How Is Blood Circulation Regulated Flashcards
Tunica intima
- endothelium.
- basement membrane.
- lamina propria (CT layer).
- internal elastic membrane (gene strayed layer of elastic fibers.
Tunica media
- smooth muscle cell bodies arranged circularly around the blood vessel.
- vasoconstriction and dilation (smooth muscle control).
Tunica externa (adventitia)
- connective tissue.
- varies from dense regular near the vessel to loose that merges with the surrounding C.T.
Elastic artery characteristics and examples
- elastic tissue.
- expand and recoil.
- are pressure reservoirs.
- conducting arteries.
- e.g. Aorta and major branches.
Muscular arteries characteristics and examples
- thick walls: 25+ layers of muscle.
- undergo vasoconstriction and vasodilation.
- distributing arteries.
- e.g. Medium size arteries.
Arteriole characteristics and examples
- decreasing in size with gradual loss of wall layers down to terminal arterioles.
- e.g. Small muscular arteries.
Venules
- Very small veins that drain capillary network.
- as diameter of venules increases, amount of smooth muscle increases.
- endothelial cells and basement membrane with a few smooth muscle cells.
Characteristics of veins
- smooth muscle cells form continuous layer: addition of tunica adventitia.
- have valves.
- thin wall and large lumens.
- are very compliant: 24x more than arteries.
What are capacitance vessels of the circulation
-veins: hold a lot of blood at very low pressure.
Capillary characteristics
- endothelial cells sitting on a basement membrane and delicate layer of loose connective tissue.
- for rapid exchange of nutrients and metabolites between blood and interstitial fluid.
What are the three types of capillaries
- continuous.
- fenestrated.
- sinusoids.
Continuous capillary characteristics and examples
No gaps between endothelial cells e.g. Muscle, skin.
Fenestrated capillary characteristics and examples
Highly permeable e.g. Kidney, endocrine glands.
Sinuoid capillary characteristics and examples
Large diameter and large fenestrae e.g. Liver, bone marrow, spleen.
What controls blood flow between the capillaries?
Controlled by the opening and closing of pre-capillary sphincters.
What does blood flow through capillary beds depend on?
Metabolic activity of the tissue.
What are arteriovenous anastomoses?
The connecting vessels through which blood can bypass capillaries and flow directly into post-capillary venules.
What are capillary beds?
The functional areas of the circulation where fluid, nutrient and metabolic exchange occurs between the blood, interstitial fluid and the cells.
What is filtration out?
Fluid exchange at the arteriolar end of a capillary: ~30L/day.
What is reabsorption in?
Fluid exchange at the venous end: ~27L/day.
Where are any excess filtered fluid and leaked proteins from the capillaries drained?
Into lymphatic capillaries which return lymph to the blood: ~3L/day.
Movement of capillary fluid when there is: positive filtration pressure?
Fluid moves out of capillary (net hydrostatic pressure>net osmotic pressure).
Movement of capillary fluid when there is: negative filtration pressure?
Fluid moves in to capillary (net hydrostatic pressure < net osmotic pressure).
What percentage of blood volume is in blood vessels at any given time? (In the systemic circulation)
84% (64% in veins, 13% arteries, 7% capillaries).
What are the three layers of blood vessel walls?
Tunica intima, tunica media, tunica externa.
What percentage of blood volume is in the heart chambers?
7%.
What percentage of blood volume is in the pulmonary vessels?
9%
What are the two types of blood flow?
- laminar flow.
- turbulent flow.
Describe laminar flow.
- outermost layer moving slowest and centre moving fastest.
- steamlined: interior of blood vessel is smooth and of equal diameter along its length.
Describe turbulent flow.
- interrupted.
- rate of flow exceeds critical velocity.
- partially responsible for heart sounds.
- sounds due to turbulence not normal in arteries and is probably due to some constriction; increases the probability of thrombosis.
What does blood flow relate to and what is it inversely proportional to?
Relates to diameter and is inversely proportional to the total cross-sectional area of a blood vessel category.
What makes blood flow?
