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Define Histology

The study of the structure of tissues by means of special staining techniques combined with light and electron technology


What is the definition of tissue?

- A collection of cells specialised to form a particular function


What are the classifications of tissue?

- Connective
- Muscle
- Epithelial
- Nervous


What is the definition of biopsy?

The removal of a small piece of tissue from an organ or part of the body for microscopic examination


What types of biopsy are there?

- Smear
- Endoscopic
- Needle
- Transvascular
- Direct incision
- Curettage


What fixatives are used?

- Glutaraldehyde
- Alcohol
- Formaldehyde


Why are fixatives used?

- Prevents biological reactions from occurring
- Preserves cells so that thin slices can be prepared


Give 2 types of staining

- Haemotoxylin and Eosin
- Periodic Acid Shift


What does H&E stain and what colour?

- BASIC parts, eg cytoplasm, are stained PINK
- ACIDIC parts, eg nucleolus, are stained BLUE


What does PAS stain and what colour?

Glycoproteins and carbohydrates are stained magenta


What types of microscopy are there?

- Phase contrast
- Dark field
- Fluorescence
- Confocal


What is the definition of Epithelia?

Sheets of contiguous cells, of various embryonic origin, that cover the external surface of the body and line internal surfaces


Why do shrinkage artefacts occur?

Because of the dehydration and rehydration of the sample


Describe and give functions and examples of simple squamous Epithelia

- Flattened cells, are wider than they are tall
- Short diffusion distance, lubrication, gas exchange, barrier, active transport by pinocytosis
- Bowman's capsule and glomerulus, alveoli, mesothelioma (body cavities - peritoneum, pleurae, pericardium), endothelium (arteries, veins, capillaries, lymphatics), inner and middle ear


Describe and give functions and examples of simple cuboidal Epithelia

- same height and width
- absorption, secretion, hormone synthesis, storage and mobilisation, barrier/covering
- exocrine glands, kidney tubules, thyroid follicles, ovary


Describe and give functions and examples of simple columnar epithelia

- Long and thin
- Absorption, secretion, lubrication, transport
- Stomach, gastric glands, small intestine, colon, gall bladder, large ducts of some exocrine glands, oviducts, uterus, ductuli efferentes of testis


What do simple columnar epithelia commonly have?

- Microvilli increase surface area in small intestine
- Glands eg goblet cells in small intestine
- Tight junctions (zone occludens) with complexes (occludin) that bind adjacent cell membranes together. Acts a barrier and regulates permeability


Describe and give functions and examples of simple pseudostratified epithelia

- Looks stratified as nuclei at different levels, but all cells are attached to the basement membrane
- Secretion, particle trapping and removal, absorption, mucus secretion
- Lining of nasal cavity, trachea and bronchi (URT), epidiymis and ductus deferens, auditory tube and part of tympanic cavity, lacrimal sac, large excretory ducts


What does simple pseudostratified epithelia commonly have?

- cilia: extensions that beat in waves to sweep mucus and dirt (and ovum in Fallopian tube)
- Glands eg goblet cells
- Stereocilia eg very long Microvilli in epididymis and ductus deferens


Describe and give functions and examples of stratified squamous epithelia

- Non-keratinised: oral cavity, oesophagus, larynx, part of anal canal (GI), vagina, surface of cornea, inner surface of eyelid
- Protection against abrasion and reduces water loss
- Keratinised: surface of the skin, parts of mouth and anal canal
- Protection against abrasion, reduces water loss, shields against Uvula light and prevents ingress of microbes


Describe and give functions and examples of stratified transitional epithelia

- Bumpy uppermost layer, usually 3 or more layers thick
- Renal calyces, ureters, bladder, female urethra
- distensibility, protection of underlying tissue from toxic chemicals


What are the key features of the basement membrane?

- Is thin, flexible and acellular
- Lies between Epithelia and underlying connective tissue
- Epithelium adheres to it
- Acts as a filter
- Can be augmented by reticular fibrils (type III collagen)


How large are most human cells?

- 10-20 um


What type of tissue is a smear biopsy used for?

- Cervix or buccal cavity


What type of tissue is a curettage biopsy used for?

- Endometrial lining of uterus


What type of tissue is a needle biopsy used for?

- Brain
- Breast
- Liver
- Kidney
- Muscle


What type of tissue is a direct incision biopsy used for?

- Skin
- Mouth
- Larynx


What tissue is an endoscopic biopsy used for?

- Lung
- Intestine
- Bladder


What type of tissue is transvascular biopsy used for?

- Heart
- Liver