Chapter 10

Blood LectureBlood Composition

Blood

Formed elements living blood "cells" suspended in plasma

Erythrocytes (red blood cells, or RBCs)

Leukocytes (white blood cells, or WBCs)

Platelets Spun tube of blood yields three layers

Hematocrit 47% 5% for males; 42% 5% for females

Physical Characteristics and Volume

Functions of Blood

Distributing substances

Regulating blood levels of substances

Protection

Distribution Functions

Regulation Functions

Protection Functions

Blood Plasma

90% water

Over 100 dissolved solutes

Nutrients, gases, hormones, wastes, proteins, inorganic ions

Plasma proteins most abundant solutes

Remain in blood; not taken up by cells

Proteins produced mostly by liver

60% albumin; 36% globulins; 4% fibrinogen

Albumin

Functions

Formed Elements

Erythrocytes

Erythrocytes

Structural characteristics contribute to gas transport

Biconcave shapehuge surface area relative to volume

>97% hemoglobin (not counting water)

No mitochondria; ATP production anaerobic; do not consume O2 they transport

Superb example of complementarity of structure and function

Erythrocyte Function

RBCs dedicated to respiratory gas transport

Hemoglobin binds reversibly with oxygen

Normal values

Males - 1318g/100ml; Females - 1216 g/100ml

Hemoglobin Structure

Globin composed of 4 polypeptide chains

Two alpha and two beta chains

Heme pigment bonded to each globin chain

Gives blood red color

Heme's central iron atom binds one O2 Each Hb molecule can transport four O2 Each RBC contains 250 million Hb molecules

Hemoglobin (Hb)

O2 loading in lungs

O2 unloading in tissues

CO2 loading in tissues

Hematopoiesis

Hematopoietic stem cells (Hemocytoblasts)

New blood cells enter blood sinusoids

Erythropoiesis: Red Blood Cell Production

Stages

Myeloid stem cell transformed into proerythroblast In 15 days proerythroblasts develop into basophilic, then polychromatic, then orthochromatic erythroblasts, and then into reticulocytes Reticulocytes enter bloodstream; in 2 days mature RBC

Erythropoiesis

As myeloid stem cell transforms

1. Ribosomes synthesized

2. Hemoglobin synthesized; iron accumulates

3. Ejection of nucleus; formation of reticulocyte (young RBC)

Reticulocyte ribosomes degraded; Then become mature erythrocytes

Reticulocyte count indicates rate of RBC formation

Regulation of Erythropoiesis

Hormonal Control of Erythropoiesis

Hormone Erythropoietin (EPO)

Causes of hypoxia

Effects of EPO

Some athletes abuse artificial EPO

Dangerous consequences

Testosterone enhances EPO production, resulting in higher RBC counts in males

Dietary Requirements for Erythropoiesis

Nutrientsamino acids, lipids, and carbohydrates

Iron

Available from diet

65% in Hb; rest in liver, spleen, and bone marrow

Free iron ions toxic

Stored in cells as ferritin and hemosiderin

Transported in blood bound to protein transferrin

Vitamin B12 and folic acid necessary for DNA synthesis for rapidly dividing cells (developing RBCs)

Fate and Destruction of Erythrocytes

Fate and Destruction of Erythrocytes

Heme and globin are separated

Iron salvaged for reuse

Heme degraded to yellow pigment bilirubin

Liver secretes bilirubin (in bile) into intestines

Degraded to pigment urobilinogen Pigment leaves body in feces as stercobilin

Globin metabolized into amino acids

Released into circulation

Erythrocyte Disorders

Anemia

Causes of Anemia

Three groups

Blood loss

Low RBC production

High RBC destruction

Causes of Anemia: Blood Loss

Hemorrhagic anemia Chronic hemorrhagic anemiaCauses of Anemia: Low RBC Production

Iron-deficiency anemia Pernicious anemia Renal anemia Aplastic anemiaCauses of Anemia: High RBC Destruction

Hemolytic anemiasCauses of Anemia: High RBC Destruction

Usually genetic basis for abnormal Hb

Globin abnormal

Fragile RBCs lyse prematurely

Causes of Anemia: High RBC Destruction

Thalassemias Sickle-cell anemia

Hemoglobin S

One amino acid wrong in a globin beta chain

RBCs crescent shaped when unload O2 or blood O2 low

RBCs rupture easily and block small vessels

Poor O2 delivery; pain

Sickle-cell Anemia

Black people of African malarial belt and descendants

Malaria Kills 1 million each year

Sickle-cell gene

Two copies ( Sickle-cell anemia

One copy ( Sickle-cell trait; milder disease; better chance to survive malaria

Sickle-cell Anemia: Treatments

Acute crisis treated with transfusions; inhaled nitric oxide

Preventing sickling

Hydroxyurea induces fetal hemoglobin (which does not sickle) formation

Blocking RBC ion channels

Stem cell transplants

Gene therapy

Erythrocyte Disorders

Polycythemia vera Secondary polycythemiaLeukocytes

Make up