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BIOMOLECULES AND CELLS > Regulation of circulation > Flashcards

Regulation of circulation Flashcards

1
Q

Depolarisation

A
  • Activation of cells by depolarisation

* Na+ channels open and Na+ ions move inside making the inside of the cell more positive than the outside

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2
Q

Hyperpolarisation

A
  • Inhibition of cells by hyperpolarisation
  • After repolarisation, some K+ channels remain open and K+ continues to go out. Then the inside of the cell is more negative than when it began.
  • It is harder to depolarise
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3
Q

How is muscle contraction triggered by depolarisation?

A
  • occurs when muscle cell membrane is depolarised (more positive inside)
  • depolarisation triggers calcium ion release from sarcoplasmic reticulum - causes contraction
  • muscle contraction is then inhibited by hyperpolarisation of the membrane
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4
Q

What controls rhythmic heart contractions?

A 
• autorhythmicity
• gap junctions
• 2 groups of pacemaker cells
- Sinoatrial node (SAN)
- Atrioventricular node (AVN)
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5
Q

SAN (Sinoatrial node)

A
  • spontaneous rhythmic depolarisation (approximately 100 times per minute if independent of nervous control)
  • SAN kicks of action potential which spreads through the atrial syncytium - immediately the atria contract
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6
Q

How does the Atrioventricular node (AVN) control heart contractions?

A
  • Action potentials sent to the ventricles via the bundle of His
  • run to the ventricular apex via right and left bundle branches
  • APs spread through ventricles via Purkinje fibres
  • ventricular syncytium
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7
Q

What is cardiac arrest?

A

Sudden loss of cardiac function when the heart abruptly stops beating

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8
Q

What is the most common loss of cardiac function?

A
  • Loss of ventricular fibrillation
  • caused by irregular activity in the heart (Arrhythmia)
  • when this happens, the heart pumps little or no blood to the body
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9
Q

What is the treatment of cardiac arrest?

A

• defibrillation using electricity to ‘shock’ the heart to try and restore its regular rhythm

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10
Q

How do you calculate mean arterial pressure (MAP)?

A

MAP = (Systolic + 2diastolic)/3

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11
Q

Why is MAP calculated that way?

A
  • diastolic part of cycle is twice as long as systolic

* therefore we calculate the weighted average

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12
Q

What is involved in the response to a change in blood pressure?

A
  • baroreceptors which then initiate the baroreceptor reflex
  • uses autonomic nervous system to effect/restore the mean arteriole pressure
  • this is a rapid response
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13
Q

What is involved in the response for an increased demand for oxygen?

A
  • chemoreceptors
  • autonomic nervous system
  • hormones
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14
Q

What are the different factors that act on blood vessels causing vasoconstriction/dilation?

A
  1. Noradrenaline from the sympathetic nervous system - vasoconstriction
  2. release of paracrine factors from endothelial cells
    • edothelin 1 - vasoconstriction
    • nitric oxide - vasodilation
  3. Hormones also affect vascular smooth muscles
    • Angiotensin II from kidney - vasoconstriction
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15
Q

Regulation of blood vessels via vasoconstriction

A
  • Norepinephrine, Angiotensin II, Endothelin-1 act via different (G-protein linked) receptors
  • Phospolipase C (PL-C) activation causes formation of Inositol tri-Phosphate (IP3)
  • IP3 stimulates the release of calcium from the sarcoplasmic reticulum (SR)
  • [Ca2+] increases causing smooth muscle contraction
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16
Q

What response occurs in the kidney when the arterial pressure declines?

A
  • Kidney blood pressure declines
  • kidney releases renin which activates angiotensin
  • angiotensin causes vessels to constrict and stimulates thirst
  • arterial pressure rises
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17
Q

What response occurs in the pituitary gland when arterial pressure declines?

A
  • Firing in arterial stretch sensors decrease since there is a decrease in arterial pressure
  • ADH (anti-dieuretic hormone - antiweeing) released from posterior pituitary
  • ADH stimulates water reabsorption by kidneys
  • arterial pressure rises
18
Q

What is meant by vasomotor tone?

A
  • Blood vessels are always a bit constricted

* this means they can either relax more or constrict more

19
Q

How is the frequency of neural electrical signals related to the diameter of blood vessels?

A
  • increased frequency of signals mean there is more norepinephrine released which bind to alpha receptors
  • vessels constrict
  • decreased frequency of signals mean less norepinephrine is released and bind to blood vessels
  • vessels dilate
20
Q

What is the positive feedback loop that occurs when arterial blood pressure falls?

