CSB520 - Cell adaptation & death

Examples of cell types that are considered connective

Connective tissue cells

Muscle – myocytes (3 types):

Smooth muscle - loose CT with smooth muscle cells - stable

Cardiac Myocytes - individual cells with single central nuclei, intercalated discs connect cells end to end allowing coordinated contraction - permanent

Skeletal muscle fibres - striated or voluntary muscle - permanent but tissue able to repair

Endothelium - Endothelial cells (lining of blood vessels)

Cartilage – Chondrocytes

Bone – Osteoblasts, Osteocytes

Fibroblasts/myofibroblasts -  (secrete collagen protein)

Fat – Adipocytes (large cells whose cytoplasm is full of fat which is often lost in sections. Nucleus against edge)

What is meant by labile, stable & permanent cells, give some examples.

Labile (continuously dividing)

•Epithelial e.g. Skin, GIT, reproductive, urinary tracts , lining of exocrine ducts

•Haemopoietic stem cells

Stable (quiescent)

•Epithelial e.g. Liver, kidney, lung, pancreas

•Smooth muscle cells, fibroblasts, endothelial cells

Permanent (non-dividing)

•Cardiac & skeletal myocytes, CNS neurons

Examples of cell types that are considered epithelial

Simple Squamous Epithelium - Single layer of cells whose cytoplasm often appears thinner than their nuclei. Allows of gases, ions and small molecules e.g. alveoli

Stratified Squamous Epithelium - (Labile) Basal cuboidal-like cells that mature as they migrate up towards the surface. At some sites, a keratinised upper layer reduces absorption but increases strength. Line surfaces exposed to abrasion, friction, physical stress:

Skin, Oral cavity, Pharynx, Oesophagus, Anal canal, Outer cervix (ectocervix), Vagina

Simple Cuboidal Epithelium - (Labile/Stable) cells are as tall as they are wide with a central nuclei. Lines protected surfaces including: Ducts of exocrine glands, Collecting tubules of the kidney, Outer surface of the ovary

Simple Columnar Epithelium - cells line surfaces involved in secretion & absorption. Sometimes microvilli are present to increase the surface area of the absorptive membrane or cilia to aid movement across the surface. Mucous secreting cells appear to have a fragile looking or poorly stained cytoplasm due to the numbers of mucous-filled vesicles within their cytoplasm

Pseudostratified Epithelium - (Stable) Specialised epithelium located in the upper respiratory tract and sections of the male reproductive system. As the name suggests, although this epithelium appears to include multiple layers of cells, there is only a single layer however, the nuclei are located at different levels of the cytoplasm giving the illusion that there are many cells

Transitional Epithelium - Restricted to urinary system, (renal calyces, ureters, urinary bladder & parts of the urethra). Allow stretch & retraction and are lined by stratified cells that when relaxed appear stratified columnar but when stretched look like stratified cuboidal/squamous.

Stratified Cuboidal/Columnar Epithelium - A fairly rare type of epithelium

Some large ducts are lined by columnar on top of cuboidal cells with cilia when located within areas of the soft palate and epiglottis. Stratified cuboidal epithelium lines the mammary glands, parts of the cochlea, germ cells of the seminiferous tubules and granulosa cells of the ovarian follicles

Examples of cell types that are considered “other”

Mesothelial cells or Mesothelium

Melanocytes

Germ Cells

Lymphoid Tissue

Bone Marrow

Haemopoietic Cells

Central Nervous System Tissue

RBC

Neutrophils

Lymphocytes

Macrophages

Describe the main differences between apoptosis & necrosis.

Apoptosis occurs in physiology & Pathology

Necrosis only in pathology

Apoptosis is active

Necrosis is passive

Apoptosis is single cell death

Necrotic cell can kill its neighbouring cells

Apoptosis does not stimulate inflammation

Necrosis stimulates inflammation

What is an infarct and how does it occur?

Neighbouring cells induced to undergo necrosis

Due to stimulation of acute inflammation

Loss of function of tissue

• scarring

• calcification

• death

Infarct is an area of necrotic tissue

Tissue Patterns of Necrosis

Coagulative: Hypoxic death (not brain)

•Protein digestion preserved cell & tissue framework

•Necrotic tissue: Heterolysis/autolysis (lysosomal)

Liquefactive: Localised bacterial infections, brain

•Auto/heterolysis > protein denaturation

•Necrotic area is soft  & fluid filled

Caseous: TB lesions

•Soft friable, ‘cheesy’ material

Fat: Adipose tissue

•Lipase activation: releases FAs from trigs→complex with Ca2+ → soaps

What determines whether a stimulus causes atrophy or infarction?

Atrophy involves apoptosis (decrease in cell number) & autophagy (decrease in cell size)

Infarct is ischaemic & haemorrhagic

What effect does ageing have on cells & organs?

Define types of cellular adaptation & understand when these processes are not possible/reversible

Atrophy - reduced size of tissue/organ due to loss of tissue. reduction in size due to individual cells undergoing a combination of autophagy & apoptosis or just apoptosis in old cells

Hyperplasia - increased number of cells

Metaplasia - the change from one normal/well-differentiated cell type to another normal/well-differentiated cell type

Hypertrophy - increased size of cells

All are reversible - but irreversible when there is repeated/sustained stress in cells (e.g trauma, smoking) allows cell survival but there is also a loss in function