Download Composition of the Blood, cont.

Chapter 12
Circulatory System
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1
Pretest
True or False
1. The pointed end of the heart is the apex.
2. The myocardium forms the bulk of the
heart wall.
3. The coronary arteries branch off the
aorta to supply the heart with oxygen
and nutrients.
4. The SA node is located in the right
atrium.
5. The adult male has 5-6 liters of blood.
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Pretest, cont.
True or False
6. Erythrocytes lack a nucleus.
7. Vitamin K is necessary for the
absorption of vitamin B12 from the
intestines.
8. Leukocytes defend the body against
disease.
9. Thrombocytes develop from large
cells known as macrophages.
10.Veins carry blood toward the heart.
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Introduction to the
Circulatory System
1. Made up of:
a. Heart: central pump
b. Blood vessels: moves blood through body
c. Blood: transport medium
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Introduction to the
Circulatory System, cont.
The Heart
1. Muscular pump
2. Provides the force necessary to circulate
blood to all tissues in body
a. Tissues need a continuous supply of oxygen
and nutrients
b. Metabolic waste products: must be removed
3. Pumps 5 liters of blood every minute
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Overview of the Heart
Form, Size, and Location of the Heart
1. Located in thoracic cavity between the lungs
a. Posterior to sternum
b. Anterior to vertebral column
2. Two thirds of heart mass: to the left of
body’s midline (one third is to the right)
3. Apex: pointed end of heart
a. Extends downward to level of fifth intercostal
space
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Overview of the Heart, cont.
4. Base: opposite end
a. Larger and less pointed than apex
b. Has several large vessels attached to it
5. Size of heart: varies with size of individual
a. Average: 9 cm wide and 12 cm long (size of a
closed fist)
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Overview of the Heart, cont.
From Jarvis C: Physical examination and health assessment, ed 4, St. Louis, 2004, Saunders
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Overview of the Heart, cont.
Coverings of the Heart
1. Pericardium: loose-fitting, double-layered
sac that encloses the heart consisting of:
a. Fibrous pericardium: outer layer of
pericardium
•
Consists of tough, white fibrous connective tissue
b. Parietal pericardium: serous membrane that
lines the fibrous pericardium
c. Visceral pericardium: parietal pericardium
reflects back onto the surface of the heart to
form the visceral pericardium
•
Also called epicardium
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Overview of the Heart, cont.
2. Pericardial cavity: small space
between parietal and visceral layers of
pericardium
a. Contains a thin layer of serous fluid
•
Reduces friction between the membranes as
they rub against each other during heart
contractions
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Overview of the Heart, cont.
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Structure of the Heart
Layers of the Heart Wall
1. Epicardium (same as the visceral
pericardium): consists of a serous
membrane
a. Thin protective layer: firmly anchored to
underlying muscle
b. Contains blood vessels: nourish heart wall
2. Myocardium: forms bulk of heart wall
a. Composed of cardiac muscle tissue
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Structure of the Heart, cont.
b. Contraction of myocardium:
•
Provides force that ejects blood from heart and
moves it through vessels
c. Endocardium: smooth inner lining of heart wall
•
•
Permits blood to move easily through heart
Also forms the valves of the heart
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Structure of the Heart, cont.
Chambers of the Heart
1. Four chambers:
a.
b.
c.
d.
Right atrium
Right ventricle
Left atrium
Left ventricle
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Structure of the Heart, cont.
2. Atria: thin-walled chambers
a. Receive blood from the veins
3. Ventricles: thick-walled chambers
a. Forcefully pump blood out of the heart
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Structure of the Heart, cont.
4. Right atrium: receives deoxygenated blood
a. From superior vena cava and inferior vena cava
•
Superior vena cava: returns blood to heart
– From head, neck, and upper extremities
•
Inferior vena cava: returns blood to heart
– From thorax, abdomen, pelvis, and lower extremities
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Structure of the Heart, cont.
5. Left atrium: receives oxygenated blood
a. From lungs through four pulmonary veins
6. Interatrial septum: partition that separates
right and left atria
a. Fossa ovalis: thin region in the septum
•
Represents an opening (foramen ovale) that is
present between the atria in the fetal heart
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Structure of the Heart, cont.
