Blood Animal Histology BIOL 241 Topic 7: Dr. Issa Al-Amri Department of Biological Sciences & Chemistry College of Arts & Sciences

Introduction A. Blood composed of fluid component called plasma, and formed elements suspended in plasma which are: 1. Red blood cells (erythrocytes) 2. White blood cells (leukocytes) 3. Platelets (thrombocytes) B. Volume of blood in average human adult = 5 L

Blood smear TEM: platelets TEM: red blood cell in capillary

Introduction C. Blood circulates in blood vessels performing following general functions: Transports nutrients, hormones, proteins, ions, oxygen (O2), carbon dioxide (CO2) and formed elements. Removes metabolic waste products. Regulates body temperature. Regulates osmotic and acid-base balance. Defends body against microbial invasion. D. Blood cells short life spans and continuously replaced by a process called homeopoiesis.

Blood constituents Plasma: Main plasma proteins: 91% water. 9% organic compounds (proteins, amino acids, hormones), inorganic salts, dissolved gases, and nutrients. Main plasma proteins: Albumin (preserves osmotic pressure, transport metabolites) ϒ-globulin (antibodies, or immunoglobulins) α & ß globulins (metal ion transport proteins) Fibrinogen (clotting proteins) Complement proteins: C1-C9 (initiate inflammatory process) 2. Serum: Yellow fluid remains after blood has clotted. Similar to plasma but lacks fibrinogen and clotting factors.

Blood constituents Formed elements of blood (studied by blood smear) Erythrocytes (red blood cells or RBCs) General features: RBCs round, anucleate, bioconcave cells, stain light pink with Giemsa stain. Average life span of an RBC is 120 days. Aged RBCs destroyed by splenic, hepatic, and bone marrow macrophages. Carbohydrate determinants for A, B, and O blood groups located on surface of RBC plasmalemma. Cytoskeletal proteins maintain shape of RBCs. Mature RBCs: no organelles but filled with hemoglobin (Hb). Contain enzymes for glycolysis, ATP production.

Blood constituents Hematocrit: Estimation of volume of packed erythrocytes per unit volume of blood: Hematocrit expressed as a percentage. Normal values: men (40%-50%) women (35%-45%), children (35%), newborns (45%-60%). Hb: Protein composed of four polypeptide chains, each covalently linked to a heme group. The four chains normally occur in humans: α, β, ϒ and δ. Each chain differs in its amino acid sequence. d. Transport: of CO2 and O2 to and from the tissues of the body carried out by erythrocytes and plasma.

Blood constituents Leukocytes (white blood cells or WBCs) Divided into two major groups: Granulocytes (granular leukocytes) Agranulocytes (non-granular leukocytes) a. Granulocytes Include: neutrophils, eosinophils, and basophils Contain specific cytoplasmic granules, lobed nuclei (2 – 5 lobes) Contain 2 types of granules: 1. Azurophilic granules: nonspecific, contain lysosomal enzymes Specific granules: according to which granulocytes classified Destruction of phagocytosed microorganisms by neutrophils by release of hydrolytic enzymes into phagosomes to destroys them. Granulocytes are nondividing cells with life span of few days, die in connective tissue by apoptosis.

Blood constituents Agranulocytes Lack specific granules but have nonspecific granules. Include lymphocytes and monocytes 1. Lymphocytes: three categories of lymphocytes: B lymphocytes, T lymphocytes, and null cell. B cells are responsible for the humoral immune response. T cells are responsible for the cellular immune response. Null cells are two types; pluripotential hemopoietic stem cells (PHSCs) and natural killer (NK) cells. They lack surface determinants of T and B cells. Monocytes: largest leukocytes (12-20 µm diameter) Phagocytic cells

Blood constituents Platelets (thrombocytes) Anucleated disk-shaped cell fragments arise from megakaryocytes in bone marrow. Surrounded by glycocalyx, which coats the plasmalemma. Calcium ions and adenosine diphosphate (ADP) increase stickiness of glycocalyx and enhance platelet adherence. Function in blood coagulation by aggregating at lesions in vessel walls and produce various factors aid in clot formation. Responsible for clot retraction and contribute to clot removal.

Bone marrow Bone marrow One of largest organs of the body. Main location of hemopoiesis. Specialized connective tissue, derived from mesenchyme. Present as two forms, yellow and red. Yellow marrow: located in long bones of adults. Its main function is fat storage. Red marrow: located in epiphyses of long bones and in flat, irregular, and short bones. Site of blood differentiation and maturation. Composed of a stromal cells (macrophages, reticular cells, fibroblasts, endothelial cells), sinusoids (large vessels), and isands of hemopoietic cells Largest cells of bone marrow are megakaryocytes (precursors of platelets).

Red bone marrow

Yellow bone marrow

Bone marrow and circulating blood Figure 1 : Bone marrow -haversian canals (H) -Volkmann’s canals (V) -osteocytes (O) -endosteum (E) -advential reticular cells (A) -sinusoids (S) megakaryocytes (M) -small nuclei (arrow) Figure 2: Bone marrow -higher mag. of fig.1 -sinusoids (arrows) Figure 3: Blood smear -erythrocytes (R) -neutrophils (N) -platelets Figure 4: Bone marrow smear -erythrocytic series (arrows) -granulocytic series (arrowheads)

Hemopiesis Hemopoiesis: Hemopoiesis or hematopoiesis is formation of blood elements. Achieved by continuous replacement by stem cells located in myeloid tissue or hemopoietic tissue. In prenatal: blood cells arise from mesoderm of yolk sac, then from spleen, liver and bone marrow. In postnatal: blood elements are derived from stem cells (capable of self-renewal and undergo enormous proliferation) located in red bone marrow.