Cardiovascular System Notes

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Structures & Functions

parietal pericardium - separates heart from longs inside the thorax

visceral epicardium - outermost layer of the heart

myocardium - muscle layer of the heart; comprises 99% of the mass of the heart

endocardium - innermost layer that lines heart chambers; continuous with endothelium lining blood vessels

sinoatrial (SA) node

"pacemaker" of the heart

group of specialized cells located inside the superior wall of the right atrium

spontaneously depolarizes, creating a signal that passes to the atria and the ventricles, causing their contraction

atrioventricular (AV) node

found in the septal wall between the atria and ventricles

can take over pacing of the heart if SA node becomes dysfunctional

also spontaneously depolarizes but at a slower rate than the SA node

overdrive suppression - SA node typically paces the heart because it generates action potentials at a higher rate

automaticity - ability of the heart to self-generate a beat

rhythmicity - ability of heart to generate its own pace of beating

autonomic nervous system significantly influences rate of spontaneous depolarization

sympathetic and parasympathetic branches of autonomic nervous system innervate the SA and AV nodes, adjusting their rates of depolarization

sympathetic nervous system increases SA node depolarization rates, increasing heart rate

parasympathetic nervous system decreases SA node depolarization rates/heart rate

parasympathetic nervous system has greater control of heart rate at rest

heart rate would increase to about 100 beats per minute without its influence

electrical conductance of the heart

action potential spreads from SA node throughout the heart

travels via two methods:

internodal conducting pathway - node to node along the conducting cells

made up of 3 separate paths of conducting cells that connect SA to AV node

once it reaches the AV node, the action potential passes through the septum by conducting through the Bundle of His and into the Purkinje Fibers

signals are distributed from here throughout the ventricular myocardium

directly from cell to cell

when cells of AV node depolarize, cells surrounding the AV node also depolarize

gap junctions between cells allow electrical signals to travel quickly throughout all the individual cells of the atria

Measuring Heart Electricity

electrocardiogram (ECG or EKG) - measures electrical activity associated with the heart

tracing - waveforms seen on a monitor

consists of 3 waves:

P waves - electrical activity just before contraction of atria

QRS waves - depolarization electrical activity simulating ventricular contraction

T waves - repolarization of ventricles prior to relaxation

ECG tracings can provide lots of information:

anatomy and placement of the heart in the chest cavity

size of the chambers

rhythm of contraction

detect changes in heart function (changes in rhythm, changes in conduction pathway of electrical signals, or development of ischemic areas -- areas lacking oxygen)

P-R interval measures time from atrial to ventricular contraction

QRS wave shows electrical activity that initiates ventricular contraction or systole

S-T interval - ventricles are depolarized

tachycardia - occurs when SA node fires rapidly

atrial tachycardia - atrial rate of contraction is much higher than ventricular rate of contraction (AV node can limit number of action potentials passing from atria to ventricles)

ventricular tachycardia - ventricles continuously firing without a consistently preceding P wave

Arrhythmias - abnormal rhythms in heart rate or conduction pathway

tachycardia - heart beats too fast

bradycardia - heart beats too slow

ventricular fibrillation - ventricle beats in uncontrolled manner; does not produce a productive heart contraction; fatal if not corrected

atrial fibrillation - common arrhythmia in which multiple cells outside of the SA node spontaneously depolarize at high rates; results in atria quivering instead of beating; most blood passes into ventricles passively due to pressure differences so it's not as damaging

increases risk of thromboemboli (blood clots that move to other parts of body) and stroke

