Blood and Erythrocytes

Circulatory System

• blood

• heart

• blood vessels

Cardiovascular System

• heart

• blood vessels

Functions of Circulatory System

• Transport

• Protection

• Regulation

Transport Function of Circulatory System

• blood carries oxygen from lungs to tissues

• blood carries metabolic waste for kidneys

• carries hormones from endocrine cells to target organs

• moves stem cells

• picks up carbon dioxide from tissues and carries it to lungs

Protection Function of Circulatory System

• several roles in inflammation, limiting infection

• white blood cells destroy microorganisms

• antibodies neutralize toxins

• RBC bind to foreign antigens and transport them to liver and spleen for disposal

Regulation Function of Circulatory System

• stabilize fluid distribution

• stabilize pH of fluids

• control body temperature

Two main components of whole blood

• plasma

• formed elements

Plamsa

• noncellular portion of blood, liquid matrix, slightly over half of blood volume

• clear, yellow fluid

• contains mainly water, proteins, nutrients, electrolytes, hormones, gases

Formed Elements

• cells and cell fragments including RBC, WBC, and platelets

Blood Fractionation

• separation of blood into basic components based on centrifugation and coagulation

Hematocrit

• packed cell volume

• percentage of blood volume that is composed of erythrocytes (RBC’s)

Buffy Coat

• sits above the RBC’s

• narrow, cream zone composed of WBC and platelets

Three Main Proteins in Plasma

• Albumin

• Globulkins

• Fibrinogen

Albumin

• smallest but most abundant plasma protein

• transports various solutes and buffer the pH of blood plasma

• responsible for colloid osmotic pressure

• contributor in blood viscosity

• transports lipids, hormones, calcium

• buffers pH

Globulins

• divided into three subclasses based on molecular weight (alpha, beta, gamma)

• play an important role in transport, clotting and immunity

Fibrinogen

• sticky protein that forms framework of blood clot

• soluble precursor ofd fibrin

Viscosity

• resistance of a fluid to flow

• thickness or stickiness of a fluid

Osmolarity

• molar concentration of dissolved particles in 1L of solution

• in order to nourish cells and remove wastes substances must pass between bloodstream and tissue fluid through capilary walls

Importance of Viscosity

• it determines the flow of blood through the vessels

Viscosity and RBC deficiency causes:

• reduced viscosity

• blood flows to easily

Viscosity and RBC surplus causes:

• viscosity is increased

• blood flows to sluggishly

Problems created with blood viscosity

• high or low can lead to heart strain and serious cardiovascular problems

Importance of blood osmolarity

• transfer of fluids depends on a balance between filtration of fluid from the capillary and its reabsorption by osmosis

Blood Osmilarity thats too high

• blood stream absorbs too much water

• raises blood volume

• causes high blood pressure and strains heart and arteries

Blood Osmolarity thats too low

• too much water remains in tissues

• tissues begin to swell

• blood pressure drops to low levels because of water loss from bloodstream

Hematopoiesis

• production of formed elements in the blood

Production of Blod before infancy

• blood cells are produced in hematopoietic tissues

• first is produced in the yolk sac

Production of formed elements after infancy

• red bone marrow produces all kinds of formed elements

• lymphocytes are produced in lymphoid tissues/organs

Hematopoietic Stem Cell (HSC)

• cell of the red bone marrow that can give rise to erythrocytes, platelets, leukocytes, and various kinds of macrophages

• multipotent stem cell

Colony Forming Units (CFU)

• more specialized version of (HSC)

• destined to produce one one or another class of formed elements

Erythrocytes

• red blood cell

• picks up oxygen from lungs and unloads it in tissues

• picks up carbon dioxide from tissues and unloads it in lungs

Erythrocyte Form

• discoidal cells with biconcave shape

• thick rim and sunken center

• loose nucleus and lack organelles and mitochondria

• rely on anaerobic respiration

Hemoglobin

• red gas transport pigment of an erythrocyte

• know for role in oxygen transport

Carbonic andhydrase (CAH)

• catalyzes the reaction CO2 +H2O → H2CO3

Hemoglobin Structure

• four protein chains called globins

• each chain has heme group

• molecule can carry up to 4 O2

Heme

• nonprotein, iron-containing prosthetic group of hemoglobin or myoglobin

• each can carry 1 molecule of O2

Where oxygen binds to on hemoglobin

• O2 binds to the ferrous ion heme

Where CO2 binds to on hemoglobin

• binds to the globin

erythropoiesis

• production of erythrocytes

• takes 3-5 days

Major developments of erythropoiesis

• reduction of cell size

• increase in cell number

• synthesis of hemoglobin

• loss of nucleus and other organelles

erythropoietin (EPO)

• hormone that is secreted by the kidneys and the liver in response to hypoxia and stimulates erythropoiesis

First Step in erythropoiesis

• HSC becomes a CFU

• CFU has receptors for EPO

• EPO stimulates CFU to transform into an erythroblast

Second Step in erythropoiesis

• erythroblasts multiply

• build up large cell population

• synthesise hemoglobin

Third Step in erythropoiesis

• nuclei shrivel/ are discharged from cell

• cell is now called a reticulocyte

• reticulocytes leave bone marrow and enter circulating blood

Fourth Step in erythropoiesis

• polyribosomes disintegrate and disappear

• cell is a mature erythrocyte

Hypoxemia

• deficiency of oxygen in the blood stream

Erythrocyte homeostasis

• RBC count is maintained by negative feedback loop

• low oxygen levels in bloodstream is detected by kidneys causing increase in EPO output

• thus increasing RBC production

Importance of Iron

• it is a key nutrient required for erythropoiesis

Hemolysis

• rupture of RBC

• causes hemoglobin to be released and leaves empty plasma membranes

Polycythemia

• RBC excess due to cancer of erythropoietic line of the red bone marrow

• can result from dehydration because water is lost from the bloodstream

• mainly caused by smoking, air pollution, high altitude, or other factors that create state of hypoxemia and stimulate erythropoietin secretion

Dangers of Polycythemia

• increased blood volume, pressure, and viscosity

• causes poor circulation cause the capillaries are congested with viscous blood

• causes major heart strain

Anemia Causes

• inadequate erythropoiesis or hemoglobin synthesis

• hemorrhagic anemia from bleeding

• hemolytic anemia from RBC destruction

Iron Deficient Anemia

• small pale erythrocytes

• caused by blood loss without getting enough dietary iron to compensate for it

Pernicioius Anemia

• autoimmune disease in which antibodies destroy stomach tissue

• causes a deficiency in vitamin B12

Hypoplastic Anemia

• caused by a decline in erythropoiesis

Aplastic Anemia

• complete failure or destruction of myeloid tissue is main cause

• causes complete cessation of erythropoiesis

Consequences of Anemia

• tissues suffer hypocia

• blood osmolarity is reduced

  • results un more fluid transferring from bloodstream to tissue space causing edema

• blood viscosity is reduced

  • less resistance to flow, heart beats faster than normal and cardiac failure may ensure

  • causes BP to drop

Sickle-Cell Disease

• hereditary hemoglobin defect

• HbS differs from normal HbA on 6th amino acid of beta chains causing it not to bind to oxygen very well

Issues with Sickle-Cell Disease

• sickled erythrocytes are sticking and clump causing blocked blood vessels

• causes intense pain in oxygen starving tissue

• can lead to organ failure, intense pain, and other issues