Fresno Criminal Defense Attorney | Blood Spatter (2) | Forensic Analysis

Blood

Throughout history blood has been considered by many civilizations to be a mystical fluid. It was recognized early on when man the great hunter noticed that bleeding animals became weaker, that blood was an essential component for existence. Early Chinese physicians linked blood to energy flow in the body and changes in blood flow were used to diagnose illnesses and disease. At one time, some western civilizations believed that evil-spirits circulated in the blood and caused disease – this resulted in the practice of bloodletting to free the body of such demons. Bloodletting was practiced by cutting veins with knives or sharp instruments or by applying blood sucking leeches to the skin. Even as recently as the 1920's some texts still promoted the use of bloodletting for treating infections such as pneumonia.

Blood, a suspension of cells in an aqueous solution of salts, organic chemicals, and proteins, makes up about ¼ of the total extra cellular body fluid and carries materials from one part of the body to another. The cellular component of blood is composed mainly of red blood cells (RBCs), which are also called erythrocytes. Erythrocytes are responsible for about 45% of the total volume of blood – a parameter known as the hematocrit. Other cellular components of blood include white blood cells or leukocytes, and platelets. 

The cell-free fraction of blood is called plasma. Plasma is composed of about 92% water, 7% proteins and the remainder consists of dissolved organic molecules such as amino acids, glucose and nitrogenous waste; K⁺, Na⁺, Cl^-, H⁺, Ca²⁺ and HCO₃^- ions; trace elements, hormones, vitamins and dissolved gases, namely O₂ and CO₂.

Plasma proteins are made mainly by the liver and secreted into the blood. The most prevalent protein in plasma is albumin, one of the factors that functions to maintain an appropriate blood volume by regulating osmotic pressure. Globulins and the clotting protein fibrinogen are also found in abundance. Other circulating proteins such as the immunoglobulin antibodies are synthesized and secreted into the blood by specialized blood cells.

Plasma proteins have many functions and include significant roles in blood clotting processes and in defense responses to the presence of foreign particles. Some proteins are carriers for steroid hormones, cholesterol, Fe2+ ions and drugs. Some plasma proteins also act as hormones and extracellular enzymes.

Types of Blood Cells

There are three main types of blood cells:

1. Red blood cells– also known as erythrocytes and RBC; these cells are nuclei free by the time they enter the circulation and play a key role in the transport of oxygen and carbon dioxide between the lungs and the tissues. These cells are the most abundant cell type found in blood. Red cells are very flexible and can squeeze into a variety of shapes. The ratio of RBC to plasma is known as the hematocrit and is expressed as the total blood volume. Hemoglobin is the oxygen carrying pigment of RBC. It is composed of 4 globular protein chains each associated with an iron containing heme group. Hemoglobin synthesis requires and adequate supply of dietary iron. Hemoglobin plays an important role in oxygen transport and if the hemoglobin content is too low, then the person becomes anemic. 
   
   2. Platelets – these cells are cell fragments that have broken off parent cells called megakaryocytes. Platelets are instrumental in coagulation, the process that produces blood clots to prevent blood loss in damaged vessels. The colorless platelets are smaller than RBC and like RBC have no nucleus. The typical platelet lifespan is about 10 days. Platelets are always present in the blood but only become active when damage has occurred to the walls of the circulatory system.
2. White blood cells– also known as leukocytes, these cells are fully functional cells in the circulation. White blood cells play instrumental roles in defending the body against invaders such as parasites, bacteria and viruses and although they are carried in the circulatory system their main work is usually conducted within the tissues.

There are 5 types of mature white blood cells:

1. Lymphocytes
   b. Monocytes
   c. Neutrophils
   d. Eosinophils
   e. Basophils

These cells can be grouped collectively as phagocytes, immunocytes and granulocytes

Blood Cell Production (Hematopoiesis)

All blood cells develop from a single precursor cell type called pluripotent hematopoietic stem cells, found primarily in bone marrow. These cells have the ability to develop into an assortment of committed stem cells, which develop into individual cell lines that differentiate into RBC, lymphocytes, other white blood cells and megakaryocytes.

