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Week 2 (Properties of Water and Histology (Four basic tissue types…
Week 2
Properties of Water and Histology
Water is able to form hydrogen bonds which determine its chemical and physical properties.
The human body is 70-80% water. It also contains a large amount of macromolecules, small molecules, ions and inorganic molecules, and miscellaneous organic molecules such as haem and vitamin derivatives.
Lipids
Carbohydrates
Nucleic acids
Four basic tissue types
Connective
Connective tissue binds and supports other tissues. Specialised tissue includes; connective tissue proper (loose areolar, dense regular, and dense irregular), cartilage, bone, blood, adipose tissue, and lymphoid tissue.
Muscular
Epithelial
There are two types of glands; multicellular and unicellular. The exocrine glands are glands with ducts and are epithelial derivatives.
Nervous
The functional cell of nervous tissue is the neurone and its function is to respond to stimuli (present in the central and peripheral nervous systems).
Functional Histology
Staining properties
Relating structure to function
Histological samples are always taken in a particular plane (e.g. cross section, longitudinal, or oblique.
Tissue preparation
The sample is firstly fixed.
This is to cross-link proteins through immersion in formaldehyde.
It is then dehydrated in alcohol.
This is to remove water with a graded alcohol series and xylene.
Then, it is embedded in wax.
This is to provide a solid medium for sectioning (65 degrees Celsius) in an oven)
Finally, the sample is sectioned
(cut to thin sections using a microtome)
, rehydrated, stained
(to differentiate between structures and done with a counter stain as well to show particular structures)
, and mounted
(prepares a permanent slide and involves a mountant)
. The most common stain is haematoxylin and eosin.
Haematoxylin is cationic (overall positive charge) and binds to negatively charged structures of the cell such as the nucleus (as it contains DNA) and ribosomes (as they contain rRNA). Eosin on the other hand is an anionic (acidic) dye that reacts with overall positively charged structures. For example, it can bind with the cytoplasm, collagen, cilia, and mitochondria. Proteins with amino (NH3+) groups also attract eosin.
Common stain for carbohydrates is
Periodic acid Schiff
, for lipids this is osmium tetroxide or Sudan Black, for elastin this is van Gieson stains, blood stains can be stained with Giemsa or Wright's stain, . Trichromes can be used to differentiate different tissues (e.g. collagen from muscle).
Cell Structure and Function
Organelles
Stereocilia
Stereocilia are similar to elongated microvilli and play the same role. Their projected nature means that they are able to increase the surface area of the surface that they are on and therefore increase nutrient and substance absorption greatly.
Vesicle
A vesicle is a transportation method that allows for proteins and other substances to be transported around the cell or in or out of the cell through endocytosis and exocytosis respectively. An example of where they are used is transporting the manufactured proteins from the ribosomes on the rER to the Golgi apparatus to be edited and distributed around the cell.
Peroxisome
Peroxisomes are organelles that assist in the detoxification of the cell. They are able to convert free radicals (also from alcohol) into hydrogen peroxide and eventually this hydrogen peroxide can be converted to water by the
peroxiredoxin molecule.
Lysosome
The lysosome is responsible for the breakdown of foreign contaminants and potential harmful products. It does this by keeping digestive enzymes in an acidic environment, and allowing these enzymes to ingest the contaminant.
Nuclear Pores
Nuclear pores are present on the nuclear envelope and are small opening which allow for substances to either leave or enter the nucleus. These may include mRNA, tRNA, rRNA, and ribosomal units.
mRNA, tRNA, and rRNA
mRNA (messenger RNA) are relatively long strands resembling half-DNA molecules. It carries he transcript code to the cytoplasm where protein synthesis occurs.
rRNA (ribosomal RNA) forms ribosomes which contains the ribosomal protein as well.
tRNA (transfer RNA) are L-shaped molecules that ferry amino acids to the ribosomes. mRNA messages are decoded here for the amino acid sequence.
In a eukaryotic cell, the process of translation and transcription involve many steps.
Nucleoplasm
Nucleoplasm is the gel-like fluid that is present within the nucleus. It is the fluid in which all of the processes of the nucleus take place.
