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CARDIO/RESP > Physiology > Flashcards

Physiology Flashcards

1
Q

What are the phases of the cardiac cycle?

A 
Ventricular diastole:
(1) Isovolumetric relaxation
(2) Passive ventricular filling 
(3) Atrial systole
Ventricular Systole:
(1) Isovolumetric contraction
(2) Ventricular ejection
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2
Q

What is the process of cardiac muscle contraction from when the AP arrives in the cardiac contractile cell?

A

(1) AP travels down T-tubule
(2) Cystolic Ca2+ levels increase (small amount from ECF and large amount from SR)
(3) Troponin-tropomyosin complex in thin filaments pulled aside
(4) Cross bridge cycling between thick and thin
(5) Thin filaments slide inward between thick filaments
(6) CONTRACTION

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3
Q

Explain the generation of a cardiac muscle AP

A

(1) Depolarisation due to fast Na+ channels
(2) Plateau phase - due to opening of slow voltage gated Ca2+ channels and closing of some K+ channels
(3) Repolarisation - due to opening of voltage gated K+ channels and closing of Ca2+ channels

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4
Q

Impulse delay is 0.16s, which areas contribute to this delay?

A

AV node: 0.09s
AV bundle: 0.04s
SA to AV node: 0.03s

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5
Q

On an electrocardiogram, what do the following represent:

(1) P wave
(2) QRS complex
(3) T wave

A

(1) P wave - atrial depolarisation
(2) QRS complex - ventricular depolarisation
(3) T wave - ventricular repolarisation

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6
Q

What does end systolic volume mean and what parameters affect it?

A

ESV - LV volume at end of contraction

Parameters (1) force of ventricle contraction (2) Resistance or ‘back pressure’ in outflow (AFTERLOAD)

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7
Q

What factors influence cardiac output?

A

Central venous pressure, blood volume, gravity, peripheral venous tone, respiration, SVR, heart rate

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8
Q

What does end diastolic volume mean and what parameters affect it?

A 
EDV - LV Volume at end of filling 
Parameters 
(1) venous filling pressure (preload)
(2) force of atrial contraction 
(3) distensibility of ventricular wall
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9
Q

What influences inotropy (force of muscle contraction)? and what are some inotropic agents?

A

Calcium!!!
+ve inotropic: adrenaline, NA, digitalis
-ve inotropic: Ach, verapamil

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10
Q

Afterload: what is the relationship between aortic pressure and stroke volume?

A

The aortic pressure on the semilunar valves must be overcome before ventricular ejection can occur. Higher aortic pressure = lower stroke volume.

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11
Q

How does exercise affect the CV parameters?

A
  • Increases preload
  • Sympathetic response: NA results in +ve isotropy
  • Increase in after load: sympathetic response results in vasoconstriction
  • Arterial pressure increases pressure on Aortic valves
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12
Q

What parameters can be changed to regulate blood pressure?

A

(1) Cardiac output
(2) Stroke volume
(3) Blood volume

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13
Q

What is Henry’s law?

A

when a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure

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14
Q

What does diffusion rate depend on?

A
  • Surface area
  • Concentration gradient
  • Thickness of membrane
  • Diffusion constant
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15
Q

What are the limitations in pulmonary gas exchange?

A

(1) Low PiO2
(2) Hypoventilation
(3) Diffusion limitations
(4) Ventilation-perfusion mismatching
(5) R –> L shunts

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16
Q

What is the VA/Q ratio?

A

Ventilation-perfusion ratio
VA - ventilation - the air that reaches the alveoli (4.2L/min)
Q - perfusion - the blood that reaches the alveoli (5L/min)
VA/Q ratio: usually 0.84

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17
Q

What does a reduced and increased VA/Q ratio mean?

A

Reduced - impaired ventilation (reduced PiO2)

Increased - impaired perfusion (decreased PaCO2 and increased PaO2)

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18
Q

What causes the changes in arteriole and bronchiole diameter?

A

Arteriole: alveolar PO2 (increase = constriction)
Bronchiole: alveolar PCO2 (increase = dilation)

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19
Q

What do the terms ‘right –> left shunt’ and ‘dead space’ mean?

A

RL shunt: deoxygenated venous blood enters arterial circulation (passes through lungs without getting oxygenated) - usually <5% CO
Dead space - ventilated alveoli don’t receive blood

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20
Q

What increases loading of oxygen onto Hb?

A

Alkalosis, decreased temperature, low PCO2 (bohr effect)

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21
Q

What increases off-loading of oxygen from Hb?

A

Acidosis, high temperature, high PCO2 (bohr effect)

22
Q

What are the three modes of CO2 transport in the blood?

A

(1) Dissolved CO2
(2) Carbamino (on Hb)
(3) Bicarbonate

23
Q

How does the phrenic nerve control breathing?

A

Phrenic nerve - controlled by the DRG

Increased phrenic nerve AP = diaphragm contracts = inspiration

decreased phrenic nerve AP = diaphragm relaxes = expire

24
Q

How is depth of breathing determined?

A

By how actively the respiratory centre stimulates respiratory muscles

25
Q

How is respiratory rate determined?

A

Rate is determined by when, how long the respiratory centre is active

26
Q

Where does the DRG receive input from?

