W4 Cardiovascular BP Flashcards
Describe 3 factors which influence peripheral resistance
- Blood viscosity: influenced by amouth of RBC and albumin. ↓ viscosity with anaemia, hypoproteinemia. ↑ viscosity with polycythaemia, dehyrdation.
- Vessel length: The longer the vessel the greater the surface area in contact with the blood and the greater the resistance. (Longer tube = ↑ resistance)
- Vessel radius: Layer of blood closest to the vessel wall has most friction, the further blood from the wall has less resistance. Thin vessels have more blood close to the vessel wall so have higher resistance.
Double the diameter, decreases resistance.
Explain how arterial pressure is influenced by peripheral resistance
Arterioles control peripheral resistance.
Neural mechanisms are coordinated by the vasmotor centre in the medulla.
Hormonal mechanisms coordinated by the renin, angiotension, alsdosterone system (RAAS), atrial natriuretic peptide (ANP), epinephrine.
Describe differences in the routing of blood during rest and exercise
Vasomotor Control Mechanisim: the vasomotor center in the medulla oblongata controls constriction of arterioles by SNS signals.
At rest: Most of bodys blood supply is in the systemic veins and venules, acting as reservoirs for vasoconstriction of veins which shifts blood to the heart or where needed.
Blood flow in the brain is constant 0.75l/min.
During exercise vasomotion redistribution of blood during cardiac output (↑HR) to skeletal muscle predominately.
Exemplify how vasomotion can be controlled by neural mechanisms
Integrates 3 autonomic reflexes
-
Baroreflexes: If changes in BP is detected by pressure receptors (aortic bodies and caraotid bodies) (baroreceptors). → alters the ratio between SN and PS output.
* If BP is high, ↑ PS impulses and ↓ SNS impulses will slow HR down, ↓ SV and dilating blood vessels.
* If BP is ↓ and ↑ in SN impulses will ↑ HR, SV and constrict arterioles and reservoir vessels.
2. Chemoreflexes: Involved in the aortic and carotid bodies; these are sensitive to hypercapnia (↑ Co2), hypoxia (↓o2) and ↓ arterial blood pH. Sends msg to Medulla.
3. Medullary ischemic reflex: acts in emergency situation involving ↓ blood flow to medulla. Sends SN to heart ( ↑ HR and CO) and blood bessels (BP) If medulla experiences low oxygen this is dangerous for the brain, may result in death.
Exemplify how vasomotion can be controlled by hormonal mechanisms
Factors that influence hemodynamics:
- Stroke volume SV
- Preload - nevous return and EDV.
- After load - pressure required to open semilunar valves (peripheral resistance)
- Force of contraction (ANS & epinephrine)
- Heart rate:
- Autonomic NS
- Hormones.
- Peripheral vascular resistance -
- Vessel dilation or constriction
- Regulated by ANS hormones.
- Blood volume:
- Water intake & loss
- Regulated by hormones; renin, angiotension, aldosterone (RAAS), atrial natriuretic peptide (ANP).
Systems that regulate blood volume also regulate vasomotion because;
Vasoconstriction ↓ vascular volume ↑ pressure
Vasodilation ↑ vascular volume ↓ pressure
Epinephrine/norepinephrine: Most blood vessels binds to a-adrenergic receptors (vasoconstrition).
Skeletal and cardiac muscle blood vessels binds to b-adrenergic receptors (vasodilation)
List and describe 3 mechanisms by which venous return is achieved
Venous return is the amount of blood returned to the heart by the veins;
- Stress-relaxation effect - veins are elastic and adapt in pressure by expanding or narrowing to maintain blood flow.
- Pressure gradient: Venules have a higher pressire than vena caba so blood flows towards the heart.
3. Gravity: drains blood from head and neck and limbs are elevated or if you’re laying flat venous return will be ↑.
Orthostatic = blood reservoir to legs
4. Skeletal muscle pump; in the limbs veins lie next to skeletal muscles and if the muscle contracts blood will be squeezed toward heart due to one-way nature of valves present in veins.
