Histology Flashcards
What is the maximum resolving power of a light microscope?
0.2µm
What is the maximum resolving power of an electron microscope?
0.2nm
What steps are involved in creating a histology slide?
Fix, embed, section and stain
What is the purpose of fixing a tissue, and what is a common fixative used?
To prevent breakdown of the tissue, and to preserve the current state of the tissue. Fixatives such as formaldehyde maintain the structure of the tissue
What steps are involved in embedding a tissue?
The tissue is dehydrated in alcohol and then penetrated with paraffin wax.
What are the basic characteristics of haematoxylin?
Haematoxylin binds to acidic or anionic components, staining them purple. These tissues are said to be basophilic.
What are the basic characteristics of eosin dye?
Eosin stains basic or cationic components of cells pink. These components are said to be acidophilic or eosinophilic
What does it mean if a tissue is amphophilic?
It binds both acidic and bsic dyes
What are the 4 basic tissue types? From which embryological layers do they derive?
Connective tissue (mesoderm), epithelium (all 3), nerve (ectoderm) and muscle (mesoderm)
What are the characteristics of red blood cells?
Biconcave discs 7.2µm in diameter. They have no nucleus and no organelles. They contain haemoglobin and transport oxygen and carbon dioxide.
In what form are erythrocytes released into the blood?
Reticulocytes, which mature over the course of a few days. They have no nucleus, but some organelles.
What are the different white blood cells?
Granulocytes:
Neutrophils, eosinophils, basophils
Mononuclear leukocytes:
Lymphocytes, macrophages
What are the characteristics of neutrophils?
Also called polymorphonuclear (PMN) cells. Have a nucleus separated into multiple lobes and a granular cytoplasm. They are phagocytic and the main cells of acute inflammation
What are the characteristics of eosinophils?
They have a bilobed nucleus and large, eosinophilic granules. They react mostly against parasites
What are the characteristics of basophils?
Bilobed nucleus with basophilic granules in the cytoplasm (filled with histamine)
What are the characteristics of lymphocytes?
Slightly larger than RBCs, with a thin ring of cytplasm surrounding a large nucleus. Three types (T, B, NK)
What are the characterics of monocytes?
They are macrophage precursors found in the blood with bean shaped nuclei, located at the edge of the cell
What are the types of connective tissue fibres?
Elastin, Collagen
How does collagen appear when stained with H&E under a light microscope?
Pink (b/c very protein rich) and wavy
Where can Collagen Type I be found?
- Connective tissue proper
- Bone
- Tendon
- Ligament
Where can Collagen Type II be found? What are some key features?
Cartilage. It is flexible and resists compression. It contains a lot of ground substance, and so stains blue in H&E.
Where can Collagen Type III be found? What are some key features?
Reticulin. Fibres are very thin and need to be specially stained in order to be visualised on a light microscope. It forms a delicate frameworks around cells of certain tissue types to support tham and to keep the cells in place.
Where can Collagen Type IV be found? What are some key features?
Basement membrane. It lies beneath epithelium and mesothelium, providing strucutral support and linking epithelium with the underlying tissue.
What special surface modifications can be found on lateral surfaces of epithelial cells?
- Zonula Occludens/Tight Junctions (TJ)
- Zonlua Adherens (ZA)/Adherens Junctions
- Macula Adherens/Desmosome (D)
- Gap Junction made of Connexin Proteins (CP)
How are the Adherens Junctions of epithelial cells structured?
Glycoproteins called cadherins project from adjacent cells into the gap between them. They interact with each other to form a ‘zipper’ and lock together.
Inside the cell, anchoring proteins connect the cadherins to actin filaments that are arranged in a marginal band around the inner circumference of the cell. These actin filaments have a capacity to contract.
How are the Desmosomes of epithelial cells structured?
Glycoproteins called Cadherins project into the gaps between cells. They interlock, holding the cells together.
These cadherins are anchored to a cytoplasmic plague in the inside surface of the cell.
Also anchored to the plaque, and thus the transmembrane proteins, are intermediate filaments such as keratin or desmin.
Describe the Gap Junctions of epithelial cells
They allow selective movement of substances between cells.
They are formed by connexin proteins that line up neighbouring cells, forming a complete channel between two cells. The combination between two connexins is called a connexon.
Describe the Hemidesmosomes of epithelial cells.
Located on the basal surface of epithelial cells, transmembrane proteins called intergrins link with lamins of the basement membrane.
Like a desmosome, these intergrins then are anchored to a plaque and then to intermediate filaments within the cell.
What are the types of exocrine gland structures?
Simple tubular, simple coiled, simple branched tubular
Describe a Goblet Cell
Unicellular exocrine glands that secrete mucous. The mucous is membrane bound and displaces the nucleus and organelles of the cell basally.
Describe an Acinus
An acinus describes a round exocrine unit. Secretory cells cluster together and secrete into a duct.
The bases of these cells are basophilic due the rough endoplasmic reticulum in this area while the apices are eosinophilic due to the high concentration of proteins.
Describe the histoogical appearance of skeletal muscle cells
Cells are long and multinucleated, with nuclei located peripherally. Cells are packed full of myofibrils which contribute to their striated appearance in longitudinal section.
How do skeletal muscle cells contract?
T-tubules (2 per sarcomere) carry the action potential into the cell. The sarcoplasmic reticulum then releases Ca2+, initiating the comtraction of sarcomeres.
Sarcomeres shorten as the thick filaments (myosin) slide over then in filaments (actin). As each sarcomere of a myofibre contracts, the entire myofibre contracts.
Describe the histological appearance of cardiac contractile cells
Cardiac contractile cells are striated and either mono- or bi-nuclear. The nuclei are located centrally and cells are connected in a branching pattern by intercalated discs.
How are the intercalated discs of cardiac contractile cells structured?
They are interdigitating junctions between cardiac contractile cells with both longitudinal and transverese directions.
The transverse portions of intercalated discs always coincide with Z-lines. In these regions, fascia adherens, which are similar to the zona adherens of epithelial cells transmit forces between cells. Desmosomes connect the intermediate filaments of neighbouring cells.
In the longitudinal regions lie gap junctions.
Describe the histological appearance of smooth muscle cells
They are thin, fusiform shaped with a centrally located nucleus.
How do smooth muscle cells contract?
Along the cell membrane are dense bodies, very similar to the Z-discs of striated muscle. These dense bodies anchor actin filaments which are then overlapped by myosin filaments. During contraction, the action of these filaments brings the dense bodies closer together, causing the cell to shrink in all dimensions
Describe the connective tissue layers surrounding peripheral nerve axons
An axon is surrounded by a Schwann cell, which may or may not be myelinating the axon. Endoneurium then surrounds these axons. Perineurium wraps a bundle of axons (called a fascicle) while epineurium surrounds the entire nerve.
