ABCT2326 Cardiovascular System(1)

The three types of transmembrane proteins are:

1. Sodium-potassium pump
2. Potassium channel
3. Sodium channel

A potentiometer measures the electrical potential difference between two points, in this case, across the plasma membrane. It helps in determining the voltage inside the cell compared to the bathing medium.

The components include:

1. Potentiometer - measures voltage.
2. Microelectrode - inserted into the cell, filled with a conducting salt solution.
3. Reference electrode - in contact with the bathing medium.
4. Bathing medium - the solution surrounding the cell.
5. Cytosol - the fluid inside the cell.
6. Plasma membrane - separates the cytosol from the bathing medium.

• Endothelial cells are tightly joined together.
• Have narrow intercellular channels that permit exchange of molecules smaller than proteins.
• Present in muscle, lungs, and adipose tissue.

The Sinoatrial (SA) Node is located in the posterior wall of the right atrium.

The primary functions of the circulatory system include:

1. Transportation of respiratory gases, nutrients, hormones, and waste removal.
2. Temperature regulation.
3. Clotting to prevent blood loss.
4. Immune function through the lymphatic system.

The cardiovascular system consists of:

• Heart: Pumps blood throughout the system.
• Blood Vessels: Carry blood from the heart to cells and back, including:
  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins

The lymphatic system plays a crucial role by:

• Picking up excess fluid filtered out in capillary beds.
• Returning this fluid to the veins.
• Housing lymph nodes, which are part of the immune system.

The total blood volume is about 5 liters.

The two main components of blood are formed elements (cells) and plasma (fluid part).

Red blood cells (RBCs) comprise most of the formed elements in blood.

Hematocrit is the percentage of red blood cells in a centrifuged blood sample. It is typically 36-46% in women and 41-53% in men.

Plasma is the straw-colored liquid part of blood that consists of H₂O and dissolved solutes, including ions, metabolites, hormones, and antibodies.

Albumin creates colloid osmotic pressure, which helps to maintain blood volume and blood pressure, essential for proper fluid balance.

Fibrinogen functions as a clotting factor in blood. It is converted to fibrin, which forms a mesh that helps to stabilize blood clots, preventing excessive bleeding.

RBCs are flattened biconcave discs, which provide increased surface area for diffusion of oxygen and carbon dioxide. This shape is crucial for their function in gas transport.

• Lack nuclei and mitochondria
• Each RBC contains 280 million hemoglobin molecules
• About 300 billion RBCs are produced each day

WBCs, or leukocytes, play a crucial role in the body's defense mechanisms against infections and diseases.

Platelets, or thrombocytes, are small, membrane-bound cell fragments that lack a nucleus and are derived from megakaryocytes in the bone marrow. Their primary function is to aid in blood clotting by constituting most of the mass of blood clots.

Platelets typically survive in the bloodstream for about 5 to 9 days.

The innermost layer of all blood vessels is called the endothelium.

Capillaries are made of only endothelial cells.

A fenestrated capillary is distinguished by:

• Pores in the endothelial cells that allow for increased permeability.
• A basement membrane that supports the structure.
• It is typically found in areas requiring rapid exchange of substances, such as the kidneys and intestines.

The main components of an elastic artery include:

• Internal elastic membrane: A layer that allows for expansion and recoil.
• Endothelium: The inner lining.
• Tunica media: Thick layer with a high content of elastic fibers.
• Tunica externa: The outer layer providing support.
• Tunica intima: The innermost layer in contact with blood.

The primary function of muscular arteries is to:

• Distribute blood to various parts of the body.
• Regulate blood flow through vasoconstriction and vasodilation due to a thicker tunica media composed of smooth muscle.
• Maintain blood pressure and control blood distribution during physical activity.

The characteristics of arterioles include:

• A very thin tunica externa and tunica media compared to larger arteries.
• A significant role in regulating blood flow and pressure due to their ability to constrict and dilate.
• They connect arteries to capillaries, facilitating the transition of blood flow.

The structural features of continuous capillaries include:

• Endothelial cells that form a continuous lining without pores.
• A basement membrane that supports the endothelial layer.
• They are found in most tissues and are important for selective permeability, allowing for the exchange of small molecules while restricting larger ones.

