Flashcards
Jan 22 tueday
Cards in this deck (66)
- 1arteriesdistribution pf blood thru out thebody and act as pressure reservoir
- 2arteriolesact as resistance vessels
invlved in the regulation and distribution of blood flow - 3venous systemcapacitance vessels
volume storge - 4Venous system:low resistance
low pressure
large volume
high compliance
“volume reservoir” - 5Arterial system:high resistance
high pressure
low volume
low compliance
“pressure reservoir” - 6Compliance of Arteries and VeinsArteries:
Thicker, stiffer, much lower compliance
Help serve as a pressure reservoir
Veins:
Much thinner, “floppier”, highly compliant (low stiffness)
Help serve as a low pressure, volume reservoir - 7Major Functions of the Arterial SystemArteries/arterioles get the blood to the tissues; they serve as conduits from the heart.
Since all fluids flow down a pressure gradient, the elastic arteries help store the kinetic energy (act as a pressure reservoir) associated with the pressure oscillations (arterial pressure falls during diastole) produced by the heart. This is particularly true of the large (>1 cm diameter), elastic arteries. The greater the amount of elastic tissue in the wall of the artery, the lower the compliance.
It is beneficial to have a smooth steady flow through the capillaries to facilitate even exchange, so the walls of the muscular arteries (medium sized arteries, with diameters between 2-10 mm) also absorb some of the energy and dampen (reduce) the pressure oscillations.
Not all areas of the body are perfused to the same degree at any given time, thus the arterial system can also control the amount of blood flow to a given region/organ by changing the resistance to flow. - 8eleastic arterieskeep pressure high
- 9Mean Arterial Pressurerepresents the force that drives blood from the heart throughout the circulatory system (= perfusion pressure)
- 10The small arteries and arterioles are the main vessels involved incontrolling flow within/to an organ and in the regulation of blood pressure
An increase in resistance to flow through one organ can decrease flow to that organ while increasing flow to other parts of the body - 11Changes in vessel diameter are most important for regulatingblood flow within/to an organ, as well as for regulating arterial pressure.
- 12Arteriolar radius/diameter can be regulated by:The autonomic nervous system (primarily the sympathetic system)
Hormones
Local paracrines and metabolites
**Small changes in radius can cause very large changes in resistance - 13Arterioles maintain tone thruRefers to continuous partially contracted state of vascular smooth muscle, effected by continual sympathetic stimulation
-----Resting tone is primarily due to sympathetic nervous system activity, via alpha-1 adrenergic receptor mediated constriction
Vessels can then either relax or constrict more - 14Vasoconstriction signalsNorepinephrine (a1-receptors)
Serotonin
Vasopressin (AVP/ADH)
Angiotensin II
Endothelin-1 - 15vasodilation signalsEpinephrine (b2-receptors)
Natriuretic peptides
Nitric oxide (NO)
Adenosine
Histamine - 16Resting tone in most vascular smooth muscle is primarily mediated by sympathetic innervation (NE);NE, binding to alpha-1 adrenergic receptors, leads to contraction of vascular smooth muscle and thus vasoconstriction, via a phospholipase C IP3 mediated effect
- 17An increase in cAMP inhibits the activity of myosin light chain kinase (MLCK), inducing relaxation and vasodilation.NE can bind to an alpha-2 adrenergic receptor, activating a Gi subunit and decreasing cAMP production, maintaining vascular smooth muscle contraction - Various other signals can bind to various receptors that activate a Gs subunit, increasing cAMP production, leading to smooth muscle relaxation and vasodilation
- 18During (rhythmic) muscular activity, contraction of a skeletal muscle squeezes the vein, whichincreasing the pressure in the compartment between a pair of upstream and downstream valves. This increased pressure keeps the down stream valve closed while pushing open the upstream valve, aiding venous return (increasing the volume of blood returning to the heart per unit time). This is particularly true for deep veins (as superficial veins are not typically surrounded by skeletal muscle).
- 19both skeletal muscle and rhytmic breathing..
- 20Functions of the Venous SystemReturn blood to the heart
Act as volume reservoir
Maintenance of arterial pressure - 21Anything that increases central venous pressure (CVP) willincrease venous return
- 22CVP is a function of:The volume of blood in the thoracic veins
The stiffness (1/compliance) of these veins - 23vasoconstriction and venous returnVenoconstriction will decrease venous compliance (increase venous tone) and increase venous return
- 24Return blood to the heartC.O. = venous return
Muscular pumps/valves - 25Act as volume reservoirHigh compliance
Large volume, low pressure system - 26Maintenance of arterial pressureMaintains capillary blood flow
Sympathetic innervation (a1) venoconstriction
Decrease venous compliance, helps push blood towards heart---> venous return - 27capollary blood flow slow velocitySlow velocity of flow through the capillaries allows efficient exchanges of gases and nutrients
Due to very large total cross-sectional surface area of capillary networks… - 28capillary Velocity is inversely proportional to total cross-sectional area.As the circulatory system branches, individual vessels have smaller diameters, but there are more of them, therefore, the total cross-sectional area increases from large arteries to capillaries, and then decreases, as vessels converge and decrease in relative number as blood flows back through the venous system.
