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The Circulatory System
The Nature of Blood Circulation
A circulatory system distributes materials throughout the vertebrate body (and some invertebrates)
Uses a transport medium called blood. A heart is a muscular organ that pumps the
transport medium (blood) through vessels. Blood and interstitial fluid (fluid between cells)
make up the body’s internal environment
Two Kinds of Circulatory Systems
Open circulatory system (arthropods, mollusks)• Blood moves through hearts and large vessels, but
also mixes with interstitial fluid
Closed circulatory system (annelids, vertebrates)• Blood remains inside heart and blood vessels • Materials diffuse between blood and interstitial fluid
at capillaries
Fig. 37-2a, p. 638
pumpaorta heart
spaces or cavities in body tissues
A In a grasshopper’s open system, a heart (not like yours) pumps blood through a vessel, a type of aorta. From there, blood moves into tissue spaces, mingles with interstitial fluid, then reenters the heart at openings in the heart wall.
Open Circulatory Systems
Fig. 37-2b, p. 638
dorsal blood vesselpump
large-diameter blood vessels
large-diameter blood vessels
two of five hearts
ventral blood vessels
gut cavity capillary bed (many small vessels that serve as a diffusion zone)
B The closed system of an earthworm confines blood inside pairs of muscular hearts near the head end and inside many blood vessels.
Closed Circulatory Systems
Evolution of Circulation in Vertebrates
Fishes• Heart with two chambers• Single circuit of circulation
Amphibians• Heart with three chambers• Two partially separated circuits
Birds and mammals• Heart with four chambers• Two fully separate circuits
Fig. 37-3a, p. 639
A In fishes, the heart has two chambers: one atrium and one ventricle. Blood flows through one circuit. It picks up oxygen in the capillary beds of the gills, and delivers it to capillary beds in all body tissues. Oxygen-poor blood then returns to the heart.
capillary beds of gills
heart
rest of body
Single Circuit of Circulation
Fig. 37-3b, p. 639
lungs B In amphibians, the heart has three chambers: two atria and one ventricle. Blood flows along two partially separated circuits. The force of one contraction pumps blood from the heart to the lungs and back. The force of a second contraction pumps blood from the heart to all body tissues and back to the heart.
right atrium
left atrium
ventricle
rest of body
Two Partially Circuits of Circulation
Circulation in Birds and Mammals
The four-chambered heart has two separate halves, each with an atrium and a ventricle
Each half pumps blood in a separate circuit• Pulmonary circuit: Blood flows from right half of
heart, to lungs (gains oxygen), to left half of heart • Systemic circuit: Blood flows from left half of
heart, to body (loses oxygen), to right half of heart
Fig. 37-3c, p. 639
C In birds and mammals, the heart has four chambers: two atria and two ventricles. The blood flows through two fully separated circuits. In one circuit, blood flows from the heart to the lungs and back. In the second circuit, blood flows from the heart to all body tissues and back.
lungs
right atrium
left atrium
right ventricle left ventricle
rest of body
Two Fully Separate Circuits of Circulation
Fig. 37-3d, p. 639
D Why flow slows in capillaries. Picture a volume of water in two fast rivers flowing into and out of a lake. The flow rate is constant, with an identical volume moving from points 1 to 3 in the same interval. However, flow velocity decreases in the lake. Why? The volume spreads out through a larger cross-sectional area and flows forward a shorter distance during the specified interval.
lake
river in river out
1 2 3 1 2 3
1 2 3
Analogy of Slowing Blood in Capillaries
Overview of Circulatory Systems
Fill in the blank.
Many animals have either an ________ or a ________ circulatory system that transports substances to and from all body tissues.
All vertebrates have a _______ circulatory system, in which blood is _______________________________.
Overview of Circulatory Systems
Many animals have either an open or a closed circulatory system that transports substances to and from all body tissues
All vertebrates have a closed circulatory system, in which blood is always contained within the heart or blood vessels
Characteristics of Blood
Blood, considering it is made of cells, can be called a large interconnect tissue.
Blood consists mainly of plasma, a protein-rich fluid that carries wastes, gases and nutrients.
Blood cells and platelets form in bone marrow and are transported in plasma.• Platelets are fragments of megakaryocytes,
active in clotting.
