Circulation + Fluid Dynamics Flashcards
Endothelium
Characteristics, Types, Roles
single cell layer that lines all components of circulatory system -> continuous system
acts as an important interface between blood + tissue
critical factor in fluid distribution, inflammation, immunity, angiogenesis, hemostasis
types:
- continuous
- fenestrated
- discontinous (sinusoidal)
range in level of control exhibited over movement of substances between blood + supplied tissue
Continuous Endothelium
strong barrier that tightly controls molecule passage
only H2O + O2 + CO2 + ions can cross membrane or via tight junctional complexes
found in = brain (BBB), muscle, lung, bone
Fenestrated Endothelium
allows controlled transfer of certain mol. + proteins
have pores + junctional complexes
provides filtration
seen in = renal glomeruli, intestinal villi, endocrine glands, choroid plexuses, ciliary processes of eye
Discontinuous Endothelium
free transfer of mol, cells, water, etc.
relatively open juncitonal complexes between endothelial cells
also associated with discontinuous basement membrane
seen in = liver sinusoids, spleen sinusoids, bone marrow, lymph nodes
Normal v Abnormal Endothelium
normal = antithrombotic + profibronilytic
v
abnormal = prothrombrotic + antifibrinolytic
Causes of Endothelial Cell Injury or Activation
oxidative stress/injury
hypoxia
inflammation
infectious agents
tissue injury
Stroke Volume
volume of blood pumped per beat by the respective ventricle
Cardiac Output
volume of blood pumped by each half of the heart per minute
Arteries + Arterioles
Arteries:
- relatively large lumen diameter
- thick + strong walls
- smooth muscle fibers for strenght
- elastic fibers for elasticity
Arterioles:
- smaller than arteries
- walls primarily of smooth muscle
- major pressure/resistance vessels of circ. system
Capillaries
site of nutrient + waste exchange between blood + tissue
major component of microcirculation
capillaries have minimal structure -> single layer of endothelial cells + NO smooth muscle
narrow lumen, low pressure -> RBCs move in single file line
slow pace + low RBC density -> aid with movement of nutrients + waste products
Postcapillary Venules + Veins
postcapillary venules provide a low resistance path for blood
- thin layers of muslce present as move away from capillary bed
veins are larger + consists of collagen w/ small amounts of elastin + smooth muscle
- low resistance path
- return blood to heart
Blood return to heart assisted by
venous valves
skeletal mm. contractions
venous vasoconstriction
cardiac-suction effect
respiratory pump
Lymphatic System
structure similar to vascular capillaries
low pressure + distensible
fluid + molecules should move into lymphatic vessels + not out
large interendothelial gaps allow movement of larger particles + substances, relative to capillaries
converge into progressively larger vessels that drain into lymph nodes
Microcirculation
environment formed by intersection of:
- blood capillaries
- lymphatic capillaries
- interstitium
- tissue cells
interstitium consists of interstitial fluid + extracellular matrix (ECM)
ECM is the tissue portion of interstitium
- structural, adhesive, absorptive components
Normal Fluid Distribution
water makes up ~60% of BW, distributed between IC + EC spaces
EC fluid subdivided between plasma + intersitium
distribution of nutrients + waste controlled by:
- pressure + conc. gradients
- physical barriers
Fluid Movement at capillary bed influenced by:
osmotic pressure
-significantly different between plasma + intersititum -> primarily d/t albumin
hydrostatic pressure
- effects of high v low pressure
rate of blood flow
- effects of high v low flow rate
Normal Fluid Distribution + Homeostasis
following capillary drainage, any fluid left in intersitium is drained by lymphatics
net effects of pressure + forces -> slightly favor fluid return to vasculature
constant fluid flow needed to continually supply nutrients to + remove waste products from cells
intersititial fluid as a buffer for plasma volume changes
Changes in hydrostatic pressure
Imbalance between IC + Interstitial Spaces
explanded plasma vol. (hypervolemia) -> increased IF
- if prolonged, fluid moves into cells along somotic + hydrostatic gradients (cell swelling)
reduced plasma vol. (hypovolemia) -> reduced IF
- if prolonged, fluid moves out of cells alomg osmotic + hydrostatic gradients (cell shrinkage)
changes in osmotic pressure
Imbalance between IC + Interstitial Spaces
increased OP -> increased intersitial OP
- if prolonged, sodium + fluid move into cells along osmotic gradient (cell swelling)
- ex) water deprivation, sodium toxicity w/ restrict water
reduced OP -> reduced interstitial osmotic gradient
- if prolonged, sodium + fluid moves out of cells along osmotic gradient (cell shrinkage)
Edema v Effusion
Imbalance Between IV + Intersititial Spaces
Edema
- abnormal accumulation of fluid in interstitium from plasma
- results inn tissue swelling within intersitial space
Effusion
- abnormal accumulation of fluid in a body cavity d/t imbalances between interstitial + intravascular compartments
Major Mechanisms of Edema/Effusion Formation
increased microvascular permeability
increased IV hydrostatic pressure
decreased IV osmotic pressure
decreased lymphatic drainage
Increased microvascular permeability
Mechanisms for Edema/Effusion
commonly a reaction to inflammatory/immune stimuli
sequence of events:
- stimulus
- vasodilation + widening of interendothelial junctions
- fluid movement out of vascular space into interstitium +/or body cavity
early on -> low protein conc. + low cellularity of fluid (transudate)
progression -> increasing protein content + influx of inflammatory cells (eventual exudate)
intention is to dilute an inflammatory agent +/- deliver needed cytokines, chemokines, cells, etc.
creates local tissue swelling or fluid accumulation in a body cavity
Increased IV Hydrostatic Pressure
Mechanisms for Edema/Effusion
usually d/t increased blood vol. in microvasculature
Causes:
- less common = hyperemia such as d/t inflammation
- mroe common = congestion
Decreased IV Osmotic Pressure
most commonly d/t severe decreases in plasma albumin conc.
Sequence of events:
- reduced albumin reduces colloidal OP
- increased fluid movement out of microvasculature into interstitium with simultaneous decreased fluid drainage from interstitium to microvasculature
- tissue edema/cavitary effusion formation
Causes of severe hypoalbuminemia:
- protein-losing nephropathy
- protein-losing enteropathy
- decreased production by liver d/t severe disease
- plasma exudation from severe, diffuse skin disease/burns
Decreased Lymphatic Drainage
compression/obstruction of lymphatic outflow -> reduces drainage of normal excess interstitial fluid
this mechanism usually limited to specific tissue area or single body cavity
causes:
- external mass/swelling (neoplastic v inflammatory)
- constriction d/t fibrosis/ligation
- internal occlusion d/t clot/barrier
Morphologic Characteristics of Edema + Effusions
edema may form in specific tissue or generalized throughout body
- swollen, doughy or fluctuant tissue
- may be cooler than adjacent unaffected tissue
- expansile v confined space effects
single body cavity, bicavitary or tricavitary:
- fluid wave
- expansile v confined space effects
Fluid Analysis of Effusion
diagnostic classification of effusion based on protein conc., nucleated cellularity, microscopic features
may help with differential diagnoses for cause of effusion
General categories:
- transudate
- exudate
- modified transudate
specific effusion types = septic, feline infectious peritonitis, hemorrhagic effusion, chylous effusion
