Download Connective tissue and Epithelial Tissue and more Study notes Histology in PDF only on Docsity!
Epithelium
- Epithelial cells are localized to three distinct areas of the body. They can be found: ○ Covering the whole external surface of the body, as part of the skin. ○ Lining interior tracts which open to the exterior, such as the ○ Respiratory, gastrointestinal and genitourinary tracts. ○ Lining interior enclosed spaces, such as blood vessels, the peritoneum, the pleura and the pericardial sac.
- Epithelial cells are classified in two ways. Firstly, they can be
- classified depending on how many layers of cells are present, and secondly, by shape.
Classification Of Epithelial Tissue
Surfaces of Epithelial Cells
Each epithelial cell has 3 surfaces:
- Basal surface
- Apical surface
- Lateral surface
Simple vs Stratified Epithelia
Simple
- Simple epithelia are defined as epithelia which are one cell layer thick –
- every cell attaches to the basement membrane.
- The basement membrane is a thin but strong, acellular layer which lies between the epithelium and the adjacent connective tissue. It is sometimes referred to as the “basal lamina”.
- The basement membrane is clinically important in cancer, as the degree to which malignant cells penetrate it is highly relevant to prognosis. The side of the cell furthest from the basement membrane is known as the apical border. Stratified
- Stratified epithelia consist of multiple layers of cells, with one layer anchored to the basement membrane, known as the basal layer.
Types of Epithelium
Simple Epithelium Simple Squamous Epithelium: Composed of a single layer of flattened cells, making it the thinnest type of epithelium. ○ Found in alveoli of the lung - gas exchange ○ Bowman's Capsule and loop of Henle of kidney - Barrier for filtration Linning of the blood and lymph vessels - exchange of gases and nutrients - passage of certain blood cells into tissues ( endothelium)
Linning of the blood cavities ( pleura, pericardium and peritoneum) - lubrication between tissues and organs( mesothelium )
Simple Cuboidal Epithelium: This type consists of a single layer of cuboidal (square- shaped) cells. ○ thyroid Follicles - hormone synthesis, storage and mobilization ○ Small ducts of exocrine glands - Absorption and passage of exocrine secretions ○ Kidney tubules - Absorption and secretion ○ Surface of ovary ( germinal epithelium ) - barrier/ covering of follicles
Simple Columnar Epithelium: This epithelium is made up of a single layer of long, thin cells. Some cells have cilia( hair - like projection) or microvilli ( finger - like projections) lining of stomach and gastric glands - absorption and secretion of gastric juices -
Microvilli form a brush border which increases surface area for absorption ○ Small intestine and colon- absorption secretion and lubrication ○ Gall bladder - Absorption of water and electrolytes from the bile Fallopian tubes - Transport of ova - some cells are ciliated to help to waft the egg along from the ovary to the uterus
Pseudostratified Epithelium- is so-called because at first glance the cells appear to be several layers thick. However, every cell attaches to the basement membrane and therefore it is defined as simple epithelium. Lining of the nasal cavity , trachea and bronchi - secretion of mucus, trapping of particles and removal of mucus ( cilia aids the passage of mucus)
Epididymis and vas deferens - absorption of fluid, secretion of substance which promotes sperm maturation and passage of sperm one motile ( stereocilia ( very long microvilli) aid the passage of sperm)
Stratified Epithelium
Overview: Stratified epithelium consists of multiple cell layers, with the basal layer anchored to the basement membrane. It is classified into different types based on cell shape and the presence of keratin, primarily serving protective and barrier functions.
Stratified Squamous Epithelium: ○ Multiple layers of cells.
○ Basal layer cells rest on the basement membrane. Cells are usually columnar in shape, lying over the columnar cells there are polyhedral or cuboidal cells.
Keratinized Stratified Squamous Epithelium:
- Upper layers of cells are dead and filled with keratin.
- Forms the epidermis of the skin.
Functions: ○ Protects against physical trauma and abrasion. ○ Prevents water loss. ○ Provides a physical barrier against microbes. ○ Protects against UV light. Non-keratinized Stratified Squamous Epithelium: Cells in the uppermost layer are live and nucleated
Cells become increasing flattened as one move towards the superficial layer Function ○ Involved in protecting against abrasion and reducing water loss. ○ Keeps surfaces moist.
Locations: ○ esophagus ○ vagina, ○ larynx, ○ mouth, ○ cornea, ○ part of the anal canal. ○ In the vagina, cells maintain a low pH via lactic acid production.
Key features: ○ No stratum corneum. ○ Uppermost layer cells are live and nucleated. ○ Cells flatten as they move towards the superficial layer. ○ Remains moist. ○ Protects underlying structures. ○ Acts as a barrier against pathogenic organisms.
Locations: ○ Cornea, ○ Oral cavity, ○ Oral pharynx,
Cancer cells don't follow normal cell replication and death processes. - Cancer cells may break away, move through blood vessels or lymphatic systems, and start growing somewhere else (metastasis). - Tumors make their own blood vessels (angiogenesis) for nutrient and oxygen supply.
In order to grow, tumors start making their own blood vessels (angiogenesis). The blood vessels supply the tumor with extra
oxygen, glucose (sugar) and hormones. As a result, the tumor can grow into surrounding tissue. It is then called invasive cancer. Carcinoma in situ: - If a malignant tumor is contained within one area and hasn't spread to the surrounding tissue, the medical term is “carcinoma in situ.” If the tumor has stopped growing, doctors say it is dormant (“dormant cancer cells”). In order to grow, tumors start making their own blood vessels (angiogenesis). The blood vessels supply the tumor with extra oxygen, glucose (sugar) and hormones. As a result, the tumor can grow into surrounding tissue. It is then called invasive cancer. Invasive cancer- Active cancer cells can enter the bloodstream or lymphatic system and travel to other parts of the body. There they start the process of forming a tumor all over again somewhere else (metastatic or secondary cancer).
Epithelial Cells junction
