Cell adaptations, ageing and accumulations

What are the 5 mechanisms cells can use to adapt to sub-lethal injury

Hypertrophy = increase in cell size (post-mitotic cells)

Hyperplasia = increase in cell number

Atrophy = decrease in cell size

Metaplasia = differentiating into a different type of cell

Dysplasia = abnormal differentiation

What is atrophy a physiological response to?

Lack of use

Lack of innervation

Lack of stimulation

Describe the metaplasia that occurs in asthma

Ciliated respiratory epithelium in bronchi changes to goblet cells to produce more mucous. Too much metaplasia = maladaptive metaplasia = too much mucous produced causing breathing difficulties

Describe the metaplasia that occurs in the prostate secondary to testicular cancer

Unclear pathogenesis

Cancer produces oestrogen

Columnar glandular epithelium changes to stratified squamous

Prostate enlargement = urination problem and accumulation of debris cause prostatitis

Explain the metaplasia caused by vitamin A deficiency in parrots

Squamous metaplasia of respiratory and upper GIT epithelium

Mechanism poorly understood

Normal ciliated pseudostratified and glandular epithelium change to stratified squamous epithelium = produces keratin = hyperkeratosis (oral cavity, nasal lacrimal duct, upper alimentary tract, respiratory tract)

Keratin can block glands causing large keratin granulomas and rhinolith formation

Features of a dysplastic epithelium

Increased number of poorly differentiated or immature cells

5 microscopic features of dysplasia

Anisocytosis

Poikilocytosis (variation in cell shape)

Hyperchromatic nuclei

Karyomegaly

Increased size/number of nucleoli

Mitotic figures

= looks like neoplasia, so can be difficult to differentiate

What is this?

Actinic keratosis (frequently develops into carcinoma)

What are

• Labile cells

• Quiescent cells

• Senescent cells

Labile = constantly dividing cells (bone marrow, enterocytes, keratinocytes)

Quiescent = not currently dividing but can be easily stimulated to divide (liver)

Senescent = cells that are told to not divide but remain metabolically active (tumour suppressor genes or damaged DNA)

What is this pigment accumulating in aged post-mitotic cells and describe what it is and 2 pathological causes

Lipofuscin

Accumulation of undigestible lipoproteins and pigments

Pathology:

• lipofuscinosis (genetic)

• Phalaris poisoning (plant, ruminants)

Can cause impaired function of neurones in excessive amounts

Example causes of hypopigmentation (2)

Vitiligo

Melanin intolerance - some skin diseases of dermo-epidermal junctions e.g. pemphigus

Name the 4 haematogenous blood and bile pigments and what are they

Haemoglobin = red staining due to contact with blood

Haemosiderin = brown in macrophages due to recently phagocytosed blood at areas of bleeding - seen histologically

Haematoidin = green in chronic bruising

Bilirubin = yellow in jaundice

What is porphyria and what changes does it cause

Heme synthesis disorder

Deposition of porphyrin pigments in tissues

Teeth and bones turn pink, and fluoresces under UV light

What porphyrin-related condition is seen in Limousin cattle?

Congenital erythropoietic poryphria

Caused by a different enzyme

No tooth discolouration

Causes photosensitivity

Cause of this muscle pigmentation

Carbon monoxide poisoning - carboxyhaemoglobin

Describe causes of methaemoglobinaemia

Methaemoglobin is constantly being formed then reduced to haemoglobin via the methaemoglobin reductase pathway

Increased methaemoglobin formation due to marked oxidant exposure *red maple in horse. can progress to haemolytic crisis)

Associated with Heinz bodies

Blood and mucous membranes appear brown

Describe cause of haemoglobin imbibition

Freezing and thawing of cadavers causes erythrocyte lysis, resulting in haemoglobin leaking out and staining nearby tissues

Static clotted blood in large blood vessels and atria can leak haemoglobin due to RBC lysis

Name and explain the cause of this pigmentation on a horse.

Carotenoids

Present in leafy vegetables

Yellow colour in adipose tissue of the animals that eat the vegerables.

Usually only seen in horses and Channel Island cattle, as other breeds seem to metabolise them in a different way

What is pathological calcification and name and explain 2 types

Deposition of calcium salts in soft tissue - usually phosphates and carbonates

Metastatic calcification (left) = due to increased calcium levels

Dystrophic calcification (right) = secondary to necrosis

Describe the gross and histological appearance of calcification

Gross:

• palpable calcium granules

• feel knife grating upon sectioning

• chalk-white colour usually. Can be yellowish/green due to eosinophils if parasites are involved

Histo:

• dark blue colour

• microtome mark due to shattering of tissue

• Von Kossa stain turns it black