Blood Vessels 2 Flashcards
Bulk flow of fluid across capillary wall is based on ____ _____.
pressure gradients
What type of plasma moves across capillaries?
protein-free
What are the 2 types of plasma movement?
- filtration
- absorption
Filtration =
movement out of capillary into interstitial space
Absorption =
movement into capillary from interstitial space
What is the purpose of plasma movement?
distribute ECF
What are the 3 types of exchange across capillary walls?
- diffusion (most common mechanism)
- transcytosis
- mediated transport
What is lipophilic diffusion?
across membrane
What is lipophobic diffusion?
through channels
What is transcytosis?
exchangeable proteins
_____ forces across capillary walls.
Starling
What are starling forces?
- forces for bulk flow
- hydrostatic and osmotic pressures
What is the hydrostatic pressure gradient?
force due to fluid
What is osmotic pressure?
osmotic force exerted on water by non permeating solutes
What is the only non permeating solute?
proteins
What type of capillary pressure can be calculated?
net filtration pressure
Filtration favoured what side?
arteriolar side
Absorption favoured what side?
venous side
Name 3 factors that affect filtration and absorption across capillaries.
- disease
- standing on feet
- injuries
How does disease affect filtration and absorption across capillaries?
kidney, heart of liver disease
How does standing on feet affect filtration and absorption across capillaries?
increases hydrostatic pressure
How do injuries affect filtration and absorption across capillaries?
- when capillaries are damaged, they leak fluid and proteins
- histamine increases capillary permeability to proteins
What is the net volume filtered/day?
- 3 L
- lymphatic system picks up and returns to circulation
Venues are smaller than _____.
arterioles
Venules connect ____ to ____.
capillaries to veins
Describe the smooth muscle and exchange in venules.
- little smooth muscle in walls
- some exchange of material between blood and interstitial fluid
Describe the size of veins.
large diameter, thin walls
What are the purposes of valves in veins. Where are they found?
- allow unidirectional blood flow
- present in peripheral veins
- absent from central veins
What does it mean when we say veins are compliant vessels?
- high compliance
- expand with little change in pressure
- function as blood reservoir
How much total blood volume in systemic veins at rest?
60%
If there is same pressure in arteries and veins, there is greater volume in ______.
veins
Name 4 factors that influence venous pressure and venous return.
- skeletal muscle pump
- respiratory pump
- blood volume
- venomotor tone
Increased blood volume =
increased venous pressure
Decreased blood volume =
decreased venous pressure
Long-term regulation of blood pressure occurs through:
regulation of blood volume
What is the skeletal muscle pump?
one-way valves in peripheral veins
What happens when skeletal muscle contracts?
- squeezes on veins, increasing pressure
- blood moves toward heart
- blood cannot move backwards due to valves
What happens when skeletal muscle relaxes?
blood flows into veins between muscles
What happens with the respiratory pump during inspiration?
- decreases pressure in thoracic cavity
- increases pressure in abdominal cavity
Pressure on veins in abdominal cavity creates:. What does this do?
- gradient favouring blood movement to thoracic cavity
- increases central venous pressure
- increases venous return
What is venomotor tone?
- contraction of smooth muscle in the wall of a vein
- innervated by SNS
- norepinephrine causes venous constricton
- increases CVP, VR
- decreases compliance
Name 3 determinants of MAP.
- HR
- SV
- TPR
MAP =
= CO x TPR
= HR x SV x TPR
CO =
= HR x SV
= MAP/TPR
Regulating ___ is critical to normal function.
MAP
MAP depends on ___.
TPR
Why does TPR drop, but BP still rise?
- drop in vascular resistance at the muscle during exercise is not fully compensated for by resistance in other organs
- increased CO
A constant CO leads to an increase in…
increase in the volume of blood contained in the aorta and an increase in mean arterial pressure when TPR increases
Name the 2 extrinsic controls of arteriole radius.
- neural
- endocrine
Describe short term regulation of MAP.
- seconds to minutes
- regulates CO and TPR
- involves the heart and blood vessels
- primary neural control
Describe long term regulation of MAP.
- minutes to days
- regulates blood volume
- involves the kidneys
- primarily hormonal control
Baroreceptors =
- pressure receptors
- aka “stretch receptors”
Arterial baroreceptors =
- sinoaortic receptors
- aortic arch
- carotid sinuses
Respond to stretching due to:
pressure changes in arteries
What is regulated variable for the negative feedback loop for regulation of MAP?
MAP
What is detector for the negative feedback loop for regulation of MAP?
baroreceptors (detect changes in MAP and pulse pressure)
What is the integration centre for the negative feedback loop for regulation of MAP?
cardiovascular centres in the brainstem
What is the controller for the negative feedback loop for regulation of MAP?
autonomic nervous system
What are the effectors for the negative feedback loop for regulation of MAP?
heart and blood vessels
What activates baroreceptors? What do they cause?
