The Circulatory System and Blood

Copyright © 2010 Pearson Education, Inc.

The Circulatory System and Blood

Copyright © 2010 Pearson Education, Inc. Figure 19.2

Large veins(capacitancevessels)

Largelymphaticvessels

Arteriovenousanastomosis

Lymphaticcapillary

Postcapillaryvenule

Sinusoid

Metarteriole

Terminal arteriole

Arterioles(resistance vessels)

Muscular arteries(distributingvessels)

Elastic arteries(conductingvessels)

Small veins(capacitancevessels)

Lymphnode

Capillaries(exchange vessels)

Precapillary sphincterThoroughfarechannel

Lymphaticsystem

Venous system Arterial systemHeart


Blood Flow Through Body Tissues

• Blood flow (tissue perfusion) is involved in

• Delivery of O2 and nutrients to, and removal of

wastes from, tissue cells

• Gas exchange (lungs)

• Absorption of nutrients (digestive tract)

• Urine formation (kidneys)

• Rate of flow is precisely the right amount to

provide for proper function


Blood Pressure


Velocity of Blood Flow

• Changes as it travels through the systemic

circulation

• Is inversely related to the total cross-sectional

area

• Is fastest in the aorta, slowest in the

capillaries, increases again in veins

• Slow capillary flow allows adequate time for

exchange between blood and tissues


Monitoring Circulatory Efficiency

• Vital signs: pulse and blood pressure, along

with respiratory rate and body temperature

• Pulse: pressure wave caused by the

expansion and recoil of arteries

• Pulse is routinely taken at wrist. Please learn

other sites (surface anatomy) where pulse is

taken.


Maintaining Blood Pressure

• Requires

• Cooperation of the heart, blood vessels, and

kidneys

• Supervision by the brain


Common carotid

artery

Brachial artery

Radial artery

Femoral artery

Popliteal artery

Posterior tibial

artery

Dorsalis pedis

artery

Superficial temporal

artery

Facial artery


Variations in Blood Pressure

• Blood pressure cycles over a 24-hour period

• BP peaks in the morning due to levels of

hormones

• Age, sex, weight, race, mood, and posture

may vary BP


Alterations in Blood Pressure

• Hypotension: low blood pressure

• Systolic pressure below 100 mm Hg

• Often associated with long life and lack of

cardiovascular illness


Homeostatic Imbalance: Hypotension

• Orthostatic hypotension: temporary low BP

and dizziness when suddenly rising from a

sitting or reclining position

• Chronic hypotension: hint of poor nutrition and

warning sign for Addison’s disease or

hypothyroidism

• Acute hypotension: important sign of

circulatory shock


Alterations in Blood Pressure

• Hypertension: high blood pressure

• Sustained elevated arterial pressure of 140/90

or higher

• May be transient adaptations during fever,

physical exertion, and emotional upset

• Often persistent in obese people


Homeostatic Imbalance: Hypertension

• Prolonged hypertension is a major cause of

heart failure, vascular disease, renal failure,

and stroke

• Primary or essential hypertension

• 90% of hypertensive conditions

• Due to several risk factors including heredity,

diet, obesity, age, stress, diabetes mellitus,

and smoking


Homeostatic Imbalance: Hypertension

• Secondary hypertension is less common

• Due to identifiable disorders, including kidney

disease, arteriosclerosis, and endocrine

disorders such as hyperthyroidism and

Cushing’s syndrome


The Major Blood Vessels

Copyright © 2010 Pearson Education, Inc. Figure 19.21b

Internal carotid artery

Common carotid arteries

Subclavian artery

Subclavian artery

Aortic archAscending aortaCoronary arteryThoracic aorta (abovediaphragm)

Renal artery

Superficial palmar arch

Radial artery

Ulnar artery

Internal iliac artery

Deep palmar arch

Vertebral artery

Brachiocephalic trunk

Axillary artery

Brachial artery

Abdominal aorta

Superior mesenteric artery

Gonadal artery

Common iliac arteryExternal iliac artery

Digital arteries

Femoral arteryPopliteal arteryAnterior tibial arteryPosterior tibial artery

Arcuate artery(b) Illustration, anterior

view

Inferior mesenteric artery

Celiac trunk

External carotid artery

Arteries of the head and trunk

Arteries that supply the upper limb

Arteries that supply the lower limb


• Superficial

temporal artery***

• Maxillary artery

• Occipital artery

• Facial artery***

• Lingual artery

• Superior thyroid

artery

Ophthalmic artery

Larynx

Thyroid gland

(overlying trachea)

Clavicle (cut)

