Abdominal bruising or severe injuries that cause difficulty in moving a limb or the feeling of liquid under the skin may indicate life-threatening injury and require the attention of a physician. Mechanism
Increased distress to tissue causes capillaries to break under the skin, allowing blood to escape and build up. As time progresses, blood seeps into the surrounding tissues, causing the bruise to darken and spread. Nerve endings within the affected tissue detect the increased pressure, which, depending on severity and location, may be perceived as pain or pressure or be asymptomatic. The damaged capillary endothelium releases endothelin, a hormone that causes narrowing of the blood vessel to minimize bleeding. As the endothelium is destroyed, the underlying von Willebrand factor is exposed and initiates coagulation, which creates a temporary clot to plug the wound and eventually leads to restoration of normal tissue. During this time, larger bruises may change color due to the breakdown of hemoglobin from within escaped red blood cells in the extracellular space. The striking colors of a bruise are caused by the phagocytosis and sequential degradation of hemoglobin to biliverdin to bilirubin to hemosiderin, with hemoglobin itself producing a red-blue color, biliverdin producing a green color, bilirubin producing a yellow color, and hemosiderin producing a golden-brown color. As these products are cleared from the area, the bruise disappears. Often the underlying tissue damage has been repaired long before this process is complete.
Often the result of strain, including sneezing, coughing, vomiting or other kind of strain
Nose

Epistaxis – nosebleed
Mouth
Tooth eruption – losing a tooth
Hematemesis – vomiting fresh blood
Hemoptysis – coughing up blood from the lungs
Lungs
Pulmonary hemorrhage
Gastrointestinal
Upper gastrointestinal bleed
Lower gastrointestinal bleed
Occult gastrointestinal bleed
Urinary tract
Hematuria – blood in the urine from urinary bleeding
Gynecologic
Vaginal bleeding
Postpartum hemorrhage
Breakthrough bleeding
Ovarian bleeding – This is a potentially catastrophic and not so rare complication among lean patients with polycystic ovary syndrome undergoing transvaginal oocyte retrieval. Anus
Melena – upper gastrointestinal bleeding
Hematochezia – lower gastrointestinal bleeding, or brisk upper gastrointestinal bleeding
Vascular
Ruptured aneurysm
Aortic transection
Iatrogenic injury

Causes
Bleeding arises due to either traumatic injury, underlying medical condition, or a combination. Traumatic injury
Traumatic bleeding is caused by some type of injury. There are different types of wounds which may cause traumatic bleeding. These include:
Abrasion – Also called a graze, this is caused by transverse action of a foreign object against the skin, and usually does not penetrate below the epidermis. Excoriation – In common with Abrasion, this is caused by mechanical destruction of the skin, although it usually has an underlying medical cause. Hematoma – Caused by damage to a blood vessel that in turn causes blood to collect in an enclosed area. Laceration – Irregular wound caused by blunt impact to soft tissue overlying hard tissue or tearing such as in childbirth. In some instances, this can also be used to describe an incision. Incision – A cut into a body tissue or organ, such as by a scalpel, made during surgery.