Blood volume and blood pressure regulation Flashcards
What does the pump depend on?
Venous return
What is the average cardiac output at rest?
5L per min
What is the purpose of arterioles?
Resistance to flow
Control where cardiac output is directed
What are the pressures in the arteriole?
35 to 15 mmHg hydrostatic gradient
1 mmHg hydrostatic interstitial
25 mmHg oncotic so capillaries favour reabsorption
How are arterioles disturbed?
accumulation of interstitial oedema, reduction in plasma oncotic pressure =- low protein concentration
What can cause disruption to arteriole pressures?
chronic liver disease and malnutrition, nephrosis
What increases interstitial oncotic pressure?
Inflammation- porous capillaries lose proteins
What increases venular hydrostatic pressure?
Deep vein thrombosis
What increases arteriolar hydrostatic pressure?
vasodilator drugs, calcium channel blockers
Blockage of lymphatic system, malignant infiltration
How is circulatory blood pressure maintained in haemorrhage?
Volume deplete. Loss of pressure, pressure over capillary lower so oncotic pressure more dominant so draw in water
What are the challenges to homeostasis?
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
What are the most important organs to provide perfusion to by maintaining blood pressure?
Brain and heart most critical, skin least
Kidney, GI, muscle
Why must blood volume be maintained?
to provide venous return necessary for adequate cardiac output and blood pressure generation- maintaining renal perfusion
How is afferent information collected?
from arterial baroreceptors in carotid sinus and arch in blood pressure regulation, volume stretch receptors and juxtaglomerular cells in blood volume regulation
What are efferent signals?
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
What are the effector organs?
heart and arterioles in blood pressure, kidneys blood volume
What are the response times?
pressure seconds minutes, volume- mins to hours
What are changes mediated by?
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
What is blood pressure?
Hydrostatic pressure within circulatory system, mmHg
Large artery- brachial (120/80
Peak systolic pressure, trough diastolic pressure
What is the equation to work out blood pressure?
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)
What is arteriole blood pressure dependent on?
heart rate, cardiac contractility, arteriolar tone
How is heart rate regulated?
Heart rate increased by noradrenaline, adrenaline, beta-1 adrenoreceptors
Decreased by acetylcholine, muscarinic receptors
How is myocardial contractility increased?
noradrenaline, adrenaline, beta 1
How is SVR influenced?
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)
What is the baroreceptor reflex?
providing second to second control of blood pressure
Where do the signals for blood pressure regulation come from?
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
How does the baroreceptor reflex vary?
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
How can changes in blood pressures be treated?
Blood pressure increase= vasoconstrictor= phenylephrine
Reduction= vasodilator= glyceryl trinitrate
Tilt table
What is the blood volume in an average person?
70 kg male= 4L (blood intravascular volume)
50-60% volume in veins- reservoir to regulate venous return, divert if necessary
Describe the role of the kidneys in blood volume regulation
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)
Where the receptors in blood volume regulation?
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
Describe the efferent signals (blood volume)
Renin-angiotensin system (angiotensin and aldosterone)= efferent arteriolar constriction (AT 1)- more filtration, systemic vasoconstriction (AT1)
What are the effects on the body from blood volume regulation?
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
Describe the renin-angiotensin system
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
What are the effects of the renin-angiotensin system?
• 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
What are the causes of haemorrhage?
major injury, complications of surgery, GI bleeding, obstetric bleeding
What are the effects on the body from haemorrhage?
Decrease in intravascular volume, venous return to the heart, ventricular filling, cardiac output, blood pressure, renal perfusion, capillary hydrostatic pressure
Describe the afferent information in haemorrhage
Afferent sensors activated- carotid baroreceptors aortic arch baroreceptors &sympathetic)
Reduce atrial filling, sympathetic NS, atrial volume stretch receptors
Juxtaglomerular sensors- arteriolar pressure decrease
Describe the efferent effects in haemorrhage
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
What are the symptoms of haemorrhage?
Symptoms- tachycardia, pale skin, cold peripheries, sweating
Response= hypotension, reduced urine output, confusion
What is syndrome of hypovolaemic shock?
failure to preserve a sufficient blood intravascular volume
How do you treat haemorrhage?
IV fluid, blood transfusion
