Week 9 HTN Flashcards
What are the 3 layers of blood vessels?
Tunica intima - endothelium, basement membrane, subendothelial CT
Tunica media - Smooth mm that secrete elastin fibers, CT w/collagen and elastin
Tunica adventitia - Loose CT, fibroblasts, nerves, vasa vasorum
Discuss the vascular endothelium
Simple squamous cells that line blood vessels and align with direction of blood flow.
Luminal surfaces express receptor and adhesion molecules important for immune response.
What are the 3 types of arteries?
- Large (elastic) arteries - closest to heart, thick media with elastic laminae, high pressure.
- Medium (muscular) arteries - distributing artieres to organs (named), thick media with lots of sm mm.
- Arterioles - Smallest arteries regulating blood flow to caps, regulate BP, thin media with 1-3 layers of sm. mm.
Elastic laminae
Elastin secreted by sm. mm forms elastic fibers which come together to form sheets of elastin.
What are the key features of arterial walls?
Thick vessel wall compared to size of lumen.
Tunica media is the most prominent layer.
Large arteries have elastic laminaie
Medium arteries have elastic fibers.
Tunica adventitia is the same size as the tunica media.
What are the three types of capillaries?
- Continuous - endothelial cells with tight junctions, pericytes, found in lung, brain, thymus, muscle.
- Fenestrated - endothelial cells with fenestrations to allow movement of fluid and sm. molecules, less pericytes, found in endocrine glands, kidney, intestines.
- Discontinuous or Sinusoids - large, irregularly shaped endothelial cells with gaps, found in liver, spleen, bone marrow.
What are the 3 types of veins?
- Large veins - largest but thin walls, large lumen, high capacitance, holds 70% of the blood volume.
- Medium veins - conducts blood from tissues, thing walls, large lumen, valves, thick adventitia w/sm. longitudinal mm and vaso vasorum, travel with medium arteries.
- Venules - receive from caps, thin walls, collapsed lumen, valves, travel with arterioles.
What are the key features of veinous walls?
Thin, distensible lumen, lumen often collapsed.
Think media.
Thick adventitia.
Valves.
What are the ways blood gets back to the heart?
Muscle pump
Respiratory pump
Venoconstriction (sympathetic tone)
What are the functions of the lymphatic system?
Return of excess fluid and protein.
Immune defense.
Transport of absorbed fat.
How does flow relate to pressure and resistance?
Flow is proportional to pressure and inversely proportional to resistance.
Pressure goes up = flow goes up
Resistance goes up = flow goes down. This relationship is exponential.
What is the most effective way to alter flow in the arterial system?
Increase or decrease the radius of the arteries.
What are the 2 overarching controls for blood pressure?
Neural (ANS)
Humoral (endocrine/renal)
These feedback loops work together.
How does the autonomic nervous system control BP?
- Vasoconstriction or vasodilation - vasomotor tone determines peripheral vascular resistance.
- Alter CO - CO=HRxSV BP=COxSVR
- Change the volume of blood in circulation - vasoconstriction shifts blood from venous system to the R heart and increases preload which results in increased CO.
These mechanisms are SHORT TERM. - RAAS & NPs changes blood volume.
How do the humoral controls affect BP?
Regulation of blood volume through Na and H2O via feedback loops in the hypothalamus, pituitary gland, adrenal cortex, and kidneys.
What is an additional way BP is altered?
Arterial elasticity (compliance)
Can be functional or structural in origin.
Functional - determined by the degree of activity.
Structural - determined by the disruption of elastin, collagen deposition, and altered extra-cellular matrix.
What is the pre-ganglionic neurotransmitter for both divisions of the autonomic nervous system?
Acetylcholine.
What is the post-ganglionic neurotransmitter for the sympathetic nerve terminals?
Norepinephrine
What is the post-ganglionic neurotransmitter for the parasympathetic nerve terminals?
Acetylcholine
Thoracolumbar outflow
T12-L2
SNS
Pre-ganglionic fibres leave spinal cord with motor nerves then branch off through white rami communicantes to the sympathetic trunk alongside the spinal column as paravertebral ganglia.
Post-ganglionic fibres that originate in ganglia, leave through gray rami communicantes and meet up with the spinal nerve.
How does venous constriction affect blood pressure?
Increased venous return to R atrium.
Increased end diastolic volume.
Increased force of ventricular contraction (stroke volume)
Overall increased CO.
Rapid result.
Craniosacral outflow
CNI-XII
S1-S5
Vagus nerve (CNX) relates to cardiovascular system.
Baroreceptor reflex
Baroreceptors in carotid sinus and aortic arch.
Via CN IX (glossopharyngeal) and CN X (vagus nerve) to the posterolateral medulla and pons.
