atrium (A)
Heart:ventricle (V)
Artery Gillcirculation
Pressure low here
Fish swimming movement aids blood circulation
Vertebrate circulation: Amphibians
AMPHIBIANS
Systemic capillaries
Lung and skin capillaries
Right Left Systemic
circuit
Pulmocutaneouscircuit
A
V
A
• Frogs and other amphibians– Have a three-chambered heart, with two
atria (singular, atrium) and one ventricle– Oxygen-rich and oxygen-poor blood—
kept separated– Both atria pump into a single ventricle,
oxygen-poor blood is pumped out of the ventricle before oxygen-rich blood enters
– Atria separated, ventricle undivided, oxygen and de-oxygenated blood are prevented from mixing by conus arteriosus, which keeps the blood apart
• The ventricle pumps blood into a forked artery– That splits the ventricle’s output into the
pulmocutaneous circuit and the systemic circuit. (Two circuits of blood flow)
• Pulmocutaneous circuit (pulmo- lung; cutaneous-skin)
– The route of circulation that directs blood to the skin and lungs.
• Systemic circuit– The branch of the circulatory system that
supplies oxygen-rich blood (oxygenated blood) to all body organs and then return oxygen-poor blood (deoxygenated blood) to the right atrium via the veins.
Vertebrate circulation: Amphibians
Sinus venosus receives oxygen-poor blood
returning from tissues and pumps it into atrium
Sinus venosus > atrium > ventricle
Conus arteriosus, an artery with fold that helps to keep blood separate
Vertebrate circulation: Reptiles (e.g. crocodiles, alligators)• Reptiles have double circulation
– With a pulmonary circuit (lungs) and a systemic circuit
• In most reptiles (turtles, lizards, snakes)—wall separating the ventricles is incomplete, partially divided ventricle—3 chambered heart
• Crocodiles and alligators have a four-chambered heart------ 2 atria, 2 ventricles
REPTILES
Systemic capillaries
Lung capillaries
Right Left
Pulmonarycircuit
V V
A A
Left Systemicaorta
Right systemicaorta
Systemic circuit
Vertebrate circulation: Mammals and birds
Systemic capillaries
• In all mammals and birds– The ventricle is completely divided
into separate right and left chambers
• The left side of the heart pumps and receives only oxygen-rich blood– While the right side receives and
pumps only oxygen-poor blood
MAMMALS AND BIRDS
Lung capillaries
Right Left Systemic
circuit
Pulmonarycircuit
VV
AA
FISHES AMPHIBIANS REPTILES MAMMALS AND BIRDS
Vertebrate circulatory systems
Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries
Lung capillaries Lung capillariesLung and skin capillariesGill capillaries
Right Left Right Left Right Left Systemic
circuitSystemic
circuit
Pulmocutaneouscircuit
Pulmonarycircuit
Pulmonarycircuit
SystemiccirculationVein
Atrium (A)
Heart:ventricle (V)
Artery Gillcirculation
A
V VV VV
A A A AALeft Systemicaorta
Right systemicaorta
Figure 42.4
Systemic circuit
The human heartL.O.
(1) Draw the structure and describe the function of the human heart(2) Describe the events of the cardiac cycle, relate the normal heart sound to the cardiac cycle
human heart: FACTS!!
Not much bigger than a FIST!! Beats about 2.5 million times in an
average lifetime, vary its output from 5 to > 20 L blood
Pericardium, Epicardium, myocardium, Endocardium
• Walls of the heart, – cardiac muscle—myocardium
• Inner surface of heart, endocardium
• Outer surface of the heart, Epicardium
• Pericardium– Connective tissue sac, encloses
the heart– Between inner and outer
pericardium form a small space, pericardial cavity contain pericardial fluid, reduce friction
Coronary arteries: arteries which supply blood to the heart muscle
What are the major blood vessels to and from the heart ??
