Histology #1- Tissues
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Define histology and cytology
- histology: microscopic anatomy (microanatomy uses a LM and fine structure uses EM) - so the study of microscopic tissue anatomy
- cytology: the study of cells typically from body fluids (smears)
*What are the five cellular characteristics of epithelia?
- I) the cohesive interaction between cells allowing the formation of continuous cell layers
- II) the existence of three types of membrane domains: apical, lateral, basal
- III) the existence of tight junctions between apical and lateral domains
- IV) the polarized distribution of the different organelles and components of the cytoskeleton
- V) the quasi-immobility of the group of epithelial cells relative to the local environment
What are the specialized structural/adhesions connecting cells in the epithelium?
- gap junctions
- adherens junctions (junction that allows the connection between cells to form lawn)
- tight junctions
What are the Four different types of tissue?
- 1. Connective tissue: Few cells, lots of extra cellular matrix (ECM)- lots of space! * specialised to bind
- 2. Nervous tissue: Excitable cells - membrane potential (have ion channels) *specialised to excite/conduct
- 3. Muscle tissue: contractile cells- intracellular motors (cytoskeleton)-->contains motor proteins in the cell that contract *specialized to contract
- 4. Epithelium*: Lawn of cells -intercellular adhesion (tight epithelium barrier, little ECM) *specialized to form lawns
What does Epithelium sit on?
A basement membrane (which is ECM)
What are the terms used to describe the in and out sides of the epithelium?
- in = basal (so the attached side where basement membrane is)
- out = apical (free not attached side)
Is the epithelia avascular?
YES -but the connective tissue is quite vascularized and inervates the epithelia
What do we mean when we say the epithelia have a high turnover?
- Lots of cell division
- and there is a large stem cell population that feeds the turnover
What are the structural features of epithelia?
- "lawn of cells"
- has a basement membrane
- polarity (by apical and basal cell surfaces)
- avascular (but richly inervated)
- high turnover
What are the fibrous ropes and tubes and connectors that give the epithelium structural integrity?
- microfilaments (found in the top villi)
- microtubules (form cytoskeleton)
- intermediate filaments ( bind the attachment sites)
What are the functional roles of Epithelia?
- 1. physical protection
- 2. control fluid flow -permeability/ capacitance
- 3. actively moves fluid across surfaces
- 4. produces specialized secretions (ie the glandular epithelium)
- 5. provides sensation (neuroepithelia)
What are the different types of epithelia?
- Simple: squamous, cuboidal, columnar
- Stratified: squamous, columnar
- and pseudostratified columnar
- and transitional
How do glands develop?
Glands develop as invaginations of epithelium
What are various types of glands defined by?
architecture: tubular, acinar, tubuloacinar
In the gland what are the duct and the glandular parts roles?
- Duct- conduit for exocrine glands (so ducts go to surface so secretions can occur)
- Glandular part- secretory
Do all glands have ducts?
- NO- ENDOCRINE glands do not have ducts
- during embryonic development these glands detach from their epithelial origins and have no ducts- their secretions go into the blood stream (ie pituitary)
What are the modes of secretion for exocrine glands?
- Merocrine gland (is salivary gland) the material is manufactured in the cells and secreted into the duct
- Apocrine gland (i.e. sweat gland) -part of the cells pinch off and contribute to the secretion
- Holocrine gland (sebaceous gland)- disintegrating cells and its content dissociate and become the secretion
What is an example of an organ that has both exocrine and endocrine secretions?
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