Chapter 36
Circulation
Sections 8-13
Albia Dugger • Miami Dade College
36.8 Blood Vessel Structure and Function
• Contracting ventricles put pressure on the blood, forcing it
through a series of vessels that vary in their structure.
• Arteries have thick walls containing smooth muscle reinforced
with elastic connective tissue
• When a ventricle contracts, artery walls to bulge and spring
back, creating a pulse
Blood Vessel Structure and Function
• Blood flows from arteries into arterioles
• In the systemic circuit, the distribution of blood to particular
body parts is adjusted by altering the diameter of arterioles
• Smooth muscle that rings each arteriole responds to signals
from the autonomic nervous system, and to chemical signals
• Sympathetic stimulation causes vasodilation of arterioles in
the extremities and vasoconstriction of arterioles of the gut
Blood Vessel Structure and Function
• A capillary is a cylinder of endothelial cells, one cell thick,
wrapped in basement membrane – its narrow diameter
facilitate exchanges between blood and interstitial fluid
• Blood flows from capillaries into venules, which empty Into
veins
• Veins are large-diameter, low-resistance vessels that convey
blood to the heart – many veins have flaplike valves that help
prevent backflow
from
the heart
to
the heart
valve
endothelium
smooth muscle
connective tissue
capillary network
B
Arteriole
D
Venule
endothelium
A Artery
C Capillary
E Vein
Figure 36-14 p638
Take-Home Message: How do blood vessels
differ in structure and function?
• Arteries are thick-walled, large-diameter vessels. Stretching
and recoil of arteries helps keep blood moving.
• Smooth muscle in the wall of arterioles allows adjustments to
blood flow in the systemic circuit.
• Capillaries are narrow tubes of epithelial cells. They are the
site of exchanges with interstitial fluid.
• Veins have valves that prevent backflow.
36.9 Blood Pressure
• Blood pressure is the pressure exerted by blood on the walls
of blood vessels
• Blood pressure is highest in arteries, then declines throughout
a cardiovascular circuit
Change in Blood Pressure
through the Systemic Circuit.
Systolic and Diastolic Pressure
• Systolic pressure, the highest pressure of a cardiac cycle,
occurs as contracting ventricles force blood into arteries
• Diastolic pressure, the lowest blood pressure of a cardiac
cycle, occurs when ventricles are relaxed
• Blood pressure is measured in millimeters of mercury (mm
Hg), and is written as systolic /diastolic
• Normal blood pressure is about 120/80 mm Hg
Measuring Blood Pressure
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
• Inability to regulate blood pressure can result in hypertension,
in which resting blood pressure remains above 140/90
Take-Home Message: How is blood pressure
recorded and regulated?
• Blood pressure is the fluid pressure exerted against a vessel
wall. It is recorded as systolic/diastolic pressure.
• Adjustments to arteriole diameter, cardiac output, and blood
volume regulate blood pressure.
36.10 Mechanisms of Capillary Exchange
• Capillary beds are diffusion zones, where blood exchanges
substances with interstitial fluid
• As blood flows through a circuit, it moves fastest through
arteries, and slowest in capillaries
• Slow flow through capillaries enhances the rate of exchanges
between the blood and interstitial fluid
Substance Exchange
• To move between the blood and interstitial fluid, a substance
must cross a capillary wall
• Oxygen, CO2 , and small lipid-soluble molecules diffuse
across endothelial cells of a capillary
• Some larger molecules enter endothelial cells by endocytosis,
diffuse through, then enter interstitial fluid by exocytosis
Fluid Exchange
• Higher blood pressure at the arterial end of a capillary bed
forces fluid out between cells
• At the venous end of the capillary, interstitial fluid enters the
capillaries by osmotic pressure
• Normally, there is a small net outward flow of fluid
• The lymphatic system returns fluid to the blood
Fluid Movement at a Capillary Bed
blood to
venule
high pressure causes
outward flow
blood
from
arteriole
inward-directed
osmotic movement
cells of
tissue
Take-Home Message: How do blood and
interstitial fluid exchange materials?
• Small molecules cross cells of a capillary by diffusion and
larger ones move across by exocytosis.
• Fluid rich in oxygen and nutrients also leaks out between cells
of the capillary wall.
36.11 Venous Function
• Veins are the body’s largest blood reservoir
• Skeletal muscle activity helps move blood at low pressure
through veins and back to the heart
• Valves in veins help prevent backflow
• Contractions of smooth muscle inside vein walls helps force
blood toward the heart
venous valve
Figure 36-18 p641
blood flow to heart
valve
open
valve
closed
valve
closed
valve
closed
Figure 36-19a p641
Take-Home Message:
What are the functions of veins?
• Veins are the body’s main blood reservoir. The amount of
blood in the veins changes depending on activity level.
• Blood pressure in veins is low. One-way valves, activity of
skeletal muscle, and respiratory muscle action all help move
the blood toward the heart.
