Download Capillaries

Human Biology Concepts and Current Issues
Seventh Edition
Michael D. Johnson
8
Heart and
Blood Vessels
© 2014 Pearson Education, Inc.
Lecture Presentations by
Robert J. Sullivan
Marist College
Blood Vessels Transport Blood
 Arteries
– Carry blood away from the heart
– Transport blood under high pressure
– Thick-walled
 Capillaries
– Exchange solutes and water with cells of the body
– Microscopic
 Veins
– Return blood to the heart
– Thin-walled
© 2014 Pearson Education, Inc.
Figure 8.1
Direction of
blood flow
Outer layer:
Connective
tissue
Middle layer:
Smooth
muscle with
elastic fibers
Vein
Inner layer:
Artery
Endothelium
Connective tissue
Smooth muscle
Endothelium
Venule
Arteriole
Capillary
Tissue cells
© 2014 Pearson Education, Inc.
Epithelial cells of
capillary endothelium
Arteries Transport Blood Away From Heart
 Structure
– Thick-walled, three layers
– Innermost layer: endothelium of squamous epithelial
cells
– Middle layer: smooth muscle
– Outer layer: connective tissue
 Function
– Arteries carry blood away from heart
– Carry blood under pressure
© 2014 Pearson Education, Inc.
Arteries Transport Blood Away From the Heart
 Aneurism—defect in arterial wall
–
–
–
–
–
–
–
Ballooning of the arterial wall
Some bulge inward, obstructing flow
Others bulge outward
Often develop slowly over time
Often symptomless, until they rupture
Rupture of aortic aneurism—rapidly fatal
May be detected by careful screening and surgically
repaired
© 2014 Pearson Education, Inc.
Arterioles and Precapillary Sphincters Regulate Blood
Flow
 Blood flow
– Heart  Arteries  Arterioles  Capillaries
 Arterioles: smallest arteries
 Precapillary sphincters: control blood flow from
arterioles into capillaries
– Vasodilation:
– Relaxation of vascular smooth muscle
– Increases blood flow to capillaries
– Vasoconstriction:
– Contraction of vascular smooth muscle
– Decreases blood flow to capillaries
© 2014 Pearson Education, Inc.
Figure 8.2
Relaxed
precapillary
sphincters
Arteriole
Capillaries
Small vein (venule)
© 2014 Pearson Education, Inc.
Constricted
precapillary
sphincters
Capillaries: Where Blood Exchanges Substances with
Tissues
 Structure
– Smallest blood vessels, microscopic
– Thin-walled: one cell-layer thick
– Porous
 Capillary beds: extensive networks of capillaries
 Function: selective exchange of substances with the
interstitial fluid
© 2014 Pearson Education, Inc.
Figure 8.3
Capillary cell
Pores through cells
Slit between cells
A medium-magnification
view showing a rich
network of capillaries
surrounding and
interconnecting small
arteries and veins.
Nucleus
RBC
A higher magnification showing
a single branching capillary.
Notice the red blood cells traveling
single file in the capillary.
© 2014 Pearson Education, Inc.
The structure of a capillary.
Figure 8.4
Precapillary sphincter
Capillary
RBCs, most proteins
Fluid (water)
O2, nutrients,
raw materials
Venule
Arteriole
Tissue cell
© 2014 Pearson Education, Inc.
CO2, wastes
Lymphatic System Helps Maintain Blood Volume
 Function
– Maintains blood volume
– Returns excess interstitial fluid to circulatory system
– Also functions in immune defenses
 Structure
– Blind-ended capillaries
– Lymphatic vessels (similar to venous system)
– Lymph—derived from interstitial fluid
© 2014 Pearson Education, Inc.
Veins Return Blood to the Heart
 Structure
– Three layers, thin-walled
– Larger lumen than arteries
– High distensibility
 Functions
– Carry blood toward the heart
– Blood flow
– Capillaries  Venules  Veins  Heart
– Serve as blood volume reservoir
© 2014 Pearson Education, Inc.
