Blood & Immune SystemBlood & Immune SystemChapter 11 & 14Chapter 11 & 14

Blood & Immune SystemBlood & Immune SystemChapter 11 & 14Chapter 11 & 14

Physical characteristics of blood

Fluid connective tissue

matrix – “plasma” with dissolved proteins

cells & cell fragments – “formed elements”

temperature – 38o C

5x more viscous than H2O

pH – 7.35-7.45

Functions of Blood

Transportation

O2/CO2; nutrients/wastes; enzymes; hormones

Regulation body temperature; pH & ion composition of interstitial fluid; intracellular fluid volume

Protection

defense against pathogens; restriction of fluid loss at injury sites

Composition of Blood

55% Plasma – liquid component of blood

45% Formed elements – cells/cellular fragments

Erythrocytes – red blood cells (RBCs)

Leukocytes – white blood cells (WBCs)

Platelets

Plasma

Formed Elements

granular

agranular

Hemopoiesis

Megakaryoblast

Erythrocytes (RBCs) Biconcave shape, flexible cells

around 5 million RBCs per mm3 blood

average “life span” of 120 days

Cells contains cytosol, no nucleus/organelles; filled with Hemoglobin (Hb)

Hemoglobin

Hemoglobin allows for transport of O2 & CO2

As RBCs get damaged/worn out, they must be removed from circulation & replaced

About 1% of the circulating RBCs are replaced each day, at at rate of about 3 million RBCs per second

Worn out RBCs are removed by phagocytic cells in the liver, spleen & bone marrow

“globin” proteins will be broken down into amino acids to be re-used by cells to make new proteins

Iron will be separated from “heme” & can be stored in the liver, & be re-used to make new Hb

the pigmented part of heme will get converted to biliverden & bilirubin (pigments), & most will get excreted as part of bile from the liver

Hemoglobin recycling

Erythropoiesis

The formation of RBCs

Occurs in bone marrow (myeloid tissue) due to hypoxia detected in kidneys

Blood Typing There are many different surface antigens (transmembrane proteins) within the plasma membrane of your RBCs. These antigens (a.k.a. “agglutinogens”) are genetically determined.

Your surface antigens are recognized by your immune defense system as “self”.

The presence or absence of 3 specific antigens (A, B & Rh) determine your “blood type”

Within your plasma, you may have specific antibodies (a.k.a. “agglutinins”) against surface antigens that are not yours.

Plasma antibodies are responsible for “protecting” you from an incompatible blood type

Blood Typing

If the Rh antigen is also present, the person is Rh+, if they do not have the Rh antigen, they are Rh-

Blood TypingWhen you combine the information from the AB & Rh antigens, the possible blood types will be:

A+/A-

B+/B-

AB+/AB-

O+/O-

When considering whether a transfusion will be compatible, it is most important to consider the donor’s surface antigens & the recipient’s plasma antibodies

Blood Typing

Unlike the AB grouping, people who are Rh- do not genetically create antibodies against Rh in their plasma.

Antibodies will only be formed after an initial exposure to Rh

This could happen during an incompatible transfusion (i.e. A+ A- ), or during pregnancy if an Rh- mom is carrying an Rh+ baby.

Rh antibody formation in a mom who is carrying an Rh+ baby will lead to “hemolytic disease of the newborn”

Leukocytes (WBCs)

More like “typical” cells with single nucleus, organelles

5 types of WBCs characterized as granular or agranular

all function in defense

average 6000-9000 WBCs/mm3 of blood

variable “life” span depending on type of WBC- days (neutrophils) to decades (lymphocytes); in sick person, some WBCs live minutes to hours

Leukocytes (WBCs)WBCs exhibit common characteristics:

amoeboid movement

diapedesis

positive chemotaxis

phagocytosis

gliding movement of cell membrane/cytoplasm; allows WBCs to move along blood vessel walls & throughout tissues

can squeeze through epithelial cells of capillary walls to migrate into tissues

WBCs are attracted to chemicals released by invading pathogens & damaged tissues

neutrophils, monocytes, & eosinophils are phagocytic

Differential Count & Functions of WBCs

“WBC differential count” – normal range (in percentage) of WBCs in the peripheral circulation

differential count will vary during specific types of disorders, depending on which type of WBC responds

