CONTROL OF CARDIOVASCULARFUNCTION

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PATH OF BLOOD FLOW

Scenario:

• You inject a medication into the client’s arm

• Within a few minutes, some of that drug has reached the client’s liver and is being deactivated

Question:

• How did it get there?7/1/2014 2

SIMPLIFIED PATH OF BLOOD FLOW

right

heart

lungs

left

heart

body

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HEART ANATOMY

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QUESTION

Tell whether the following statement is true or false:

The pulmonary circulation moves blood through the left side of the heart.

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ANSWER

False

The right side of the heart pumps blood to the lungs through the pulmonary arteries, where gas exchange takes place. The left side of the heart is considered systemic circulation because blood is pumped to all body tissues.

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THE HEART LAYERS

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THE BASICS OF CELL FIRING

• Cells begin with a negative charge: resting membrane potential

• Stimulus causes some Na+ channels to open

• Na+ diffuses in, making the cell more positive

Threshold potential

Resting membrane potential

Stimulus

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THE BASICS OF CELL FIRING (CONT.)

• At threshold potential, more Na+ channels open

• Na+ rushes in, making the cell very positive: depolarization

• Action potential: the cell responds (e.g., by contracting)

Threshold potential

Resting membrane potential

Stimulus

Action potential

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THE BASICS OF CELL FIRING (CONT.)

• K+ channels open

• K+ diffuses out, making the cell negative again: repolarization

• Na+/K+ ATPaseremoves the Na+ from the cell and pumps the K+ back in

Threshold potential

Resting membrane potential

Stimulus

Action potential

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CARDIAC CELL FIRING

• Cells begin with a negative charge: resting membrane potential

• Calcium leak lets Ca2+

diffuse in, making the cell more positive

Threshold potential

Resting membrane potential

Calcium leak

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CARDIAC MUSCLE FIRING (CONT.)

• At threshold potential, more Na+ channels open

• Na+ rushes in, making the cell very positive: depolarization

• Action potential: the cell responds (e.g., by contracting)

Threshold potential

Resting membrane potential

Action potential

Calcium leak

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CARDIAC MUSCLE FIRING (CONT.)

• K+ channels open

• K+ diffuses out, making the cell negative again, but Ca2+ channels are still allowing Ca2+ to enter

• The cell remains positive: plateau

Threshold potential

PLATEAU

Action potential

Calcium leak

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CARDIAC MUSCLE FIRING (CONT.)

• During plateau, the muscle contracts strongly

• Then the Ca2+

channels shut and it repolarizes

Threshold potential

PLATEAU

Action potential

Calcium leak

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QUESTION

Which ion channels allow cardiac muscle to fire without a stimulus?

a. Na+

b. K+

c. Ca2+

d. Cl-

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ANSWER

c. Ca2+

In the S-A node and A-V node, resting cardiac muscle cells have open Ca2+ channels. This allows Ca2+ to leak into the cells, making them more positive (the cells reach threshold this way without the need for a stimulus).

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HEART CONTRACTION

How would each of the following affect heart contraction:

• A calcium-channel blocker

• A Na+ channel blocker

• A drug that opened Na+ channels

• A drug that opened K+ channels7/1/2014 18

CARDIAC CYCLE—DIASTOLE

• Ventricles relaxed

• Blood entering atria

• Blood flows through AV valves into ventricles

• Semilunar valves are closed

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ECG

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CARDIAC CYCLE—SYSTOLE

• Ventricles contract

• Blood pushes against AV valves and they shut

• Blood pushes through semilunar valves into aorta and pulmonary trunk

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QUESTION

Which of the following statements is true about ventricular systole?

a. Atria contract

b. Ventricles contract

c. AV valves are open

d. Semilunar valves are closed

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ANSWER

b. Ventricles contract

During ventricular systole, the ventricles contract. Because blood is being forced from the ventricle, semilunar valves must be open and AV valves, closed. The atria is in diastole (relaxation) during ventricular systole.

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CARDIAC CYCLE

Discussion:• Arrange these steps in the proper order:

– Ventricles relax – First heart sound– Systole – Semilunar valves open– Diastole – AV valves close– AV valves open – Semilunar valves close– Ventricles contract – Second heart sound

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PRESSURE, RESISTANCE, FLOW

• Fluid flow through a vessel depends on:

– The pressure difference between ends of the vessel

• Pressure pushes the fluid through

• Pressure keeps the vessel from collapsing

– The vessel’s resistance to fluid flow

• Small vessels have more resistance

• More viscous fluids have greater resistance

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PRESSURE, RESISTANCE, FLOW OF BLOOD

• Blood flow through a vessel depends on:

– Heart creating pressure difference between ends of the vessel

• Heart pushing the blood through

• Blood pressure keeping the vessels open

– The vessel’s resistance to fluid flow

• Constricting arterioles increasing resistance

• Increased hematocrit increasing resistance

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DISCUSSION

How will each of these factors affect arteriole size and peripheral resistance?