Brachiocephalic

trunk

Internal thoracic

artery

Basilar artery

Vertebral artery

Internal

carotid artery

Subclavian

artery

Axillary

artery

(b) Arteries of the head and neck, right aspect

External

carotid artery

Common

carotid artery

Thyrocervical

trunk

Costocervical

trunk

Branches of

the external

carotid artery

***routes for infection

Copyright © 2010 Pearson Education, Inc. Figure 19.22d

Frontal lobe

Optic chiasma

Middle

cerebral

artery

Internalcarotid arteryMammillarybody

Temporal

lobe

Occipital lobe

Cerebral arterialcircle (circle of Willis)

• Posteriorcerebral artery

Basilar artery

Vertebral artery

Cerebellum

• Posteriorcommunicating artery

(d) Major arteries serving the brain (inferior view, right side

of cerebellum and part of right temporal lobe removed)

Pons

• Anteriorcerebral artery

• Anteriorcommunicating artery

Posterior

Anterior


Vertebral artery

Costocervical trunk

Thoracoacromial artery

Axillary artery

Subscapular artery

Radial artery

Ulnar artery

Brachial artery

Suprascapular artery

Thyrocervical trunk

Posterior circumflex

humeral artery

Anterior circumflex

humeral artery

Deep artery of arm

Common

interosseous

artery

Deep palmar archSuperficial palmar archDigital arteries

Common carotid

arteries

Right subclavian artery

Left subclavian artery

Brachiocephalic trunk

Posterior intercostal

arteries

Anterior intercostal

arteryInternal thoracic artery

Lateral thoracic artery

Descending aorta

(b) Illustration, anterior view


Liver (cut) Diaphragm

Esophagus

Left gastric

artery

Superior

mesenteric

mesenteric

Left

gastroepiploic

artery

Spleen

Stomach

Pancreas

(major portion lies

posterior to stomach)

Splenic artery

Inferior vena cava

Celiac trunk

Hepatic artery

proper

Common hepatic

artery

Gastroduodenal

artery

Right gastric artery

Gallbladder

Abdominal aorta

Right

gastroepiploic

artery

Duodenum

(b) The celiac trunk and its major branches. The left half of the liver has been removed.

Duodenal ulcers and the hepatopancreaticoduodenal artery

Copyright © 2010 Pearson Education, Inc. Figure 19.24c

(c) Major branches of the abdominal aorta.

Hiatus (opening)

for inferior

vena cava

Diaphragm

Inferior

phrenic artery

Middle

suprarenal

artery

Renal artery

Superior

mesenteric

artery

Median sacral

arteryCommon

iliac artery

Ureter

Gonadal

(testicular or

ovarian) artery

Hiatus (opening)

for esophagus

Celiac trunk

Adrenal

(suprarenal)

gland

Kidney

Abdominal aorta

Lumbar arteriesInferior

mesenteric

artery

Copyright © 2010 Pearson Education, Inc. Figure 19.24d

(d) Distribution of the superior and inferior mesenteric arteries.

The transverse colon has been pulled superiorly.

Celiac trunk Transverse colon

Inferior mesenteric

artery

Aorta

Descending colon

Sigmoid colon

Rectum

Superior

mesenteric artery

Ascending colon

Ileum

Right common iliac

artery

Appendix

Cecum

Branches ofthe inferior mesenteric artery

• Left colic artery• Sigmoidal arteries• Superior rectal

artery

Branches ofthe superiormesenteric artery

• Middle colic artery• Intestinal arteries• Right colic artery• Ileocolic artery


Common iliac artery

Deep artery of thigh

Obturator artery

Femoral artery

Adductor hiatus

Popliteal artery

Anterior tibial artery

Posterior tibial artery

Fibular artery

Dorsalis pedis artery

Arcuate artery

Dorsal metatarsal

arteries

(b) Anterior view

Internal iliac artery

Superior gluteal artery

External iliac artery

Lateral circumflex

femoral artery

Medial circumflex

femoral artery


(c) Posterior view

Popliteal artery

Anterior tibial artery

Fibular artery

Dorsalis pedis artery

(from top of foot)

