Endothelium conference

FUNCTIONS:

COVER ORGANS, LINE VISCERA AND BLOOD VESSELS, SECRETORY CELLS OF GLANDS

DISTINGUISHING FEATURES AND DISTRIBUTION:

ALWAYS SIT ON A BASEMENT MEMBRANE, BUT COME IN A VARIETY OF CONFIGURATIONS: CLASSIFIED ON THE BASIS OF THE SHAPE OF THE SURFACE CELLS AND WHETHER ONE (SIMPLE) OR MORE (STRATIFIED) LAYERS OF CELLS ARE STACKED UPON EACH OTHER. THESE CELLS ARE ALWAYS ATTACHED TO THEIR NEIGHBORS BY DESMOSOMES, TIGHT JUNCTIONS, AND GAP JUNCTIONS.

Epithelium

SIMPLE SQUAMOUS – SINGLE LAYERS OF FLAT

CELLS (BLOOD VESSELS, COVERING OF

ORGANS)

STRATIFIED SQUAMOUS – MULTIPLE LAYERS OF

CELLS WITH FLAT ONES AT THE SURFACE

(SKIN, GUMS)

SIMPLE CUBOIDAL – SINGLE LAYER OF SQUARE

CELLS (KIDNEY TUBULES, LIVER CELLS, MANY

OTHERS)

SIMPLE COLUMNAR – SINGLE LAYER OF TALL,

THIN CELLS (INTESTINAL EPITHELIUM)

Epithelium HISTOLOGICAL INDENTIFICATION

ORIGIN AND DISTRIBUTION OF

EPITHELIUM

ECTODERM - EPIDERMIS OF SKIN AND EPITHELIUM OF CORNEA TOGETHER COVERS THE ENTIRE SURFACE OF THE BODY; SEBACEOUS AND MAMMARY GLANDS

ENDODERM - ALIMENTARY TRACT,

LIVER, PANCREAS, GASTRIC

GLANDS, INTESTINAL GLANDS – ENDOCRINE GLANDS - LOSE

CONNECTION WITH SURFACE

MESODERM – ENDOTHELIUM - LINING OF BLOOD VESSELS

– MESOTHELIUM - LINING SEROUS CAVITIES

ECTODERM

ENDODERM

MESODERM

MESENCHYMAL

CELLS

Endothelial cells

Smooth muscle cells

Fibroblasts

Terminal bars

ZONULA OCCLUDENS - TIGHT JUNCTION (BELT)

TRANSCYTOSIS TO GET ANTIBODIES INTO SECRETIONS

SURFACE SPECIALIZATIONS OF EPITHELIA

EXTRACELLULAR MATRIX -

GROUND SUBSTANCE

FIBRONECTIN - BIOLOGICAL GLUE

– (GLYCOPROTEIN)

– BINDS CELLS TO EXTRACELLULAR

– MATRIX AND TO EACH OTHER (FIBRONECTOUS JUNCTIONS)

EPITHELIA ARE SPECIALIZED

FOR FUNCTIONS ABSORPTION - INTESTINE

SECRETION - PANCREAS

TRANSPORT - EYE, ENDOTHELIUM IN VESSELS

EXCRETION - KIDNEY

PROTECTION – AGAINST

MECHANICAL

DAMAGE AND

DEHYDRATION

SENSORY RECEPTION –

PAIN TO AVOID

INJURY, TASTE BUDS,

OLFACTORY, ETC.

CONTRACTION –

MYOEPITHELIUM

SURFACE SPECIALIZATIONS OF EPITHELIA

ENDOTHELIUM IN VESSELS

SIMPLE SQUAMOUS

Blood vessels

Which luminal surface would be

provide less turbulence to blood?

EM 10a: Endothelial cells lining

capillary with pericyte in the vessel

wall.

1. Lumen

2. Endothelial cell

3. Tight junction

CARDIOVASCULAR

SYSTEM COMPONENT FUNCTION

HEART - PRODUCE BLOOD

PRESSURE (SYSTOLE)

ELASTIC ARTERIES - CONDUCT BLOOD AND MAINTAIN PRESSURE DURING DIASTOLE

MUSCULAR ARTERIES - DISTRIBUTE BLOOD, MAINTAIN PRESSURE

ARTERIOLES - PERIPHERAL RESISTANCE AND DISTRIBUTE BLOOD

CAPILLARIES - EXCHANGE NUTRIENTS AND WASTE

VENULES - COLLECT BLOOD FROM CAPILLARIES

(EDEMA)

VEINS - TRANSMIT BLOOD TO LARGE VEINS,

RESERVOIR

LARGER VEINS - RECEIVE LYMPH AND RETURN BLOOD TO

HEART, BLOOD RESERVOIR

CARDIOVASCULAR

SYSTEM

HEART PRODUCES BLOOD

PRESSURE (SYSTOLE)

Vessels are structurally adapted to physical and metabolic requirements.