Cardiac Cycles

cardiac cycle has two distinct phases:

diastole - muscles are relaxed and chambers fill passively with blood

there is both an atrial diastole and a ventricular diastole but "diastole" commonly refers to ventricular diastole

atrial diastole

blood enters left atrium from pulmonary vein and right atrium from inferior and superior vena cava

ventricular diastole

atria are in diastolic period

ventricular pressure drops as relaxation begin

when pressure in ventricles drops below atrial pressure, AV valves open

blood passively pours into the atria and flows through the open AV valves into the ventricles

pressure builds as blood collects in ventricle

SA node depolarizes, initiating atrial systole

contraction of atrium forces more blood into the ventricle in diastole

90% of blood enters passively and 10% enters during atrial systole

systole - heart muscles contract

atrial systole helps fill the ventricles

ventricular systole pushes blood into the pulmonary artery and aorta

increasing volume of blood in ventricles increases pressure

when this pressure exceeds that in the atria, the AV valves are forced closed

closing of AV valves creates the first heart sound (lub)

atria finish systole and are in diastolic period

heart contracts in repeatable sequence; first atria, then ventricles, allowing blood to flow in one direction

isovolumetric contraction - contraction of ventricles at onset of systole when both AV and semilunar valves on either side of ventricle are closed; volume of blood in ventricles does not change but increases pressure in ventricles

when ventricular pressures exceed arterial pressures (pulmonary and aortic), pulmonary and aortic semilunar valves open to eject blood

when ventricles enter diastole, ventricular pressures fall and the valves close again

this creates the second heart sound (dub)

Heart Calculations

cardiac output - measure of the heart's efficiency; the amount of blood pumped per minute

cardiac output = heart rate (beats per minute) x stroke volume (volume of pumped blood per minute)

stroke volume affected by:

preload - amount of blood that flows into the heart immediately before it contracts

mainly dependent on flow rate of blood through the veins (venous return)

venous return increases when systemic venous pressure increases

can also increase through medications that stiffen (decrease compliance) of veins

Frank-Starling Relationship - force of heart muscle contraction will increase with an increase in end-diastolic ventricular volume

myocardial contractility - changes the force myocardial cells generate by adjusting the amount of calcium in the cytosol

increase in contractility increases the levels of cytosolic calcium

decrease in contractility has the opposite effect

more cytosolic calcium maximizes the number of crossbridges that have the potential to form

mainly affected by sympathetic branch of autonomic nervous system (greater the number of signals the myocardial cells are receiving, the higher the contractility becomes)

afterload - pressure the ventricle needs to develop to eject blood

pressure in the aorta that the heart has to overcome to eject blood

doesn't have much effect on cardiac output for most people

when arterial pressure rises about 50% above normal, it may decrease stroke volume

as heart rate increases, cardiac output increases (up to a point - at very high heart rates, heart may not have time to fill appropriately)

The Arteries

blood flow - volume of blood that moves through any vessel or tissue in a given amount of time

commonly measured in mL/min or L/min

total blood flow (or cardiac output) - amount of blood that moves through either the systemic or pulmonary vessels in one minute

blood pressure (BP) - force per unit area that blood exerts on a vessel wall

measured in millimeters of mercury (mmHg)

clinically, refers to systemic arterial pressure in the biggest arteries close to the heart, where BP is similar to that generated by the heart

BP decreases continuously along each path that blood flow can take through the vascular system

systolic blood pressure - highest arterial pressure achieved during systole

diastolic blood pressure - lowest arterial pressure reached during diastole

BP & Pulse Measurements

pulse - moving wave of pressure; matches the heart rate

sphygmomanometer - inflatable cuff used to measure BP

mean arterial pressure (MAP) - average arterial BP

1/3 of the distance between systolic and diastolic BP

MAP = diastolic BP + 1/3 (systolic BP - diastolic BP)

Factors Influencing BP

vascular resistance - friction as blood moves through a vessel

total peripheral resistance - resistance to blood flow as it moves from the aorta to the vena cavae

change in pressure = flow x resistance

resistance = change in pressure / flow

vessel lumen size

smaller the lumen, greater the resistance

most changes in lumen size are due to vasoconstriction and vasodilation of arteries and arterioles

blood viscosity - measurement of a fluid's internal resistance, which determines its ability to flow

depends on thickness or stickiness of fluid

low viscosity flows quickly

high viscosity flows slowly

mostly depends on ratio of red blood cells to blood plasma

the more red blood cells, the more viscous the blood

amount of plasma proteins can also affect viscosity

blood vessel length

direct correlation between length of blood vessel and amount of resistance

as length increases, so does resistance

resistance to blood flow increases in people who are overweight because extra fat means more miles of blood vessels to supply them with blood - common consequence is hypertension

