Physiology 4+5 Flashcards
(91 cards)
1
Q
What is blood pressure?
A
Outward hydrostatic pressure exerted by blood on blood vessel walls
2
Q
What is systolic arterial blood pressure?
A
Pressure exerted by blood on walls of the aorta and systemic arteries when the heart contracts
3
Q
What is normal value for systolic arterial blood pressure?
A
Should not reach or exceed 140 mm Hg under resting conditions
4
Q
What is diastolic arterial blood pressure?
A
Pressure exerted by blood on walls of the aorta and systemic arteries when the heart relaxes
5
Q
What is normal value for diastolic arterial blood pressure?
A
Should not reach or exceed 90 mm Hg under resting conditions
6
Q
What is hypertension? (2)
A
- Clinic blood pressure of 140/90 mmHg or higher
* Day time average of 135/85 mmHg or higher
7
Q
What is pulse pressure?
A
Difference between systolic and diastolic blood pressures
e.g. 120 - 80 = 40 mm Hg
8
Q
What are normal values for pulse pressure?
A
Between 30 and 50 mmHg
9
Q
What is a sphygmomanometer used for?
A
Indirect measurement of arterial blood pressure
10
Q
What is the normal flow of blood in an artery?
A
Laminar
11
Q
Is laminar flow audible through stethoscope?
A
No, no sound heard in normal patent artery
12
Q
What will happen if external pressure (e.g. cuff) exceeds systolic blood pressure?
A
Will occlude artery and no sound is heart through stethoscope
13
Q
When is arterial blood flow heard through a stethoscope?
A
- When external pressure kept between systolic and diastolic pressure, flow will become turbulent when blood pressure exceeds cuff pressure
- Turbulent flow is audible through stethoscope
14
Q
What is first korotkoff sound?
A
Heard at peak systolic pressure (when blood pressure first exceeds cuff pressure)
15
Q
What are korotkoff sounds 2 + 3?
A
Intermittent sounds due to turbulent spurts of flow
16
Q
What is 4th korotkoff sound?
A
Heard at minimum/diastolic pressure (muffled, muted sound)
17
Q
What is 5th Korotkoff “sound”?
A
No sound is heard because of smooth laminar flow
18
Q
What point is diastolic pressure recorded? Why?
A
- 5th Korotkoff sound (point at which sound disappears)
* More reproducible
19
Q
What drives blood around systemic circulation?
A
Pressure gradient between aorta and right atrium
20
Q
What is the main driving force for blood flow?
A
Mean arterial pressure (MAP) because RA pressure is close to zero
21
Q
What is the equation for pressure gradient between RA and aorta?
A
Pressure gradient = Mean Arterial Pressure (MAP) - Central Venous (right atrial) Pressure (CVP)
22
Q
What is Mean Arterial blood Pressure?
A
Average arterial blood pressure during a single cardiac cycle
23
Q
What is the equation for Mean Arterial blood Pressure using systolic diastolic pressures?
A
MAP = [(2 x diastolic pressure) + systolic pressure] / 3
OR
MAP = DBP + 1/3 pulse pressure
24
Q
What is normal arterial blood pressure?
A
<140 systolic
<90 diastolic
25
What is the normal range of Mean Arterial blood Pressure?
70 - 105 mm Hg
26
How high does MAP have to be to perfuse coronary arteries, brain and kidneys?
At least 60 mm HG
27
Why must MAP be regulated within narrow ranges? (2)
To ensure
* Pressure is high enough to perfuse brain, heart and kidneys
* Pressure is not too high to damage blood vessels or put extra strain on heart
28
What is the equation for MAP without using systolic and diastolic blood pressures?
MAP = Cardiac output (CO) x Systemic Vascular Resistance (SVR)
29
Equation for cardiac output?
CO = HR x SV
30
What is systemic vascular resistance (total peripheral resistance)?
Sum of resistance of all vasculature in systemic circulation
31
In systemic vascular resistance, what are the major resistance vessels?
Arterioles
32
What is the effect of parasympathetic stimulation of the heart?