Blood Cells
Red blood cells (erythrocytes)• Contain hemoglobin that carries oxygen from
lungs to tissues• Quantified in cell count
White blood cells (leukocytes)• Defend the body from pathogens• Neutrophils, basophils, eosinophils, monocytes,
and lymphocytes (B and T cells)
Fig. 37-4, p. 640
Stepped Art
Components Amounts Main Functions
Plasma Portion (50-60% of total blood volume)
Cellular Portion (40-50% of total blood volume; numbers per microliter)
1. Water 91-92% of totalplasma volume
Solvent
2. Plasma proteins (albumins, globulins, fibrinogen, etc. 7-8%
Defense, clotting, lipid transport, extracellular fluid volume controls
3. Ions, sugars, lipids, amino acids, hormones, vitamins, dissolved gases, etc.
1-2%Nutrition, defense, respiration, extracellular fluid volume controls, cell communication, etc.
1. Red blood cells
Red blood cell
4,600,000-5,400,000Oxygen, carbon dioxide transport to and from lungs
2. White blood cells: Neutophils Lymphoctyes Monocytes (macrophages) Eosinophils Basophils
White blood cell
3,000-6,7501,000-2,700150-720100-38025-90
Fast-acting phagocytosisImmune responsesPhagocytosisKilling parasitic wormsAnti-inflammatory secretions
3. Plateletsplatelet
250,000-300,000 Roles in blood clotting
Components of Human Blood
Fig. 37-5, p. 641
stem cell in bone marrow
myeloid stem cell lymphoid stem cell
red blood cell granulocyte monocyteprecursor precursor precursor
megakaryocytes
platelets red blood cells (erythrocytes)
neutrophilseosinophils
basophils monocytes (immature
phagocytes)B lymphocytes (mature in bone
marrow)
T lymphocytes (mature in
thymus)
Cellular Components of Human Blood
Hemostasis
Hemostasis = Heme (blood) stasis (balance)• Keeping blood pressure/volume stable.
How do we stop bleeding? Initiated by a hormone cascade when an injury
is sustained and blood vessels are broken. Hemostasis is a three-phase process that stops
blood loss, constructs a framework for repairs• Damaged vessel constricts• Platelets accumulate• Cascading enzyme reactions involving plasma
proteins cause clot formation
Fig. 37-6, p. 642
Stepped Art
StimulusA blood vessel is damaged.
Phase 1 responseA vascular spasm constricts the vessel.
Phase 2 responsePlatelets stick together plugging the site.
Phase 3 responseClot formation starts:
2. Factor X converts prothrombin in plasma to thrombin
3. Thrombin converts fibrinogen, a plasma protein, to fibrin threads.
4. Fibrin forms a net that entangles cells and platelets, forming a clot.
1. Enzyme cascade results in activation of Factor X.
Three-Phase Process of Hemostasis
Blood Typing
Blood type• Genetically determined differences in molecules
on the surface of red blood cells
Agglutination• Clumping of foreign cells by plasma proteins• When blood of incompatible types mixes, the
immune system attacks the unfamiliar molecules
Agglutination
Light micrographs showing (a) an absence of agglutination in a mixture of two different yet compatible blood types and (b) agglutination in a mixture of incompatible types.
ABO Blood Typing
Blood type O is a universal donor; blood type AB can receive blood from any donor
Fig. 37-8, p. 643
Blood Type of DonorO A B AB
O
A
B
Blo
od
Typ
e o
f R
ecip
ien
t
AB
Mixing ABO Blood Types
Rh Blood Typing
An Rh- mother may develop Rh+ antibodies if blood from an Rh+ child enters her bloodstream during childbirth
These antibodies may attack the red blood cells of the next Rh+ fetus
Rh Complications of Pregnancy
How Rh differences can complicate pregnancy.
Blood Composition and Function
Fill in the blanks. Vertebrate blood is a fluid connective ________.
It consists of _______, ________, ________, and _________ (the transport medium)
_____ _______ cells function in gas exchange; _____ _______ cells defend tissues, and _________ function in clotting
Blood Composition and Function
Vertebrate blood is a fluid connective tissue
It consists of red blood cells, white blood cells, platelets, and plasma (the transport medium)
Red blood cells function in gas exchange; white blood cells defend tissues, and platelets function in clotting
Human Cardiovascular System
The term “cardiovascular” comes from the Greek kardia (for heart) and Latin vasculum (vessel)
In a cardiovascular circuit, blood flows from the heart through arteries, arterioles, capillaries, venules, veins, and back to the heart.
