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What is histology?

The study of microscopic structures of tissues and organs is called histology or microanatomy.


List seven functions performed by epithelial cells.

1. Protects, covers, and lines
2. Acts as interface layer separating and defining the beginning and ending of different types of tissues
3. Filters biochemical substances
4. Absorbs nutrients
5. Provides sensory input
6. Manufactures secretions
7. Manufactures excretions


What four attributes characterize epithelial tissue in general?

1. They are polar. Each cell has an apical surface (faces the lumen) and a basal surface (faces underlying connective tissue).
2. Cells are connected by junctional complexes.
3. They are avascular and rely on underlying connective tissue to provide oxygen and nutrients.
4. Most epithelial cells are innervated (except those in stomach, intestines, and cervix) and provide valuable sensory input.


List four types of cellular junctions. Describe them.

TIGHT JUNCTION; Fusion of outermost layers of plasma membranes of adjoining cells. Found in tissues in which there can be no leaks, such as in the urinary bladder or in the digestive tract.
DESMOSOME: Strong, welded plaque or thickening connecting the membranes of adjacent cells (like velcro). Tough junctions found most commonly in tissues undergoing repeat tension and stretching, such as skin, heart, and uterus.
HEMIDESMOSOME: Look like half a desmosome and link epithelial cells to basement membrane.
GAP JUNCTION: Cells are linked by tubular channel proteins called connexons. Most commonly found in intestinal epithelial cells, the heart, and smooth muscle tissue. Can quickly transport electrical signals from one cell to another and therefore help with the contraction of cardiac and smooth muscle.


How does the basement membrane act as a partial barrier between the epithelial cell and the underlying connective tissue?

Nutrient substances that are absorbed and waste that is excreted by the epithelium diffuse across the basement membrane (or basal lamina) into the blood supply of the connective tissue.
Oxygen and nutrient molecules supplied to epithelial cells from capillaries in the underlying connective tissue also diffuse through the basal lamina.


Why do some epithelial cells have cilia and microvilli? What role do they play? Where are the cells with these specialized surfaces found in the body?

Surface of cell covered with microvilli (called brush border) increases the surface area of cell greatly (by about 20x, thereby increasing its absorptive ability). These cells are usually found in the intestinal and urinary tracts.
Cilia are usually found on cells in respiratory & urogenital tracts (trachea = helps propel mucus and debris; oviduct = help newly expelled ova into the oviduct).


What is a gland?

A cell or group of cells that have the ability to manufacture and discharge secretions.
Typical glandular epithelial cells are recognized by their prominent ER, Golgi, and secretory granules.


How do glands develop embryologically?

Multicellular glands form from an infolding layer of epithelial cells. Initially ducts and tubules are formed that maintain contact with the surface epithelium. Later on, some glands lose the ducts and become separated from the parent epithelial sheet.


Difference and example of endocrine and exocrine glands

ENDOCRINE: Do not have ducts or tubules; their secretions are distributed throughout the body; produce and secrete hormones into bloodstream or lymphatic system. Examples: Pituitary gland in brain and adrenal gland near kidney.
EXOCRINE: Possess ducts, except for goblet cells. More common than endocrine cells. Discharge secretions directly into nearby areas where they may cover cell surfaces or empty into body cavities. Secretions act locally and will normally not enter circulation. Examples: Sweat & salivary glands; liver & pancreas secreting bile and digestive enzymes.


Where are goblet cells found and what type of secretion do they produce?

It's a modified columnar epithelial cell (ductless) and is found among the columnar cells of the respiratory and digestive tracts and in the conjunctiva of the eye.
They secrete mucin, a thick, sticky mixture of glycoproteins and proteoglycans that when mixed with water becomes mucus. Mucus helps protect apical surface of epithelium and entraps microorganisms & foreign particles.


How are multicellular exocrine glands constructed?

Two distinct components: a secretory unit in which secretions are produced by secretory cells and a duct that carries the secretion to the deposition site.


Describe merocrine, apocrine, and holocrine glands? How do they differ from one another?

Merocrine: Majority of glands; package secretions into granules & release them via exocytosis as they are manufactured; secretory cells remain intact. Examples: sweat and salivary glands and pancreas.
Apocrine: Lose the top part of cell, called apex, during secretion. Granules are not released once manufactured; they are stored till apex is full, then cell pinches in two, releasing apex into duct system. Cell repairs itself and repeats process. Examples: Mammary tissue and some sweat glands.
Holocrine: Also store granules until needed, however, entire cell is destroyed upon release. Example: Sebaceous glands.


How are serous and mucous secretions different?

Serous: Watery, contain high concentration of enzymes
Mucous: Thick, viscous, and composed of glycoproteins

Cells producing both are common in digestive and respiratory tracts!


Describe similarities and differences of connective and epithelial tissue!

Similarities: Both can be found in most organs. Blood vessels, such as the coronary arteries, are composed of both.
Differences: Epithelial tissue covers & lines, while connective tissue provides support. Connective tissue is composed primarily of nonliving extracellular matrix; it's vascularized; can exist farther apart than epithelial cells.