Decrease in heart rate, which results in decreased cardiac output, resulting in decreased MAP
33
What is the effect of sympathetic stimulation of the heart? (2)
* Increase in heart rate, resulting in increased cardiac output and MAP
* Increase in force of contraction which increases SV, leading to increased CO and MAP
34
What is the effect of sympathetic stimulation of arterioles?
Vasoconstriction, increasing SVR, resulting in increased MAP
35
What is the effect of sympathetic stimulation of veins?
Vasoconstriction, causing increased venous return (EDV), resulting in increased SV, CO and MAP
36
What is the baroreceptor reflex?
Short-term regulation of Mean Arterial blood Pressure
37
What are the components of baroreceptor reflex? (3)
* Pressure sensors - baroreceptors
* Control centre - medulla
* Effectors - Heart (HR, SV) and blood vessels (SVR)
38
How does baroreceptor reflex regulate MAP?
Negative feedback
39
What are the 2 types of baroreceptors? How do signals from them reach the medulla?
* Carotid baroreceptors - glossopharyngeal nerve (CN IX)
| * Aortic baroreceptor - vagus nerve (CN X)
40
Where are aortic baroreceptors found? Carotid?
* Aortic arch
| * Carotid sinus
41
What are baroreceptors?
Stretch receptors
42
What are baroreceptor responses to increased BP? (4)
* Increase in carotid and aortic baroreceptor firing
* Increased vagal efferent activity
* Decrease in sympathetic efferent activity
* Decrease in sympathetic vasoconstrictor activity
43
What are baroreceptor responses to decreased BP? (4)
* Decrease in carotid and aortic baroreceptor firing
* Decreased vagal efferent activity
* Increase in sympathetic efferent activity
* Increase in sympathetic vasoconstrictor activity
44
What happens when a normal person suddenly stands up from lying position? (3)
* Venous return to heart decreases (effect of gravity)
* MAP decreases
* Baroreceptor firing rate decreases
45
How do baroreceptors prevent postural hypotension?(3)
* Vagal tone to heart decreases and sympathetic tone increases - increased HR and SV
* Sympathetic constrictor tone to arterioles increases - increases SVR
* Sympathetic constrictor tone to veins increases - increases venous return and SV
46
What is the result of the baroreceptor response to postural hypotension? (4)
* Rapid correction of fall in MAP
* HR increases
* SV increases
* SVR increases
47
What does the increase in SVR result in when healthy people stand from lying position?
Slight increase in DBP
48
What does postural hypotension result from?
Failure of baroreceptor responses to gravitational shifts in blood when moving from horizontal to vertical position
49
What is baroreceptor response to increased blood pressure?
* Baroreceptor firing rate increases
* Vagal tone to heart increases and sympathetic tone decreases - decreased HR and SV
* Sympathetic constrictor tone to arterioles decreases - decreases SVR
* Sympathetic constrictor tone to veins decreases - decreases venous return and SV
50
What happens to baroreceptor firing if blood pressure is sustained? Therefore, what information cannot be provided by baroreceptors?
* Baroreceptor firing decreases
| * Cannot supply info about prevailing steady state blood pressure
51
What is the only thing baroreceptors respond to?
Acute changes in blood pressure
52
If baroreceptor firing decreases if high blood pressure is sustained, what is MAP controlled by in the longer term?
Blood volume
53
How can blood volume (and thus MAP) be controlled?
By controlling extracellular fluid volume
54
What percentage of body weight in a 70kg man is water?
60% (~42 L)
55
What is the equation for total body fluid?
Total body fluid = intracellular fluid (2/3) + extracellular fluid (1/3)
56
What proportion of total body fluid is intracellular fluid? Extracellular fluid?
* 2/3rds
| * 1/3rd
57
What is the equation for ECF volume?
ECFV = plasma volume (PV) + interstitial fluid volume (IFV)
58
What is interstitial fluid?
Fluid that bathes the cells and acts as go-between for blood and body cells
59
What happens if plasma volume falls?
Compensatory mechanisms shift fluid from interstitial compartment to plasma compartment
60
How is PV and hence ready state blood volume and MAP controlled?
Controlling ECFV
61
What 2 main factors affect extracellular fluid volume?
