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

Which organ in the body regulates erythrocyte production

Kidney

Which factor stimulates platelet formation

Trombopoietin

Cell producing platelets

Megakaryocytes

Pulmonary Circuit

Receives oxygen-poor blood from body tissues and pumps it to the lungs to eliminate CO2 and pick up O2

Systemic circuit

Receives oxygenated blood from lungs and pumps it to the body tissues to deliver O2 and pick up CO2

Layers of the heart

• Heart wall

  • Epicardium

  • Myocardium

  • Endocardium

• Serous pericardium

• Pericardial cavity

• Fibrous pericardium

Cardiac Muscle bundles

Cardiac muscle is in a circular and spiral arrangement

It contacts as a coordinated unit in order to efficiently circulate blood

Chambers of the heart

• Two superior atria and two inferior ventricles

• Interatrial septum

  • separates atria

• Interventricular septum

  • separates ventricles

Arteries and veins

Arteries carry blood away from the heart

Veins carry blood back towards the heart.

Pulmonary arteries

Carry deoxygenated blood from the right ventricle to the lungs

Superior / Inferior Vena cava

Large veins that return deoxygenated blood from the systemic circulation to the right atrium of the heart

Superior: return blood above the heart

Inferior: return blood from below the heart

Pulmonary Veins

Carry oxygenated blood from the lungs back to the left atrium of the heart

Right atrium

Receives deoxygenated blood from the systemic circulation from the superior and inferior vena cava

Left atrium

Receives oxygenated bloods from the pulmonary veins and pumps it into the left ventricle

Mitral valve

Ensures one way blood flow from the left atrium to the left ventricle

Tricuspid valve

ensures one way blood flow from the right atrium to the right ventricle

Aortic valve

Prevents blood from returning to the left ventricle while pumping blood through the aorta

Pulmonary valve

Prevents blood flow back into the right ventricle through the pulmonary arteries

Right ventricle

Pumps deoxygenated blood received from the right atrium into the pulmonary artery

Left ventricle

Receives oxygenated blood from the left atrium and pumps it through the aortic valve into the systemic circulation

Atrioventricular valves

Two types of tricuspid and mitral valves that regulate blood flow between the atria and ventricles

Semilunar valves

Prevent blood from returning to the ventricles

Pacemaker cells

• Pacemaker potential

  • K+ channels close, slow Na+ channels open

    • Na+ influx causes interior to become more positive, nearing threshold

  • Depolarization

    • threshold (-40 mv) Ca2+ channels open

      • Big influx of Ca2+, leading to rising phase of action potential

  • Repolarization: Ca+ channels close. K channels open

    • efflux of K+ causes interior cell membrane to become more negative once again

Setting the rhythm of the conduction system

Nodes in the heart that allow for rhythm for heartbeat.

Sinoatrial (SA) node

“Pacemaker”

Located below the superior vena cava

Generates impulses

Atrioventricular (AV) node

Above the tricuspid valve

Allows the atrium to contract before the ventricle.

Atrioventricular Bundle

Electrical connection between the atria to the ventricles

Right and left bundle branches

Conducts impulses through the inter-ventricular septum (space between left and right atrium)

Purkinje fibers

Depolarizes the contractile cells of both ventricles

Innervation of the heart

Autonomic nervous system can innervate the heart, both innervate at the SA and AV node.

Sympathetic cardiac nerve: increases heart rate and force of contraction

Parasympathetic vagus nerve: decreases heart rate

Action potential of cardiac cells

1. Depolarization: Due to Na+ influx through fast voltage gated Na channels, A positive feedback cycle rapidly opens many Na channels, depolarizing the membrane

2. Plateau phase: Due to Ca2+ influx through slow Ca2+ channels. This keeps the cell depolarizer because most K+ channels are closed

3. Repolarization: is due to Ca2+ channels inactivating and K+ channels opening. This allows K+ efflux, which brings the membrane potential back to its resting voltage.