Flashcards in Epithelial tissues & glands Deck (30):
What is a gland?
Epithelial cell or collection of cells (epithelium invagination) specialised for secretion.
According to what can glands be classified?
1. Destination of secretion
2. Gland structure
3. Nature of secretion
4. Method of discharge
How are glands classified according to destination of secretion?
1. Exocrine glands: have ducts to carry secretions to surface (e.g. Goblet cells secrete mucus from epithelium of upper respiratory tract)
2. Endocrine glands: are 'ductless' but secrete directly into the bloodstream
How are glands classified according to structure?
- Can be: unicellular (e.g. Goblet cell) or multicellular.
- Can be: tubular, acinar or alveolar.
- Can be: coiled or branched.
How can glands be classified according to method of secretion?
1. Merocrine = exocytosis (vast majority of glands)
2. Apocrine = secreted droplets covered by plasmalemma (e.g. Mammary gland - fat droplets in milk)
3. Holocrine = whole cell breaks down, e.g. Sebaceous gland of skin undergoes holocrine secretion to fill hair follicle with sebum.
What are the 3 major salivary glands?
Give an example of an organ that is both an exocrine and an endocrine gland.
- endocrine cells in pancreatic ilets secrete insulin
- exocrine cells in pancreatic acini secrete alkali and enzymes
How does CF affect glands of patients?
- Absence of CFTR in apical membrane of epithelial cells lining sweat gland ducts - poor reabsorption of chloride ions - sweat is rich in chloride and sodium ions (sweat testing for abnormally salty sweat).
- Exocrine pancreas secretions thickened as contain too little water
1) blocking of the ducts - exocrine pancreas painfully inflamed (pancreatitis) and fibrotic.
2) gut receives insufficient pancreatic digestive enzyme - malabsorption.
Skin is composed of which type of epithelium?
- Stratified squamous epithelium (also found in oral cavity)
What is the function of skin?
- Protects against abrasion/physical trauma and pathogens
- Prevents water loss
- Shields against UV light damage
Describe the layers of the skin epidermis.
- Stratum corneum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
Which cells are found in the skin epidermis?
- Keratinocytes: synthesise keratins (heterodimeric fibrous proteins) which contribute to strength of epidermis).
- Keratinocyte mitosis occurs mainly in basal layer. Daughter keratinocytes then move upwards to form stratum spinosum, where terminal differentiation begins and cells lose their ability to divide.
- Stratum corneum = layer of dead keratinocytes.
Apart from keratinocytes, which cells are found in the epidermis?
- Melanocytes: dendritic cells of neural crest origin which occur at intervals along the basal layer of the epidermis. Produce melanin pigment.
- Langerhans cells: dendritic cells of BM origin, scattered throughout prickle cell layer. Highly specialised capacity to present antigen to T lymphocytes. Mediate immune reactions, e.g. Allergic contact dermatitis.
What is transitional epithelium and where is it found?
- Found in bladder.
- Specialised type of stratified epithelium that can stretch without breaking - from stratified cuboidal (empty bladder) to stratified squamous (full bladder)
What are the functions of transitional (urinary) epithelium?
- Protection of underlying tissue from toxic chemicals
What are epithelia?
Sheets of contiguous cells, of varied embryonic origin, that cover the external surface of the body (i.e. Skin) and line internal surfaces (e.g. GI, GU & resp tracts, blood & lymphatic vessels, pericardial & pleural sacs and peritoneum).
What is the basement membrane?
- Thin, flexible, acellular layer which lies between epithelial cells and the subtending connective tissue.
- Consists of a basal lamina laid down by epithelial cells. Thickness can be augmented by a variably thick layer of reticular fibrils (type 3 collagen), elaborated by the subtending connective tissue.
What is the function of the basement membrane?
1) Strong flexible layer to which epithelial cells adhere
2) Cellular and molecular filter
What is the endothelium?
Simple squamous epithelium lining blood and lymph vessels.
What is mesothelium?
Simple squamous epithelium lining body cavities - pericardium, pleura, peritoneum.
Where can simple squamous epithelium be found?
- Lining of blood and lymph vessels (endothelium)
- Lining of body cavities - pericardium, pleura, peritoneum (mesothelium)
- Pulmonary alveoli (gas exchange epithelium)
- Bowman's capsule and Loop of Henle (kidney)
What are the functions of simple squamous epithelium?
(Good Nifflers Like Bright Accessories)
- Gas and Nutrient exchange (endothelium and alveoli)
- Lubrication (pericardium, pleura, peritoneum)
- Barrier (Bowman's capsule)
- Active transport by pinocytosis (endo- and mesothelium)
Where is simple cuboidal epithelium located and what is its function?
- Thyroid follicles - hormone synthesis, storage & mobilisation
- Small ducts of many exocrine glands - absorption & conduit
- Surface of ovary - barrier/covering
- Kidney tubules - absorption & secretion
Where is simple columnar epithelium found and what is its functions?
- Stomach lining & gastric glands - secretion
- Small intestine & colon - absorption, secretion & lubrication
- Gallbladder - absorption
- Oviducts - transport (cells are ciliated), uterus
Where is pseudostratified epithelium found?
- Lining of conducting portion of respiratory system - nasal cavity, trachea & bronchi
What are the functions of pseudostratified epithelium?
- Secretion, e.g. Of mucus by Goblet cells
- Particle trapping and removal (are ciliated)
Where can non-keratinised stratified squamous epithelium be found and what is the functions of this.
- Located e.g.
- Oral cavity
- Surface of cornea and inner surface of eyelid
- Protection against abrasion
- Reduced water loss but remains moist
What is the difference between mucous and serous membranes?
- Mucous membranes: line certain internal tubes which open to the exterior, i.e. The digestive, respiratory and urinary tracts. These mucosae bear mucus-secreting cells to varying degrees.
- Serous membranes: thin, two-part membranes which line certain closed body cavities and envelop the viscera. Line the:
- peritoneum (envelops many abdominal organs)
- pleural sacs (envelop the lungs)
- pericardial sac (envelops the heart)
Secrete a lubricating fluid which promotes relatively friction-free movement of the structures they surround.
What is a mucous membrane composed of?
- An epithelium (type depends on site) lining the lumen of the tube.
- An adjacent layer of connective tissue (lamina propria).
- In the alimentary tract, a 3rd layer consisting of smooth muscle cells (muscularis mucosae).