Page 151 - 84 human physiolofy part-1

The Cardiovascular System

Circulatory Shock

Circulatory Shock is a severe condition that results from reduced blood circulation.

Thrombus

A thrombus, or blood clot, is the final product of the blood coagulation step in hemostasis. It is
achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral
coagulation system (i.e. clotting factors). A thrombus is physiologic in cases of injury, but pathologic
in case of thrombosis.

Preventing blood clots reduces the risk of stroke, heart attack and pulmonary embolism. Heparin
and warfarin are often used to inhibit the formation and growth of existing blood clots, thereby
allowing the body to shrink and dissolve the blood clots through normal methods.

Embolism

An embolism occurs when an object (the embolus) migrates from one part of the body (through
circulation) and causes a blockage (occlusion) of a blood vessel in another part of the body. Blood clots
form the most common embolic material by far: other possible embolic materials include fat globules
(a fat embolism), air bubbles (an air embolism), septic emboli (containing pus and bacteria), or
amniotic fluid.

Stroke

A stroke, also known as cerebrovascular accident (CVA), is an acute neurological injury whereby
the blood supply to a part of the brain is interrupted. Strokes can be classified into two major
categories: ischemic and hemorrhagic. ~80% of strokes are due to ischemia.

• Ischemic Stroke: In ischemic stroke, which occurs in approximately 85-90% of strokes, a
blood vessel becomes occluded and the blood supply to part of the brain is totally or partially
blocked. Ischemic stroke is commonly divided into thrombotic stroke, embolic stroke, systemic
hypoperfusion (Watershed or Border Zone stroke), or venous thrombosis
• Hemorrhagic Stroke: A hemorrhagic stroke, or cerebral hemorrhage, is a form of stroke
that occurs when a blood vessel in the brain ruptures or bleeds. Like ischemic strokes,
hemorrhagic strokes interrupt the brain's blood supply because the bleeding vessel can no longer
carry the blood to its target tissue. In addition, blood irritates brain tissue, disrupting the delicate
chemical balance, and, if the bleeding continues, it can cause increased intracranial pressure
which physically impinges on brain tissue and restricts blood flow into the brain. In this respect,
hemorrhagic strokes are more dangerous than their more common counterpart, ischemic strokes.
There are two types of hemorrhagic stroke: intracerebral hemorrhage, and subarachnoid
hemorrhage.

The term "brain attack" is starting to come into use in the United States for stroke, just as the term
"heart attack" is used for myocardial infarction, where a cutoff of blood causes necrosis to the tissue of
the heart. Many hospitals have "brain attack" teams within their neurology departments specifically for
swift treatment of stroke.

Heart Attack

Wikibooks | 151