Microcirculation & Lymphatics

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3 types of capillaries

Back 1

Continous capillaries
Fenestrated capillaries
Discontinous Capillaries

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Organ location continuous capillaries

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(skeletal muscle, cardiac muscle, skin, lung, fat, CT, BBB)

Front 3

Organ location fenestrated capillaries

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((sinusoids)glomerulus, exocrine gland, intestinal mucosa, ciliary body, choroid plexus, synovial lining joints & endocrine glands)

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Organ location discontinous capillaries

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(“sinusoids” in liver, bone marrow, spleen)

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Description Continous capillaries

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Circumference = 1-3 endothelial cells(very active cells, NO production) + basement membrane. Endothelial cells connected w/ tight jxs. Limiting exchange, BUT lipid insoluble transfers this way.

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Description fenestrated capillaries

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Have endothelial cells like continous subtype BUT has fenestra (perforated windows) w/ thin (5nm) diaphragms. Fenestra ↑ exchange 10X

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Description discontinous capillaries

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inter-endothelial gaps (100nm wide) (compare to fenestra 5nm). Additionally, basement membrane discontinous. Allows large particles to move into blood/tissue.

Front 8

Transcapillary Fluid Filtration & Reabsorption Formula

Back 8

J_f= L_p*S [(P_C-P_T )- σ (π_C-π_T )]
Jf = transcapillary fluid flux Lp = HYDRAULIC CONDUCTIVITY (FLUID PERMEABILITY)
S = capillary surface area PC = capillary hydrostatic pressure
PT = tissue hydrostatic pressure π_c = capillary colloid pressure
π_t = tissue colloid pressure σ = plasma protein reflection coef.(accounts permeabilty specific protein)

Front 9

General trend transcapillary flux

Back 9

So fluid flux is dependent on Hydrostatic pressure gradient and the oncotic pressure gradient. Lp desscribes how the fluid viscosity would affect the flow.

Front 10

Define edema

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Edema – accumulation of fluid in interstitial space. Results when net filtration > lymph drainage rate.

Front 11

3 examples of how changes in starling forces causes edema

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1.Arteriolar vasodilation ↑Pc increasse in capillary hydrostatic pressure = ↑flux
2.Liver failure ↓π_C decrease protein production causing decrease oncontic pressure
3. Burns/Inflammation ↑LP Δ in capillary integrity = ↑ conductivty & ↑ net flux

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4 functions of lymphatic system

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1. Return of Excess filtered fluid – 7200L pumped per day. Net flow from vessel results in 3L/day . Lymphatic system returns this to venous circulation.
2. Defense against disease – lymph travels through lymph nodes. Lymph nodes have resident phagocytic cells that kill bacteria. Additionally, mature B & T lymphocytes reside here and mediate anti-body & cell meddiated immune responses.
3. Transport of absorbed fat – Packaged particlesto large cross GI cappilaries. BUT they can enter GI lymph for transport.
4. Return of filtered protein – If abnormal amts. protein pass through capillary then fluid will follow (oncotic pressure). This would be dangerous and thus excess protein is returned to venous system.

Front 13

define lymphadema

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Compromised normal lymphatic function. Causing ↑ interstitial fluid accumulation = swelling. Occasionally the mmune system will become involved in theis pathology.

Front 14

4 factors augment venous return

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1. Sympathetically-induced venous contraction – scattered smooth muscle in venous system is highly innervated by sympathetic system. Constrict = ↑pressure = ↑gradient (→ venules constriction> vein)
2. Skeletal muscle pump – squeezing vessels + unidirectional valves = ↑ venous return. i.e. Calf Muscle Pump & sitting airplane too long.
3. Respiratory activity – Inspiration = ↓chest cavity pressure (below atmosph.) = distension vena cava = ↑ venous return w/ inspiration
4. Cardiac Suction Effect – W/ each atria relaxation pressure ↓ causing suction = increase gradient & venous return.

Front 15

Virchow's Triad

Back 15

Virchows triad are risk factors for DVT. Frequently DVT develop behind valves. (a FOUNDATIONS TOPIC). Predispoistion to DVT occurs when 2/3 risk factors are present.
1. Blood stasis
2. Blood vessel injury
3. Hypercoaguable state

Front 16

definition central venous pressure

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Central Venous Pressure – BP venous system near RA (measured if catheter = thoracic vena cava near RA)

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Factors that shift Venous return curve (verbal)

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1. Venous blood volume (↑ vol = ↑venous return) & (↓ vol = ↓ venous return)
2. Venous tone (↑vasoconstriction = ↑venous return)

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Venous Return Curve Shift

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