Ch. 20 - Vascular/Circulation Flashcards
Diffusion
substances leave or enter blood based on their concentration gradient. Oxygen, hormones, and nutrients move from blood to interstitial fluid and Co2 and wastes diffuse from tissue to blood.
Small solute diffusion
can diffuse through endothelial cells or intercellular clefts.
Larger solute diffusion
pass through fenestrations or gaps in sinusoids
Vesicular transport
endothelial cells use pinocytosis and exocytosis to transport certain hormones and fatty acids.
Bulk flow
fluids flow down pressure gradient. movement depends on net pressure of opposing forces of hydrostatic pressure vs. colloid pressure
Filtration
fluid moves out of blood; fluid and small solutes flow easily through capillary’s openings. Occurs on arterial end of capillary
Reabsorption
fluid moves back into blood. Occurs on venous end.
Hydrostatic pressure
force exerted by a fluid
Blood hydrostatic pressure (HPb)
force exerted per unit area by blood on vessel wall. Promotes filtration from capillary.
Interstitial fluid hydrostatic pressure (HPif)
force of interstitial fluid on outside of blood vessel. Close to 0 in most tissues.
Colloid Osmotic pressure
the pull on water due to the presence of proteins.
Blood colloid osmotic pressure (COPb)
draws fluid into blood due to blood proteins like albumin. promotes reabsorption (opposes dominant hydrostatic pressure). clinically called oncotic pressure.
Interstitial fluid colloid osmotic pressure (COPif)
draws fluid into interstitial fluid. Since few proteins in interstitial fluid, this is relatively low ( 0-5 mm Hg)
Net Filtration Pressure
difference between net hydrostat pressure and net colloid osmotic pressure. It changes along the length of a capillary (higher at arterial end because NFP favors filtration over reabsorption)
NFP= (HPb - HPif) - (COPb -COPif)
Net hydrostatic pressure
difference b/w blood and interstitial fluid hydrostatic pressures
Net colloid osmotic pressure
difference b/w blood and interstitial fluid osmotic pressure.
Lymphatic system role
picks up excess fluid (15%) not reabsorbed at venous capillary end, filters it and returns it to venous circulation.
Local blood flow
not all capillaries are filled simultaneously so local blood flow varies (measured in mL per min) Local flow is dependent on degree of tissue vascularity, myogenic response, local regulatory factors altering blood flow, and total blood flow.
Degree of vascularization
extent of blood vessels in a tissue. Metabolically active tissues (skeletal muscle, heart, brain) have high vascularization while tendons, epithelia, cornea, ect. have low or none.
angiogenesis
formation of new vessels; occurs over weeks to months to increase perfusion. Can increase in adipose tissue with weight gain, exercise, and in response to gradual blockage.
Regression
return to previous state of blood vessels. Examples: skeletal muscle when individual becomes sedentary and in adipose when fat is lost.
Tumor angiogenesis
since cancer cells require oxygen and nutrients, they trigger growth of new cells by secreting molecules that cause host cells to release growth factors.
Myogenic response
smooth muscle in blood vessel wall keeps local flow relatively constant. So if bp rises and more blood enters arteriole, it will stretch and the smooth muscle will respond by contracting to reduce flow. If too little flow, it will relax providing more flow.
Vasoactive chemicals
alter blood flow
vasodilators
a vasoactive chemical that dilates arterioles and relaxes precapillary sphincters to increase flow into capillary beds
vasoconstrictors
constrict arterioles and cause contraction of precapillary sphincters to decrease flow into capillary beds.
autoregulation
process by which tissue controls local blood flow. When tissue activity increases, varied stimuli (low o2 and nutrients and high carbon dioxide, lactic acid, H and K) signal inadequate perfusion and act as vasodilator. This is negative feedback b/c as perfusion increases, vessels constrict.
