Cardiovascular

Whats the main general function of the cardiovascular system?

Transport and exchange

• Delivers supplies to the cells far removed from the site of uptake and manufacture

• Transports wastes from the cells elimination elsewhere

Explain the supplies the cardiovascular system delivers and explain them.

• Oxygen = Done viaspecialized blood cells called erythrocytes which are anearobic

• Water = plays role in blood pressure regulation and hydration

• Nutrients = From digestive system which we use for energy/ ATP

• Hormones = Synthesized in various tissues (pituitary, endocrine) used as form of communication

• Antibodies and leukocytes = role in immunity

• Platelets = Role in stopping bleeding

• Heat = All heat created in core, cardiovascular transports/ distributes heat to keep body warm.

Explain the “wastes” it transports and explain a bit about them

• Carbon dioxide = Build up of this causes problems, need to eliminate CO2 same rate as take up O2, done by lungs

• Urea = CO2 + amino make it up, comes out through kidneys some as sweat

• Bilirubin = Breakdown product of hemoglobin, if builds up you get jaundice usually due to liver damage

Whatre the 3 main components of the cardiovascular system?

1. Blood = Medium for the bulk transport of materials

2. Heart = Hydraulic pressure gradient generator (pump)

3. Vasculature = Closed, dual circuit for the one way flow of blood

What does the term bulk transport mean for blood?

• Means that everythings carried together like a river, all molecules move in the SAME direction kinda like wind

• Blood moves through a pressure gradient (high to low)

Whats the dual circuit in the vasculature?

1. Pulmonary circuit (low pressure, low resistance) = Supplies alveoli in places where gas exchange happens and the pressure is lower cuz it has to fight against a low resistance to blood flow, need to put low pressure to get the same result

2. Systemic circuit (high pressure, high resistance) = Basically whats in all cells, lots of bloos vessels = lot of pressure cuz more resistance. More pressure to get same flow rate

Left pump and right pumo beat same but left pump is stronger cuz more pressure cuz more resistance to get flow rate. Left side is lot thicker than right.

What are the components of blood?

1. Plasma

2. Erythrocytes (RBCs)

3. Leukocytes

4. Platelets

What is blood and how much of it is in our body?

• Complex suspension of water, solutes which dissolves in plasma and formed elements which are cells and cell fragments

• ~5 to 5.5 liters in volume, blood on average 7-10% of body mass

Whats plasma made of?

• Composed of water (~90%) and a variety of dissolved:
  

• Proteins = albumins which are the most common and transports water and lipid soluble proteins, globulins, fibrinogens which remains in blood inactivated until wound shows up to clot, hormones

• Electrolytes = Na+, Cl-, K+, HCO3-, concentration of all of them is regulated by kidneys

• Gases = N2, O2 and CO2

• Metabolic waste products = urea, creatinine

Whats serum?

• Plasma from which fibrinogen and other clotting proteins have been removed so it doesnt gum up diagnostic tests (protein free plasma)

Whatre erythrocytes?

• Red blood cells

• The most numerous type of blood cell with ~5 billion per ml of blood which is 25 trillion RBCs

• Are anaerobic, picks up and transports blood but cant consume it

Whats the shape and function of RBCs?

• Flat hemoglobin containing biconcave disks that lack organelles (No nucleus, lysozyme, mitochondria, E.R)

• Function to transport O2 (and plays indirect role in CO2 transport

Whats the lifespan of RBCs?

• Short lived (~120 days) - rapidly produced in the bone marrow.

• Since no nucleus, cant repair damage ever.

Whats hematocrit (Hct)?

• The % of blood volume that is erythrocytes (~42 women to ~47% men)

What do kidney cells do when theres low blood O2 saturation?

• Kidney cells release erythroopoietin in response to low blood O2 saturation, stimulating RBC production

Whats anemia and polycythemia?

• Anemia = Low blood cells cuz of iron

• Polycythemia = Happens at high elevation and causes a lot of epo, even though it carries more oxygen its harder on the heart

What kind of cells are most cells in the body?

• Anearobic cuz RBCs are anaerobic

Explain leukocytes/ white blood cells

• Plays a central role in the bodys immune response

• Primarily acts outside of the bloodstream, make their way into interstitial fluids where they fight invaders/ infections

• Cant get into the blood brain barrier

• Mobile units of the bodys protective system

Whats the acronym for leukocytes?