Capillary Exchange

3 mechanisms by which substances enter and leave capillaries:

diffusion - passive movement of solute from area of high concentration to area of low concentration

transcytosis - combination of endocytosis and exocytosis necessary when the substance to be transported cannot be exposed to the cytoplasm of an intervening cell

important for moving large lipid-insoluble molecules

bulk flow - movement of fluid, ions, and other small molecules dissolved in the fluid (due to pressure gradients)

filtration - movement of fluids from arterial end of capillaries into interstitial fluid

reabsorption - movement of fluids from interstitial fluid into the capillaries at the venous end of the capillary bed

Filtration & Reabsorption

capillary exchange driven by two types of pressure:

hydrostatic pressure - caused by fluid pressing against the vessel walls or another physical barrier (same as the blood pressure measured within the capillary)

osmotic pressure - caused by presence of non-diffusing solutes within the fluid

colloid osmotic pressure - osmotic pressure created by large plasma proteins

net filtration pressure (NFP) - sum of hydrostatic and colloid osmotic pressure; can promote either filtration or reabsorption or neither (if balanced)

four pressures contribute to NFP

blood hydrostatic pressure

interstitial fluid hydrostatic pressure

blood colloid osmotic pressure

interstitial fluid colloid osmotic pressure

Starling's Law of Capillaries

Starling's law of the capillaries - movement of fluid between capillaries and interstitial fluid is due to net effect of all four pressures described above

Edema

edema - accumulation of excess fluid in the tissues

physiological causes:

standing too long without moving feet or legs

pregnancy

side effect of medication

can be a sign of serious underlying medical condition, such as heart failure

each cause leads to imbalance in rates of filtration and reabsorption during capillary exchange

Venous Return

venous return - volume of blood in systemic veins that is flowing back to the heart

skeletal muscle pump - uses muscle contractions in the legs to force venous blood upwards toward the heart

peripheral veins in legs have one-way valves that route blood away from legs and toward heart

contraction of leg muscles squeezes veins and propels blood

lack of use of skeletal muscle pump leads to lower leg edema (common in people who are bedridden or confined to a wheelchair)

respiratory pump - sequential compression and decompression of veins (operates on abdominal and thoracic veins)

downward movement of diaphragm (inhale) reduces pressure in thoracic cavity and increases pressure in abdominal cavity

the resulting compression of abdominal veins pushes blood into decompressed thoracic veins and then into the right atrium

when exhaling, pressures reverse and one-way valves prevent blood from flowing back into abdominal veins from thoracic veins

Overview of Circulatory Pathways

circulatory routes:

pulmonary circuit - right ventricle pumps blood to lungs

systemic circuit - left ventricle pumps blood to organs and tissues

blood in systemic circuit must be pumped farther than blood in pulmonary circuit

pulmonary arteries have larger diameter, thinner walls, and more elastic tissue

peak systolic pressure is much lower in right ventricle than left ventricle due to these characteristics

pulmonary circuit

flow is matched to ventilation so oxygen can move from alveoli into the bloodstream and carbon dioxide can move from bloodstream to alveoli

pulmonary trunk - originates at right ventricle

divides into right pulmonary artery and left pulmonary artery

pulmonary arteries are the only ones transporting oxygen-poor blood

pulmonary arteries divide into 3 lobar arteries in right lung and 2 lobar arteries in left lung

each supplies blood to one lung lobe

these divide into capillaries around the alveoli

pulmonary capillaries merge into venules

venules unite to become pulmonary veins

two veins leave each lung and transport oxygenated blood into left side of heart

systemic circuit

oxygen-poor blood returns to heart through superior vena cava, inferior vena cava, and coronary sinus