Reactive Hyperemia
increase in blood flow after it is temporarily disrupted to replenish oxygen, nutrients, and eliminate wastes. (ex: enter warm room after being in cold)
Inflammation
damaged tissue, leukocytes, and platelets release vasoactive chemicals. Histamine and bradykinin cause arterioles to dilate and are released in response to trauma, allergy, infection, or exercise. May also stimulate release of nitric oxide, another vasodilator. Tissue damage can also lead to release of vasoconstrictors (prostaglandins and thromboxanes) help prevent blood loss through damaged vessels.
prostaglandins and thromboxanes
help prevent blood loss though damaged vessel
histamine and bradykinin
released in response to trauma, allergy, infection, exercise to dilate arterioles.
total blood flow
amount of blood transported through vasculature per unit of time. equal to cardiac output. (about 5.25 L/min). If it increases, more blood is available to tissues, regulation of total flow depends on both heart and vessels. Therefore if total blood flow increases, so will local flow.
mean arterial pressure (MAP)
average arterial blood pressure across entire cardiac cycle. Since diastole lasts longer than systole, mean is weighted to be closer to diastolic pressure. MAP of lower than 60 may indicate insufficient blood flow.
MAP= diastolic + 1/3 pulse pressure
if bp is 120/80 then…
Map= 80 + 40/3 = 93
Capillary blood pressure
pressure no longer fluctuates between systolic and diastolic; pressure is smooth. Needs to be high enough to exchange substances but low enough to prevent damage. Arterial end = 40mm Hg
Venous end = 20 mm Hg
accounts for filtration and reabsorption at respective ends.
Venous blood pressure
venous return of blood to the heard depends on pressure gradient, skeletal muscle pump, and respiratory pump. Venous pressure is low and not pulsatile; pressure gradient is small. (BP is 20 mm Hg in venules and almost 0 in vena cava). skeletal muscle pumps assist venous return.
Skeletal muscle pumps
assiste venous return from limbs. blood is pushed by muscle contraction and valves prevent backflow. Blood moves more quickly during exercise so it can pool in leg veins with prolonged inactivity.
Respiratory pump
assists in venous return in the thorax. in inspiration: diaphragm contracts so abdominal pressure increases and thoracic pressure decreases, moving blood towards thoracic cavity.
in expiration: diaphragm relaxes so blood in thoracic cavity is driven towards heart and blood in lower limbs is allowed into abdomen.
Resistance
the friction blood encounters due to contact between blood wall and vessel wall. resistance opposes blood flow. Affected by viscosity, vessel length, and lumen size.
Peripheral resistance
resistance of blood in blood vessels as opposed to heart.
Viscosity
resistance of fluid to its flow. greater viscosity raises resistance and is dependent on percentage of particles in fluid. decreases with anemia (low blood cell count) and increases with blood doping or dehydration (greater percentage of cells due to decreased fluid to carry them.
Vessel length
longer vessels create more resistance b/c friction occurs along length of vessel. Weight gain (angiogenesis) or loss (regression) changes vessel length.
Vessel radius
smaller radius creates more resistance. Flow is proportional to radius to the 4th power. (radius increase by 1mm to 2mm increases flow by 16 times)
laminar flow
different flow rate within vessel; faster in center and slower near vessel wall.
Autonomic reflexes
regulate bp short-term. involve nuclei in medulla oblongata. Quickly adjust cardiac output, resistance or both to meet momentary pressure needs (standing)
Cardiovascular center of medulla: autonomic nuclei
Cardiac center: influences bp by influencing CO
Vasomotor center: influences bp by influencing vessel diameter.
Cardiac center nuclei
Cardioaccerleratory center: orgin of sympathetic pathways to SA node. Increases heart rate and force of contraction to increase CO and bp.
Cardioinhibitory center: orgin of parasympathetic pathways to SA and AV nodes. Activity decreases hr and slows conduction of electrical signals to decrease CO and bp.
vasomotor center
orgin of sympathetic pathways to smooth muscle of blood vessels. blood vessels then release norepinephrine and adrenal medulla to release EPI and Ne.
Blood vessel muscle receptors
most blood vessels smooth muscle cells have a1 receptors that bond to NE and EPI to cause vessel constriction. Some blood vessels have b2 receptors that bind to NE and EPI for vasodilation.
Sympathetic activation and adrenal secretion leads to
increased peripheral resistance: more blood vessels are stimulated to constrict than dilate so bp increases
larger circulating blood volume: vasoconstriction of veins shifts blood from venous reservoirs; bp increases
redistribution of blood flow: more blood to skeletal muscle and heart.