Two Circuits of the Human Cardiovascular System
Pulmonary circuit• Oxygen-poor blood flows from the heart, through
a pair of lungs, then back to the heart• Blood takes up oxygen in the lungs
Systemic circuit• Oxygenated blood flows from the heart (through
the aorta) into capillary beds where it gives up O2 and takes up CO2, then flows back to the heart
Fig. 37-10a, p. 644
right pulmonary artery left pulmonary artery
capillary bed of right lung
capillary bed of left lung
pulmonary trunk
to systemic circuit
from systemic circuit
pulmonary veins
heart
Pulmonary Circuit of the Human Cardiovascular System
Accessing the lungs to rid blood stream of excess CO2 & to replenish O2
Blood vessels carrying oxygenated blood are shown in red. Those that hold oxygen-poor blood are color-coded blue.
capillary beds of head, upper extremities
(pulmonary vessels to and from thoracic cavity)
to pulmonary circuit
aorta
from pulmonary circuit
heart
capillary beds of other organs in thoracic cavity(diaphragm, the
muscular partition between thoracic and abdominal cavities) capillary bed of liver
capillary beds of intestines
BSystemic Circuit for
Blood Flow capillary beds of other abdominal organs and lower extremities
Systemic Circuit of the Human Cardiovascular System
Pulmonary and systemic circuits of the human cardiovascular system. Blood vessels carrying oxygenated blood are shown in red. Those that hold oxygen-poor blood are color-coded blue.
Accessing the rest of the body to deliver O2
& to retrieve CO2
The Pulmonary CircuitDoes?
The Systemic CircuitDoes?
Deo
xyge
nate
d bl
ood
brou
ght t
o th
e lu
ngs
to re
plen
ish
O2
Oxygenated blood sent
to heart to distribute O2
throughout body
Blue = deoxygenatedRed = oxygenated
Fig. 37-12, p. 645
food, water intake oxygen intake
Digestive System Respiratory System elimination of carbon dioxide
nutrients, water, salts oxygen carbon dioxide
Circulatory System Urinary System
water, solutes
elimination of food residues
rapid transport to and from all living cells
elimination of excess water, salts, wastes
The Circulatory System and Homeostasis
Functional links between the circulatory system and other organ systems with major roles in maintaining the internal environment.
The Human Heart
A sac of connective tissue (pericardium) surrounds the heart muscle (myocardium)
Endothelium lines heart chambers and blood vessels
Heart valves keep blood moving in one direction• AV valves separate atria and ventricles• Semilunar valves separate ventricles and arteries
Fig. 37-13b, p. 646
right lung left lungribs 1–8
B The heart is located between the lungs in the thoracic cavity.
1
3
2
4
5
6
7
8pericardium
diaphragm
The Human Heart
Fig. 37-13a, p. 646
superior vena cava (flow from head, arms)
arch of aorta
trunk of pulmonary arteries (to lungs)right semilunar valve
(shown closed) to pulmonary trunk left semilunar valve
(closed) to aortaright pulmonary veins (from lungs) left pulmonary veins
(from lungs)
right atrium left atrium
right AV valve (opened)
left AV valve (opened)
right ventricle left ventricle
(muscles that prevent valve from everting)
endothelium and underlying connective tissue
inferior vena cava (from trunk, legs)
myocardium
septum (partition between heart’s two halves)
inner layer of pericardium
heart’s apex
The Human Heart
Fig. 37-13c, p. 646
C Outer appearance. Pads of fat on the heart’s surface are normal.
The Human Heart
The Cardiac Cycle
Cardiac cycle: Heart muscle alternates between diastole (relaxation) and systole (contraction)• Blood collects in atria• AV valves open, blood flows into ventricles• Contraction of ventricles drives blood circulation• Ventricles contract with a wringing motion from
bottom to top
Fig. 37-14, p. 647
D Ventricles relax. Semilunar valves close as atria begin filling for the next cardiac cycle.
A Atria fill. Fluid pressure opens the AV valves, blood flows into the ventricles.
B Next, atria contract. As fluid pressure rises in the ventricles, AV valves close.
C Ventricles contract. Semilunar valves open. Blood flows into aorta and pulmonary artery.