Structure and functions of the four heart chamber
• The heart has four chamber– The receiving chambers: right atrium, left atrium– The discharging chambers: right ventricle, left
ventricle• The internal partition (septum) that divides
the heart longitudinally is called – Interatrial septum (between atria)– Interventricular septum (between ventricles)– Fossa ovalis is located in the interatrial septum, remnant of
the fetal foramen ovale
• Bloods enters the right atrium through:– (1) anterior vena cava: returns blood from body
regions above the diaphragm (upper body)– (2) posterior vena cava: returns blood from body
regions below the diaphragm (lower body)
Aorta
Left pulmonaryveins
Semilunar(aortic) valve
Bicuspid valve
Left ventricle
Right ventricle
Right pulmonaryveins
Anterior vena cava
Right pulmonary artery
Semilunar(pulmonary) valve
Tricuspidvalve
Posterior vena cava
Right atrium
Left pulmonary artery
Leftatrium
I LCLS
Aortic arch> Innominate artery (IA), Left common carotid artery (LCCA), Left Subclavian artery (LSA)
Upper limb (arm)
Head & necka.k.a Brachiocephalic
trunk
Brachio- = arm;
Cephalic- = head
Fetal Foramen ovale become Fossa ovalis
• Foramen ovale (fetal heart)– an opening on the interatrial septum– Lets blood flow directly from right to left atrium– So very little passes to the non-functional lungs
• Fossa ovalis– Shallow depression
Foramen ovale closes shortly after birth, become fossa ovalis.
When an infant takes its first breath, the lung expand and blood flow to the lung increases---blood return from lung to heart---increase pressure in left atrium, pushes a valve against the interatrial septum.
Ductus arteriosus---a vessel linking pulmonary artery and aorta
Ductus arteriosus closes by vasoconstriction almost immediately after birth, becomes the ligamentum arteriosum
Heart valves• Blood flows through the heart in one direction
• This one-way traffic is enforced by four heart valves:– the paired atrioventricular (AV) and semilunar (SL) valves
• AV valves held in place by chordae tendinae (KOR-de TEN-di-nee), “heartstrings”– Attach valves to the papillary muscles at the wall of the
ventricles, prevent from opening backward into atria, ensure the valves open in one direction.
• Both the left AV (bicuspid/mitral valve, two cusps/flaps) and the right AV (tricuspid valve, three cusps/flaps) open when the ventricles relaxes.– When the ventricles contract, the AV valves close, forcing
blood to leave the heart via the two semilunar valves • SL valves (pulmonary valve and aortic valve)
– Guard the exits from the heart
AV valve
AV valve
Semilunar valve
Semilunar valve
Semilunar valve and atrioventricular valve, which is which?? Where are they located?
AV valves located between the atria and ventricles
Semilunar valves located between the ventricles and blood vessels of the heart
Fig. 43-9, p. 929
Superior vena cavaAorta
Left pulmonary arteries
Right pulmonary arteries
Pulmonary artery
Pulmonary veins
Pulmonary valveLeft atrium
Right atrium Mitral valve
Pulmonary veins Aortic valve
Chordae tendineae (“heartstrings”)Tricuspid valve
Papillary muscles
Right ventricle Left ventricle
Inferior vena cava Interventricular septum
Aorta
• Heart valves– Dictate a one-way flow of blood through the heart
• Blood begins its flow– With the right ventricle pumping blood to the
lungs
Mammalian Circulation: The Pathway
• In the lungs
– The blood loads O2 and unloads CO2
• Oxygen-rich blood from the lungs– Enters the heart at the left
atrium and is pumped to the body tissues by the left ventricle
• Blood returns to the heart– Through the right atrium
Pulmonary veins
Pulmonary artery
Posterior vena cava
Anterior vena cava
Right Left
Pathway of blood through the heart• The heart is a double pump that serves two
circulations.
• The blood vessels that carry blood to and from the lungs form the pulmonary circuit, strictly serves gas exchange.
• The right side of the heart (right ventricle) is the pulmonary circuit pump, to the lung.
Oxygen-poor OR carbon dioxide-rich blood returning from the body right atrium right ventricle pumps it to the lung via pulmonary artery
• The blood vessels that carry blood to and from all body tissues constitute the systemic circuit.
• The left side of the heart (left ventricle) is the systemic circuit pump, that has to pump blood through the entire systemic circulation against high resistance.
Oxygenated blood leaving the lungs return to the left atrium left ventricle pump through the aorta the body tissues (gases and nutrients exchange) right atrium through anterior and posterior vena cava
The cardiovascular system:On the right side, blood flows out to the lungs, pulmonary circulation
While on the left side, blood flows into aorta and to the systemic circulation.
