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Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 33
Circulation
(Sections 33.5 - 33.8)
Albia Dugger • Miami Dade College
33.5 Characteristics
and Functions of Blood
• Plasma, the protein-rich fluid portion of blood, distributes
essential nutrients and solutes to cells
• Blood cells tumbling along in plasma carry oxygen and defend
the body
Functions of Blood
• The function of the circulatory system is to move blood
• Blood carries essential oxygen and nutrients to cells, and
washes away their metabolic wastes
• Blood facilitates internal communications by distributing
hormones and serves as a highway for cells and proteins that
protect and repair tissues
Human Blood
Volume and Composition
• Average-sized adults hold about 5 liters of blood (more than
10 pints)
• Blood consists of plasma, blood cells, and platelets
• Plasma is mostly water
• Platelets and all blood cells arise from stem cells in bone
Plasma
• Plasma constitutes about 50-60% of the blood volume
• Plasma is mostly water with hundreds of different plasma
proteins dissolved in it
• plasma
• Fluid portion of blood
Red Blood Cells
• Red blood cells (erythrocytes) contain hemoglobin that
functions in oxygen transport
• Erythrocytes transport oxygen from lungs to aerobically
respiring cells and carry carbon dioxide wastes from them
•
red blood cell (ertythrocyte)
• Hemoglobin-filled blood cell that carries oxygen
Cell Count
• A cell count is a measure of the quantity of cells of one type
in 1 microliter (1/1,000,000 liter) of blood
• Anemia is a disorder in which the red blood cell count
declines or red blood cells are defective
• cell count
• Number of cells of one type per microliter of blood
White Blood Cells
• White blood cells (leukocytes) have roles in day-to-day
tissue maintenance and repair and in defenses against
pathogens
• The cells differ in their size, nuclear shape, and staining traits,
as well as function
• white blood cell (leukocyte)
• Blood cell with a role in housekeeping and defense
White Blood Cells (cont.)
• Neutrophils, the most abundant white cells, are phagocytes
that engulf bacteria and debris
• Eosinophils attack larger parasites, such as worms
• Basophils secrete chemicals that have a role in inflammation
White Blood Cells (cont.)
• Monocytes move into the tissues, where they develop into
phagocytic cells (macrophages) that interact with lymphocytes
to bring about immune responses
• There are two types of lymphocytes: B cells and T cells
• Both protect the body against specific threats
• B cells mature in bone,
• T cells mature in the thymus
Platelets and Hemostasis
• Platelets adhere to an injured site and help form a blood clot
• Large cells (megakaryocytes) form in bone marrow and break
up into membrane-wrapped fragments of cytoplasm
(platelets) that last five to nine days
• Clotting (hemostasis) stops blood loss from an injured vessel
and provides a framework to begin repairs
Key Terms
• platelet
• Cell fragment that helps blood clot
• hemostasis
• Process by which blood clots in response to injury
Hemostasis
• Clot formation involves a cascade of enzyme reactions:
• Fibrinogen, a soluble plasma protein, is converted to
insoluble fibrin by an enzyme (thrombin) which circulates
in blood as the inactive precursor prothrombin
• Prothrombin is activated by an enzyme that is activated by
another enzyme, and so on
• fibrin
• Threadlike protein formed during blood clotting from the
soluble plasma protein fibrinogen
Steps in Hemostasis
•
•
•
•
Stimulus: A blood vessel is damaged
Phase 1 response: Vessel constricts
Phase 2 response: Platelets stick together, plugging the site
Phase 3 response: Clot formation
1. Enzyme cascade activates enzyme thrombin
2. Thrombin converts fibrinogen to fibrin threads
3. Fibrin forms a net that entangles cells and platelets,
forming a clot
Hemostasis
• Final clotting
phase: blood
cells and
platelets in a
fibrin net
Components of Human Blood
Components of Human Blood
Components
Amounts
Main Functions
Plasma Portion (50–60% of total blood volume)
1. Water
91–92% of total Solvent
plasma volume Defense, clotting, lipid
2. Plasma proteins
transport, extracellular
(albumins,
7–8%
fluid volume controls
globulins,
Nutrition, defense,
3. fibrinogen,
Ions, sugars,
lipids, 1–2%
etc.)
respiration, extracellular fluid
amino acids, hormones,
volume controls, cell
vitamins, dissolved
communication, etc.
gases, etc.