7. Right ventricle: receives blood from the
right atrium
a. Pumps it to lungs, where it picks up oxygen
8. Left ventricle: receives blood from left
atrium
a. Pumps it to tissues of body
9. Interventricular septum: thick, muscular
partition between the right and left ventricles
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Structure of the Heart, cont.
From Jarvis C: Physical examination and health assessment, ed 4, St. Louis, 2004, Saunders
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Structure of the Heart, cont.
Valves of the Heart
1. Atrioventricular (AV) valves
a. Permit the flow of blood from atria into
corresponding ventricle
b. Prevent backflow of blood from ventricles into
atria
c. Consist of a fibrous connective tissue ring and
double folds of endocardium
•
Form the cusps of the valve
– Attached to papillary muscles in the ventricles by
chordae tendineae
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Structure of the Heart, cont.
d. Tricuspid valve: between right atrium and right
ventricle
•
Has three cusps
e. Bicuspid (mitral) valve: between left atrium and
left ventricle
•
Has two cusps
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Structure of the Heart, cont.
2. Semilunar (SL) valves
a. Located at the bases of the large vessels that
carry blood from the ventricles
b. Each valve consists of three cuplike cusps
c. Prevent the flow of blood back into the
ventricles
d. Pulmonary SL valve: located at the exit of the
right ventricle
•
In the base of the pulmonary trunk
e. Aortic SL valve: located at the exit of the left
ventricle
•
In the base of the aorta
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Structure of the Heart, cont.
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Structure of the Heart, cont.
Pathway of Blood through the Heart
1. Both atria contract at the same time
2. Both ventricles contract at the same time
3. Heart functions as two pumps:
a. Pulmonary circulation: pump on the right side
•
Pumps blood to lungs
b. Systemic circulation: pump on the left side
•
Pumps blood to rest of body
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Structure of the Heart, cont.
4. Blood flow through the heart
a. Blood enters right atrium through superior vena
cava and inferior vena cava
•
Low in oxygen and high in carbon dioxide
b. Flows through tricuspid valve into right ventricle
c. Passes through pulmonary SL valve
d. Flows into pulmonary trunk and into pulmonary
arteries
e. Blood carried to lungs
f. Carbon dioxide is released and oxygen is
picked up
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Structure of the Heart, cont.
g. Pulmonary veins carry blood to left atrium
h. Blood flows through bicuspid valve into left
ventricle
i. Flows through aortic SL valve into aorta
j. Distributed to all parts of the body through the
systemic circulation
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Structure of the Heart, cont.
Blood Supply to the Myocardium
1. Myocardium: needs a continuous supply of
oxygen and nutrients
a. Has an extensive network of blood vessels
2. Two coronary arteries: branch from aorta
a. Right and left coronary arteries
•
Have numerous branches
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Physiology of the Heart
1. Functions:
a. Pump blood to the lungs through the pulmonary
circulation
b. Pump blood to the rest of the body through the
systemic circulation
2. Accomplished by contraction and relaxation
of the cardiac muscle in the myocardium
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Physiology of the Heart, cont.
Conduction System
Components of the Conduction System
1. Sinoatrial node (SA node)
a. Located in the right atrium: near entrance of
superior vena cava
b. Initiates impulses: without neural stimulation
•
70-80 times per minute
c. Establishes basic rhythm of the heartbeat
•
Called the pacemaker of the heart
d. Impulses travel throughout atrial myocardium
•
•
Cause atria to contract simultaneously
Impulses reach AV node
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Physiology of the Heart, cont.
2. Atrioventricular Node (AV node)
a. Located in floor of right atrium: near interatrial
septum
b. Cells in the AV node: conduct impulses more
slowly
•
Causes brief delay as impulses travel through the
node
– Allows time for atria to finish contracting before the
ventricles begin contracting
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Physiology of the Heart, cont.
3. Atrioventricular bundle, bundle branches, and
conduction myofibers
a. From AV node:
•
Impulses travel through AV bundle (bundle of His) to
right and left bundle branches
b. Bundle branches
•
•
Extend along the right and left sides of the
interventricular septum
Branch profusely to form conduction myofibers
(Purkinje fibers)
c. Conduction myofibers: transmit impulses to
myocardium
•
Cause ventricles to contract simultaneously
– Blood is forced out through SL valves into aorta
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Physiology of the Heart, cont.
