Blood volume and blood pressure regulation

Question 1

What does the pump depend on?

Answer 1

Venous return

Question 2

What is the average cardiac output at rest?

Answer 2

5L per min

Question 3

What is the purpose of arterioles?

Answer 3

Resistance to flow

Control where cardiac output is directed

Question 4

What are the pressures in the arteriole?

Answer 4

35 to 15 mmHg hydrostatic gradient
1 mmHg hydrostatic interstitial
25 mmHg oncotic so capillaries favour reabsorption

Question 5

How are arterioles disturbed?

Answer 5

accumulation of interstitial oedema, reduction in plasma oncotic pressure =- low protein concentration

Question 6

What can cause disruption to arteriole pressures?

Answer 6

chronic liver disease and malnutrition, nephrosis

Question 7

What increases interstitial oncotic pressure?

Answer 7

Inflammation- porous capillaries lose proteins

Question 8

What increases venular hydrostatic pressure?

Answer 8

Deep vein thrombosis

Question 9

What increases arteriolar hydrostatic pressure?

Answer 9

vasodilator drugs, calcium channel blockers

Blockage of lymphatic system, malignant infiltration

Question 10

How is circulatory blood pressure maintained in haemorrhage?

Answer 10

Volume deplete. Loss of pressure, pressure over capillary lower so oncotic pressure more dominant so draw in water

Question 11

What are the challenges to homeostasis?

Answer 11

Fluid deprivation= lack of access to water , fluid overload= excess oral intake/ IV, fluid depletion= excessive fluid loss diarrhoea, exercise and meals, temp changes, postural changes, acceleration zero gravity

Question 12

What are the most important organs to provide perfusion to by maintaining blood pressure?

Answer 12

Brain and heart most critical, skin least

Kidney, GI, muscle

Question 13

Why must blood volume be maintained?

Answer 13

to provide venous return necessary for adequate cardiac output and blood pressure generation- maintaining renal perfusion

Question 14

How is afferent information collected?

Answer 14

from arterial baroreceptors in carotid sinus and arch in blood pressure regulation, volume stretch receptors and juxtaglomerular cells in blood volume regulation

Question 15

What are efferent signals?

Answer 15

autonomic NS, circulating hormones renin-angiotensin system (angiotensin 2) adrenaline and vasopressin/ local factors NO, endothelin, kinins, prostaglandins, renin-angiotensin in blood pressure
circulating hormones rein-angiotensin system (aldosterone)natriuretic peptides, vasopressin

Question 16

What are the effector organs?

Answer 16

heart and arterioles in blood pressure, kidneys blood volume

Question 17

What are the response times?

Answer 17

pressure seconds minutes, volume- mins to hours

Question 18

What are changes mediated by?

Answer 18

G protein receptors,= agonists bind, signal transduction, requires bonding of intermediate protein- beta-adrenergic, alpha-1-adrenergic muscarinic cholinergic
Secondary messenger- signal amplification, biological effect, muscle

Question 19

What is blood pressure?

Answer 19

Hydrostatic pressure within circulatory system, mmHg
Large artery- brachial (120/80
Peak systolic pressure, trough diastolic pressure

Question 20

What is the equation to work out blood pressure?

Answer 20

ABP (arteriole blood pressure)= CO X SVR (Systemic vascular resistance)
SVR majority provided by arterioles
Altered muscle tone
R= resistance, L length of vessel, n= viscosity of blood, r= radius of vessel (Poiseuille equation)

Question 21

What is arteriole blood pressure dependent on?

Answer 21

heart rate, cardiac contractility, arteriolar tone

Question 22

How is heart rate regulated?

Answer 22

Heart rate increased by noradrenaline, adrenaline, beta-1 adrenoreceptors
Decreased by acetylcholine, muscarinic receptors

Question 23

How is myocardial contractility increased?

Answer 23

noradrenaline, adrenaline, beta 1

Question 24

How is SVR influenced?

Answer 24

radius of lumen- tone of media (smooth muscle)- post ganglionic sympathetic, noradrenaline vasoconstriction- alpha 1
Adrenaline vasodilation beta 2
Angiotensin 2=2 released when renin-angiotensin system active, vasopressin= posterior pituitary gland when plasma volume reduced, osmolality increased, NA (circulating hormones)- constriction
Local= endothelin (constriction), NO (dilation)

Question 25

What is the baroreceptor reflex?

Answer 25

providing second to second control of blood pressure

Question 26

Where do the signals for blood pressure regulation come from?