- stretch of vessels
- cause depolarization and sends APs to the CNS to exert its effects via the ANS
When does the baroreceptor reflex reset to a higher pressure?
during exercise
What is the cardiovascular control centre? What does it regulate?
- medulla
- BP
What do low pressure baroreceptors do with input into the cardiovascular control centre?
right atrium and large systemic veins (aka volume receptors) monitor venous pressure
Where are chemoreceptors found and what did they do with input into the cardiovascular control centre?
- brain and carotids
- monitor O2, CO2, H+
What do higher brain centres do with input into cardiovascular control centre?
- hypothalamus (fight or flight response coordination, vessel resistance response to changes in core temperature)
- cerebral cortex
What is involved in the input to the cardiovascular control centre?
- arterial baroreceptors
- low pressure baroreceptors
- chemoreceptors
- proprioceptors, other receptors in organs
- higher brain centres
What is involved in the output to the cardiovascular control centre?
- SNS: SA node, contractile fibres, vessels
- PNS: SA node
Parasympathetic input to cardiovascular effectors goes where and does what?
- SA node (decreases HR)
- AV node
Sympathetic input to cardiovascular effectors goes where and does what?
- SA node (increases HR)
- AV node
- Ventricular myocardium (increases contractility)
- Arterioles (increases resistance)
- Veins (increases venomotor tone)
What is a “quick fix” for a drop in MAP?
- baroreceptor reflex
- does not correct the problem
Long-term regulation of MAP occurs through:
renal regulation of blood volume
What does hypertension do to baroreceptors?
“resets” the set point of the baroreceptors, cannot be returned to normal
How can baroreceptor fix create further problems?
- if blood volume is not restored
- local controls (metabolites) will override the response and MAP will begin to decrease again
Describe the baroreceptor reflex.
- negative feedback loop to maintain blood pressure at normal level
- Detectors = baroreceptors
- Afferents = visceral afferents
- Integration center = cardiovascular control center
- Efferents = autonomic nervous system
- Effectors = heart, arterioles, and veins
What does epinephrine act on and what does it do to MAP?
- Acts on smooth muscle of arterioles (increases TPR)
- Acts on smooth muscle of veins (increases venomotor tone)
- Acts on heart (increases HR and SV (CO))
- MAP increases
What does vasopressin (ADH) and angiotensin II do?
- Vasoconstrictors
- Increase TPR
- Increase MAP
Epinephrine is released by ____ ____ in response to ______ activity.
- adrenal medulla
- sympathetic activity
Epinephrine vasodilator what muscle?
cardiac and skeletal
Vasopressin gets stimuli from where?
baroreceptors and changes in plasma concentrations of solute
What effect does vasopressin have?
- consticts vessels
- increases water retention
Angiotensin II gets stimuli from where?
kidneys
What effect does angiotensin II have?
- constricts vessels
- increases water reabsorption (through aldosterone)
- stimulates thirst
Where are low pressure baroreceptors (volume receptors) found?
- walls of large systemic veins
- walls of the right atrium
What activates low pressure baroreceptors?
decrease in blood volume
What is the response of low pressure baroreceptors?
- parallel with the baroreceptor reflex
- increase SNS activity
- increase vasopressin
Chemoreceptors respond to:
increases in CO2 levels in blood
What is the primary function of chemoreceptors?
regulate blood CO2 levels
What are the 2 effects that chemoreceptors have on ventilation?
- increases CO2
- increases TPR
- decreases HR
- increased MAP
What happens when CO2 rises?
- chemoreceptors activated
- CV control centre response (medulla)
- ventilation increases
- HR decreases (conserves O2)
- TPR increases to prevent dangerous drop in BP
Thermoregulatory responses are mediated by:
- hypothalamus
- thermoreceptors
Thermoreceptors respond to:
increased body temperature
What is the response from thermoreceptors?
- decrease sympathetic activity to skin
- vasodilation to skin
- increase heat loss to environment
______ takes precedence over the baroreceptor reflex.
thermoregulation
What is the possible consequence of thermoregulation?
- decreased TPR
- decreased MAP
Name exercise training adaptations.
- LV-EDV increases (enhanced blood volume)
- LV hypertrophy (0-25%)
- coronary artery growth and response to stimuli (mechanical and hormonal)
Name some performance responses to exercise training adaptations.
- cardiac myocytes: hypertrophy
- increased VO2 max: 50% due to increased SV and 50% due to greater O2 movement into tissues
- decreased RHR with training = increased diastolic filling time (= greater EDV, greater SV, and lower HR)