Chapter 6
Biology 25: Human
Biology
Prof. Gonsalves
Los Angeles City College
Loosely Based on Mader’s Human
Biology,7th edition
1. Blood
Average Blood Volume: 4 to 6 liters.
Blood composition:
55% Plasma (fluid matrix of water, salts, proteins, etc.)
45% Cellular elements:

Red Blood Cells (RBCs): 5-6 million RBCs/ml of blood. Contain
hemoglobin which transport oxygen and CO2.

White Blood Cells (WBCs): 5,000-10,000 WBCs/ml of blood. Play a
essential role in immunity and defense. Include:


Lymphocytes: T cells and B cells

Macrophages (phagocytes)

Granulocytes: Neutrophils, basophils, and eosinophils.
Platelets: Cellular fragments. 250,000- 400,000/ml of blood.
Important in blood clotting.
Composition of Blood
Formed Elements.
 Erythrocytes.
 Leukocytes.
 Platelets.
 Plasma.

Composition of Human Blood
Plasma
Straw-colored liquid.
 Consists of H20 and dissolved solutes.
 Ions, metabolites, hormones, antibodies.
 Na+ is the major solute of the plasma.

Plasma Proteins
Constitute 7-9% of plasma.
 Provide the colloid osmotic pressure
needed to draw H20 from interstitial fluid
to capillaries.
 Maintain blood pressure.
 Albumin:
 Accounts for 60-80% of plasma
proteins.

Plasma Proteins
Globulins:
 a globulin:
 Transport lipids and fat soluble vitamins.
 b globulin:
 Transport lipids and fat soluble vitamins.
 g globulin:
 Antibodies that function in immunity.

Plasma Proteins

Fibrinogen:
 Constitutes 4% of plasma proteins.
 Important clotting factor.
 Converted into fibrin during the clotting
process.
Formed Elements of Blood

Include 2 types of blood cells:
 RBCs (red blood cells):
 Most numerous of the two.
 WBCs (white blood cells).
Erythrocytes
Flattened biconcave discs.
 Provides increased surface area through
which gas can diffuse.
 Lack nuclei and mitochondria.
 Half-life ~ 120 days.
 Contain 280 million hemoglobin with 4
heme chains (contain iron).

Leukocytes





Contain nuclei and mitochondria.
Move in amoeboid fashion.
 Can squeeze through capillary walls
(diapedesis).
Almost invisible, so named after stains.
Neutrophils are the most abundant WBC.
 Accounts for 50 – 70% of WBCs.
Involved in immune function.
Platelets






Also called thrombocytes.
Smallest of formed elements.
 Are fragments of megakaryocytes.
 Lack nuclei.
Have amoeboid movement.
Important in blood clotting:
Constitute most of the mass of the clot.
 Release serotonin to reduce blood flow to area.
Secrete growth factors
 Maintain the integrity of blood vessel wall.
Hematopoiesis






Formation of blood cells.
2 types of hematopoiesis:
Erythropoiesis:
 Formation of RBCs.
Leukopoiesis:
 Formation of WBCs.
Occurs in myeloid tissue (bone marrow of long
bones) and lymphoid tissue.
Stem cells differentiate into blood cells.
Erythropoiesis





Active process.
2.5 million RBCs are produced every second.
Regulated by erythropoietin.
 Erythropoietin binds to membrane receptors,
stimulating cell division.
Old cells are destroyed in spleen and liver.
 Iron recycled back to myeloid tissue to be
reused in RBC synthesis.
Need iron, vitamin B12 and folic acid for synthesis.
Leukopoiesis


Cytokines stimulate different types and stages of WBCs
production.
Multipotent growth factor-1, interleukin-1, and interleukin3:


Granulocyte-colony stimulating factor:


Stimulate development of different types of
WBC cells.
Stimulates development of neutrophils.
Granulocyte-monocyte colony stimulating factor:

Simulates development of monocytes and
eosinophils.
Blood Clotting

Hemostatic mechanisms:


Cessation of bleeding.
Breakage of endothelial lining exposes collagen
proteins causing:
Vasoconstriction.
 Platelet plug.
 Web of fibrin.

Function of Platelets
Platelets normally repelled away from
endothelial lining by prostacyclin
(prostaglandin).
 Do not want to clot normal vessels.

Damage to Endothelian Wall
Exposes subendothelial tissue to blood.
 Platelet release reaction:
 Endothelial cells secrete von Willebrand
factor to cause platelets to adhere to
collagen.
 Platelet secretory granules release ADP,
serotonin and thromboxane A2.