Arteries carry blood away from the heart and are characterized by their muscular and elastic structure. They expand during systole and recoil during diastole, which helps maintain smooth blood flow. Small arteries and arterioles provide most resistance in the circulatory system.

Capillaries facilitate the exchange of dissolved gases, nutrients, and wastes between blood and tissues.

Blood flow through a capillary bed is determined by the state of precapillary sphincters of the arteriole supplying it.

Capillaries provide an extensive surface area for the exchange of substances between blood and tissues.

The precapillary sphincter regulates blood flow into the capillary network by contracting or relaxing, thus controlling the amount of blood that enters the capillaries based on the tissue's metabolic needs.

Arterioles are smaller, more muscular branches of arteries that lead to capillaries. They play a crucial role in regulating blood flow and blood pressure by constricting or dilating, unlike arteries which primarily serve to transport blood from the heart.

The metarteriole serves as a transitional vessel between arterioles and capillaries, allowing for the regulation of blood flow into the capillary beds and facilitating the exchange of nutrients and waste products.

The arteriovenous shunt allows blood to bypass the capillary network, directly connecting arterioles to venules. This can be significant in regulating blood flow and temperature, especially in response to physiological demands.

• Fenestrated capillaries contain 'windows' or pores that penetrate the endothelial lining.
• Allow rapid exchange of water and solutes between blood and interstitial fluid.
• Present in the brain, endocrine organs (e.g., hypothalamus), intestinal tract, and kidneys.

Veins carry blood to the heart and contain the majority of blood in the circulatory system.

Veins have 1-way venous valves that ensure blood moves only toward the heart, preventing backflow.

Blood is moved toward the heart by:

1. Contraction of surrounding skeletal muscles (skeletal muscle pump)
2. Pressure drops in the chest during breathing

Veins contain very low pressure (about 2mm Hg), which is insufficient to return blood to the heart without assistance from other mechanisms.

Veins are very compliant, meaning they can expand readily to accommodate a large volume of blood.

Pulmonary circulation is the path of blood from the right ventricle through the lungs and back to the heart.

Systemic circulation is the path of blood from the left ventricle to the body and back to the heart.

The rate of flow through systemic circulation is equal to the flow rate through the pulmonary circuit.

The main components of the pulmonary circuit include:

• Pulmonary arteries: Carry deoxygenated blood from the right ventricle to the lungs.
• Pulmonary veins: Carry oxygenated blood from the lungs to the left atrium.

The main components of the systemic circuit include:

• Systemic arteries: Carry oxygenated blood from the left ventricle to the body.
• Systemic veins: Carry deoxygenated blood from the body back to the right atrium.

Blood flow through the heart involves:

1. Deoxygenated blood enters the right atrium from the systemic veins.
2. Blood moves to the right ventricle, which pumps it to the pulmonary arteries.
3. In the lungs, blood is oxygenated and returns to the left atrium via the pulmonary veins.
4. Oxygenated blood flows into the left ventricle, which pumps it into the systemic arteries to supply the body.

Deoxygenated blood from tissues enters the superior and inferior vena cavae, which empty into the right atrium. It then moves to the right ventricle, which pumps it through the pulmonary arteries to the lungs for oxygenation.

Oxygenated blood from the lungs passes through the pulmonary veins to the left atrium, then to the left ventricle, which pumps it through the aorta to supply the body with oxygenated blood.

The three layers of the heart wall are:

1. Epicardium (Outer Layer) - Also known as visceral pericardium, it covers the heart.
2. Myocardium (Middle Layer) - The muscular wall of the heart, consisting of concentric layers of cardiac muscle tissue, with atrial myocardium wrapping around great vessels and two divisions of ventricular myocardium.
3. Endocardium (Inner Layer) - Composed of simple squamous epithelium.

The three main layers of the heart wall are:

1. Epicardium (visceral pericardium)

   • Mesothelium
   • Areolar tissue

2. Myocardium

   • Cardiac muscle tissue
   • Cardiac muscle cells
   • Connective tissues

3. Endocardium

   • Endothelium
   • Areolar tissue

Intercalated discs are specialized structures that interconnect cardiac muscle cells. Their functions include:

• Securing cardiac muscle cells by desmosomes
• Linking cells through gap junctions
• Conveying the force of contraction
• Propagating action potentials between cells

The primary function of the Sinoatrial (SA) Node is to begin atrial activation, acting as the heart's natural pacemaker.