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Physiology of the Heart, cont.
Cardiac Cycle
1. Consists of one heartbeat
a. Two atria contract at same time
b. Then relax while two ventricles contract
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Physiology of the Heart, cont.
2. With a heart rate of 75 beats per minute,
one cardiac cycle lasts 0.8 second
a. Atrial systole: contraction of the atria
(0.1 second)
•
•
•
AV valves are open
Ventricles are in diastole (relaxed)
Blood is forced into ventricles
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Physiology of the Heart, cont.
b. Ventricular systole: contraction of ventricles
(0.3 second)
•
Atria are in diastole (relaxed)
– Are filling with blood returned through venae cavae
c. All chambers are in simultaneous diastole (0.4
second)
•
70% of ventricular filling occurs during this period
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Physiology of the Heart, cont.
Heart Sounds
1. First heart sound: lubb
a. Caused by closure of AV valves
2. Second heart sound: dupp
a. Caused by closure of SL valves
3. Pause between dupp of the first beat
and lubb of second beat
a. Entire heart is resting
4. Abnormal heart sounds: murmurs
a. Caused by faulty valves
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Blood
1. Primary transport medium
a. Provides cells with nutrients and oxygen
b. Removes metabolic wastes
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Functions and Characteristics
of the Blood
1. Connective tissue
2. Consists of cells and cell fragments (formed
elements) suspended in an intercellular
matrix (plasma)
3. Blood is the only liquid tissue in the body
4. Blood volume in an average adult:
a. Female: 4-5 liters
b. Male: 5-6 liters
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Functions and Characteristics
of the Blood, cont.
5. Functions:
a. Transportation
•
•
Carries oxygen and nutrients to cells
Transports carbon dioxide and nitrogenous wastes
– From the tissues to the lungs and kidneys
•
Carries hormones from endocrine glands to target
tissues
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Functions and Characteristics
of the Blood, cont.
b. Regulation
•
Regulates body temperature
– Removes heat from skeletal muscles:
1) Transports it to other regions
2) Transports it to skin, where it can be dissipated
•
Fluid and electrolyte balance
– Salts and plasma proteins contribute to the osmotic
pressure
•
pH regulation through the action of buffers in the
blood
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Functions and Characteristics
of the Blood, cont.
c. Protection
•
Clotting mechanisms: prevent fluid loss through
hemorrhage
– When blood vessels are damaged
•
Phagocytic white blood cells
– Help protect against microorganisms
•
Antibodies in the plasma
– Help protect against disease
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Composition of the Blood
1. Plasma: 55% of blood volume
2. Red blood cells: 45% of blood volume
3. Buffy coat: consists of WBCs and platelets
a. Forms a thin white layer between the plasma
and RBCs
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Composition of the Blood, cont.
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Composition of the Blood, cont.
Plasma
1. Liquid portion of the blood
a. 90% water
b. Remaining portion: approximately 100 different
organic and inorganic solutes
Plasma Proteins
1. Most abundant solute
2. Remain in blood and interstitial fluid
a. Are not used for energy
3. Many are synthesized in liver
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Composition of the Blood, cont.
4. Types
a. Albumins
•
•
•
•
60% of plasma proteins
Produced in liver
Contribute to osmotic pressure of blood
Play role in maintaining fluid balance between blood
and interstitial fluid
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Composition of the Blood, cont.
– If the osmotic pressure of blood decreases, fluid
moves from blood into interstitial spaces
1) Results in edema
2) Decreases blood volume
3) In severe cases: may reduce blood pressure
– If blood osmotic pressure increases: fluid moves from
interstitial spaces into blood
1) Increases blood volume
2) Increases blood pressure
3) Decreases amount of water available to cells
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Composition of the Blood, cont.
b. Globulins
•
•
36% of the plasma proteins
Three types:
–
–
Alpha and beta globulins: produced in the liver
1) Transport lipids and fat-soluble vitamins in blood
Gamma globulins: produced in lymphoid tissue
1) Are antibodies that function in immunity
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Composition of the Blood, cont.
c. Fibrinogen
•
•
•
4% of plasma proteins
Produced in liver
Functions in blood clotting
– During clotting process: soluble fibrinogen is converted
into insoluble fibrin
1) Forms the foundation of a blood clot
– When blood clots in a test tube, liquid that remains is
called serum
1) Similar to plasma
2) But has no fibrinogen (fibrinogen is converted to
fibrin)
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Composition of the Blood, cont.
