MCAT Biology - The Cardiovascular System

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humoralism

the human body is composed of four fluids or substances called humors: black bile, yellow bile, phlegm, and blood

health is balance of these four fluids; illness is caused by an imbalance

bealieved and practiced as late as 19th c. from Greak/ROman physicians

bloodletting

physicians would withdraw significant amounts of blood from their patients to restore balance to the four humors; drawing blood from major veins/arteries, scarificator devices, leeches

modern medical uses of leeches

in microsurgery to help prevent blood coagulation

in reconstructive surgery to stimulate circulation to the reattached tissue

cardiovascular system

consists of a muscular four-chambered heart, blood vessels, and blood

heart

acts as (two) pump(s), distributing blood through the vasculature; four-chambered structure composed predominantly of cardiac muscle; left side of the heart is more muscular than the right side of the heart

vasculature/blood vessels

arteries, capillaries, and veins

blood

connective tissues that carries oxygen and nutrients around the body

pulmonary circulation

first pump; right side of the heart accepts deoxygenated blood returning from the body and moves it to the lungs by way of the pulmonary arteries

systemic circulation

second pump; the left side of the heart, which receives oxygenated blood from the lungs by way of the pulmonary veins and forces it out to the body through the aorta

atria

thin-walled structures where blood is received; contract to push blood into the ventricles

venae cavae

deoxygenated blood entering the right atrium

pulmonary veins

oxygenated blood entering the left atrium

ventricles

contract to send blood out of the heart; more muscular

pulmonary arteries

blood from right ventricle to lungs

aorta

blood from left ventricle to systemic circulation

atrioventricular valves

separates atria from ventricles

semilunar valves

ventricles are separated from the vasculature; three leaflets

tricuspid valve

between right atrium and the right ventricle; three leaflets

mitral/bicuspid valve

between the left atrium and the left ventricle; two leaflets

circulatory valves

allow the heart muscle to create the pressure within the ventricles necessary to propel the blood forward within the circulation, while also preventing backflow of blood

pulmonary valve

separates the right ventricle from the pulmonary circulation

aortic valve

separates the left ventricle from the aorta

SA node

Impulse initiation; generates 60–100 signals per minute without requiring any neurological input; small collection of cells is located in the wall of the right atrium; depolarization wave spreads from the SA node, causes the two atria to contract simultaneously

atrial kick

increase in atrial pressure during atrial systole that forces a little more blood into the ventricles; accounts for about 5–30 percent of cardiac output

AV node

sits at the junction of the atria and ventricles; signal is delayed here toallow the ventricles to fill completely before they contract

bundle of His

after AV node; embedded in the interventricular septum (wall)

Purkinje fibers

distribute the electrical signal through the ventricular muscle

intercalated discs

connect muscle cells; contain many gap junctions directly connecting the cytoplasm of adjacent cells; allows for coordinated ventricular contraction

electrical conduction system of heart

Cardiac muscle has myogenic activity, meaning that it can contract without any neurological input. The SA node generates about 60–100 beats per minute, even if all innervation to the heart is cut. The neurological input to the heart is important in speeding up and slowing the rate of contraction, but not generating it in the first place.

electrocardiogram (ECG or EKG)

heart’s electrical impulses can be detected on the body’s surface by placing electrodes on the skin on opposite sides of the heart; incredibly powerful tools for assessing the status of a patient’s heart

circulation

the flow of blood through the body

vagus nerve

parasympathetic signals slow down heart rate

systole

ventricular contraction and closure of the AV valves occurs and blood is pumped out of the ventricles; Contraction of the ventricles generates a higher pressure

diastole

ventricles are relaxed, the semilunar valves are closed, and blood from the atria fills the ventricles; relaxation of atria causes the pressure to decrease

The Cardiac Cycle

normal events of one heartbeat, including pressures in the left atrium, left ventricle, and aorta; left ventricular volume; normal and pathologic heart sounds; and an EKG

cardiac output

total blood volume pumped by a ventricle in a minute; same in each; connected in series; product of heart rate and stroke volume

about 5 liters per minute

heart rate (HR)

beats per minute

stroke volume (SV)

volume of blood pumped per beat

lub-dub

first sound, S1, is produced when the two AV valves close at the start of systole to prevent backflow into the atria

second sound, S2, is produced when the two semilunar valves close at the end of systole to prevent backflow into the ventricles

extra sounds - stiffness of the heart muscle or high blood pressure

Heart murmurs

so loud as to be audible without a stethoscope, may arise when the valves malfunction and become either narrow and stiff or wide and floppy, resulting in abnormal flow patterns across the valve

ventricular tachycardia

very rapid rate of ventricular contraction; cannot properly fill with blood and, paradoxically, stops pumping blood despite its fast rate. Systemic pressures drop precipitously. Death will result unless the heart is forced out of this abnormal rhythm.

