Question

Answer the questions in the photo.

1. Please identify the 4 chambers of the heart, and the 4 valves that regulate flow through the heart and out of the heart. 2. Describe how the heart sounds (S1 and S2) relate to our understanding of the cardiac cycle. How does this correlate with the EKG tracing? Why is this coordination critical in enabling the heart to develop pressure gradients, and maintain adequate cardiac output? 3. We discussed the Frank-Starling Law of the Heart, and how it informs our understanding of the importance of preload in determining cardiac output. In the context of that information, why is exercise good for cardiac output? 4. Describe the electrical conduction system of the heart, and how the graphic representation of the EKG allows us to track the signal for contraction. Given that knowledge, indicate what EKG waves are coincident with S1, S2, End systolic volume, and End diastolic volume. What are the formed elements of the blood? Which formed element carries oxygen? What fraction of the oxygen delivered to tissues is carried by that type of cell? How does this inform our understanding of maximizing oxygen transport? 6. What is shock? What are the types of shock? 7. How does feedback inhibition(negative feedback) regulate the endocrine system? Use the Hypothalamic-pituitary- thyroid axis as an example. 5.

Answer 1

1 Ans) Four chambers and Four valves of that regulate flow of blood through and out of the Heart:

The heart has four chambers (two atria and two ventricles). There is a wall (septum) between the two atria and another wall between the two ventricles. Arteries and veins go into and out of the heart. Arteries carry blood away from the heart and veins carry blood to the heart. The flow of blood through the vessels and chambers of the heart is controlled by valves.

The heart consists of four chambers in which blood flows:

• Blood enters the right atrium and passes through the right ventricle. The right ventricle pumps the blood to the lungs where it becomes oxygenated.
• The oxygenated blood is brought back to the heart by the pulmonary veins which enter the left atrium. From the left atrium blood flows into the left ventricle.
• The left ventricle pumps the blood to the aorta which will distribute the oxygenated blood to all parts of the body.

Four valves regulate blood flow through your heart:

• Tricuspid valve. This valve is located between the right atrium and the right ventricle. It regulates blood flow between the right atrium and right ventricle.

• Pulmonary valve. The pulmonary valve is located between the right ventricle and the pulmonary artery. It controls blood flow from the right ventricle into the pulmonary arteries, which carry blood to your lungs to pick up oxygen.

• Mitral valve. This valve is located between the left atrium and the left ventricle. It has only 2 leaflets. It lets oxygen-rich blood from your lungs pass from the left atrium into the left ventricle.

• Aortic valve. The aortic valve is located between the left ventricle and the aorta. It opens the way for oxygen-rich blood to pass from the left ventricle into the aorta, your body’s largest artery.

2 Ans) The period of time that begins with contraction of the atria and ends with ventricular relaxation is known as the cardiac cycle. The period of contraction that the heart undergoes while it pumps blood into circulation is called systole. The period of relaxation that occurs as the chambers fill with blood is called diastole. Both the atria and ventricles undergo systole and diastole, and it is essential that these components be carefully regulated and coordinated to ensure blood is pumped efficiently to the body.

The first heart sound (S1) represents closure of the atrioventricular (mitral and tricuspid) valves as the ventricular pressures exceed atrial pressures at the beginning of systole. S1 is normally a single sound because mitral and tricuspid valve closure occurs almost simultaneously. Clinically, S1 corresponds to the pulse.

The second heart sound (S2) represents closure of the semilunar (aortic and pulmonary) valves. S2 is normally split because the aortic valve (A2) closes before the pulmonary valve (P2). The closing pressure (the diastolic arterial pressure) on the left is 80 mmHg as compared to only 10 mmHg on the right. This higher closing pressure leads to earlier closure of the aortic valve. In addition, the more muscular and stiff "less compliant" left ventricle (LV) empties earlier than the right ventricle. The venous return to the right ventricle (RV) increases during inspiration due to negative intrathoracic pressure and P2 is even more delayed, so it is normal for the split of the second heart sound to widen during inspiration and to narrow during expiration. Clinically, this is more remarkable with slow heart rates.

Isovolumetric ventricular contraction: This phase marks the beginning of systole and starts with the appearance of the QRS complex on the EKG and the closure of the AV valves at point.

Reduced ejection: This phase marks the beginning of ventricular repolarization by the onset of the T wave on the EKG.

Image attached below

3 Ans) The Frank-Starling Law is the description of cardiac hemodynamics as it relates to myocyte stretch and contractility. The Frank-Starling Law states that the stroke volume of the left ventricle will increase as the left ventricular volume increases due to the myocyte stretch causing a more forceful systolic contraction. This assumes that other factors remain constant.

Preload can be defined as the initial stretching of the cardiac myocytes prior to contraction. Preload, therefore, is related to muscule sarcomere length. Because sarcomere length cannot be determined in the intact heart, other indices of preload are used such as ventricular end-diastolic volume or pressure.