• Lactic acid • Low PO2

• Cold • Histamine

• Endothelin • Heat

• NO • Adenosine

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BLOOD PRESSURE

• BP = CO x PR• Blood Pressure = Cardiac Output × Peripheral

Resistance

• CO = SV X HR

• In healthy adult – Highest pressure(systolic)- < 120 mmHg

– Lowest pressure (diastolic) < 80 mmHg

• Difference between systolic and diastolic pressure = pulse pressure

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REGULATION OF BP

Short term regulation of BP relies on neural and hormonal mechanisms

A) Neural centers are located in the reticular formation of lower pons and medulla of the brain

• Area also called cardiovascular center • ANS control of BP is mediated by intrinsic

circulatory reflexes, extrinsic reflexes, and higher neural control centers

• Intrinsic mechanism involves Baroreceptors and chemoreceptors

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REGULATION OF BP CON’T

• Baroreceptors– Pressure sensitive receptors

– Located in the walls of blood vessels and heart

– Carotid & aortic baroreceptors are located in strategically

– Send impulse to the cardiovascular centers

• Arterial chemoreceptors– Sensitive to changes in oxygen, Carbondioxide, and

Hydrogen ion content of blood

– Located in carotid and aortic bodies

– Can also induce widespread vasoconstriction 7/1/2014 31

HORMONAL MECHANISMS

• Involves: renin- angiotensin- aldosterone mechanism, Vasopressin, epinephrine

• Renin– An enzyme found in the juxtaglomerula cells of the kidneys

– Released in blood where it converts angiotensinogen(plasma protein) to angiotensin I

– Angiotensin I is converted to angiotensin II in the lungs by Angiotensin Converting Enzyme (ACE) present in the endothelium of the lung vessels

– Angiotensin II :• Is a strong vasoconstrictor (arterioles and Veins)

• Stimulates aldosterone secretion from adrenal (cortex) gland bringing about Na/water retention by kidneys

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VASOPRESSIN

• Released from the posterior pituitary gland in response to decreased blood volume and BP, increased osmolality of body fluids

• Has vasoconstrictor effect on blood vessels especially those of the planchnic circulation that supplies the abdominal viscera

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HYPERSTENSION

• Classified into Primary (essential) and secondary hypertension

• Essential is the most common accounting for 90-95% of HT cases

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BP classification Systolic BP(mmHg) Diastolic BP (mmHg)

Normal < 120 And < 80

Pre-hypertension 120 – 139 And 80 – 89

Stage 1 Hypertension 140 – 149 And 90 - 99

Stage 2 Hypertension ≥ 160 ≥ 100

RISK FACTORS FOR HT

• Family history, race, age related increase

• Life style

– High sodium intake, excessive calorie intake and obesity, physical inactivity, excessive alcohol intake

• Oral contraceptives

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MANIFESTATION

• Target organ damage affecting the following organs

• Heart– Left ventricular hypertrophy

– Angina or prior myocardial infarction

– Prior coronary revascularization

– Heart failure

• Brain – Stroke or transient ischemic attack

• Chronic kidney disease

• Peripheral vascular disease

• Retinopathy 7/1/2014 36

DIAGNOSIS

• Repeated BP measurement

• BP measurement should be taken when the person is relaxed and has rested for at least 5 minutes and had not smoked or taken caffeinwithin 30 minutes

• Pharmacological treatment based on:

– severity of disease

– Presence of target organ disease

– Existence of other conditions and risk factors 7/1/2014 37

DRUGS USED

• Diuretics

• β-adrenergic receptor blockers

• ACE inhibitors

• Angiotensin II receptor blockers

• Central alpha 2 adrenergic agonists

• Alpha 1 adrenergic receptor blockers

• Vasodilators

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SECONDARY HYPERTENSION

• Most common causes are: Kidney disease, adrenocortical disorder, phenochromocytoma, coarctation of the aorta, drugs such as cocaine

• HT arising from kidney disease is usually a result of: – Acute glomerulonephrites– Acute renal failure– End stage renal disease

• 80% of patients with Chronic renal failure have HT • Most acute kidney disorders result in decreased urine

formation, retension of water & Na and HT • Reduced renal blood flow causes the affected kidney

to release excess amounts of renin

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ORTHOSTATIC HYPERTENSION

• Read about its causes and management

• Also read about venous thrombosis especially Deep Vein Thrombosis( DVT)

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QUESTION

Tell whether the following statements is true or false:

In patients with hypertension (high blood pressure), peripheral resistance is increased.

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ANSWER

True

In hypertension, blood vessels are constricted/narrowed. Smaller vessels increase resistance (it’s harder to push the same amount of fluid/blood through a tube that has become smaller).

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LYMPH VESSELS CARRY TISSUE FLUID BACK TO THE VEINS

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