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Levels of Organization

Molecular Composition of Plasma

oxygenated blood - oxygen bound to heme groups in red blood cells give blood a red pigment

deoxygenated blood - darker in color because has larger fraction of hemoglobin that isn't combined with oxygen

heme groups are part of larger hemoglobin molecules found in large concentrations within red blood cells (RBCs)

formed elements of blood include RBCs, white blood cells (WBCs), and platelets

plasma - fluid of blood with no cells

composed of water, proteins, salts, and gases

pH of blood plasma ranges from 7.35 to 7.45

specific gravity between 1.050 and 1.060; specific gravity is measure of blood density in relation to pure water (1.000)

serum - portion of plasma that doesn't have blood-clotting proteins

plasma proteins - albumin, globulins, and fibrinogen

albumin - synthesized by liver and functions to maintain colloid osmotic pressure in blood compartment

helps prevent leakage of fluid into interstitial spaces and edema

transport protein that carries small molecules, such as bilirubin, metals, hormones, and medications through blood

globulins (alpha, beta, and gamma)

alpha and beta - transport lipids and metals

gamma- antibodies released by immune cells that attack microorganisms and foreign molecules

fibrinogen - important for formation of blood clots

hypoalbuminemia

decreased levels of albumin in the blood

typically decrease secondary to liver disease, loss of albumin in urine, poor nutrition, or gastrointestinal disorders that interrupt normal nutrient absorption

medications carried by albumin may have increased concentrations of unbound drug in the plasma leading to even normal doses seeming like an overdose

Hemostasis

hemostasis - process of stopping bleeding from damaged blood vessel

3 major activities:

vasoconstriction - vascular spasm (constriction of blood vessel at site of injury

platelet aggregation - platelets stick to collagen fibers that become exposed when endothelial cell lining of blood vessels is damaged and therefore begin to plug up the hole

release secretory granules that signal binding of more platelets

process continues until enough platelets have aggregated to form a platelet plug

loose meshwork of interconnected platelets

formation of fibrin clot

thrombus (clot) forms via coagulation

coagulation - series of reactions resulting in formation of fibrin protein

fibrin protein crosslinks with other fibrin proteins and platelets

fibrinogen forms fibrin

clotting factors - plasma proteins that create a cascade of enzymatic reactions

calcium is required for steps to occur

chelating agent - inhibits coagulation by binding to calcium and making it unavailable

two pathways for coagulation:

intrinsic pathway - activated when plasma is exposed to collagen after endothelial cell injury or when blood is exposed to negatively charged surfaces such as glass

extrinsic pathway - triggered by chemicals released by damaged cells of blood vessel wall

Fibrinolysis - process by which blood clot is broken down

clot retraction - gradual removal of fibrin threads that make up the clot

kallikrein - converts plasminogen (inactive) into plasmin & plays a role in production of bradykinin

plasmin - splits fibrin polymers

bradykinin - stimulates vasodilation to help counter vasoconstrictive effects of serotonin and prostaglandins that were released by platelets during clot formation

problems in blood clotting:

decreased platelet levels

genetic defects leading to insufficient or abnormal clotting factors (hemophilias)

lack of production of clotting factors in the liver (where many are formed)

certain clotting factors require vitamin K so conditions resulting in malabsorption of fat lead to deficiency of vitamin K and increased bleeding times

thromboemboli - blood clots that break free from site of injury

get trapped within small blood vessels, blocking flow through vessels

heparin - used during surgery to inactivate thrombin

Warfarin - oral drug used for long-term reduction in clotting

Main Types of Blood Cells

red blood cells (RBCs) - also known as erythrocytes; function mainly in gas exchange

contain hemoglobin - a protein that contains iron and to which both oxygen and carbon dioxide are able to bind

white blood cells (WBCs) - also known as leukocytes

granulocytes - possess numerous granules in their cytoplasm

agranulocytes - do not have granules

platelets - smaller fragments of large cells called megakaryocytes

lack a nucleus but have a plasma membrane surrounding a cytoplasm and a few organelles

Red Blood Cells

red blood cells = RBCs = erythrocytes

contain hemoglobin (Hbg) - special protein containing iron

depressed center maximizes surface area of RBCs to facilitate O2 and CO2 exchange

flattened shape allows RBCs to travel through narrow capillaries

don't have nuclei or many other organelles to leave room for hemoglobin

this means they don't have DNA necessary to reproduce, grow, and carry out functions of maintenance and repair (which limits the lifespan of the cells -- 120 days)

hemoglobin

consists of 4 heme groups (non-protein) and 4 globin (protein) molecules

heme + oxygen creates red color of blood

each hemoglobin molecule can transport up to 4 oxygen atoms (one bound to each heme group)