Pulmonary vein
Right atrium
Right ventricle
Posteriorvena cava
Capillaries ofabdominal organsand hind limbs
Aorta
Left ventricle
Left atriumPulmonary vein
Pulmonaryartery
Capillariesof left lung
Capillaries ofhead and forelimbs
Anteriorvena cava
Pulmonaryartery
Capillariesof right lung
Aorta
Figure 42.5
1
10
11
5
4
6
2
9
33
7
8
• Although equal volumes of blood are flowing in the pulmonary and systemic circuits, the two ventricles have very unequal work loads.– The pulmonary circuit, served by the right ventricle is a low
pressure circulation whereas– The systemic circuit, associated by the left ventricle, takes
a long pathway through the entire body, has a higher blood pressure.
– The pressure needed to keep the blood flowing in the pulmonary circulation (typically 4kPa) is much less than needed in the systemic circulation (typically 16kPa)
– Thus, the walls of the left ventricle are thicker and more muscular than those in the right ventricle.
Anatomical differences in the right and left ventricles
Cardiac cycle
• The sequence of heart beat (heart contracts and relaxes)– In a rhythmic cycle called the cardiac cycle
• The contraction or pumping phase of the cycle– Is called systole (atrial systole; ventricular
systole)
• The relaxation or filling phase of the cycle– Is called diastole (atrial diastole; ventricular
diastole)
The cardiac cycle
Figure 42.7
Semilunarvalvesclosed
AV valvesopen
AV valvesclosed
Semilunarvalvesopen
Atrial and ventricular diastole
1
Atrial systole; ventricular diastole
2
Ventricular systole; atrial diastole
3
0.1 sec
0.3 sec0.4 sec
Cardiac cycle refers to events occurring during one heart beat.
For a human adult at rest, a pulse of about 75 beats per min, one complete cardiac cycle takes about 0.8s.
(1) During a relaxation phase, blood returning from large veins flows into the atria and ventricles.
(2) Atrial systole forces all remaining blood out of the atria into the ventricles.
(3) Ventricular systole pumps blood into the large arteries.
Fig. 43-11, p. 931
Superior vena cava Aorta Pulmonary artery
Semilunar valvesRight atriumPulmonary veinTricuspid valveLeft atriumInferior vena cavaMitral valve
1 Atrial systole. Atria contract, pushing blood through open tricuspid and mitral valves into ventricles. Semilunar valves are closed.
5 Period of falling pressure. Blood flows from veins into relaxed atria.
Right ventricle
Left ventricle
2 Beginning of ventricular systole. Ventricles contract; pressure within ventricles increases and closes tricuspid and mitral valves, causing first heart sound.
Heart sounds
4 Beginning of ventricular diastole. Pressure in relaxing ventricles drops below that in arteries. Semilunar valves snap shut, causing second heart sound.
3 Period of rising pressure. Semilunar valves open when pressure in ventricle exceeds that in arteries. Blood spurts into aorta and pulmonary artery.
“lub”
“dup”
Heart Sound• Normal heart sounds arise from the closing of heart
valves.
• During each cardiac cycle, two distinguishable sounds can be heard with a stethoscope : “lub-dup”
• The first sound– “lub” : created by the recoil of blood against the
closed AV valves (during ventricular systole). • The second sound
– “dup” : created by the recoil of blood against the semilunar valves (during ventricular diastole).
• Abnormal or unusual heart sounds are called heart murmurs (a defect in one or more valves).– Some are born with heart murmurs, some damaged by
infection (e.g. rheumatic fever).
“lub”
“dup”
Pulse: Think of the water hose!!
During the passage of blood from ventricle into the aorta and along the entire systemic circulation, a wave of dilation (expansion) sweeps along a linear fashion followed immediately by a wave of contraction.
These alternate contractions and dilations may be felt as the pulse if a finger is placed above an artery that lies close to skin.
The pulse is actually a measure of the heartbeat.
Pulse• The elastic walls of the arteries expand
when they receive the blood expelled from the ventricles.
• By feeling your pulse, your heart rate can be measured.
• Pulse: the rhythmic stretching of arteries caused by the pressure of blood driven by the powerful contractions of the ventricles
Cardiac output• The volume of blood that left the ventricle,
pumps into the systemic circuit in 1 minute is called– Cardiac output
• Cardiac output depends on two factors:– (1) Heart rate (pulse) = no. of beats (ventricular
contraction) per minute – (2) Stroke volume = the amount of blood pumped by
left ventricle with each beat.