WBC response based on functions of specific type

Differential Count & Functions of WBCs Neutrophils - 50-70%

Lymphocytes – 20-30%

Monocytes – 4-8%

Eosinophils – 2-4%

Basophils - <1%

function in acute bacterial infections; phagocytic

function in “immunity” – specific resistance to disease

function in chronic bacterial infections; migrate into tissues to become “wandering macrophages”

active against parasites & elevated in allergic reactions; destroy antibody-coated antigens by phagocytosis

release chemicals (histamine, heparin) during tissue inflammation

Platelets (Thrombocytes)

Cellular fragments (cell membrane “packet” filled with cytoplasm) from large Megakaryocytes found within bone marrow

around 350,000 platelets/mm3

platelets circulate for 9-12 days before being removed from circulation

platelets function in “hemostasis” – the processes that stop bleeding from damaged blood vessels

HemostasisThere are three overlapping processes of hemostasis:

1. Vascular spasm – damage to BV wall causes the smooth muscle within the wall to spasm vasoconstriction & decreased blood loss through vessel; begins within a few seconds of injury, lasts about 30 minutes

2. Platelet plug formation – damaged BV endothelium gets sticky & circulating platelets stick to the endothelium & each other, creating a platelet plug; begins within 15 seconds of BV damage; may be enough to stop bleeding completely within a small BV (i.e. capillary)

3. Coagulation – blood clotting; complex series of steps resulting in the conversion of fibrinogen fibrin

Overview of Coagulation

• initiated by both “extrinsic” (tissue) & “intrinsic” (platelet) factors

• both pathways result in activation of Factor X (10)

• activation of Factor X begins the “common pathway”

• all 3 pathways require the presence of Ca2+ & vitamin K

Coagulation

Extrinsic pathway –

begins with damage to surrounding tissues & BV endothelium which cause the release of “tissue factors”

eventually results in the formation of an enzyme (“Factor X activator”) capable of activating Factor X

shorter, quicker pathway for initiation of coagulation

Intrinsic pathway –

begins with the release of “platelet factors”

eventually results in the formation of “Factor X activator”

more complicated, slower pathway of coagulation

Coagulation Common pathway –

begins with the activation of Factor X, by the production of Factor X activator from either the extrinsic or intrinsic pathway

the activation of Factor X results in the formation of the enzyme Prothrombinase

Prothrombinase converts Prothrombin (a clotting protein) Thrombin (an enzyme)

Thrombin converts Fibrinogen (soluble protein) Fibrin (insoluble protein strands that create the actual clot)

Clot Retraction, Repair & Removal Once the clot has begun to form, the fibrin threads & trapped platelets cause the edges of the damaged vessel to pull together causing “clot retraction”

Repair to the damage vessel & surrounding tissues occur as fibroblasts invade the area & endothelial cells regenerate

Eventually the clot gets removed by the enzyme “plasmin” in a process known as “fibrinolysis”

A clot which remains present in an intact vessel is known as a “thrombus”. Thrombi can block blood flow & pieces can dislodge creating an “embolism”

Immunity ( Chap 14, p. 464-471)

Humans have two major types of defense mechanisms: Non-specific defenses & Specific defenses

Non-specific defenses

do not distinguish between one threat and another

are present at birth

include: physical barriers (e.g. skin), phagocytic cells, inflammation, fevers, etc.

Specific defenses

protect against specifically identified threats (i.e. may defend against one particular bacterial infection but not a different one)

many specific defenses develop after birth upon exposure to an antigen (Ag); an antigen can be a pathogen (disease-causing organism), foreign protein (e.g. toxin), abnormal or infected body cell, foreign tissue transplant

specific defenses produce a state of long-term protection known as “Immunity”

Immunity ( Chap 14, p. 464-471)

Immunity = specific resistance to disease

depends on coordinated activity of T & B lymphocytes

T cells- involved in “cell-mediated (aka cellular) immunity”; defense against abnormal cells & intracellular pathogens

B cells- involved in “antibody-mediated (aka humoral) immunity”; defense against pathogens (Ag’s) in body fluids (blood/lymph)

Fig. 14-11)

Overview of Immunity

Immunity is either “innate” or “acquired”

Innate Immunity

present at birth

independent of previous exposure to Ag

genetically determined

species dependent

Acquired Immunity arises throughout life by active or passive means

Active immunity – development of resistance (i.e. antibody (Ab) production) to specific disease secondary to exposure to specific Ag (pathogen)

naturally acquired active immunity – natural exposure results in immune response & development of long term immunity

induced (artificial) active immunity – deliberate “artificial” exposure to Ag (i.e. vaccine/immunization)