arteries

Blood travels away from the heart; Most arteries contain oxygenated blood (except pumonary and umbilical); highly muscular and elastic, creating tremendous resistance; maintains a high pressure and forces blood forward

arterioles

smaller, muscular arteries; connect arteries to capillaries

capillaries

vessels with a single endothelial cell layer and are so small that red blood cells must pass through the capillaries in a single-file line; perfuse the tissues; allows easy diffusion of gases (O2 and CO2), nutrients (most notably, glucose), wastes (ammonia and urea, among others), hormones

venules

small veins; connect capillaries to the larger veins of the body

veins

Blood enters the heart; usually deoxygenated blood (except pulmonary and umbilical); less recoil than arteries; stretch to accommodate larger quantities of blood; large ones contain valves to push the blood forward and prevent backflow

endothelial cells

maintain the vessel by releasing chemicals that aid in vasodilation and vasoconstriction; allow white blood cells to pass through the vessel wall and into the tissues during an inflammatory response; release certain chemicals when damaged that are involved in the formation of blood clots to repair the vessel and stop bleeding

heart attack / myocardial infarction

lack of bloodflow through the coronary arteries, which results in decreased oxygen delivery to the cardiac muscle itself

β-blocker

blocks the sympathetic stimulation of the heart, resulting in lower heart rate and lower contractility; oxygen demand is diminished, which helps to prevent further damage to cardiac tissue

bruise / contusion

capillaries are damaged, blood can leave the capillaries and enter the interstitial space

varicose veins

distended where blood has pooled

pulmonary emboli (thromboemboli)

clots that block segments of the pulmonary arteries and produce rapid, labored breathing and chest pain; may be fatal

deep vein thrombosis

may form in the deep veins of the legs as a result of injury, inactivity (blood stasis), or a hypercoagulable state (a tendency for the blood to clot excessively)

heparin/warfarin

prevent clots

blood flow through heart

RA →RV→lungs→LA→LV→body and back

portal systems

blood will pass through two capillary beds in series before returning to the heart

hepatic portal system

blood leaving capillary beds in the walls of the gut passes through the hepatic portal vein before reaching the capillary beds in the liver

hypophyseal portal system

blood leaving capillary beds in the hypothalamus travels to a capillary bed in the anterior pituitary to allow for paracrine secretion of releasing hormones

renal portal system

blood leaving the glomerulus travels through an efferent arteriole before surrounding the nephron in a capillary network called the vasa recta

Plasma

liquid portion of blood, an aqueous mixture of nutrients, salts, respiratory gases, hormones, and blood proteins; 55% of blood

serum (pl. sera)

Plasma can be further refined via the removal of clotting factors and fibrinogens; used in a variety of medical testing procedures such as antibody testing and blood typing

hematopoietic stem cells

originate in the bone marrow; orgin of all blood cells

erythrocyte / red blood cell

specialized cell designed for oxygen transport; contains about 250 million molecules of hemoglobin; biconcave (no nucleus, mitochondria or other organelles) - fits through capillaries and increases surface area; live for 120 days in the bloodstream before cells in the liver and spleen phagocytize them for their parts.

adult hemoglobin (HbA)

protein complex made of four cooperative subunits, each of which has a prosthetic heme gorup that can bind a molecule of oxygen at the central iron ion; measured in grams per deciliter (13.5 - 17.5 for males, 12.0 - 16.0 for females); also has low affinity for CO₂ and high affinity for protons (H⁺)

Hematocrit

measure of how much of the blood sample consists of red blood cells, given as a percentage; 41 - 53% for males and 36 - 46% for females.