36.12 Blood and Cardiovascular Disorders
• Red blood cell disorders
• Anemias are caused by low red blood cell counts
• Thalassemias disrupt hemoglobin synthesis
• Polycythemia is an excess of red blood cells
• White blood cell disorders
• Infectious mononucleosis increases monocyte production
• Leukemias are cancers originating from stem cells in bone
• Lymphomas are cancers that originate from B or T
lymphocytes
Blood and Cardiovascular Disorders
• Atherosclerosis is a buildup of lipids such as cholesterol in the
arterial wall that narrows the lumen
• Cholesterol may be bound into low-density lipoproteins
(LDLs) which are deposited in blood vessels; or into highdensity lipoproteins (HDLs) and taken up by the liver
An Atherosclerotic Plaque
Stroke and Heart Attack
• Atherosclerosis increases the risk of stroke and heart attack
• Clogged coronary arteries can be treated with a bypass or
angioplasty
• Angioplasty is also used to open partially blocked carotid
arteries in the neck that supply blood to the brain
Coronary Bypass Surgery
A Coronary bypass surgery.
Veins from another part of the
body are used to divert blood
past the blockages. This
illustration shows a “double
bypass,” in which veins are
placed to divert blood around
two blocked coronary arteries.
vein from leg;
used to bypass
blockage
blocked
coronary artery
Balloon Angioplasty and Stent
plaque flattened by
balloon angioplasty
stent (metal mesh) placed
to keep artery open
B Balloon angioplasty and the placement of a stent. After
a balloonlike device is inflated in an artery to open it and
flatten the plaque, a tube of metal (the stent) is inserted
and left in place to keep the artery open.
Hypertension
• Hypertension is chronically high blood pressure above 140/90
• Hypertension makes the heart work harder than normal,
which can cause it to enlarge and to function less efficiently
• High blood pressure also increases risk of atherosclerosis
Rhythms and Arrhythmias
• Electrocardiograms (ECGs) record the electrical activity of a
beating heart
• They can also reveal arrhythmias, which are abnormal heart
rhythms caused by malfunction of the SA node
• Bradycardia is a below-average resting cardiac rate
• Tachycardia is a faster than normal heart rate
• Palpitations are occasional episodes of tachycardia
• Atrial fibrillation disrupts atrial contractions
• Ventricular fibrillation causes death
Electrocardiograms
Take-Home Message:
What factors impair circulatory function?
• Altered blood cell number or quality can alter blood’s ability to
carry out its functions.
• Atherosclerosis and hypertension raise the risk of heart attack
and stroke.
• Problems with the cardiac pacemaker cause arrhythmias.
Video: Repairing Damaged Hearts with Patients’
Own Stem Cells
36.13 Interactions With
the Lymphatic System
• Vessels and organs of the lymphatic system interact closely
with the circulatory system
• The lymph vascular system consists of lymph capillaries
and vessels that collect water and solutes from interstitial fluid
and deliver them to the circulatory system
• Fluid that moves through these vessels is called lymph
Three Functions of
the Lymph Vascular System
• Returns fluids and plasma proteins that leak out of capillaries
to the circulatory system
• Delivers fats absorbed from the small intestine to the blood
• Transports cellular debris, pathogens, and foreign cells to
lymph nodes
Lymphoid Organs and Tissues
• Lymph nodes filter lymph before it enters blood and identify
pathogens
• Tonsils in throat and adenoids in nasal cavity respond to
inhaled pathogens
• The spleen filters pathogens, worn out blood cells, and
platelets from blood
• The thymus gland matures T lymphocytes essential to the
immune system
Tonsils
Defense against
bacteria and other
foreign agents
Right lymphatic duct
Drains right upper portion
of the body
Thymus gland
Site where certain white
blood cells acquire means
to chemically recognize
specific foreign invaders
Thoracic duct
Drains most of the body
Spleen
Major site of antibody
production; disposal
site for old red blood cells
and foreign debris; site of
red blood cell formation
in the embryo
Some of the
lymph nodes
Filter bacteria and
many other agents of
disease from lymph
Some of the
lymph vessels
Return excess interstitial
fluid and reclaimable
solutes to the blood
Bone marrow
Marrow in some
bones is production
site for infectionfighting blood cells
(as well as red blood
cells and platelets)
Figure 36-23a p644
lymph
capillary
interstitial
fluid
flaplike
“valve”
made of
overlapping
cells at tip
of lymph
capillary
B
capillary bed
Figure 36-23b p644
lymph trickles past organized
arrays of lymphocytes
valve (prevents backflow)
C Lymph node
Figure 36-23c p644
Take-Home Message: What are the functions
of the lymphatic system?
• The lymph vascular system consists of tubes that collect and
deliver excess water and solutes from interstitial fluid to blood.
It also carries absorbed fats to the blood, and delivers disease
agents to lymph nodes.
• The system’s lymphoid organs, including lymph nodes, have
specific roles in body defenses.