Regulation of circulation

Question 1

Depolarisation

Answer 1

• Activation of cells by depolarisation

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

Question 2

Hyperpolarisation

Answer 2

• 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

Question 3

How is muscle contraction triggered by depolarisation?

Answer 3

• 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

Question 4

What controls rhythmic heart contractions?

Answer 4

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

Question 5

SAN (Sinoatrial node)

Answer 5

• 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

Question 6

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

Answer 6

• 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

Question 7

What is cardiac arrest?

Answer 7

Sudden loss of cardiac function when the heart abruptly stops beating

Question 8

What is the most common loss of cardiac function?

Answer 8

• 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

Question 9

What is the treatment of cardiac arrest?

Answer 9

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

Question 10

How do you calculate mean arterial pressure (MAP)?

Answer 10

MAP = (Systolic + 2diastolic)/3

Question 11

Why is MAP calculated that way?

Answer 11

• diastolic part of cycle is twice as long as systolic

* therefore we calculate the weighted average

Question 12

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

Answer 12

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

Question 13

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

Answer 13

• chemoreceptors
• autonomic nervous system
• hormones

Question 14

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

Answer 14

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

Question 15

Regulation of blood vessels via vasoconstriction

Answer 15

• 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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

• 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

Question 18

What is meant by vasomotor tone?

Answer 18

• Blood vessels are always a bit constricted

* this means they can either relax more or constrict more

Question 19

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

Answer 19

• 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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

Sympathetic Nerves

• Noradrenaline binds to Beta 1 adrenoreceptors

Question 22

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

Answer 22

• 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

Question 23

How are pacemaker cells involved in increasing the heart rate?

Answer 23

• 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

Question 24

What is the baroreceptor reflex?

Answer 24

Initiates response to bring MAP back to normal

Question 25

Postural/Orthostatic hypotension

Answer 25

* '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

Question 26

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

Answer 26

• 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

Question 27

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

Answer 27

* 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

Question 28

What chemoreceptors are involved in regulating the ANS?

Answer 28

* arterial chemoreceptors - detect changes in blood chemical composition (CO2 and O2) * medullary chemoreceptors - detect changes in increases in CO2 levels

Question 29

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

Answer 29

* 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

Question 30

Does norepinephrine influence vasoconstriction or vasodilation?

Answer 30

- Sympathic neurons - Neural type - Causes vasocontriction

Question 31

Does endothelin influence vasoconstriction or vasodilation?

Answer 31

- Vascular enothelium - Paracrine - Vasoconstriction

Question 32

Does angiotensin influence vasoconstriction or vasodilation?

Answer 32

- Sourced from plasma - Endocrine - Vasoconstriction

Question 33

How does CO2 affect blood flow?

Answer 33

- Sourced from multiple tissues - Metabolite - Vasodilation

Question 34

How does nitric oxide influence blood flow?

Answer 34

- Sourced from vascular endothelium - Paracrine - Vasodilation

Question 35

How does bradykinin influence blood flow?

Answer 35

Sourced from multiple tissues - Paracrine - Causes vasodilation

Question 36

How does vasodilation occur?

Answer 36

* 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

Question 37

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

Answer 37

Parasympathetic Nerves | • Acetylcholine (ACh) binds to Muscarinic (M2) receptors

Question 38

What is pre-eclampsia?

Answer 38

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

Question 39

What are the effects of pre-eclampsia?

Answer 39

Reduced sensitivity to bradykinin and abnormal vasorelaxation occurs

Question 40

Repolarisation

Answer 40

* 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.

Question 41

What is the atrial syncytium?

Answer 41

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

Question 42

List the steps in an action potential

Answer 42

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