Platelet Release Reaction





Serotonin and thromboxane A2 stimulate
vasoconstriction.
ADP and thromboxane A2 make other
platelets “sticky”.
Platelets adhere to collagen.
Produce platelet plug.
Strengthened by activation of plasma
clotting factors.
Clotting Factors
Platelet plug strengthened by fibrin.
 Clot reaction:
 Contraction of the platelet mass forms a
more compact plug.
 Conversion of fibrinogen to fibrin
occurs.
 Fluid squeezed from the clot is called serum
(plasma without fibrin).

Conversion of Fibrinogen to Fibrin

Intrinsic Pathway:
 Initiated by exposure of blood to a negatively
charged surface (collagen).
 This activates Factor XII (protease), which
activates other clotting factors.
++ and phospholipids convert prothrombin to
 Ca
thrombin.
 Thrombin converts fibrinogen to fibrin.
 Produces meshwork of insoluble fibrin
polymers.
Extrinsic Pathway
Thromboplastin is not a part of the blood,
so called extrinsic pathway.
 Damaged tissue release a thromboplastin.
 Thromboplastin initiates a short cut to
formation of fibrin.

Dissolution of Clots




Activated factor XII converts an inactive
molecule into the active form (kallikrein).
Kallikrein converts plasminogen to
plasmin.
Plasmin is an enzyme that digests the
fibrin.
Clot dissolution occurs.
Types of Blood Vessels
A. Arteries and Arterioles:

Carry blood away from heart to body.

Have high pressure.

Have thick muscular walls, which make them elastic
and contractile.


Vasoconstriction: Arteries contract:

Reducing flow of blood into capillaries.

Increasing blood pressure.
Vasodilation: Arteries relax:

Increasing blood flow into capillaries.

Decreasing blood pressure.
Types of Blood Vessels
Capillaries: Only blood vessels whose walls are thin enough
to permit gas exchange.
Blood flows through capillaries relatively slowly, allowing
sufficient time for diffusion or active transport of
substances across walls.
Only about 5 to 10% of capillaries have blood flowing
through them. Only a few organs (brain and heart)
always carry full load of blood.
Blood flow to different organs is controlled by precapillary
sphincters of smooth muscle.
Types of Blood Vessels
Veins and Venules:

Collect blood from all tissues and organs and carry it back
towards heart.

Have low pressure and thin walls.

Veins have small valves that prevent backflow of blood
towards capillaries, especially when standing. If the
valves cease to work properly, may result in:

Varicose veins: Distended veins in thighs and legs.

Hemorroids: Distended veins and inflammation of the
rectal and anal areas.
Lymphatic and Immune System
Components: Lymph, lymphatic vessels, bone marrow, thymus,
spleen, and lymph nodes.
Functions:




Defends against infection: bacteria, fungi,
viruses, etc.
Destruction of cancer and foreign cells.
Synthesis of antibodies and other immune
molecules.
Synthesis of white blood cells.
Homeostatic Role:

Returns fluid and proteins that have leaked
from blood capillaries into tissues.
 Up to 4 liters of fluid every day.
 Fluid returned near heart/venae cavae.
Red Blood Cell Antigens


ABO system:
Major group of antigens of RBCs.

Type A:


Type B:


Only B antigens present.
Type AB:


Only A antigens present.
Both A and B antigens present.
Type O:

Neither A or B antigens present.
RBC Antigens
Each person inherits 2 genes that control
the production of ABO groups.
 Type A:
 May have inherited A gene from each
parent.
 May have inherited A gene from 1 parent
and O gene from the other.

RBC Antigens



Type B:
 May have inherited B gene from each parent.
 May have inherited B gene from 1 parent and O
gene from the other parent.
Type AB:
 Inherited the A gene from one parent and the B
gene from the other parent.
Type O:
 Inherited O gene from each parent.
Transfusion Reactions



If blood types do not match, the recipient’s
antibodies attach to donor’s RBCs and
agglutinate.
Type O:
 Universal donor.
 Recipient’s antibodies cannot agglutinate the
donor’s RBCs.
Type AB universal recipient:
 Lack the anti-A and anti-B antibodies.
 Cannot agglutinate donor’s RBCs.
Rh Factor




Another group of antigens found on RBCs.
Rh positive:
 Have these antigens.
Rh negative:
 Do not have these antigens.
Significant when Rh negative mother give birth to
Rh positive baby.
 At birth, mother may become exposed to Rh
positive blood of fetus.
 Mother at subsequent pregnancies may produce
antibodies against the Rh factor.