Venous Circulation Flashcards
Explain the functions of veins
- Forward function, change their capacitance to maintain cardiac filling & cardiac output
- Backward function, drain the capillariesat lowest pressure as their resustance is minimal.
Explain the functional characteristics of veins
- Veins are large capauciatnce vessels act as blood reservoir, accomodate 60% of blood
- Veins can accomodate inc in volume with minimal inc in pressure
- More filling of veins causes stretch & marked inc in pressure and they become as stiff as arteries
- Veins can tolerate high pressure without blow
- Sympathetic innervation is less to veins than arteries
GR: Veins can inc in volume without inc in pressure, describe the shape progression
Because they have reserve in their shape
They are normally flattened except at periphery, then become elliptical then oval then circular with inc filling
GR; The behaviour of veins in becoming stiff as art when subjected to marked filling is protective
Mobilizqtion of blood towards heart
Inc capillary hydrostatic pressure and inc filtration from capillaries to minimize circulatiry overload
GR: Veins can tolerate high pressure
Mention a surgical app
Because collagen, the principal component in their walls is extremely strong
They are used as arterial grafts
Describe the role of sympathetic on veins
Venoconstriction:
A. Shift of the pressure/volume relation to the left
B. Decreased capacitance of veins with more mobilization of blood towards heart
Mention the components of venous pressure
Mean circulatory pressure
The added pressure due to activity of the heart
Define CVP
It is the pressure in right atrium & big veins in the thorax = zero.
Define MSFP
It reoresents the degree of filling of the heart and all vessels with blood, it depends on the volume of blood in relation to CV capacitance, can be measured in any vessel when heart is stopped, noemally abou 7 mmHg.
Mention the values of pressure in differenet components of venous system
- Venules, 10-12 mmHg
- Small veins, 8-10 mmHg
- Veins, 6-8 mmHg
- Vena cava, 0-2 mmHg
The speed of blood in venae cavae is …..
25 cm/sec
The reference point is a circular line at level of .,,,.
4th sternocostal joint
What happens when pressure at the reference point is increased?
Inc vent filling & force of contraction, more blood is pumped out, which leads to dec pressure at this point.
GR: The big veins of thorax are not collapsed while neck veins are collapsed
Because the intrathoracic pressure is -ve while the pressure in neck veins is zero so they are collapsed by the atmospheric pressure.
GR: although venous sinuses of skull have -ve pressure they are not collapsed
Because the skull doesn’t transmit atmospheric pressure to them and their walls are made of tough fibrous tissue which keep them patent.
Define HIP
It is a subdiaphragmatic point (2-3 inches below the opening if IVC in diaphragm) which doesn’t change on changing position. The level of this point represents the level at which the force of gravity is balanced by antigravity forces.
HIP is shifted downwards/upwards in which cases?
D, when gravity overrides antig mechanisms as in block of alpha adrenergic receptors or blood loss in hemorrhage.
U, opposite, as in inc BV, venomotor tone, applying external pressure on body as in water immersion.
GR: Filling pressure is decreased on standing from supine position
As the heart is located above HIP leading dec cardiac filling & CO about 30%.
Mention Vis-A-Fronto factors
Thoracoabdominal pump
Cardiac suction
Describe thoracoabdominal pump
CVP is decreased by more -ve intrathoracic pressure during inspiration & -ve pressure breathing
Opposite occurs in expiration & +ve pressure breathing
Mention conditions in which cardiac suction efficiency is inc/dec (VR)
Inc, during rapid ejection & increased cardiac activity by symp
Dec, congestive heart failure
Describe the effect of pressure gradient on VR
Constructed capillaries & dilated arterioles inc pressure gradient (PVP), & vice versa due to pooling of blood in tissues.
Without muscle contraction, on dependency ….. of blood is dislocated to vessels below level of heart, BP in LL becomes …., but this is lowered by muscle pump to …..
70%
90 mmHg
17 mmHg
What is the function of venous valves?
They are not an antigravity mechanism, they only ensure heart ward flow of blood, without them muscle pump is ineffective.
Venoconsriction starts within …. & is fullfilled within …. of standing, during this time ….. is the main mechanism of VR.
7 sec
2-3 min
Muscle pump
What is the aim of arteriolar VC on standing?
Dec blood inflow into the distensible veins from the arterial side to limit the pooling of blood into them.
Decsribe benefits & harms of resistance exercise
Imrove muscle strength & bone density
Cause sharp increase in systolic & diastolic BP, could prove harmful to individuals with heart & vascular disease
Mention mechanisms of inc in HR
Psychic stimuli Dec vagal tone on heart Inc sympathetic tone on heart Adrenaline Proprioceptive impulses from exercising Inc body temperature Bainbridge refkex due to inc VR
GR: increased cardiac output during aerobic exercise
Due to inc HR
& INC CO due to inc preload, inotropy (due to psychic stimuli, inc symp discharge, ipdec vagal tone, inc CA) & dec afterload (due to dec TPR).
What is the effect of aerobic exercise of ABP
SBP show great inc
DBP is not changed or slighly dec due to VD of skelltal ms BV due to local metabolites
MAP is slightly inc while PP is inreased
Mention effect of aerobic exercise on different circukation
Coronary, pulmonary & skeletal muscle show increased blood flow
Cerebral flow is unchanged
Splanchnic blood flow decreases
Describe the benefits of exercise on CV health
- Decreased HR during rest & during exercise it is inc to lesser extent than sedentary person
- Inc stroke volume in rest & exercise
- Physiological cardiac hypertrophy, protect from cardiac fibrosis/death & cell death
- Antiatherogenic & antihypertensive
- Improve HR & SV reserve
- Decrease incidence & severity of heart attacks
- Improve coronary perfusion by better production of NO & Prostacyclin
Describe acute & chronic effects on TPR (aerobic exercise)
Decreased in both
Describe chronic effects of exercise on BP
Decreases below pre-exercise values and remain decreased upto 12 hrs after exercise session
