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VT 106
Comparative Anatomy and Physiology
Blood and Blood Vessels
CARDIOVASCULAR SYSTEM – BLOOD
Functions of Blood
transportation – nutrients, gases, wastes, hormones, cells
regulation of homeostasis – pH, body temperature, fluid and electrolytes
protection – phagocytosis, clotting, immunity
COMPONENTS OF BLOOD – liquid connective tissue
1) Plasma – liquid matrix (91% water, 9% solutes)
plasma proteins (7%) – maintain blood osmotic pressure
most produced by the liver
albumins (60%) – transport proteins
globulins (35%) – some transport proteins
immunoglobulins (antibodies) – immune function
fibrinogen (4%) – blood clotting protein
other solutes (2%)
electrolytes – osmotic pressure, cell functions
nutrients – from digestive tract
wastes – from cellular metabolism
gases – oxygen, carbon dioxide
enzymes and hormones
2) Formed Elements – cells and cell fragments
red blood cells (RBCs) – erythrocytes
transport oxygen
white blood cells (WBCs) – leukocytes
protective functions
platelets – thrombocytes
blood clotting
HEMATOPOIESIS – formation of blood cells
embryo – hemopoiesis occurs in yolk sac
fetus – occurs in liver, spleen, thymus
birth to adult – occurs mainly in red bone marrow
birds – occurs mainly in the spleen
Red Marrow – within spongy bone
pluripotent stem cells – cells that give rise to all blood cells
derived from embryonic mesenchyme
differentiate to form different types of blood cells
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Regulation of Hematopoiesis
erythropoiesis – formation of red blood cells
erythropoietin (EPO) – hormone from kidneys that stimulates
production of RBCs
thrombopoiesis – formation of platelets
thrombopoietin (TPO) – hormone from kidneys and liver that
stimulates production of platelets
leukopoiesis – formation of white blood cells
colony-stimulating factors (cytokines)
stimulate specific WBC lines in response to infections or
cell damage
thymic hormones – from thymus
stimulate T-lymphocyte production
RED BLOOD CELLS (ERYTHROCYTES) around 260 million/drop of blood
Anatomy of RBCs – adapted to carry large amount of oxygen and travel freely
through blood vessels
biconcave disc – flexible, large surface to volume ratio
no nucleus and few organelles in mature cells of mammals
no mitochondria – anaerobic respiration
1/3 of cell’s weight is hemoglobin (molecule that binds oxygen)
(bird and reptile RBCs are nucleated and elliptical in shape)
Hemoglobin – around 280mil molecules/RBC
globin – 4 polypeptide chains folded in complex globular shape
heme – 4 iron-containing pigments (1 attached to each polypeptide)
each iron binds 1 oxygen molecule reversibly
oxyhemoglobin – saturated with oxygen (in lungs) – bright red
deoxyhemoglobin – not saturated (in tissues) – dark and purplish
anemia – low RBC count or low Hb content
low O2 carrying capacity of blood
RBC Formation and Turnover – about 3 mil new RBC/sec
1) low cellular oxygen (hypoxia) stimulates EPO production
2) EPO stimulates stem cells in marrow to divide and differentiate
3) reticulocytes (immature RBCs) eject nucleus and enter bloodstream
RBC lifespan is 1-5 months
extravascular hemolysis – old blood cells removed by macrophages
occurs mainly in spleen and liver
globin – amino acids recycled
heme – iron is recycled, pigment molecule is broken down
bilirubin – yellow by-product excreted by liver
liver disease – jaundice (icterus)
intravascular hemolysis – a few blood cells rupture in blood vessels
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WHITE BLOOD CELLS (LEUKOCYTES)
numbers fluctuate in response to disease states
leukocytosis – high WBC count
differential count – number of the 5 types of WBC/100 WBC
leukopenia – low WBC count, susceptible to infections
leukemia – cancer of WBC stem cells
severe leukocytosis can result in anemia as marrow and blood are
taken over by WBCs
Granulocytes – contain vesicles with characteristic staining properties
Eosinophils
increase due to allergies, parasites, autoimmune disease
release secretions which reduce inflammation and destroy parasites
phagocytize small antigen-antibody complexes
Basophils
increase due to allergies
enter damaged tissues and secrete histamine and heparin
cause inflammation
Neutrophils (Heterophils in birds)
increase rapidly due to most infections and injuries (esp. bacteria)
stress response – glucocorticoids trigger release of neutrophils
phagocytes - contain lysozymes; kill and digest many microbes
Agranulocytes – granules not visible with typical staining
Monocytes – form in bone marrow and mature in tissues
increase in viral or fungal infections, chronic diseases
differentiate into macrophages in tissues
aggressive phagocytes
attract other WBCs, and fibroblasts to wall-off injury
Lymphocytes – form in marrow and mature in lymphatic tissues