Baroreceptors
nerve endings that respond to stretch of vessel wall. Firing rate changes when bp changes. Located in tunica externa of aortic arch and carotid sinuses.
Aortic arch baroreceptors
transmit signals to cardiovascular center through vagus nerve and is important in regulating systemic bp.
Carotid sinus baroreceptors
transmit nerve signals to cardiovascular center via glossopharyngeal nerve. Monitor bp in head, and neck. More sensitive to bp changes than aortic arch.
Baroreceptor reflexes
Initiated by change in BP. Best for allowing quick changes in BP… not long term.
If BP decreases, vessel stretch declines and baroreceptor firing rate decreases. This activated cardioacceleratory center(increases CO) and vasomotor SNS pathways to increase vasoconstriction.
If BP increases, baroreceptor firing rate increases and causes cardioacceleratory center to send less signals along sympathetic pathways. Cardioinhibitory center activates PNS to SA and AV nodes. Vasomotor center cents less signals along SNS
Systemic gradient
Difference between pressure in arteries near the heart and in vena cava. Driving force to move blood through vasculature. Increasing gradient (by increasing cardiac output) increases total blood flow.
Mean arterial blood pressure - vena cava bp
Chemoreceptor reflexes
Stimulation of chemo receptors brings about negative feedback to return blood chemistry to normal. Respond to high carbon dioxide, low pH, and very low oxygen. Causes increase in BP and shift blood to the lungs, expire CO2, and raise pH.
Co2 + h2o —> h2co3 (unstable acid) —> hco3 + h
Location of main peripheral chemoreceptors
Aortic bodies: in aortic arch; send signals via vagus nerve.
Carotid bodies: are at bifurcation of common carotid artery; send signals via glossopharyngeal nerve
Hypothalamus
Can increase cardiac output and resistance do to increase body temperature or fight or flight response
Limbic system
Can alter blood pressure in response to emotions or memories. (Anxiety, hunger, anger) can increase BP and resistance
Renin- angiotensin system
Liver makes and secretes inactive angiotensinogen. Kidneys release renin In response to low BP or SNS activity. Renin converts Angiotensinogen to angiotensin I. Angiotensin converting enzyme (ACE) converts angiotensin I to II
Angiotensin II
Raises BP by acting as a powerful vasoconstrictor. Stimulates thirst center (to increase blood volume). Axon kidneys to decrease your information. Stimulates release of aldosterone and anti-diuretic hormone to decrease urine loss
Aldosterone
Helps maintain blood volume and pressure. Released from adrenal cortex. Increases absorption of sodium ions in water in the kidney therefore decreasing urine output
Antidiuretic hormone
Helps maintain or elevate BP. Releases triggered by nerve cells from hypothalamus. Increases water reabsorption and kidneys,Stimulates thirst center, and in large amounts causes vasoconstriction
Atrial natriuretic peptide ANP
Decreases BP. Is released from atria of heart when walls are stretched my high blood volume; stimulates vasodilation and increases urine output
Relationship between mechanisms for blood pressure and blood pressure
Cardiac output, resistance, and blood volume; An increase in at least one of these Will increase blood pressure.
Measuring blood pressure
BP is measured using a sphygmomanometer. A stethoscope is placed on the brachial artery as it collapses and refills.
Systolic pressure (pressure in arteries when heart contracts) Is heard one VP is sufficiently high enough to overcome cuff pressure
Diastolic pressure (pressure in arteries when heart relaxes) Is one sounds are no longer heard as flow smooths out
Hypertension
Chronically elevated BP with a systolic pressure > 140 or diastolic > 90. Many people have no symptoms until level is severe. May damage blood vessel walls, making atherosclerosis more likely and second arteriole walls causing arteriosclerosis. Major cause of heart failure and can cause strokes and kidney failure
Hypotension
Chronically low BP with symptoms of fatigue, dizziness, and fainting. Systolic< 90 or diastolic < 60
Orthostatic hypotension
Drop in BP after sudden standing. Causes dizziness, lightheadedness, and fainting and occurs because blood pressure regulation is not occurring quickly enough