Cardiac output (L/min) = HR (beats/min) X SV (ml/beat)
= 70 beats/min X 75 mL/beat = 5.25 L/min
Coordination of the heart
• The heart has an innate ability to beat on their own.
• The sinoatrial node (SAN), a small patch of specialized cardiac muscle, located in the wall of the right atrium near the entrance of the anterior vena cava.
• It acts as the pacemaker, sets the rhythm of the heart
• The pacemaker is influenced by– Nerves, hormones, body temperature (temp, HR)
and exercise.
Sinoatrial node (SAN)
• The cells of the SAN are spontaneously active or myogenic (self excitable), contract rhythmically in the absence of stimulation.
• Nerve that carry impulse to the heart, influence rate and strength of contraction, do NOT initiate heartbeat
• Excitation originating in the SAN spreads out across the atria, producing a uniform contraction called atrial systole, which fill ventricles with blood.
• Excitation must pass to the ventricles by the way of the atrioventricular node (AVN), a second group of specialized cells located near the base of atria.
Coordination of the heart beat
• From the AVN, the impulse sweeps to the atrioventricular bundle (bundle of His) and through the right and left bundle branches.
• The bundle branches carry signals downward to the base of the heart.
• The signals are transmitted to a network of Purkinje fibers within the ventricle walls.
• Thus, the contraction, called ventricular systole, starts at the bottom of the heart and spread upwards, forcing the blood out from the ventricles into the aorta and pulmonary artery.
Coordination of the heart beat….continue
SAN> Atrial muscle fibers (atria contract)>AVN > AV bundle “Bundle of His”> Right and Left AV bundle branches > Purkinje fibers> ventricular fibers (ventricles contract)
Fig. 43-10a, p. 930
Right atrium
SA node or pacemaker
Left atrium
AV bundleAV node
Purkinje fibersLeft ventricle
Right and left branches of AV bundleRight ventricle
1.
2. 3.
4.
5.
Electrocardiogram (ECG)• The electrical activity of a person’s heart can be
detected by placing metal electrodes on the external surface of his body, usually on the legs, arms and chest.
• The graphic recording of electrical changes during the heart activity, called an electrocardiogram (ECG).
• Diagnosis of heart diseases: monitoring changes in heart rate (tracing electrical changes in the heart), used in conjunction with exercise machines.
• The normal ECG pattern
Abnormalities in the ECGWhat does that implies?
Irregular rhythm of the heartImpulse transmission is delayed,
blocked at some point in the conduction of the heartWhat is the solution??
Artificial pacemakers
P-wave, QRS region, T-wave
• The P-wave represents the electrical activity (atrial depolarization, loss of resting potential) and contraction of the atria as excitation spreads outwards from the SAN.
• QRS region corresponds to excitation of the ventricles (ventricular depolarization; ventricular contraction). Its complicated shape reveals the different size of the two ventricles and the time required for each to depolarize.
• The final T-wave signals recovery of the ventricles (ventricular repolarization) at the end of contraction, muscle relaxing, ventricles starting to fill with blood
Each beat of the heart is characterized by five separable wave regions on the ECG.
Fig. 40-7a, p. 853
Spike
Depolarization Repolarization
Threshold level
Resting state
Mem
bra
ne
po
ten
tial
(m
V)
Time (milliseconds)
(a) Action potential.
The control of heart rhythm2 Signals are delayed
at AV node.1 Pacemaker generates
wave of signals to contract.
3 Signals passto heart apex.
4 Signals spreadThroughoutventricles.
Figure 42.8
SA node(pacemaker)
AV node Bundlebranches
Heartapex
Purkinjefibers
ECG
P
Q
R
S
T
Bundle of His
• The pattern of circulation: – Blood is pumped through pulmonary and systemic
circuits
• The pulmonary circulation oxygenates the blood• The systemic circulation delivers blood to the
tissues– The carotid arteries supply the brain (head) & neck– The subclavian arteries supply the upper appendages– The mesenteric arteries supply the intestines– The renal arteries supply the kidneys– The iliac arteries supply the lower appendages
Systemic circulation
• Veins return blood to the right side of the heart– Jugular veins return blood from the
brain– Subclavian veins, from the upper
appendages– Renal veins, from kidneys– Iliac veins, from lower appendages– Hepatic veins, from the liver
Renal, iliac and hepatic veins empty into the Posterior vena cava
Jugular and subclavian veins empty into the Anterior vena cava
Systemic circulation
Blood vessel: The blood’s highway
• Arteries – Carry blood from the heart– Smaller arteries: arterioles– Branch into arterioles that convey blood to capillaries
• Capillaries– The sites of chemical exchange between the blood and interstitial fluid– Network of these vessels: capillary beds
(Lies between arterioles and venules) – Capillaries converge into venules and venules converge into veins.