A

Higher centres
Pontine centres
CNS and peripheral chemoreceptors
Respiratory muscles

27
Q

What are the functions of the:

(1) Pneumotaxic area
(2) Apneustic area

A

(1) Pneumotaxic area - limits inspiration, reduced inspiration and increased rate
(2) Apneustic area - inhibits inspiratory switch off which prolongs inspiration

28
Q

Where are the central chemoreceptors located and what do they measure?

A

Location: beneath ventral surface of medulla
Measures: sensitive to changes in CO2 but mostly to H+ in the CSF
–> results in increased rate and depth of breathing

29
Q

Where are the peripheral chemoreceptors located and what do they measure?

A

Location: carotid and aortic arteries
Measure: hypoxia - changes in PO2, and to a small degree CO2, temp and pH
–> when excited (substantial drop in O2) they increase inspiration

30
Q

What is the inflation reflex?/Hering-breuer reflex

A
  • Stretch receptors are stimulated by lung inflation
  • inhibitory signals to medullary respiratory centre ENDS inhalation to allow expiration to occur
  • -> more of a protective response than normal regulatory mechanism
31
Q

What two factors cause increased ventilation during exercise?

A

(1) Brain - psychological anticipation and cortical motor activation of muscles/resp
(2) Proprioceptor impulses - respiratory centres

32
Q

What are the upper airway receptors?

A

Vagal afferents: pharyngeal and laryngeal receptors

sense flow, temp, pressure, muscle contraction and obstruction

33
Q

What are the lower airway receptors?

A

Myelinated pulmonary receptors - respond to mechano-irritant/touch (causes excitation like cough)

Unmyelinated pulmonary receptors - stimulated by chemicals (cause airway defence reflex like bronchoconstriction, mucous secretion)

34
Q

What sets the heart rate and how can the autonomic nervous system regulate it?

A

Set by: pacemaker cells rate of depolarisation
Parasymp: increases potassium conductance , slowing depolarisation and heart rate (does NOT affect force of contraction)
Symp: increases depolarisation rate, increasing heart rate and contraction rate (inotropy) - because the nerves synapse on the SA node and myocardium

35
Q

What affects systemic vascular resistance?

A

(1) size of lumen
(2) blood viscosity
(3) total blood vessel length

36
Q

How is blood pressure measured short term and long term?

A

Short term - baroreceptors

Long term - kidney via renin/angiotensin system

37
Q

Where are the baroreceptors located and how do they respond to blood pressure?

A

Carotid sinus - regulates BP in the brain
Aortic reflex - regulates systemic BP
- When blood pressure falls, baroreceptors are stretched less and the rate of impulses to CV slows down
- CV decreases parasympathetic stim. and increases sympathetic stim.

38
Q

How is the renin-angiotensin-aldosterone system involved in long term blood pressure regulation?

A

RAS - raises BP by vasoconstriction and secretion of aldosterone (increases sodium/water retention to increase BP)

39
Q

How is atrial natriuretic peptide involved in blood pressure?

A

ANP release by atrial cells - cause vasodilation, promoting loss of sodium and reduced BV to lower BP

40
Q

What are the 2 pressures that drive filtration in the kidneys?

A

Hydrostatic pressure - pressure difference across glomerulus (blood vs filtrate)
Osmotic pressure - transport solutes to set up an osmotic gradient

41
Q

What does the glomerular filtration rate depend on?

A

(1) permeability of membrane
(2) surface area of membrane
(3) filtration pressure

42
Q

How do we sense blood pressure?

A

(1) stretch (baroreceptors)
(2) osmolarity
(3) kidney function - speed of filtration

43
Q

How does the renin-angiotensin-aldosterone system respond to decreased arterial pressure?

A

Renin in the kidney converts a plasma protein to Angiotensin 1, which is converted to At 2 by ACE enzyme in the lungs. At 2 causes renal retention of water and salt and vasoconstriction to increased arterial pressure. Aldosterone also increases sodium reabsorption - water follows to increase BP.

44
Q

What are the pressure that promote filtration in the circulation?

A

(1) capillary hydrostatic pressure

(2) interstitial fluid osmotic pressure

45
Q

What are the pressures that promote reabsorption in the circulation?

A

(1) Plasma colloid osmotic pressure

(2) interstitial fluid hydrostatic pressure

46
Q

What pressures contribute to oedema?

A

o Increased capillary hydrostatic pressure
o Decreased plasma oncotic pressure (PCOP) – reduce plasma albumin
o Increased interstitial fluid oncotic pressure (IFOP) – increase capillary permeability
o Decreased interstitial fluid hydrostatic pressure (IFHP)

47
Q

What are the consequences of veno-constriction?

A
  • reduces capacitance
  • increases venous return
  • increases CO
48
Q

What are the systemic controls for vasoconstriction?

A

♣ NA – sympathetic postganglionic neurons
♣ Serotonin – gut ECL cells platelets
♣ Vasopressin – ADH – posterior pituitary
♣ Angiotensin II – part of RAS

49
Q

What are the systemic controls for vasodilation?

A

♣ Adrenaline (B2 receptors) from adrenal medulla
♣ Ach – parasympathetic postganglionis neurons
♣ ANP – from atrial myocardium and brain
♣ VIP – from neurones

50
Q

What does the DRG receive input from?

A

(1) higher centres
(2) pontine centres
(3) CNS and peripheral chemoreceptors
(4) Respiratory muscles

CARDIO/RESP (5 decks)

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