Tissues Flashcards
What do tissues contribute to homeostasis?
Individual body cells are specialized for division of labour to maintain homeostasis
So that we can rely on specific tissues for their specific functions; nervous tissue specifically for communcation, muscle tissue specifically for movement …
What are the 4 primary tissue types and their main function(s)?
- Epithelial = covering
- Connective = support
- Muscle = movement
- Nervous = communication
Epithelial tissue = ?
Sheet of cells tha covers a body surface or lines a body cavity, often a single layer of cells
Creates boundaries between liquid, food and other substances enerting the body
2 types of epithelial tissue = ?
- Covering and lining epithelia - lining the trachea, boundary between air in the body lining the bronchi
- Glandular epithelia - sweat glands
List some functions of epithelial tissue
Protection; from outside and inside of the body, can be mechanical, chemical or infectious (against microorganisms) - skin
Absorbtion; break down products of digestion - GI tract
Filtration; filtering the waste from the blood - kidney
Excretion; moving of waste products to be discarded - kidney
Secretion; acid-secretion, secretion of digestive enzymes - glands/GI tract
Sensory reception - taste buds, olfactory membranes
5 structural characteristics of epithelial tissue ?
- Polarity - apical exposed to outside, basial to underlying tissue exhibits apical-basal polarity
- Apical surfaces often specialize having microvilli or cilia
- Because they are single layered, one surface faces up and the other down [facing the lumen into stomach/respiratory system = apical // sitting on supporting basal lamina facing out = basal] - Specialized contacts - tight junctions and desmosomes
- Because they need to be very strong so as to not let things like stomach acid leak
- Help epithelial cells to remain as a function layer lining the stomach as we digest food - Supported by connective tissue - basement membrane is composed of basal lamina (underlying supportive sheet of primarily glycoproteins) sitting on top of a reticular lamina (primarily collagen fibers)
- Important to provide attachment sites and physical support of epithelial cells to CT and for any necessary cell movement to retain a continuous structure as cells are being made - Innervated by avascular - will not come into contact with blood vessels therefore they rely on diffusion of oxygen and glucose that are within the underlying tissue
- Innervated = supplied by nerve fibers
- Avascular = contains no blood vessels - Regeneration - high regenerative capacity
- Can replace themselves during cell mitosis
- Because epithelial tissue ften creates boundaries where the body is vulnerable to lots of physical/chemical wear and tear they are easily destroyed
What is a tight junction vs a desmosome
- Tight junctions = important in preventing fluids from leaking
- Desmosomes = allow for plasma membranes of adjacent cells to firmly attach to each other with a slight space
What are the 2 classification criteria for epithelial tissue
- Cell shape = squamous, cuboidal, columnar
- Number of layers = simple (single), stratified (multiple)
Simple epithelia is used for absorption, secretion and filtration.
What are the characteristics and functions of;
1. Simple squamous?
2, Simple Cuboidal?
3. Simple Columnar?
- Thin and permeable; filtration and diffusion (found in endothelium, kidney, lungs)
- Thicker to be more functional; secretion and absorption (found in kidneys, tubules, small glands)
- Taller with lots of microvilli to increase SA for transporters, lots of area for vesicles; secretion and absorption (GI tract)
What is pseudostratified columnar epithelia?
Where can it be found?
Ciliated
Looks stratified but is not
Single layer - found in respiratory tract where cilia and mucus secretion are local specializations but have te appearance of stratified.
What is stratified squamous ?
What is the most widespread example found in the body?
Protective role; basal cells and most commonly cuboidal constantly undergo mitosis to keep regenerating below layers
Most widespread example is our skin
Apical layers are constantly sloshed off (replaced)
The furthest cells from the deepest layer contain less blood vessels - they provide physical protection but cells are essentially dead and no longer viable for mitosis
What is transitional epithelia? Where can it be found?
Stratified with mix of cuboidal and squamous
Found lining the bladder - an organ that has to fill (fills with urine and empties quite quickly , constantly changes in sectioned appearance based on filling level of urine)
Basal layers aer cuboidal and apical layers become increasingly flattened and squamous like.
Difference between endocrine and exocrine glands?
Exocrine = release of products through external secretion; mucuous, sweat, oil, salivary glands, liver, pancreas
Endocrine = release of products through internal secretion; ductless - products are hormones
Both can be unicellular or multicellular
What is a goblet cell?
Unicellular exocrine gland
Has no ducts
More apical areas accumulate a product forming a goblet shape due to swelling
What are the 3 types of secretory methods? Give a brief description of each
- Merocrine = exocytosis
- Most common type
- Constantly producing products and packing them in vesicles , vesicles are then released into lumen to move into duct towards target
- Ex. Pancrease, salivary glands, most sweat glands - Holocrine = cell ruptures
- Only oil producing sebaceous glands
- cells ruptured are sacrificed - Apocrine = cell apex pinches off wih secretory product and repairs itself
- Only apex of cell ruptures off releasing liquid rich products