1 RBC has about a quarter of a billion hemoglobin molecules!

oxyhemoglobin (HbO2) - oxygenated hemoglobin

deoxyhemoglobin (Hb) - hemoglobin no longer carrying oxygen

carbaminohemoglobin (HbCO2) - hemoglobin that has picked up carbon dioxide

bicarbonate (HCO3-) - bulk of carbon dioxide is transported in this form in the plasma

carbonic anhydrase (enzyme found in high concentrations in erythrocytes) - catalyzes conversion of carbon dioxide and water into bicarbonate

erythropoiesis - process by which bone marrow stem cells develop into erythroblasts that further differentiate into reticulocytes and then mature before being released into circulation

erythropoietin - hormone from liver and kidneys that regulates rate of RBC production

macrophages in spleen and liver remove damaged RBCs from circulation

phagocytose old RBCs

separate protein (globin) and non-protein (heme) portions of hemoglobin

protein chains further degraded into amino acids and dispersed into circulation

iron extracted from heme and stored or enters bloodstream

stored iron attaches to ferritin and hemosiderin proteins to prevent buildup of toxic free iron

iron in bloodstream attached to molecule called transferrin, this is picked up by various tissues where it is used to regenerate erythrocytes

blood groups

non-compatible blood transfusion can result in clumping together (agglutination) or destruction (hemolysis) of donated RBCs

ABO group

O allele results in no antigen being created

A and B alleles are dominant over O allele; AA or AO = A; BB or BO = B

A and B alleles are codominant; A + B = AB

antibodies (agglutinins) present in plasma

O produces anti-A and anti-B antigens (universal donor)

AB produces no antigens (universal acceptor)

A produces anti-B antigens

B produces anti-A antigens

Rh group

dominant D allele determine is person is Rh+ with wither DD, Dd, or dd

O- = no A, B, or D antigens

A+ = A antigen and D antigen

Rh- blood doesn't produce anti-D antibodies unless exposed to significant amounts of blood containing D antigen

RBC Disorders

anemia - condition in which oxygen carrying capacity of blood is reduced

iron deficiency anemia - caused by poor dietary intake of iron or blood loss; leads to failure to synthesize adequate levels of RBCs

pernicious anemia - caused by poor intestinal absorption of B12, which is necessary for RBC production; leads to failure to synthesize adequate levels of RBCs

folic acid deficiency anemia - caused by poor intake of dietary folic acid, inability to absorb folic acid, or medications that interfere with folic acid utilization; leads to failure to synthesize adequate levels of RBCs

hemolytic anemia - caused by genetic or acquired disease that alters shape of RBCs or toxins/drugs; leads to rapid degeneration of RBCs

sickle cell anemia - inherited disease leading to sickle shape in RBCs; leads to clumping of RBCs, which blocks blood vessels

thalassemias - inherited diseases that is most common in individuals from Greek, Italian, Asian, African, or Middle Eastern descent; leads to abnormal hemoglobin

WBCs

white blood cells = WBCs = leukocytes

certain leukocytes have ability to move into interstitial spaces of body tissues to attach foreign agents and protect body from infection

diapedesis - process of squeezing through pores in capillary walls to leave capillary

made possible by leukocytes' ability to rearrange cytoskeletal matrix to change their shape

5 common types:

granulocytes - nonspecific immune system responders that respond to injury and build up inflammatory response against microbes or toxins regardless of body's previous exposure to the foreign agent; have multilobulated nuclei

neutrophils

most abundant (50-70%of WBCs)