A
  • decreased blood flow to tissue
  • local accumulation of metabolic wastes
  • autoregulatory widening of vessels
21
Q

Autonomic Innervation (supply of nerves to the heart) for sympathetic nerves

A

Sympathetic Nerves

• Noradrenaline binds to Beta 1 adrenoreceptors

22
Q

How are pacemaker cells involved in the reducing the heart rate?

A
  • Parasympathetic - reduce heart rate
  • Ach bind to muscarinic receptors in the SAN - become hyperpolarised
  • it is harder for depolarisation to occur
  • there is a decrease in heart rate and there is a greater interval between each beat
23
Q

How are pacemaker cells involved in increasing the heart rate?

A
  • adrenaline binds to beta adrenoreceptors
  • beta adrenoreceptors act on SAN and causes depolarisation which increases heart rate
  • myocytes also have increased [Ca2+] - causes heart to beat with greater force
24
Q

What is the baroreceptor reflex?

A

Initiates response to bring MAP back to normal

25
Q

Postural/Orthostatic hypotension

A
  • ‘dizzy spell’ when someone stands up too fast - increases with age
  • occurs when person’s BP suddenly falls as they stand up
  • overall effect is a transitory insufficient blood perfusion in the upper part of the body, particularly the brain
26
Q

What are baroreceptors and how do their signalling change when MAP is too high/low?

A

• Baroreceptors detect the amount of stretch in the blood vessels and signals it to the brain

When BP is too high
• More stretch in the vessels, so more action potentials sent to the brain

When BP is too low
• less stretch in the vessels and hence less signals are sent to the brain

27
Q

What happens after the detection of a sudden fall in BP?

A
  • MAP drops
  • baroreceptor firing is lower
  • CNS wants to then increase the MAP
  • Sympathetic increases - total peripheral resistance and cardiac output increases
  • Parasympathetic decreases - cardiac output increases

Arterial pressure then increases

28
Q

What chemoreceptors are involved in regulating the ANS?

A
  • arterial chemoreceptors - detect changes in blood chemical composition (CO2 and O2)
  • medullary chemoreceptors - detect changes in increases in CO2 levels
29
Q

What happens when there is an increased deman of oxygen due to exercise?

A
  • rapid response
  • involves central command, chemoreceptors, autonomic nervous system and hormones
  • Redistribution of blood flow - decreased blood flow to visceral beds and increased flow to skeletal muscle
  • this causes increased cardiac output - elevated heart rate
  • increased breathing rate
30
Q

Does norepinephrine influence vasoconstriction or vasodilation?

A
  • Sympathic neurons
  • Neural type
  • Causes vasocontriction
31
Q

Does endothelin influence vasoconstriction or vasodilation?

A
  • Vascular enothelium
  • Paracrine
  • Vasoconstriction
32
Q

Does angiotensin influence vasoconstriction or vasodilation?

A
  • Sourced from plasma
  • Endocrine
  • Vasoconstriction
33
Q

How does CO2 affect blood flow?

A
  • Sourced from multiple tissues
  • Metabolite
  • Vasodilation
34
Q

How does nitric oxide influence blood flow?

A
  • Sourced from vascular endothelium
  • Paracrine
  • Vasodilation
35
Q

How does bradykinin influence blood flow?

A

Sourced from multiple tissues

  • Paracrine
  • Causes vasodilation
36
Q

How does vasodilation occur?

A
  • Bradykinin binds to the receptor inside the endothelial cell which increases calcium production in that call
  • Increase in Ca2+ opens calcium gates K channels
  • Potassium flows out creating a difference in charges
37
Q

Autonomic Innervation (supply of nerves to the heart) for parasympathetic nerves

A

Parasympathetic Nerves

• Acetylcholine (ACh) binds to Muscarinic (M2) receptors

38
Q

What is pre-eclampsia?

A

A pregnancy-specific cardiovascular disease that is characterised by hypertension and excess levels of serum protein in urine

39
Q

What are the effects of pre-eclampsia?

A

Reduced sensitivity to bradykinin and abnormal vasorelaxation occurs

40
Q

Repolarisation

A
  • following depolarisation
  • sodium channels open and Na+ ions move into the cell causing the inside of the cell to become more positive than the outside.
41
Q

What is the atrial syncytium?

A

A network of cardiac muscle cells connected by gap junctions that allow coordinated contractions of the atria.

42
Q

List the steps in an action potential

A
  1. resting membrane potential
  2. depolarisation
  3. repolarisation
  4. hyperpolarisation

BIOMOLECULES AND CELLS (32 decks)

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