Capillary Exchange

Physiology 534 with Stephenson at Michigan State University

About this deck

By: Lauren Hasler
Textbook:

Histology: A Text and Atlas: With Correlated Cell and Molecular Biology (Histology (Ross))

Langman's Medical Embryology, Eleventh Edition: North American Edition

Medical Physiology: Principles for Clinical Medicine (MEDICAL PHYSIOLOGY (RHOADES))
Created: 2010-12-11
Size: 29 flashcards
Views: 8

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what does convection do?

= substances are delivered to and taken away from tissues by blood flow

what does diffusion do?

= major mechanism for exchange of substances b/w blood and tissue occurs, once blood is in capillaries

-only effective over short distances: cells bust be w/in 100 microns of a capillary and active cells = w/in 20 microns

What are the different types of capillaries?

- classified by their walls:

1) continuous capillaries: the smallest opening in walls

-in heart, skeletal muscle, skin, and special subtype in most regions of the brain

2) Fenestrated capillaries: larger openings in walls, basal lamina is continuous

- in endocrine glands and intestine, w/ special subtype in kidneys

3) Discontinuous capillaries (aka sinusoidal): large in diameter, largest openings between and though EC's, discontinuous basal lamina, irregular shape

- in liver, spleen, and bone marrow

microanatomy of continuos capillaries

- promotes rapid exchange of gases, metabolites, and chemical messenger b/w blood and tissue

- wall composed of endothelium, basal lamina, and pericytes: pericytes are multipotential progenitors → become fibroblasts, EC's, or vascular smooth muscle

- TJ's and pinocytotic vessels: clefts/pore where TJ's b/w EC's are interrupted

Small water soluble molecule and fat soluble substances move through continuos capillaries?

1) H2O soluble: water filled clefts or pores b/w adjacent EC's = intercellular cleft where TJ' b/w EC's are interrupted

2) fat soluble: through plasma membranes of EC's

how do continuos capillaries serve as the blood brain barrier?

= no water filled clefts b/w EC's → TJ's are not interrupted

- fat soluble substances still diffuse though plasma membranes

- water soluble substance cross by carrier mediated transport

How does macromolecules transport in continuous capillaries?

two pathways:

1) large clefts (rare)

2) Pinocytosis: in both directions but net movement = plasma → ISF

transport in fenestrated capillaries

- have larger opening in EC's filled only by a thin diaphragm: water and solutes (including macromolecules) diffuse through this

why are capillaries so suited for diffusion?

1. lg. total surface area

2. thin wall

3. short distances for diffusion

what does the rate of diffusion depend on?

1. Concentration difference b/w capillary blood and tissue
a. capillary blood flow: ↑ flow = ↑ transfer
b. Tissue metabolism: ↑ CO2 released by mt. = ↑ CO2 dumped into capillary
2. Permeability and surface area of capillary walls

What results in pressure differences across the capillary wall?

1. Ultrafiltration of plasma without proteins across continuous capillaries

-pressure gradient dictates wither filtration (out) or reabsorption (in) occurs

What does the pressure gradient depend on?

1. capillary hydrostatic pressure

2. ISF hydrostatic pressure

3. plasma colloid osmotic pressure = pressure from solutes in the blood vessels that draw fluid in

4. ISF colloid osmotic pressure = pressure from solutes in ISF that draw fluid out of blood

what influences capillary hydrostatic pressure?

= upstream and downstream pressures and resistance's:

1)Upstream:

a) arteriolar dilation = ↑ Pc

b) arteriolar constriction = ↓Pc because of the increased pressure drop across the constricted arterioles even though Pa may rise

c) ↑ arterial pressure w/o arteriolar constriction = ↑Pc

2) Downstream:

a) ↑ venous pressure is transmitted back to the capillaries = ↑Pc

What influences interstitial hydrostatic pressure?

= ISF volume and tissue compliance

1) ISF volume is increased by:

a) ↑ capillary filtration

b) ↓ capillary reabsorption

c) ↓ lymph flow

What determines capillary colloid pressure?

= plasma protein concentration = mass/volume

1) ↓ mass = ↓ protein synthesis

2) ↓/↑ volume = dehydration/hydration and internal shift in ECF b/w plasma and ISF

what determines ISF colloid osmotic pressure?

= ISF protein concentration: mass/volume

a) mass altered by protein leaving in lymph and coming from plasma

b) volume altered with net capillary filtration and lymph flow

What is the effect of lymph flow?

- protein and plasma steadily leaks form plasma to ISF → lymphatics return ISF w/ protein to circulation

- in absence of lymph ultrafiltrate atics: COPi = COPp

- lymph flow ↑ by ↑Pi

what is the accumulation of excess ISF?

= edema

what are the safety factors against edema?

1. ↑ ISF hydrostatic pressure (Pi)

2. ↓ ISP COP (COPi)

3. ↑ lymph flow

how do safety factors limit edema from ↑ venous pressure?

↑ Pv → ↑filtration → ↑ISF volume (causes ↓ COPi) → ↑Pi (limits ↑ filtration) → ↑ lymph flow →:

1) limits ↑ISF volume

2) ↓ COPi which limits ↑filtration

What are some examples of the ISF control system for edema going wring?

1. Kwashiorkor: malnutrition with inadequate protein intake

2. Elephantiasis: destruction if inguinal lymph nodes by microfilaria

3. acute edema cause by arteriolar dilation and increased capillary permeability to plasma proteins

What is the mechanism for Kwashiorkor?

= ↓ plasma protein → ↓COPp → ↑ filtration → ↑ ISF volume = edema

- all 3 safety factors of ↑Pi, ↑ lymph flow, and ↓ COPi will limit the edema but there will still be edema of abdomen, feet, and hands from decreased albumin protein

What is the mechanism for elephantiasis?

= lymph obstruction → ↓ lymph flow →:

1. ↑ISF volume

2. ↑COPi → ↑ capillary filtration

- only safety factor is ↑Pi from the ↑ ISF volume: this will limit the ↑ capillary filtration

-eventually COPi = COPp where ↑ISF is only limited by Pi = Pc

What is the mechanism for acute edema from an allergic reaction? and what is the treatment?

= release of histamine →:

1. ↑Pc → ↑Filtration →ISF volume

2. ↑ capillary permiability to plasma proteins → ↑ COPi → Filtration

- all 3 safety factors of ↑Pi, ↑ lymph flow, and ↓ COPi will limit the edema

-treatment = high dose of epinephrin = ↓Pc by vasoconstriction

how does heart failure cause edema?

heart failure causes retention of NA+ and H2O = ↑ venous hydrostatic pressure and ↑Pc → ↑filtration ↑ ISF volume = pitting edema

-all 3 safety factors of ↑Pi, ↑ lymph flow, and ↓ COPi will limit the edema

why does a decrease in plasma protein concentration cause edema?

↓ plasma protein concentration → ↓ osmotic drawing of water into the capillaries → ↑ filtration → → edmema

what can cause cutaneous edema?

1) ↑ Capillary permeability to protein

2) blockage of lymph vessels

3) increased right atrial pressure: ↑ venous pressure → ↑filtration ↑ ISF volume

4) obstruction of cutaneous viens: ↑Pc → ↑ filtration → ↑ ISF volume

what effect does increasing the number of open capillaries have on the permeability of solutes through the capillary wall?

= no effect

what effect does increasing the number of open capillaries have on the velocity of flow through any individual capillary?

= slows the velocity of flow because there are more parallel pathways for the blood flowing into the muscle to follow