Nonprotein Molecules That Contain Nitrogen
1. Plasma solutes that contain nitrogen
a. Amino acids: products of protein digestion
•
•
Absorbed into blood
Transported to cells that need them
b. Urea and uric acid: waste products of protein
and nucleic acid catabolism
•
Transported to the kidneys for excretion
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Composition of the Blood, cont.
Nutrients and Gases
1. Simple nutrients: end products of digestion
a. Transported in the blood
b. Include:
•
•
•
Amino acids: from protein digestion
Glucose and other simple sugars: from carbohydrate
digestion
Fatty acids: from lipid digestion
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Composition of the Blood, cont.
2. Respiratory gases
a. Oxygen and carbon dioxide
b. 3% of oxygen and 7%-10% of carbon dioxide
•
Transported as dissolved gases
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Composition of the Blood, cont.
Electrolytes
1. Inorganic ions
2. Contribute to osmotic pressure of plasma
3. Common electrolytes in plasma:
a.
b.
c.
d.
e.
f.
Sodium (Na+)
Potassium (K+)
Calcium (Ca++)
Chloride (Cl-)
Bicarbonate (HCO3-)
Phosphate (PO4-3)
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Composition of the Blood, cont.
Formed Elements
1. Erythrocytes: red blood cells
2. Leukocytes: white blood cells
3. Thrombocytes: platelets
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Composition of the Blood, cont.
4. Hematopoiesis: production of blood cells
a. Before birth: occurs primarily in liver and spleen
b. After birth:
•
•
Red bone marrow in specific regions of body
Some WBCs are produced in lymphoid tissue
c. Hemocytoblast: a stem cell in the bone
marrow from which blood cells develop
•
Seven different cell lines develop from the
hemocytoblast
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Composition of the Blood, cont.
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Composition of the Blood, cont.
Erythrocytes
1. Characteristics and functions of RBCs
a. Most numerous of formed elements
b. RBC range for adult:
•
•
Female: 4-5.5 million RBCs/cubic millimeter (mm3) of
blood
Male: 4.5-6.2 million RBCs/cubic millimeter (mm3) of
blood
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Composition of the Blood, cont.
c. Biconcave disks: thin in middle and thicker
around periphery
•
•
Provide flexibility for moving through capillaries
Provide maximum surface area for diffusion of gases
d. Mature RBCs: do not have a nucleus
(anucleate)
•
•
During development: nucleus is lost from cell
Gives cell more room for hemoglobin
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Composition of the Blood, cont.
e. Develop from stem cells in red bone marrow
•
Move from bone marrow into blood while still
immature
– Reticulocyte: immature erythrocyte
f. Functions: of erythrocytes:
•
Transport oxygen and, to a lesser extent, carbon
dioxide
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Composition of the Blood, cont.
g. Hemoglobin
• Makes up one third of each erythrocyte
• Consists of two parts:
– Heme: formed from a pigment that contains iron
– Globin: protein
• Heme combines with oxygen in the lungs:
oxyhemoglobin
– Bright red
• Oxygen is released to diffuse into tissue cells:
deoxyhemoglobin
– Darker red in color
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Composition of the Blood, cont.
2. Production of erythrocytes
a. Negative feedback mechanism
b. Erythropoietin: stimulates erythrocyte
production
c. Liver produces erythropoietin in inactive form
•
Secretes it into blood
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Composition of the Blood, cont.
d. Renal erythropoietic factor (REF): activates
erythropoietin
e. When blood oxygen concentration is low:
•
Kidneys release REF into blood
– Activates erythropoietin
f. Stimulates red bone marrow to produce RBCs
g. Additional RBCs: combine with oxygen
•
Increases blood oxygen concentration
h. As blood oxygen concentration increases:
•
Levels of REF and active erythropoietin decrease
– RBC production decreases
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Composition of the Blood, cont.
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Composition of the Blood, cont.
i.