• Never = neutrophils

• Let = Lymphocytes

• Monkeys = monocytes

• Eat = Eosinophils

• Bananas = Basophils

What % of blood do platelets and leukocytes make up?

• 1% of blood, unless theres an infection

Explain what platelets are

• Only found in mammals and are shortlived (1-10 days)

• Are cellular fragments (they lack a nucleus) that are shed into the plasma from large bone marrow cells called megakaryocytes

• Primary function is hemostasis

What does binding of platelets to collagen do?

• Binding of platelets to exposed collagen at the wound site activates them, platelet aggregation and release of serotonin (acts as vasoconstrictor, so smooth muscle cells at wound site constricted from a blood clot

Understand the path of blood flow diagram

Whatre the 4 chambers of the heart?

• Contains four chambers (2 atria and ventricles), each of which are connected to specific blood vessels (arteries and veins)

• Wall on left side way thicker than right site

Whatre the 3 layers of the heart and what do they do?

1. Endocardium

• Senses blood flow and blood pressure, in certain parts of heart, will release chemicals that have impact on blood volume

• Thin inner lining of specialized epithelial tissue

2. Myocardium

• Heart muscle, within heart, formed by a thick layer of contractile cells (99% of total) arranged in circular (atria) and spiral patterns (ventricles)

• Cardiac muscle cells held together by intercalated disks that contain many gap junctions which have low resistance to electrical signals so they can pass through them, if one heart cell depolarizes and contracts, all heart cells will do it

• A network of non-contractile cells (1%)

• Cardiac tissue is directly supplied by O2 and nutrients via the coronary circulation (1st branches off the aorta)

3. Epicardium (=visceral pericardium)

• Inner layer of a serous membrane that surrounds the heart; secretes pericardial fluid (lubricant that lowers resistance) into precardial activity

4. Pericardial sac

• Formed by epicardium and parietal pericardium, which is fused to an outer fibrous pericardium (connective tissue)

• Prevents over distension of heart; anchors the heart to the diaphragm and thoracic wall

Whats the heart and its pumps?

• It’s a muscular 4 chambered organ bisected by an interventricular septum into 2 separate, yet coordinated pumps

  • Each side pumps an equal volume of blood per beat on average, however, the force (and hence pressure) generated By the left ventricle is much greater than the right ventricle

• Pressure gradients created during the heartbeat cycle drive blood flow from atrial to ventricles, and from ventricles to arteries

How is the backflow inhibited in the heart?

• Backflow inhibited by 2 sets of passive one way heart valves

1. Atrioventricular (AV) valves = between atria and ventricles (bicuspid left and tricuspid right valves)

2. Semilunar valves = Between ventricles and the main arteries

What kind of pressure opens and closes valves of heart?

• Positive pressure behind valves opens them

• Positive pressure ahead of valves closes them

What does each valve have and what does it do?

Each valve is encircled by a connective tissue ring attached to the central fibrous skeleton that separates the atria (contracts downwards) and ventricles (contract bottom to upwards)

• It stops the spread of action potentials between these structures

• Provides firm origin and insertion sites for cardiac muscle

  • Contraction of atria forces blood downwards

  • Contraction of ventricles forces blood upwards

Whats the heartbeat and whats it coordinated by?

• The heartbeat is an orderly wave of contraction that sweeps through the myocardium

• Coordinated by specialized non-contractile muscle cells (they lack sarcomeres) that generate and condcut action potentials (AP)

Whatre the 2 types of non contractile muscle cells in heart?

1. Autorhythmic pacemaker cells - primarily found in right atria

• Sinoatrial (SA) node = ~75 depols/min (natural pacemaker of the heart)

• Atrioventricular (AV) node = ~50 depols/min (small diameter cells with few gap junctions and low AP conducting speed (holds it for 1/10 of a second on accident)

2. Large diameter conducting cells - 30 depols/min (some in ventricle are autorhythmic) = These allow for rapid spread of depolarization through the heart

Whats firing rate of non contractile muscle cells influenced by?

• Firing rate influenced by nervous and endocrine systems

Whatre the different conducting cells and what do they do?