Posterolateral medulla and pons send signals to vasoconstrictor and vasodilator centres.
Results in decreased SNS outflow in response to increased blood pressure.
Negative feedback loop.
ANP & BNP
Released by atrial myocytes, ventricles in response to stretch, Ang II, endothelin, and SNS activity.
Venodilation.
Decreased central venous pressure (CVP).
Decreased venous return to RA.
Decreased CO.
Arterial dilation.
Decreased peripheral resistance.
Vasodilation is via increased cGMP
Increased GFR
Decrease renin release.
Net result is decreased BP
Local regulation of blood flow.
Regulated by metabolic requirements.
Vasodilation caused by increased:
PCO2
Lactic acid
H+
K+
Adenosine
ADP
Histamine
Bradykinin
Prostacyclin
Endothelial derived NO
Vasoconstriction caused by decreased:
PO2
5-HT (serotonin)
Endothelin
Nitric Oxide
Released from endothelial cells in response to shear stress, Ach, serotonin, bradykinin, thrombin.
Activates GC which converts GTP to cGMP and activates cGMP-dependent kinase.
Effect only lasts seconds.
Autoregulation
Despite fluctuations in BP, blood flow to most tissues is maintained at a relatively constant rate.
What 2 theories explain autoregulation?
Metabolic theory: Factors causing vasodilation get “washed out” leading to vasoconstriction.
Mygenic theory: Stretch of vessel walls causes contraction of smooth mm.
What areas does autoregulation not apply to and how are they regulated?
Brain: Increase PaCO2 and H+ cause vasodilation, increasing cerebral blood flow.
Kidneys: Increase in NaCl leads macula densa to release ATP which is converted to adenosine, leading to Ca release, vasoctx of afferent arteriole, decrease secretion of renin.
When do symptoms of hypertension begin to develop?
Only when there is advanced damage in the target organs (brain, eyes, heart, kidneys).
What is diagnosis of HTN based on?
Solely on accurate measurement of BP.
How does HTN affect target organs?
Simulates vascular remodeling
Accelerates atherosclerosis
These lead to increased peripheral vascular resistance and reduced flow to tissues.
What is the most common type of hypertension?
Primary (95%)
Secondary (5%)
How is treatment of hypertension determined?
Tailored to the patient based on age, frailty, lifestyle factors, and co-morbidities.
True hypertensive emergencies
Uncommon. Severely elevated BP with TOD.
Includes:
Encephalopathy; headache, vomiting, confusion, seizures, coma
Intracranial hemorrhage
Angina pectoris; increased afterload leads to increase work and O2 consumption
Impaired LV contractility leads to cardiogenic pulmonary edema
Aortic coarctation
Ischemic stroke
Acute kidney injury; delirium, pericardial effusion, edema, hyperkalemia, acidosis, increased creatinine, nitogen, urea.
Marked BP elevation post transplant and some surgeries.
Treating very high BP in other situations is unwarranted and can be harmful.
Epidemiology of HTN
Prevalence doubled btwn 1990-2021 in low and middle-income regions.
Prevalence decreased in high-income countries.
1/4 Canadians age 20-79.
M>W.
Risk at 60 years of age is 50%.
Lifetime risk for newcomers is 90%.
What factors are associated with HTN?
Obesity
Reduced fruit and veg intake
Lower levels of exercise
Diabetes
Chronic kidney disease
What percentage of HTN patients have their BP controlled (<140/90)?
Only 2/3.
Adequate treatment in Canada seems to be waning.
What is considered the major culprit in HTN?
High sodium content in processed foods.
HTN and CV risk
CV disease is 2nd leading cause of death in BC.
MI, stroke, peripheral vascular disease.
HTN accelerates atherosclerosis, increasing the risk of CV disease.
HTN patients often have other CV risk factors (obesity, T2D, dyslipidemia)
What levels of BP reduction are associated with reduced risk of MI and stroke in those under 60 years of age?
Lower 10-15 mmHg systolic
Lower 5-6 mmHg diastolic
NNT (50 year old males)
120 for 5 years to prevent 1 death.
Gold standard for diagnosis of HTN
Hypertension Canada’s guidelines.
Mean office BP: >180/110
OBPM: >140/90 averaged across 3 separate readings at least one week apart.
AOBP/ABPM/HBPM: >135/85
Diabetes OBPM >130/80 for 3 or more separate readings on different days.
Primary HTN
HTN diagnosis with no obvious causes to explain it.
Likely multifactorial.
Mosaic theory of HTN involves intersection of genetic, environmental, adaptive, neural, mechanical, and hormonal factors.
Likely genetic factors.
Genes identified that code for the subunits on tubular Na channels - leads to increased Na retention.