Leukocytes / white blood cells

comprise less than 1 percent of total blood volume; about 4,500–11,000 leukocytes per microliter of blood; crucial part of the immune system, acting as our defenders against pathogens, foreign cells, cancer, and other materials not recognized as self

granulocytes

granular leukocytes; contain cytoplasmic granules that are visible by microscopy that contain a variety of compounds that are toxic to invading microbes, relased through exocytosis; involved in inflammatory reactions, allergies, pus formation, and destruction of bacteria and parasites

neutrophils

type of phagocytic granulocyte

eosinophils

type of granulocyte; one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates

basophils

largest and least common type of granulocyte

agranulocytes

do not contain granules that are released by exocytosis

lymphocytes

important in the specific immune response; some act as primary responders against an infection, while others function to maintain a long-term memory bank of pathogen recognition; vaccination

specific immune response

the body’s targeted fight against particular pathogens, such as viruses and bacteria

B-cells

lymphocytes that mature in the bone marrow; responsible for antibody generation

T-cells

lymphocytes that mature in the thymus; kill virally infected cells and activate other immune cells

monocytes

phagocytize foreign matter such as bacteria

macrophages

monocytes that enter an organ

microglia

macrophages in CNS

Langerhans cells

macrophages in skin

osteoclasts

macrophages in bone

thrombocytes / platelets

cell fragments or shards released from megakaryocytes; assist in blood clotting; present in high concentrations (150,000–400,000 per microliter of blood); come into contact with exposed collagen → release their contents and begin to aggregate

megakaryocytes

bone marrow cells that shatter into platelets

hematopoiesis

production of blood cells and platelets; triggered by a number of hormones, growth factors, and cytokines

erythropoietin

secreted by the kidney; stimulates mainly red blood cell development

thrombopoietin

secreted by the liver and kidney; stimulates mainly platelet development

antigens

surface proteins that identify a cell; any specific target (usually a protein) to which the immune system can react

ABO Antigens

comprised of three alleles for blood type; A/I^A and B/I^B are codominant, O/i is recessive; dominant allles express self-antigen and produce anti-other antibodies

universal donors

type O; blood will not cause ABO-related hemolysis in any recipient

universal recipients

type AB; receive blood from all blood types: no blood antigen is foreign to individuals who have AB blood, so no adverse reactions will occur upon transfusion

Antibodies

created in response to an antigen, and they specifically target that antigen

Rh factor

first described in rhesus monkeys; surface protein expressed on red blood cells; Rh-positive (Rh⁺) or Rh-negative (Rh^-) refers to the presence or absence of a specific allele called D; can also be indicated with a plus or minus superscript on the ABO blood type; autosomal dominant inheritance

erythroblastosis fetalis

if mother is Rh^- and first baby is Rh⁺, the risk exists for every subsequent RH⁺ child that maternal anti-Rh antibodies can cross the placenta and attack the fetal blood cells, resulting in hemolysis of the fetal cells

sphygmomanometer

measure the gauge pressure in the systemic circulation, which is the pressure above and beyond atmospheric pressure (760 mmHg at sea level)

Blood pressure

measure of the force per unit area exerted on the wall of the blood vessels; expressed as a ratio of the systolic (ventricular contraction) to diastolic (ventricular relaxation) pressures; normal between 90/60 and 120/80; regulated using baroreceptors in the walls of the vasculature

ΔP = CO × TPR

where ΔP is the pressure differential across the circulation, CO is the cardiac output, and TPR is the total peripheral (vascular) resistance

hypertension

high blood pressure; pathological state that may result in damage to the blood vessels and organs

Baroreceptors

specialized neurons that detect changes in the mechanical forces on the walls of the vessel

blood pressure low → sympathetic nervous system → vasoconstriction → increasing the blood pressure

blood pressure high → sympathetic impulses decrease → vasodilation→ lowering the blood pressure

chemoreceptors

sense when the osmolarity of the blood is too high, possible dehydration

promotes the release of ADH/vasopressin → increasing blood volume and pressure, diluting blood

renin–angiotensin–aldosterone system

Low perfusion to the juxtaglomerular cells of the kidney → aldosterone release → increases the reabsorption of sodium → by extension, water → increasing the blood volume and pressure

atrial natriuretic peptide (ANP)

specialized atrial cells secrete hormone; aids in the loss of salt within the nephron, acting as a natural diuretic with loss of fluid

concentration gradients

one side of a semi-permeable mebrane has a higher concentration of a given substance than the other