Cellular Portion (40–50% of total blood volume; numbers per microliter)
1. Red blood cells 4, 600,000–5,400,000 Oxygen, carbon dioxide
transport to and from
2. White blood cells:
lungs
3,000–6,750 Fast-acting phagocytosis
Neutrophils
Immune responses
Lymphocytes
1,000–2,700
Phagocytosis
Monocytes
150–720
(macrophages)
100–380
Killing parasitic worms
Eosinophils
Secretions promote inflammation
25–90
3. Basophils
Platelets
250,000–300,000Roles in blood clotting
red
white
platelet
blood cellblood cell
Fig. 33.9, p. 544
ANIMATION: White blood cells
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ANIMATION: Hemostasis
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33.6 Blood Vessel
Structure and Function
• As blood flows through a circuit, it passes through a series of
vessels that differ in their structure and function:
• Arteries
• Arterioles
• Capillaries
• Venules
• Veins
Rapid Transport in Arteries
• Thick-walled arteries smooth out pressure variations
• The bulging of an artery with each ventricular contraction is
referred to as the pulse
• As the artery wall recoils, it keeps blood flowing away from
the heart
• pulse
• Brief stretching of artery walls that occurs when ventricles
contract
Artery Structure
• Arteries are large-diameter vessels that have a muscular wall
reinforced with elastic tissue
Artery Structure
outer
coat
smooth
muscle
basement
membrane endothelium
A Artery
elastic tissue elastic tissue
Fig. 33.11a, p. 546
Adjusting Flow at Arterioles
• In the systemic circuit, the body adjusts the distribution of
blood by altering the diameter of arterioles
• Smooth muscle that rings each arteriole responds to
commands from the central nervous system
• Sympathetic stimulation causes vasodilation (widening) of
arterioles in the extremities and vasoconstriction
(narrowing) of arterioles of the gut
Key Terms
• vasodilation
• Widening of a blood vessel when smooth muscle that
rings it relaxes
• vasoconstriction
• Narrowing of a blood vessel when smooth muscle that
rings it contracts
Arteriole Structure
• Smooth muscle that rings each arteriole responds to
sympathetic and parasympathetic stimulation
Arteriole Structure
outer
coat
smooth muscle rings
over elastic tissue
basement
membrane
endothelium
B Arteriole
Fig. 33.11b, p. 546
Exchanges at Capillaries
• Oxygen, CO2, and other substances are exchanged across
capillary walls
• Their thin walls and narrow diameter, barely wider than a red
blood cell, facilitate exchanges between blood and interstitial
fluid
Capillary Structure
• A capillary is a cylinder of endothelial cells, one cell thick,
wrapped in basement membrane
Capillary Structure
basement
membrane
endothelium
C Capillary
Fig. 33.11c, p. 546
Return to the Heart: Venules and Veins
• Blood from several capillaries flows into thin-walled venules,
which join together to form veins
• Veins are large-diameter, low-resistance transport tubes that
carry blood to the heart
• Many veins, especially in the legs, have flaplike valves that
help prevent backflow
Vein Structure
• Veins are large-diameter vessels with flaplike valves
Vein Structure
outer
coat
smooth muscle, basement
elastic fibers
membrane
endothelium
D Vein
valve
Fig. 33.11d, p. 546
ANIMATION: Vessel anatomy
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ANIMATION: Carbon dioxide
transport in the blood
33.7 Blood Pressure
• Blood pressure is pressure exerted by blood against the wall
of the vessel that encloses it
• Blood pressure results from the force exerted by ventricular
contraction
• It declines as blood proceeds through a circuit and is usually
recorded as systolic pressure over diastolic pressure
Key Terms
• blood pressure
• Pressure exerted by blood against a vessel wall
• systolic pressure
• Blood pressure when ventricles are contracting
• Highest pressure of a cardiac cycle
• diastolic pressure
• Blood pressure when ventricles are relaxed
• Lowest pressure of a cardiac cycle
Measuring Blood Pressure
• Blood pressure depends on:
• Total blood volume
• How much blood the ventricles pump out (cardiac output)
• The degree of arteriole dilation
• Blood pressure is measured in millimeters of mercury (mm
Hg), written as systolic value/diastolic value
•
Normal pressure is about 120/80 mm Hg, or “120 over 80”
Blood Pressure Change
Blood Pressure Change
arteries
capillaries
veins
Blood pressure (mm Hg)
(systolic)
120
80
(diastolic)
40
0
arterioles
venules
Fig. 33.12, p. 547
Measuring Blood Pressure
• Cuff is inflated with air
(no sound)
• Pressure is released
until sounds are heard
(systolic pressure)
• Sounds eventually stop
as more air is released
(diastolic pressure)
ANIMATION: Measuring blood
pressure
Hypertension
• Inability to regulate blood pressure can result in hypertension
(resting blood pressure above 140/90)
• High blood pressure makes the heart and kidneys work
harder, increasing risk of heart disease or kidney failure
• Heredity and diet contributes to risk for high blood pressure
33.8 Capillary Exchange
• Blood flow slows in capillaries because their collective crosssectional area is far greater than that of the arterioles that
deliver blood to them, or the veins that carry blood away
Slowdown at Capillaries
• Slow flow through narrow vessels enhances the rate of
exchanges between the blood and interstitial fluid
• The more time blood spends in a capillary, the more time
there is for exchanges to take place
How Substances Cross Capillary Walls
• Substances leave a capillary by diffusion, exocytosis, or in
fluid that seeps out between cells
• Oxygen, carbon dioxide, and small lipid-soluble molecules
diffuse across a capillary’s endothelial cells
• Fluid that seeps out of a capillary at the arterial end is
balanced by osmotic uptake of water nearer the vein end
• Normally, there is a small net outward flow of fluid from
capillaries
Forces Affecting Capillary Exchange
Forces Affecting Capillary Exchange
blood to
venule
high pressure causes
outward flow
cells of
tissue
blood
from
arteriole
A At a capillary’s arteriole
end, blood pressure forces
plasma fluid out between
cells of the capillary wall.
Plasma proteins remain in
the vessel, making plasma
more concentrated.
inward-directed
osmotic movement
B Plasma, with its
dissolved proteins,
has a greater solute
concentration than
the interstitial fluid.
Thus, at the far end
of the capillary,
where blood
pressure is lower,
water moves into
the vessel by
osmosis.
Fig. 33.14, p. 548
Animation: Facilitating Transfer