HAEMOLYMPH

Haemolymph is the "blood" of insects. It is the watery fluid that fills the haemocoel. Haemolymph contains ions, molecules and cells. Often clear and colourless in most insects, some insects haemolymph may contain various pigments, making it appear yellow, blue, green, and in some rare cases of immature aquatic and endoparasitic flies, red due to the presence of haemoglobin.
All chemical exchanges between insect tissues are mediated through the haemolymph. The main difference between insect haemolymph and vertebrate blood is that haemolymph rarely contains respiratory pigments, and has a very low oxygen-transportation capacity. Respiration takes place in the tracheal system, which is mediated by the internal pressure of the haemolymph (the trachea opens and closes, creating a vacuum, as the haemolymph pressure changes).
Haemolymph is important to insect ventilation, thermoregulation, and molting (in breaking the old cuticle and expanding the new cuticle).
Haemolymph is a reserve of water for the insect. The soft-bodied insect larvae can be 20-40% haemolymph by weight, and the adult form is usually a bit less than 20% haemolymph (desiccation is always a problem for adult insects). The main constituent of haemolymph is plasma. Insect plasma is characterized by high concentrations of amino acids and organic phosphates.
Haemolymph not only provides nutrient transfer in the body, it provides protection for the insect. Haemolymph provides protection and defence from physical injury, disease organisms, parasites or other foreign objects entering the body, and sometimes from predation. In some insects, the haemolymph contains distasteful chemicals, which make the insect taste bad to predators (see aposematism). While an insect does have an immune system, please note that it is not as highly specialized as is the complex immunoglobin-based vertebrate immune system.

Blood Vessels

Blood vessels form a tubular network that allows blood to travels from the heart to the tissues and back to the heart again. Blood that leaves the heart passes into arteries. Large arteries branch into progressively smaller arteries that function to deliver blood to various regions of the body. Small arteries branch into even smaller vessels called arterioles, which function to regulate the flow of blood into different tissues. Arterioles branch into capillaries, the smallest of all blood vessels. Capillaries are the sites of nutrient and waste exchange between the blood and body cells. Capillaries are microscopic vessels that join the arterial system with the venous system. Blood coming out of the capillaries passes into vessels of increasing diameter as it flows back toward the heart. Capillaries join to form venules, which then merge to form small veins. Small veins unite to form large veins that eventually deliver blood back to the heart.

Arteries

Arteries serve as (1) efficient conduits for the movement of blood and (2) pressure reservoirs that keep blood moving during diastole. Arteries have a large internal diameter and thus offer little resistance to the flow of blood. Arteries also contain an elastic layer in their walls. Elastin is a protein fiber that has elastic qualities. During systole, large arteries distend with blood as their elastic walls stretch. During diastole, the walls rebound, thus pushing blood along. In this way the arteries act as a pressure reservoir that maintains a constant flow of blood through the capillaries despite pressure fluctuation during the cardiac cycle. Arteries also have a smooth muscular layer that functions to regulate the flow of blood through the artery. Contraction of the smooth muscle decreases the internal diameter of the vessel in a process called vasoconstriction. Relaxation of the smooth muscle increases the intermnal diameter in a process called vasodilation.

Arterioles
Arterioles serve as (1) the major determinant of blood pressure and (2) as the major determinant of blood flow to the individual organs Arterioles have a much smaller diameter than arteries and thus provide significant resistance to the flow of blood. This resistance creates pressure in the circulatory system. Pressure is required to provide adequate flow of blood to all parts of the body. Blood flow to individual organs can be regulated by controlling the diameter of the arterioles. Vasodilation of an arteriole lowers resistance and results in an increase in flow through that particular arteriole. Vasoconstriction of an arteriole increases resistance and results in decreased flow through that particular arteriole.

Capillaries

Capillaries are the smallest and most numerous of blood vessels. Capillaries function as the site of exchange of nutrients and wastes between blood and tissues. The anatomy of capillaries is well suited to the task of efficient exchange. Capillary walls are composed of a single layer of epithelial cells surrounded by a basement layer of connective tissue. The thin nature of the walls facilitates efficient diffusion of oxygen and carbon dioxide. Most capillaries also have pores between cells that allow for bulk transport of fluid and dissolved substances from the blood into the tissues and visa versa.
Although capillaries are extremely numerous (40 billion in the body), collectively they hold only about 5% of the total blood volume at any one time. This is because most capillaries are closed most of the time. Precapillary sphincters, which are bands of smooth muscle that wrap around arterioles, control the amount of blood flowing in a particular capillary bed. Contraction of the sphincter shuts off blood flow to a capillary bed, while relaxation of the sphincter allows blood to flow.

Veins

Veins are larger and more compliant (stretchable) than arteries, thus they can hold more blood. In fact, the veins act somewhat like a blood reservoir, containing 60% of the total blood volume at rest. As physical activity increases, the veins undergo vasoconstriction, driving more blood back to the heart and increasing circulation. Also, the return of venous blood to the heart is aided by one-way valves that insure unidirectional flow of blood

HEART ATTACK

A heart attack occurs when blood flow to a section of heart muscle becomes blocked. If the flow of blood isn’t restored quickly, the section of heart muscle becomes damaged from lack of oxygen and begins to die.