• Veins– Return blood to the heart– Smaller veins: venules
Blood vessels: Arteries> arterioles> capillaries> venules >
veins
REMEMBER: Arteries and veins are distinguished by the direction in which they carry blood, NOT by the characteristic of the blood they contain.
Blood Vessel: Structure and Function
The “infrastructure” of the circulatory system
– network of blood vessels
All blood vessels (artery, arteriole, venule, vein except capillaries)
– are built of three similar layers; (1)Outer layer: Connective tissue (2)Middle layer: Smooth muscle (3)Inner layer: Endothelium
Capillaries: lack the two outer layers, consist of endothelium and basement membrane
- To facilitate the exchange of substances between the blood and the interstitial fluid that bathes the cell.
Figure 42.9: The structure of blood vessels.
Artery Vein
100 µm
Artery Vein
ArterioleVenule
Connectivetissue
Smoothmuscle
Endothelium
Connectivetissue
Smoothmuscle
Endothelium
Valve
Endothelium
Basementmembrane
Capillary
Arteries(1)Connective tissue (tunica externa: inelastic)(2)Smooth muscle (tunica media: thickest layer) The functional contractions of the artery are
carried out by this layer.(3) Endothelium (intima: elastic membrane)
Veins • Have similar 3 structure walls except that they
are thinner.• Rely on a series of one-way valves working
together with the squeezing pressure exerted by the nearby skeletal muscle.
• Structural differences in arteries, veins, and capillaries– Correlate with their different functions
• Arteries have thicker walls (middle and outer layers)
– To accommodate the high pressure of blood pumped from the heart
– Their elasticity helps maintain blood pressure even when the heart relaxes between contractions.
• In the thinner-walled veins– Blood flows back to the heart mainly as a result
of muscle action– Blood is convey back to the heart at low velocity
and pressure
Figure 42.10: Blood flow in veins
Direction of blood flowin vein (toward heart)
Valve (open)
Skeletal muscle
Valve (closed)
Contraction of skeletal muscles helps move blood through the veins.
Several mechanisms assist the return of venous blood to the
heart(1) Rhythmic contraction of smooth muscles in
walls of venules and vein(2) Contraction of skeletal muscles during
exercise(3) Change in pressure within thoracic (chest) cavity during inhalation causes vena cava and other large vein expand and filled with blood
Blood flow velocity
• The velocity of blood flow varies in the circulatory system– And is slowest in the
capillary beds as a result of the high resistance and large total cross-sectional area
5,0004,0003,0002,0001,000
0
Aor
ta
Art
erie
s
Art
erio
les
Cap
illar
ies
Ven
ules
Vei
ns
Ven
ae c
avae
Pre
ssur
e (m
m H
g)V
eloc
ity (
cm/s
ec)
Are
a (c
m2)
Systolicpressure
Diastolicpressure
50403020100
120100806040200
Figure 42.11: The interrelationship of blood flow velocity, cross sectional area pf blood vessels and blood pressure
Blood pressure
depends on blood flow and resistance to blood flow
CO increases, increase blood flow, blood pressure increases, BP greatest in the artery, very low in the vein
Peripheral resistance> friction between blood and vessel’s wall---blood viscosity, size of the blood vessel lumen, total blood vessel length
Vasoconstriction of bv raises BP, vasodilation lowers BPDuring hemorrhage or chronic bleeding, blood volume reduced, blood pressure drop.
A high dietary in-take of salts causes water retention, increases blood volume, raises blood pressure.