Plantar arch

Medial plantar

artery

Lateral plantar

artery

Posterior tibial

artery


Renal vein

Splenic vein

Basilic vein

Brachial vein

Cephalic vein

Dural venous sinuses

External jugular vein

Vertebral vein

Internal jugular vein

Superior vena cava

Right and left

brachiocephalic veins

Axillary vein

Great cardiac vein

Hepatic veins

Hepatic portal vein

Superior mesenteric

veinInferior vena cava

Ulnar vein

Radial vein

Common iliac vein

External iliac vein

Internal iliac vein

Digital veins

Femoral vein

Great saphenous vein

Popliteal vein

Posterior tibial vein

Anterior tibial vein

Small saphenous vein

Dorsal venous arch

(b) Illustration, anterior

view. The vessels of the

pulmonary circulation

are not shown. Dorsal metatarsal veins

Inferior mesenteric vein

Median cubital vein

Subclavian vein

Veins of the head and trunk Veins that drain

the upper limb

Veins that drain

the lower limb


(c) Dural venous sinuses of the brain

Confluence

of sinuses

Superior sagittal

sinus

Falx cerebri

Inferior sagittal

sinus

Straight sinus

Cavernous

sinus

Transverse

sinuses

Sigmoid sinus

Jugular foramen

Right internal

jugular vein

Cavernous sinus,

cranial nerves, and

migraines


(c) The hepatic portal circulation.

Hepatic veins

Liver

Spleen

Gastric veins

Inferior vena cava

Inferior vena cava

(not part of hepatic

portal system)

Splenic vein

Right gastroepiploic

vein

Inferior

mesenteric vein

Superior

mesenteric vein

Large intestine

Hepatic portal

vein

Small intestine

Rectum


Popliteal vein

Common iliac vein

Fibular vein

Anterior tibial vein

Dorsalis pedis vein

Dorsal venous arch

Dorsal metatarsal

veins(b) Anterior view

Internal iliac veinExternal iliac veinInguinal ligament

Femoral veinGreat saphenous

vein (superficial)

Small saphenous

veinCoronary bypass

surgery and other

grafts


The Heart









Cardiac Muscle Tissue



The Path of Blood Flow

Copyright © 2010 Pearson Education, Inc. Figure 19.19a

R. pulmon-

ary veins

Pulmonary

trunk

Pulmonary capillaries

of the R. lung

Pulmonary capillaries

of the L. lungR. pulmonary

artery

L. pulmonary

artery

To

systemic

circulation

L. pulmonary

veins

(a) Schematic flowchart.

From

systemic

circulationRA

RV LV

LA


The Heart Beat: Electrical Conduction








The Fetal Heart


Developmental Aspects

• Fetal shunts (foramen ovale and ductus

arteriosus) bypass nonfunctional lungs

• Ductus venosus bypasses the liver

• Umbilical vein and arteries circulate blood to

and from the placenta


between atrium



Structure of Blood Vessel Walls

• Arteries and veins

• Tunica intima, tunica media, and tunica

externa

• Lumen

• Central blood-containing space

• Capillaries

• Endothelium with sparse basal lamina


Tunica media(smooth muscle andelastic fibers)

Tunica externa

(collagen fibers)

Lumen

Artery

LumenVein

Internal elastic lamina

External elastic lamina

Valve

(b)

Endothelial cellsBasement membrane

Capillary

network

Capillary

Tunica intima

• Endothelium• Subendothelial layer


Tunics

• Tunica intima

• Endothelium lines the lumen of all vessels

• In vessels larger than 1 mm, a subendothelial

connective tissue basement membrane is

present


Tunics

• Tunica media

• Smooth muscle and sheets of elastin

• Sympathetic vasomotor nerve fibers control

vasoconstriction and vasodilation of vessels


Tunics

• Tunica externa (tunica adventitia)

• Collagen fibers protect and reinforce

• Larger vessels contain vasa vasorum to

nourish the external layer

Copyright © 2010 Pearson Education, Inc. Table 19.1 (1 of 2)


Elastic (Conducting) Arteries

• Large thick-walled arteries with elastin in all

three tunics

• Aorta and its major branches

• Large lumen offers low-resistance

• Act as pressure reservoirs—expand and recoil

as blood is ejected from the heart


Muscular (Distributing) Arteries and

Arterioles

• Distal to elastic arteries; deliver blood to body

organs

• Have thick tunica media with more smooth

muscle

• Active in vasoconstriction


Arterioles

• Smallest arteries

• Lead to capillary beds

• Control flow into capillary beds via

vasodilation and vasoconstriction

Copyright © 2010 Pearson Education, Inc. Figure 19.1a

Artery

Vein

(a)


Venules

• Formed when capillary beds unite

• Very porous; allow fluids and WBCs into

tissues

• Postcapillary venules consist of endothelium

and a few pericytes

• Larger venules have one or two layers of

smooth muscle cells


Veins

• Formed when venules converge

• Have thinner walls, larger lumens compared with corresponding arteries

• Blood pressure is lower than in arteries

• Thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks

• Called capacitance vessels (blood reservoirs); contain up to 65% of the blood supply


Capillaries

• Microscopic blood vessels

• Walls of thin tunica intima, one cell thick

• Pericytes help stabilize their walls and control

permeability

• Size allows only a single RBC to pass at a

time


Capillaries

• In all tissues except for cartilage, epithelia,

cornea and lens of eye

• Functions: exchange of gases, nutrients,

wastes, hormones, etc.