mediate immune responses
B cells – antibody-mediated immunity
T cells – cell-mediated immunity
natural killer (NK) cells – immune surveillance
PLATELETS (THROMBOCYTES)
megakaryocyte – huge precursor cell in red marrow
fragments into up to 4 thousand platelets
pieces of cell membrane containing vesicles which aid in hemostasis
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HEMOSTASIS – stoping bleeding
hemorrhage – loss of a large amount of blood
3 phases:
1) vascular spasm – injured vessel constricts
triggered by sympathetic reflexes and local chemical signals
2) platelet plug formation
platelet adhesion – platelets stick to tissues exposed by vessel damage
platelet aggregation – platelets release vesicles, attracting more platelets
to the site
3) coagulation (clotting) phase – conversion of fibrinogen (a soluble plasma
protein) to fibrin (an insoluble protein)
clot – network of fibrin strands and blood cells that seals damaged site
clotting factors – 12 substances involved in clotting
calcium ions + 11 proteins (most produced by liver, some by
platelets and damaged blood vessel)
Vitamin K – from diet and produced by intestinal bacteria
required for synthesis of 4 clotting factors
serum – blood plasma minus clotting factors
clot retraction – fibrin threads contract, pulling edges wound together
anticoagulant – substance that delays or prevents clotting
heparin – secreted by basophils and mast cells, used in blood tubes
EDTA – used in blood tubes
aspirin – inhibits vascular spasm and platelet aggregation
thrombosis – clotting in an unbroken vessel
roughened endothelium (cholesterol plaques)
thromboembolism – clot breaks loose in bloodstream
BLOOD TYPES
blood antigens – RBC surface glycoproteins and glycolipids that are genetically
determined
blood type – classification based on presence or absence of antigens on RBCs
Blood Transfusions – transfer of whole blood or blood components
cross-reaction – an individual given a transfusion of blood with antigens
not found on its own RBCs can have an immune response
agglutination – clumping of RBCs
hemolysis – rupture of RBCs
blood typing – blood tested with known antiserum to determine the blood type
cross-matching – donor blood mixed with recipient serum to test for reactions
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CARDIOVASCULAR SYSTEM – BLOOD VESSELS
Arteries – muscular, elastic vessels
carry blood away from the heart
Capillaries – tiny, thin-walled vessels
site of exchange of substances between blood and tissues
Veins – large, relatively thin-walled vessels
carry blood to the heart
Systemic Circuit
arteries carry oxygenated blood away from heart
veins carry deoxygenated blood to the heart
Pulmonary Circuit
arteries carry deoxygenated blood away from heart
veins carry oxygenated blood to the heart
ANATOMY OF BLOOD VESSELS
3 layers (tunics):
tunica interna – inner layer
endothelium – simple squamous epithelium
tunica media – middle layer
circular smooth muscle – regulates vessel diameter
tunica externa – outer layer
fibrous connective tissue – gives strength, elasticity
Arteries – vessels with thick, muscular tunica media and lots of elastic fibers
stretch to accommodate surge of blood from heart, then recoil to push blood
forward through vessels
this elasticity maintains pressure in the arteries when heart is relaxed
arteries branch to deliver blood to all tissues, muscle determines vessel diameter
vasoconstriction – decreased diameter, less blood flow to tissue
vasodilation – increased diameter, more blood flow to tissue
arterioles – tiny, thin-walled branches with a little muscle
control blood flow into capillary beds
Capillaries – extremely thin-walled, microscopic vessels within tissues
only endothelium and basement membrane
found in most tissues; number depends on metabolic needs of tissue
exchange vessels – site of diffusion of materials between blood and tissues
water and solutes cross through gaps within or between cells
sinusoids – capillaries with large gaps found in red marrow, liver and spleen
allow blood cells and plasma proteins to enter or exit blood stream
capillary bed – network of 10-100 capillaries supplying a tissue region
arterioles supplying bed open and close based on needs of tissue
venules – small vessels that carry blood from capillaries to the larger veins
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Veins – large, thin-walled vessels with reduced muscle and elastic fibers
pressure in veins is normally very low, can stretch out to store blood
constrict or dilate to regulate amount of blood returning to the heart
valves – one-way cusps that help keep blood flowing towards heart
skeletal muscle pump – contraction of limb muscles compresses veins
helps return blood to heart
respiratory pump – pressure changes in the thoracic cavity during