Blood PressureBlood Pressure
–Is the force that blood exerts against the inner wall of a vessel–Determined by CO, blood vol. , and resistance to blood flow–Expressed as a fraction, systolic--numerator, diastolic --denominator
Systolic pressure–Is the pressure in the arteries during ventricular systole–Is the highest pressure in the arteries–< 120 mm Hg
Diastolic pressure–Is the pressure in the arteries during diastole–Is lower than systolic pressure–< 80 mm Hg
A normal blood pressure,
measured in the upper arm with a sphygmomanomet
er—110/73 mm Hg
The blood pressure• Produced by two primary events
The first force: the force of the heartbeat imposed on the blood leaving the ventricle (cardiac output/blood flow)
The second force: the peripheral resistance (back pressure) to that force, imposed by the arteries and, more significantly, the arterioles
For example,
When water moves through a garden hose, the pressure within the hose is determined by the head of pressure at the source and the resistance along the hose and its end. If the nozzle of the hose is constricted, the hydrostatic pressure will rise. Similarly, if the hose itself is sharply bent, the resistance to flow increases sharply and the pressure will go way up.
Blood pressure
Artery
Rubber cuffinflatedwith air
Arteryclosed
120
Pressurein cuff above 120
A typical blood pressure reading for a 20-year-oldis 120/70. The units for these numbers are mm of mercury (Hg); a blood pressure of 120 is a force that can support a column of mercury 120 mm high.
1
A sphygmomanometer, an inflatable cuff attached to apressure gauge, measures blood pressure in an artery.The cuff is wrapped around the upper arm and inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery.
2 A stethoscope is used to listen for sounds of blood flow
below the cuff. If the artery is closed, there is no pulse below the cuff. The cuff is gradually deflated until blood begins to flow into the forearm, and sounds from blood pulsing into the artery below the cuff can be heard with the stethoscope. This occurs when the blood pressure is greater than the pressure exerted by the cuff. The pressure at this point is the systolic pressure.
3
The cuff is loosened further until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure remaining in the artery when the heart is relaxed.
4
120
Pressurein cuff below 120
Pressurein cuff below 70
Sounds audible instethoscope
Sounds stop
Blood pressurereading: 120/70
70
Figure 42.12: Measurement of blood pressure. Blood pressure is recorded as two numbers separated by a slash. First number= systolic pressure; the second number= diastolic pressure
Capillary Function• Capillaries in major organs are usually filled to
capacity (brain, heart, kidney and liver)– But in many other sites, the blood supply varies– Blood is divert from one destination to another
For example,
After a meal, blood supply increases in the digestive tract. During strenuous exercise, blood is diverted from the digestive tract and supplied more generously to skeletal muscles and skin.
• Two mechanisms regulate the distribution of blood in capillary beds– In one mechanism
• Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel
– In a second mechanism• Precapillary sphincters control the flow of
blood between arterioles and venules• Precapillary sphincters? -rings of smooth muscle located at the
entrance to capillary beds.
Capillary Function
Figure 42.13 a–c
Precapillary sphincters Thoroughfare
channel
ArterioleCapillaries
Venule
(a) Sphincters relaxed
(b) Sphincters contracted
VenuleArteriole
(c) Capillaries and larger vessels (SEM)
20 m
• The critical exchange of substances between the blood and interstitial fluid– Takes place across the
thin endothelial walls of the capillaries
• The difference between blood pressure and osmotic pressure– Drives fluids out of capillaries at the arteriole end and
into capillaries at the venule end• Interstitial fluid:
– The internal environmental in vertebrates, exchanges nutrients and wastes with blood carried in capillaries.
Capillary Red Blood cell
15 m
Tissue cell
INTERSTITIAL FLUID
CapillaryNet fluidmovement out
Net fluidmovement in
Direction of blood flow
Blood pressureOsmotic pressure
Inward flow
Outward flow
Pre
ssur
e
Arterial end of capillary Venule end
At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary.
Figure 42.14: Fluid exchange between capillaries and the interstitial fluid
At the arterial end of acapillary, blood pressure is
greater than osmotic pressure,and fluid flows out of the
capillary into the interstitial fluid.
Fluid Return by the Lymphatic System
• The lymphatic system functions– (1) Collects and returns interstitial fluid
to the blood– (2) Aids in body defense– (3) Absorbs lipids from the digestive tract
• Fluid reenters the circulation– Directly at the venous end of the
capillary bed and indirectly through the lymphatic system
• Interstitial fluid diffuses into tiny lymph capillaries intermingled among capillaries of the cardiovascular system.
• Once inside the lymphatic system, the fluid is called lymph.
• Its composition is about the same as that of interstitial fluid.
