Circulation + Fluid Dynamics

Question 1

Endothelium

Characteristics, Types, Roles

Answer 1

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

Question 2

Continuous Endothelium

Answer 2

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

Question 3

Fenestrated Endothelium

Answer 3

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

Question 4

Discontinuous Endothelium

Answer 4

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

Question 5

Normal v Abnormal Endothelium

Answer 5

normal = antithrombotic + profibronilytic
v
abnormal = prothrombrotic + antifibrinolytic

Question 6

Causes of Endothelial Cell Injury or Activation

Answer 6

oxidative stress/injury
hypoxia
inflammation
infectious agents
tissue injury

Question 7

Stroke Volume

Answer 7

volume of blood pumped per beat by the respective ventricle

Question 8

Cardiac Output

Answer 8

volume of blood pumped by each half of the heart per minute

Question 9

Arteries + Arterioles

Answer 9

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

Question 10

Capillaries

Answer 10

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

Question 11

Postcapillary Venules + Veins

Answer 11

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

Question 12

Blood return to heart assisted by

Answer 12

venous valves
skeletal mm. contractions
venous vasoconstriction
cardiac-suction effect
respiratory pump

Question 13

Lymphatic System

Answer 13

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

Question 14

Microcirculation

Answer 14

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

Question 15

Normal Fluid Distribution

Answer 15

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

Question 16

Fluid Movement at capillary bed influenced by:

Answer 16

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

Question 17

Normal Fluid Distribution + Homeostasis

Answer 17

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

Question 18

Changes in hydrostatic pressure

Imbalance between IC + Interstitial Spaces

Answer 18

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)

Question 19

changes in osmotic pressure

Imbalance between IC + Interstitial Spaces

Answer 19

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)

Question 20

Edema v Effusion

Imbalance Between IV + Intersititial Spaces

Answer 20

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

Question 21

Major Mechanisms of Edema/Effusion Formation

Answer 21

increased microvascular permeability
increased IV hydrostatic pressure
decreased IV osmotic pressure
decreased lymphatic drainage

Question 22

Increased microvascular permeability

Mechanisms for Edema/Effusion

Answer 22

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

Question 23

Increased IV Hydrostatic Pressure

Mechanisms for Edema/Effusion

Answer 23

usually d/t increased blood vol. in microvasculature

Causes:
- less common = hyperemia such as d/t inflammation
- mroe common = congestion

Question 24

Decreased IV Osmotic Pressure

Answer 24

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

Question 25

Decreased Lymphatic Drainage

Answer 25

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

Question 26

Morphologic Characteristics of Edema + Effusions

Answer 26

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

Question 27

Fluid Analysis of Effusion

Answer 27

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