Blood Vessels Part 3: Exam 2

Question 1

Regulation of Blood Pressure

Answer 1

• maintaining BP requires cooperation of heart, blood vessels and kidneys
• 3 main factors regulating blood pressure:
  1) cardiac output (CO)
  2) peripheral resistance (PR)
  3) blood volume
• blood pressure varies with CO, PR, and blood volume
• factors can be affected by:
  
  • short term regulation: neural controls
  • short term regulation: hormonal controls
  • long term regulation: renal controls

Question 2

Short Term Regulation: Neural Controls

Answer 2

• two main neural mechanisms control peripheral resistance
  1) MAP is maintained by altering blood vessel diameter, which alters resistance
  - example: blood volume drops, all vessels constrict (except those to heart and brain)
  2) can alter blood distribution to organs in response to specific demands

Question 3

Neural Controls Operate Via Reflex Arcs that Involve:

Answer 3

• Cardiovascular Center of Medulla
  
  • cardiovascular center: composed of clusters of sympathetic neurons in medulla
  • consists of:
    - cardiac centers: cardioinhibitory and cardioacceleratory centers
    - vasomotor centers: sends steady impulses by sympathetic efferents called vasomotor fibers to blood vessels (vasomotor tone: cause continuous moderate constrictions)
  • receives inputs from baroreceptors, chemoreceptors, and higher brain center
• Baroreceptor Reflexes
  
  • located in carotid sinuses, aortic arch, and walls of large arteries of neck and thorax
  • if MAP is high:
    - increased blood pressure stimulates baroreceptors to increase input to vasomotor center
    - inhibits vasomotor and cardioacceleatory centers
    - stimulates cardioinhibitory center
    - results in decreased blood pressure
  • resulting decrease in blood pressure due to 2 mechanisms:
    1) vasodilation: decreased output from vasomotor center causes dilation
    - arteriolar vasodilation: reduces peripheral resistance, MAP falls
    - venodilation: shifts blood to venous reservoirs, decreases venous return and CO
    2) decreased cardiac output: impulses to cardiac centers inhibit sympathetic activity and stimulate parasympathetic
    - reduces heart rate and contractility; CO decrease causes decrease in MAP
  • if MAP is low:
    - reflex vasoconstriction is initated that increases CO and blood pressure
    - example: upon standing, BP falls and triggers:
    - carotoid sinus reflex: baroreceptors that monitor BP to ensure enough blood to brain
    - aortic reflex: maintains BP in systemic circuit
  • baroreceptors are ineffective if altered blood pressure is sustained
    - become adapted to hypertension, so not triggered by elevated BP levels
• Chemoreceptor Reflexes
  
  • aortic arch and large arteries of neck show increase in CO2 or drop in pH or O2
  • cause increased blood pressurre by:
    - signaling cardioacceleatory center to increase CO
    - signaling vasomotor center to increase vasoconstriction
• Influence of Higher Brain Centers
  
  • reflexes that regulate BP are found in medulla
  • hypothalamus and cerebral cortex can modify arterial pressure via relays to medulla
  • hypothalamus increases blood pressure during stress
  • hypothalamus mediates redistribution of blood flow during exercise and changes in body temp

Question 4

Short Term Mechanisms: Hormonal Controls

Answer 4

• hormones regulate BP in short term by changes in peripheral resistance or long term by changes in blood volume
• adrenal medulla hormones
  - epinephrine and norepinephrine from adrenal gland increase CO and vasoconstriction
• angiotensin II stimulates vasoconstriction
• ADH: high levels can cause vasoconstriction
• atrial natriuretic peptide decreases BP by antagonizing aldosterone, causing decreased blood volume

Question 5

Long Term Mechanism: Renal Regulation

Answer 5

• baroreceptors adapt to chronic high or low BP so are ineffective for long term regulation
• control BP by altering blood volume by kidneys
• kidneys regulate arterial blood pressure by”
  1) direct renal mechanism
  - alters blood volume independently of hormones
  - increased BP or blood volume cause elimination of more urine, reduce BP
  - decreased BP or blood volume cause kidney to conserve water, BP rises
  2) indirect renal mechanism (renin-angiotensin-aldosterone)
  - angiotensin II acts in 4 ways to stabilize arterial BP and ECF:
  - stimulates aldosterone secretion
  - causes ADH release from posterior pituitary
  - triggers hypothalamic thirst center to drink more water
  - acts as a potent vasoconstrictor, increases BP

Question 6

Summary of Blood Pressure Regulation

Answer 6

• goal of blood pressure regulation is to keep blood pressure high to provide adquate tissue perfusion, not so high that blood vessels are damaged
  
  • example: if BP to brain is too low, perfusion is inadequate and person loses consiousness
  • if BP to brain is too high, person could have stroke

Question 7

Homeostatic Imbalances in Blood Pressure

Answer 7

• transient elevations in BP occur during changes in posture, physical exertion, emotional upset, fever
• age, sex, weight, race, mood, and posture may also cause BP to vary
• Hypertension
  
  • sustained elevated arterial pressure of 140/90 mm Hg or higher
  • prehypertension if values elevated but not yet in hypertension range
    - can be transiet adaptions during fever, physical exertion, and emotional upset
    - persistent in obese people
    prolonged hypertension is major cause of heart failure, vascular disease, renal failure, and stroke
    - heart works harder, myocardium enlarges, weakens, and becomes flabby
  • also accelerates atherosclerosis
• Primary Hypertension
  
  • 90% of hypertensive conditions
  • no underlying cause found
  • risk factor: hereditary, diet, obesity, age, diabetes mellitus, stress and smoking
  • no cure, can be controlled
    - restrict salt, fat, cholesterol intake
    - increase exercise, weight loss, stop smoking
    
    • antihypertensive drugs
• Secondary Hypertension
  
  • less common
  • due to identifable disorders like obstructed renal arteries, kidney disease, and endocrine disorders such as hyperthyroidism and Cushings syndrom
  • treatment: focus on correct underlying cause
• Hypotension
  
  • low BP below 90/60 mm Hg
  • not a concern unless causes it causes inadequate blood flow to tissues
  • associated with long life and lack of cardio illness
• Circulatory Shock
  
  • condition where blood vessels inadequately fill and cannot circulate blood normally
    - inadequate blood flow cannot meet tissue needs