Needed for RBC production:
•
•
•
Iron
Vitamin B12
Folic acid
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Composition of the Blood, cont.
j. Intrinsic factor:
•
•
•
Produced by stomach
Needed for absorption of vitamin B12 in the intestines
Without intrinsic factor: vitamin B12 cannot be
absorbed
– Results in pernicious anemia
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Composition of the Blood, cont.
3. Destruction of erythrocytes
a. Lifespan of an erythrocyte: 120 days
b. As erythrocyte ages:
•
Cell membrane becomes fragile
c. Macrophages (phagocytic cells in spleen and
liver) remove them from circulation
d. Replaced by an equal number of new cells
•
2 million erythrocytes are destroyed and replaced
every second
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Composition of the Blood, cont.
e. Hemoglobin separates into heme and globulin:
•
Heme broken down into:
– Iron compound: used to make new hemoglobin
– Bilirubin: yellow bile pigment
1) Becomes part of bile
•
Globin (protein)
– Broken down into amino acids: added to supply of
amino acids available in body
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Composition of the Blood, cont.
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Composition of the Blood, cont.
Leukocytes
1. Characteristics and functions of WBCs
a.
b.
c.
d.
Larger than erythrocytes
Fewer in number
Normal WBC count: 4,500-11,000 cells/mm3
Derived from hemocytoblast stem cells
•
Do not lose their nuclei
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Composition of the Blood, cont.
e. Leukocytes do most of their work in the tissues
•
•
Use blood as transport medium
Move through capillary walls into tissue spaces:
diapedesis
f. Provide a defense against organisms that
cause disease
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Composition of the Blood, cont.
Types of Leukocytes
1. Granular leukocytes (granulocytes):
granules in the cytoplasm
a. Neutrophils
•
•
•
Normal range: 50%-70% of WBCs
Purple, multilobed nucleus (3-5 lobes)
Many fine granules in cytoplasm
– Stain violet-pink
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Composition of the Blood, cont.
•
Band: immature neutrophil
– Curved, nonsegmented nuclei
– 0%-5% of neutrophils: normally present in band
form
•
•
•
First leukocytes to respond to tissue damage
Engulf bacteria by phagocytosis
Neutrophils and bands: increase during acute
infections
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Composition of the Blood, cont.
b. Eosinophils
•
•
•
•
Normal range: 1%-4% of WBCs
Segmented nucleus (no more than two lobes)
Large granules in the cytoplasm: stain bright reddish
orange
Functions:
– Neutralize histamine
1) Number increases during allergic reactions
– Destroy parasitic worms
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Composition of the Blood, cont.
c. Basophils
• Normal range: 0%-1% of WBCs
• S-shaped nucleus
• Large, coarse granules in cytoplasms
– Stain dark bluish-black
– Almost completely obscure details of nucleus
• Secrete histamine and heparin
– Histamine: dilates blood vessels
1) Increases blood flow to damaged tissues
2) Dilates blood vessels in allergic reactions
– Heparin: inhibits blood clot formation
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Composition of the Blood, cont.
2. Nongranular leukocytes (agranulocytes):
no granules in the cytoplasm
a. Lymphocytes
•
•
Normal range: 20%-35% of WBCs
Large round or slightly indented nucleus
– Stains a deep purplish blue
•
•
•
Small rim of sky-blue cytoplasm around nucleus
Produces antibodies
Increase in lymphocytes: occurs with certain viral
diseases
– Infectious mononucleosis, mumps, chickenpox, rubella,
viral hepatitis
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Composition of the Blood, cont.
b. Monocytes
•
•
•
Largest WBC
Normal range: 3%-8% of WBCs
U-shaped or kidney-shaped nucleus
– Surrounded by abundant cytoplasm: stains grayishblue
•
Macrophages: monocytes that leave the blood and
enter the tissues
– Engulf bacteria and cellular debris
– Finishes the cleanup process started by neutrophils
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Composition of the Blood, cont.
Thrombocytes
1. Also known as platelets
2. Consist of small fragments of large cells:
megakaryocytes
3. Develop from hemocytoblasts in red bone
marrow
4. Normal range: 150,000 to 500,000
platelets/mm3 of blood
5. Functions:
a. Close breaks in blood vessels
•
Become sticky and clump together to form platelet plugs
b. Initiate the formation of blood clots
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Hemostasis
1. Blood vessels that are torn or cut: permit blood
to escape
a. Into surrounding tissues or to outside of the body
b. Excessive blood loss: may result in death
2. Injured blood vessels: trigger reactions to
minimize blood loss and tissue damage
3. Hemostasis: the stoppage of bleeding
a. Consists of three processes:
•
•
•
Vascular constriction
Platelet plug formation
Coagulation
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Hemostasis, cont.