Copyright © 2010 Pearson Education, Inc. Figure 19.16 (1 of 2)

Red blood

cell in lumen

Endothelial cell

Intercellular cleft

Fenestration

(pore)Endothelial cell nucleus

Tight junction

Basement membrane

Pinocytotic vesicles

Copyright © 2010 Pearson Education, Inc. Figure 19.16 (2 of 2)

Basementmembrane

Endothelialfenestration(pore)

Intercellularcleft

Pinocytoticvesicles

Caveolae

4 Transportvia vesicles orcaveolae (largesubstances)

3 Movementthroughfenestrations (water-soluble substances)

2 Movementthrough intercellular clefts (water-soluble substances)

1 Diffusionthrough membrane (lipid-soluble substances)

Lumen


Sinusoidal Capillaries

• Fewer tight junctions, larger intercellular

clefts, large lumens

• Usually fenestrated

• Allow large molecules and blood cells to pass

between the blood and surrounding tissues

• Found in the liver, bone marrow, spleen


Nucleus of

endothelial

cell

Red blood

cell in lumen

Endothelial

cell

Tight junction

Incomplete

basement

membrane

Large

intercellular

cleft

(c) Sinusoidal capillary. Most permeable. Occurs in

special locations (e.g., liver, bone marrow, spleen).


Capillary Beds

• Interwoven networks of capillaries form the

microcirculation between arterioles and

venules


Blood Flow Through Capillary Beds

• Precapillary sphincters regulate blood flow

into true capillaries

• Regulated by local chemical conditions and

vasomotor nerves (sympathetic division of

ANS).


(a) Sphincters open—blood flows through true capillaries.

(b) Sphincters closed—blood flows through metarteriole

thoroughfare channel and bypasses true capillaries.

Precapillary

sphincters Metarteriole

Vascular shunt

Terminal arteriole Postcapillary venule

Terminal arteriole Postcapillary venule

Thoroughfare channel

True capillaries


Blood Composition

• Blood: a fluid connective tissue composed of

• Plasma

• Formed elements

• Erythrocytes (red blood cells, or RBCs)

• Leukocytes (white blood cells, or WBCs)

• Platelets


Blood Composition

• Hematocrit

• Percent of blood volume that is RBCs

• 47% ± 5% for males

• 42% ± 5% for females


1 Withdraw

blood and place

in tube.

2 Centrifuge the

blood sample.

Plasma• 55% of whole blood• Least dense componentBuffy coat• Leukocytes and platelets• <1% of whole bloodErythrocytes

• 45% of whole blood• Most densecomponent

Formed

elements


Physical Characteristics and Volume

• Sticky, opaque fluid

• Color scarlet to dark red

• pH 7.35–7.45

• 38C (100.4F)

• ~8% of body weight

• Average volume: 5–6 L for males, and 4–5

L for females


Functions of Blood

1. Distribution of

• O2 and nutrients to body cells

• Metabolic wastes to the lungs and kidneys

for elimination

• Hormones from endocrine organs to target

organs


Functions of Blood

2. Regulation of

• Body temperature by absorbing and

distributing heat

• Normal pH using buffers

• Adequate fluid volume in the circulatory

system


Functions of Blood

3. Protection against

• Blood loss

• Plasma proteins and platelets initiate clot formation

• Infection

• Antibodies

• Complement proteins

• WBCs defend against foreign invaders


Blood Plasma

• 90% water

• Proteins are mostly produced by the liver

• 60% albumin

• 36% globulins

• 4% fibrinogen


Blood Plasma

• Nitrogenous by-products of metabolism—

lactic acid, urea, creatinine

• Nutrients—glucose, carbohydrates, amino

acids

• Electrolytes—Na+, K+, Ca2+, Cl–, HCO3–

• Respiratory gases—O2 and CO2

• Hormones


Formed Elements

• Only WBCs are complete cells

• RBCs have no nuclei or organelles

• Platelets are cell fragments

• Most formed elements survive in the

bloodstream for only a few days

• Most blood cells originate in bone marrow

• Most blood cells do not divide


Formed

elements

Platelets

Leukocytes

Erythrocytes

Differential

WBC count

(All total 4800 –

10,800/l)

Neutrophils (50 – 70%)

Lymphocytes (25 – 45%)

Eosinophils (2 – 4%)

Basophils (0.5 – 1%)

Monocytes (3 – 8%)

Agranulocytes

Granulocytes




Platelets

Neutrophils Lymphocyte

Erythrocytes Monocyte


Erythrocytes

• Biconcave discs, anucleate, essentially no

organelles

• Filled with hemoglobin (Hb) for gas transport

• Provide flexibility to change shape as

necessary

• Are the major factor contributing to blood

viscosity


2.5 µm

7.5 µm

Side view (cut)

Top view


Erythrocytes

• Structural characteristics contribute to gas transport

• Biconcave shape—huge surface area relative to volume

• >97% hemoglobin (not counting water)

• No mitochondria; ATP production is anaerobic; no O2 is used in generation of ATP

• A superb example of complementarities of structure and function!