Passive immunity – development of immunity due to transfer of “pre-made” antibodies

naturally acquired passive immunity – Ab’s transferred from mom baby across placenta or in breast-milk

induced (artificial) passive immunity – administration of Ab’s to fight disease after exposure to pathogen

Properties of Immunity

Immunity has four general properties:Specificity

Versatility

Memory

Tolerance

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Properties of Immunity Specificity – T & B cells have specific receptors that will allow them to only recognize & target a specific Ag; this process is known as “antigen recognition”

Versatility – millions of different lymphocyte populations, each with specific Ag recognizing receptors; allows for “anticipation” of potential Ag’s

Memory – after initial exposure, long term acquired immunity occurs through the production of memory cells; secondary exposure results in stronger faster response to previously recognized Ag

Tolerance – immune cells recognize self-antigens & “tolerate” (ignore) them, only going after foreign (non-self) Ag’s

Overview of the immune response The purpose of the immune response is to inactivate or destroy pathogens, abnormal cells & foreign molecules (such as toxins)

In order for the response to occur, lymphocytes must be “activated” by the process of antigen recognition

T cells are usually activated first, & then B cells. T cells mainly rely on activation by phagocytic cells collectively known as “antigen presenting cells (APC’s)”

Once activated, T cells both attack the invader, & stimulate the activation of B cells

Activated B cells mature into “plasma cells” which produce specific antibodies designed to inactivate the harmful antigen.

Cell Mediated (a.k.a. Cellular) Immunity

In order for T cells to respond, they must first be activated by exposure to an antigen which is bound to membrane receptors of phagocytic antigen presenting cells (APC’s) (“antigen recognition”)

These membrane receptors on cells are called “MHC proteins” (major histocompatibility complex proteins), & are genetically determined (i.e. differ among individuals)

Antigens bound to MHC proteins “tell” the T lymphocyte what the specific foreign invader is (i.e. a specific bacteria) so that the lymphocytes can mount a cellular defense

Cell Mediated (a.k.a. Cellular) ImmunityOnce a T cell is activated by the presentation of the combined MHC/Ag, it will clone (by mitosis) & differentiate into:

cytotoxic T cells – seek out the specific pathogen/infected cell that contains the targeted Ag & destroys it by secreting various chemicals

helper T cells – necessary for coordination of both specific & non-specific defenses, as well as for stimulating both cell-mediated & antibody-mediated immunity.

In cell-mediated immunity they release chemicals (cytokines) that strengthen the activity of cytotoxic T cells.

In antibody-mediated immunity they release cytokines that stimulate activated B cell division & differentiation into plasma cells

Cell Mediated (a.k.a. Cellular) Immunity

memory T cells – remain “in reserve” so if same Ag appears, these cells can immediately differentiate into cytotoxic & helper T cells, causing a swift secondary response to the invasion

suppressor T cells – activated more slowly than the other T cells; inhibit the response of the immune cells to prevent potential “autoimmune” response

Antigens

bacteria

viruses

ANTIGENS

bacteria

viruses

SPECIFIC DEFENSES

(Immune response)

CELL MEDIATED IMMUNITY

APC’s phagocytize Ag & activate T cells

Direct physical &

chemical attack

Activated T cells clone & differentiate into: Cytotoxic T cells Helper T cells Memory T cells Suppressor T cells

Antibody Mediated (Humoral) Immunity B cells must also be activated before they can respond to an invading Ag

The body has millions of different B cell populations, each B cell has its own particular antibody (Ab) molecule within its cell membrane

When the corresponding Ag invades the interstitial fluid surrounding the B cell, the Ag binds to the Ab & is taken into the cell, eventually being displayed on the B cell’s MHC protein. The B cell is now “sensitized”

Helper T cells (that had been previously activated to the same Ag) then attach to the sensitized B cells & activate them by secreting chemicals (cytokines)

Cytokine secretion results in B cell cloning & differentiation into plasma cells & memory cells

Antibody Mediated (Humoral) Immunity

Plasma cells produce millions of copies of antibodies which are released into the blood & lymph

Antibodies seek out & bind to the Ag forming an “Ab-Ag complex”, eventually leading to the elimination of the antigen by various means

Memory cells remain in reserve to respond to any subsequent exposure by the same Ag. Upon secondary exposure, memory B cells quickly differentiate into Ab producing plasma cells

Antibody Mediated (Humoral) Immunity

Antibody Mediated (Humoral) Immunity

Review of Immune Response