Hematopoiesis begins early in embryonic development and continues for the duration of a person's life. Bone marrow that is actively producing blood cells is red-pink in color due to the presence of hemoglobin, whereas inactive bone marrow is yellow in color. Active marrow produces new blood cells of which 25% are usually RBC and the other 75% are white blood cells. White blood cells have shorter life spans than RBC, and need to be replaced more frequently. Neutrophils have a 6-hour half-life whereas RBC can exist in the circulation for up to 4 months.

Hematopoiesis is controlled by chemical factors called cytokines, which are peptides and proteins produced by specific cells that affect the growth and activity of other cells. 

Some commonly known cytokines involved in hematopoiesis, their source, and effects are listed below:

Hemostasis

Since the body can only function when the cells receive enough oxygen, it has ways of protecting itself when blood loss occurs. The body responds to blood loss by increasing vasoconstriction and fluid retention; platelet cells circulating in the blood become activated and a cascade clotting reaction takes place at the site of an open wound that forms a clot that will stop the bleeding.

Hemostasis is the name given to keeping blood within a damaged blood vessel; the process has three major steps:

Scabs are external blood clots that we are all quite familiar with, however internal blood clots can also form that are potentially life threatening if they break away in the circulating blood and become wedged in a major blood vessel supplying the heart or brain. Normal clotting time for blood that has left the body ranges from 3 to 15 minutes in healthy individuals.

Hemodynamics

Blood is circulated through the vasculature of the body by the heart and functions to deliver nutrients and oxygen to the cells of our body and to facilitate the removal of waste products. The heart, which functions as two hydraulic pumps in series, pushes blood out through the main artery called the dorsal aorta. The dorsal aorta divides and branches into many smaller systemic arteries that supply each region of the body with freshly oxygenated blood. Arteries have very muscular walls with strong elastic properties; an inner wall of epithelial cells lines the artery, which makes it extremely smooth allowing the blood to flow unimpeded. Pressure produced by the contraction of the left ventricle is stored in the elastic walls of the arteries and slowly releases through elastic recoil, maintaining a continuous driving pressure for blood flow during the time the heart ventricles are relaxing. The rhythmic pumping of the heart combined with the contractile forces of the arteries circulates the blood efficiently.

As arterial branches divide further and further they form arterioles. Arterioles are a high resistance outlet for blood flow and direct blood flow to individual tissues by selectively constricting and dilating. The diameter of arterioles is regulated by the presence of several local signaling factors such as the amount of oxygen in the tissues and hormonal controls.

Blood continues to flow from arterioles into the capillaries. Compared to arteries (and veins), capillary walls are only one epithelial cell thick and are rather fragile. Blood cells can only flow through capillaries in single file as oxygen, carbon dioxide, nutrients and waste products diffuse back and forth across the leaky epithelial capillary wall to, and from, the surrounding tissues and organs. The capillaries deliver deoxygenated blood and waste products to the veins for transport back to lungs for re-oxygenation and then again to the heart for recirculation.

Blood vessels are made from different layers of smooth muscle, fibrous and elastic connective tissue that surround an inner lining of endothelium which plays an important role in blood pressure regulation, blood vessel growth and the absorption of materials. The thickness and type of connective tissues and the amount of muscle tissue differs within the different types of vessels.

Most blood vessels contain vascular smooth muscle that encircles the vessel. Contraction of the muscle constricts the vessel (vasoconstriction) and decreases blood flow; relaxation results in the lumen of the vessel widening (vasodilation), thereby increasing blood flow to the area. Usually the smooth muscles cells are partially contracted at all times. In order to facilitate exchange of materials between the blood and interstitial fluid surrounding tissues, capillaries do not have supporting smooth muscle connective tissue.