Vascular Constriction
1. First response to blood vessel injury
2. Contraction of smooth muscle in vessel
walls (constriction)
a. Restricts flow of blood through opening in the
vessel
b. Lasts only a few minutes
c. Allows enough time for other aspects of
hemostasis to begin
3. Platelets secrete a chemical: serotonin
a. Stimulates smooth muscle contraction in vessel
wall
•
Prolongs the vascular constriction
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Hemostasis, cont.
Platelet Plug Formation
1. Normally platelets do not:
a. Stick to each other
b. Stick to blood vessel walls
2. When blood vessel breaks:
a. Underlying connective tissue is exposed
b. Attracts platelets
•
•
Accumulate in damaged region
Adhere to connective tissue and each other
c. Creates a platelet plug
•
Obstructs tear in the vessel
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Hemostasis, cont.
Coagulation
1. Formation of a blood clot
2. Procoagulants: factors in the blood that
promote clotting
3. Anticoagulants: factors in the blood that
inhibit clotting
4. Normally anticoagulants override
procoagulants
a. Blood remains fluid and does not clot
5. When vessels damaged: procoagulants
increase activity
a. Results in the formation of a clot
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Hemostasis, cont.
6. Involves a series of chemical reactions
a. Platelets and damaged tissues release chemicals
•
Initiate a series of reactions: result in formation of
prothrombin activator
b. In the presence of calcium ions and prothrombin
activator:
•
Prothrombin (inactive) is converted thrombin (active)
c. Thrombin converts fibrinogen (inactive) fibrin
(active)
•
Fibrin threads: form a mesh
– Adheres to damaged tissue
– Traps blood cells and platelets to form the clot
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Hemostasis, cont.
7. After a clot has formed:
a. Fibrin strands contract: clot retraction
•
Causes clot to shrink
–
–
–
–
Pulls edges of damaged tissue closer together
Reduces blood flow to area
Reduces probability of infection
Enhances healing
b. Fibroblasts migrate into clot
•
Form fibrous connective tissue
– Repairs damaged area
8. Clot is eventually dissolved: fibrinolysis
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Blood Types
ABO Blood Groups
1. Based on the presence or absence of
certain antigens
a. On the surface of RBC membrane
2. Blood types are inherited
3. Blood types:
a.
b.
c.
d.
Type A: A antigen
Type B: B antigen
Type AB: A and B antigens
Type O: neither A nor B antigens
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Blood Types, cont.
4. Certain blood antibodies: develop in plasma
shortly after birth
a.
b.
c.
d.
Type A blood:
Type B blood:
Type AB blood:
Type O blood:
B antibodies
A antibodies
Neither A nor B antibodies
A and B antibodies
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Blood Types, cont.
Rh Blood Groups
1. First studied in rhesus monkey
2. Rh positive (Rh+): Rh antigen
a. 85% of population
3. Rh negative (Rh-): do not have Rh antigen
a. 15% of population
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Blood Types, cont.
4. Inherited trait
5. Normally: neither Rh+ nor Rh- individuals
have Rh antibodies
a. If Rh- person is exposed to Rh+ blood (through
blood transfusion or transfer of blood between a
mother and fetus)
•
Individual develops Rh antibodies
b. If exposed to Rh+ blood a second time:
•
Transfusion reaction results
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Blood Vessels
1. Channels through which blood is distributed
to body tissues
2. Pulmonary vessels: transport blood from
right ventricle to lungs and back to left
atrium
3. Systemic vessels: carry blood from left
ventricle to all parts of the body and then
return it to right atrium
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Blood Vessels, cont.
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Classification and Structure of
Blood Vessels
Arteries
1. Carry blood away from heart
2. Pulmonary arteries: transport blood that
has a low oxygen content
a. From right ventricle to lungs
3. Systemic arteries: transport oxygenated
blood from left ventricle to body tissues
4. Blood is pumped from ventricles into large
elastic arteries
a. Branch repeatedly into smaller arteries
•
Branching results in microscopic arteries: arterioles
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Classification and Structure of
Blood Vessels, cont.
