Blood

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Blood: Brief Notes
Composition and Functions of Blood Hematopoiesis_ Hemostasis		Links for Journal Club Blood safety in an age of AIDS Blood bank safety Protecting Blood Supply
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What_can_you_learn from a blood test?
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Composition and Functions of Blood

Blood Concept Map
Blood Power Point

Functions of Blood

	1.	Transports oxygen, carbon dioxide
	2.	Regulates temperature, pH
	3.	Protection from damage and foreign invaders

Components of Blood

		Function
Plasma (Liquid phase)		Solvent, suspension, liquid matrix
Formed elements (Solid phase)
	Platelets (thrombocytes)	Participate in clotting
BLOOD CELLS
	Erythrocytes (Red blood cells)	Transport O2, CO2
	Leukocytes (White blood cells)	Immunity / Protection
	Neutrophils	Acute infections
	Eosinophils	Parasites, Allergies
	Basophils	Allergies, Tissue damage
	Monocytes	Chronic infections
	Lymphocytes	Immunity (antibodies & cellular immunity)

Hematopoiesis - Formation of Blood Cells

Blood cells produced in:

Embryo – yolk sac

Birth – bone marrow (spleen, liver)

To maturity - # sites in bone marrow decreases

Adult – flat bones, vertebrae, prox. femur, pelvis

Pluripotent stem cells à all blood cells

Hematopoiesis:
General Principles

Cells arise from pluripotent stem cells (hemocytoblast) in bone marrow

Maturation pathways differ

Once a cell is committed, it cannot change

Hematopoiesis:
General Principles

Commitment signaled by membrane surface proteins (receptors) that respond to hormones or growth factors

Receptors à further specialization

Erythropoiesis: RBC

Stem cell: Hemocytoblast à

Committed cell: Proerythroblast

3 phases à mature cell

Time: 3 – 5 days

Control of RBC Production

Regulated by ability to carry O₂

Kidney produces erythropoietin (EPO) when O₂ decreases

EPO stimulates committed cells in red marrow to mature more rapidly

1-2 days à increase reticulocyte count

Genetically engineered EPO used by kidney dialysis patients

RBC disorders: Anemia

Anemia – Symptom of underlying problem

Means "lacking blood"

fatigue, shortness of breath, pale, chilly

Low hemoglobin content due to:

Iron deficiency

Increased blood volume

Abnormal Hemoglobin

Thalassemia

Sickle cell anemia

RBC disorders: Polycythemia

•Abnormal excess RBC

•Blood is too thick à clots, stroke, heart failure

•Bone marrow cancer

•High altitudes

•Blood doping (athletes)

What can you learn from a blood test?

Hemostasis: Stop the bleeding!

Normal blood vessel showing
RBC, WBC, platelets,
clotting factors (CF).

A break in the vessel wall begins leaking blood.

Spasms in blood vessel wall prevent blood loss (not shown)

1. Vasoconstriction

Injury to blood vessel

Vessel constricts

Blood loss reduced

Platelets stick together to form a plug at injury site.

2. Formation of Platelet Plug

Platelets adhere to exposed collagen fibers forming a
barrier against blood loss

Cascade of reactions à formation of a fibrin mesh to hold clot in place.

> 30 substances involved

3. Coagulation

Cascade of reactions begins

Creates a network of fibers that hold clot in place

This is a positive feedback mechanism: each step further amplifies
the clotting process

Coagulation

Phase 1:

2 pathways:

Intrinsic factors – present in blood

Extrinsic factors – produced by tissue trauma

Goal: Produce prothrombin activator

Coagulation cascade

Phase 2

Regulated at many steps

Precursors in system à active form

Small stimulus becomes magnified with cascade reactions

Watch: Hemostasis in action

Inappropriate clotting

Thrombus – clot formation in unbroken vessel

Embolism – floating clot

Therapy – anti-coagulants block clotting at specific steps.

Example: Aspirin blocks platelet aggregation

Bleeding disorders

1. Thrombocytopenia

Decreased platelets<