Chapter 4- Tissues Flashcards
Tissues
any grouping of cells that are similar in structure and carry out a similar or common function in the body.
Benefits of tissues
cellular specialization allows the body to carry out complicated functions
Drawback of tissues
destruction of one cell type could be catastrophic. A disease could enter the body to target the cells of one tissue. If a tissue is destroyed, there’s not much you can do
What are the 4 primary types of tissues?
- Nervous tissue- control tissue
- Muscle tissue- movement tissue
- Epithelial tissue- covering tissue
- Connective tissue- support tissue
Muscle tissue
Movement tissue- innervated, well vascularized
What must occur for muscle contraction?
Microfilaments actin and myosin allow for muscle contraction/movement- they do this by physically interacting with each other- this must occur for contraction
What are the 2 types of muscle tissue?
- Skeletal
- Cardiac
- Smooth
Skeletal muscle
voluntary control with striations. Attaches to bones and uses the bones to produce movement. A single muscle cell has multiple nuclei.
Skeletal muscle uses the bones like levers to move
cardiac muscle
involuntary control with striations, found only in the walls of the heart
Uninucleate- one nucleus per cell
Smooth muscle
involuntary control without striations. Found in the walls of hollow organs (not including the heart) to squeeze substances through the organ.
Also uninucleate
Epithelial tissue
The type of tissue that covers body surfaces, lines cavities, and forms glands
Epithelial tissue functions (2)
- Boundary forming, separates one area/region of the body from another
- Substances received or given off by the body must pass through the epithelium
What are the 2 forms of epithelial tissue
- Covering epithelium
2. Glandular epithelium
Covering epithelium
outer layer of skin, dips into and lines the urogenital, digestive, and respiratory systems. Covers the wall/organs of closed body cavities
Glandular epithelium
makes up the glands of the body
Apical basal polarity
Epithelial tissue has 2 surfaces that differ in structure in function. The apical surface and the basal surface
Apical surface
the exposed side of epithelial tissue- faces the lumen or outside of the body. Most have microvilli, others have cilia. The skin you can see is the apical surface of the epithelial layer
Lumen
an empty space through which something travels
Microvilli function
used to increase surface area, like the epithelia lining the intestines and kidney tubules
Cilia function
create current to propel substances through open space, like those lining the trachea
Basal surface
attaches to connective tissue
Has attached basal lamina- filters what can/can’t enter the epithelial layer. Also acts as a scaffolding along which epithelial cells can migrate to repair a wound.
Basal lamina
The basal lamina is a noncellular and adhesive sheet attached to the basal surface of epithelial tissue that consists mostly of glycoproteins secreted by the epithelial cells and some collagen fibers. Filters what can and can’t enter the cell, is one of the layers in the basement membrane
How are epithelial cells held together?
Joined by tight junctions and desmosomes
Epithelial tissue forms sheets- prevents passage of material between cells, resists mechanical stress
Basement membrane
lies between epithelial layer and connective tissue
Functions- reinforces epithelial sheet to resist stretching/tearing, defines epithelial boundary. Reinforces the desmosomes to strengthen the attachment. It has 2 layers: the basal lamina and the reticular lamina.
Semipermeable to certain substances- this is necessary because nutrients must diffuse through to the epithelium
Reticular lamina
contains fibers that belong to connective tissue. Deep to the basal lamina
What is an important characteristic of
cancerous epithelial cells?
An important characteristic of cancerous epithelial cells is their failure to respect the basement membrane boundary, which they penetrate to invade the tissues underneath
Does the epithelium have blood vessels?
No, it is avascular. It receives nourishment by diffusion and disposes of waste the same way
Is the epithelium innervated?
Yes
Is the epithelium able to regenerate?
Yes, there is a high capacity for regeneration.
Epithelial layers are subject to high levels of abrasion and hostile conditions (internal and external). For example, the stomach has a low pH, so the epithelia is constantly being destroyed
What begins when the epithelium is damaged?
When epithelial tissue is damaged, cell reproduction begins. If dead cells are not replaced, you lose the function
How many parts does the name of epithelial tissue have?
Two parts, like a first and last name. Thickness comes first, then the shape of the cells
Simple epithelia
Refers to the thickness of the tissue- contains only 1 layer of cells. Usually seen where absorption, secretion, and filtration are desired and a thin barrier is necessary, especially in areas where quick diffusion is needed, like the alveoli. These cells usually have the same shape.
Stratified epithelia
Refers to the thickness of the tissue- contains 2+ layers of cells. Usually seen in areas subjected to high levels of abrasion/contact (chemical or mechanical stress) like the skin surface and the inside of the mouth. These cells can have different shapes and are therefore named according to the shape of the cells in their apical layer
Squamous epithelia
The cells are flattened/squashed, the nucleus is flattened as well
Cuboidal epithelia
The cells are cube shaped and the nucleus is spherical
Columnar epithelia
The cells are tall and column shaped, the nucleus is elongated and closer to the cell base
Why isn’t simple epithelia used for protection?
There’s only one layer of cells
Simple squamous epithelium
Resemble a tiled floor, thin and permeable- includes the mesothelium and endothelium
Simple squamous epithelium function
absorption, secretion, filtration- part of the filtration membrane in the kidneys that filters blood to make urine.
Found in the lungs- must bring in oxygen at a regular rate and dispose of CO2 quickly- a thin layer allows for quick diffusion.
