Control of Hypertension Flashcards
Describe characteristics of an artery.
Muscular and elastic.
Describe a characteristic of arteriole.
Muscular
Describe the walls of a capillary.
Thin-walled
How muscular is a venue?
Slightly muscular
What are the primary functions of the venous system?
Acts as conduits and reservoirs for blood storage and transport.
Define Heart Rate (HR).
The number of times the heart beats per minute (normally 60-85 bpm at rest).
What is Stroke Volume (SV)?
The volume of blood ejected from the heart in one beat (around 70 mL at rest).
How do you calculate Cardiac Output (CO)?
CO = HR × SV. It’s the volume of blood ejected from the heart per minute (about 5L at rest).
What is Mean Arterial Blood Pressure (MABP) and how is it calculated?
MABP is the average pressure exerted on arterial walls. It’s around cardiac output × peripheral resistance.
What factors affect arterial blood pressure?
Stroke volume, ventricular contraction, artery elasticity, and peripheral resistance.
What is stroke volume also known as?
Circulatory volume
When does the MABP reach 0mmHg?
As blood throughs through the vasculature as it enters the right atrium.
How would you describe the behaviour of arteries in response to pressure?
Compliant - smoothing pressure out as you go through arterial tree - decreasing pressure
What is the order of arterial tree?
Aorta, arteries, arterioles, capillaries, venues, veins, vena cava
What happens if the arteries aren’t compliant?
Too much pressure - causing them to burst
What are factors that affect resistance?
Viscosity of blood, length of blood vessel, radius/diameter of artery
What is the primary determinant of vascular resistance?
The radius/diameter of the artery, which has a major influence on resistance according to Poiseuille’s law.
What role do arterioles, capillaries, and venules play in vascular resistance?
These vessels play the biggest role in controlling vascular resistance.
When is the cross-sectional area greatest?
Capillaries
What is important regarding to arteriole smooth muscle?
Tone
In which capillary tree is velocity of blood flow greatest?
Aorta - arteries - arterioles
Why does the velocity decrease whilst cross-sectional areas increase?
To facilitate exchange
Why is the cross-section greatest in the capillaries?
Due to large amounts of gaseous exchange
What picks up velocity of blood flow?
Vena cava picks up velocity to return the blood to the heart
Spotter Question: How to identify between vein vs artery
Vein has a larger diameter and is less muscular
What is the Baroreceptor Reflex?
A mechanism that regulates heart rate in response to changes in blood pressure via baroreceptors.
What does the cardiovascular centre do?
Regulates heart rate in response to increased blood pressure
What does the sino atrial node regulate?
Heart rate - effectively pacemaker of the heart
Where do CVS signals go to?
Cardiac accelerator nerve
What happens during atrial stretch in response to increased venous return?
When venous return is raised - wall right atrium stretch - the atrial myocytes in the atrium releases atrial natriuretic peptide (ANP), leading to vasodilation and increased Na+ excretion (water follows), inhibits secretion of ADH - lowering blood pressure.
What are the stages of hypertension according to NICE?
Stage I: 140/90 to 159/99 mmHg
Stage II: 160/100 to 179/119 mmHg
Stage III: 180/120 mmHg or higher.
What are the two types of hypertension?
Primary - no single cause
Secondary - another underlying disease causing elevated blood pressure
What are the values for AMPB hypertension?
135/85 - 149/94 mmHg
What are modifiable risk factors for hypertension?
Aerobic exercise, weight management, smoking cessation, diet, and stress management.
How does exercise affect cardiac output and blood pressure?
Exercise increases heart rate and stroke volume, raising cardiac output and temporarily increasing blood pressure.
How can malfunctioning ion channels cause damage?
Malfunctioning ion channels and pumps in the peripheral vasculature (small artierioles)
Can lead to chronically increased vascular tone
Raises vascular resistance to flow
What are endocrine signalling?
Adrenaline
Antidiuretic hormone (ADH, vasopressin)
Atrial natriuretic peptide (ANP)
Renin-angiotension-aldosterone system
Where and when is adrenaline released?
Released from adrenal medulla in response to lowered blood pressure.
How does adrenaline reduce blood pressure?
Two ways:
Speeds heart rate and force of ventricular contraction - makes heart work harder increasing blood pressure.
Dilated skeletal muscle and constricts splanchnic (mesenteric) vascular bed - moves blood to the muscle.
Does adrenaline have an affect on arterial blood pressure?
No, but does increase cardiac output and systolic blood pressure.
What are antidiuretic hormones?
AKA vasopressin
Makes kidneys produce urine with less water
Where are antidiuretic hormones released from and when?
Posterior part of pituitary in response to decreased blood pressure and increased plasma osmolarity.
What slows the release of antidiuretic hormones?
Ethanol / alcohol
What are the two mechanisms of antidiuretic hormones?
Promotes reabsorption of water in kidney
Constricts blood vessels if present at high concentration.
How do antidiuretic hormones keep blood pressure up?
Increase SV and TPR
What are the side effects of antidiuretic hormones?
Associated with nocturia and poor sleep
Poor sleep risk factor already for hypertension
Inappropriate or prolonged use in elderly is not an intervention
What is the Renin-Angiotensin-Aldosterone System (RAAS)?
A hormone system that regulates blood pressure by increasing blood volume and constricting blood vessels through renin and aldosterone actions.
Where is renin released?
In walls of afferent arterioles of kidney glomeruli.
When is renin produced?
In response to lowered kidney perfusion pressures caused by other things - eg. lowered blood pressure
How does renin work?
Acts on a protein called angiotensinogen (protein in circulation, but inactive) and cleaves precursor at specific sites to form angiotensin I
What happens to angiotensin I?
Converted to angiotensin II
What does angiotensin II do?
Raises blood pressure more than I
What is the enzyme for conversion of angiotensin I to II?
angiotensin converting enzyme ACE
What do ACE inhibitors do?
Block conversion of I to II - blocks blood pressure raising effect
What can angiotensin II turn into?
Angiotensin III by action of aminopeptidase cleaving off the N-terminal aspirate residue
What does angiotensin-aldosterone do?
Dispogenic - thirst
Stimulated ADH secretion
What is the ratio of angiotensin II and III?
5:1
What do angiotensin II and III do?
Stimulate production in the activate cortex
Stimulate production in the activate cortex
Activate aldosterone secretions from adrenal cortex
How does Atrial Natriuretic Peptide (ANP) lower blood pressure?
Promotes Na+ and water excretion, inhibits ADH and aldosterone secretion, and acts as a vasodilator.
Can slow renin release
What does aldosterone act to do?
Increase reabsorption of sodium (water follows) in the kidney - keeps blood volume up - aldosterone keeps up blood pressure
Where is atrial natriuretic peptide released from?
Atria - in response to stretch by increased blood volume
What is Conn’s Syndrome (Primary Aldosteronism)?
A condition where excessive aldosterone is produced, raising blood pressure, often treated with surgery or spironolactone.
What is Addison’s Disease?
A rare disorder causing low cortisol and aldosterone levels, leading to sodium loss, reduced blood volume, and postural hypotension.
What are some common causes of hypotension?
Dehydration, heart failure, arrhythmias, shock, medication, pregnancy, and orthostatic hypotension.
