Thursday, February 07, 2008
Tuesday, February 05, 2008
A thrombus is a stationary mass of blood elements that remains attached to its place of origin along the wall of a blood vessel.
Thrombi are not clots although they are partially made up of clotted blood. Unlike most clots, a thrombus is always the result of a pathologic event. Clots are normal (usually) and occur outside a blood vessel.
The formation of a thrombus is not initially dependent on the clotting process. Thombi begin endothelial injury and an initial platelet clump. Layers of platelets are added followed by the adherence of white blood cells. A clot then adds volume as the thrombus grows.
You can find a full text article concerning deep vein thrombosis here and another full text article here.
An embolus is an intravascular object (air, tumor fragment, broken off thrombus, calcium fragments) that circulates in the bloodstream until it becomes lodged in a vessel obstructing the blood flow.
Ischemia is a lack of oxygen supply to a tissue usually due to obstruction of blood flow.
Lack of oxygen supply to a tissue can result in a tissue death called an infarct
See photos of an infarct of the heart here.
Shock is a state of systemic low blood flow. It can occur due to a loss of blood or because cardiac output is reduced.
Cardiogenic shock occurs when the heart is incapable of maintaining blood pressure. You can read much more about cardiogenic shock here.
Hypovolemic shock is a result of an underfilled vascular space, usually the result of hemorrhage. It can also be caused by fluid loss in cases of severe burns or diarrhea. Read more about hypovolemic shock here.
Septic shock is associated with systemic bacterial infections (sepsis) usually gram-negative bacterial infections. It is due to a massive inflammatory response to the infection. Read more about septic shock here.
Above figure from Heartzine.Go there to learn about circulatory system.
To review your anatomy of the circulatory system go to this great website at the Texas Heart Institute.
60% of the human body is water. So an average person of 155 lbs is made up of 93 lbs of water and 62 lbs of solids. The 42 liters of water can be broken down this way:
Interstitial (space outside the blood vessels and in between cells) 8 liters
Plasma 3 liters
Cerebrospinal fluid and other 6 liters
For a total of 17 liters
A total of 25 liters (including Red Blood Cells)
Blood pressure is the force of blood pushing against the walls of arteries. It's expressed as the number of millimeters it can force a column of mercury upwards.
Normal blood pressure is a reading of 120/80 or lower. High blood pressure is a reading of 140/90 or greater.
Another type of pressure is osmotic pressure. Osmotic pressure is the amount of hemodynamic pressure that must be applied on the side with low water concentration to prevent water from passing into the saltier side.
Go to this Colorado State osmotic pressure simulator site and you can see the effects of increasing or decreasing solute on either side of a permeable membrane.
You can learn about osmotic pressure here (interactive) and here (physics).
Edema is a shift of water from the vascular space into another compartment, usually the interstitial compartment. Here is one website that discusses edema in general.
Low protein edema also called a transudate, occurs when there is excess venous pressure (hydrostatic edema) or low plasma osmotic pressure. Each of these conditions allows water to leave the vascular spaces and enter the tissue spaces.
One example of low protein edema is varicose veins due to excess venous pressure. Read more about varicose veins here.
Osmotic edema is another type of low protein edema. It occurs when plasma albumin levels are abnormally low allowing water to escape from the vascular space to the interstitial space. Osmotic edema is often associated with liver disease because the liver is the primary producer of albumin.
Generalized edema (anasarca) is another example of low protein edema.
High Protein Edema is the fluid accumulation seen in inflammation. Inflammatory edema would be seen in a sprained joint.
Lymphedema is due to obstucted lymphatics. See more here.
Cerebral and pulmonary edema can be fatal. Swelling of the brain results in increased pressure on the brain. Pulmonary edema can impair gas transport and exchange or encourage bacterial growth.
William Harvey is the 17th century physician who hypothesized that blood moved in a circle. This was quite different from the accepted view of the time. Galen had postulated 1700 years previously that there were two kinds of blood, arterial and veinous, each with their own pathway to the tissues where it was consumed.
