session 6 Flashcards
factors affecting blood flow
- vascular resistance
- venous return (how much blood is returning to heart)
- speed of blood flow
- blood pressure
Blood pressure is
hydrostatic pressure exerted by blood on walls of blood vessels
Caused by ventricle contraction
components of blood pressure
- systolic blood pressure
- highest artery pressure during systole
- diastolic blood pressure
- lowest artery pressure during diastole
mean arterial pressure (MAP)
- average blood pressure in arteries
- MAP = diastolic BP + 1/3(systolic - diastolic BP)
factors affecting blood pressure
- cardiac output
- dependent on HR and SV
- blood volume
- vascular resistance
- opposition to blood flow
- caused by lumen size, thickness of blood and length of the vessel
- elasticity of arteries
systemic vascular resistance (SVR)/ total peripheral resistance (TPR)
all vascular resistances offered by systemic blood vessels
*
what is venous return and how is it achieved
- volume of blood flowing back to heart through systemic veins
- depends on
- pressure difference in venules and right atrium
-
skeletal msucle pump
- contraction/relaxation of skeletal muscles
- opens and closes venous valves
-
respiratory pump
- diaphragm movement changing abdominal pressure
velocity of blood flow
-
velocity inversely related to cross sectional area of blood vessels
- blow flows slowly whre cross sectional area is greatest
- Blood flow decreases from aorta to arteries, is slowest in capillaries
circulation time
time for blood drop to pass from right atrium through pulmonary circulation, back to left atrium, through systemic circulation down to foot and back to right atrium
usually 1 min in resting person
blood pressure and blood volume are controlled by adjusting heart rate, stroke volume, blood volume and vascular resistance.
This is done thorugh several negative feedback mechanisms….
- cardiovascular centre
- nervous system
- hormones
- auto regulation
cardiovascular centre for blood flow and pressure control
- group of neurons in medulla oblongata that regulate HR, contraction and vessel diameter
- output from CV centre through
- sympathetic impulses incresae HR and contractility
- parasympathetic impulses along vagus nerves decrease heart rate
- output from CV centre through
nervous system control of blood flow and pressure
- nervous system regulated BP by
-
baroreceptor reflex
- pressure sensitive neurons in aorta, carotid arteries
- monitor stretch of wall
- low BP -> low baroreceptor feedback -> CV centre increases sympahtetic stimulation -> increases HR and contractility
-
chemoreceptro reflex
- monitor chemical composotion of blood ie o2, co2 and H+
- located in carotid sinus and aortic arch
- eg hypoxia or acidosis -> chemoreceptor stimulation -> increased sympathetic stimulation -> vasoconstriction and increased BP
-
baroreceptor reflex
hormonal control of BP and blood flow
-
renin-angiotenisin-aldosterone system
- changes blood volume and therefore BP
-
epinephrine and norepinephrine
- (adrenaline and noradrenaline)
- released from adrenal medulla
-
antidiuretic hormone (ADH)
- from posterior pituitary
- causes vasoconstriction
-
atrial natriuretic peptide
- released by cells in atria of heart when BP rises
- causes vasodilation
autoregulation of BP
- automatic adjustment to meet metabolic demands
-
physical changes
- warming = vasodilation
- cooling = vasoconstriction
-
vasodilating and vasoconstricting chemicals
- vasodilators being H+, lactic acid, histamine and NO
- vasoconstrictors being thromboxane, serotonin, endothelins
-
changes in o2 levels
- systemic vessels dilate with low o2 while pulmonary vessels constrict
methods of checking circulation
- pulse
- created by pressure in elastic artery caused by left ventricle systole
- blood pressure
- measured with a sphygmomanometer
- determines systolic and diastolic pressure
- can hear heart sounds (korotkoff sounds)
what is pulse pressure
The difference between systolic and diastolic
define shock
failure of CV system to deliver o2 and nutrients
- negative feedback systems attempt to fix
- eg ADH, vasodilators, renin-angiotensin-aldosterone
disorders of homeostatic imbalance
- hypertension
- systolic above 140
- diastolic above 90
- results in damage to blood vessels, heart, brain and kidneys
- managed with lifestyle changes and various drugs
primary hypertension
90-95% of all hypertension cases
No known/obvious cause for persistent hypertension
secondary hypertension
has a known underlying cuase
eg. obstruction of renal blood flow or damaged renal tissue
aging and the CV system
- general changes in CVS associated with aging
- decreasled compliance of aorta
- lowered CO and max HR
- incresed systolic pressure
- HDL decreases and LDL increases
circulatory routes
-
systemic circulation
-
from left side of heart to rest of body and back to right side
- coronary circ
- cerebral circ
- hepatic portal circ
-
from left side of heart to rest of body and back to right side
-
pulmonary circulation
- from right side of heart to lungs and back to left side
-
foetal circulation
- from foetal heart through umbilical cord and back
oxygenated and deoxygenated blood
- oxygenated blood
- flows through systmeic arteries
- deoxygenated blood
- returns to heart through systemic veins that drain blood into superior or inferior vena cava -> right atrium
aorta and its regions
- Aorta is largest artery of the body
- branches are
- ascending aorta
- arch of aorta
- descending aorta
branches of ascending aorta and arch of aorta
- ascending = right and left coronary arteries
- arch =
- brachiocephalic trunk ->
- right common carotid
- right subclavian
- left common carotid
- left subclavian artery
- brachiocephalic trunk ->
subclavian branches
- vertebral artery
- axillary artery
- brachial artery
- radial and ulnar branches
common carotid branches
- external carotid arteries
- fro external skull structure
- internal carotid arteries
- for eyeballs and brain
descending aorta composed of
-
Thoracic aorta
- having visceral and parietal branches
-
Abdominal aorta
- continuation of thoracic aorta after it passes diaphragm
- visceral branches
- coeliac artery
- mesenteric arteries
- parietal branches
abdominal aorta segments to become
left and right common iliac arteries
- these divide again into left/right external/internal iliac
external iliac artery becomes..
femoral artery -> popliteal artery
Veins can be deep or superficial. All drain blood to
- superior vena cava
- drains head and upper extremities
- inferior vena cava
- drains abdomen, pelvis and lower limbs
- coronary sinus
- drains heart muscle
hepatic portal circulatio
- carries blood between two capillary networks
- Veins of pancreas, spleen, stomach, intestines and gallbladder -> direct blood into hepatic portal vein of liver before -> heart
- enables nutrient utilisation and blood detoxification
