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Cardiorespiratory > Control Of Circulation > Flashcards

Control Of Circulation Flashcards

1
Q

Why do we need to control our circulation?

A

Maintain blood flow
Maintain arterial pressure
Distribute blood flow
Auto-regulate/homeostasis
Function normally
Prevent catastrophe!
(maladapt in disease)

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2
Q

What are components of Circulation?

A

Anatomy
Blood
Pressure
Volume
Flow

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3
Q

Features of Arteries

A

Low resistance conduits
Elastic
Cushion systole
Maintain blood flow to organs during diastole

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4
Q

What are arterioles?

A

Principal site of resistance to vascular flow
Therefore, TPR = Total Arteriolar Resistance
Determined by local, neural and hormonal factors
Major role in determining arterial pressure
Major role in distributing flow to tissue/organs

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5
Q

What is TPR?

A

Vascular smooth muscle (VSM) determines radius
VSM Contracts = ↓Radius = ↑Resistance ↓Flow
VSM Relaxes = ↑Radius = ↓Resistance ↑Flow
Or Vasoconstriction and Vasodilatation
VSM never completely relaxed = myogenic tone

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6
Q

Features of Capillaries

A

40,000km and large area = slow flow
Allows time for nutrient/waste exchange
Plasma or interstitial fluid flow determines the distribution of ECF between these compartments
Flow also determined by
Arteriolar resistance
No. of open pre-capillary sphincters

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7
Q

Features of Veins

A

Compliant
Low resistance conduits
Capacitance vessels
Up to 70% of blood volume but only 10mmHg
Valves aid venous return (VR) against gravity
Skeletal muscle/Respiratory pump aids return
SNS mediated vasoconstriction maintains VR/VP

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8
Q

Features of Lymphatics

A

Fluid/protein excess filtered from capillaries
Return of this interstitial fluid to CV system
Thoracic duct; left subclavian vein
Uni-directional flow aided by
Smooth muscle in lymphatic vessels
Skeletal muscle pump
Respiratory pump

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9
Q

Cardiac Output Equation

A

Cardiac Output (CO) = Heart Rate (HR) x Stroke Volume (SV)

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10
Q

Blood Pressure Equation

A

CO x Total Peripheral Resistance (TPR)
(like Ohm’s law: V=IR)

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11
Q

Pulse Pressure (PP) Equation

A

Systolic – Diastolic Pressure

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12
Q

Mean Arterial Pressure Equation

A

Diastolic Pressure + 1/3 PP

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13
Q

What is Frank-Starling Mechanism?

A

SV increases as End-Diastolic Volume increases
Due to Length-Tension (L-T) relationship of muscle
↑EDV = ↑Stretch = ↑Force of contraction
Cardiac muscle at rest is NOT at its optimum length
↑VR = ↑EDV = ↑SV = ↑CO (even if HR constant)

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14
Q

What is Blood Pressure?

A

BP = Pressure of blood within and against the arteries
Systolic = Highest, when ventricles contract (100-150mmHg)
Diastolic = Lowest, when ventricles relax (not zero, due to aortic valve and aortic elasticity .. 60-90mmHg)
Mean arterial pressure = D + 1/3(S-D)
Measured using a sphygmomanometer
Using brachial artery
Convenient to compress
Level of heart

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15
Q

How is Blood Pressure measured?

A

Ingredients:
Arm, Sphygmomanometer, Stethoscope, 2 Ears

Directions:
Inflate cuff to above systolic BP, until pulse
impalpable or Korotkoff sounds absent.

Serving suggestion:
Slowly deflate cuff, listening all the time.

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16
Q

Blood Pressure Sounds

A

0) > Systolic Pressure = no flow, no sounds

1) Systolic pressure = high velocity = tap

2-4) Between S and D = thud

5) Diastolic pressure = sounds disappear

17
Q

What are components of Blood pressure control?

