10.4.13 Kin 272 class notes- Tissue needs increaseo CO (cardiac output) (Q) must increase Increase HR (heart rate) Increase EF (ejection fraction)- Preloado Filling it more, increase pressure, send more through heart- Afterloado Aorta, pushing more out, stretching aorta wall, recoils it, gets rid of its pressure faster- Increase contractilityo Heart needs to contract with more forceo More calcium Ca++o Process: Use norepinephrine Bind to receptor Initiates g protein Moves over, activates adenyl cyclase Does this with energy from breaking apart GTP  GDP Adenyl cyclase makes ATP into cAMP (chemical 2nd messenger)- Used for lots of things- Is going to allow us to achieve three things Calcium channel in membrane – once you have created/activated cAMP- Has three optionso 1. Activate this calcium channel to increase extra cellular Ca++ to pull more calcium into the cell Turns the channel ono Cyclic AMP has 2 effects on SR (sarcoplasmic reticulum – houses calcium 2. Increase Ca++ uptake after contraction -allows SR to reuptake after contraction -pulls Ca++ in fastero 3. Increase rate of Ca++ release from SR activates enzymes which affect Ca++ releaseo it is like this in case you don’t really need it!o Only when contractility is really neededo Used as a last resorto System used at high end exercise, heart is compromisedo Used to maintain cardiac output- Summary ^- @ rest CO = 4-6 L/min- @exercise CO= 30-50 L/min- heart rate:o autonomic innervationo medulla: cardiac center two pieces:- cardiac acceletory center- cardiac inhibitory center barroreceptors- pressure- aorta and carotid sinuses chemorecetorso sense changes in pH and in oxygen levelso increase/decrease HR based on chem. changes vagus nerve- cranial nerve- number 10- connects directly to heart- parasympathetically driveno works to keep you at resto if you need heart rate to go up (increase) remove vagus stimulation- conduction system:o heart rate <3 how many times you engage in a cardiac cycle per minuteo atrial contraction, ventricle contractiono contraction from an electrical sideo it’s a bundle of excitable muscle fibers! Have a component in them with a resting membrane potential positve on inside, negative on outside, due to balance of ions, sodium and potassium- at rest: sodium channels closed- 2/3 K channels are closed- negative on inside, positive on outside- excitability – can conduct electricityo done by receiving threshold stimulus  depolarizationo Na+ channel opens, charges reverse, chain reaction of charge changing, continuously causes the next sodium channel to open…o  action potential chain reaction of Na+ channels opening and charges changingo  repolarization Reestablish rest- This process is how the heart contracts and tells the other parts to contracto Parts of muscle fibers that have resting membrane potential – nerves do The part of the muscle fiber: sarcoplasmic reticulum, myofibril, t-tubules –receive info from neurotransmitter, depolarize, send message to SR (its excitable)- Same excitable like tissue- Upper right of atria – bundle of muscle fiberso Have an unstable resting potentialo Highly excitableo Resting membrane potential unstableo Always in upper right corner of right atriao Long name: sino-atrial node - “SA node” for short Another name: pace maker- Pace maker is a bundle of excitable muscle fibers that have unstable resting potentialo What does that mean? Resting potential is supposed to be…- Inside -70 to – 90- Outside is +10- (rest)- this varies greatly in the SA node- jumps around a lot- unstable!- Sodium potassium channels allowing a flux to enter/leaveo this affects you: easier to depolarize ito threshold potential is exceedly low, easy to stimulate that’s why its called the pace maker stimulates itself  contractso SA node sets the heart rate for the entire rest of the heart Huge problem: because it is so unstable, easy to stimulate Would set your heart rate above 100 bpm (which is high) Two things to combat this:- 1. Nerve connected to it: vagus nerve- Vagus nerve driven by parasympathetic system- its inhibitory- Slows it down- Bundle of fibers in interatrial septum – where all four chambers meet (atrio ventricular node (AV node))- 2. AV node  slows down the signalo sets true resting HRo down to 60/70 bpmo doesn’t connect to any musculatureo sends depolarization messageso next segment is y segment that splits itself in halfo “bundle of His” receives electrical stimulus from AV valve depolariazes send messages to left and right bundle branches (muscularfibers that function as nerves) end in teeny tiny fibers protruding into walls of ventricles (Purkinje fibers) – gets the ventricle to depolarize and