Stepped Art
The Cardiac Cycle
Cardiac Muscle
Cardiac muscle cells are striated (divided into sarcomeres) and have many mitochondria
Cells attach end to end at intercalated discs
Neighboring cells communicate through gap junctions that conduct waves of excitation
Fig. 37-15, p. 647
intercalated disk a branching cardiac muscle cell (part of one cardiac muscle fiber)
b Part of a gap junction across the plasma membrane of a cardiac muscle cell. The junctions connect cytoplasm of adjoining cells and allow electrical signals that stimulate contraction to spread swiftly between them.
Cardiac Muscle Cells and Gap Junctions
How the Heart Beats
Cardiac pacemaker (SA node)• A clump of noncontracting cells in the right
atrium’s wall spontaneously fires action potentials about 70 times per minute
Cardiac conduction system• Signal spreads from SA node to AV node and
junctional fibers in the septum, so heart contracts in a coordinated fashion
Fig. 37-16, p. 647
SA node (cardiac pacemaker)
AV node (the only point of electrical contact between atria and ventricles)
junctional fibers
branchings of junctional fibers (carry electrical signals through the ventricles)
The Cardiac Conduction System
The Human Heart and Two Flow Circuits
Fill in the blanks The ______-chambered human heart pumps
blood through _____ separate circuits of blood vessels
One circuit extends through _____________, the other through _______ tissue only.
Both circuits loop back to the __________, which keeps blood flowing through the _______ circuits.
The Human Heart and Two Flow Circuits
The four-chambered human heart pumps blood through two separate circuits of blood vessels
One circuit extends through all body regions, the other through lung tissue only.
Both circuits loop back to the heart, which keeps blood flowing through the two circuits.
Part II
Pressure, Transport, and Flow Distribution
Fig. 37-11, p. 645
Jugular Veins Carotid Arteries
Ascending Aorta Superior Vena Cava
Pulmonary Arteries
Pulmonary VeinsCoronary Arteries
Hepatic Vein Brachial Artery
Renal Vein Renal Artery
Inferior Vena Cava Abdominal Aorta
Iliac Veins Iliac Arteries
Femoral ArteryFemoral Vein
Major Blood Vessels of the Human Cardiovascular System
Pressure, Transport, and Flow Distribution
Contracting ventricles put pressure on the blood, forcing it through a series of vessels• Arteries carry blood from ventricles to arterioles• Arterioles control blood distribution to capillaries• Capillaries exchange substances• Venules collect blood from capillaries• Veins deliver blood back to heart
Fig. 37-17a, p. 648
outer coat
smooth muscle
basement membrane endothelium
Artery
elastic tissue elastic tissue
Human Blood Vessels
Fig. 37-17b, p. 648
outer coat
smooth muscle rings over elastic tissue
basement membrane endothelium
Arteriole
Human Blood Vessels
Fig. 37-17c, p. 648
basement membrane endothelium
Capillary
(venules have a similar structure)
Human Blood Vessels
Fig. 37-17d, p. 648
outer coat
smooth muscle, elastic fibers
basement membrane endothelium
Vein
valve
Human Blood Vessels
Blood Pressure
Blood pressure• The pressure exerted by blood on the walls of
blood vessels• Highest in arteries, then declines through circuit• Rate of blood flow depends on the difference in
blood pressure between two points, and resistance to flow
Fig. 37-18, p. 648
arteries capillaries veins
arterioles venules
Blood Pressure in the Systolic Circuit: Plot of fluid pressure for a volume of blood as it flows through the systemic circuit. Systolic pressure occurs when ventricles contract, diastolic when ventricles are relaxed.
