Ch 9 Part 1 Flashcards
Goals of the circulatory system
Distribute nutrients from digestive tract, liver, and adipose.
Transport O2 and CO2.
Transport metabolic waste to excretory system (kidneys).
Transport hormones.
Homeostasis of body temperature.
Hemostasis - blood clotting.
Perfusion, Ischemia, hypoxia
Perfusion: flow of blood through tissue.
Ischemia: inadequate blood flow.
Hypoxia: Adequate circulation, but inadequate O2
Components of Circulatory System
Heart - Arteries (high pressure) - arterioles - capillaries (single cells form wall, allows for diffusion of material) - venules - veins (low pressure)
Endothelial Cells
Blood vessels all have a thin layer of endothelial cells (this is the only layer for capillaries)
Endothelial cells contribute to:
Vaso-constric/dillation
Inflammation
Angiogenesis (creation of new blood vessels)
Thrombosis - blood clotting: undamaged endothelial cells secrete anti-clotting substances to prevent coagulation cascade.
Right V Left Heart
Right - pumps blood to lungs
Left - pumps to body
Pulmonary circulation
Heart - Lungs - Heart
Systemic Circulation
Heart - rest of body - Heart
Division of Pulmonary and Systemic Circulation
Avoids having to pump blood through two capillary beds which would require significant pressure.
Exceptions = Portal System.
Portal Systems
Hepatic portal system: Blood moves through capillaries in intestine, travels in veins to liver, blood passes through capillary bed in liver.
Hypothalamic-hypophysial system: Blood passes through capillaries in hypothalamus - moves through portal viens - then to capillaries in pituitary.
Benefit is direct transport from one system to another without having to move through entire body. ie.
Nutrients –> Liver
Hormones –> Pituitary
Atria
Reserves, “waiting rooms” - blood can collect from veins before being pumped to ventricles.
Right Atrium
Receives deoxygenated blood from systemic circulation.
From inferior vena cava and superior vena cava.
Pumps to right ventricle.
Left Atrium
Receives Oxygenated blood from the lungs via Pulmonary veins.
transfers to left ventricle which pumps oxygenated blood to rest to systemic circulation via aorta.
Coronary Arteries
First branches from Aorta feed back to the heart to oxygenate the muscles.
Coronary Veins
Deoxygenated blood from heart is brought back to the right atrium via the coronary sinus.
Note, this is the only blood that does not return to the heart via the inferior of superior vena cava.
Atrioventricular Valve
Required to divide atria and ventricle and prevent backflow.
AV Valve between left atrium and left ventricle is bicuspid or mitral valve.
If bicuspid breaks, result is blood flowing through aorta and back to left atrium. Consequence is elevated pulmonary blood pressure and pulmonary edema.
Tricuspid valve is between right atria and ventricle.
Pulmonary and Aortic semilunar valves
Are between large arteries and ventricles.
Varicose Veins
result of valve failure in veins that normally prevent backflow.
Pregnant women often suffer from varicose veins.
Cardiac Cycle
Happens at the same time on both sides.
Two periods: Diastole and Systole.
Diastole: Ventricles are relaxed, blood flows from atria to ventricles. Atria contract.
Systeole: Ventricles contract; AV valves close; pressure builds; semilunar valves open and blood moves to aorta and pulmonary artery.
Begins at Lub (Closure of AV valve), ends at Dup sound (Closure of semilunar valves).
2/3 of blood are ejected during systole, ejection fraction.
Stroke volume
Amnt of blood pumped with each systole
Cardiac Output (CO)
Amnt of blood pumped per minute.
CO (L/min) = stroke volume (L/beat) * heart rate (beats/min)
ie. CO = SV * HR
Mechanisms to increase Cardiac Output
Increase Heart Rate
Increase Stroke Volume
Frank-Starling mechanism
Frank-Starling Mechanism
If ventricles are stretched, they will contract more forcefully. That is, if they are filled with more blood.
Increase venous return via vena cava.
This is largely controlled autonomically.
How to increase venous return?
Increase blood in system (ie. retain water)
Contraction of large veins. Valves are essential here.
Dilation of arterioles.
Cardiac Muscles
Like all muscle cells, are able to propagate an AP across their surface (like neurons).
Functional Syncytium
Distinct from neurons in that all connected via gap junctions. There are no chemical synapses in cardiac muscles.
Gap junctions are found in the intercalated disks (connections between cardiac muscles).
Note: Atria and ventricles are seperate syncytia.
Cardiac Conduction System
While atria and ventricles are separate syncytia, they are connected by cardiac conduction system which allows transfer of the AP - though this creates a delay as it passes through A-V node.
Allows atria to contract first.