- 29Unlike other vessels, capillary walls only consist of aa single endothelial layer and its corresponding basement membrane
---Because capillaries are the site of diffusive exchange, the capillary wall is very thin (to maximize diffusion) and is only composed of its endothelial layer and the basement membrane that endothelium sits on
There is no smooth muscle or any other connective tissue in the walls of a capillar
Facilitates exchange of nutrients, metabolic gases and wastes between tissues and blood - 30Continuous capillaries:most common, abundant in skin, muscle and neural tissue
- complete, but permeable basement membrane
- intercellular clefts (“leaky” tight junctions) allow for the flux of water, ions, and small organic molecules (i.e., glucose); other, larger solutes may move across the capillary endothelium by transcellular vesicular trafficking - 31Fenestrated capillaries:- the capillary endothelium has a large number of pores (= fenestrations) (but still has a complete basement membrane), thus increasing its permeability, allowing faster rates of water (and solute) flux
- found in the kidneys, intestines and some endocrine glands ---> organs that require high rates of transepithelial absorption - 32Sinusoidal capillaries:- highly modified, very “leaky” with larger diameters
- discontinuous endothelium and an incomplete (or missing) basement membrane
- found where blood cells and/or proteins need to cross the endothelium (liver, bone marrow, spleen) - 33Flux Across Capillary WallsLipophilic molecules can diffuse across endothelial membranes
---H2O, ions, simple sugars move through intracellular clefts
---Larger (but still small) molecules move through fenestrations
Larger proteins (i.e., antibodies) move across in vesicles (transcytosis)
Water and solutes may also be filtered across the capillary - 34The three ways in which water and solutes may cross a capillary include:Diffusion ---> lipid soluble molecules and gases
Transcytosis: for large, lipid-insoluble molecules (including antibodies, protein hormones like insulin)
Filtration (or bulk flow): pressure driven (see next slide), faster than diffusion - 35The permeability of the capillary is part of the filtration coefficient, k.The greater the capillary permeability (ie, fenestrated vs continuous), the larger the value for k and the greater the rate of filtration.
- 36pressure that pushes fliud out FILTRATION--capillary hydrostatic pressure changes over length of systemic capillary
-interstitial protein oncotic pressure - 37pressure that pushes fliud in RESOPTIPONinterstitial hydrostatic pressure
capillary protein oncotic pressure - 38Net filtration pressure (NFP)the difference between the pressures that force fluid out of the capillary (filtration) and the pressures that would pull fluid into the capillary (absorption).
A positive NFP means there will be an overall filtration of fluid out of the capillary;
a negative NFP means net fluid absorption into the capillary - 39An NFP > 0 (positive) means the net filtration pressures (mostly Pcap) are greater than the net reabsorptive pressures (cap + Pint) An NFP < 0 (negative) means the net filtration pressures (mostly Pcap) are less than the net reabsorptive pressures (cap + Pint).
- 40Relationship Between Capillaries and Lymph VesselsLymphatic system takes up excess fluid filtered from the capillary beds and returns it to the venous system near the subclavian arteries (by the collar bones)
- 41Net filtration from the arterial end of a capillary typically slightly exceeds (by about 1% of the plasma volume) the reabsorption of fluid on the venous end, leading to an addition of fluid into the interstitial spaceThis fluid must be returned to the circulatory system some how and that is through the lymphatic system.
- 42Edema caused by---Increased capillary hydrostatic pressure
Usually an indication of elevated venous pressure, often due to heart failure
----Decreases capillary protein oncotic pressure (decreased plasma protein concentration)
Plasma protein concentrations can decrease due to malnutrition, burns and liver or kidney disease
----Increased capillary permeability (K) due to proinflammatory signals or capillary damage
----Increased interstitial protein oncotic pressure
Due to leaky capillaries - 43Lymphatic SystemCollects fluid lost into interstitial spaces; returns to venous system
Interstitial fluid is taken up into lymphatic capillaries, where it is called lymph
Movement through lymphatic ducts is passive (i.e., no heart pump); unidirectional via valves in vessels and localized compression by muscles and viscera
Lymph is filtered along the way at lymph nodes
Transports immune system agents (e.g. lymphocytes, leukocytes) via lymph - 44Paratracheal Nodes lead toBronchomediastinal
Trunk - 45Two lymphatic drainage systems for lungsPeribronchial network
Subpleural network - 46Peribronchial networkfollows bronchial tree inside lungs, drains lymph from bronchi and most of lungs.
