Page 156 - Cardiac Nursing

9/0
0
9/2
8:2
009
2-1
p13
52.
qxd
52.
32
e 1
32
ara
Apt
M
5 A
P
g
P
LWBK340-c06_06_p132-152.qxd 09/09/2009 08:25 AM Page 132 Aptara
L L LWB
LWB K34 0-c 06_ p13 2-1 52. qxd 0 9/0 9/2 009 0 0 8:2 5 A M P a a g e 1 32 Apt ara
K34
06_
0-c
K34
CHAPTER
a
a
a
i
l
o
a
g
i
C
t
o
i
g
H H H H Hematopoiesis, Coagulation, and Bleeding
g
m
a
e
e
a
n
o
l
l
l
u
u
l
i
l
,
i
,
,
p
d
B
s
l
a
C
e
e
o
d
o
C
n
o
Nancy Munro
Thee physiologicall ffuunctions f bllood include nutrition, oxy-
Th ph ys io lo gi ca l ti on of b o od i nc u d Th c el li i m at e te d at h as
The stem cellis an immature (undifferenntiated) cellll that has
b
er
ge g nation, resppiration, and excretion. These various components th thee ccapacity to reproducee itself and to mature (diffferentiaate) into
ti
uc
at
,
en
p
od
it
nd
y
t
e)
e
lf
A
xi
es
o
yp
c
b
e
s
A
ll
s
of bllood accomplish these functions. Appro imatelly 55% of f an anyy of the diffferent types off blood cells. Ass hthe stem cell divides
d
of
h
el
f
ma
d
i
ns
po
tu
ti
re
ff
rt
at
di
o
ed
os
pl
wh
ma
as
mp
lu
vo
oo
me
co
s
i
ic
bl bloodd volume is composed off plasma, which is a transport an and maturess, itt differenntiates into one of two committed cell
ra
h
is
a
t
T
medium for ions, proteins, hormones, and end products of cel- lines: lymphoid or myyeloid progenitorr cells. The com imitted lym-
s.
om
he
ed
ni
m
c
ll
ce
to
tt
i
i
lular metabolism. The most important ions carried in the plasma phoid progenitor cell eventually matures into T and B lympho-
i
Th
are sodium, potassium, chloride, hydrogen, magnesium, and cytes and natural killer cells. The committed myeloid stem pro-
calcium. Examples of proteins transported in the plasma are im- genitor cell develops into (1) the megakaryocyte–erthrocyte
munoglobulins and the coagulation proteins. Formed elements precursors leading to the development of platelets and RBC and
or cells including red blood cells (RBC; erythrocytes), white (2) the granulocyte–monocyte precursors leading to the develop-
4
blood cells (WBC; leukocytes), and platelets (thrombocytes) ment of the granulocyte and monocyte. Maturation of these cell
constitute the other 45% of blood volume. Erythrocytes trans- lines is influenced by multiple growth factors such as granulocyte
port oxygen to the tissues and carbon dioxide to the lungs for ex- colony-stimulating factor, erythropoietin, thrombopoietin, inter-
4
cretion. Leukocytes protect against infection and play a major leukins, interferon, and many others. As the various types of
role in the inflammatory process. Thrombocytes, along with co- blood cells mature, they are released into the peripheral circula-
agulation proteins, protect against blood loss through the for- tion. Figure 6-1 shows a model for hematopoietic cell differenti-
mation of blood clots. 1 ation.
Because these functions are vital, a significant blood loss has
devastating consequences for all body tissues. A complex series of Red Blood Cells
events leading to hemostasis achieves protection against such
blood losses and potential exsanguination from injuries. The en- The major role of the RBC is respiration, which is the exchange of
dothelium of the vasculature plays a vital role in the coagulation gases. The mature RBC is a biconcave disc filled with hemoglobin
process and is now considered an organ by the Margaux III but it does not have a nucleus. The lack of a nucleus allows the
Conference on Critical Illness: The Endothelium: An Under- RBC to change shape and facilitates movement through small cap-
2
recognized Organ in Critical Illness. The endothelial cell partic- illary beds. Heme, the iron-containing pigment, is the actual
ipates by releasing mediators that effect coagulation and the role oxygen-transporting portion of the hemoglobin molecule. Oxygen
of the vessel’s participation in hemostasis. The equally complex diffuses from the alveoli into the alveolar capillaries and binds to
mechanism of fibrinolysis, which dissolves clots, balances this each of four to five sites on the heme portion of hemoglobin. One
system. Normal blood flow through the vasculature depends gram of hemoglobin can carry 1.34 to 1.36 milliliters of oxygen.
partly on the balance of these two systems, hemostasis and fibri- The remarkable oxygen-binding capacity of the RBC is influenced
nolysis. Recent research has also revealed a link between coagula- by three factors that affect the oxyhemoglobin dissociation curve:
tion and the inflammatory process that has caused the scientific pH, temperature, and the amount of 2,3-diphosphogylcerate (see
3
community to re-examine the process of atherosclerosis. Knowl- Chapter 2). Tissue metabolism produces carbon dioxide as a waste
edge of these normal processes is important as a basis for under- product that is also transported from the tissues by the RBC. Car-
standing the many alterations that may result from disease states bon dioxide diffuses into the RBC and combines with water to
or drug administration. form carbonic acid that further dissociates to the hydrogen and bi-
carbonate ions. The bicarbonate ion is inactivated when combined
with hydrogen ions to again form water and carbon dioxide, which
HEMATOPOIETIC CELLS is eliminated at the alveoli.
The rate of bone marrow stem cell differentiation into erythro-
Hematopoiesis, or the production of blood cells, occurs primarily cytes is primarily controlled by erythropoietin. Most of this hor-
in the bone marrow. The liver, spleen, lymph nodes, and thymus mone is produced by the kidney. The creation of RBC is influenced
are involved in hematopoiesis during embryonic life, but after by the oxygen content of the blood as sensed by the kidneys. Pro-
birth extramedullary (outside the bone marrow) hematopoiesis duction also requires necessary substrates including vitamin B 12 ,
occurs only during abnormal circumstances. If it occurs at all af- vitamin B 6 , folic acid, and iron. The vitamins and folic acid are ob-
ter birth, extramedullary hematopoiesis occurs mainly in the liver tained from dietary sources, as is iron. However, most iron is
and spleen. The hematopoietic stem cell resides mainly in the gained through the recycling of the RBC in the spleen. RBC pro-
bone marrow and in small numbers in the peripheral blood. The duction is increased at times of blood loss, at high altitude, and in
the
types
of
all
pulmonary diseases that affect the transport of oxygen from thethe
blood
cell
s:
of
ce
stem
hematopoietic
hematopoietic stem cell is the source of all the types of blood cells: pulmonar y diseases that affect the transpor t o f o xygen fr om
cell
the
sour
is
RBC, WBC, and platelets. lungs to the blood. It takes approximately 3 to 5 days for RBC to
132