Veins Return Blood to the Heart
 Three Mechanisms assisting in blood return
1. Contraction of skeletal muscles
2. One-way valves permit only one-way blood flow
3. Pressure changes associated with breathing push
blood toward the heart
© 2014 Pearson Education, Inc.
Figure 8.5
Valve
(open)
One-way
valves
(closed)
Calf muscles
relaxed
© 2014 Pearson Education, Inc.
Calf muscles
contracted
Figure 8.6
© 2014 Pearson Education, Inc.
Figure 8.7
Aorta
Superior
vena cava
Right pulmonary
artery
Left pulmonary artery
Pulmonary trunk
Left pulmonary veins
Pulmonary
semilunar valve
Right atrium
Right
atrioventricular
(AV) valve
Right ventricle
Inferior vena cava
Left atrium
Aortic semilunar valve
Left atrioventricular
(AV) valve
Left ventricle
Chordae tendineae
Papillary muscles
Septum
Epicardium
Myocardium
Endocardium
© 2014 Pearson Education, Inc.
The Heart Is Mostly Muscle
 Surrounded by fibrous sac—pericardium
– Protects and anchors the heart
 Layers of the heart
– Epicardium: thin layer of epithelial and connective
tissue
– Myocardium: thick layer of cardiac muscle
– Electrical signals flow directly from cell to cell
– This is what contracts when the heart beats
– Endocardium: thin layer of endothelial tissue
– Continuous with lining of blood vessels
© 2014 Pearson Education, Inc.
The Heart Has Four Chambers and Four Valves
 Four chambers
– Two atria: upper chambers
– Two ventricles: lower chambers
– Septum, muscular partition separates right and left
sides of the heart
 Four valves—prevent backflow
– Two atrioventricular (AV) valves
– Tricuspid valve (right side)
– Bicuspid (mitral) valve (left side)
– Two semilunar valves
– Pulmonary valve
– Aortic valve
© 2014 Pearson Education, Inc.
The Pulmonary Circuit Provides for Gas Exchange
1. Deoxygenated blood from the body travels through
the vena cava to the right atrium
2. Through the right AV valve into the right ventricle
3. Through the pulmonary semilunar valve into the
pulmonary trunk and the lungs
4. Blood is oxygenated and CO2 is given up within
pulmonary capillaries
5. Oxygenated blood travels through the pulmonary
veins into the left atrium
6. Through the left AV valve into the left ventricle
© 2014 Pearson Education, Inc.
The Systemic Circuit Serves the Rest of the Body
1. Oxygenated blood travels from the left ventricle
through the aortic semilunar valve into the aorta
2. Through branching arteries and arterioles to tissues
3. Through the arterioles to capillaries
4. Within capillaries, nutrients and oxygen are
delivered and wastes are picked up
5. From capillaries into venules and veins
6. To the vena cava and into the right atrium
© 2014 Pearson Education, Inc.
Figure 8.8
Systemic Circuit
Head and
upper
limbs
Lung
capillaries
Pulmonary
Circuit
Heart
Lung
capillaries
Aorta
Torso and
Lower limbs
© 2014 Pearson Education, Inc.
Figure 8.9
Jugular vein
Carotid artery
Superior
vena cava
Inferior
vena cava
Renal vein
Common
iliac vein
Common
iliac artery
© 2014 Pearson Education, Inc.
Subclavian vein
Subclavian artery
Aorta
Renal artery
Femoral vein
Femoral artery
Great saphenous
vein
The Systematic Circuit Serves the Rest of the Body
 Coronary arteries
– Arteries that supply the heart muscle itself
– Supply the myocardium
– Small diameter—may become partially or completely
blocked by atherosclerosis
© 2014 Pearson Education, Inc.
Figure 8.10
Aorta
Superior
vena cava
Pulmonary
trunk
Right
coronary
artery
Cardiac
veins
Inferior
vena cava
© 2014 Pearson Education, Inc.
