Chief function of blood
- Delivery of substances needed for cellular metabolism
- Removal of wastes
- Defense against microorganism and injury
- Maintenance of acid-base balance
Composition of blood
•Body contains 6 quarts of blood
* Plasma * Plasma proteins * Cells
Plasma
- Fluid component
- 90% water and 10 % solutes
- Organic and inorganic
Plasma proteins
•Produced in the liver
* Albumins (most abundant)
* Function as carriers and control the plasma oncotic pressure
* Globulins
* Carrier proteins and immunoglobulins (antibodies)
* Clotting factors
* Mainly fibrinogenCells (Formed elements)
- Erythrocytes (Red blood cells)
- Leukocytes (white blood cells)
- Thrombocytes (platelets)
Erythrocytes (Red blood cells)
- Most abundant cells of the blood
- primarily responsible for tissue oxygenation
- Bioconcavity and reversible deformity
- lacks nucleus
Leukocytes (White blood cells)
•Defend the body against organisms that cause infection and also remove debris, including dead or injured host cells of all kinds
- Granulocytes
- Granules in cytoplasm contain enzymes
- Inflammatory and immune functions
•Agranulocytes
Granulocytes
mnemonic - BEN
- Neutrophils
- Phagocytes in early inflammation
- Eosinophils
- Eosinophils ingest antigen-antibody complexes
- Induced by IgE hypersensitivity
- Immune fighting in parasitic infections
- Basophils
- Central cell in inflammation
- Basophils = in blood
- Mast cells = vascularized connective tissue (not WBC)
Agranulocytes
are known as mononuclear leukocytes, are white blood cells with a one-lobed nucleus. They are characterized by the absence of granules in their cytoplasm.
*Monocytes and macrophages make up the mononuclear phagocyte system (MPS)
- Lymphocytes
- T cells - maturated in the thymus
- B cells - produce antibodies
* immature B cells are produced in the bone marrow and migrate to secondary lymphoid tissues where some develop into mature B cells. - Natural kill (NK) cells
- a lymphocyte able to bind to certain tumor cells and virus-infected cells without the stimulation of antigens, and kill them by the insertion of granules containing perforin.
Thrombocytes (Platelets)
A platelet. Crucial to normal blood clotting. Although platelets are sometimes classed as blood cells, they are not. They are fragments of a large cell called a megakaryocyte (literally, a large cell).
Thrombopoietin
a hormone that regulates blood platelet production by promoting the proliferation and maturation of megakaryocyte progenitor cells and the development of megakaryocytes into blood platelets
*The Liver is the major producer of Thrombopoietin in the human body.
Spleen
- The largest secondary lymphoid organ
- Masses of lymphoid tissue containing macrophages, T cells, B cells
- Phagocytosis of old, damaged, and dead blood cells
- blood storage
Lymph nodes
A small bean-shaped structure that is part of the body’s immune system and hematologic system
- Facilitates maturation of lymphocytes
- Transports lymphatic fluid back to the circulation
- Cleanses the lymphatic fluid of microorganisms and foreign particles
Mononuclear Phagocyte System (MPS)
- The MPS consists of monocytes in blood and mature macrophages in the tissues
- Cells of the MPS ingest and destroy microorganisms and foreign material
- The MPS is mostly in the liver and spleen
Hematopoiesis
The formation and development of blood cells
*Production in the spleen and liver of the fetus and only in the bone marrow after birth
- Two stages
- Mitosis
- Maturation and differentiation
- Pluripotent stem cells
- One of the “cells that are self-replicating, are derived from human embryos or human fetal tissue, and are known to develop into cells and tissues of the three primary germ layers
Bone marrow
There are two types of bone marrow:
•RED or active (hematopoietic), also called myeloid tissue
* Produces red blood cells, white blood cells and platelets
* Gets its red color from the hemoglobin in the erythroid cells
* Hematopoietic cells mature and migrate into sinusoids to enter the circulation when they are formed.
* Highly vascular
•YELLOW or stromal
* Produces fat, cartilage, and bone
* Gets its yellow color from the carotenoids in the fat droplets in the high number of fat cells
* Paucity of vasculature- Adult active bone marrow found:
- Pelvic bones, vertebrae, cranium and mandible, sternum and ribs, humerus and femur
Erythropoiesis
The production of red blood cells.
- Erythrocytes are derived from erythroblasts (normoblasts)
- Maturation is stimulated by erythropoietin
- Erythropoietin is produced by the kidney
*In each step the quantity of hemoglobin increases and the nucleus decreases in size
Regulation of erythropoiesis
*Numbers of circulating red cells in healthy individuals remain constant
- Hypoxia stimulates the production and release of erythropoietin
- Increase production of RBCs and release from marrow
*The peritubular cells of the kidney produce erythropoietin (EPO)
Hemoglobin
- Oxygen-carrying protein of the erythrocyte
- A single erythrocyte contains as many as 300-400 million hemoglobin molecules
- Two pairs of protein subunits (globins)
- Each subunit contains iron-protoporphyrin complex (heme)
Nutritional requirements for hemoglobin (Hb) synthesis
*Proteins / Amino acids
- Vitamins
- B12, B6, B2, E, and C; folic acid; pantothenic acid; and niacin
- Minerals
- iron and copper
*Folate
Destruction of Aged RBCs
- Aged red cells (senescent) are destroyed by macrophages of the MPS
- Primarily in the spleen
- The liver takes over if the spleen is non-functioning/ absent
- Globin chains are broken down into amino acids
- Porphyrin is reduced to bilirubin, transported to the liver, and secreted in the bile
- Role of B12 & Folate in RBC life span
Leukopoeisis
- Leukocytes arise from stem cells in the bone marrow
- Granulocytes mature in the bone marrow
- Agranulocytes are released into the bloodstream before they fully mature
Thrombopoeisis
- Endomitosis
- The megakaryocyte undergoes the nuclear phase of cell division but fails to undergo division
- The megakaryocyte expands due to the doubling of the DNA and breaks up into fragments
- Platelet levels are maintained by thrombopoietin
- Platelets circulate for 10 days before losing their functional capacity
Hemostasis
- Hemostasis means to arrest or stop bleeding
- Requires:
- Platelets
- Clotting factors
- Blood flow and shear forces
- Endothelial cells
- Fibrinolysis
