Circulatory Disorders in Veterinary Pathology: Congestion and Hyperaemia

In veterinary pathology, we need to be aware of the circulatory system disorders and the diseases that can lead to these disorders. In this post, we look at the circulatory system and two of the disorders, congestion and hyperaemia.

The Circulatory System

Cells are mostly made up of water and live in the interstitial fluid. For a good explanation of interstitial fluid watch this video below.

In the circulatory system, there is intracellular fluid, interstitial fluid and circulating plasma.

Intracellular fluid is fluid that exists within the cells of multi-celled organisms. The intracellular fluid is therefore stored within the intracellular compartments of the body. Intracellular fluid is often referred to as cytosol when discussing cellular functions.

Animal Health Blood and Circulatory System

Fluid can move between interstitial fluid and plasma and so a disease can affect both of these because they are so closely linked. This is not the case with intracellular fluid though, even if the other two compartments change, it does remain constant.

Intracellular fluid is fluid inside the cell.

Congestion and Hyperaemia

Both congestion and hyperaemia cause tissue to become more red due to an increase in blood volume

What is Congestion?

Congestion is caused by a functional or structural blockage, causing a decrease in blood flow moving out of the tissues. It is a passive process.

What is Hyperaemia?

Hyperaemia is caused by an increase in blood flow into the tissues and it's an active process.

Let's talk more about Congestion...

There are 3 types:

  1. Local - kept to one tissue or one area of tissue. This is commonly caused by the restriction of the lumen in a blood vessel because of pressure on the blood vessel from outside of it.

  2. Systemic - this is caused by an obstruction in the heart which restricts blood flow coming out of the heart. This is usually a chronic problem. Endocarditis is inflammation of the heart valve, which can cause congestion. Diseases that can change the structure of the heart such as white muscle disease and compression of the heat such as from traumatic pericarditis, can also cause blood flow out of the heart to be reduced.

  3. Hypostatic - When blood gravitates to the lowest part of the body after death and largely depends on what way the animal was lying when it died. Always take the position the animal was lying in into consideration. In pathology, you need to be able to tell hypostatic congestion from pathological congestion.

Passive Congestion in Veterinary Pathology

Passive congestion is commonly found in post mortems but does not mean it is due to an underlying disease.


If you are looking at congested lungs, you will see reddish-blue lungs. They'll also be heavier because of oedema fluid and because there is more blood volume in them.


If the liver is congested, it is usually due to right-sided heart failure and can show "nutmeg liver".

If a liver is congested it will be round, large and dark red with dark red blood oozing from the cut surface.


  • Active process

  • Happens in muscles in response to exercise

  • In pathology, it is caused by inflammation and also can be due to toxins

Remember that congestion and hyperaemia are opposite in nature, one is passive (congestion) and the other is active (hyperaemia) BUT both cause tissue to become more red due to both creating more blood volume. They can happen together because hyperaemia causes inflammation and swelling and this can hinder venous drainage, causing congestion.

Want to know more? Check back next Monday for the post on Oedema, Shock, Haemorrhage and Homeostasis.