* Water excess or deficit
| * Na+ excess or deficit
62
How do hormones act as effectors to regulate water ECFV?
Regulate water and sat balance in the body
63
What is the water and salt balance in healthy people?
Stable water and salt balance where water input = water output
64
What hormones regulate ECFV? (3)
* The Renin-Angiotensin- Aldosterone System - RAAS
* Natriuretic Peptides – NPs
* Antidiuretic Hormone (Arginine Vasopressin) - ADH
65
What is the role of the Renin-Angiotensin-Aldosterone System?
Regulation of plasma volume and SVR (hence regulation of MAP)
66
What are the components of the RAA system? (3)
* Renin
* Angiotensin
* Aldosterone
67
Explain how RAAS increases blood pressure (MAP)
* Renin released from kidneys and stimulates formation of angiotensin I in the blood from angiotensinogen
* Angiotensin I converted to angiotensin II by Angiotensin converting enzyme - ACE
* Angiotensin II stimulates release of Aldosterone from adrenal cortex and causes systemic vasoconstriction (increases SVR) - also stimulates thirst and ADH release (increases plasma volume)
* Aldosterone acts on kidneys to increase sodium and water retention – increases plasma volume
68
What is angiotensinogen produced by? ACE?
* Angiotensinogen - liver
| * ACE - pulmonary vascular endothelium
69
What is aldosterone?
Steroid hormone
70
What is the rate limiting step for RAAS?
Renin secretion
71
What is RAAS regulated by? What are these mechanisms? (3)
Mechanisms that stimulate release of renin from juxtaglomerular apparatus in the kidney
* Renal artery hypotension
* Stimulation of renal sympathetic nerves
* Decreased [Na+] in renal tubular fluid
72
What causes renal artery hypotension? What detects decreased [Na+] in renal tubular fluid?
* Systemic hypotension (decreased blood pressure)
| * Decreased [Na+] sensed by macula densa (specialised cells in kidney tubules)
73
Wha are natriuretic peptides (NPs)?
Peptide hormones synthesised by heart (also brain and other organs)
74
When are NPs released? (2)
In response to cardiac distension or neurohormonal stimuli
75
What is the role of NPs? (3)
* Cause excretion of salt and water in the kidneys so reduce blood volume and blood pressure
* Decrease renin release, decrease BP
* Vasodilators, decrease SVR and BP
76
What do NPs counter-regulate?
Renin-Angiotensin-Aldosterone System
77
What natriuretic peptides are released by the heart? (2)
* Atrial Natriuretic peptide (ANP)
| * Brain-type Natriuretic Peptide (BNP)
78
What is ANP?
28 amino acid peptide produced and stored by atrial myocytes
79
When is ANP released?
In response to atrial distension (e.g. in hypervolemia)
80
What is BNP?
32 amino acid peptide synthesised by heart, brain and other organs
81
How is BNP produced? (3)
* First synthesised as prepro-BNP
* Cleaved to pro-BNP (108 amino acids)
* Cleaved to BNP (32 amino acids)
82
What can be measured in patients with suspected heart failure? (2)
* Serum BNP
| * NT-pro-BNP (76 amino acids)
83
What is antidiuretic hormone (ADH)?
Peptide hormone derived from pre-hormone precursor synthesised by hypothalamus and stored in posterior pituitary
84
What is the other name for ADH?
Vasopressin
85
What is ADH secretion stimulated by? (2)
* Reduced ECF volume
| * Increased ECF (plasma) osmolality
86
What is does plasma osmolality reflect?
Solute-water balance
87
What is plasma osmolality monitored by?
Osmoreceptors in brain close to hypothalamus
88
What does ADH do?
* Acts in kidney tubules to increase reabsortion of water (concentrates urine) - increases extracellular and plasma volume and so cardiac output and BP
* Vasoconstriction - increases SVR and BP
89
When is vasoconstrictive effect on ADH important?
Hypovalaemic shock (e.g. haemorrhage)
90
What is short-term regulation of MAP controlled by? Long term?
* Short term = baroreceptor reflex
| * Long term = controlling blood volume by hormones
91
What is the purpose of ADH?
Helps body deal with fluid loads/deficits
