PHYSIOLOGY NOTES
,
, CARDIOVACULAR PHYSIOLOGY
CARDIOVASCULAR SYSTEM AND BLOOD
GENERAL OVERVIEW
FUNCTIONS
The cardiovascular system (CVS) is one of the fundamental systems of the human body, immediately
active during the embryonic life. Indeed, it is probably the first system to become functional. It was
seen that during the lifespan of an average duration the heart beats about 3
billion times, thereby guaranteeing the maintenance of the homeostasis.
Although it is largely active, only about 1% of cardiomyocytes are replaced per
year. For that reason, the heart is very sensitive to ischemia, which is a condition
in which blood does not reach the tissue.
The CVS has three main functions, which are:
• Transport: it transports both nutrients (e. g. oxygen) and remove
metabolic or toxic products (e. g. ammonia, CO2, etc.).
• Regulation of the total extracellular fluid: it is essential for the
homeostasis, blood pressure regulation, thermoregulation, and cardiac
output.
• Regulation of physiological functions: it is involved in the regulation of
several functions, such as the transport of hormones, or the regulation
of the body temperature.
Note that the last two main functions are two homeostatic activity that are carried out by this system.
COMPONENTS
The cardiovascular system is made of different elements, in which three main components can be
identified; they are:
• Blood: it is composed of the plasma and corpuscular elements; the former represents the
liquid portion that contains several soluble substances (e. g. plasma proteins), whereas the
latter represent the cells that are present in the blood (i. e. erythrocytes and leukocytes); the
plasma-corpuscular elements ratio is of about 55-45.
• Heart: it is the pump of the CVS, which is made of two types of chambers (i. e. atria, superior
chambers, and ventricles, inferior chambers); the cardiac output (CO) is the total volume that
is pumped by the heart per minute.
• Blood vessels: they are divided into different categories, which are:
Arteries: they are vessels that are characterised by an elastic components and act as
pressure reservoirs.
Arterioles: they are vessels that are
the major sites of resistance to flow;
they can change calibre, thus either
increasing or reducing the pressure
and the blood flow.
Capillaries: they are vessels that are
characterised by three main
features, which are that they are
short, thin, and the blood moves
slowly; these main features facilitate
diffusion of oxygen, CO2, and metabolites.
Venules: they are vessels that are formed after capillaries; they are also the site of
metabolite exchange, although they are less important than capillaries.
Veins: they are vessels that present a low pressure and a high volume; most of blood
is found in veins (about 60%).
, BLOOD
INTRODUCTION AND HAEMATOCRIT
The blood is one of the main elements of the cardiovascular system. It is subdivided into plasma and
corpuscular components. About 55% of the blood is made of plasma, whereas about 45% of cells.
Among cells, almost all of them (about 99%) is made of erythrocytes.
By centrifugating the blood, it is possible to separate the different
components of the blood. In this way it is calculate the haematocrit. The
haematocrit refers to the percentage of the blood volume that is
composed of blood cells. It averages 42% for women and 45% for men.
The blood represents about 7-8% of body mass, it is of 5.5L in a 70kg man,
and 250ml in a newborn of 3.2kg. The erythrocyte volume is of about 2.5L.
PLASMA
The plasma is made of several chemical compounds, both organic and inorganic. However, the most
abundant element is the water (94.5%). The plasma represents about 4% of body mass. It is about 2.8-
3L in men and 2.4L in women.
In the plasma several plasma proteins
are found, such as albumin, that is the
most abundant, globulins, fibrinogen,
that is involved in the coagulation
cascade, and transferrin, that is involved
in the iron transport. Plasma proteins,
and in particular albumin, are important
for the oncotic, or colloidal pressure.
This is the pressure that is required to
attract extracellular fluid in capillaries
during the process of metabolite
exchange.
Together with plasma proteins, several
ions are present, such as K+, Na+, and Ca2+
ions. As it will be seen, Ca2+ ions play a
crucial role during the coagulation cascade.
Furthermore, glucose, fatty acids, cholesterol, and other lipids constitute the plasma.
CELLULAR COMPONENTS
The blood cells belong to two main types of cells, which are the erythrocytes and the leukocytes. The
former are the most represented (about 99%), whereas the latter are different, which are
neutrophiles, eosinophiles, basophiles, monocytes, and
lymphocytes. Furthermore, also thrombocytes, or platelets are
present. Note that only leukocytes are nucleated cells since
erythrocytes are anuclated and platelets are fragments of cells (i.
e. megakaryocytes).
Blood cells derive from the haematopoietic stem cells (HSCs),
which in adults are mostly found in the bone marrow. The
abundance of HSC in the different bones vary according to the age.
For instance, in children most HSCs are found in the tibia, but in
elderly they are largely present in
vertebrae and in the sternum.
