Cardiovascular control - chapter 7

The right side of the heart pumps blood through the ____ circuit

pulmonary

The pulmonary side sends blood that has circulated throughout the body to the lungs for...

reoxygentation

The left side of the heart is part of the ___ circuit

systemic

Blood from the systemic side is ultimately sent to all body parts and systems. The left side of the heart receives ___ blood from the lungs and sends it out to supply all body tissues.

Oxygenated

Major functions of the cardiovascular system

- delivers O2, nutrients

- removes CO2, other waste

- transports hormones, nutrients, gasses, enzymes, etc

- temperature balance and fluid regulation (urinary system)

- acid-base balance

- immune function

Right heart: pulmonary circulation

- pumps deoxygenated blood from body to the lungs

- superior, inferior vena cava --> RA --> tricuspid valve --> RV --> pulmonary valve --> pulmonary arteries --> lungs

Left heart: systemic circulation

- pumps oxygenated blood from lungs to the body

- lungs --> pulmonary veins --> LA --> mitral valve --> LV --> aortic valve --> aorta

4 pulmonary veins:

2 R and 2 L

Transport O2 rich blood

2 pulmonary arteries:

- transport O2 poor blood

Myocardium

- cardiac muscle

- LV has most myocardium

- must pump blood through systemic circulation

- thicker wall than RV (LV pumps through resistance)

- LV hypertrophies with exercise and disease

- exercise adaptations are different than disease adaptations

Myocardium

- Differs from skeletal muscle

- only one fiber type (highly oxidative, high capillary density, high number of mitochondria, striated)

- myocardium contracts as single unit - functional syncytium

- individual cardiac muscle fibers connected by intercalated disks

- desmosomes hold individual cells together

- gap junctions allow rapid transmission of action potentials

Myocardium contraction

- cardiac muscle contraction

- calcium-induced calcium release (CICR)

- AP spreads rapidly along sarcolemma from cell to cell via gap junctions

- Reach inside of cell via T-tubules

- Ca2+ enter via dihydropyridine receptor (DHPR) in T-tubules

- causes RYR to release Ca2+ from SR

Coronary arteries

- provide primary blood supply to myocardium

- originate from base of aorta and encircle myocardium

Intrinsic control of heart activity: cardiac conduction system

- spontaneous rhythmicity: special heart cells generate and spread electrical signal

- Sinoatrial (SA) node

- atrioventricular (AV) node

- AV bundle (bundle of His)

- Purkinje fibers

- electrical signal spreads via gap junctions

- intrinsic heart rate (HR): 100 beats/min (originates at SA node)

- observed in heart transplant patients

Sinoatrial (SA) node (pacemaker)

- generates impulses ~ 100 beats/min (sinus rhythm)

- depolarizes fastest

- spread to via RA/LA to AV node

- stimulates atrial contraction

Atrioventricular (AV) node

- delays impulses ~ 0.13 s

- depolarizes 50 beats/min in absence of SA node input

AV bundle (or bundle of his)

- only electrical connection between atria and ventricles

- send to apex of heart

Right and left bundle branches

two pathways in inter-ventricular septum that carry impulses toward apex

Purkinje fibers

- complete pathway into apex and ventricular walls

- stimulate ventricular contraction

AV bundle and Purkinje fibers depolarize only 30 beats/min in absence of AV node input

Parasympathetic (PSNS)

- reaches heart via vagus nerve (10th cranial nerve)

- carries impulses to SA, AV nodes

- releases ACh, hyperpolarizes cells

- decreases HR, force of contraction

- decreases HR below intrinsic HR

- intrinsic HR: 100 bpm

- normal resting HR (RHR): 60 to 100 bpm

- elite endurance athlete: 35 bpm

Sympathetic (SNS)

- opposite effects of PSNS

- carries impulses to SA, AV nodes

- releases NE, facilitates depolarization

- increases HR, force of contraction

- increases HR above intrinsic HR (100 bpm)

- determines HR during physical, emotional stress

endocrine system

also plays a role through Epi and NE

Autonomic control of HR

PNS dominates when HR less than 100 bpm

once exercise begins, HR first increases due to withdrawl of vagal tone

electrocardiogram (ECG)

- ECG: recording of heart's electrical activity

- 10 electrodes, 12 leads

- different electrical views

- diagnostic tool

- three basic phases

- p wave

- QRS complex

- T wave

P wave

atrial depolarizaton (SA node to AV node)

QRS complex

ventricular depolarization (AV bundle to purkinje fibers and through ventricles)

T wave

ventricular repolarization

Bradycardia (pathological vs. exercise induced):

RHR less than 60 bpm

Tachycardia (pathological vs. exercise induced)

RHR greater than 100 bpm

Premature ventricular contraction (PVCs)

skipped or extra beats; result from impulses originating outside SA node

Atrial flutter, fibrillation

atria depolarize 200-400 bpm

Ventricular tachycardia

3 more PVCs

Ventricular fibrillation

depolarization of ventricular tissue is random and uncoordinated (not injecting any blood to system, very problematic, might need to be shocked back to normal heart beat)

Cardiac cycle

includes all the mechanical and electrical events that occur during one heartbeat

Stroke volume (SV)

volume of blood pumped in one heartbeat

- during systole, most (not all) blood ejected

- EDV - ESV = SV (~60 -80)

Ejection fraction (EF)

percent of EDV pumped

- SV/EDV=%EF

- clinical index of heart contractile function

Cardiac output (Q)

- total volume of blood pumped per minute

- Q= HRxSV

- resting cardiac output is ~ 4.2 to 5.6 L/min

- average total blood volume ~ 5L

- total blood volume circulates once every minute!