- 47Subpleural networkcollects lymph from peripheral lungs and visceral pleura, drains to tracheobronchial nodes, then to bronchomediastinal trunks.
- 48Finally, lymph from chest wall, including parietal pleura, drains primarily tointercostal and parasternal nodes.
- 49Lymph from the anterior thorax flowsLaterally to axillary lymph nodes, and then through a series of axillary and subclavian trunks that parallel the axillary and subclavian vessels.
Medially to parasternal lymph nodes, and then through internal thoracic ducts that parallel the internal thoracic vessels. These in turn may drain into any of the large trunks in the brachiocephalic region: bronchomediastinal, subclavian, or thoracic and right lymphatic. - 50the posterior thoracic wall drains toIntercostal lymph nodes (previous slide; also called paravertebral nodes)
- 51The heart and brain are unique. The heart will increase absolute flow, butmaintain its relative proportion of CO; the brain will hold its absolute flow rate approximately constant, which decreases its relative flow rate.
- 52Local (Intrinsic) Control of Blood FlowThis is the primary mechanism used change arteriolar resistance to blood flow within an organ/tissue to match flow with the metabolic needs of the tissue
2 mechanisms - 53Two primary mechanisms:(Myogenic) autoregulation in response to changes in local blood pressure
Changes in the concentration of local metabolites = metabolic regulation
-Active hyperemia
-Reactive hyperemia - 54Myogenic Autoregulation of Blood Flow(smooth) muscle generated self regulation in response to the local environment, usually in response to a change in arterial pressure
- 55Autoregulationmaintenance of an approximately constant blood flow in the face of a change in pressure
- 56how autoregulation worksPhysical response (a): an increase in arterial pressure causes an increase in blood flow
Physiological response/compensation (b): vasoconstriction to reduce flow back towards its initial resting rate, even while pressure is still elevated - 57Active hyperemiaThe increase in blood flow that accompanies an increased metabolic rate in a local tissue/organ
Common with increased regional muscle contraction - 58Reactive hyperemiaA transient increase in tissue blood flow following a period of low perfusion/occlusion (ischemia); local vasodilators build up during the occlusion induced hypoxia, the hyperemia occurs after perfusion is restored
can occur following removal of a tourniquet, unclamping an artery after surgery, medically reopening a blocked vessel - 59Coronary CirculationThe heart extracts > 70% of the oxygen in the blood in the coronary arteries
Autoregulation helps maintain normal coronary blood flow even if there are changes in aortic pressure
Control of blood flow through the coronary vessels is primarily via local, metabolic control
---------Hypoxia, adenosine, and NO are key signals which induce dilation of the coronary vessels, decreasing resistance to flow
Adenosine induces vasodilation when it binds to purinergic receptors - 60Cerebral Blood FlowInterruption of blood flow to the brain for more than a few seconds leads to unconsciousness
The rate of blood flow to the brain doesn’t change much
Circulating vasoactive substances have little effect on cerebral blood flow*
Autonomic innervation present, but has little effect on blood flow under most conditions - 61------Blood flow to the brain must be preserved in all situations; usually occurs by rapid systemic adjustments to regulate mean arterial pressure (MAP).
- 62The rate of blood flow to the brain doesn’t change muchStrong autoregulation present above a MAP of 60 mmHg
Little overall organ level variation in O2 consumption
But intracerebral blood flow matches regional neuronal activity - 63Cerebral blood flow is sensitive toPCO2* and an increase in PCO2 leads to vasodilation
An increase in PCO2 leads to a decrease in cerebral resistance and an increase in cerebral blood flow; a decrease in PCO2 leads to a decrease in cerebral blood flow
The actual change in vascular tone is due to CO2 induced changes in [H+]** - 64Local metabolic regulation is the primary mechanism by which blood flow within the brain is regulatedLikely mediators include: CO2/H+, K+, hypoxia, adenosine
- 65Hypoxia will induce cerebral vasodilationBut, unlike decreased CO2, hyperoxia will have little effect on cerebral blood flow
- 66Cutaneous CirculationBlood flow to the skin is regulated primarily to regulate body temperature
Cutaneous blood flow is regulated by the sympathetic NS
A decrease in body temperature decreases blood flow to the skin
An increase in body temperature increases blood flow to the skin
An increase in core body temperature has more complex influences on cutaneous blood flow
Active vasodilation is linked to the onset of sweating
Local vasoactive substances can impact cutaneous flow in response to damage
Information
- Description
- Flashcards on Jan 22 tueday, created by Shylla T on 22/01/2020.
- Created by
- Shylla T
- Views
- 0
- Rating