The key structural features of cardiac muscle cells include:

1. Mitochondria - Represented by small blue ovals, indicating high energy demand.
2. Intercalated discs - Specialized connections between cardiac muscle cells that facilitate communication and synchronized contraction.
3. Nucleus - Typically centrally located within the cell.
4. Bundles of myofibrils - Organized structures that enable contraction of the muscle cells.

The main components of an intercalated disc include:

1. Gap junctions - Allow for direct communication between cardiac muscle cells.
2. Z-lines - Bound to opposing plasma membranes, providing structural support.
3. Desmosomes - Provide mechanical strength by anchoring the cells together.

1. Small size
2. Single, central nucleus
3. Branching interconnections between cells
4. Intercalated discs

The heart has 4 chambers:

1. Atria:

   • 2 atria (right and left) receive blood from the venous system.

2. Ventricles:

   • 2 ventricles (right and left) pump blood to the arteries.

The two sides of the heart function as two separate pumps, which are separated by a muscular septum. This structure allows for efficient circulation of blood through the body.

Cardiac muscle tissue forms concentric layers that wrap around the atria and spiral within the walls of the ventricles.

The cardiac (fibrous) skeleton serves several important functions:

1. Structural Support: It encircles the heart valves and the bases of the pulmonary trunk and aorta.
2. Separation: It structurally and functionally separates the ventricles from the atria.
3. Electrical Insulation: It electrically insulates the ventricular cells from atrial cells, preventing direct electrical conduction between them.

During ventricular contraction:

• The AV valves (right AV or tricuspid valve and left AV or bicuspid valve) are closed.
• The semilunar valves (aortic valve and pulmonary valve) are open, allowing blood to flow from the ventricles into the aorta and pulmonary trunk.

During ventricular contraction, the left AV valve is attached to the chordae tendineae and papillary muscles. This connection helps to keep the valve closed, preventing backflow of blood into the left atrium.

• The right ventricle has a thinner wall and develops less pressure than the left ventricle.
• The right ventricle is pouch-shaped, while the left ventricle is round.

The left ventricle is larger in volume and has relatively thin walls when dilated, while the right ventricle has thicker and more folded walls when contracted. In the contracted state, the left ventricle's volume is significantly reduced, and its walls become thicker compared to the dilated state.

The atrioventricular (AV) valves allow blood to flow from the atria into the ventricles in a one-way direction, preventing backflow during ventricular contraction.

The two atrioventricular valves are the tricuspid valve, located between the right atrium and right ventricle, and the bicuspid (mitral) valve, located between the left atrium and left ventricle.

During ventricular contraction, the atrioventricular valves are closed to prevent backflow of blood into the atria, while the semilunar valves are open to allow blood to flow into the aorta and pulmonary trunk.

The semilunar valves, which include the pulmonary and aortic valves, prevent the backflow of blood from the pulmonary arteries and aorta into the right and left ventricles, respectively.

During ventricular contraction, the AV valves are closed while the semilunar valves are open, allowing blood to flow from the ventricles into the pulmonary arteries and aorta.

The left AV valve is attached to the chordae tendineae and papillary muscles, which help maintain its closure during ventricular contraction.

The contraction of papillary muscles, which are connected to the AV valves by chorda tendinea, prevents the everting of AV valves during ventricular contraction.

During ventricular contraction, blood is pumped through the aortic and pulmonary semilunar valves, which close during relaxation.

The opening and closing of valves results from pressure differences within the heart chambers.

When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed.

When the ventricles are relaxed, the chordae tendineae are loose and the papillary muscles are relaxed.

When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed.

When the ventricles are relaxed, the chordae tendineae are loose and the papillary muscles are relaxed.

During the relaxation phase, the left ventricle is relaxed and filling with blood.

During ventricular contraction, the AV valves (tricuspid and bicuspid) are closed, preventing backflow of blood into the atria.