Erythrocyte Function

• RBCs are dedicated to respiratory gas

transport

• Hemoglobin binds reversibly with O2

• Hemoglobin structure

• Protein globin + Heme pigment

• Iron atom in each heme can bind to one O2 molecule

• Each Hb molecule can transport four O2

• oxygen


Heme

group

(a) Hemoglobin consists of globin (two

alpha and two beta polypeptide

chains) and four heme groups.

(b) Iron-containing heme pigment.

a Globin chains

b Globin chains


Hemoglobin (Hb)

• O2 loading in the lungs

• Produces oxyhemoglobin (ruby red)

• O2 unloading in the tissues

• Produces deoxyhemoglobin or reduced

hemoglobin (dark red)

• CO2 loading in the tissues

• Produces carbaminohemoglobin (carries 20%

of CO2 in the blood)


Hematopoiesis

• Hematopoiesis (hemopoiesis): blood cell

formation

• Occurs in red bone marrow of axial skeleton,

girdles and proximal epiphyses of humerus

and femur

• Hemocytoblasts (hematopoietic stem cells)

• Give rise to all formed elements


Erythropoiesis

Erythropoiesis: red blood cell production

• Ejection of the nucleus and formation of

reticulocytes

• Reticulocytes then become mature

erythrocytes


Stem cell

HemocytoblastProerythro-

blast

Early

erythroblast

Late

erythroblast Normoblast

Phase 1

Ribosome

synthesis

Phase 2

Hemoglobin

accumulation

Phase 3

Ejection of

nucleus

Reticulo-

cyte

Erythro-

cyte

Committed

cell

Developmental pathway


Regulation of Erythropoiesis

• Too few RBCs leads to tissue hypoxia

• Too many RBCs increases blood viscosity

• Balance between RBC production and

destruction depends on

• Hormonal controls

• Adequate supplies of iron, amino acids, and B

vitamins


Hormonal Control of Erythropoiesis

• Erythropoietin (EPO)

• Direct stimulus for erythropoiesis

• Released by the kidneys in response to

hypoxia


Hormonal Control of Erythropoiesis

• Causes of hypoxia

• Hemorrhage or increased RBC destruction

reduces RBC numbers

• Insufficient hemoglobin (e.g., iron deficiency)

• Reduced availability of O2 (e.g., high altitudes)


Dietary Requirements for Erythropoiesis

• Nutrients—amino acids, lipids, and carbohydrates

• Iron

• Stored in Hb (65%), the liver, spleen, and bone

marrow

• Stored in cells as ferritin and hemosiderin

• Transported loosely bound to the protein transferrin

• Vitamin B12 and folic acid—necessary for DNA

synthesis for cell division


Fate and Destruction of Erythrocytes

• Life span: 100–120 days

• Old RBCs become fragile, and Hb begins to

degenerate

• Macrophages engulf dying RBCs in the

spleen


Fate and Destruction of Erythrocytes

• Heme and globin are separated

• Iron is salvaged for reuse

• Heme is degraded to yellow the pigment bilirubin

• Liver secretes bilirubin (in bile) into the intestines

• Degraded pigment leaves the body in feces as stercobilin

• Globin is metabolized into amino acids


Erythrocyte Disorders

• Anemia: blood has abnormally low O2-

carrying capacity

• A sign rather than a disease itself

• Blood O2 levels cannot support normal

metabolism

• Accompanied by fatigue, paleness, shortness

of breath, and chills


Causes of Anemia

1. Insufficient erythrocytes

• Hemorrhagic anemia: acute or chronic loss

of blood

• Hemolytic anemia: RBCs rupture

prematurely

• Aplastic anemia: destruction or inhibition of

red bone marrow


Causes of Anemia

2. Low hemoglobin content

• Iron-deficiency anemia

• Secondary result of hemorrhagic anemia or

• Inadequate intake of iron-containing foods

or

• Impaired iron absorption

3. Abnormal hemoglobin


Causes of Anemia

4. Pernicious anemia

• Deficiency of vitamin B12

• Lack of intrinsic factor needed for absorption

of B12

• Treated by intramuscular injection of B12 or

application of Nascobal


Causes of Anemia

5. Sickle-cell anemia

• Defective gene codes for abnormal

hemoglobin (HbS)