breathing help return blood to the heart
Collateral Circulation – alternate pathway for blood flow in a region if one vessel
becomes blocked
infarction – death of tissue due to blockage of blood flow into a tissue
HEMODYNAMICS – forces involved in circulating blood
Blood Pressure – pressure in arteries, generated by ventricular systole and
maintained by elastic recoil and vasoconstriction of arteries
adequate blood pressure is needed to drive blood flow into capillary beds
systolic pressure – highest arterial pressure during ventricular systole
diastolic pressure – lowest arterial pressure during ventricular diastole
elastic recoil of arteries maintains pressure on blood
vasoconstriction maintains vascular resistance
pulse – palpable change in artery diameter during systole and diastole
pulse pressure = systolic BP – diastolic BP
Vascular Resistance – opposition to blood flow due to friction against vessel walls
adequate resistance is needed to maintain blood pressure
(there is not enough blood to fill all of the blood vessels at once)
regulated by diameter of arteries and arterioles
vasoconstriction – smaller vessel = more resistance to blood flow
increases blood pressure
vasodilation – larger vessel = less resistance to blood flow
decreases blood pressure
CAPILLARY EXCHANGE – exchange of solutes between blood and tissues
Filtration – capillary blood pressure forces fluid and small solutes out of
capillaries into interstitial spaces around cells
Reabsorption – blood osmotic pressure pulls fluid and small solutes from
interstitial spaces back into capillaries
diffusion – solutes exchanged from high concentration to low concentration
from blood into cells – oxygen, nutrients, hormones
from cells into blood – carbon dioxide, wastes, hormones
(plasma proteins and blood cells only diffuse through sinusoid capillaries)
only 85% of filtered fluid is reabsorbed; excess collected by lymphatic system
edema – excess fluid accumulation in tissues
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REGULATION OF BLOOD PRESSURE AND BLOOD FLOW
tissue perfusion – amount of blood being supplied to tissues; must supply needs
of tissues for oxygen and nutrients, and removal of wastes
blood pressure depends on:
cardiac output – heart rate X stroke volume
vascular resistance – diameter of arteries and arterioles
Autoregulation of Capillary Beds – blood flow to capillary beds increases or
decreases based on needs of the cells
local factors cause dilation or constriction of arterioles
vasodilators – associated with increased metabolism
low oxygen, high carbon dioxide, low pH (eg. lactic acid)
inflammatory chemicals – (eg. histamine)
vasoconstrictors – associated with decreased metabolism
high oxygen, low carbon dioxide, high pH
various clotting factors
Neural Regulation – when stressed, large numbers of tissues need more blood flow
nerve signals to vessels all over the body act to maintain blood pressure and
direct blood flow where it is needed most
cardiovascular center – medulla oblongata
baroreceptors detect blood pressure
chemoreceptors detect blood O2, CO2, and pH (H+)
sympathetic neurons – regulate vessel diameter (resistance)
vasoconstriction in most arteries = increases blood pressure
constriction of veins = increases venous return to heart
more blood returned to heart = more cardiac output
vasodilation to tissues needed most (eg. brain, muscles)
Hormonal Regulation – triggered by drop in blood pressure and reduced blood
flow and oxygenation of tissues
RAA system – stimulated by decreased blood flow to kidneys
aldosterone – kidneys retain sodium and water
increases blood volume = increased blood pressure
ADH – kidneys produce less urine
increases blood volume = increased blood pressure
erythropoietin – increases formation of RBCs
increases blood volume = increased blood pressure
epinephrine – part of sympathetic response
increases cardiac output and regulates resistance
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SHOCK – cardiovascular system fails to deliver adequate oxygen to meet cellular needs
throughout body
hypovolemic shock – low blood volume
hemorrhage
dehydration – diarrhea, vomiting, sweating
diabetes – excessive urine production
cardiogenic shock – poor heart function
heart disease or damage, valve problems, arrhythmias
vascular shock – decreased vascular resistance
anaphylactic shock – allergy vasodilators
neurogenic shock – CV center dysfunction (head trauma)
septic shock – bacterial toxins
obstructive shock – blockage of blood flow
heartworms
pulmonary thromboembolism
signs and symptoms of shock
low BP
rapid HR
weak, rapid pulse
cool, pale skin and nausea (sympathetic effects)
impaired mental state
reduced urination and increased thirst
acidosis (low plasma pH)
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