Three constituents of connective tissue

Ground substance (liquid to gel to solid)
Fibers (Collagenous, reticular, elastic)
Cells (Fixed and wandering)


Seven functions of connective tissue

1. Metabolic & structural connections between other tissues
2. Forms a protective sheath around organs
3. Helps insulate the body
4. Reserve for energy
5. Provides frame supporting the body
6. Medium transporting substances from one region of body to another
7. Vital role in healing process and control of invading microorgaanisms.


1. What are GAGs and what role do they play in connex tissue?
2. Why do animals with joint injuries sometimes receives dietary supplements of GAGs?

1. Glycosaminoglycans
Ground substance of connex tissue
Most common is hyaluronic acid combined w/2% protein
Medium through which cells exchange nutrients & waste w/bloodstream.
Acts as shock-absorbing cushion
Helps protect more delicate cells it envelops
Effective obstacle for invading microorganisms
2. Since GAGs act as shock-absorbing cushions it can help with achy joints, if they're shock-absorbing material has maybe worn off.


Comparison of collagenous, reticular, and elastic fibers

Collagenous: Strong, thick strands composed of structural protein collagen. Able to resist pulling forces, therefore found in tendons and ligaments. White in color, wavy when not under pressure. Loose variety surround and protect organs; dense are seen in tendons.
Reticular: Composed of collagen, too, but is thin and delicate, branched into networks. Supports highly cellular organs, such endocrine glands, lymph nodes, spleen, bone marrow, and liver. Also found around blood vessels, nerves, muscle fibers, and capillaries.
Elastic: Primarily of protein elastin. Branched and form networks, but lack tensile strength. Are coiled and can stretch like a rubber band. Found in vocal cords, lungs, skin, and walls of blood vessels. Yellow in color.


Fibroblasts, what are they and what role do they have in connex tissue?

Most noteworthy fixed cell
Large, irregularly shaped cell that manufactures and secretes both the fibers and the ground substance characteristic for this matrix.
Can reproduce and are metabolically very active
Each connex tissue is characterized by its predominant fibroblast.
Once cell is mature, the name changes from fibroblast to fibrocyte. Can revert if additional matrix is required later.


Three examples of transient cells. What are their form and function?

Leukocytes, mast cells and macrophages
Leukocytes: White blood cells, found in blood, move into connex tissue in large numbers during infection. Large and round compared to RBC. Engulf and digest invading microbes or manufacture antibodies attaching to microbes to destroy them.
Mast cells: Oval in shape, with large number of dark-staining granules stored in cytoplasm. Granules contain histamine and heparin, which can initiate inflammatory response. Tend to be found near blood vessels.
Macrophages: Massive, irregularly shaped phagocytizing scavenger; may be either fixed or transient. Engulf microbes, dead cells, and debris subsequently digested in the macrophage's lysosomes. Important part of immune system. Different names, depending on tissue: Kupffer cells in liver; microglial cells in brain; histiocytes in loose connex tissue.


Two broad categories of connex tissues

Connective tissue proper
Specialized connective tissue


Components of areolar tissue

Loose array of fibers suspended in gel-like ground substance
Incl. all three types of fibers and many cells, such as macrophages, fibroblasts, mast cells, and some WBCs.


Difference between brown and white fat

White fat: found throughout body, espc. in deep layers of skin. Filled with lipid, organelles and nuclei pushed to side, cell becomes large sphere.
Brown fat: found in newborn animals and in animals that hibernate during winter. Important role in temp regulation, as it produces heat. Nuclei are also eccentrically placed, but lipid is stored in multiple small vesicles. Contains high number of mitochondria. More vascular than white fat


Three subtypes of dense connective tissue

Dense regular (tendons and ligaments)
Dense irregular (Dermis of skin, organ capsules, submucosa of digestive tract)
Elastic (space between vertebrae, walls of arteries, stomach, bronchi, bladder and regions of heart)


Three examples of specialized connex tissue. Similarities & differences to connex tissue proper?

Both provide support and protection. Texture and appearance are different.


Why is cartilage limited in thickness and slow to heal?

Receives its nutrition from surrounding membrane, in order for all chondrocytes to be well nourished the thickness of cartilage is limited.
Cartilage is avascular and therefore very slow to heal.


Three types of cartilage, differences and similarities

Hyaline and elastic both have their fibers suspended in a firm matrix, whereas the matrix of fibrocartilage is less firm. Chondrocytes (or cartilage cells) sit in lacunae for both hyaline and elastic.
Elastic provides more flexibility than hyaline, while both hyaline and fibrocartilage are able to withstand compressive forces.


Bone and blood are so different but both represent types of connex tissue. Why?

Blood is produced in bone marrow.


Two tissue types of membranes

Epithelial and connective


Where are mucous membranes and what is their function?

Line body cavities that are exposed to the outside, such as the anus, mouth and nares. Often contain glands, which secrete protective and lubricating mucus, which decreases friction and assists with passing of food and waste.