module 2 systems physiology

Functions of Blood (3 main functions)

Transport; Regulation; Protection

Transport function of blood

Transports O2 and nutrients to body cells; Transports metabolic wastes to lungs and kidneys

Regulation functions of blood

Maintains body temperature by absorbing and distributing heat; Maintains normal pH; Maintains adequate fluid volume in circulatory system

Protection functions of blood

Prevents blood loss; Platelets initiate clot formation; Prevents infection through antibodies and white blood cells

Plasma

About 55% of blood; Liquid portion of blood

Formed elements

About 45% of blood; Includes red blood cells, white blood cells, and platelets

Buffy coat

Thin layer between plasma and red blood cells; Contains white blood cells and platelets

Layers of centrifuged blood

Top: Plasma (~55%); Middle: Buffy coat (WBCs and platelets); Bottom: Red blood cells (~45%)

Erythrocytes

Red blood cells

Function of erythrocytes

Contain hemoglobin; Transport oxygen and carbon dioxide

Hemoglobin

Protein in red blood cells that transports oxygen

Components of hemoglobin

Globin chains and heme groups

Globin chains

Polypeptide chains in hemoglobin

Heme group

Contains iron (Fe2+)

Role of iron in hemoglobin

Iron binds oxygen allowing oxygen to attach to hemoglobin

Types of blood vessels

Arteries; Arterioles; Capillaries; Venules; Veins

Two circulatory circuits

Systemic circulation and pulmonary circulation

Pulmonary circulation

Carries oxygen-poor blood and returns oxygen-rich blood

Systemic circulation

Carries oxygen-rich blood and returns oxygen-poor blood

Blood pressure

Force exerted by blood; Measured in mmHg

Direction of blood flow

Blood flows from region of higher pressure to region of lower pressure

Flow

Volume of blood moved per unit time; Measured in mL/min

Resistance

Difficulty for blood to flow between two points; Measure of friction that impedes flow

Blood viscosity

Thickness of blood

Cause of viscosity

Friction between molecules of a flowing fluid

Factors affecting viscosity

Water volume; Number of erythrocytes

Total blood vessel length

Remains constant

Blood vessel radius effect

Dilated vessels decrease resistance; Constricted vessels increase resistance

Most important determinant of resistance

Blood vessel radius

Symptom of low iron levels

Fatigue due to decreased hemoglobin and decreased oxygen delivery

Hematopoiesis

Formation of all blood cells

Hematopoietic stem cells

Hemocytoblasts; Give rise to all formed blood elements

Committed cells

Cells that cannot change into another cell type

RBC developmental pathway

Hematopoietic stem cell → Proerythroblast → Basophilic erythroblast → Polychromatic erythroblast → Orthochromatic erythroblast → Reticulocyte → Erythrocyte

Phase 1 of RBC development

Ribosome synthesis

Phase 2 of RBC development

Hemoglobin accumulation

Phase 3 of RBC development

Ejection of nucleus

Erythropoiesis

Process of formation of red blood cells; Takes about 15 days

Reticulocyte count

Measure of erythropoiesis

Low reticulocyte count

<0.5%; Low rate of erythropoiesis

High reticulocyte count

>2%; High rate of erythropoiesis

Too few RBCs cause

Tissue hypoxia

Too many RBCs cause

Increased blood viscosity

Iron in the body

65% in hemoglobin; Rest stored in liver, spleen, and bone marrow

Iron storage proteins

Ferritin and hemosiderin

Iron transport protein

Transferrin

Vitamins required for RBC production

Vitamin B12 and folic acid

Function of vitamin B12 and folate

Required for DNA synthesis during RBC development

Erythropoietin (EPO)

Hormone that stimulates formation of red blood cells

Target organ of EPO

Red bone marrow

Causes of hypoxia

Decreased RBC numbers; Insufficient hemoglobin; Reduced oxygen availability

Examples of reduced oxygen availability

High altitude; Lung diseases such as pneumonia

Regulation of EPO

High oxygen levels inhibit EPO; Too many erythrocytes inhibit EPO

Effect of testosterone on EPO

Increases EPO production leading to higher RBC counts in males

Why athletes abuse EPO

Increases hematocrit; Improves stamina and athletic performance

Danger of EPO abuse

Increased blood viscosity leading to blood clots, stroke, and heart failure

RBC lifespan

About 120 days

RBC destruction

Old RBCs become fragile; Hemoglobin degenerates; Spleen macrophages engulf dying RBCs

Hemoglobin breakdown products

Heme; Iron; Globin

Iron after RBC breakdown

Stored as ferritin or hemosiderin

Heme breakdown

Converted into bilirubin

Fate of bilirubin

Secreted in bile and enters intestines

Urobilinogen

Formed from bilirubin in intestines

Stercobilin

Formed from urobilinogen and excreted in feces

Globin breakdown

Broken into amino acids and reused

Major erythrocyte disorders

Anemia and polycythemia

Anemia

Low oxygen-carrying capacity of blood insufficient for normal metabolism

Anemia symptoms

Fatigue; Pallor; Dyspnea; Chills

Iron deficiency anemia

Caused by dietary iron deficiency or impaired absorption; Common in menstruating women

Pernicious anemia

Vitamin B12 deficiency caused by autoimmune destruction of stomach mucosa preventing intrinsic factor production

Treatment for pernicious anemia

Vitamin B12 injections or nasal gel

Aplastic anemia

Bone marrow failure caused by toxic drugs or cancer; All formed blood elements decrease

Results of aplastic anemia

Clotting problems and immune defects

Treatment for aplastic anemia

Bone marrow transplant

Hemorrhagic anemia

Caused by rapid blood loss such as bleeding ulcer

Treatment for hemorrhagic anemia

Blood replacement and stopping bleeding

Renal anemia

Caused by inadequate EPO secretion from kidneys

Treatment for renal anemia

Synthetic EPO

Hemolytic anemia

Excessive destruction of RBCs; Example sickle cell disease

Polycythemia

Abnormal excess of RBCs causing increased blood viscosity

Polycythemia vera

Bone marrow cancer causing excess RBC production; Hematocrit >80%

Treatment for polycythemia vera

Therapeutic phlebotomy

Secondary polycythemia

Caused by low oxygen levels or increased EPO production

Examples of secondary polycythemia

High altitude; Excess EPO

Outcome of EPO overdose

Increased blood viscosity leading to heart attacks or strokes

Normal blood composition

55% plasma; 45% RBCs

Polycythemia blood composition

20% plasma; 80% RBCs

Leukocytes

White blood cells; Function is defense against disease and infection

Normal WBC range

4,800-10,800 WBCs per µL of blood

Leukocytosis

WBC count greater than 11,000 per µL; Usually response to infection

Two categories of leukocytes

Granulocytes and agranulocytes

Granulocytes

Neutrophils; Eosinophils; Basophils

Agranulocytes

Lymphocytes and monocytes

Neutrophils

60-70% of leukocytes; Phagocytic; Destroy bacteria; Contain defensins

Eosinophils

2-4% of leukocytes; Destroy parasitic worms; Involved in allergies and asthma

Basophils

0.5-1% of leukocytes; Release histamine; Involved in allergic reactions

Mast cells

Basophils that leave blood and enter tissues

Histamine

Inflammatory chemical causing vasodilation and attracting WBCs

Lymphocytes

20-25% of leukocytes; Important for immunity

T lymphocytes

Attack virus-infected cells and tumor cells