• Causes RBCs to become sickle shaped in

low-oxygen situations


Erythrocyte Disorders

• Polycythemia: excess of RBCs that increase

blood viscosity

• Results from:

• Polycythemia vera—bone marrow cancer

• Secondary polycythemia—when less O2 is

available (high altitude)

• Blood doping


Leukocytes

• Make up <1% of total blood volume

• Can leave capillaries via diapedesis

• Move through tissue spaces by ameboid

motion and positive chemotaxis

• Leukocytosis: WBC count over 11,000/mm3

• Normal response to bacterial or viral invasion


Lymphocytes

• Large, circular nuclei with a thin rim of blue

cytoplasm

• Mostly in lymphoid tissue; few circulate in the

blood

• Crucial to immunity


Lymphocytes

• Two types

• T cells act against virus-infected cells and

tumor cells

• B cells give rise to plasma cells, which

produce antibodies


Monocytes

• The largest leukocytes

• Abundant cytoplasm

• U- or kidney-shaped nuclei


Monocytes

• Leave circulation, enter tissues, and

differentiate into macrophages

• Actively phagocytic cells; crucial against

viruses, intracellular bacterial parasites, and

chronic infections

• Activate lymphocytes to mount an immune

response


Leukopoiesis

• Production of WBCs

• Stimulated by chemical messengers from

bone marrow and mature WBCs

• All leukocytes originate from hemocytoblasts


Leukocyte Disorders

• Leukopenia

• Abnormally low WBC count—drug induced

• Leukemias

• Cancerous conditions involving WBCs

• Named according to the abnormal WBC clone involved

• Myelocytic leukemia involves myeloblasts

• Lymphocytic leukemia involves lymphocytes

• Acute leukemia involves blast-type cells and primarily affects children

• Chronic leukemia is more prevalent in older people


Leukemia

• Bone marrow totally occupied with cancerous

leukocytes

• Immature nonfunctional WBCs in the

bloodstream

• Death caused by internal hemorrhage and

overwhelming infections

• Treatments include irradiation, antileukemic

drugs, and stem cell transplants


Platelets

• Small fragments of megakaryocytes

• Formation is regulated by thrombopoietin

• Blue-staining outer region, purple granules

• Granules contain serotonin, Ca2+, enzymes,

ADP, and platelet-derived growth factor

(PDGF)


Platelets

• Form a temporary platelet plug that helps seal breaks in blood vessels


Hemostasis

• Fast series of reactions for stoppage of

bleeding

1. Vascular spasm

2. Platelet plug formation

3. Coagulation (blood clotting)


What causes vascular spasm?

• Vasoconstriction of damaged blood vessel

• Triggers

• Direct injury

• Chemicals released by endothelial cells and

platelets

• Pain reflexes


Platelet Plug Formation

At site of blood vessel injury, platelets stick to

exposed collagen fibers, then swell, become

spiked and sticky, and release chemical

messengers causing more platelets


Coagulation

• A set of reactions in which blood is

transformed from a liquid to a gel

• Reinforces the platelet plug with fibrin

threads


Collagen

fibers

Platelets

Fibrin

Step Vascular spasm

• Smooth muscle contracts,

causing vasoconstriction.

Step Platelet plug

formation• Injury to lining of vessel

exposes collagen fibers;

platelets adhere.

• Platelets release chemicals

that make nearby platelets

sticky; platelet plug forms.

Step Coagulation

• Fibrin forms a mesh that traps

red blood cells and platelets,

forming the clot.

1

2

3



Clot Retraction

• Actin and myosin in platelets contract within

30–60 minutes

• Platelets pull on the fibrin strands, squeezing

serum from the clot


Clot Repair

• Platelet-derived growth factor (PDGF)

stimulates division of smooth muscle cells and

fibroblasts to rebuild blood vessel wall

• Vascular endothelial growth factor (VEGF)

stimulates endothelial cells to multiply and

restore the endothelial lining


Disorders of Hemostasis

Thromboembolytic disorders: undesirable clot formation

• Thrombus: clot that develops and persists in an unbroken blood vessel

• May block circulation, leading to tissue death

• Embolus: a thrombus freely floating in the blood stream

• Pulmonary emboli impair the ability of the body to obtain oxygen

• Cerebral emboli can cause strokes

• Prevented by

• Aspirin

• Antiprostaglandin that inhibits thromboxane A2

• Heparin

• Anticoagulant used clinically for pre- and postoperative cardiac care

• Warfarin

• Used for those prone to atrial fibrillation


Disorders of HemostasisBleeding disorders: abnormalities that prevent normal clot

formation

Thrombocytopenia: deficient number of circulating platelets

• Widespread hemorrhage, for example, due to suppression or destruction of bone marrow (e.g., malignancy, radiation)