The fact that blood flow is directly proportional to pressure differences and inversely proportional to resistance.
What is blood flow?
Volume of blood flow per unit time (e.g. ml/min).
-e.g. CO output at rest it 5 L/min, therefore blood flow through the aorta is 5 L/min.
Explain Flow= (P1-P2)/R
P1- pressure in vessel at point 1.
P2- pressure in vessel at point 2.
R- resistance to flow.
What is resistance to flow (R) proportional to?
- directly proportional to vessel length and blood viscosity.
- inversely proportional to vessel diameter.
What affects blood flow?
- Pressure differences created by the heart (blood leaving the heart: HIGH pressure, blood coming back to the heart: LOW pressure)(CO).
- Blood vessel diameter (resistance): small change in diameter drastically changed the resistance.
Explain how blood vessel diameter affects blood flow.
- The larger the diameter of a vessel => less resistance to flow => increased blood flow.
- blood flow through tissues is altered in the short term by varying the radius (r) of the resistance vessels- the arterioles (this means that dilating or constructing arterioles can send blood to one part of the body or another).
What mechanisms can diameter of vessels be altered by?
- intrinsic: local metabolic factors, vasoactive factors, myogenic stretch.
- extrinsic: neural and hormonal.
Intrinsic (local) control
- In most tissues, blood flow is proportional to metabolic needs of tissues.
- blood flow increases when tissue metabolism increases.
Extrinsic control
- Responsible for intergrated blood flow- routing blood maintenance of MAP in all regions of the body.
- achieved by neural and hormonal factor.
List some vasodilators.
- Histamine, bradykinins, prostacyclins.
- ANP (atrial natriuretic peptide).
- adrenaline also acts on B2 reception to cause vasodilation.
List some vasoconstrictors.
- Endothelin-1, leukotrienes, thromboxane-A2.
- angiotensin II and ADH.
- noradrenaline and adrenaline act on reception to cause vasoconstriction.
Explain myogenic stretch
- passive stretch (e.g. Surge in blood flow) of blood vessels causes vasoconstriction.
- conversely, decreased stretch (e.g. Sudden drop in blood flow) causes vasodilation.
PP equation
SBP-DBP
MAP equation
MAP=DBP + 1/3 PP
BP equation
BP= CO x TPR
CO equation
CO=HR x SV
What is MAP regulated around?
-MAP is regulated around “normal” levels by negative feedback regulatory mechanisms.
What are the short term control mechanisms for MAP?
- The baroreceptor reflex.
- Hormonal influences.
- Chemoreceptor reflexes.
- Higher CNS centres.
- CNS ischaemic response.
What are the long term control mechanisms for MAP?
- Direct renal mechanisms.
2. Indirect hormonal control mechanisms.
What does an expanded blood volume do to MAP?
Raised MAP.
What does a failing blood volume do to MAP?
-reduced MAP.
What parts of the cardiovascular centre in the medulla oblongata are essential for overall MAP regulation?
- cardioregulatory.
- vasomotor centre.
What does the cardioregulatory centre influence?
The heart.
What does the vasomotor centre influence?
Blood vessels.
What are baroreceptors?
- high pressure stretch receptors located in the aortic arch and carotid sinus.
- connected by afferent “buffer” sensory never to cardiovascular centre.
Explain the baroreceptor reflex.
.
Explain hormonal influences on MAP.
- adrenaline and noradrenaline- increase CO, TPR and MAP.
- angiotensin II and ADH- increase vasoconstriction, TPR and MAP.
- ANP secreted by the cardiac atria when blood volume rises-causes vasodilation, lowered TPR and MAP.
Explain chemoreceptor reflex influences on MAP.
May affect MAP in emergencies, when atrial blood CO2 rises or pH or arterial O2 fall.
Explain higher CNS centres influences on MAP.
Have input to the cardiovascular centre causing MAP changes in response to pain, stress, fear and other emotional factors.
Explain CNS ischaemic response influence on MAP.