Blood flows from the capillaries into small vessels called venules. The smallest venules are similar in size to capillaries and also have a thin epithelium and negligible connective tissue for support; larger venules have more smooth muscle associated with them. Blood flows from venules into larger veins that increase in diameter as they become proximal to the heart. The largest vein, the vena cava, empties into the right atrium of the heart. 

The venous system is much less elastic than the arterial system so blood is transported back to the heart under much less pressure. Valves positioned along each vein prevent the backflow of blood and keeps it moving in one direction against the force of gravity (think about blood flowing from the foot back towards the lungs and heart). The circulatory system is made up of more veins than arteries and the diameter of veins is much larger, and they lie closer to the surface of the skin than arteries do. Oxygenated blood in the arteries is very bright red in color, whereas the deoxygenated blood in the veins is a much darker purplish-red color, and may appear blue as it passes through veins close to the surface of the skin.

Angiogenesis

New blood vessels are formed through the process of angiogenesis. Angiogenesis occurs in children to maintain capillary growth to meet the needs of normal physiological growth, and in adults during wound healing, regrowth of the uterine lining after menstruation, and during endurance training to supply enhanced blood flow to the skeletal and heart muscle. Angiogenic processes are controlled by angiogenic and antiangiogenic cytokines. 

Although several growth factors promote angiogenesis, the two main growth factors that promote cell division (mitosis) are vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF), which can be characterized as mitogens. These growth factors are produced by smooth muscle cell. Angiogenesis inhibitors include the cytokines angiostatin, which is made from the blood protein plasminogen and endostatin.

Blood Pressure

Blood pressure is the highest in the arteries and falls continuously as blood flows through the circulatory system; the decrease in pressure occurs as energy is lost due to the resistance of blood vessels to blood flow and friction between the blood cells. When a blood vessel is breached the rate and volume of blood loss is typically related to the type and size of vessel. Arterial breach can result in pulsatile spurting and venous breach tends to result in blood oozing or flowing from the wound due to the decreased pressure imposed on the system. Mean arterial pressure is directly related to cardiac output and the total peripheral resistance resulting from the muscle tone of the arterioles. Cardiac output is proportionally related to heart rate and the volume of blood pumped into the arterial tree with each heartbeat.

Bruising

Bruising is the result of bleeding under the skin when superficial blood vessels are damaged and blood leaks into the perivascular tissues. The color, shape and location of a bruise changes with age as the blood pigment is broken down and reabsorbed. In some cases a bruise may never form even though there is damage to the underlying vessels, in other cases it may take hours or days for the bruise to develop. Ageing of bruises is not an exact process, however fresh bruises can appear as red, purple or blue-black within an hour of the initial damage and fade to green-yellow within about 18 hours. 

The site of bruising might not indicate the exact site of impact since gravity and the presence of tissues can allow blood to track to sites remote from the initial impact. The amount of bruising depends on the site and force of impact. Soft tissue areas such as the abdomen may show little bruising, but areas with underlying bones tend to bruise more easily. The susceptibility to bruising increases in the presence of certain conditions that affect the fragility of the blood vessels, or that slow or prevent clotting. Such conditions include hemophilia, alcoholism, hepatobiliary dysfunction and, or, the presence of anticoagulant drugs, aspirin and steroids. The very young and the aged also tend to bruise easily.

Hypostasis

Blood only flows from a wound when a pressure system exists to maintain circulation. When irreversible circulatory arrest occurs, the absence of blood pressure, tissue turgor, underlying pressures and hydrostatic pressure results in blood and body fluids pooling due to the forces of gravity. This is known as hypostasis and results in blood pooling in the lowest levels of the cardiovascular system. If a body is supine (on its back) the blood will pool in the buttocks, thighs calves and back of the neck. When the blood pools in capillaries close to the skin surface, visible pink patches appear. In the early stages of hypostasis the patches are small and lightly colored, but the patches join together to form darker patches as time passes. The color becomes darker pink and possibly blue as any oxygen still present in the blood is used up. Certain features of post mortem lividity (livor mortis) have diagnostic and criminal relevance, and include the presence, distribution and color of the lividity.

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