• Treated with transfusion of concentrated platelets

Impaired liver function

• Inability to synthesize procoagulants

• Causes include vitamin K deficiency, hepatitis, and cirrhosis

• Liver disease can also prevent the liver from producing bile, impairing fat and vitamin K absorption

Hemophilias include several similar hereditary bleeding disorders

• Symptoms include prolonged bleeding, especially into joint cavities

• Treated with plasma transfusions and injection of missing factors


Human Blood Groups

• RBC membranes bear 30 types glycoprotein antigens that are

• Perceived as foreign if transfused blood is mismatched

• Unique to each individual

Presence or absence of each antigen is used to classify blood cells into different groups


ABO Blood Groups

• Types A, B, AB, and O

• Based on the presence or absence of two agglutinogens (A and B) on the surface of the RBCs

• Blood may contain anti-A or anti-B antibodies (agglutinins) that act against transfused RBCs

• Anti-A or anti-B form in the blood at about 2 months of age

Copyright © 2010 Pearson Education, Inc. Table 17.4


Rh Blood Groups

• There are 45 different Rh agglutinogens (Rh factors)

• C, D, and E are most common

• Rh+ indicates presence of D

• Anti-Rh antibodies form if an Rh– individual receives

Rh+ blood


Hemolytic Disease of the Newborn

• Also called erythroblastosis fetalis

• Anti-Rh antibodies cross the placenta and destroy the RBCs of an Rh+ baby

• The baby can be treated with prebirthtransfusions and exchange transfusions after birth


Transfusions

• Whole-blood transfusions are used when

blood loss is substantial

• Packed red cells (plasma removed) are used

to restore oxygen-carrying capacity

• Transfusion of incompatible blood can be fatal


Transfusion Reactions

• Occur if mismatched blood is infused

• Donor’s cells

• Are attacked by the recipient’s plasma agglutinins

• Agglutinate and clog small vessels

• Rupture and release free hemoglobin into the bloodstream

• Result in

• Diminished oxygen-carrying capacity

• Hemoglobin in kidney tubules and renal failure


Restoring Blood Volume

• Death from shock may result from low blood volume

• Volume must be replaced immediately with

• Normal saline or multiple-electrolyte solution that

mimics plasma electrolyte composition

• Plasma expanders (e.g., purified human serum

albumin, hetastarch, and dextran)

• Mimic osmotic properties of albumin

• More expensive and may cause significant

complications


Diagnostic Blood Tests

• Hematocrit

• Blood glucose tests

• Microscopic examination reveals variations in size and shape of RBCs, indications of anemias

• Differential WBC count

• Prothrombin time and platelet counts assess hemostasis

• SMAC, a blood chemistry profile

• Complete blood count (CBC)


Autoregulation

• Automatic adjustment of blood flow to each tissue in

proportion to its requirements at any given point in

time

• Is controlled intrinsically by modifying the diameter of

local arterioles feeding the capillaries

• Two types of autoregulation

1.Metabolic

2.Myogenic


Metabolic

controls

pH Sympathetic

a Receptors

b ReceptorsEpinephrine,

norepinephrine

Angiotensin II

Antidiuretic

hormone (ADH)

Atrial

natriuretic

peptide (ANP)

Dilates

Constricts

Prostaglandins

Adenosine

Nitric oxide

Endothelins

Stretch

O2

CO2

K+

Amounts of:

Amounts of:

Nerves

Hormones

Myogenic

controls

Intrinsic mechanisms(autoregulation)

• Distribute blood flow to individual

organs and tissues as needed

Extrinsic mechanisms

• Maintain mean arterial pressure (MAP)

• Redistribute blood during exercise and

thermoregulation


Long-Term Autoregulation

• Angiogenesis

• Occurs when short-term autoregulation cannot

meet tissue nutrient requirements

• The number of vessels to a region increases

and existing vessels enlarge

• Common in the heart when a coronary vessel

is occluded, or throughout the body in people

in high-altitude areas


Fluid Movements: Bulk Flow

• Extremely important in determining relative

fluid volumes in the blood and interstitial

space

• Direction and amount of fluid flow depends on

two opposing forces: hydrostatic and colloid

osmotic pressures


Circulatory Shock

• Any condition in which

• Blood vessels are inadequately filled

• Blood cannot circulate normally

• Results in inadequate blood flow to meet

tissue needs


Circulatory Shock

• Hypovolemic shock: results from large-scale

blood loss

• Vascular shock: results from extreme

vasodilation and decreased peripheral

resistance

• Cardiogenic shock results when an inefficient

heart cannot sustain adequate circulation


Maintaining Blood Pressure

• The main factors influencing blood pressure:

• Cardiac output (CO)

• Peripheral resistance (PR)

• Blood volume


Cardiac Output (CO)

• Determined by venous return and neural and

hormonal controls

• Resting heart rate is maintained by the

cardioinhibitory center via the

parasympathetic vagus nerves

• Stroke volume is controlled by venous return


Cardiac Output (CO)

• During stress, the cardioacceleratory center

increases heart rate and stroke volume via

sympathetic stimulation


Control of Blood Pressure

• Short-term neural and hormonal controls

• Counteract fluctuations in blood pressure by

altering peripheral resistance

• Long-term renal regulation

• Counteracts fluctuations in blood pressure by

altering blood volume


Short-Term Mechanisms: Neural Controls

• Neural controls of peripheral resistance

• altering blood vessel diameter

• Alter blood distribution


Short-Term Mechanisms: Neural Controls

• Neural controls operate via reflex arcs that

involve

• Baroreceptors

• Vasomotor centers and vasomotor fibers

• Vascular smooth muscle


Short-Term Mechanisms: Baroreceptor-

Initiated Reflexes

• Baroreceptors are located in

• Carotid sinuses

• Aortic arch


Short-Term Mechanisms: Baroreceptor-

Initiated Reflexes

• Increased blood pressure stimulates baroreceptors to

• causing arteriole dilation and venodilation

• Stimulates the cardioinhibitory center

• Baroreceptors in the carotid sinus reflex protect the blood

supply to the brain

• Baroreceptors in the aortic reflex help maintain adequate

blood pressure in the systemic circuit


Short-Term Mechanisms:

Chemoreceptor-Initiated Reflexes

• Chemoreceptors are located in the

• Carotid sinus

• Aortic arch

• Large arteries of the neck


Short-Term Mechanisms:

Chemoreceptor-Initiated Reflexes

• Chemoreceptors respond to rise in CO2, drop

in pH or O2

• Increase blood pressure

• Are more important in the regulation of

respiratory rate (Chapter 22)


Influence of Higher Brain Centers

• Reflexes that regulate BP are integrated in the

medulla

• Higher brain centers in the cortex and

hypothalamus can modify BP via relays to the

medulla


Short-Term Mechanisms: Hormonal

Controls

• Adrenal medulla hormones norepinephrine

(NE) and epinephrine cause generalized

vasoconstriction and increase cardiac output

• Angiotensin II, generated by kidney release of

renin, causes vasoconstriction


Short-Term Mechanisms: Hormonal

Controls

• Atrial natriuretic peptide causes blood volume

and blood pressure to decline, causes

generalized vasodilation

• Antidiuretic hormone (ADH)(vasopressin)

causes intense vasoconstriction in cases of

extremely low BP


Long-Term Mechanisms: Renal Regulation

• Baroreceptors quickly adapt to chronic high

or low BP

• Long-term mechanisms step in to control

BP by altering blood volume

• Kidneys act directly and indirectly to

regulate arterial blood pressure

1. Direct renal mechanism

2. Indirect renal (renin-angiotensin) mechanism


Direct Renal Mechanism

• Alters blood volume independently of

hormones

• Increased BP or blood volume causes the

kidneys to eliminate more urine, thus reducing

BP

• Decreased BP or blood volume causes the

kidneys to conserve water, and BP rises


Leukocytes

• Make up <1% of total blood volume

• Can leave capillaries via diapedesis

• Move through tissue spaces by ameboid

motion and positive chemotaxis

• Leukocytosis: WBC count over 11,000/mm3

• Normal response to bacterial or viral invasion


Lymphocytes

• Large, dark-purple, circular nuclei with a thin

rim of blue cytoplasm

• Mostly in lymphoid tissue; few circulate in the

blood

• Crucial to immunity


Lymphocytes

• Two types

• T cells act against virus-infected cells and

tumor cells

• B cells give rise to plasma cells, which

produce antibodies


Monocytes

• The largest leukocytes

• Abundant pale-blue cytoplasm

• Dark purple-staining, U- or kidney-shaped

nuclei


Monocytes

• Leave circulation, enter tissues, and

differentiate into macrophages

• Actively phagocytic cells; crucial against

viruses, intracellular bacterial parasites, and

chronic infections

• Activate lymphocytes to mount an immune

response

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The Circulatory System and Blood