CARDIOVASCULAR

SYSTEM VEINS - TRANSMIT BLOOD TO LARGE

VEINS RESERVOIR

LARGER VEINS - RECEIVE LYMPH AND

RETURN BLOOD TO HEART, BLOOD

RESERVOIR

VOLUME:

5-6 L = 12-13

PINTS/PERSON

METHODS OF TRANSPORT

THROUGH CAPILLARY WALLS

DIFFUSION

VESICLE

TRANSPORT

CHANNELS

BETWEEN

JUNCTIONS

Typical

endothelial

tight junction

and marginal

fold

ENDOTHELIUM - ACTIVE CELL

HAS ENZYMES AND RECEPTORS

TRANSPORT THROUGH THIN

CYTOPLASM WITHOUT MUCH

ENERGY REQUIRED

FLAT FOR LESS TURBULANCE

NEGATIVELY CHARGED

SURFACE

NOT WETABLE SURFACE

SUMMARY Vessels are structurally adapted to physical and metabolic requirements.

CELL

MEMBRANE

PLASMALEMMA - 8.5 - 10 nm

FUNCTION

• POSSESS RECEPTORS FOR HORMONES

• POSSESS MECHANISMS FOR GENERATING MESSENGER

MOLECULES THAT ACTIVTAE THE CELL’S

PHYSIOLOGICAL RESPONSES TO STIMULI

LIGAND INTERACTIONS with receptors

SPECIFICITY

SATURABILITY

SUMMARY continued:

MEMBRANES AND RECEPTORS

MEMBRANES ARE IMPORTANT IN CELLS

• COMPARTMENTALIZATION

• SEGREGATION OF PRODUCTS

(VECTORAL REACTIONS)

• DEVELOPMENT OF GRADIENTS

• RECEPTORS PROVIDE MECHANISMS

FOR CELL’S PHYSIOLOGICAL

RESPONSE TO EXTERNAL STIMULI

Conference considerations

• Receptor-mediated transport model

• Transport chambers to measure crossing

• SDS gel electrophoresis for MW/degradation

• Transport chambers to measure direction

• Electron microscopy for cellular detail to trace

pathway through cell

• Patient’s problem due to

– Transferrin receptors

– Transport endosomes

– Other possible

Insulin receptors do

not recycle

clathrin coated vesicle

(dots label clathrin coat)

uncoated vesicle

(no dots)

CONFERENCE ON ENDOTHELIAL CELLS The following paragraph introduced a paper in Science: "The mechanism by

which macromolecules such as polypeptide hormones are transported across

non-fenestrated capillaries is not well understood. Endothelial cells probably

have an important role in this process, since they are connected by tight

junctions and thus form a major barrier for the rapid diffusion of hormones to

their target cells. The control of hormonal transport across the vascular barrier

may be a rate limiting and regulating step for the mediation of hormonal action

in many tissues.“

Because of the obvious potential clinical importance of endothelial cell transport

for hormone action, drug delivery, and pathology, you decide to study the

process in detail. Being clever, you have devised the following tissue culture

model system that will permit you to examine transport of molecules across

endothelial cells in the absence of all the other competing influences that would

occur in whole animals. You have two chambers separated by a dialysis

membrane of large pore size (it permits molecules of <100,000 MW to pass

freely). You wish to examine transport of transferrin, an 80,000 MW protein that

carries iron in the blood and delivers it to cells.

After you treat one surface of the dialysis membrane with fibronectin, you

discover that bovine endothelial cells will attach and grow on it. These cells also

have receptors for transferrin, so you are in a position where you can add

transferrin or other molecules to one side of the chamber and measure the rate of

transport to the other side of the chamber.

1. Using your assay system, you now need to develop the methodology to

study transferrin transport.

a) How could you detect movement of transferrin from one chamber to the

other? How could you test if it was degraded during transfer?

b) How could you determine if transferrin transport was specific (i.e.,

receptor-mediated) or if nonspecific transport occurred (e.g., leakage of

transferrin through portions of the filter where the cells are non-confluent).

c) Transferrin transport could be unidirectional or bidirectional. How

would you test this? If transport were unidirectional, speculate on

reasons why cells are unable to transport transferrin in the reverse direction.

2. How could you trace the pathway of transport of transferrin across the cell

membrane and cytoplasm of a vascular (endothelial) cell?

3. Using endothelial cells isolated from patients who are unable to take up

transferrin into their tissues, how could you determine if their inability to use

transferrin is due to defective transferrin receptors, defective transport of

endosomes, or some other problem?