Transcript Structure

Chapter 14
Blood
Structure & Function
• Blood is a type of connective tissue (consists of
cells in a matrix)
• Function – transports O2 & nutrients, maintains
homeostasis, protection from blood loss &
infection
• pH – 7.35-7.45
• Volume – 5L (in avg. adult male)
• Temp. – 100.4 º F.
• Accounts for 8% of body weight
• Color varies from scarlet (O2 rich) to dark red
(O2 poor)
Structure
• Composition –
• composed of 3
types of cells
(called solid portion):
• 1. RBCs –
erythrocytes
• 2. WBCs – leukocytes
• 3. platelets - thrombocytes
Structure
• The solid portion makes up 45% of a blood
sample
• Called the hematocrit
(HCT) or packed cell
volume (PCV)
• Matrix (liquid portion) – plasma;
clear, straw-colored
• Makes up remaining 55% of
sample; mostly H2O, nutrients, etc.
Hematopoiesis – Production of blood cells
(RBCs, WBCs & platelets)
Erythrocytes (RBCs)
• Structure:
• 1. biconcave disks
• three advantages:
A. increase SA
B. no point within the cytoplasm is far
from the surface; ideal for gas
exchange
C. flexible; can squeeze thru tiny b.v.
Erythrocytes
• Structure:
• 2. Contain hemoglobin (Hb);
allows them to carry
resp. gases more efficiently
• 3. Mature RBCs lack nuclei; allows more
room for Hb (each RBC is 1/3 Hb by
volume)
• Normal RBC count: 4-6 million/mm³ of blood (in
avg. adult) (slight incr. after meals or exercise;
decr. from anemia, leukemia, or hemorrhage)
Hemoglobin
• Hb consists of the protein globin→
• Each has 4 polypeptide chains
& 4 heme groups (pigment)
where O2 binds
• Hb combines easily w/O2 – called affinity ( or attraction)
for O2
• Produces oxyhemoglobin; makes blood bright red
• When O2 is released from the RBC, deoxyhemoglobin
is produced; makes blood dark bluish-red
Hemoglobin
• Normal Hb levels – 14-18 gm/100 ml of
blood (in avg. adult male)
• Cyanosis – occurs when O2 is deficient
(hypoxia) & levels of deoxyhemoglobin
incr.
• Symptoms – bluish lips &
nail beds, dizziness, fainting,
fatigue, muscle weakness
Leukocytes- WCBs
• 2 main classes:
• Granulocytes – have a grainy cytoplasm
• Agranulocytes – have a clear cytoplasm
Types
There are 5 types of white blood cells:
Granulocytes
• Neutrophils
40-75%
• Eosinophils
5%
• Basophils
0.5%
Agranulocytes
• Lymphocytes 20-50%
• Monocytes
1-5%
The range is because the requirement for
different types of WBCs vary from time to time.
Neutrophils
Structure:
• Multilobed nucleus
• Inconspicuous granules
Amount:
• 3-7,000/mm³
Functions:
• Engulfing bacteria & viruses
(phagocytosis)
Life Span:
• hours → days
Eosinophils
Structure:
• Bilobed nucleus
• Large, red granules
Amount:
• 100-400/mm³
Functions:
• phagocytosis
• Protects against parasitic infections
• Neutralize histamines (their amts. incr. during
hay fever & allergy attacks)
Life Span – hours → days
Basophils
Structure:
• Lobed nucleus
• Large granules, but fewer
Amount:
• 20-50/mm³
Functions:
• Become mast cells when they leave b.v. & produce
histamines
• Respond to allergens rapidly (anaphylactic shock)
• Produce heparin (anticoagulant)
Life Span – hours → days
Monocytes
Structure:
• Largest WBC
• U-shaped nucleus
• Grayish blue cytoplasm
Amount:
• 100-700/mm³
Functions:
• Phagocytosis
• Become macrophages & remove dead cells
Life Span – weeks → months
Lymphocytes
Structure:
• Most numerous in children;
2nd most in adults
• Spherical nucleus
• Small “ring”of cytoplasm; pale blue
Amount:
• 1500-3000/mm³
Functions:
• T cells – attack foreign antigens directly
• B cells – produce antibodies for immunity
Life Span – months → lifetime
White Blood Cell Count
• Normal adult has 5,000-10,000 cells/mm3
• Leukocytosis- WBC count above 10,000
cells/mm3
– Can be a sign of acute infection
– Occurs during times of stress and vigorous
exercise.
• Leukopenia- WBC below above 10,000
cells/mm3
– Can be a sign of virus such as influenza,
measles, mumps and HIV
Thrombocytes- Platelets
• Fragments of giant cells
(megakaryocytes) (each produces
b/t 5-10,000 platelets)
• Pieces break off these
cells in bone marrow
• Enter circulation – live for approx.
1 wk.; destroyed by spleen & liver
• Disk-shaped, w/o nucleus
• ½ the size of an RBC
• Release serotonin to contract
blood vessel walls.
Function
• Normal platelet count –
130,000-360,000/mm³
• Stem blood flow (hemostasis) 2 ways:
1. Form a platelet plug
2. Initiate the clotting
process
Platelet Plug Formation
1. B.V.damaged
2. Some blood
escapes
3. Platelets adhere to
each other & rough
surfaces
4. When platelets come in
contact w/collagen from connective tissue, they develop
spiny projections; helps them adhere
5. Eventually platelet plug is formed & bleeding stops
Blood Clots
• Thrombus – blood clot that forms in a b.v.
abnormally
• Embolus – blood clot or
fragment of one that
dislodges & travels to
major organ
Plasma
• Clear, straw-colored fluid; matrix of blood
• 92% water
• Functions:
1. transport
2. maintain fluid balance
3. maintain pH
Contents of Plasma
•
Contains 3 plasma proteins (all produced in the liver):
1.
Albumin – accounts for 60% of all plasma proteins maintains osmotic pressure (keeps concentration of
H2O & solutes in plasma stable
- example – a decrease in albumin causes cells to lose
H2O; it collects in interstitial spaces (b/t cells) & causes
edema
Plasma Proteins
2. Globulins – Accounts for 36%
of all plasma proteins
- transports lipids & vitamins
3. Fibrinogen – Accounts for 4% of all
plasma proteins
- responsible for blood clotting
Other Substances
Plasma also contains:
• nonprotein nitrogenous substances –
amino acids, urea, uric acid
• electrolytes – release ions when dissolved
in H2O; maintain osmotic pressure & pH;
include Na, K, Cl, Ca Mg, bicarbonate,
PO4 & SO4 ions