5. Artery wall
a. Tunica intima: innermost layer
b. Tunica media: middle layer
•
•
•
•
Consists of smooth muscle
Usually the thickest layer
Provides support for the vessel
Changes vessel diameter
– To regulate blood flow and blood pressure
c. Tunica externa: outermost layer
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Classification and Structure of
Blood Vessels, cont.
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Classification and Structure of
Blood Vessels, cont.
Capillaries
1. Smallest and most numerous of the blood
vessels
2. Form connection between:
a. Vessels that carry blood away from the heart
(arteries)
b. Vessels that return blood to heart (veins)
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Classification and Structure of
Blood Vessels, cont.
3. Capillary wall: consists of a thin endothelium
(one cell layer)
a. Permits exchange of materials between:
•
•
Blood in the capillary
Adjacent tissue cells
4. Capillary is so small: erythrocytes must pass
through them in single file
a. Slows blood flow
•
Allows time for transport of substances across
capillary endothelium
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Classification and Structure of
Blood Vessels, cont.
Veins
1. Carry blood toward heart
2. After blood passes through capillaries:
a. Enters the smallest veins: venules
b. Flows into progressively larger veins until
reaches the heart
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Classification and Structure of
Blood Vessels, cont.
3. Vein walls: same three layers as the arteries
a. Less smooth muscle and connective tissue
•
Makes walls of veins thinner and less rigid than those
of arteries
– Blood in the veins has less pressure than blood in the
arteries
– Veins can hold more blood: holds 70% of the total
blood volume
4. Venous valves: located in medium and
large veins
a. Keep blood flowing toward heart
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Circulatory Pathways
1. The blood vessels of the body are
functionally divided into two distinct circuits:
a. Pulmonary circuit
b. Systemic circuit
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Circulatory Pathways, cont.
Pulmonary Circuit
1. Transports blood from right side of the heart
to lungs
a. Then returns it to left side of heart
2. Contains oxygen-poor blood (increased
levels of carbon dioxide)
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Circulatory Pathways, cont.
3. Pathway for pulmonary circuit
a. Blood is returned to right atrium from the tissue
cells of the body
b. Blood passes through tricuspid valve into right
ventricle
c. During ventricular systole: blood is ejected
through pulmonary SL valve
•
Into pulmonary trunk: divides into right and left
pulmonary arteries
d. Each pulmonary artery enters a lung
•
Divides into smaller vessels until they become
capillaries
e. Capillaries of the lungs: form networks
•
Surround the air sacs: alveoli
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Circulatory Pathways, cont.
f. CO2 diffuses from capillary blood into alveoli
g. O2 diffuses from alveoli into blood
h. Oxygenated blood enters pulmonary venules
•
Form progressively larger veins
– Until two pulmonary veins emerge from each lung
i.
Blood is carried to left atrium
4. In pulmonary circuit:
a. Arteries carry deoxygenated blood away from
heart
b. Veins carry oxygenated blood to heart
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Circulatory Pathways, cont.
Systemic Circuit
1.
2.
3.
4.
Provides blood supply to all body tissues
Carries oxygen and nutrients to cells
Picks up carbon dioxide and waste products
Carries oxygenated blood from left ventricle
through the arteries to the capillaries in the
tissues
5. From tissue capillaries: deoxygenated blood
returns through a system of veins to right
atrium
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Circulatory Pathways, cont.
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Posttest
True or False
1. The peritoneum is the loose-fitting sac
that encloses the heart.
2. The superior vena cava returns blood
to the heart from the lower extremities.
3. The mitral valve is located between
the right atrium and right ventricle.
4. When the ventricles are contracting,
the AV valves are open.
5. The buffy coat is made up of white
blood cells and platelets.
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Posttest, cont.
True or False
6. An immature erythrocyte is a band.
7. Bile is the yellow pigment that results
from the breakdown of hemoglobin.
8. Acute infections cause an increase in
the number of neutrophils.
9. Thrombin converts fibrinogen to fibrin.
10. Microscopic arteries are known as
arterioles.
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