Harvey wrote: Since all things, both argument and ocular demonstration, show that the blood passes through the lungs and heart by the force of the ventricles, and is sent for distribution to all parts of the body, where it makes its way into the veins and porosites of the flesh, and then flows by the veins from the circumference on every side to the centre, from the lesser to the greater veins, and is by them finally discharged into the vena cava and right auricle of the heart, and this in such a quantity or in such a flux and reflux thither by the arteries, hither by the veins, as cannot possibly be supplied by the ingesta, and is much greater than can be required for mere purposes of nutrition; it is absolutely necessary to conclude that the blood in the animal body is impelled in a circle, and is in a state of ceaseless motion.
That is one hell of a sentence!
Harvey knew blood moved in a circle but he was unable to determine exactly how. He did not have the technology to observe the small capillaries that connected the arterial and veinous vessels.
Harvey was one of the first to use the scientific method in his work. He said:
I profess to learn and teach anatomy not from books but from dissections,not from the tenets for Philosophers but from the fabric of Nature.
You can learn more about William Harvey here.
After injury and inflammation comes repair. Repair is the restoration of normal structure and function to injured tissue.
Read about it here.
Tissue regeneration requires an intact supporting stromal framework.
One element of this framework is the extracellular matrix. Read about extracellular matrix here.
The other stromal framework element is the basement membrane.
Photomicrograph from here.
Without the support of the extracellular matrix and basement membrane, tissues cannot return to normal and scarring occurs.
Angiogenesis is the growth of new blood vessels into the wound. View this NIH tutorial on angiogenesis in relation to tumor metastasis. It's a slide show, so just keep clicking on the arrow in the upper right corner.
There is also an entire issue of Nature devoted to angiogenesis with free text available here. This article is especially good.
Scar development follows angiogenesis. Read about scar development here.
What about tissue repair of the perineal region that is torn during childbirth?
You can read about this at these links here, here and here. Or you can listen to an NPR report on the topic here.
Above image from here.
Stem cells are primative, undifferentiated cells that have the capacity to proliferate and differentiate into more mature types of cells.
Some forms of tissue regeneration require stem cells.
You can go here to see animations about stem cells (you need Flash Player installed).
There is also stem cell information in lay terms at the NIH Stem Cell Information website.
Embryonic stem cells are obtained from human fertilized eggs called blastocysts. These stem cells are often refered to as "totipotent stem cells".
You can view an animated tutorial on human embryonic stem cells at this website and also at this website.
Adult stem cells are multipotent and are normally obtained from the bone marrow. A bone marrow transplant can be considered a stem cell transplant.
More recently, stem cells have been obtained from umbilical cords of recently born babies.
Stem cells were first cultured at my Alma Mater, The University of Wisconsin by James Thomson (paper cited above). Lots of stem cell info at this UW website.
The human body can regulate its core temperature to between 98 and 100 degrees F. If skin temperature drops below 37 degrees C. the body attempts to conserve heat by constricting the blood supply to the body surface. Shivering is the bodys attempt to produce more heat through muscle activity. Because no external work is performed during shivering, all the energy released is in the form of heat. Here is a short review on body temperature regulation. Also here.
Hypothermia (stage 1) occurs when the body temperature reaches 95 degrees or lower. Read about hypothermia at this Coast Guard website.
Hyperthermia occurs when the body produces more heat than it can dissipate. Body temperatures above 104 degrees F are life threatening. You can listen to scientist talk about how the human body copes with heat at this NPR website.
Fever (pyrexia)is an increase in body temperature as a response to bacterial or viral infection or to tissue injury. It's a temporary elevation in the bodies thermoregulatory setpoint. Generally, fever is not an illness because it's a defense response against infections. Body temperature can also increase due to hard exercise; ovulation; excess thyroid secretions and central nervous system damage. Cancer can also induce fever. More about fevers here.