Cytoplasm
The cytoplasm is the jelly-like fluid which is present between the nucleus and the plasma membrane. It contains all of the organelles and dissolved solutes and plays a key role for maintaining the cell's structure and a stable internal environment. The fluid where the elements of the cell are suspended is called the cytosol. All chemical reactions occur at this site as well.
Microvilli
Microvilli are the main absorptive cellular projections. They are present in the small intestine and greatly increase the surface area of the small intestine in order for it to absorb more nutrients from the food that passes through it.
The row of microvilli can also be referred to as the 'brush border'
.
Cilia
Cilia are finger-like projections from the surface of, for example, pseudostratified columnar cells in the respiratory tract. Their ability to beat rhythmically together means that they are able to push substances across them. In the respiratory tract this is the transportation of harmful and waste substances out of the body, and in the Fallopian tubes, the transportation of a fertilised egg.
Flagellum
Another type of cellular projection. The flagellum also propagates from centrioles on the plasma membrane of cells The main function of flagella is to provide motility to cells. They are seen with bacterial cells and spermatozoa.
Desmosome
Desmosomes are another type of junction between cells. They are formed by intracellular plaques that connect between adjacent cells and allow the cells to be held together and also have the ability to form sheets.
Tight Junction
A tight junction holds cells together. It is essential for surfaces that act as protection or an interface. They form barriers and limit the passage of molecules.
Gap Junction
Gap junctions allow for the passage of molecules and other substances across cells as they have small channels that allow this. They allow the cells to stick to one another as well.
Plasma Membrane
The plasma membrane is the main method of maintaining boundaries for the cell. It consists of a phospholipid bilayer which is the main order that allows for cellular interaction. It can also contain
integral and peripheral proteins
. Integral proteins can protrude from either one face or two faces of the plasma membrane (called transmembrane proteins). They contain a hydrophobic and hydrophilic end and can form pores for the movement of water-soluble molecules. Others can bind to a substance and move it through the membrane. Some are enzymes and others receptors for hormonal and chemical messages. Peripheral proteins are not embedded in the lipid bilayer and attach loosely to the integral proteins and are easily moved without disrupting the membrane. They support the membrane from the cytoplasmic side and can be involved in mechanical functions such as changing cell shape during cell division, muscle contraction, and linking cells together.
Golgi Apparatus
The Golgi Apparatus is the traffic controller of the cell. It packages and distributes the proteins made by the ribosomes of the endoplasmic reticulum around the cell. It can also attach certain functional groups to proteins to change their function. The Golgi apparatus can create lysosomes and package digestive enzymes into them.
Intermediate Filaments
The intermediate filaments are the guy-wires of the cell and allow it to not succumb to forces of tension or compression. They are able to act across the entirety of the cell (make up cytoskeleton).
They are insoluble proteins that are the most stable and attach to desmosomes.
Microtubules
Microtubules assist in mitosis and meiosis. Kinetochore microtubules attach to the kinetochore proteins of a sister chromatid and when anaphase occurs, pulls on this kinetochore protein to separate the chromatids. Non-kinetochore chromatids on the other hand allow for the expansion of the cell and assists cytokinesis.
They are also able to act as 'railroads' to transport organelles such as mitochondria and other substances with the assistance of motor proteins.
Microfilaments
Microfilaments provide a meshwork for the plasma membrane of the cell. They are thin filaments which make up the cytoskeleton and can allow for the crawling movements of the cell.
They allow for the cell to change in endocytosis and exocytosis and are broken down and reformed as required.
Ribosomes
Ribosomes are mostly protein (65%) and 35% rRNA. The role of ribosomes is to synthesise proteins for use around the cell. They can be attached to the rER or can be freely floating in the cytoplasm and be assigned a particular role.
Nuclear Envelope
The nuclear envelope is the border between the nucleus and the cytoplasm. It contains the nucleolus and many other substances. It acts as a barrier. rRNA/ribosomal subunits, mRNA, and tRNA move out of the nuclear envelope. Proteins that move in include; ribosomal proteins, transcription factors, and enzymes involves in DNA and mRNA synthesis.