1. Internodal and interatrial pathways = They carry impulses generated in SA node to the AV node and left atrium respectively, which results in the atria contracting in unison from top down

2. Atrioventricular bundle = Sole electrical pathway connecting the atria to the ventricles; splits into 2 bundle branches, signal gets stuck in AV node but has window and wire connecting AV node to central fibrous skeleton

• Following a ~100 msec delay in the AV node, signal quickly transferred through central fibrous skeleton to apex of heart (bundle goes into left and right)

• AV node has 1/10 sec between atrial and ventricular contraction which is important ensures atrial and ventricular contraction which is important as it ensures atria empty fully before ventricles begin contraction

3. Purkinje fibers = Extensive network of branches that spread upwards towards the valves, transmitting signal to contractile cells as they go, the result of this is that the ventricles contract in unison from apex upwards

Understand diagram of heart and flow from SA node to AV node

Whats the difference between myocardial contractile cells and skeletal muscle cells?

• Unlike skeletal muscle cells, contractile myocytes have very long duration APs (~250 secs) due to prolonged openeing of Ca2+ channels

• Consequently, the absolute refractory period is almost as long as the contractile response (contraction + relaxation)

• Because of long refractory period, heart has no summation and tetanus unlike skeletal muscle does, this prevention of summation and tetanus allows adequate time for the heart chambers to refill between beats

• Heart muscle ignores all extra depols cuz “all or none” depols in heart

Explain the caveat with the all or none AP

• Is all or none but still under some regulation, can be faster when nervous system is invoked and also under hormones such as epinephrine

What does the ECG do?

• Electrical activity of the heart detected by pairs of electrodes at 3 points on the skins surface

• Not a direct recording of heart, just showing overall spread/sum of electrical current through the heart during the cardia cycle

Whats visible in the QRS sequence?

• R = always visible

What do the flat lines on ecg do and what do they mean?

Flat horizontal lines denote periods of stable electrical activity

• Ex: when all cells of atria (PR) or ventricle (ST) are depolarized

• Ex: When all myocytes are repolarized during the TP segment

Its the isoelectric point (PR, ST, TP)

Whats the most variable segment?

• TP segment

Whats all the different steps of electrical activity that happen in this diagram?

1. Atrial depolarization

2. Av nodal delay = where signal gets stuck for 1/10 sec where we see PR

3. Ventricular depolarization = Cells of atria are also repolarizing, don’t see this cuz happening also at QRS complex

4. All fibers in the ventricle contracting = Period of true ventricular contraction, ST segment

5. Ventricular repolarization = T wave, repol happens outside inwards and depol happens inside outwards

6. Ventricles relaxing (6 & 1) = Period of passive ventricular filling, TP segment

Atrial repolarizing is masked by the QRS complex

Whats all the different steps of physical activity that happen in this diagram?

• During steps 1 and 2 its atrial contraction

• During just step 2 its atria emptying to top up ventricles

• During step 3 and 4 its ventricles contracting where it goes from ventricles to aorta and closes valves behind it

• During 4 and 5 its ventricles emptying (until ½ way thru T wave) and semilunar valves have to close

• During 6 and 1 its ventricles passively filling

Whatre some different ECG abnormalities that cause arrythmias?

1. Heart block

2. Atrial fibrillation

3. Pre-ventricular contractions

4. Ventricular fibrillation

Explain heart block

Due to damage to the AV node caused by things like alcohol and stress

1. 1st degree = decreased rate of AP movement through AV node (i.e. longer PR segment) when signal gets stuck at AV node for too long

2. 2nd degree = 1 of every 3 to 5 atrial AP waves is “dropped”, atrial contracts but doesnt go to ventricles, P wave is there but no QRS complex so ventricles dont contract, called skipped beat, if ventricles dont contract they fill up with blood

   1. 3rd degree = complete blockage of signal from atria to ventricles which causes AV node to be non-functional so now signals move from SA node to AV node to ventricles and signal dies in fiber, means that signal wont go from atrial ventricle, but autorhythmic cells stimulate slow ventricle contraction then but shows 2 diff signals in atria and ventricle, this causes no synchrony between atrial and ventricular activities

Explain atrial fibrillation

Caused due to damage to SA node

• No P wave and irregular QRS complex rhythym

• Atrial beat rapidly and weakly; increases risk of blood clots (because atria not contracting properly)

Explain pre-ventricular contractions

• Common condition whereby a heartbeat is initiated by Purkinje fibers in the ventricles

• Abnormal QRS complex and inverted T wave followed by an extended segment

Explain ventricular fibrillation (“VFib”)

Happens usually immediately after heart attack event

Means no blood leaving heart so no blood going to brain

Heart muscle is no longer depolarizing synchronously making coordinated pumping action impossible

Immediate treatment is defibrillation, which causes every signal to depolarize