Blood

Blood

Connective tissue consisting of a liquid matrix (plasma) and formed elements (cells and cell fragments)

Primary functions of blood

Transportation, regulation, protection, and clot formation

Transportation (blood)

Oxygen, nutrients, waste products

Signaling molecules in blood

Hormones

Blood pH regulation

Buffers in blood maintain acid-base balance

Blood osmotic regulation

Exchange of ions between blood and tissues

Thermoregulation (blood)

Heat distribution via movement to skin surface

Immune protection (blood)

WBCs defend against pathogens

Clotting function (blood)

Prevents excessive blood loss

Plasma

Liquid matrix of blood (~55% of total blood volume)

Plasma composition

91% water, 9% solutes

Plasma proteins

Albumins, globulins, fibrinogen

Formed elements

Cells and cell fragments (~45% of blood)

Total blood volume (female)

4–5 L

Total blood volume (male)

5–6 L

Red blood cells (RBCs)

Erythrocytes; most abundant cells (~95% of blood cells)

RBC structure

Biconcave, no nucleus

RBC function

Transport oxygen and carbon dioxide

Hemoglobin

Protein in RBCs that carries oxygen

Hemoglobin structure

4 subunits (globin chains + heme groups with iron)

Oxygen transport in blood

98.5% bound to hemoglobin

RBC lifespan turnover

~2.5 million destroyed per second

Daily RBC replacement

~1% replaced daily

Nutrients needed for RBC production

Iron, vitamin B12, folate

Organ that removes old RBCs

Spleen

Hormone that stimulates RBC production

Erythropoietin (EPO)

Organ that releases EPO

Kidneys

Trigger for EPO release

Low blood oxygen levels

White blood cells (WBCs)

Leukocytes; immune cells (~5% of blood cells)

do wbcs have a nucleus?

yes unlike RBCs

Platelets

Cell fragments derived from megakaryocytes

Platelet function

Assist in clotting and blood loss prevention

Platelet lifespan

5–9 days

Platelet surface proteins

Allow adhesion to damaged vessels

Hematopoiesis

Production of blood cells

Location of hematopoiesis (embryo)

Yolk sac, liver, spleen, thymus, lymph nodes, bone marrow

Location of hematopoiesis (adult)

Red bone marrow

Exception for WBC development

T cells mature in thymus

Hemocytoblasts

Stem cells that give rise to all blood cells

Differentiation

Process by which cells become specialized

Two stem cell lines

Myeloid stem cells and lymphoid stem cells

Lymphoid stem cells

Produce lymphocytes (B cells, T cells)

Myeloid stem cells

Produce RBCs, platelets, and several WBC types

Proerythroblasts

Develop into RBCs

Myeloblasts

Develop into innate immune cells

Monoblasts

Develop into monocytes

Megakaryoblasts

Develop into platelets

Hemostasis

Cessation of bleeding

hemorrhage

failure of hemostasis (excessive bleeding)

Three steps of hemostasis

Vascular spasm, platelet plug formation, coagulation

Vascular spasm

Constriction of blood vessels to reduce blood loss

Trigger of vascular spasm

Endothelins released from damaged vessel lining

Endothelin receptor antagonists (ERAs)

Drugs used to treat pulmonary hypertension

Platelet plug formation

Temporary seal formed by platelets

Steps of platelet plug formation

Adhesion, release reaction, aggregation

Coagulation

Process of blood clot formation

Blood clot

Fibrin mesh trapping cells and fluid

Clotting factors

Plasma proteins required for coagulation

Activation of clotting factors

Occurs in cascade after injury

Calcium role in coagulation

Required for some reactions

Coagulation cascade

Series of reactions activating clotting factors

Extrinsic pathway

Triggered by external tissue damage

Intrinsic pathway

Triggered by internal vessel damage

Common pathway

Final pathway leading to fibrin formation

Extrinsic pathway steps

Damage → Factor III → Factor VII → Factor X → common pathway

Intrinsic pathway steps

Factor XII → XI → IX + VIII → Factor X → common pathway

Factor VIII deficiency

Hemophilia A

Common pathway steps

Factor X → prothrombin → thrombin → fibrinogen → fibrin

Fibrin

Insoluble protein forming clot mesh

Fibrinolysis

Breakdown of clot

Enzyme for fibrinolysis

Plasmin

Bradykinin

Causes vasodilation after clot formation

Complete blood count (CBC)

Blood test measuring key components

Hematocrit

Percentage of blood volume made of RBCs

Erythrocytosis

Too many RBCs

Causes of erythrocytosis

Dehydration, cancer

Effect of erythrocytosis

Thick blood, harder to pump, hypertension risk

Anemia

Low hemoglobin levels

Causes of anemia

Iron deficiency, folate deficiency, blood loss, bone marrow issues

Leukemia

Cancer of red bone marrow

Leukocytosis

Elevated WBC count indicating infection or inflammation

HIV progression to AIDS

CD4 count <200 cells/mm³

Normal CD4 count

500–1600 cells/mm³