S- or C-shaped nucleus with 3-6 lobules connected via strands of chromatin

first responders during bacterial infection

chemotaxis - chemicals released by damaged cells draw neutrophils

attack via phagocytosis

granules within neutrophils release defensins (antimicrobial compounds) and lysozymes to destroy microbes

pus - culmination of destroyed neutrophils, bacteria, and dead tissue

eosinophils

bilobed nucleus linked by thin strand of chromatin

phagocytose foreign molecules, particularly in parasitic infection and allergic reactions

play a role in modulating activity of basophils

basophils

contain 2-5 U- or S-shaped lobules

granules contain histamine, serotonin, and heparin

cells release histamine during an inflammatory response to tissue damage and microbial invasion

agranulocytes - have spherical (nonlobulated) nuclei; no granules

lymphocytes

have round nucleus that fills up most of the cell

the only WBCs that reenter the bloodstream after moving into tissue to attack foreign agents

two types (both originate in bone marrow):

T lymphocytes (T cells) - grow and mature in thymus gland

attack abnormal cells in the body, such as virally infected cells, tumor cells, and donor transplant cells

B lymphocytes (B cells) - mature in bone marrow and then move to lymph nodes and similar tissue

sense and attach invading antigens (foreign substance in the body) such as toxins, viruses, or bacteria

divide into plasma cells that make antibodies aimed at neutralizing and destroying these antigens

monocytes

kidney shaped cells

have capacity to leave bloodstream and enter tissue where they mature into cells called macrophages

macrophages phagocytose microbes and tissue debris

WBC Disorders

leukocytosis - abnormally high number of mature WBCs

mononucleosis - monocyte numbers greatly increase in response to viral infection

can lead to enlarged spleen and lymph nodes

leukopenia - abnormally low levels of WBCs; commonly occurs with use of steroids like cortisone

neutropenia - abnormally low levels of neutrophils, leading to increased risk of infections that are more likely to develop into life-threatening conditions

leukemia - high number of WBCs due to cancerous proliferation of immature, nonfunctional WBCs

Platelets

platelets - primarily involved in hemostasis; lack a nucleus

platelets are smaller fragments of larger cells called megakaryocytes

platelets are repelled by endothelial lining of blood vessels under normal circumstances because endothelial cells release prostacyclin

prostacyclin levels fall during vascular injury, so platelets are able to bind to damaged area

Hematopoiesis & Stem Cells

hematopoiesis (formation of blood cells) occurs in red bone marrow of body

all the different types of blood cells can be traced back to stem cells in bone marrow

myeloid progenitor - most mature in myeloid tissues of red bone marrow in skull, vertebrae, & rib cage

RBCs

granular WBCs (neutrophils, eosinophils, and basophils)

platelets

monocytes

lymphoid progenitor - typically mature in lymphoid tissues throughout body, like spleen, tonsils, and lymph nodes

T and B lymphocytes

Cells of the Vessels

endothelial cells - line the inside of any surface that comes in contact w/ blood (inside of heart and every blood vessel)

vascular endothelium - line blood vessels

endocardium - endothelium on interior surfaces of heart chambers

only one layer thick

functions:

mechanical-chemical stimulation - sense changes in local chemical/mechanical environment and signal underlying muscle cells

immune response - cytokines released by immune system activate endothelial cells to promote association with circulating immune cells; pores open between endothelial cells to allow immune cells to leave lumen of vessel and invade tissue

forming new blood vessels (angiogenesis)

vascular endothelial growth factor (VEGF) - stimulates endothelial cells to divide

cells break down extracellular matrix and form new blood vessels

preventing clot formation (thrombus prevention)

smooth muscle cells - form layer outside of endothelial cells

provide strength to blood vessels

allow for blood vessel adaptation (vasoconstriction and vasodilation)

adjust contraction based on sensed stretch or the concentration of various chemical factors

Extracellular matrix (ECM) of vessels

all vessels except capillaries have one or more layers of connective tissue

connective tissue layers provide structure, support, and determine how easily vessels with passively expand

tunica externa (adventitia) - outer layer of connective tissue

internal elastic lamina - only found in some vessels; found between endothelial layer and smooth muscle layer

elastin - gives blood vessel ability to deform and return to original form when internal or external pressures are applied

collagen - found in tunica externa and provides stiffness to blood vessel to prevent rupture

hematocrit (hct) = fraction of blood composed of RBCs

Muscle Cells of the Heart

3 types of cells that make up the myocardium:

pacemaker cells (nodal cells) - found within sinoatrial (SA) and atrioventricular (AV) nodes

conducting cells - carry action potentials at high rate from SA to AV node and then from AV node to the rest of the ventricular cells

myocardial cells - 99% of the mass of the heart; function is to contract

Vascular Tissue

3 vessel wall layers called tunics:

tunica interna - forms inner lining of blood vessels

endothelium in a continuous sheet

supported by basement membrane composed largely of collagen fibers providing strength and flexibility

basement membrane anchors endothelium to outermost component of tunica interna (internal elastic lamina)

internal elastic lamina - sheet of elastic fibers with numerous openings to allow movement of solutes between layers

tunica media

composed of smooth muscle and connective tissue layers

smooth muscle cells oriented to encircle the lumen of the vessel

smooth muscle cells regulate size of vessel lumen based on stimulus of associated neurons, circulating hormones, or local signaling molecules

connective tissue composed of elastic fibers interspersed within muscle cell layers and a separate sheet-like layer (external elastic lumina)

tunica externa - outermost layer

composed mostly of collagen fibers

contains many nerves and (in larger vessels) a system of vessels that supply the vessel tissues called the vasa vasorum

The Heart

heart made of 2 pumps connected by series of tube-like vessels that create circulatory system

pumps separated by thick wall called the septum

valves of heart prevent blood from flowing in opposite direction

AV valves - separate atria from ventricles

tricuspid valve - separates right atrium from right ventricle

has 3 flaps (cusps)

on vetricular side, has long muscular cords (chordate tendinae) extending from inferior side of each cusp

attach to cusp on one end and papillary muscle on the other end

papillary muscles prevent valves from inverting back into atria during ventricular contraction

ventricular pressure causes flap to close

bicuspid valve (mitral valve) - separates left atrium from left ventricle

semilunar valves - located between ventricles and arteries

pulmonary semilunar valve (pulmonary valve) - remains closed when ventricle is filling and opens during ventricular contraction because pressure is greater inside ventricle

aortic semilunar valve (aortic valve)

pericardium - fluid-filled membranous structure that separates heart from lungs; made up of visceral pericardium (outer epicardial layer of heart) and parietal pericardium

heart has 3 layers:

endocardium - innermost layer forming barrier between blood and muscle

myocardium - thickest layer formed of cardiac muscle

epicardium - thin layer of cells covering outside of heart

cardiac tamponade - infection of pericardium that leads to increased pressure exerted on exterior of heart and prevents heart from filling fully

Blood Vessels

arteries -> arterioles -> capillary networks -> venules -> veins

aorta is divided into:

ascending aorta

coronary arteries branch from here

aortic arch

brachiocephalic trunk - right upper limb, head, neck

right subclavian artery - right upper limb, brain, spinal cord, neck, shoulder, thoracic viscera and wall, scapular muscles

right vertebral artery - posterior part of brain

axillary artery - passes through armpit

brachial artery - passes through upper arm

radial artery - passes through lateral forearm

ulnar artery - passes through medial forearm

right common carotid artery - head and neck

left common carotid artery - head and neck

left subclavian artery - similar branching to right subclavian artery

thoracic aorta - supply structures of the thorax

abdominal aorta - supply structures of the abdomen and lower limbs

bifurcates into right and left common iliac arteries

brain has special arterial circle (circle of Willis)

provides collateral pathways to ensure uninterrupted blood supply to brain if some arteries are blocked

arterial supply of thorax and abdomen has both visceral (serving the organs) and parietal (serving the wall structures) branches

Arteries

arteries can be classified by function:

elastic arteries (conducting arteries) - vast capacity for expansion and retraction

arteries with largest diameters in the body are elastic arteries

temporarily store blood by expanding and slowly recoiling

muscular arteries (distributing arteries) - higher percentage of muscle cells (thick tunica media)