During ventricular contraction, the semilunar valves (aortic and pulmonary) are open, allowing blood to flow into the aorta and pulmonary artery.

The left AV valve (bicuspid) is attached to the chordae tendineae and papillary muscles, which help maintain its closure during ventricular contraction.

During ventricular contraction, the AV valves are closed and the semilunar valves are open.

The chordae tendineae are tense and connect to the contracted papillary muscles, helping to keep the AV valves closed during ventricular contraction.

The aortic valve is open during the contraction of the left ventricle, allowing blood to flow into the aorta.

1. Conducting system: Initiates and distributes electrical impulses that stimulate contraction and controls the heartbeat.

2. Contractile cells: Produce contractions that propel blood.

The cardiac cycle begins with an action potential at the sinoatrial (SA) node.

The action potential is transmitted through the conducting system, which includes the internodal pathways, atrioventricular (AV) node, AV bundle, bundle branches, and Purkinje fibers.

The action potentials produced in the cardiac muscle cells lead to contraction of the heart muscle, enabling effective pumping of blood.

The main structures of the conducting system include:

1. Sinoatrial (SA) node - located in the wall of the right atrium.
2. Atrioventricular (AV) node - found at the junction between the atria and ventricles.
3. Conducting cells - distributed throughout the myocardium.

The conducting cells interconnect the Sinoatrial (SA) and Atrioventricular (AV) nodes and distribute the electrical stimulus through the myocardium. They are responsible for coordinating the heart's rhythm by ensuring that the electrical impulses travel efficiently through the heart muscle.

The conducting system includes:

1. Internodal pathways in the atria
2. AV bundle and bundle branches in the ventricles
3. Purkinje fibers that further distribute the impulse throughout the ventricles

The Sinoatrial (SA) Node is connected to the Atrioventricular (AV) Node by internodal pathways.

The SA node (sinoatrial node) acts as the primary pacemaker of the heart, generating electrical impulses that initiate the heartbeat. These impulses cause depolarizations in autorhythmic cells, which then rapidly spread to adjacent contractile cells through gap junctions, coordinating heart contractions.

Depolarizations of autorhythmic cells in the SA node rapidly spread to adjacent contractile cells through gap junctions, leading to synchronized contraction of the heart muscle. This process is essential for maintaining an effective heartbeat and proper blood circulation.

The cyclical pattern in the membrane potential graphs of both autorhythmic cells and contractile cells indicates the rhythmic nature of heart activity. The autorhythmic cells exhibit spontaneous depolarization, while the contractile cells respond to these depolarizations, resulting in coordinated contractions of the heart muscle.

The sodium-potassium pump transports sodium ions (Na+) out of the cell and potassium ions (K+) into the cell, maintaining the electrochemical gradient essential for various cellular functions.

The potassium channel transports potassium ions (K+) into the cell, while the sodium channel transports sodium ions (Na+) into the cell, allowing for selective ion movement across the membrane.

The presence of positively charged ions (represented by red plus signs) and negatively charged ions (represented by blue minus signs) in both the bathing medium and cytosol creates a voltage difference across the plasma membrane. This difference is what the potentiometer measures, reflecting the electrical potential of the cell.

The threshold is the membrane potential level that, when reached, triggers the next action, such as the opening of Ca2+ channels.

During depolarization, the interior voltage of the cell becomes less negative.

Repolarization is the process that occurs after depolarization, where the membrane potential returns to a negative value.

During hyperpolarization, the interior voltage of the cell becomes more negative.

The pacemaker potential, also known as prepotential, is the resting potential of conducting cells that gradually depolarizes toward the threshold. It is significant because the SA node depolarizes first, establishing the heart rate.

Spontaneous depolarization is caused by Na+ flowing through the HCN channel, which opens when the membrane is hyperpolarized.

At the threshold voltage of -40mV, voltage-gated Ca2+ channels open, leading to an upstroke and contraction of the cardiac muscle.

Repolarization is achieved by the opening of voltage-gated K+ channels, which allows K+ to flow out of the cell, returning the membrane potential to a more negative value.

The membrane voltage begins at around -60mV and gradually depolarizes to the -40mV threshold, followed by a rapid spike during the action potential and then returning to a lower voltage to start the cycle again.