On the contrary, in foetal life the
liver and the spleen has
haematopoietic activity. Note that
,
, CARDIOVACULAR PHYSIOLOGY
CARDIOVASCULAR SYSTEM AND BLOOD
GENERAL OVERVIEW
FUNCTIONS
The cardiovascular system (CVS) is one of the fundamental systems of the human body, immediately
active during the embryonic life. Indeed, it is probably the first system to become functional. It was
seen that during the lifespan of an average duration the heart beats about 3
billion times, thereby guaranteeing the maintenance of the homeostasis.
Although it is largely active, only about 1% of cardiomyocytes are replaced per
year. For that reason, the heart is very sensitive to ischemia, which is a condition
in which blood does not reach the tissue.
The CVS has three main functions, which are:
• Transport: it transports both nutrients (e. g. oxygen) and remove
metabolic or toxic products (e. g. ammonia, CO2, etc.).
• Regulation of the total extracellular fluid: it is essential for the
homeostasis, blood pressure regulation, thermoregulation, and cardiac
output.
• Regulation of physiological functions: it is involved in the regulation of
several functions, such as the transport of hormones, or the regulation
of the body temperature.
Note that the last two main functions are two homeostatic activity that are carried out by this system.
COMPONENTS
The cardiovascular system is made of different elements, in which three main components can be
identified; they are:
• Blood: it is composed of the plasma and corpuscular elements; the former represents the
liquid portion that contains several soluble substances (e. g. plasma proteins), whereas the
latter represent the cells that are present in the blood (i. e. erythrocytes and leukocytes); the
plasma-corpuscular elements ratio is of about 55-45.
• Heart: it is the pump of the CVS, which is made of two types of chambers (i. e. atria, superior
chambers, and ventricles, inferior chambers); the cardiac output (CO) is the total volume that
is pumped by the heart per minute.
• Blood vessels: they are divided into different categories, which are:
Arteries: they are vessels that are characterised by an elastic components and act as
pressure reservoirs.
Arterioles: they are vessels that are
the major sites of resistance to flow;
they can change calibre, thus either
increasing or reducing the pressure
and the blood flow.
Capillaries: they are vessels that are
characterised by three main
features, which are that they are
short, thin, and the blood moves
slowly; these main features facilitate
diffusion of oxygen, CO2, and metabolites.
Venules: they are vessels that are formed after capillaries; they are also the site of
metabolite exchange, although they are less important than capillaries.
Veins: they are vessels that present a low pressure and a high volume; most of blood
is found in veins (about 60%).
, BLOOD
INTRODUCTION AND HAEMATOCRIT
The blood is one of the main elements of the cardiovascular system. It is subdivided into plasma and
corpuscular components. About 55% of the blood is made of plasma, whereas about 45% of cells.
Among cells, almost all of them (about 99%) is made of erythrocytes.
By centrifugating the blood, it is possible to separate the different
components of the blood. In this way it is calculate the haematocrit. The
haematocrit refers to the percentage of the blood volume that is
composed of blood cells. It averages 42% for women and 45% for men.
The blood represents about 7-8% of body mass, it is of 5.5L in a 70kg man,
and 250ml in a newborn of 3.2kg. The erythrocyte volume is of about 2.5L.
PLASMA
The plasma is made of several chemical compounds, both organic and inorganic. However, the most
abundant element is the water (94.5%). The plasma represents about 4% of body mass. It is about 2.8-
3L in men and 2.4L in women.
In the plasma several plasma proteins
are found, such as albumin, that is the
most abundant, globulins, fibrinogen,
that is involved in the coagulation
cascade, and transferrin, that is involved
in the iron transport. Plasma proteins,
and in particular albumin, are important
for the oncotic, or colloidal pressure.
This is the pressure that is required to
attract extracellular fluid in capillaries
during the process of metabolite
exchange.
Together with plasma proteins, several
ions are present, such as K+, Na+, and Ca2+
ions. As it will be seen, Ca2+ ions play a
crucial role during the coagulation cascade.
Furthermore, glucose, fatty acids, cholesterol, and other lipids constitute the plasma.
CELLULAR COMPONENTS
The blood cells belong to two main types of cells, which are the erythrocytes and the leukocytes. The
former are the most represented (about 99%), whereas the latter are different, which are
neutrophiles, eosinophiles, basophiles, monocytes, and
lymphocytes. Furthermore, also thrombocytes, or platelets are
present. Note that only leukocytes are nucleated cells since
erythrocytes are anuclated and platelets are fragments of cells (i.
e. megakaryocytes).
Blood cells derive from the haematopoietic stem cells (HSCs),
which in adults are mostly found in the bone marrow. The
abundance of HSC in the different bones vary according to the age.
For instance, in children most HSCs are found in the tibia, but in
elderly they are largely present in
vertebrae and in the sternum.
On the contrary, in foetal life the
liver and the spleen has
haematopoietic activity. Note that
