Understanding Blood: Composition, Function, and Pulse

Posted on Nov 26, 2024 in Biology

Sports Medicine

Sports medicine applies scientific and medical principles to athletic performance and physical activity, leveraging exercise for preventive and therapeutic benefits to maintain health and mitigate risks associated with insufficient or excessive physical exertion.

Blood Composition

Like any tissue, blood comprises cells and extracellular components (the extracellular matrix). These two fractions are:

Cellular Components (Formed Elements): Semisolid elements and particles (corpuscles) including cells and cell-derived components.
Blood Plasma: A translucent, yellowish fluid representing the liquid extracellular matrix in which cellular components are suspended.

Formed elements constitute about 45% of blood volume, known as the hematocrit, primarily attributed to red blood cells. The remaining 55% is blood plasma.

Blood’s formed elements vary in size, structure, and function, grouped into:

Blood Cells: White blood cells or leukocytes, which circulate in the blood and perform functions in other tissues.
Cell Derivatives: Not strictly cells but cell fragments, including red blood cells (erythrocytes) and platelets, functioning exclusively within the vascular system.

Red Blood Cells

Red blood cells (erythrocytes) transport oxygen throughout the body.

Erythrocytes make up about 96% of formed elements. A normal count is approximately 4.8 million per cc (or ml) in women and 5.4 million per cc in men.

These corpuscles lack a nucleus and organelles in mammals and are not strictly cells. They contain enzyme pathways, and their cytoplasm is filled with hemoglobin, an oxygen-transporting protein. Contrary to common belief, carbon dioxide is transported in the blood dissolved (8%), as carbamino compounds (27%), and as bicarbonate, which regulates blood pH. The plasma membrane of red blood cells contains glycoproteins (CDs) that determine blood groups and other identifiers.

Red blood cells are disc-shaped, biconcave, and lack nuclei, which are expelled in the bone marrow before entering the bloodstream (this differs in birds, amphibians, and some animals). Adult human red blood cells are formed in the bone marrow.

Hemoglobin

Hemoglobin, found exclusively in red blood cells, is a pigment protein containing a “heme” group. It also carries carbon dioxide, mostly dissolved in blood plasma.

Normal hemoglobin levels range from 12 to 18 g/dL of blood, proportional to the quantity and quality of red blood cells. Hemoglobin constitutes up to 90% of the cell mass and gives blood its red color when oxygenated.

After a lifespan of 120 days, red blood cells are destroyed and removed from the blood by the spleen, liver, and bone marrow, where hemoglobin is broken down into bilirubin, and iron is recycled to form new hemoglobin.

White Blood Cells

Blood circulating white blood cell with possible upper right. Increased X1024. M.όptico.

White blood cells (leukocytes) are cellular effectors of the immune system, using blood as a vehicle to reach different parts of the body. They destroy infectious agents and infected cells and secrete protective substances like antibodies.

A normal white blood cell count ranges from 4,500 to 11,500 cells per mm³ (or microliter) of blood, varying with physiological conditions (pregnancy, stress, sport, age) and pathological conditions (infection, cancer, immunosuppression, aplasia).

Leukocytes are classified based on their cytoplasm (staining) and nucleus (morphology):

Granulocytes (Polymorphonuclear Cells): Neutrophils, basophils, and eosinophils, with a polymorphic nucleus and numerous granules in the cytoplasm.
Agranulocytes (Monomorphonuclear Cells): Lymphocytes and monocytes, lacking granules and having a rounded nucleus.

Granulocytes

Neutrophils: Present at 2,500 to 7,500 cells per mm³ (55-70% of leukocytes). They engulf foreign substances. Their nucleus has 3-5 lobes.
Basophils: Present at 0.1 to 1.5 cells per mm³ (0.2-1.2% of leukocytes). They secrete heparin and histamine. Their nucleus is often covered by granules.
Eosinophils: Present at 50 to 500 cells per mm³ (1-4% of leukocytes). They increase in parasitic diseases, allergies, and asthma. Their nucleus has two lobes connected by a thin chromatin thread.

Agranulocytes

Monocytes: Present at 150 to 900 cells per mm³ (2-8% of leukocytes). They increase during viral or parasitic infections and some tumors. They differentiate into macrophages in tissues.
Lymphocytes: Present at 1,300 to 4,000 per mm³ (24-32% of leukocytes). They increase in viral infections and neoplastic diseases but may decrease in immunodeficiencies. They are specific effectors of the immune system, with B and T lymphocytes.

B lymphocytes produce antibodies for humoral immunity. T lymphocytes recognize and destroy virus-infected cells and regulate the immune response. Both B and T lymphocytes have immunological memory.

Platelets

Platelets (thrombocytes) are small cell fragments (2-3 mm diameter) produced in the bone marrow from megakaryocyte fragmentation. A normal count is 150,000 to 450,000 platelets per mm³.

Platelets plug injuries in blood vessels, contributing to clot formation (hemostasis) and wound closure.

Blood Plasma

Blood plasma is the liquid portion of blood, a salty, yellowish, translucent fluid denser than water. The total plasma volume is 40-50 mL/kg body weight.

Plasma is an aqueous solution containing 91% water, 8% proteins (fibrinogen, globulins, albumin, lipoproteins), and traces of hormones, electrolytes, etc. Plasma proteins transport nutrients like copper, iron, and hormones. Plasma components are formed in the liver (albumin and fibrinogen), endocrine glands (hormones), and the intestine.

Besides carrying blood cells, plasma transports nutrients and waste. Serum is the fluid remaining after blood coagulation.

Plasma contains proteins, amino acids, carbohydrates, lipids, salts, hormones, enzymes, antibodies, urea, dissolved gases, and inorganic substances like sodium, potassium, calcium chloride, carbonate, and bicarbonate.

Pulse

Radial pulse check.

In medicine, the pulse is the palpable expansion of arteries caused by blood circulation from the heart. It is typically felt where arteries are close to the skin, such as the wrists or neck.

Pressure waves move along flexible blood vessels, not by the forward movement of blood. When the heart contracts, blood is ejected into the aorta, causing it to expand. This creates a pressure wave (pulse wave) that travels through the arteries. The pulse wave velocity is 3-6 m/s in the aorta, 7-10 m/s in large arteries, and 15-35 m/s in small arteries. The pressure pulse travels faster than blood flow.

The term “pulse” is often used to refer to heart rate (beats per minute). In most people, pulse accurately measures heart rate. However, in arrhythmias, some heartbeats are ineffective, leading to an irregular pulse or a pulse deficit. Heart rate is then determined by auscultation of the heart apex.

A normal resting pulse for an adult is 60-100 beats per minute. It can drop to 40 during sleep and rise to 200 during intense exercise. Pulse is generally faster in younger individuals.

Pulse characteristics (rhythm, amplitude, wave shape) reflect cardiovascular health. Absence of pulse in the temples may indicate giant cell arteritis, while absence or decrease in limbs may indicate peripheral occlusive disease.

The pulse is felt by lightly pressing an artery against a bone using the index and middle fingers (not the thumb, which has its own pulse). For carotid, femoral, or brachial arteries, the thumb can be used. Alternatively, the heartbeat can be heard using a stethoscope or by pressing an ear against the chest.

Introduction

Everyone knows we can not live without blood. And the blood of our bodies is pumped by the heart through a complex network of veins and arteries.

Thanks to the blood can breathe and defend us from infections and if we cut ourselves with something we do not bleed for the wound, is a liquid without which we can not live.

We also need animals, the plants have a similar thing called “sap.”