Blood Flow
Thick, elastic arteries smooth out variations in blood pressure during the cardiac cycle
Arterioles respond to signals from the autonomic and nervous systems, and to chemical signals, to direct blood flow to different parts of the body
Fig. 37-19, p. 649
liver 6%
heart’s right half heart’s left half
lungs100%
skeletal muscle
brain13%
15%kidneys
20%digestive tract
21%
cardiac muscle3%
bone5%
skin 9%
all other regions 8%
Distribution of Cardiac Output in a Resting Person
Figure It Out: What percentage of the brain’s blood supply arrives from the heart’s right half? Answer: None
Controlling Blood Pressure
Blood pressure depends on total blood volume, how much blood the ventricles pump (cardiac output), and whether arterioles are constricted or dilated
Receptors in the aorta and carotid arteries monitor blood pressure and send signals to the medulla, which regulates cardiac output and arteriole diameter
Measuring Blood Pressure
Diffusion at Capillaries, Then Back to the Heart
Capillary• A cylinder of endothelial cells, one cell thick• Capillary beds are diffusion zones, where blood
exchanges substances with interstitial fluid• Hydrostatic pressure moves materials out
(ultrafiltration)• Osmotic pressure moves water in (capillary
reabsorption)
blood to venule
high pressure causes outward flow
inward-directed osmotic movementcells of
tissue
Bblood from arteriole
A
Fluid Movement at a Capillary Bed
Fluid movement at a capillary bed. Fluid crosses a capillary wall by way of ultrafiltration and reabsorption. (a) At the capillary’s arteriole end, a difference between blood pressure and interstitial fluid pressure forces out plasma, but few plasma proteins, through clefts between endothelial cells of the capillary wall. Ultrafiltration is the outward flow of fluid across the capillary wall as a result of hydrostatic pressure. (b) Reabsorption is the osmotic movement of some interstitial fluid into the capillary. It happens when the water concentration between interstitial fluid and the plasma differs. Plasma, with its dissolved proteins, has a greater solute concentration and therefore a lower water concentration. Reabsorption near the end of a capillary bed tends to balance ultrafiltration at the start of it. Normally, there is only a small net filtration of fluid, which vessels of the lymphatic system return to blood (Section 37.10).
Venous Pressure
Venules deliver blood from capillaries to veins
Veins deliver blood to the heart• Large-diameter, blood volume reservoirs• Valves help prevent backflow• Amount of blood in veins varies with activity level
Fig. 37-22a, p. 651
venous valve
Venous Valve ActionVenous valve action. (a) Valves in medium-sized veins prevent the backflow of blood. Adjacent skeletal muscles helps raise fluid pressure inside a vein. (b) These muscles bulge into a vein as they contract. Pressure inside the vein rises and helps keeps blood flowing forward. (c) When muscles relax, the pressure that they exerted on the vein is lifted. Venous valves shut and cut off backflow.
blood flow to heart
valve open
valve closed
valve closed
valve closed
Key Concepts Blood Vessel Structure and Function
The heart pumps blood rhythmically, on its own
Adjustments at arterioles regulate how blood volume is distributed among tissues
Exchange of gases, wastes, and nutrients between the blood and tissues takes place at capillaries
Blood and Cardiovascular Disorders
Red blood cell disorders• Anemias, beta-thalassemias, polycythemia
White blood cell disorders• Infectious mononucleosis, leukemias, lymphomas
Clotting disorders• Hemophilia, thrombus, embolus
Blood and Cardiovascular Disorders
Atherosclerosis• Buildup of lipids in the arterial wall that narrows
the lumen, may rupture and trigger heart attack
Fig. 37-23a, p. 652
wall of artery, cross-section
unobstructed lumen of a normal artery
Fig. 37-23b, p. 652
atherosclerotic plaque
blood clot sticking to plaque
narrowed lumen
Clogged Coronary Arteries
Fig. 37-24a, p. 653
coronary artery
The photo shows coronary arteries and other blood vessels that service the heart. Resins were injected into them. Then the cardiac tissues were dissolved to make an accurate, three-dimensional corrosion cast.
Fig. 37-24b, p. 653
aorta
coronary artery blockage
location of a shunt made of a section taken from one of the patient’s other blood vessels
The sketch shows two coronary bypasses (color-coded green), which extend from the aorta past two clogged parts of the coronary arteries.
Blood and Cardiovascular Disorders
Hypertension – a silent killer• Chronic blood pressure above 140/90
High blood pressure and atherosclerosis increase the risk of heart attack and stroke
Fig. 37-25, p. 653
one normal heartbeat
0 0.2 0.4 0.6 0.8a time (seconds)
bradycardia (here, 46 beats per minute)
tachycardia (here, 136 beats per minute)
b
cventricular fibrillation
d
Blood and Cardiovascular Disorders
Arrhythmias – abnormal heart rhythms• EKGs record
electrical activity of cardiac cycle
Risk Factors
Cardiovascular disorders are the leading cause of death in the United States
Risk factors• Tobacco smoking, family history, hypertension,
high cholesterol, diabetes mellitus, obesity, age, physical inactivity, gender
Key Concepts When the System Breaks Down
Cardiovascular problems include clogged blood vessels or abnormal heart rhythms
Some problems have a genetic basis; most are related to age or life-style
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