• The lymphatic system return lymph into the circulatory system, at the base of the subclavian veins
Fluid Return by the Lymphatic System
• Lymph vessels (like veins) – have valves, to prevent the backflow of fluid
toward the capillaries. – depend mainly the movement of skeletal muscles,
to squeeze fluid toward the heart.• Lymph nodes
– Filter the lymph and attack viruses and bacteria.– This defense is carried out by specialized white
blood cells that inhabit the lymph nodes.• Lymph capillaries
– penetrate small intestine villi and absorb fats, thus transporting them from the digestive system to the circulatory system.
Tonsils, thymus gland, and spleen—masses of lymph tissue, part of lymphatic system
The lymphatic system plays an important role in fluid homeostasis• Bloods enters a capillary network---
under high pressure, plasma forced out of the capillaries into tissues
• Plasma that leaves the b.v. called interstitial fluid OR tissue fluid---contain glucose, a.a., nutrients, var. of salts, oxygen
• Force pushing plasma out from blood is hydrostatic pressure (blood pressure against capillary wall)
A shortage of proteins within the blood, largely albumin, would inhibit the
reabsorption of fluid at the venule end of a capillary bed.
The failure to reabsorb fluid will produce a generalized swelling known as edema.
“Blood is a connective tissue with cells suspended in
plasma.”• Blood in the circulatory systems of
vertebrates– Is a specialized connective tissue
Blood
Blood: Composition and Function
• Blood consists of several kinds of cells– Suspended in a liquid matrix called
plasma, 55% of the blood vol.
• The cellular elements (platelets and blood cells)– Occupy about 45% of the volume of blood
Plasma• Blood plasma is ~90-92% water
• ~7-10% dissolved materials (Proteins, glucose, ions, hormones, wastes and gases)
– Inorganic salts in the form of dissolved ions, referred to as electrolytes
• Types of plasma proteins– E.g. Albumin, fibrinogen, globulins (, , γ or
Immunoglobulins)– Function in lipid transport, immunity, and blood
clotting
• plasma proteins---albumins and globulins– influence blood pH, blood’s osmotic pressure
(maintain blood vol.), and viscosity
Figure 42.15: The composition of mammalian plasma
Plasma 55%
Constituent Major functions
Water Solvent forcarrying othersubstances
SodiumPotassiumCalciumMagnesiumChlorideBicarbonate
Osmotic balancepH buffering, andregulation of membranepermeability
Albumin
Fibrinogen
Immunoglobulins(antibodies)
Plasma proteins
Ions (blood electrolytes)
Osmotic balance,pH buffering
Substances transported by bloodNutrients (such as glucose, fatty acids, vitamins)Waste products of metabolismRespiratory gases (O2 and CO2)Hormones
Defense
Separatedbloodelements
Clotting
The composition of mammalian plasma
When the proteins involved in blood
clotting removed from plasma, liquid called
serum
Cellular Elements
• Suspended in blood plasma are two classes of cells– Red blood cells, which transport oxygen– White blood cells, which function in defense
• A third cellular element, platelets– Are fragments of cells that are involved in
clotting (stop hemorrhage/bleeding)
The shape of the red blood cell is often described as a
biconcave disc.What is the evidence from this
photograph that these cells could have a biconcave shape?
Erythrocytes (RBC): “bags” of hemoglobin
• Red blood cells, or erythrocytes– Biconcave disc:
• thinner in the center than at the edges– 7- 8.5m in diameter, Lifespan: 120 days or 3-4
months– Are by far the most numerous blood cells– Produced within the red bone marrow of
certain bones: • Vertebrae, ribs, breastbone, skull bones and
long bones
RBC production, regulated by hormone, erythropoietin
RBC• Mature red blood cells lack a nucleus, have no
organelles
• The bulk of the RBC is taken up by protein hemoglobin. Hemoglobin is the chief transport protein involved in carrying oxygen.
• An erythrocyte contains about 250 million molecules of hemoglobin, Each hemoglobin binds up to four molecules of O2.
