MCAT Kaplan Biology Chapter 7: The Cardiovascular System

Cardiovascular system

Consists of a four-chambered heart, blood vessels and blood.

Heart

Four chambered structure composed mostly of cardiac muscle. Has two pumps to support two different circulations.

Pulmonary circulation

Right side of heart accepts deoxygenated blood from the body and moves it to the lungs using the pulmonary artery for oxygenation.

Systemic circulation

Left side of the heart receives oxygenated blood from the lungs via pulmonary veins and forces it out to the body through the aorta.

Atria

Thin-walled structures where blood is received from either the venae cavae or the pulmonary veins (oxygenated blood to left side of heart).

Venae cavae

Channel in which deoxygenated blood enters right side of the heart from the body.

Ventricles

Blood enters this chamber from the aorta. These fill and then contract to send blood to the lungs and for systemic circulation.

Note that the ventricles are far more muscular than the atria, allowing for more powerful contractions that are necessary to push blood through the rest of the body.

Atrioventricular valves

Separate the atria and ventricles.

Semilunar valves

Separate the ventricles from the vasculature.

Tricuspid valve

Valve between the right atrium and the right ventricle.

• Atrioventricular valves: LAB RAT

• Left Atrium = Bicuspid

• Right Atrium = Tricuspid

Mitral or bicuspid valve

Valve between the left atrium and the left ventricle.

Pulmonary valve

Separates the right ventricle from the pulmonary circulation.

Aortic valve

Separates the left ventricle from the aorta.

Sinoatrial node (SA node)

Impulse initiation begins here, which generates 60-100 signals per minute without requiring any neurological input.

This small collection of cells is located in the wall of the right atrium.

It causes the two atria to contract simultaneously.

Atrial systole (contraction)

Results in an increase in atrial pressure that forces a little more blood into the ventricles.

Atrial kick

The extra blood volume from atrial systole accounts for 5-30% of cardiac output.

Atrioventricular node (AV node)

Signal reaches here after SA node. This node sits at the junction of the atria and ventricles. The signal is delayed here to let ventricles to fill before they contract.

Bundle of His what it is and what is its location

Signal travels here after AV node. In combination with the Purkinje fibers, they distribute the electrical signal through the ventricular muscle.

Interventricular septum

Location of the bundle of His.

Purkinje fibers

Electrical signal travels here along with the bundle of His and distributes the electrical signal to the ventricular muscle.

Intercalated discs

Connect muscle cells, and contain many gap junctions directly connecting the cytoplasm of adjacent cells, thereby allowing for coordinated ventricular contraction.

what does cardiac muscle have and what does it mean

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

relate heart rate to nodes

The SA node has an intrinsic rhythm of 60–100 signals per minute, so the normal human heart rate is 60–100 beats per minute. Highly conditioned athletes may have heart rates significantly lower than 60, in the range of 40–50 beats per minute. Stress, exercise, excitement, surprise, or danger can cause the heart rate to rise significantly above 100.

see EKG diagram how to read

what systems cotrol the cardiovascular system and what works against it

The circulatory system is under autonomic control. The autonomic system consists of the sympathetic (“fight-or-flight”) and parasympathetic (“rest-and-digest”) branches, controls the heart and affects the vasculature. Sympathetic signals speed up the heart rate and increase the contractility of cardiac muscle, while parasympathetic signals, provided by the vagus nerve, slow down the heart rate.

Vagus nerve

Give signals to the parasympathetic nervous system to slow down heart rate and decrease cardiac muscle contractility.

Systole phase of heartbeat

Ventricular contraction and closure of the AV valves occurs and blood is pumped out of the ventricles.

Diastole phase of heartbeat

The heart is relaxed and semilunar valves are closed, causing blood from the atria to fill in the ventricles.

Cardiac output

Total blood volume pumped by a ventricle in a minute.

Cardiac output = Heart rate * Stroke volume

Heart rate

It is the beats per minute.

Stroke volume

The volume of blood pumped per beat.

see real world info diagrams

Arteries

Blood vessels which carry blood away from the heart. The largest artery in systemic circulation is the aorta.

Major arteries divide the bloodflow from the aorta to different peripheral tissues.

Most contain oxygenated blood other than the pulmonary artery and umbilical artery.

They are highly muscular and elastic.

Arterioles

Branches from arteries. Lead to capillaries.

Capillaries

Perfuse blood into the tissues. Have a single endothelial cell layer and are extremely small to the point that RBCs must pass through in single file. The thin wall allows for the easy diffusion of gases, nutrients and wastes.

Venules

Joined capillaries. These form together to make veins.

They also connect veins to capillaries.

Veins

Joined venules which carry blood to the heart.

Thin-walled, inelastic vessels that transport blood to the heart. Most carry deoxygenated blood other than the pulmonary and umbilical veins.

Larger veins have valves to prevent backflow from the extremely high pressure.

Endothelial cells

Line all blood vessels and help maintain the vessel by releasing chemicals that aid in vasodilation and vasoconstriction. They also allow WBCs to pass during inflammatory response.

Also release chemicals to form blood clots to stop bleeding.

Superior vena cava

Returns blood from the portions of the body above the heart.

Inferior vena cava

Returns blood from the portions of the body under the heart.

Portal systems in the body

Three portal systems.

Hepatic portal system

Hypophyseal portal system

Renal portal system

Hepatic portal system

Blood leaving the capillary beds in the walls of the gut passes through this system 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 from the glomerulus travels through an efferent arteriole before surrounding the nephron in a capillary network called the vasa recta.

Plasma

Liquid portion of blood. Aqueous mixture of nutrients, salts, respiratory gases, hormones and blood proteins.

Erythrocytes (RBCs)

Specialized cell designed for oxygen transport.

