OCCURS WHEN THERE IS A PROBLEM WITH BLOOD RETURNING TO THE HEART
For the deoxygenated blood to return to the heart, the pressure within the veins must be higher than that of the heart. The pressure within the heart when the heart relaxes is lower than other regions of the body, thus producing a pressure gradient allowing blood flow back into the heart. However, this alone is not enough to ensure all the blood comes back to the heart. This is made possible by the calf muscle pump. This pseudo-pump increases the pressure within the vein by the contraction of the surrounding skeletal muscles. Once the muscle contracts it compresses the veins forcing the blood to hit against the valves within the veins and open them to allow blood to flow. Once the muscle relaxes the valves close and prevents blood flow through the vein. This “pump” contributes to 90% of venous return from the legs by working against the hydrostatic pressure (force exerted on blood due to gravity).
Pooling of blood cause by chronic venous insufficiency can lead to:
Swelling of the legs,
Aches and Pains
Read more on Venous Insufficiency, its causes, symptoms and treatment methods - John Hopkins Medicine
REFERS TO THE LOCALISED SWELLING OF THE BODY CAUSED BY AN ABNORMAL ACCUMULATION OF EXCESSIVE AMOUNTS OF INTERSTITIAL FLUID
The lymphatic system plays two vital roles within the human body:
Aids the primary circulation of blood within the body, and
Helps with the immune response
The nutrient exchange takes place at the tissues and organs via capillary vessels. Capillary vessels are very thin (thickness ~ 1 cell) resulting in high surface areas which maximises the efficiency of nutrient transfer. As the heart needs to pump blood throughout the entire body, it exerts high pressures on the blood vessels. As a result of the high pressure combined with very thin capillary vessels, fluid (interstitial fluid) seeps through the capillary vessel and escapes the primary circulation system. If this fluid is not removed, the pooling of the fluid would result in swelling of the region (oedemas) which could in turn push against the blood vessels and constrict the flow of blood. This where the Lymphatic system helps in removing this excess fluid and taking it back to the circulatory system.
Once this interstitial fluid enters the lymphatics system it is called lymph. The lymph re-enters the veins just before the heart, at this location the pressure within the blood vessels is much lower compared to other regions of the body, hence this pressure difference along with the skeletal-muscle pump facilities with the movement of the fluid within the lymph vessels.
The lymphatic system consists of lymph vessels and lymph nodes. Lymph vessels are spread over the entire body. Hence, theoretically lymphedema can occur in all parts of the body. However, a majority of cases seen occur in the lower limbs; the lower extremity (90%), upper extremity (10%), or genitalia (<1%) .
Lymphedema can be categorised as either primary or secondary lymphedema.
Primary lymphedema – genetic aberration (pre-programmed to have lymphedema), it must be noted that this does not mean the lymphedema is congenital, it can appear at any stage of a person’s life,
Secondary lymphedema – is that which is acquired due to external factors. The main cause for acquired lymphedema is due to the removal of lymph nodes during cancer treatment. However new research shows that obesity is eclipsing cancer as the main cause of secondary lymphedema.
Lymphedema can result in:
Swelling of part or all your limb
Aching or discomfort
Hardening and thickening of the skin (fibrosis)
Read more on the causes, symptoms and treatment options for lymphedema - John Hopkins Medicine
DEEP VEIN THROMBOSIS
A CHRONIC DISEASE THAT OCCURS WHEN A BLOOD CLOT (THROMBUS) FORMS IN THE DEEP VEINS OF THE BODY
DVT usually forms in the lower limbs.
The key factors that influence the development of venous thrombosis is outlined by the Virchow Triad. 
In a healthy human, the formation of these clots are usually broken down by the body before they become life threatening. However, if the thrombus manages to grow into a large clot, it could result in the constriction of blood flow through the vessels. This results in pain in the affected areas, accompanied by swelling and redness. However, some DVTs do not show any symptoms.
Pulmonary embolism (blood clot in the lung) is a serious condition that stems from DVT. This occurs when the thrombus formed in the deep veins breaks off (embolus) and is transported to the lungs via the blood vessels. Once at the lungs the thrombus clogs up the blood flow through the lungs, which could result in Congestive Heart Failure (CHF)
The key factors that influence the development of venous thrombosis is shown in Virchow’s Triad.
DVT can show symptoms of:
Pain in your leg.
Cramping of legs
Red or dis-colored skin on the leg.
A feeling of warmth in the affected leg
However, DVT can also present its self without showing any symptoms
Read more on the causes, symptoms and treatment methods for Deep Vein Thrombosis - John Hopkins Medicine
A CONDITION THAT IS CAUSED BY INFLAMED JOINTS
There are many types of arthritis; however, the two most common types are:
Osteoarthritis -caused by regular wear and tear of the cartilage that acts as a buffer between two joints. This is the most common type of arthritis and is brought about by old age.
Rheumatoid Arthritis – an autoimmune disorder that can affect one or more joints where the lining of the joint is caused to erode which results in the bones disintegrating as they rub against each other.
Arthritis brings about:
Severe pain around the joint
Swelling around the affected joint
Increased stiffness of the joint
Read more on the causes, symptoms and treatment options for Osteoarthritis - John Hopkins Medicine