Arteries

carry blood away from heart

- elastic arteries: known as conducting arteries

- muscular/distributing arteries

Arterioles

resistance vessels

- control blood flow, feed capillaries

capillaries

exchange vessels

- site of nutrient and waste exchange

venules

collect blood from capillaries

veins

capacitance vessels

- carry blood from venules back to heart

Systolic pressure (SBP)

- highest pressure in artery (during systole) (contraction)

- top number, ~ 110 to 120 mmHg

Diastolic pressure (DBP)

- lowest pressure in artery (during diastole) (relaxation)

- bottom number, ~ 70 to 80 mmHg

Mean arterial pressure (MAP)

- average pressure over entire cardiac cycle

- MAP = 2/3DBP +1/3 SBP or DBP + 1/3PP

- pulse pressure (PP) = SBP - DBP

General Hemodynamics

- blood flow: required by all tissues

- Pressure: force that drives flow

- provided by heart contraction

- blood flows from region of high pressure (LV, arteries) to region of low pressure (veins, RA)

- pressure gradient = 100 mmHg (aortic MAP) - 0 mmHg (right atrium) therefore, pressure gradient = 100 mmHg

- Resistance: force that opposes flow

- provided by physical properties of vessels

- R= [n x L/r^4] (radius is the most important factor)

- Blood flow Q= delta pressure/R

- Pressure = QxR

- R

- small changes in arteriole radius affect R

- vasoconstriction, vasodilation

- Arteriole: resistance vessels

- control systemic R

- site of most potent vasoconstriction and vasodilation

sources of resistance

- vascular resistance

- vessel length

- vessel diameter: most prominent source of resistance

blood pressure drop

- pressure highest in large arteries

- arterioles (resistance vessels) are responsible for ~ 70-80% of their drop in MAP

- lowest in large veins

- veins known as capacitance vessels

- capillary pressure lower but high enough to facilitate exchange of nutrients and gases across membrane

Distribution of blood

- blood flows to where needed most

- often regions of high metabolism which increases blood flow

- other examples: blood flow changes after eating, in the heat

- at rest (q= 5 L/min)

- liver, kidneys receive 50% of Q

- skeletal muscle receives ~15-20% of Q

- during heavy exercise (Q=25 L/min)

- exercising muscles receive 80% of Q via VD

- flow to liver, kidneys decreases via VC

Intrinsic control of blood flow

- ability of local tissues to dilate or constrict the arterioles that serve them and alter regional blood flow depending on immediate needs of those tissues

three types of intrinsic control

1. metabolic: increase O2 demand

2. endothelium-mediated vasodilation: increase shear stress (ex: flow)

3. myogenic contraction: pressure changes within vessel

Extrinsic neural control of blood flow

- upstream of local, intrinsic control

- redistribution of flow at organ, system level

- SNS innervates smooth muscle in arteries and arterioles

- baseline sympathetic activity --> vasomotor tone

- increase sympathetic activity --> increase vasoconstriction

- decrease sympathetic activity --> decrease vasoconstriction (passive vasodilation)

How do we overcome SNS to increase blood flow to active skeletal muscle?

functional sympatholysis

- "sympatho"- sympathetic nervous system

- "lysis" - breakdown, opposition, inhibit

- together, opposing the action of sympathetic nervous system

- local dilator substance's released from exercising muscle, overcoming sympathetic vasoconstriction and producing and overall vasodilation in the muscle (sympatholysis)

- metabolic waste products

- vasoactive molecules released from active skeletal muscle and endothelium that oppose sympathetic vasoconstriction such as nitric oxide (NO) or adenosine, vasodilators

Local control of muscle blood flow

- during aerobic exercise, blood flow to exercising muscle must increase to match metabolic demand of that muscle

- sympathetic vasoconstriction reduces blood flow to renal and splanchnic circulation to make more blood flow available for skeletal muscle

- sympathetic stimulation of constrictor fibers in arteriolar walls supplying skeletal muscle also increases

Distribution of venous blood

- at rest veins contain 2/3 blood volume

- high capacity to hold blood volume

- elastic, balloon like vessel walls

- serve as blood reservoir

- venous reservoir can be liberated, sent back to heart and into arteries

- sympathetic stimulation

- venoconstriciton (of veins and venules)

integrative control of blood pressure

- BP maintained by autonomic reflexes

- Baroreceptors

- chemoreceptors, mechanoreceptors in muscle

baroreceptors

- located aortic arch and carotid arteries

- sensitive to changes in arterial pressure

- afferent signals from baroreceptor to brain

- efferent signals form brain to heart and vessels

- adjust arterial pressure back to normal

return of blood to heart

- upright posture makes venous return to heart more difficult

- 3 mechanisms assist venous return

- one way venous valves

- muscle pump

- respiratory pump

blood major function

1. transportation (O2, waste, nutrients)

2. temperature regulation

3. acid base (pH) balance

Blood volume

5-6 in men

4-5 in women

whole blood = plasma + formed elements

Red blood cells

anucleate (no nucleus), cannot reproduce

-replaced regularly via hematopoiesis

- life span ~ 4 months

- produced and destroyed at equal rates

hemoglobin

- oxygen transporting protein in red blood cells (4 O2/hemoglobin)

- heme (pigment, iron, O2) + globin (protein)

- 250 million hemoglobin/red blood cells

- oxygen carrying capacity: 20 mL O2/100 mL blood

Blood viscocity

-thickness of blood

-twice as viscous as water

-viscosity increases as hematocrit increases

-plasma volume must increase as red blood cells increase

- occurs in athletes after training, acclimation

- hematocrit and viscosity remain stable

- otherwise, blood flow or O2 transport may suffer