Smooth Endoplasmic Reticulum
The smooth endoplasmic reticulum (sER) has many roles. It can synthesise cholesterol and lipids (sex hormones as well), convert glycogen into glucose, and detoxify the cell environment by breaking down alcohol.
In the muscles, the sarcoplasmic reticulum can break down calcium stores to be released into the blood.
Rough Endoplasmic Reticulum
The rough endoplasmic reticulum (rER) is responsible for the synthesis of ribosomes and facilitates the ribosomes as they generate proteins. The rER also allows for vesicles to be created to allow for proteins to be transported from it to the Golgi apparatus.
It also synthesises protein-based hormones.
Nucleolus
The nucleolus contains the DNA (genetic information) for the cell and also specifically is the site of the synthesis of ribosomal units.
Nucleus
The nucleus contains the DNA required for the synthesis of future generations of cells as well as for the operation of the cells. It also is the site of ribosomal unit generation and the generation of mRNA, tRNA, and rRNA.
Mitochondria
Mitochondria generate the energy for the cell. This is through the synthesis of adenosine triphosphate (ATP). Mitochondria also contain many cristae which increase their surface area and ability to generate energy. Mitochondria genes synthesise for 1% of the proteins required for its operation, whilst the rest is dictated by the nuclear DNA.
Principle of Complementarity
Biochemical activities of cells depend upon their specific subcellular structures.
Basic functions of cells
Growth and division
Maintaining boundaries
Generation of wastes
Exchange mechanisms with the environment
Synthesis of biological macromolecules
Production of energy
Stem Cells
Stem cells are cells that are able to divide and create a certain type of cell. For example, stem cells that are found in epithelial tissue on the surface of the skin, are able to generate stratified squamous keratinised epithelium (skin cells) that mature and eventually die and form the layers of the skin.
Embryonic Stem Cells
These stem cells are able to give rise to a multitude of different types of cells in the human body. They make up the blastocyst and can give rise to fat cells, neurons, macrophages, smooth muscle cells, and glial cells (cells that assist in the management of the brain (removing excess neuronal connections)).
Cell Structure and Function (continued)
Basic cell functions and the necessary functions of life
Both are related
Necessary functions of life:
Maintaining boundaries, movement, responsiveness, digestion, excretion, reproduction, growth, and metabolism.
Basic cell functions:
Maintaining boundaries, exchanging mechanisms with the environment, producing energy, synthesising biological molecules, generating wastes, and growing and dividing.
In terms of DNA, there are special transcription factors that regulate gene expression so that different "types" of cells produce the different "types" of proteins that are needed for the structures and functions of the cell type.
Central tenants of Cell Theory
The cell is the basic structural and functional unit of living organisms.
Activities of an organism depend on the individual and collective activities of its cells.
Principle of Complementarity:
Biochemical activities of the cell depend on their specific subcellular structures.
Continuity of life has a cellular basis.
Membrane specialisations
Desmosomes
Desmosomes are created by the internal plaques of two cells joining to one another in order to form a tight bond that allows for the cells to be attached and even form sheets.
The internal plaques are connected from the cytoskeleton of the cells with intercellular filaments.
Tight junctions
Tight junctions serve the purpose of attaching the cells together so that they are unable to move. They are the tightest of all junctions.
Gap junctions
Gap junctions allow for the passage of molecules across cells. They are present on the plasma membrane and also allow for cells to be attached to one another.
These junctions are present with protein channels which allow for communication between cells as well and are especially important with cardiac muscle.
The translation and transcription process is multi-stepped.
Health Advocate and Professional Theme
The Biopsychosocial Model
Biological factors
Genetic variability, anatomy, and physiology.
Psychological factors
Cognitions (thoughts and beliefs), behaviour (coping strategies), emotions, and personality.
Social factors
Social support, employment, social class, cultural background, environment, and healthcare access.
Humans have some responsibility in the cause of their illness. These illness are caused by a combination of these biological, social, and psychological actors. The whole person should be treated, and the responsibility for the treatment is shared between the individual and the medical professional.
The relationship between mind and body is emphasised and that health is a continuum. People are never fully 'out of' an illness.