Answer 26

Afferent info= arterial baroreceptors= carotid sinus- glossopharyngeal nerve (1X), aortic arch- vagus nerve (X) Mechano-sensory neurones, respond to stretch CNS- vasomotor centre medulla oblongata Efferent signals- SN (reduced blood pressure)- increase rate and contractility- tachycardia (beta 1)/ blood vessels arteriolar constriction (alpha 1) venoconstriction (a1)/ adrenal medulla- secretion of catecholamines (a, na)/ kidneys arteriole constriction (a1), renin secretion (b1) Para= bradycardia, muscarinic

Question 27

How does the baroreceptor reflex vary?

Answer 27

Baroreflex sensitive in younger individuals Hypertension- chronic- high blood pressure, allowed to reset reflex Baroreceptor reflex critical to defence of blood pressure and cerebral blood flow

Question 28

How can changes in blood pressures be treated?

Answer 28

Blood pressure increase= vasoconstrictor= phenylephrine Reduction= vasodilator= glyceryl trinitrate Tilt table

Question 29

What is the blood volume in an average person?

Answer 29

70 kg male= 4L (blood intravascular volume) | 50-60% volume in veins- reservoir to regulate venous return, divert if necessary

Question 30

Describe the role of the kidneys in blood volume regulation

Answer 30

renal blood flow 1.25 L/min (25% CO) GFR (Glomerular filtration rate)= 125 mL/min (180L/day) Urine output- 1.5 L/day (1 ml/min)

Question 31

Where the receptors in blood volume regulation?

Answer 31

Volume sensors= kidneys= juxtaglomerular cells sense low Na ions delivery and urine flow, release renin Heart- low pressure stretch receptors in atrium (venous return)- sympathetic NS

Question 32

Describe the efferent signals (blood volume)

Answer 32

Renin-angiotensin system (angiotensin and aldosterone)= efferent arteriolar constriction (AT 1)- more filtration, systemic vasoconstriction (AT1)

Question 33

What are the effects on the body from blood volume regulation?

Answer 33

``` Aldosterone release (adrenal cortex) conserve sodium Vasopressin release (posterior pituitary), thirst Sympathetic nerves- tachycardia and increased contractility Arteriolar constriction and venoconstriction= less reservoirs Renin secretion and arteriolar constriction Sodium and ester retention= vasopressin, natriuretic peptides ```

Question 34

Describe the renin-angiotensin system

Answer 34

macula densa closely packed specialised cells lining wall of cortical thick ascending limb- distal convoluted tubule, sensitive to NacL conc in ascending limb= decreased= decreased resistance (vasodilation in afferent arteriole- increase GFR hydrostatic pressure increases), increased renin release from cells of arterioles- storage sites of enzyme renin Renin cleaves deck of peptides (angiotensin 1) from angiotensinogen- cleaved to angiotensin 2 by angiotensin converting enzyme- various actions

Question 35

What are the effects of the renin-angiotensin system?

Answer 35

• AT 2 effects= arteriolar vasoconstriction preserves ABP and glomerular perfusion/ aldosterone release stimulates sodium and water retention/ vasopressin secretion stimulates water retention and thirst stimulates water intake Renin angiotensin system critical to defence of renal blood flow and extracellular fluid volumes

Question 36

What are the causes of haemorrhage?

Answer 36

major injury, complications of surgery, GI bleeding, obstetric bleeding

Question 37

What are the effects on the body from haemorrhage?

Answer 37

Decrease in intravascular volume, venous return to the heart, ventricular filling, cardiac output, blood pressure, renal perfusion, capillary hydrostatic pressure

Question 38

Describe the afferent information in haemorrhage

Answer 38

Afferent sensors activated- carotid baroreceptors aortic arch baroreceptors &sympathetic) Reduce atrial filling, sympathetic NS, atrial volume stretch receptors Juxtaglomerular sensors- arteriolar pressure decrease

Question 39

Describe the efferent effects in haemorrhage

Answer 39

Efferent- tachycardia, contractility increased, vasoconstriction, venoconstriction, catecholamine secretion, sweating Renin release, all-mediated vasoconstriction, aldosterone release, vasopressin release Passive reabsorption of water from interstitial fluid

Question 40

What are the symptoms of haemorrhage?

Answer 40

Symptoms- tachycardia, pale skin, cold peripheries, sweating | Response= hypotension, reduced urine output, confusion

Question 41

What is syndrome of hypovolaemic shock?

Answer 41

failure to preserve a sufficient blood intravascular volume

Question 42

How do you treat haemorrhage?

Answer 42

IV fluid, blood transfusion