5. Respiratory pump: aids in the flow of blood from the abdomincal cavity to the thoracic cavity.
6. Cardiac suction - created during ventricular diastole with rapid enlargement of the ventricular cavity.
7. Exercise: ↑ venus return in many ways. By: ↑ HR, ↑BP, vessels of skeletal muscles lung heart ↑ flow. Venous pooling: inactivity/
Describe the process of capillary exchange and its role in blood volume regulation
Capillary exchange is the movement of substrates between blood and interstitial fluid. Important for the diffusion of gases, wastes, particles.
The direction of fluid movement affects blood volume and blood pressure.
Fluid out= ↓ blood vol = ↓ BP
Fluid in = ↑ blood vol = ↑ BP.
Their are two pushing forces:
- Blood hydrostatic pressure: pressure of blood pushing onto the vessel wall.
- Colloid osmotic pressure: concentration of solutes affects the movement of water by osmosis. The blood is more concentrated than interstitial fluid. The plasma protein albumin and Na+ concentration mainly responsible for this pressure
- Changes in total BV changes the amount of blood returned to the heart.
- The atrial end of the capillary fluid leaves the capillary to go into interstitial fluid.
- At the venous end of a capillary fluid comes back into the capillary. Not all fluid that left returns. (85%).
- The lymp system recovers the extra fluid.
Explain the role of ADH, RAAS and ANH in blood volume regulation
RAAS: Renin, angiotension, aldosterone system - ↑ Na+ (and fluid) retention (aldosterone) ↑ ADH ↑ fluid retnetion (angiotension II) SNS vasoconstriction (angiotension II)
ADH: Antidiuretic horome - ↑ fluid retention = blood volume = vasoconstriction
ANP: Atrial Natriuretic Peptide - ↑ Na+ (and fluid) = ↓ blood volume, generalised vasodilation.
- ↑ Blood osmolarity detected by osmoreceptors in hypothalamus.
- Thirst response activated
- ADH released from posterior pituitary (RAAS)
- Water is pumped out of urine in kidney collecting duct back into blood, ↑ fluid retention ↑ BP. Atrial Natriuretic Peptide.
Describe how blood pressure is expressed and measured
Arterial blood pressure is measured with the aid of a sphygmomanometer and thethoscope.
Systolic BP/diastolic BP.
Systolic BP: force of blood pushing against artery walls as ventricle contract.
Diastolic BP: for the blood pushing against artery walls when ventricles are replaced during isvolumetric ventricular contraction
Detail how pulse pressure and mean arterial pressure are calculated
Pulse pressure: systolic BP - diastolic BP. Gives an indication of the force of the pressure with each contraction.
A consistently high PP can indicate a lack of elasticity in the great vessles or problems with back flow of blood in the chambers. Used to calculate “mean arterial pressure”.
Explain how the blood pressure gradient and peripheral resistance are related to the minute volume of blood.
Minute Volume of BLood = volume of blood circulating through the body per minute.
Flow = change in pressure / resistance.
Describe how the velocity of blood flow is governed.
Physical principal: when a liquid flows from an area of one cross-sectional size to an area of larger size, it’s velocity decrease in the area with larger cross-section
Define pulse and identify the factors most responsible for its existence
Defined as the alternate expansion and recoil of an artery.
Clinical significance: reveals important information about cardiovascular system, blood vessels and circulation.
Physiological significance: expansion stores energy released during recoil, maintaining a relatively constant blood flow.
Identify where the major pulse points can be found and state the name of the artery for each area
Wherever an artery lies near the surface and over a bone.
- Radial artery - at wrist
- Temporal artery: in front of the ear
- Common carotid: anterior edge of the sternocleiodmastoid muscle.
- Facial artery: lower margin of mandible.
- Brachial artery: bend of elbow
- Femoral artery: middle of groin
- Popliteral artery: behind knee