Mesothelium
A type of simple squamous epithelium, epithelium of the serous membranes that cover the ventral body cavity and organs
Endothelium
A type of simple squamous epithelium, forms slick/slippery linings. Lymphatic vessels and cardiovascular system- promotes the flow of the circulating material. Capillaries consist exclusively of epithelium- thinness encourages efficient exchange of nutrients and wastes between the bloodstream and surrounding tissue cells
Simple cuboidal epithelium
Single layer of cells as tall as they are wide
Nuclei are spherical and stain darkly
Locations- kidney tubules, ovary surface, some small glands
Simple cuboidal epithelium function
secretion and absorption
Simple columnar epithelium
Single layer of tall, closely packed cells. Many have microvilli on the apical surface of absorptive cells and tubular glands made primarily of cells that secrete mucus containing intestinal juice. Some have cilia that help move substances or cells through an internal passageway
Simple columnar epithelium functions
absorption and secretion
Simple columnar epithelium locations
digestive tract, gallbladder, small bronchi, uterine tubes, parts of uterus
Pseudostratified columnar epithelium
“False” stratified cell nuclei lie at different levels- the nuclei are displaced so it looks like there are multiple layers of cells.
Only some cells stretch from the apical surface to the basal surface. “Short” cells give rise to “tall” cells (the cells are different sizes). Shorter cells attach to the basement membrane
If tall cells are killed off, the shorter cells will replace them to prevent a loss of function.
Pseudostratified columnar epithelium function
secretion and absorption. Many types are ciliated.
Pseudostratified columnar epithelium locations
respiratory tract (cilia propels sheets of dust trapping mucus away from the lungs), male ducts, ducts of large glands The respiratory tract has a ciliated version with mucus containing goblet cells
How does stratified epithelia regenerate?
regenerate from the bottom up, the cells closest to the basement membrane divide mitotically to replace cells being rubbed off on the top
Stratified squamous epithelia function?
Thick, forms a good protective barrier
Why are the apical cells in stratified squamous epithelia poorly nourished?
the epithelium depends on diffusion for nutrients so apical cells in thicker tissues might actually be dead
Where is stratified squamous epithelia found in general?
Forms the external surface of the skin and extends a short distance into every body opening that is directly continuous with the skin
Where is the stratified squamous epithelia keratinized?
The outer layer (epidermis) of the skin is keratinized (its surface cells contain the tough protective protein keratin). The other stratified squamous epithelia of the body are non keratinized.
Stratified cuboidal epithelia
rare, usually consists of just 2 layers
Locations- mostly ducts of sweat glands and mammary glands, has 2 layers of cuboidal cells. Layers are mostly too thick to function
Stratified columnar epithelia
also rare, only apical cells are columnar
Locations- male urethra, part of pharynx, some ducts. Occurs at transition areas or junctions between two layers of epithelia
Transitional epithelium
Basal cells are mostly cuboidal/columnar, apical cell shape varies.
Typical of urinary organs- constantly being stretched- allows for greater flow of urine to flow through a tubelike organ
As the organs are stretched, the cells will look squamous in appearance
Cells will change shape as bladder fills/empties
Glands
one or more cells that produce and secrete a particular product (called a secretion)
Secretion
an aqueous fluid that contains proteins. Manufactured from the blood supply. Secretion is an active process- glandular cells obtain needed substances from the blood and transform them chemically into a product that is then discharged from the cell
What makes secretions different from each other?
The type of protein found in them makes one different from another
How are glands classified?
- Location of release- endocrine vs exocrine
2. Number of cells that makes up gland- unicellular vs multicellular
Endocrine glands
ductless glands. They release their secretion directly into the bloodstream (internally). They are not epithelial in nature and are multicellular. They produce hormones that are released to extracellular space via exocytosis
What types of organs/systems can endocrine glands form?
Can form
- Compact multicellular organs (cells are clumped together into a common structure) or
- Diffuse endocrine systems (the cells making up a gland are spread out).
Hormones
chemical messengers- target specific organs to respond in a specific way. They will go from the extracellular space to the blood or lymphatic fluid and travel to specific target organs.
Exocrine glands
secrete products onto surfaces/into cavities (externally secreting). Epithelial in nature, have a duct- a tube that empties the secretion onto a surface or into a body cavity- not into the bloodstream. Can be unicellular or multicellular.
Unicellular exocrine glands
release product onto surface via exocytosis. Individual cells that are scattered through epithelia with cells of different functions
Tend to be embedded in surrounding epithelial tissue
Example- goblet cells (digestive system), mucous cells (respiratory system)
Both produce and secrete mucin- dissolves in water to create mucus
Multicellular exocrine glands
release product onto surface via a duct- more structurally complex. Multicellular epithelial glands form by invagination (inward growth) of an epithelial sheet into the underlying connective tissue. These glands can be classified by structure (simple or compund) and mode of secretion.
Exocrine gland examples (5)
liver, pancreas (endocrine and exocrine), salivary glands, sweat glands, oil glands
What are the 2 parts of the multicellular exocrine gland?
- Duct- derived from epithelium. It’s just a passageway
2. Acinus- secretory unit made up of cells that produce and secrete product
How are multicellular exocrine glands classified based on structure?
- Simple- unbranched duct- one straight tube into secretory unit (acinus) or
- Compound- branched duct(s)
How are multicellular exocrine glands classified based on mode of secretion?
- Merocrine
- Holocrine
- Apocrine