Cardiac
vein
Left
coronary
artery
The Cardiac Cycle: The Heart Contracts and Relaxes
 Atrial systole
– Both atria contract
– AV valves open, semilunar valves are closed
– Ventricles fill
 Ventricular systole
– Both ventricles contract
– AV valves close, semilunar valves open
 Diastole
– Both atria and ventricles relax
– Semilunar valves close
© 2014 Pearson Education, Inc.
Figure 8.11
Right atrium
Left atrium
Pulmonary
semilunar valve
Aortic semilunar valve
Left AV valve
Right AV valve
Left ventricle
Atrial systole. Both atria
Right ventricle
0.1 second
Diastole
contract, forcing blood
into the ventricles. The AV
valves are open, and the
semilunar valves are
closed.
Systole
0.4 second
Aorta
Pulmonary trunk
0.3 second
Diastole. The ventricles
relax and begin to fill
passively with blood
through the open AV
valves. The semilunar
valves are closed, and the
atria remain relaxed.
© 2014 Pearson Education, Inc.
Ventricular systole. Both ventricles
contract, causing the AV valves to
close and the semilunar valves to open.
Blood is ejected into the pulmonary
trunk and aorta. The atria relax.
Heart Sounds Reflect Closing Heart Valves
 Lub-dub heart sound
– Lub: closing of both AV valves during ventricular
systole
– Dub: closing of both semilunar valves during
ventricular diastole
 Heart murmurs
– Caused when blood flow is disturbed
– May be a sign of a defective valve
© 2014 Pearson Education, Inc.
Cardiac Conduction System Coordinates Contraction
 Sinoatrial (SA) node—small mass of cardiac cells in
upper right atrium
– Cardiac pacemaker
– Initiates the heartbeat spontaneously
– Pace can be modified by nervous system
 Atrioventricular (AV) node
– Located between atria and ventricles
– Relays impulse
 Atrioventricular (AV) bundle and Purkinje fibers
– Located in septum and ventricles
– Carry impulse to ventricles
© 2014 Pearson Education, Inc.
Figure 8.13
Sinoatrial
(SA) node
Atrioventricular
(AV) node
AV bundle
Bundle branches
Purkinje fibers
© 2014 Pearson Education, Inc.
Electrocardiogram (EKG/ECG) Records the Heart’s
Electrical Activity
 Tracks the electrical activity of the heart
 A healthy heart produces a characteristic pattern
 Three formations
– P wave: impulse across atria
– QRS complex: spread of impulse down septum,
around ventricles in Purkinje fibers
– T wave: end of electrical activity in ventricles
 EKGs can detect
– Arrhythmias
– Ventricular fibrillation
© 2014 Pearson Education, Inc.
Figure 8.14
An ECG being recorded.
R
T
P
Q
S
A normal ECG recording.
Ventricular fibrillation.
© 2014 Pearson Education, Inc.
Blood Exerts Pressure Against Vessel Walls
 The force that the blood exerts on the wall of the
blood vessels
– Systolic pressure: highest pressure, as blood is
ejected during ventricular systole
– Diastolic pressure: lowest pressure, during
ventricular diastole
 Measurement
– Sphygmomanometer: device used to measure blood
pressure
– “Normal” readings
– Systolic pressure <120 mmHg
– Diastolic pressure <80 mmHg
© 2014 Pearson Education, Inc.
Blood pressure (mm Hg)
Figure 8.15
Systolic
pressure
120
80
40
0
© 2014 Pearson Education, Inc.
Diastolic
pressure
Figure 8.16
Blood pressure (mm Hg)
140
Column of mercury
indicating pressure
in mm Hg
Cuff pressure
Blood pressure
1
120
100
80
2
60
0
Sphygmomanometer:
Squeezable bulb
Inflatable
rubber cuff
Air valve
Artery
Stethoscope
A clinician inflates the cuff with air and then allows the
pressure in the cuff to fall gradually while using a
stethoscope to listen for the sounds of blood movement
through the artery.