Emergency situation, reduced blood flow leads to decreased oxygen, increased carbon dioxide, and reduced pH within the medulla oblongata, stimulates neurons in vasomotor centre, which stimulates vasoconstriction and increases MAP.
Explain direct renal mechanisms on MAP.
- increased blood volume => increased renal plasma filtration and renal fluid excretion reducing blood volume and decreasing MAP.
- decreased blood volume: decreased renal plasma filtration and renal fluid excretion thereby conserving blood volume and increasing MAP.
Explain indirect hormonal control mechanisms on MAP.
- fine-tune the direct renal control.
- renin-angiotensin-aldosterone system (RAA system).
What is the difference between an artery and a vein?
- an artery has a small lumen, thick walls, no valves, has a elastic lamina present and conducts blood away from heart at high pressure.
- a vein has a large lumen, thin walls, valves, no elastic lamina and accommodates large volumes of blood at low pressure; known as capacitance vessels.
Which wall layer is thickest in an artery?
Tunica media.
Which wall layer is thickest in a vein?
Tunica externa.
What material forms the bulk of the tunica media in large elastic arteries?
Elastic fibres.
What material forms the bulk of the tunica media in medium muscular arteries?
Muscle.
What structure must the descending aorta pass through to enter the abdominal cavity?
The diaphragm.
List the three main arteries that arise from the aortic arch in the order in which they arise.
- brachiocephalic artery.
- left common carotid artery.
- left subclavian artery.
What parts of the body does the brachiocephalic artery supply?
Right side of head and right upper limb.
What parts of the body does the left common carotid artery supply?
Left side head.
What parts of the body does the left subclavian artery supply?
Left upper limb.
What two main arteries does the brachiocephalic artery divide into and what part of the body do they supply?
- right common carotid artery: right side head.
- right subclavian artery: right upper limb.
What parts of the body does the pulmonary trunk supply?
The right and left lungs.
What parts of the body does the left pulmonary artery supply?
The left lung.
The axillary artery is a continuation of another vessel which is located below the clavicle and bring blood from the thorax to the upper limb; name this vessel?
Right subclavian artery.
Which artery can be used to palpable the pulse in the foot?
Dorsalis pedis artery.
All vessels that supply the organs of the abdomen arise from the single main blood vessel running anterior to the vertebral column.
Abdominal aorta.
What paired vessels supply the diaphragm?
Inferior phrenic arteries.
What paired vessels supply the adrenal glands?
The left and right adrenal arteries.
What paired vessels supply the kidneys?
The left and right renal arteries.
What paired vessels supply the gonads (testis in males, ovaries in females)?
The left and right gonadal arteries.
What are the three unpaired vessels of the abdominal aorta?
- coeliac trunk.
- superior mesenteric.
- inferior mesenteric.
What are the four paired branches arising from the abdominal aorta?
- inferior phrenic arteries.
- left and right adrenal arteries.
- left and right renal arteries.
- left and right gonadal arteries.
What structures does the coeliac trunk supply? And what is its embryological development?
- foregut.
- stomach, duodenum, liver, gall bladder and pancreas.
What structures does the superior mesenteric artery supply? And what is its embryological development?
- midgut.
- jejenum, ileum, ascending colon, transverse colon, caecum and appendix.
What structures does the inferior mesenteric artery supply? And what is its embryological development?
- hindgut.
- descending colon, sigmoid colon, rectum and anus.
Name six location on the body where the arterial pulse may be taken.
- radial.
- carotid.
- brachial.
- popliteal.
- facial.
- dorsalis pedis.
Why is the brachial artery used when taking blood pressure?
Brachial artery is at the same level as the heart giving the best picture of pressure during ventricular systole and diastole.
Define total peripheral resistance.
The friction blood encounters as it passes through vessels. Blood flow is inversely proportional to resistance i.e. As resistance increases, blood flow decreases.
What does peripheral resistance depend on?
Blood viscosity, vessel length and vessel radius.
What is hydrostatic pressure?
Hydrostatic pressure forces fluid out of the capillary.
What is osmotic pressure?
Osmotic pressure draws fluids back into the capillary.