Have a biconcave shape to travel through tiny capillaries and also to increase the cell's surface area for greater gas exchange.

Hemoglobin

Located in RBCs and each molecule can pick up 4 oxygen molecules.

Normal for males- 13.5 to 17.5

females- 12 to 16

The binding and releasing of oxygen to or form the iron atom in the heme group is an oxidation reduction reaction.

Has a lower affinity for carbon dioxide.

Hemocrit

Measurement of how much of the blood sample consists of RBCs.

Normal for males- 41 to 53%

females- 36 to 46%

Leukocytes (WBCs)

Crucial part of the immune system as they defend against pathogens.

Granulocytes

Neurophils, eosinophils and basophils.

Leukocytes which contain cytoplasmic granules that are visible by microscopy. The granules are toxic to invading microbes and are involved in inflammatory reactions, allergies, pus formation and destruction of bacteria and parasites.

Agranulocytes

Consist of lymphocytes and monocytes. Do not contain granules.

Lymphocytes

Important in specific immune response which is the body's targeted fight against particular pathogens, such as viruses and bacteria.

Some lymphocytes are primary responders against an infection, while other maintain a long-term memory bank of pathogen recognition.

Monocytes

Agranulocyte which phagocytizes foreign matter such as bacteria. Once they leave the bloodstream and enter an organ they are called macrophages.

Macrophage

Monocyte which is located in the organ.

Microglia

Macrophage in the central nervous system.

Langerhans cells

Macrophage in the skin.

Osteoclasts

Macrophage in the bone.

Thrombocytes (platelets)

Cell fragments released from cells in bone marrow known as megakaryocytes. They assist in blood clotting.

Hematopoiesis

Production of blood cells and platelets. Triggered by a number of hormones, growth factors and cytokines.

Erythropoeitin

Secreted by the kidney and stimulates RBC development and thrombopoietin.

Thrombopoietin

Secreted by the liver and kidney and stimulates platelet development.

Antigens

Any specific target (usually a protein) to which the immune system can react to.

ABO antigens

A and B alleles are codominant and O allele is recessive to both.

A blood type produces A antigens.

B blood type produces B antigens.

O blood type produces no antigens.

Universal donor

People with type O blood because they have no antigens and will not cause hemolysis when this blood is transfused into other people.

Universal recipient

People with AB blood because they produce both antigens so not antigens are foreign when blood is transfused.

Rh factor

Surface protein expressed on RBCs. Can be Rh negative or positive. Positive means there is an allele D present and negative means it is absent.

Erythroblastosis fetalis

When fetal cells are destroyed due to anti-Rh antibodies which do not recognize the Rh antigens on the fetus.

Blood pressure

Kept high throughout the body in order to propel blood forward. Hypertension is a condition in which blood pressure is excessively high and causes damage to vessels. It is measured in force per unit area exerted on the wall to the blood vessels and organs.

The pressure gradient across the circulatory system drives cardiac output through a given vascular resistance.

Pressure differential = Cardiac output * total peripheral resistance

BP is regulated using baroreceptors in the walls of the vasculature.

Sphygmomanometer

Measure the gauge pressure in the systemic circulation, which is pressure above and beyond atmospheric pressure.

Baroreceptors

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

When BP is low, they can stimulate the sympathetic nervous system to increase BP by vasoconstriction.

When osmolarity of blood is high, they stimulate ADH to increase the reabsorption of water to increase in blood volume and pressure.

Atrial natriuretic peptide

This is a hormone which aids in the loss of salt within the nephron, acting as a natural diuretic with loss of fluid. It is a weak diuretic.

Oxygen saturation

The percentage of hemoglobin molecules carrying oxygen. Healthy is over 97%.

Cooperative binding

As more oxygen bind to heme groups, the affinity of oxygen to heme groups increases.

The removal of an oxygen likewise triggers a conformational shift which decreases the affinity of oxygen to the heme groups, making it easier for the oxygens to leave.

Carbonic anhydrase

Catalyzes the combination reaction between carbon dioxide and water to form carbonic acid. This dissociates into a proton and the bicarbonate anion, which both easily dissolve in blood and can transport wastes easier. The alveolar capillaries reverse the effects of the anhydrase.

Bohr effect

The decreased affinity of hemoglobin for oxygen due to the increase of protons.

Fetal hemoglobin

Has a higher affinity for oxygen compared to adult hemoglobin.

Hydrostatic pressure

The force per unit area that the blood exerts against the vessel walls. Generated by the contraction of the heart and the elasticity of the arteries, and can be measured upstream in the large arteries as blood pressure.

Osmotic pressure

The "sucking" pressure generated by solutes as they attempt to draw water into the bloodstream. AKA oncotic pressure.

Starling forces

Higher hydrostatic pressure in arteriole than oncotic pressure so water is being pushed through.

As fluid moves out of the vessels the hydrostatic pressure drops significantly, but the osmostic pressure stays the same. At the venule end of the capillary bed, there is a net efflux of water back into circulation.

These forces maintain proper fluid volumes and solute concentrations inside and outside of the vasculature.

Edema

Caused by accumulation of excess fluid in the interstitium.

Thoracic duct

Lymphatic fluid is returned to the central circulatory system by this channel.

Clots

Composed of both coagulation factors and platelets to prevent blood loss.

Tissue factor

Protein found in blood vessels.

Coagulation factors

Sense tissue factor and collagen, and initiate a complex activation cascade. The endpoint is the activation of prothrombin to form thrombin by thromboplastin.

Thrombin

Can convert to fibronogen which turns into fibrin.

Fibrin

Forms small fibers which aggregate and cross-link into a woven structure to capture RBCs and plateletes to form a stable clot over the area of damage.

Plasmin

Generated from plasminogen, and it breaks down clots.