ANP 1105 The Cardiovascular System

Blood as Connective tissue

focuses on red blood cells and platelets, immune system mostly excluded, except blood types

Functions and components of blood

Transports nutrients, oxygen, amino acids, ions, hormones

Maintains homeostasis: Temperature, pH

protects against infection

Blood sample contents

55% plasma

1% Buffy coat

45% erythrocytes

Plasma

contains mostly water, electrolytes, and proteins

Structure of blood cell

Red Blood cell (erythrocytes): biconcave, no nucleus, no mitochondria

High surface area for gas exchange

Filled with hemoglobin; main function is oxygen transport

Platelets

made cell fragments

circulate freely, prevented from sticking by nitric oxide and prostacyclin and endothelium.

Leukocytes

immune cells, less than 1% blood

Hemoglobin

four polypeptide chains (2 alpha, 2 beta), each with a heme group

each heme binds one O2 molecule (4 per hemoglobin)

each RBC has ~250 million hemoglobin molecules (~1 billion O2 molecules per RBC)

RBC production and lifecycle

hematopoiesis in bone marrow from hemopoietic stem cells

stimulated by erythropoietin from kidneys

triggered by low O2, low RBC, low hemoglobin

Mature RBC: make ribosomes, produce hemoglobin, eject nucleus and mitochondria

Blood disorders

Sickle cell anemia: Causes erythrocytes to sickle under low O2, leads to blockages.

Blood doping: reinjecting stored red blood cells or using synthetic erythropoietin to boost oxygen capacity

When injury occurs

injury triggers vascular spasm, then platelet plug formation

platelets release chemicals to attract more platelets, forming a plug

Coagulation

fibrin proteins form a mesh, trapping cells and platelets

Clotting cascade

• Intrinsic (slower, many steps, triggered by vessel damage)

• Extrinsic (faster, triggered by tissue factor)

Anticoagulants

Anticoagulants prevent unwanted clot formation

Thromboembolic disorders

clots form in unbroken vessels 

Bleeding disorders

hemophilia, lack of clotting factors or platelets

Blood types

Blood types based on antigens: A, B, AB, O

Immune system recognizes self-antigens; reacts to foreign antigens

Type A: anti-B antibodies

Type B: anti-A antibodies

Type O: both anti-A and anti-B

Type AB: none