Endothelium conference

Epithelium FUNCTIONS: DISTINGUISHING FEATURES AND DISTRIBUTION: 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 HISTOLOGICAL INDENTIFICATION 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)

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 MESODERM ENDODERM

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 TRANSCYTOSIS TO GET ANTIBODIES INTO SECRETIONS

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

Blood vessels SIMPLE SQUAMOUS

Which luminal surface would be provide less turbulence to blood?

EM 10a: Endothelial cells lining capillary with pericyte in the vessel wall. Lumen Endothelial cell 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   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?