HistoLecture2 PDF - Cellular Structures

Cellular structures January 15th, 2025  Today’s Learning Objectives List and describe different methods of staining Choose the best stain based on the tissue and desired outcome of your staining Describe the functions of key cellular structures Identify cellular structures based on...

Cellular structures January 15th, 2025  Today’s Learning Objectives List and describe different methods of staining Choose the best stain based on the tissue and desired outcome of your staining Describe the functions of key cellular structures Identify cellular structures based on appearance in H&E staining Predict which cellular structures might be especially prominent in a cell based on its function, or predict the function of a cell based on prominent cellular structures  Review Assemble into groups or 2-3 for beginning of class review activities Each group will discuss review questions, and I will call on group to share answers  Review: microscopy and slide preparation Microscopy is an important tool for the study of histology. Which microscope would you use if you wanted to: – Examine a slide stained with traditional H&E staining? – Examine a slide stained with a fluorescent antibody (immunostaining)? – Examine very small internal structures, like ribosomes or chromosomes? Before they can be examined under the microscope, tissue samples must be ______ either with chemicals like formaldehyde or by freezing in liquid nitrogen Tissue samples are then sectioned, mounted onto slides, and stained  H & E staining Hematoxylin and eosin: most common histological staining technique; great for examining general characteristics of cells and tissues Hematoxylin alone Eosin alone H & E together Basic dye Acidic dye Stains DNA, RNA, and Stains lysosomes, ribosomes mitochondria, and collagen Ross and Pawlina, Histology  Common histological stains H&E: basic staining protocol used for general examination of cell and tissue structure Verhoeff’s stain: Elastin fibers stained black PAS staining: Sugars and starches stain dark purple/magenta Mallory trichrome: good for connective tissues; collagen stains blue, elastin pink or yellow, and muscle fibers red Silver stain: sensitive staining method for small protein fibers Verhoeff’s Silver stain H&E PAS Mallory Trichrome  Review After staining a tissue sample with H&E, you note that the cells within this tissue stain bright pink. – Which dye is responsible for the pink coloration of your sample? – What cell structure(s) do you think is(are) enriched in this tissue based on its appearance following H&E staining? Which type of stain would you use to: – Examine reticular tissue, which is full of very fine fibers? – Examine elastic fiber distribution in cartilage of the ear? – Examine glycogen concentration in the liver before and after a large meal?  Cellular structures Cells can contain a variety of organelles and subcellular structures to support their functions Cellular structures to review today: Plasma membrane Nucleus Ribosomes Endoplasmic reticulum Golgi apparatus Secretory vesicles Mitochondria Cytoskeleton Cellular inclusions  Organize into small groups to review the functions of cellular structures: Return to your small groups I will assign each group a structure; within your group, brainstorm what you remember about that structure: – Plasma membrane – Nucleus – Ribosomes – Endoplasmic reticulum Smooth Rough – Golgi apparatus – Mitochondria Plasma membrane  Plasma membrane Typically does not stain intensely with H&E (lipids stain poorly in H&E); if visible, just a thin pink line Can use EM to view in more detail H&E TEM  The nucleus TEM H&E  The nucleus Basophilic, therefore purple in H&E staining, due to abundance of nucleic acids (both DNA and RNA) Nuclear appearance can change in ways that are often linked to cell activity! Euchromatic nuclei  Ribosomes TEM  Ribosomes When ribosomes are concentrated in one part of the cell, the cytoplasm there will be basophilic as a result and appear purple in H&E staining – Basophilic due to abundance of nucleic acids in ribosome – rRNA, mRNA, and tRNA What might you infer about the activities of a cell with an abundant supply of ribosomes in its cytoplasm?  Endoplasmic reticulum Two types: smooth and rough Endoplasmic reticulum Smooth ER does not typically stain intensely in H&E staining due to abundance of lipids Rough ER is rich in ribosomes, which means it stains the same way that ribosomes do – basophilic and purple in H&E due to enrichment of rRNA, mRNA, and tRNA Golgi apparatus  Golgi apparatus In most cell types Golgi will not be abundant enough to be apparent However, in a few cell types that produce and secrete massive amounts of proteins, Golgi may affect cell appearance in H&E – Golgi typically When Golgi is very well- developed in a cell, it is typically appears as a pale pink- pale-staining but acidophilic staining region near nucleus  Secretory vesicles In cells with important secretory functions, secretory vesicles often accumulate in the cytoplasm to the extent that they are apparent in H&E staining Appearance of these secretory vesicles varies depending on the secretory product itself – Mucus and lipid secretions stain poorly in H&E and therefore appear pale or even clear – Secreted proteins are often acidophilic and appear pink in H&E Secretory granules  Mitochondria Aerobic respiration and ATP production Detailed structure apparent using TEM  Mitochondria Mitochondria are acidophilic (stain intensely pink) in H&E Cells with abundant mitochondria have pink cytoplasm as a result What can you infer about the activity/function of a cell with abundant mitochondria within its cytoplasm? What cell types might you expect to have abundant mitochondria?  The cytoskeleton Network of protein filaments found throughout the cell Provide internal structure, and also assist with specialized functions such as intracellular transport, cell movement, and cell division Three types: – Microtubules – Intermediate filaments – Microfilaments (actin filaments)  The cytoskeleton Must use electron microscopy or immunostaining to visualize any part of the cytoskeleton Microtubules: – Green in bottom image – Made of a protein called tubulin – Involved in intracellular transport; particularly important in large cells such as neurons  The cytoskeleton Must use electron microscopy or immunostaining to visualize any part of the cytoskeleton Intermediate filaments: – EM in top image – Made of different proteins in different cell types; common ones include keratin and vimentin – Form network throughout cytoplasm to provide structure – Also attach to cell-cell junctions to reinforce cell-cell connections; particularly important in cells that must adhere tightly to one another  The cytoskeleton Must use electron microscopy or immunostaining to visualize any part of the cytoskeleton Microfilaments (actin filaments): – Red in bottom image – Smallest filaments, comprised of actin – Concentrated beneath plasma membrane; important for cell movement  Cellular inclusions Some cells have a storage function and thus have abundant deposits within their cytoplasm that are not membrane bound but are apparent in H&E staining Glycogen inclusions Lipid droplets do not stain at all with H&E (stained with PAS)  Cellular structures: Structure = Function Different cell types are specialized for different functions – and that is reflected in the broad variation of cell shape and structure we will see throughout the semester: Very few organelles Lots of RER, Lots of RER and Lots of RER on one Golgi, and Golgi but no side, but secretory secretory secretory granules granules on the granules other side (polarized)  Cellular structures: Structure = Function Cell appearance in H&E staining differs depending on cell structure and function These cells have very basophilic cytoplasm, and also have very euchromatic nuclei – What structures might be enriched in the cytoplasm of these cells? – What might these features suggest about the function of these cells? Cell appearance in H&E staining differs depending on cell structure and function The parietal cells in this image have very acidophilic cytoplasm – What structures might be enriched in the cytoplasm of these cells? – What does that tell you about the function of these cells? Cell appearance in H&E staining differs depending on cell structure and function The cells in this image have multiple white structures in their cytoplasm What do you think these structures might be?  Reminders No lab tomorrow Friday: – Begin to discuss epithelial tissues – Quiz 1: Will cover material from Monday and Friday (will not include epithelia) Available on Canvas from Friday at 8 am until Sunday at 8 pm Next week: – No class Monday – MLK Day – Lab starts on Thursday