Cardiovascular System—
Physiology of the Great Vessels
Lecture 4
We’re going to look at the physiology of the “vascular” part of
cardiovascular, the blood vessels and the blood itself. The blood
is actually an organ. It functions as a unit and has speci c jobs to
perform, and so we really have to look at the whole blood system as
if it were an organ.
I
n this lecture, we examine the physiology of the large blood vessels. We
will study how these vessels control blood ow, regulate blood pressure,
and control bleeding when a vessel is ruptured. We will also examine
the composition of blood itself and the functions of each of its constituent
parts—plasma, white blood cells, and red blood cells.
Overview of the anatomy of the blood
Blood is an organ, that is, a system of tissues of different kinds that work
together to perform a speci c function in the body. The human body contains
5–6 liters (1.5 gallons) of blood, constituting some 8–9% of total body weight.
The blood separates into three layers after centrifugation. The densest (bottom)
layer is made up of red blood cells, or erythrocytes (about 45% by volume).
The lightest layer (top) is plasma (about 55% by volume). The middle density
is white blood cells (leukocytes, or the “buffy coat”—about 1% by volume). A
hemoglobin reading measures the amount of the hemoglobin molecule in the
blood. Hematocrit is the percent by volume of red blood cells.
Plasma (the liquid part) is made of the following:
Clotting proteins
Antibodies that ght off infection
Electrolytes (sodium, potassium, chloride)
Water
21
, The functions of blood include transportation, protection, and homeostasis.
Transportation
The blood transports oxygen to all of the body’s tissues.
It removes carbon dioxide from tissues.
Nutrients from the GI tract are absorbed into blood.
Blood removes wastes from the cells for excretion.
Blood circulates hormones and other chemicals from sites of
manufacture to target organs.
Lecture 4: Cardiovascular System—Physiology of the Great Vessels
Protection
The blood stops bleeding, ghts infection, and transports cells and antibodies
of the immune system to ght foreign invaders.
Homeostasis
The blood maintains the equilibrium of the internal milieu. The
body has a very narrow range of acceptable internal conditions.
It maintains pH (acid-base equilibrium) between 7.1 and 7.4.
It regulates temperature through shunting mechanisms. Alcohol
opens capillary sphincters, especially in the skin, which returns
warm blood to the skin in cold conditions. Although this feels
pleasant, it draws heat away from the body’s core and can result
in death.
It regulates total uid and electrolyte balance.
Blood composition
Ninety-two percent of total body weight is water, bone, and other tissue.
The tissue is also mostly water. Whole blood makes up about 8% of total
22
Physiology of the Great Vessels
Lecture 4
We’re going to look at the physiology of the “vascular” part of
cardiovascular, the blood vessels and the blood itself. The blood
is actually an organ. It functions as a unit and has speci c jobs to
perform, and so we really have to look at the whole blood system as
if it were an organ.
I
n this lecture, we examine the physiology of the large blood vessels. We
will study how these vessels control blood ow, regulate blood pressure,
and control bleeding when a vessel is ruptured. We will also examine
the composition of blood itself and the functions of each of its constituent
parts—plasma, white blood cells, and red blood cells.
Overview of the anatomy of the blood
Blood is an organ, that is, a system of tissues of different kinds that work
together to perform a speci c function in the body. The human body contains
5–6 liters (1.5 gallons) of blood, constituting some 8–9% of total body weight.
The blood separates into three layers after centrifugation. The densest (bottom)
layer is made up of red blood cells, or erythrocytes (about 45% by volume).
The lightest layer (top) is plasma (about 55% by volume). The middle density
is white blood cells (leukocytes, or the “buffy coat”—about 1% by volume). A
hemoglobin reading measures the amount of the hemoglobin molecule in the
blood. Hematocrit is the percent by volume of red blood cells.
Plasma (the liquid part) is made of the following:
Clotting proteins
Antibodies that ght off infection
Electrolytes (sodium, potassium, chloride)
Water
21
, The functions of blood include transportation, protection, and homeostasis.
Transportation
The blood transports oxygen to all of the body’s tissues.
It removes carbon dioxide from tissues.
Nutrients from the GI tract are absorbed into blood.
Blood removes wastes from the cells for excretion.
Blood circulates hormones and other chemicals from sites of
manufacture to target organs.
Lecture 4: Cardiovascular System—Physiology of the Great Vessels
Protection
The blood stops bleeding, ghts infection, and transports cells and antibodies
of the immune system to ght foreign invaders.
Homeostasis
The blood maintains the equilibrium of the internal milieu. The
body has a very narrow range of acceptable internal conditions.
It maintains pH (acid-base equilibrium) between 7.1 and 7.4.
It regulates temperature through shunting mechanisms. Alcohol
opens capillary sphincters, especially in the skin, which returns
warm blood to the skin in cold conditions. Although this feels
pleasant, it draws heat away from the body’s core and can result
in death.
It regulates total uid and electrolyte balance.
Blood composition
Ninety-two percent of total body weight is water, bone, and other tissue.
The tissue is also mostly water. Whole blood makes up about 8% of total
22