When venous return to the heart is increased, the end-diastolic pressure and volume of the ventricles are increased, which stretches the sarcomeres, thereby increasing their preload. In contrast, hypovolemia resulting from a loss of blood volume (e.g., hemorrhage) leads to less ventricular filling and therefore shorter sacromere lengths (reduced preload). Changes in ventricular preload dramatically affect ventricular stroke volume by what is called the Frank-Starling mechanism. Increased preload increases stroke volume, whereas decreased preload decreases stroke volume by altering the force of contraction of the cardiac muscle.

Exercise strengthens muscles in our body, it helps your heart muscle become more efficient and better able to pump blood throughout your body. The heart pushes out more blood with each beat, allowing it to beat slower and keep your blood pressure under control.

4 Ans) The electrical conduction system of the heart transmits signals generated usually by the sinoatrial node to cause contraction of the heart muscle. The pacemaking signal generated in the sinoatrial node travels through the right atrium to the atrioventricular node, along the Bundle of His and through bundle branches to cause contraction of the heart muscle. This signal stimulates contraction first of the right and left atrium, and then the right and left ventricles. This process allows blood to be pumped throughout the body.

• The electrical signal begins in the sinoatrial node (1) which is located in the right atrium and travels to the right and left atria, causing them to contract and pump blood into the ventricles. This electrical signal is recorded as the P wave on the ECG. The PR Interval is the time, in seconds, from the beginning of the P wave to the beginning of the QRS complex.
• The electrical signal passes from the atria to the ventricles through the atrioventricular (AV) node (2). The signal slows down as it passes through this node, allowing the ventricles to fill with blood. This slowing signal appears as a flat line on the ECG between the end of the P wave and the beginning of the Q wave. The PR segment represents the electrical conduction through the atria and the delay of the electrical impulse in the atrioventricular node.
• After the signal leaves the AV node it travels along a pathway called the bundle of His (3) and into the right and left bundle branches (4, 5). The signal travels across the heart’s ventricles causing them to contract, pumping blood to the lungs and the body. This signal is recorded as the QRS waves on the ECG. Because these waves occur in rapid succession they are usually considered together as the QRS complex.
• The ventricles then recover to their normal electrical state, shown as the T wave. The muscles relax and stop contracting, allowing the atria to fill with blood and the entire process repeats with each heartbeat. The ST segment connects the QRS complex and the T wave and represents the beginning of the electrical recovery of the ventricles.
• The QT interval represents the time during which the ventricles are stimulated and recover after the stimulation. This interval shortens at a faster heart rate and lengthens at a slower heart rate.

(Information regarding End systolic volume and End diastolic volume(S1, S2) is explained in 2 Ans)

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fig: EKG wave explaination

5 Ans) The formed elements are cells and cell fragments suspended in the plasma. The three classes of formed elements are the erythrocytes (red blood cells), leukocytes (white blood cells), and the thrombocytes (platelets).

The primary functions of erythrocytes are to pick up inhaled oxygen from the lungs and transport it to the body’s tissues, and to pick up some (about 24 percent) carbon dioxide waste at the tissues and transport it to the lungs for exhalation.

In 100 ml of blood, there is about 15 g of Hb(Erythrocyte protein), so that 100 ml of blood has the capacity to bind 20.1 ml of oxygen. This quantity is called the oxygen-binding capacity of blood (C_B).

Red blood cells (RBC), increases the oxygen-carrying capacity of formed elements in blood.

6 Ans) Shock is a life-threatening condition that occurs when the body is not getting enough blood flow. Lack of blood flow means the cells and organs do not get enough oxygen and nutrients to function properly. Many organs can be damaged as a result. Shock requires immediate treatment and can get worse very rapidly.

Five types of Shock:

Anaphylactic

Anaphylactic shock is caused by an allergic reaction. Common triggers are medications such as penicillin, latex, bee stings, and foods such as nuts or shellfish.

Cardiogenic

Cardiogenic shock is typically caused by myocardial infarction, otherwise known as a heart attack.

Hypovolemic

Hypovolemic shock happens when the body loses 20% or more of its blood supply, which typically occurs through injury or accident.

Neurogenic

Neurogenic shock is a distributed type that typically occurs after damage to the pathways of the central nervous system, particularly to the spinal cord.

Septic

Septic shock is the result of system-wide bacterial, viral, or fungal infection, known as sepsis. Because septic shock is directly related to sepsis.

7 Ans) Thyroid hormones, in turn, regulate the biology of virtually every cell of the body. In a classical endocrine negative feedback loop, thyroid hormones bind to nuclear receptors in the hypothalamus and pituitary to inhibit synthesis of both TRH and TSH, respectively.

The Thyroid axis regulates development, energy metabolism, and growth and the axis is controlled by complex central and peripheral signals mediated mainly by hypothalamic TRH and pituitary TSH(Thyroid Stimulating Harmone). Thyrotroph cells express TSH and comprise about 5% of the functional hormone-secreting anterior pituitary cells with relatively small secretory granules ranging from 120 to 150 μm. TSH comprises a specific β-subunit and common α-subunit shared with LH and FSH(Follicle stimulating harmone). TSH binds to a GPCR on thyroid follicular cells to stimulate thyroid hormone (T4) synthesis and release. T4 is converted in the periphery to the more active (triiodothyronine)T3 which elicits most thyroid cellular actions.

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