A

Autoregulation
Local mediators
Humoral factors
Baroreceptors
Central (neural) control

18
Q

Explain the balance of extrinsic and extrinsic control

A

Brain & heart: intrinsic control dominates to maintain BF to vital organs

Skin: BF is important in general vasoconstrictor response and also in responses to temperature (extrinsic) via hypothalamus

Skeletal muscle: dual effects:- at rest, vasoconstrictor (extrinsic) tone is dominant; upon exercise, intrinsic mechanisms predominate

19
Q

Give an example of a Vasoconstrictor (Local Humoral Factors)

A

Endothelin-1

20
Q

Give examples of Vasodilators (Local Humoral Factors)

A

Hypoxia
Adenosine
Bradykinin
NO
K+, CO2, H+
Tissue breakdown products

21
Q

What are control functions of the endothelium?

A

Essential for control of the circulation
EDRF = Nitric Oxide (NO) = potent vasodilator
L-Arg is converted into NO by NO synthetase
Prostacyclin = potent vasodilator
Endothelin = potent vasoconstrictor

22
Q

Give examples of Vasoconstrictors (Circulating Hormonal Factors)

A

Epinephrine (skin)
Angiotensin II
Vasopressin

23
Q

Give examples of Vasodilators (Circulating Hormonal Factors)

A

Epinephrine (muscle)
Atrial Natriuretic Peptide

24
Q

What are Baroreceptors?

A

Pressure sensing
Primary (Arterial) =carotid sinus & aortic arch
Secondary = veins, myocardium, pulmonary vessels
Afferent Glossopharyngeal (IX);
Efferents sympathetic and Vagus (X)
Firing rate proportional to MAP and PP, integrated in the medulla
↑BP ⇒ ↑Firing ⇒ ↑PNS/↓SNS ⇒ ↓CO/TPR = ↓BP
and vice versa

25
Q

What are arterial baroreceptors?

A

Key role in short-term regulation of BP; minute to minute control, response to exercise, haemorrhage

If arterial pressure deviates from ‘norm’ for more than a few days they ‘adapt’/’reset’ to new baseline pressure eg. in hypertension

The major factor in long-term BP control is blood volume

26
Q

What are Cardiopulmonary baroreceptors?

A

Atria, ventricles, PA
Stimulation = ↓vasoconstrictor
centre in medulla, = ↓ BP
Also ↓release angiotensin, aldosterone & vasopressin (ADH), leading to fluid loss
Play an important role in blood volume regulation

27
Q

What are the main neural influences on the medulla?

A

Baroreceptors
Chemoreceptors
Hypothalamus
Cerebral cortex
Skin
Changes in blood [O2] and [CO2]

28
Q

What are central chemoreceptors?

A

Chemosensitive regions in medulla

↑PaCO2 = vasoconstriction, ↑peripheral resistance, ↑BP

↓PaCO2 = ↓medullary tonic activity, ↓BP

Similar changes with ↑ and ↓ pH

PaO2 less effect on medulla; Moderate ↓ = vasoconstriction; Severe ↓ = general depression

Effects of PaO2 mainly via peripheral chemoreceptors

29
Q

What are key central effectors ?

A

Peripheral

Blood vessels (vasodilatation and vasoconstriction: affects TPR)

Heart (rate and contractility:
CO = HR x SV)

Kidney (fluid balance:
longer term control)

30
Q

What is orthostatic hypotension?

A

Aetiology = standing quickly, too long, dehydration, hot room
Symptoms = lightheaded, sweating, syncope
Physiology = Fall in BP and Venous Pooling (X nerve)
Failure to reflexly maintain BP and HR
Perfusion to brain reduced
Treatment = lay supine and elevate limbs to ↑VR
Frank-Starling leads to improved SV and CO
Investigate: Lying/ standing BP; tilt test

Common cause: BP drugs, B blockers, vasodilators
Lifestyle adaptation

31
Q

What is POTS?

A

Postural orthostatic tachycardia syndrome

Standing
Palpitation, dizzy, near syncope, sweating, debilitating
Physiology = Excess tachycardia response
Investigate = Tilt test
HR↑ >40bpm; BP usually OK
Not well understood

Cardiorespiratory (27 decks)

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