© 2014 Pearson Education, Inc.
2
4
6
8
10
Time (seconds)
A schematic representation of the pulses of
arterial blood pressure superimposed over
the steadily declining cuff pressure. Systolic
pressure is recorded at cuff pressure 1 when
sounds are first heard. Diastolic pressure is
recorded at cuff pressure 2 when sounds cease.
Hypertension: High Blood Pressure Can Be
Dangerous
 Sustained elevation in blood pressure
– Systolic pressure  140 mmHg
– Diastolic pressure  90 mmHg
 Risk factor for cardiovascular disease
– Higher blood pressure causes greater strain on
cardiovascular system
– Blood vessels react by becoming hardened and
scarred
– Strain on heart from having to work harder
 Silent killer, no symptoms
© 2014 Pearson Education, Inc.
Table 8.1
© 2014 Pearson Education, Inc.
Table 8.2
© 2014 Pearson Education, Inc.
Hypotension: When Blood Pressure Is Too Low
 Low blood pressure
 If low enough, may cause dizziness or fainting
 May follow abrupt changes in body position
– Standing up suddenly
 May result from excessive blood loss or fluid loss
from burns
© 2014 Pearson Education, Inc.
How the Cardiovascular System Is Regulated
 Importance of maintaining a constant arterial blood
pressure
 Constant arterial pressure is achieved by
1. Regulation of heart rate
2. Force of contraction
3. Regulation of diameter of arterioles
 Local blood flows are adjusted to meet local
requirements
© 2014 Pearson Education, Inc.
Baroreceptors Maintain Arterial Blood Pressure
 Baroreceptors: pressure receptors in aorta and
carotid arteries
 Steps in mechanism
1. Blood pressure rises, vessels stretched
2. Signals sent to the cardiovascular center in the brain
3. Heart signaled to lower heart rate and force of
contraction
4. Arterioles vasodilate, increasing blood flow to tissues
5. Combined effect lowers blood pressure
 Mechanism reversed if blood pressure is too low
© 2014 Pearson Education, Inc.
Nerves and Hormones Adjust Cardiac Output
 Amount of blood pumped into aorta in one minute
 Cardiac output  heart rate  stroke volume
– Heart rate: beats/minute (bpm)
– Resting adult heart rate  approx. 75 bpm
– Stroke volume:
– Resting adult stroke volume  70 ml/beat
 Resting cardiac output
– 75 bpm  70 ml/beat  5.25 liters/min.
© 2014 Pearson Education, Inc.
Nerves and Hormones Adjust Cardiac Output
 Medulla oblongata: cardiovascular center of brain
– Receives inputs from baroreceptors and other
receptors
– Output goes through two sets of nerves
1. Sympathetic nerves—constrict blood vessels, raising
blood pressure
2. Parasympathetic nerves—dilate blood vessels, lowering
blood pressure
 Hormones: epinephrine and norepinephrin
– Secreted by adrenal glands when sympathetic system
is activated
– Increase cardiac output
© 2014 Pearson Education, Inc.
Local Requirements Dictate Local Blood Flows
 Precapillary sphincters allow fine-tuning of blood flow
to local tissues as needed
 Metabolically active tissue—needs more O2,
sphincters open, vasodilation
 If blood pressure drops precipitously, blood pressure
control would cause vasoconstriction to many organs
and shunt blood to brain and heart where blood
supply and pressure must be maintained
© 2014 Pearson Education, Inc.
Figure 8.17
Blood flow
Diffusion of
vasodilating
substance
Cell
Arteriole
Precapillary
sphincter
Capillary
Vasodilating
substance
produced
during
metabolism
At rest, very little of the vasodilating
substance would be produced, and
flow would be minimal.
© 2014 Pearson Education, Inc.
