Histology Flashcards by Niamh Berry

Components of the cell and the percentage at which they occur

Water = 90%
Protein = 15%
Lipid = 2.5%
Carbohydrate = 1.5%
Inorganic = 1%

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Which has more water - embryonic cells or older cells?

Embryonic cells

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Features common to all eukaryotic cells

an outer membrane.
an inner cytosol – which is a solution of proteins, electrolytes & carbohydrates. It has both fluid and gel-like properties.
a cytoskeleton that determines the shape and fluidity of the cell. It is made from thin and intermediate filaments and microtubules.
membrane bound organelles within the cytosol.
other structures within the cytoplasm which may or may not be bound by a membrane and these are called inclusions.

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What does the plasmalemma do?

Separates the inner cytosol from the outside environment

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What is the plasmalemma made up of?

It is a bimolecular layer of amphipathic molecules with hydrophilic heads on the outer and inner surfaces and hydrophobic fatty acid chains pointing towards the middle.
Contains integral proteins and has cholesterol embedded in it

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Examples of integral proteins in the plasmalemma

Receptors, channels, transporters, enzymes and cell attachment proteins

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What are organelles? Give examples

Organelles are small, intracellular “organs” with a specific function and structural organisation.
Examples include mitochondria, rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi apparatus, lysosomes and the nucleus

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What do inclusions represent?

They represent components that have been synthesised by the cell itself or taken up from the extracellular environment

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What do cytoskeletal proteins do?

They are filamentous cytoskeletal proteins that maintain several functions of the cell

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3 main classes of filaments, their diameter and what proteins they are composed of

Microfilaments - 7nm diameter, composed of actin
Intermediate filaments - >10nm diameter, composed of 6 main proteins which vary in cell types
Microtubules - 25nm diameter, composed of 2 tubular proteins (α and β)

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Where do microtubules originate from?

A special organising centre called the centrosome

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What are MAPs?

Microtubule-associated proteins are stabilising proteins found in the microtubules

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What are the functions of Kinesin and Dynein?

Kinesin is an ATPase which attaches to the microtubules and moves towards the cell periphery
Dynein is an ATPase which attaches to the microtubules and moves towards the cell centre

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What is the periunuclear cistern?

The structure which lies between the inner and outer nucleus membrane. It is continuous with the cistern of the endoplasmic reticulum

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Where are mRNA, tRNA and rRNA transcribed?

mRNA and tRNA are transcribed in the nucleus and rRNA is transcribed in the nucleolus within the nucleus

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What are Euchromatin and Heterochromatin?

Euchromatin is DNA that is more dispersed within the nucleus and is undergoing transcription
Heterochromatin is DNA that is highly condensed in the nucleus and is not undergoing transcription

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What does the endoplasmic reticulum do?

Forms a network of interconnecting membrane-bound compartments within the cell

Rough Endoplasmic Reticulum:

Which organelles are on the surface?
What vital role does it have?

The rough endoplasmic reticulum is studded with ribosomes.

It has a vital role in the synthesis of proteins destined for insertion into membranes or for secretion

What does the amount of endoplasmic reticulum present in the cell vary with?

How active the cell is. Cells that are relatively metabolically active have relatively little endoplasmic reticulum

Smooth Endoplasmic Reticulum:

- What does it do?

The smooth endoplasmic reticulum continues the processing of proteins produced in the rough endoplasmic reticulum
It is the site of the synthesis of lipids

What is the Golgi apparatus composed of?

A group of flattened, membrane-bound cisternae

What is the function of the Golgi apparatus?

It is involved in the modification and packaging of macromolecules that were synthesised the endoplasmic reticulum. E.g. adds sugars, cleaves proteins and sorts macromolecules into vesicles

What is the typical length of mitochondria?

0.5-2µm

What are intercellular junctions?

Specialised membrane structures which link individual cells together into a functional unit

Where are intercellular junctions particularly prominent?

Epithelium

3 main types of intercellular junctions and their basic function

``` Occluding junctions (aka tight junctions or zonula occludens) - link cells to form a diffusion barrier Anchoring junctions - provide mechanical stability Communicating junctions - allow movement of molecules between cells ```

Function of desmosomes

Link intermediate filaments to adjacent cells

Where are desmosomes most common?

In the skin where they provide mechanical stability

What is a junctional complex?

Close association of several types of junctions found in certain epithelial tissues

Describe the structure of communicating junctions

Each junction has a circular path studded with several hundred pores which are produced from connexion proteins

Ways which materials can move across the cell membrane

Diffusion Via transport proteins (pumps or channels) By incorporation into vesicles (vesicular transport)

Describe endocytosis

Material from the extracellular space is incorporated into the cell by this mechanism. The cell membrane invaginates, fuses and the newly made endocytotic vesicle buds into the cell

Describe phagocytosis

Bacteria or larger particulate material from the extracellular space binds to the cell surface receptors triggering extensions of the cell to engulf it forming a phagosome. The phagosome binds with a lysosome carrying digestive enzymes to form a phagolysosome

Steps in preparing tissue for light microscopy

1. Tissue is 'fixed' (preserved) usually by formalin 2. Tissue is thinly sliced (1-15µm) to allow light to penetrate 3. Tissue is impregnated with a support material (usually wax) 4. Thin sections are cut on a microtome and put on microscope slides 5. Wax is washed out and the tissue is rehydrated, producing distortions from the original tissue called artifacts 6. Tissue is stained

In preparation for light microscopy, how is the tissue impregnated with a support material?

The tissue is dehydrated, put into organic solvent and placed in hot wax until it has fully penetrated the tissue

The most common combination of stains used in light microscopy

H&E - haematoxylin and eosin

What is haematoxylin?

A basic dye which has an affinity for acidic molecules and stains them purple/blue (e.g. nucleus, ribosomes)

What is eosin?

An acidic dye which has an affinity for basic molecules and stains them pinkish red. Most proteins in the cytoplasm are basic and so the majority of the cytoplasm is usually stained pink/red

4 basic tissue types

Epithelium, connective tissue, muscle, nervous tissue

Where are epithelia found?

Covering the surfaces of the body or lining hollow organs, and they also form many glands

Roles of connective tissue

Forms the framework of the body but also has a dynamic role in the development, growth and homeostasis of tissues, and, via fat, in energy storage