University:
Texas A&M University
Course:
BIOL 319 | Integrated Human Anatomy and Physiology I
Academic year:

2019
Views:

27

Pages:

49
Author:

Tyshawn Shaffer

5.Transport, Endocytosis, and Phagocytosis Cell membrane Cell membrane – plasmalemma – 8.5-10 nm Cell membrane Necessary for life Marks limits of cell (defines cell) Separates cell from its environment Can not be a complete barrier, some items must pass. Cell membranes are semipermeable Cell membrane Four classes of items that must pass - Nutrients (AA, O2, fatty acids, CHO, etc.,) - Waste (CO2 and products of metabolism) - Informational molecules (hormones, growth and chemotaxic factors) - Cell products (secretions, bacteria, RBC {250 billion cells/day}) Cell membrane Plasmalemma - 8.5 - 10 nm Function • Contain antigenic molecules, which are the basis of cell recognition and tissue specificity • Regular internal environment - ion pumps Cell Membrane Plasmalemma 8.5 - 10 nm Function: • Possess receptors for hormones • Possess mechanisms for generating messenger molecules that activate the cell’s physiological responses to stimuli HISTO 61 HISTO 61 Transport of small molecules across membranes Simple diffusion (cross freely) Passive, facilitated, and Active transport Cell membranes are semipermeable Simple diffusion (cross freely) Passive, facilitated, and Active transport Specific (high affinity) but can be saturated Exocytosis - release of secretory products into extracellular compartment • Membrane-bound granules move to surface • Granule membranes fuse with plasma membrane • Contents flow extracellularly • Invaginating vesicles - remove excess membrane from cell membrane • Minute vesicles like pinocytosis vesicles Exocytosis Exocytosis Endocytosis Budding Cell membrane Merocrine Merocrine = Exocytosis Apocrine Apocrine = Budding Apocrine allows hydrophobic cargo to be dispersed in water as if it were hydrophilic Transport of macromolecules: endocytosis 1. 2. Fluid (or bulk) flows Receptor mediated endocytosis • Specific receptor • Coates pits (clathrin) • Lysosomal fusion with endosomes BULK FLOW LDL and receptor separates at lower pH Insulin receptors do not recycle! clathrin coated vesicle (dots label clathrin coat) uncoated vesicle (no dots) Endocytosis - bulk uptake of materials Pinocytosis - cell drinking Phagocytosis - cell eating • Attachment – binding of particle ligand to membrane receptors • Interiorization by pseudopods Ingestion of particles: phagocytosis • Mononuclear phagocyte system macrophage • Opsonized particles • Membrane zippering mechanism Membrane zippering mechanism nucleus Sites of low pH in the cell Primary lysosome Secondary SER