<Ul> <Li> Shock is the ineffective perfusion of tissues, and can be caused by a variety of conditions including blood loss, infection, poor cardiac output . </Li> <Li> Atherosclerosis reduces the flow of blood through arteries, because atheroma lines arteries and narrows them . Atheroma tends to increase with age, and its progression can be compounded by many causes including smoking, high blood pressure, excess circulating lipids (hyperlipidemia), and diabetes mellitus . </Li> <Li> Coagulation can form a thrombosis, which can obstruct vessels . </Li> <Li> Problems with blood composition, the pumping action of the heart, or narrowing of blood vessels can have many consequences including hypoxia (lack of oxygen) of the tissues supplied . The term ischemia refers to tissue that is inadequately perfused with blood, and infarction refers to tissue death (necrosis), which can occur when the blood supply has been blocked (or is very inadequate). </Li> </Ul> <Li> Shock is the ineffective perfusion of tissues, and can be caused by a variety of conditions including blood loss, infection, poor cardiac output . </Li> <Li> Atherosclerosis reduces the flow of blood through arteries, because atheroma lines arteries and narrows them . Atheroma tends to increase with age, and its progression can be compounded by many causes including smoking, high blood pressure, excess circulating lipids (hyperlipidemia), and diabetes mellitus . </Li> <Li> Coagulation can form a thrombosis, which can obstruct vessels . </Li>

When a person is at rest approximately how much blood is being held within the veins