Question

1. What percentage of a drawn blood sample would be plasma after it has been spun down in the centrifuge?

2. LIST Three factors that affect Stroke Volume. b. LIST Three factors that affect Heart Rate? What is EDV? What is ESV?

Answer 1

1. Centrifugation of blood refers to fragmenting the blood into its components.

After centrifugation, there are three distinct layers that can be seen:

• Plasma: It is found in the uppermost layer of the column. The main constituents are ions, water, proteins, nutrients, gases, etc. It constitutes 55% of the total centrifuged blood.
• Buffy coat : It has the WBCs and platelets and are found in the middle layer. They form around 1% of total centrifuged blood.
• Erythrocytes: Composed of RBCs and found at the bottom due to the weight of the red blood cells. It is almost 44%.

2. Three factors affecting stroke volume:

• Preload- It is the volume of blood present in the ventricles after diastole. This is directly proportional to stroke volume. This can be raised due to increased venous return and fas filling. This can be decreased due to hypoxia, imbalance in pH, etc. Here end-diastolic volume is altered.
• Contractility- Ability of the heart muscles to contract. This is proportional to stroke volume. This can be increased due to sympathetic stimulation, glucagon, etc, and can be decreased due to parasympathetic stimulation, hypoxia, etc. It alters the end-systolic volume.
• Afterload- It refers to the amount of resistance the left ventricle needs to overcome to pump or circulate the blood. It is indirectly proportional to the stroke volume. This is modified by vascular resistance.

Three factors affecting heart rate:

• Characteristics such as age, sex, lifestyle, stress, body temperature, blood volume, diseased condition, etc.
• Autonomic innervation: Sympathetic or parasympathetic innervation can alter the heart rate. The sympathetic system increases the heart rate and the parasympathetic system decreases the heart rate. Also control centers present in the medulla oblongata can change heart rate through receptors ( chemoreceptors and baroreceptors).
• Certain hormones can alter the heart rate such as thyroid hormone and epinephrine by stimulating the SA node of the heart.

EDV- End diastolic volume refers to the volume of blood present in the ventricles at the end of the diastole. This can also be referred to as the amount of blood in the ventricles just before the systole.
ESV- volume of blood present in the ventricle at the end of the systole. It amounts to the lowest volume of blood present in the ventricles in the whole cardiac cycle.