Hemostasis and the Heart

Page 1

The Heart: Basics

Capillaries:

pulmonary capillaries: drops off CO2 and takes in O2 from the lungs

systemic capillaries: drops off O2 and takes in CO2 from the cells of the body

Parts of the Heart: Heart allows blood to travel from high to low pressure

RIGHT SIDE

Superior and Inferior Vena Cava: blood is pumped through these into the right atrium

tricuspid valve: held by chordae tendinae, allows the blood to properly enter the right ventricle without backflow

Pulmonary valve (semilunar valve): allows blood to be pumped from right ventricle to the heart

Pulmonary artery: transfers blood from the heart to the lungs

LEFT SIDE

Pulmonary vein: sends blood from the lungs to the heart

Mitral valve: allows the blood from the left atrium to enter the left ventricle without any backflow

Aortic valve (semilunar valve): allows blood from the left ventricle to enter the aorta

Aorta: allows blood to be pumped to the rest of the body

An important fact about valves: they are a plane of fibrous, non-conducting connective tissue, they are only one way

Page 2

Layers of the Heart

Endocardium: the inner layer, thin, smooth endothelium

Myocardium: the actual muscle part of the heart, spiral organization

Epicardium: the outer layer that is thin

Septum: in between the two ventricles

Histology of Intercalated Discs, Syncytium

Cardiac Muscle junctions: when one muscle cell contracts, the other one does as well

Desmosomes: allow for strength and mechanical functioning of the syncytium

Gap Junctions: allow ions to pass from the cells of cardiac muscles for action potential

Syncytium: allows cells to move to allow a coordinated contraction

Pericardial Sacs:

Fibrous Pericardial:

outermost layer of the heart that protects and keeps it in place

Serous Pericardial:

Parietal Pericardium:

attaches to the fibrous pericardium

external layer:

Visceral Pericardium:

actually part of the epicardium

internal layer

pericardial fluid in between the parietal pericardium and visceral pericardium

Page 3

Components of Blood

Red Blood Cells: 45%

4 heme groups, can carry 4 oxygen molecules

Plasma: 55%

Buffy Coat: <1%

made up of white blood cells and platelets

Hemostasis:

How are red blood cells are made?

kidneys release a hormone called erythropoietin which stimulates the bone marrow to create RBCs

normal endothelial cells lining vessels produce prostacyclin to prevent platelets from attaching

When there is a cut, prostacyclin production stops, resulting in platelet binding

Blood Clots

Step 1: vascular spasms: constriction of blood vessels to reduce blood loss

Step 2: Formation of platelet plug to block the injury site

collagen protein exposed would allow platelets to attach to their receptors

platelets then release thromboxane A2 and ADP to allow more platelets to attach

Step 3: Blood Coagulation to form the fibrin meshwork

Thrombin causes more thrombin to come

thrombin helps change fibrinogen to fibrin and stabilize fibrin, allows aggregation of platelets

Page 4

Hemostasis (continued):

Check on system (slows down thrombin production if too much):

Antithrombin III: always present in blood, but when AT-III encounters thrombin, it inactivates it

Thrombomodulin: present on endothelial cells, binds to thrombin and activates Protein C

Activated Protein C inactivates factors needed for thrombin creation

Fibrin Meshwork: inactivates thrombin itself

Breaking down the clot:

tissue plasminogen activator (t-PA) activates plasminogen to plasmin-> dissolution of clot

thrombolysis: breaking down the clot

Anticoagulation:

platelet inhibitors:

aspirin: inhibits cyclooxygenase

clopidogrel: inhibits binding of ADP

heparin: facilitates binding of thrombin with antithrombin (stops thrombin)

coumadin:

competes with Vitamin K, which is required for clotting

blood will not clot effectively without these factors

Thrombolytics: activates plasminogen to plasmin so that it can dissolve clots