Aging in Circulatory System

arteriosclerosis - conditions that make the arteries less elastic (hardening of the arteries); increases resistance to blood flow

calcific arteriosclerosis - calcium deposition in walls of vessels

senile arteriosclerosis - degenerative loss of elastic fibers with age

atherosclerosis - formation of plaques on arterial walls making them stiffer

plaques are made of fatty material containing cholesterol

may eventually be replaced with connective tissue and deposits of calcium

plaques can rupture, initiating a blood clot at the site

high levels of LDL ("bad" cholesterol) can lead to development of atherosclerosis

congestive heart failure - caused by impaired pumping efficiency in the heart

Arterioles/Capillaries/Venules

arterioles - tunica interna and tunica externa are thin; tunica media has 1-2 layers of muscle cells

rich supply of sympathetic nerve fibers

arterioles constrict when they receive a high number of signals from the sympathetic nervous system, and vice versa when they receive less signals

hormonal signals and local signaling molecules can also lead arterioles to constrict/dilate

capillaries - form extensive networks throughout the entire body

have only a tunica interna to facilitate rapid exchange of gases and solutes

3 types of capillaries:

continuous capillary

lowest permeability rate

common in muscle, nervous, and connective tissues

smooth tubes with narrow intercellular clefts between endothelial cells

basement membrane is whole and without pores

small molecules like glucose and oxygen can readily pass between cells, but larger molecules cannot

fenestrated capillary

have numerous fenestrae (windows) - plasma membranes from opposite sides of a cell adhere and exclude cytoplasm

membranes of fenestrations are composed of material more porous than typical phospholipid bilayer

basement membrane has openings or pores that increase permeability of vessels

allow for faster solute exchange but still exclude larger molecules from passing through

found in areas requiring rapid absorption or filtration, such as small intestines, kidneys, and choroid plexuses of brain

sinusoid capillary

limited to areas where blood cells move in and out of the bloodstream (found where blood cells are formed -- red bone marrow -- and where large proteins enter the bloodstream -- liver)

endothelial cells are widely separated and contain large pores without membrane coverings

basement membrane is sparse or missing

venules - much thinner walls than arteries and arterioles

arteries retain shape without blood but veins collapse

Veins

tunica interna and tunica media are quite thin

both internal and external elastic laminae are absent or very thin

capable of great expansion to hold variable volume of blood

venous valves - augment venous return; most commonly found in limbs

formed by extensions of tunica interna that create flaps in the vessel lumen

valves close when blood in a vein tries to move backward

venous sinuses - large-diameter veins with extremely thin walls and no smooth muscle

dense connective tissue surrounding the vessel provides support

collection points for oxygen-poor blood

includes coronary sinus of heart and dural sinuses of brain

anastomoses - connecting channels between veins

portal veins - drain one capillary network and transfer blood to another organ or tissue to empty into another capillary network

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Homeostasis

autoregulation - tissue's ability to meet metabolic needs by automatically altering its blood flow

Hormonal Regulation

renin-angiotensin-aldosterone system

decrease in blood pressure or renal blood flow stimulates cells in kidney to secrete renin

pathway produces hormone angiotensin II, which increases BP:

vasoconstriction - leads to increased peripheral vascular resistance

causes kidney tubules to reabsorb sodium

high plasma angiotensin also triggers higher production of aldosterone by adrenal cortex

acts on kidneys to increase reabsorption of sodium ions

increased Na+ leads to enhanced water reabsorption by kidneys and causes total blood volume to rise, elevating BP

epinephrine and norepinephrine - sympathetic stimulation promotes release of these hormones by adrenal medulla

increase heart rate (chronotropy)

increase force of contraction (inotropy) - this increases stroke volume

these two factors combined increase cardiac output

increase in CO will lead to increase in arterial pressure

epinephrine/norepinephrine also constrict arterioles and veins in abdominal organs and skin while dilating vessels in heart and skeletal muscle

this results in increased blood flow to muscles during physical activity

antidiuretic hormone (ADH) - prompted by decreased blood volume or dehydration

produced in hypothalamus and stored in posterior pituitary

causes kidney to retain water

retention leads to increased blood volume and increasing preload

at very high levels, it causes peripheral blood vessels to constrict to help raise BP

atrial natriuretic peptide (ANP) - secreted by myocytes of atria

decreases BP:

dilates blood vessels

reduces blood volume by increasing excretion of salt