Voltage-gated Channels in Heart
Voltage gated Na channels (fast Na Channels) - important, though insufficient to drive total propagation of signal through heart (requires gap junctions).
Ca Channels (slow): Result in cell being depolarized for longer periods. Causes plateau phase.
T tubules
Cardiac muscle involutions that allow AP to travel down and allow entry of Ca from extracellular environment. Also causes the sarcoplasmic reticulum to release calcium (internal).
Result is the contraction of actin-myosin fibers.
Neuron and hormone influence on heart
Can alter contractility (rate and strength, but not required to keep the heart beating.
Sinoatrial (SA) Node
The pacemaker of the heart. Located by the right atrium.
AP initiated here - it exhibits automaticity. AP is propogated to all other conduction cells in heart and to atrial myocytes.
Note that the AV node and the Purkinje fibers can depolarize spontaneously, but SA node has the most Na leak channels. If SA is damaged, other regions will takeover but have a slower rate.
AP is commonly divided into three phases.
Phase 0; Phase 3; Phase 4 (other cardiac myocytes have phase 1 and 2)
Phase 4
Unstable resting potential.
Result of Na leak channels that allow for rythmic excitation. By brining voltage-gated Ca channels to threshold potential.
Phase 0
Voltage-gated Ca channels open. The upstroke of the pacemaker potential. Slower rise than with Na channels.
Note that other Skeletal muscles and myocytes fire with influx of Na. SA node is unique in this sense.
Phase 3
Repolarization: Closure of Ca channels and opening of K+ channels.
AP differences in cardiac muscles (relative to SA node and conduction system cells)
Long duration (~300 milliseconds)
Phase 0: (depol) Transient increase in Na conductance aided by conduction through gap junctions. Reaches threshold for voltage gated Na channels and open.
Phase 1: (initial repol) Na+ inactivates; K+ open; opening of Ca2+ channels which leads to
Phase 2: plateau phase.
Phase 3: (repol) Ca2+ channels close and K+ continues to repolarize.
Phase 4: (resting mem. potential) result of Na/K ATPase and K+ leak channels.
Conduction pathway in hearts
Spreads AP very quickly without causing contraction.
Connects SA node to atrioventricular (AV) node. ie. the internodal tract. AP travels near instantaneously.
Propagation through the atria is slower.
at AV node AP is delayed, before passing through the AV bundle (bundle of His). Bundle divides into LEFT and RIGHT bundles and becomes purkinje fibers as spreads over inferior of heart (spreads AP rapidly). Note that bottom of heart is considered the APEX, and contraction occurs here first and travels toward the BASE.
Autonomic regulation of Heart
Does not initiate heart beat, but can regulate.
Basal rate of heart is 120 bpm, but Autonomic parasympathetic nervous system is perpetually polarizing it (Vagal tone). Postganglionic neurons innervate the SA node and release ACh.
Sympathetic Nervous System
affects during flight or fight response
Sympathetic Post-ganglionic nerves innervate the heart directly and release nor-epinephrine.
Epinephrine from adrena medulla also binds cardiac muscle.
Regulation of Cardiac System
Requires input, integration, and output.
input is complicated, but specific receptors like baroreceptors monitor pressure.
Baroreceptors
When blood pressure is too high, signal to increase vagal tone and decrease sympathetic input.
If pressure is too low increase sympathetic input and decrease vagal tone.
Hemodynamics
Study of blood flow.
Flow is driven by differences in pressure.
deltaP = Q*R
where P is pressure gradient (mm Hg); Q stands for blood flow; R is peripheral resistance.
Takeaway: Blood pressure is directly related to cardiac output and peripheral resistance. And that if we want to change blood pressure, we have to change CO or peripheral resistance.
Determinant of resistance in cardiac system
Principally is constriction of arteriolar smooth muscle or PRECAPILLARY SPHINCTERS.
Peripheral Resistance
Controlled by the Sympathetic Nervous System that innervates precapillary sphincters.
Basal blood pressure is necessary to ensure all tissues receive blood.
adrenergic tone!
Can also direct blood flow to specific systems. For example, can cause contraction of precapillary sphincters in intestines and relax skeletal muscles, diverting blood away from intestines.
Doctors measuring BP
Systemic Arterial Pressure, 120/80. (important because pressure in vena cava is essentially 0)
120 mm HG is Systolic Pressure
80 mm HG is diastolic pressure. This is still high, but necessary to keep driving force for blood.
Use sphygmomanometer
Pulse Pressure
Difference between systolic and diastolic pressure
Local Autoregulation
Tissues that need more blood can auto-petition for it.
Build up of specific metabolic waste stimulates vasodilation of arteriolar smooth muscle causing increased blood flow.
Local autoregulation is the principle determinant of coronary blood flow and can overide the nervous system.