Heart attacks occur most often as a result of a condition called coronary artery disease (CAD). In CAD, a fatty material called plaque (plak) builds up over many years on the inside walls of the coronary arteries (the arteries that supply blood and oxygen to your heart). Eventually, an area of plaque can rupture, causing a blood clot to form on the surface of the plaque. If the clot becomes large enough, it can mostly or completely block the flow of oxygen-rich blood to the part of the heart muscle fed by the artery.

Heart With Muscle Damage and a Blocked Artery

Figure A is an overview of a heart and coronary artery showing damage (dead heart muscle) caused by a heart attack. Figure B is a cross-section of the coronary artery with plaque buildup and a blood clot.
During a heart attack, if the blockage in the coronary artery isn’t treated quickly, the heart muscle will begin to die and be replaced by scar tissue. This heart damage may not be obvious, or it may cause severe or long-lasting problems.
Severe problems linked to heart attack can include heart failure and life-threatening arrhythmias (irregular heartbeats). Heart failure is a condition in which the heart can’t pump enough blood throughout the body. Ventricular fibrillation is a serious arrhythmia that can cause death if not treated quickly.

Get Help Quickly

Acting fast at the first sign of heart attack symptoms can save your life and limit damage to your heart. Treatment is most effective when started within 1 hour of the beginning of symptoms.
The most common heart attack signs and symptoms are:
Chest discomfort or pain—uncomfortable pressure, squeezing, fullness, or pain in the center of the chest that can be mild or strong. This discomfort or pain lasts more than a few minutes or goes away and comes back.
Upper body discomfort in one or both arms, the back, neck, jaw, or stomach.
Shortness of breath may occur with or before chest discomfort.
Other signs include nausea (feeling sick to your stomach), vomiting, lightheadedness or fainting, or breaking out in a cold sweat

EMBOLISM

Definition
An embolism is an obstruction in a blood vessel due to a blood clot or other foreign matter that gets stuck while traveling through the bloodstream. The plural of embolism is emboli.

Description
Emboli have moved from the place where they were formed through the bloodstream to another part of the body, where they obstruct an artery and block the flow of blood. The emboli are usually formed from blood clots but are occasionally comprised of air, fat, or tumor tissue. Embolic events can be multiple and small, or single and massive. They can be life-threatening and require immediate emergency medical care. There are three general categories of emboli: arterial, gas, and pulmonary. Pulmonary emboli are the most common.

Arterial embolism
In arterial emboli, blood flow is blocked at the junction of major arteries, most often at the groin, knee, or thigh. Arterial emboli are generally a complication of heart disease. An arterial embolism in the brain (cerebral embolism) causes stroke, which can be fatal. An estimated 5-14% of all strokes are caused by cerebral emboli. Arterial emboli to the extremities can lead to tissue death and amputation of the affected limb if not treated effectively within hours. Intestines and kidneys can also suffer damage from emboli.

Gas embolism
Gas emboli result from the compression of respiratory gases into the blood and other tissues due to rapid changes in environmental pressure, for example, while flying or scuba diving. As external pressure decreases, gases (like nitrogen) that are dissolved in the blood and other tissues become small bubbles that can block blood flow and cause organ damage.

Pulmonary embolism

In a pulmonary embolism, a common illness, blood flow is blocked at a pulmonary artery. When emboli block the main pulmonary artery, and in cases where there are no initial symptoms, a pulmonary embolism can quickly become fatal. According to the American Heart Association, an estimated 600,000 Americans develop pulmonary emboli annually and 60,000 die from it.
A pulmonary embolism is difficult to diagnose. Less than 10% of patients who die from a pulmonary embolism were diagnosed with the condition. More than 90% of cases of pulmonary emboli are complications of deep vein thrombosis, blood clots in the deep vein of the leg or pelvis.

Causes and symptoms
Arterial emboli are usually a complication of heart disease where blood clots form in the heart's chambers. Gas emboli are caused by rapid changes in environmental pressure that could happen when flying or scuba diving. A pulmonary embolism is caused by blood clots that travel through the blood stream to the lungs and block a pulmonary artery. More than 90% of the cases of pulmonary embolism are a complication of deep vein thrombosis, which typically occurs in patients who have had orthopedic surgery and patients with cancer or other chronic illnesses like congestive heart failure.

Risk factors for arterial and pulmonary emboli include: prolonged bed rest, surgery, childbirth, heart attack, stroke, congestive heart failure, cancer, obesity, a broken hip or leg, oral contraceptives, sickle cell anemia, chest trauma, certain congenital heart defects, and old age. Risk factors for gas emboli include: scuba diving, amateur plane flight, exercise, injury, obesity, dehydration, excessive alcohol, colds, and medications such as narcotics and antihistamines.

Symptoms of an arterial embolism include:
severe pain in the area of the embolism
pale, bluish cool skin
numbness
tingling
muscular weakness or paralysis

Common symptoms of a pulmonary embolism include:
labored breathing, sometimes accompanied by chest pain
a rapid pulse
a cough that may produce sputum
a low-grade fever
fluid build-up in the lungs

Less common symptoms include:
coughing up blood
pain caused by movement or breathing
leg swelling
bluish skin
fainting
swollen neck veins