• When blood circulates through the liver and spleen, phagocytic cells remove worn-out RBCs from the circulationAnemia is a deficiency of hemoglobin, or no. of RBC, or BOTH---due to
bleeding, decreased production of hemoglobin or RBCs due to lack of iron, or destruction of RBCs (sickle cell anemia)
RBC: Facts!!Biconcave shape gives 30% more surface area
than a sphere Easily deformed—important in passing through
tiny capillariesRBCs have no mitochondria, don’t use the
oxygen they carry, rely on glucose absorbed from the blood plasma
Their metabolism entirely anaerobic!! (Hence, short lifespan)
Leukocytes (WBC)
• Larger than erythrocytes (RBC)• Have a nucleus, lack hemoglobin• The blood contains five major types of
white blood cells, or leukocytes– Basophils, eosinophils, neutrophils,
monocytes, and lymphocytes, – which function in defense (by phagocytizing bacteria and debris or by
producing antibodies)
Leukemia is a cancer of WBC, overabundance of these immature cells, leads to impaired clotting
Leucocytes (WBC)
Two main groups:• Granulocytes:
– Basophils, eosinophils, neutrophils>Have granules in their cytoplasm>Have a multilobed nucleus
• Nongranulocytes (agranulocytes)– Lymphocytes and monocytes
>Do NOT have granules and have nonlobular nuclei– Lymphocytes (T and B cells)
>T cells: attack cells containing bacteria>B cells: produce antibodies
Figure 42.15: Cellular elements of the mammalian blood
Cellular elements 45%
Cell type Numberper L (mm3) of blood
Functions
Erythrocytes(red blood cells) 5–6 million Transport oxygen
and help transportcarbon dioxide
Leukocytes(white blood cells)
5,000–10,000 Defense andimmunity
Eosinophil
Basophil
Platelets
NeutrophilMonocyte
Lymphocyte
250,000400,000
Blood clotting
Separatedbloodelements
The cellular elements of mammalian blood
Platelets (Thrombocytes)
• Are rounded bodies (cell fragments that bud off from megakaryocytes in bone marrow)
• 2-3m in diameter, no nuclei
• Essential in blood clotting, they initiate blood clotting process by releasing clotting factors
Stem Cells and the Replacement of Cellular
Elements
• The cellular elements of blood wear out– And are replaced constantly throughout
a person’s life
Erythrocytes, leukocytes, and platelets all develop from a common source
B cells T cells
Lymphoidstem cells
Pluripotent stem cells(in bone marrow)
Myeloidstem cells
Erythrocytes
PlateletsMonocytes
Neutrophils
Eosinophils
Basophils
Lymphocytes
Figure 42.16
–A single population of cells called pluripotent stem cells in the red marrow of bones
Pluripotent: ability to develop into many different cell types of the body
Blood Clotting
– The clotting process is initiated by injury to blood-vessel walls.
– The clot consists of a network of fibrin and blood cells
A cascade of complex reactions
– Converts fibrinogen to fibrin, forming a clot
5 µm
The clotting process begins when the endothelium of a vessel is damaged, exposing connective tissue in the vessel wall to blood. Plateletsadhere to collagen fibers in the connective tissue and release a substance thatmakes nearby platelets sticky.
1The platelets form a plug that providesemergency protectionagainst blood loss.
2
This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via amultistep process: Clotting factors released from the clumped platelets or damaged cells mix with clotting factors in the plasma, forming an activation cascade that converts a plasma protein called prothrombin to its active form, thrombin. Thrombin itself is an enzyme that catalyzes the final step of the clotting process, the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch (see colorized SEM).
3
Plateletplug
Collagen fibers
Platelet releases chemicalsthat make nearby platelets sticky
Clotting factors from:PlateletsDamaged cellsPlasma (factors include calcium, vitamin K)
Prothrombin Thrombin
Fibrinogen Fibrin
Fibrin clot Red blood cell
Figure 42.17
Cardiovascular disease
• atherosclerosis– Is caused by the buildup of cholesterol within
arteries
250 µm Atherosclerosis
(a) Normal artery (b) Partly clogged artery50 µm
Smooth muscle
Connective tissue
Endothelium
Plaque
Cardiovascular disease: Atherosclerosis
Atherosclerosis– narrowing of the coronary arteries,
inadequate supply of blood to the heart muscle, lead to angina.
– angina: pain in the chest because of narrowing of the arteries supplying blood to the heart muscle)
Cardiovascular diseases: disorders of the heart and the blood vessels
• Hypertension, or high blood pressure– Promotes atherosclerosis and increases the risk
of heart attack and stroke
• A heart attack– Is the death of cardiac muscle tissue resulting
from blockage of one or more coronary arteries
• A stroke– Is the death of nervous tissue in the brain,
usually resulting from rupture or blockage of arteries in the head
END OF LECTURE