Hydrostatic pressure and plasma oncotic pressure are both related to the flow of fluid in and out of blood vessels, but they work in different ways and have different functions.
Hydrostatic Pressure
Hydrostatic pressure refers to the force exerted by a fluid (in this case, blood) against the walls of a container (in this case, the blood vessels). The term hydrostatic pressure is often used to describe the pressure within the circulatory system, specifically within the blood vessels.
In the blood vessels, hydrostatic pressure is generated by the pumping action of the heart, which propels blood through the vessels. The pressure is highest in the arteries, where it is needed to push blood to the body’s farthest reaches, and it decreases as the blood flows through the arterioles, capillaries, venules and veins.
The pressure in the blood vessels is measured in millimetres of mercury (mmHg) and is commonly referred to as blood pressure. The normal range for blood pressure is 120/80 mmHg, which means the pressure in the arteries is 120 mmHg when the heart beats (systolic pressure) and 80 mmHg when the heart is at rest (diastolic pressure). High blood pressure (hypertension) is defined as a systolic pressure of 130 mmHg or higher and a diastolic pressure of 80 mmHg or higher.
The hydrostatic pressure also plays a role in the flow of fluid and substances across the capillary wall, in a process called filtration, which is important for the delivery of oxygen and nutrients to the cells and the removal of waste products.
Changes in the hydrostatic pressure can indicate different health conditions like hypertension, hypotension, heart failure and more. Monitoring the blood pressure, and managing it if it’s high, is important for maintaining good cardiovascular health.
Plasma Oncotic Pressure
Plasma oncotic pressure, also known as colloid osmotic pressure, is a type of osmotic pressure that is created by the presence of dissolved particles, such as proteins, in the blood plasma. These particles, particularly the protein albumin, create an osmotic gradient that helps to pull fluid back into the blood vessels from the surrounding tissues.
The main function of plasma oncotic pressure is to maintain the balance of fluid between the blood vessels and the surrounding tissues, also known as fluid homeostasis. It works in conjunction with hydrostatic pressure to regulate the flow of fluid in and out of blood vessels.
When the plasma oncotic pressure is high, as in most healthy individuals, it helps to keep fluid from leaking out of the blood vessels into the surrounding tissues. This is important for maintaining normal blood volume and blood pressure. On the other hand, when the plasma oncotic pressure is low, as in some disease states, it can lead to an accumulation of fluid in the surrounding tissues, a condition known as edema.
Low plasma oncotic pressure can be caused by a variety of conditions, including liver disease, kidney disease, and certain types of cancer, which can lead to a decrease in the production of proteins like albumin. In such cases, a treatment may include replacement of albumin or other plasma proteins.