Blood Flow through the body Flashcards
In what direction does blood flow in during circulation?
High pressure to low pressure
Organization of blood vessels in order from leaving the heart
Arteries - arterioles - capillaries - venules - veins
Characteristics of arteries
- Large diameter
- Thin walls (relative to the diameter)
- Very elastic
- Low resistance
Characteristics of arterioles
- small diameter
- thick walls (relative to the diameter)
- lots of smooth muscle (innervated by SNS)
- CONTROLS BLOOD FLOW
MAP = ?
TPR x CO
Characteristics of capillaries
- one cell thick
- extremely thin walls - allows for gas exchange (diffusion)
- low blood pressure
Two types of capillaries
- Continuous capillary (less permeable)
- Fenestrated capillary (more permeable due to pores connecting it straight to the tissue)
What are Starling forces?
- forces which dictate filtration and reabsorption in the capillaries
- many different forces due to different molecules and gradients
What is edema?
- swelling due to excess fluids accumulating in tissue
- due to excess filtration from capillaries
Characteristics of veins
- large diameter
- very thin walls compared to diameter
- very low blood pressure
- smooth muscle innervated by SNS
What is the skeletal muscle pump in veins?
- smooth muscle in veins constrict in order to bring blood back to the heart
- special valves prevent back flow
- SNS can cause these smooth muscles to contract faster/harder
How does the SNS increase blood flow through venous return?
- innervates smooth muscles in veins (alpha adrenergic receptors)
- faster/stronger contractions = higher EDV (preload)
- higher EDV = increased stroke volume = increase CO
What are the three types of mechanisms used to regulate blood flow?
- Neural mechanisms (SNS and PNS)
- Humoral mechanisms (substances in blood)
- Local (tissue environment)
True/False - The PNS innervates blood vessels and slows blood flow using direct blood vessel control
False
- Only SNS innervates blood vessels (alpha adrenergic receptors)
What are 4 humoral molecules which regulate blood flow?
Vasoconstrictors (stimulus is a decrease in BP)
- ADH
- Angiotensin ll
Vasodilators (stimulus is an increase in BP)
- Atrial natriuretic peptide
- Histamine
Can epinephrine cause vasoconstriction AND vasodilation?
Yes
Vasoconstriction - by binding to alpha adrenergic receptors on blood vessels
Vasodilation - by binding to Beta 2 adrenergic receptors on heart, increasing blood flow indirectly causing blood vessels to dilate due to increased blood flow
The two local mechanisms that control blood flow
Myogenic Theory - increased blood pressure means arterioles stretch, so arterioles contract back after stretching to original state or smaller to control blood flow
Metabolite Theory - change in metabolic needs/metabolites in the blood = higher/lower blood flow
What are the receptors which detect changes in MAP and send signals to the CV centre in the medulla called?
- baroreceptors (mechanoreceptors)
Where are the mechanoreceptors that regulate MAP located?
- walls of aortic arch and the carotid arteries
How does the nervous system adjust the MAP when the it decreases?
- SNS activation
- heart pumps faster and harder = more CO
- Blood vessels constrict = higher TPR
How does the nervous system adjust the MAP when it increases?
- PNS activation
- Heart pumps slower and weaker = lower CO
- PNS activated = no SNS activation on vessels meaning vasodilation = lower TPR
What is hypertension?
- high blood pressure
Blood pressure >140 mm Hg
Targets for treating hypertension
- lowering TPR
- lowering CO
Treatments for hypertension
- beta blockers (block SNS activity on heart)
- Calcium channel blockers
- Angiotensin-converting enzyme inhibitors (ACE inhibitors)
- Angiotensin ll receptor blockers (ARBs)
