Blood
Blood constitutes about 7% of body
weight (about 5.5 litres in a man weighing 70 kilos).
Remember blood volumes are much lower
in children;
6 months - 500 mls 1 year - 1 litre 10
years -2
litres
Composition of blood
Plasma and cells
Plasma
yellowish
fluid consists of
about 90% of water
Plasma proteins
Albumin globulin fibrinogen prothrombin
Inorganic salts
sodium chloride sodium
bicarbonate potassium
phosphate magnesium calcium
iron
copper
iodine
Nutrients
amino
acids glucose fatty acids vitamins
Organic wastes
Urea uric
acid creatinine
Other contents
Hormones antibodies gases
Blood pH is about 7.4 and is well
buffered
Cellular content
Blood cells are mostly produced in the
bone marrow found in the hollow medullary cavity of bones.
Three varieties of blood cells
Erythrocytes
- red blood cells Leucocytes - white blood cells
Thrombocytes
- platelets
Erythrocytes
Biconcave discs, 7 microns in
diameter, 2.2 microns thick.
Contain haemoglobin, a red pigment
oxygen
+ haemoglobin -----
oxyhaemoglobin (in lungs)
oxyhaemoglobin -----
oxygen + deoxyhaemoglobin (in tissues)
Erythropoietin stimulates the
production of RBCs in response to low oxygen levels
Erythropoisis
Every mm3 of blood
contains about 5 million RBCs
Haematocrit (packed cell volume) men - 40
- 54% women - 36 - 47%
Every 100 mls of blood has
men 13 - 18
grams of haemoglobin.
women 11.5
- 16.5 grams of haemoglobin.
If Hb is normal then every 100 mls of
blood will carry 20 mls of oxygen to tissues.
RBCs live to between 100-120 days then
they are destroyed (haemolysis)
Leucocytes - WBCs
About 7 000 - 8 000 per mm3 of blood
About 1% of blood volume
Divisions of WBCs:-
Granulocytes
Non-granulocytes
Granulocytes
About 70% of all WBCs
Granular
appearance due to many vesicles
All
are polymorphs
All
are phagocytic to an extent
All
have amoeboid movement
Neutrophils
Most
common, 90 - 95% of granulocytes
May
migrate out of capillary walls
One
of first line defence against infection
Pus
contains many dead neutrophils
Eosinophils
about
6% of granulocytes
Increase
in allergic and parasitic conditions
Kill
parasitic worms
Have
antihistamine properties.
Destroy
antigen-antibody complexes.
Basophils
Least
common, less than 1% of granulocytes
Circulating
mast cells
Liberates
heparin and histamine
Heparin - anticoagulant
Histamine
- dilates small blood vessels
Non-granulocytes
Lymphocytes
About 25% of all WBCs
B produce antibodies
T
helpers stimulate
B lymphocytes to produce antibodies
T
suppresser inhibit antibody
production
T
killer directly
attack larger pathogens
Monocytes
About 5% of all WBCs Phagocytic
Can
migrate through capillary walls Amoeboid
movement
Plasma cells
Produce antibodies, (differentiated B
lymphocytes)
Thrombocytes, (platelets)
About
300 000 per mm3 Essential for
clotting
Fragments
of a type of white cell found in the bone marrow called megakaryocytes
Review of functions of blood
Macrophages
Macro
- big Phage
- to eat
Monocytes
migrate to sites of infection and enlarge up to 80 um
They
are very phagocytic Some
circulate in the blood
Some
are fixed to "police" specific areas eg. skin, liver, lungs, brain,
spleen,
lymph
nodes and bone marrow Long
lived
Microphages
The granulocytes, mostly the
neutrophils
Micro -
little Phage
- to eat
General functions
Transport
of oxygen from lungs to tissues
Transport
of carbon dioxide from tissues to lungs
Transport
of hormones from glands to target tissue
Transport
of nutrients from gut to tissues
Transport
of waste products of metabolism from tissues to excretory organs
Transport
of heat Protection from
infection Clotting