Cardiovascular System

Blood

Composition of Blood

Blood is the body’s only fluid tissue It is composed of liquid plasma and formed elements Formed elements include:

– Erythrocytes, or red blood cells (RBCs)– Leukocytes, or white blood cells (WBCs)– Platelets (Thrombocytes)

Hematocrit – the percentage of RBCs out of the total blood volume

Composition of Blood

Figure 18.1

Physical Characteristics and Volume

Blood is a viscous, opaque fluid with a metallic taste.

Color varies from scarlet (oxygen-rich) to dark red (oxygen-poor)

The pH of blood is 7.35–7.45Temperature is 38C, slightly higher than

“normal” body temperatureAverage volume of blood is 5–6 L for males,

and 4–5 L for females

Functions of BloodTransports gases, nutrients,

hormones, and metabolic wastes

Regulates pH and electrolyte balance

Hemostasis: maintains blood volume

Defends the body against toxins and pathogens

Stabilizes body temperature

Blood Plasma

Plasma makes up 55% of the total blood volume:– 92% of plasma is water– Proteins

Albumins: maintain osmotic pressure of blood Globulins: antibodies and transport proteins Fibrinogens: involved in blood clotting

– Nonprotein nitrogenous substances – lactic acid, urea, creatinine

– Organic nutrients – glucose, carbohydrates, amino acids– Electrolytes – sodium, potassium, calcium, chloride,

bicarbonate – Respiratory gases – oxygen and carbon dioxide

Erythrocytes (RBCs)

Biconcave discsLack a nucleusFilled with hemoglobin

(Hb), a protein that functions in transporting Oxygen and Carbon Dioxide

Normally produced in the red marrow of bones.

Erythrocyte Function Erythrocytes are dedicated to respiratory gas transport Hemoglobin reversibly binds with oxygen and carbon

dioxide Hemoglobin is composed of:

– The protein globin, made up of two alpha and two beta chains, each bound to a heme group.

– Each heme group carries an atom of iron, which can bind to oxygen.

– As oxygen levels decrease, hemoglobin molecules release oxygen and the globin portion binds to carbon dioxide.

Each hemoglobin molecule can transport four molecules of oxygen

Erythrocyte Function

Hormonal Control of Erythropoiesis

Erythropoietin (EPO) release by the kidneys is triggered by:– Hypoxia (low oxygen) due to decreased RBCs– Decreased oxygen availability (high altitude)– Increased tissue demand for oxygen (exercise)

Enhanced erythropoiesis increases the: – RBC count in circulating blood– Oxygen carrying ability of the blood increases

Hormonal Control of Erythropoiesis

Figure 18.6

Leukocytes (WBCs)

Leukocytes, the only blood components that are complete cells:– Are less numerous than RBCs– Make up 1% of the total blood volume (normal count

6000-9000 per cubic mm.)– Can leave capillaries through tissue spaces via

diapedesisLeukocytosis – WBC count over 11,000 per

cubic mm.– Normal response to bacterial or viral invasion

Leukocytes (WBCs)Two categories:

– Granulocytes:Neutrophils: Phagocytic, release cytotoxic

chemicalsEosinophils: attack antibody-labeled and parasitic pathogensBasophils: release histamines, enhance

inflammation– Agranulocytes

Lymphocytes: provides specific immune response

Monocytes: macrophages engulf pathogens or debris

Platelets

Cell fragments Functions in the clotting mechanism (Hemostasis) Forms a temporary “Platelet Plug” that helps seal

breaks in blood vessels.

Red blood cells

White blood cells

Platelets

LymphocyteNeutrophil

Monocyte

Eosinophil

Lymphocyte

Basophil

Monocyte

Neutrophil

1

2

3

4

5

6

1. Monocyte

2. Lymphocyte

3. Eosinophil

4. Neutrophil

5. Basophil

6. Neutrophil

Sickle cell anemia: abnormal formation of hemoglobin, which causes RBC’s to be deformed, and causes poor oxygen circulation, and blood clots.

Leukemia: Cancer of blood forming tissues, causing elevated levels of and abnormal formation of WBC’s.

Hemostasis

A series of reactions designed for stoppage of bleeding

During hemostasis, three phases occur in rapid sequence– Vascular Phase– Platelet Phase– Coagulation (blood clotting) Phase

Hemostasis

Hemostasis

Vascular Phase:– Smooth muscles in the walls of blood vessels

constrict– The decrease in the diameter of the blood vessel

slows and sometimes stops blood loss.– Endothelial cells at an injury site become sticky, and

cells may stick together further blocking the injury site.

Hemostasis

Platelet Phase:– Platelets attach to “sticky” endothelial cells at the

injury site.– As more platelets arrive, a “Platelet Plug” forms, a

mass of cells that may block the break in the vessel wall.

Hemostasis

Coagulation Phase:– Coagulation = Blood Clotting– Occurs when a series of steps results in the formation

of fibrin.– Fibrin is an insoluble protein “net” that traps blood

cells and platelets which form a blood clot.– The blood clot seals off the damaged portion of the

blood vessel.

Blood Typing

A system of categorizing blood based on the surface antigens of RBC’s (agglutinogens)

Three of the most important antigens: A, B and Rh

When serum containing anti-A or anti-B agglutinins is added to blood, agglutination will occur between the agglutinin and the corresponding agglutinogens

Positive reactions indicate agglutination (clumping) and incompatible blood type.