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Life Sciences => Physiology & Medicine => Topic started by: Igor on 13/11/2006 17:34:32

Title: How do emboli cause haemorrhages?
Post by: Igor on 13/11/2006 17:34:32

How do emboli cause haemorrhages ?, e.g. splinter haemorrhages caused by endocarditis.

Does the blockage create a build up of pressure which causes the vessel to fail ?,

Or does the infarction cause surrounding tissue, including blood vessels, to die,
i.e. is necrosis responsible for the haemorrhage?

Title: Re: How do emboli cause haemorrhages?
Post by: iko on 13/11/2006 22:05:00

Hi Igor,
...the second hypothesis is more correct:

quote:

---

Or does the infarction cause surrounding tissue, including blood vessels, to die,
i.e. is necrosis responsible for the haemorrhage?
Igor

---

...but before cells death (necrosis) you should simply consider hypoxia as initial damage to the tissue that normally receive oxigen from blood flow.
Septic (bacteria) or thrombotic (clots) microembolism (or both) stop regular blood circulation.
Hypoxia makes cells shift to anaerobic glycolysis for energy production and excessive and toxic accumulation of lactate and pyruvate leading to 'capillary leakage', i.e. extravasation of plasma proteins and white and red cells into the surrounding tissue (petechiae, splinter haemorrhages).
Necrosis of part of the hypoxic tissue comes later, after prolonged hypoxia, leading to permanent damage.

Skin petechial haemarrhages and splinter haemorrhages

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.medibyte.com%2Fcme%2Ftutorial08%2Ffig1.jpg&hash=add5e346d69970bba0803c8a10f72fcb)
http://www.medibyte.com/cme/tutorial08/fig1.jpg

Here you can find more details from:
INFECTIVE ENDOCARDITIS
by Sam Firoozi, Dept. of Cardiological Sciences, St. Georges Hospital, edited by Sanjay Sharma copyright 2001 Medibyte.com
http://www.medibyte.com/cme/tutorial08/tutiend.htm

ikod

 

Title: Re: How do emboli cause haemorrhages?
Post by: chris on 13/11/2006 23:05:27

Hello Igor.

Infective emboli, such as those seen in endocarditis (infection of the heart and valves) or septicaemia (blood infection), trigger skin haemorrhages (known as petechiae) because the infectious material lodges in small capillaries and then triggers a localised immune response which damages the blood vessel and causes bleeding.

Usually this reponse results from activation of the components of the complement cascade, the products of which can cause bystander damage to adjacent healthy tissues, such as capillary walls. This damage causes capillary leak and some blood to spill out into the interstitial (extravascular) space. Complement can be activated by immune complexes (antibody stuck onto antigen), or directly by some bacterial cell wall components.

Another reason why emboli cause haemorrhage is due to distal infarction of the tissue supplied by an embolised blood vessel. This is most often seen in the lung after a pulmonary embolism, and in the brain following an embolic (occlusive) stroke.

Under these circumstances an embolic body lodges in a blood vessel (pulmonary or cerebral artery), occluding blood flow. The distal tissue is infarcted (fatally starved of oxygen) and dies. This includes the cells forming the blood vessel wall. As a result, when blood flow is restored, or when blood flows into the affected area via collateral vessels, haemorrhage occurs because the damaged blood vessels are highly leaky.

This is why patients who have had a pulmonary embolus cough up blood, and why patients who have had an embolic stroke can subsequently show signs of intracerebral bleeding.


Chris

Title: Re: How do emboli cause haemorrhages?
Post by: Igor on 16/11/2006 15:45:51

Thank you Iko,

Thank you Chris,

I had not considered an immune response (inflammation) as an explanation for this type of haemorrhage.