With increased metabolic activity,
the presence of more of the
substance in the interstitial space
would cause the arteriole and
precapillary sphincter to vasodilate,
increasing flow.
Exercise: Increased Blood Flow and Cardiac Output
 Blood flow to active skeletal muscles increases
 Cardiac output (CO) is increased to maintain blood
pressure
– Non-athletes: up to 20–25 liters/min
– Trained athletes: up to 35 liters/min
© 2014 Pearson Education, Inc.
Cardiovascular Disorders: A Major Health Issue
 Angina
– Sensation of pain and tightness in chest
– Caused by narrowing of coronary arteries and
diminished blood flow to coronary muscle
– May be accompanied by shortness of breath and
sensation of choking or suffocating
– Usually temporary
– Angiography: allows visualization of coronary arteries,
enables diagnosis of angina
– Treatment:
– Medication
– Balloon angioplasty
– Coronary artery bypass graft
© 2014 Pearson Education, Inc.
Figure 8.18
© 2014 Pearson Education, Inc.
Cardiac Disorders: A Major Health Issue
 Heart attack (myocardial infarction)
– Sudden death of an area of myocardium
– Symptoms:
– Intense chest pain, tightness or pressure on chest,
radiating left arm pain, jaw and back pain, nausea
– Requires immediate medical attention
– Diagnosis: ECG and presence of certain enzymes in
the blood
– Treatment and/or prevention
– Control of arrhythmias
– Clot-dissolving medications
– Coronary artery bypass graft (CABG)—vein from leg is
grafted to bypass obstructed coronary artery
© 2014 Pearson Education, Inc.
Figure 8.19
Aorta
Vein
grafts
Plaque
blocking
blood flow
© 2014 Pearson Education, Inc.
Cardiac Disorders: A Major Health Issue
 Heart failure
– Heart muscle becomes weaker, less efficient
– Congestive heart failure: weakness of heart causes
fluid back-up in interstitial spaces
– Out of breath, swollen ankles, legs, neck veins
– Why does the heart weaken?
– Age, prior heart attacks, leaky heart valves, lung disease
– Treatment
– Improve cardiac performance, efficiency
– Prevent accumulation of interstitial fluid
© 2014 Pearson Education, Inc.
Cardiac Disorders: A Major Health Issue
 Embolism
– Sudden blockage of a blood vessel by material
floating in the bloodstream
– Often a blood clot broken away from a larger clot
elsewhere
– May be cholesterol deposits, tissue fragments, cancer
cells, clumps of bacterial, bubbles of air
– Locations
– Pulmonary embolism—chest pain, shortness of breath
– Cerebral embolism—may cause a stroke
– Cardiac embolism—may cause heart attack
© 2014 Pearson Education, Inc.
Cardiovascular Disorders: A Major Health Issue
 Stroke
– Damage to part of brain caused by an interruption in
blood supply
– Two common causes
– Embolism blocking a brain blood vessel
– Rupture of a cerebral artery
– Symptoms: depend on area of brain affected
– Immediate medical care is crucial
– If embolism, patient receives clot-dissolving drugs
– If rupture, surgical repair sometimes possible
– Recovery may require extensive rehabilitation
© 2014 Pearson Education, Inc.
Replacing a Failing Heart
 Heart transplants
– Expensive
– Average post-transplant survival: 15 years
– Problem: shortage of healthy hearts
 Temporary solution to shortage of transplant organs:
– Artificial heart
– Xenotransplant (heart from another animal species)
© 2014 Pearson Education, Inc.
Figure 8.20
The SynCardia heart.
© 2014 Pearson Education, Inc.
The AbioCor heart.
Reducing Your Risk of Cardiovascular Disease
 Don’t smoke
– Smokers have twice the risk of heart disease
 Watch cholesterol levels
– Risk increases with increasing blood cholesterol




Engage in regular moderate exercise
Maintain a healthy weight
Keep diabetes under control
Avoid chronic stress
© 2014 Pearson Education, Inc.