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covers the body surfaces, lines the body cavities, and forms the majority of glands.
A minimal amount of extracellular matrix separates the cells in an epithelium.
apical surface is exposed either to the external environment or to some internal body space and may have microvilli or cilia. Basal surface where the epithelium is attached to the underlying connective tissue
this type of tissue lacks blood, so in order to obtain nutrients either directly from the apical surface or from diffusion across the basal surface
epithelial tissues protect both external and internal surfaces from dehydration, abrasion, and destruction by physical, chemical, and biological agents.
epithelial cells of "gatekeepers" usually exhibit a range of permeability; it may be relatively impermeable to some substances, while promoting and assisting the passage of other molecules.
individual glands cells may be scattered among other cell types in the epithelium, or a large group of gland cells may form either an exocrine gland or an endocrine gland that produces specific secretions.
the sensory endings-and those in the underlying connective tissue-continuously supply information to the nervous system concerning touch, pressure, temperature, and pain.
- is one cell layer thick, and all of the epithelial cells are in direct contact with the basement membrane.
- It can be found in areas where stress in minimal and where filtration, absorption, or secretion is the primary function
- Examples of locations the lining of the air sacs of the lung, the intestines, and blood vessels
- contains two or more layer of epithelial cells. It resembles a brick wall, where the bricks in contract with the ground represent the basal layer and the bricks at the top of the wall represent the apical (superficial layer).
- It is found in areas likely to be subjected to abrasive activities or mechanical stresses, as multiple layers of cells are better to able to resists the wear and tear.
- Examples skin, internal lining of the pharynx, and esophagus.
- looks layered because the cells' nuclei are distributed at different levels between the apical and basal surfaces.
- Examples, simple epithelium, because cells are attached to the basement membrane
are flat, wide, and somewhat irregular in shape and are arranged like flattened floor tiles, and the nucleus is somewhat flattened.
are about as tall as they are wide, the cells do not resemble perfect cubes because their edges are somewhat rounded.
are slender and taller than they are wide. The cell nucleus is oval and usually oriented lengthwise and in the basal region of the cell
these cells can readily change their shape, depending upon how stretched the epithelium becomes. They occur where the epithelium cycles between distended and relaxed states, such as in the lining of the bladder, which fills with urine and is later emptied.
Simple squamous epithelium
- is the thinnest possible barrier, because it consists of a single layer of flattened cells.
- -This epithelium is extremely delicate and highly specialized to allow rapid movement of molecules across its surface by diffusion, osmosis, or filtration.
- -It forms the lining of the air sacs of the lung, where this thin epithelium is well suited for the exchange or oxygen and carbon dioxide between the blood and the inhaled air
- Example- lining of the lumen of blood vessels and lymph vessel walls
is the name given to the simple squamous epithelium that forms the serous membrane of the body cavities.
Simple cuboidal epithelium
- contains uniformly shaped cells that are about as tall as they are wide and their main function is to absorb fluids and other materials across the apical surface, and to secrete specific molecules.
- It forms the walls of kidney tubules, where it participates in the reabsorption of nutrients, ions, and water that is filtered out of the body.
- Examples- surface of the ovary and lines the follicles of the thyroid gland.
Simple columnar epithelium
is composed of a single layer of cells that are taller than they are wide and it is ideal for both secretory and absorptive functions it. It has two forms, one with cilia and one covered with cilia.
Pseudostratified columnar epithelium
it consists of multiple layers of cells and is also either ciliated or nonciliated.
Stratified squamous epithelium
is designed to protect against abrasion and friction and it has multiple cell layers, and only the deepest layer of cells is in direct contact with the basement membrane. It protects underlying tissues from damage due to activities that cause abrasion and friction. It can be either nonkeratinized or keratinized.
Stratified cuboidal epithelium
contains two or more layers of cells, and the superficial cells trend to be cuboidal in shape. This tissue forms the walls of the ducts of most exocrine glands, such as the ducts of the sweat glands in the skin. and it can also strengthens the walls of the gland ducts and some sections of the male urethra
Stratified columnar epithelium
is relatively rare in the body and consist of two or more layers of cells, but only the cells at the apical surface are columnar in shape. (protects and secretes and is found in the large ducts of salivary glands and in the membranous segment of the male urethra
is limited to the urinary tract (urinary bladder, ureters, and part of the urethra). The shape varies, if it is basal the cells appear cuboidal or polyhedral and the apical cells are large and round.
are immature, undifferentiated cells that are able to divide into two cells, the first of which is another stem cell, and the other is a cell that could differentiate into a specialized, mature cell with a unique function.
Most differentiated to least differentiated
Unipotent, multipotent, pluripotent, and totipotent
are either individual cells or multicellular organs composed predominantly of epithelial tissue and secrete substances either for use elsewhere in the body or for elimination from the body.
lack ducts and secrete their products, called hormones, directly into the interstitial fluid and blood.
- these glands usually maintain their connection with the epithelial surface by means of a duct (an epithelium-lined tube through which the glands sections are discharged onto the epithelial surface.
- Examples- sweat glands, mammary glands, and salivary glands.
Unicellular exocrine glands
typically do not contain a duct, and they are located close to the surface of the epithelium in which they reside. (goblet cell)
Multicellular exocrine glands
contain numerous cells that work together to produce a secretion.
if the secretory portion and the duct are the uniform diameter; this forms an expanded sac, the gland is called acinar. Glands with both tubules and acini are called tubuloacinar glands.
package their secretions into secretory vesicles and release the secretions by exocytosis. (lacrimal glands; salivary glands; some sweat glands; the exocrine glands of the pancreas; and the gastric glands of the stomach)
produce their secretion by the apical membrane around a portion of secretion. Glandular cells repair the damage and then continue to produce new secretions in the same manner. (Mammary glands and some sweat glands in the axillary and pubic region)
are formed from cells that accumulate a product; the entire cell then disintegrates. (oil producing glands in the skin)
is the most diverse, abundant, and widely distributed of the tissues and is designed to support, protect, and bind organs. (tendons, and ligaments, body fat, cartilage, bone, and blood). The functions are physical protection, support, and structural, framework, binding of structures, storage, transport, and immune protection
are stationary cells that are permanently housed within the connective tissue. (fibroblasts, adipocytes, mesenchymal cells, fixed macrophages)
continuously move throughout the connective issue proper and are components of the immune system. (mast cells, plasma cells, free macrophages, other leukocytes)
Embryonic connective tissue
- Mesenchyme-it begins to differentiate in the developing fetus and it forms the connective tissues that ultimately are found in the adult body.
- Mucous connective tissue- it is immature protein fibers and is located within the umbilical cord only
Loose connective tissue
they can act as the bodys packing material by supporting and surrounding structures and organs. There are three types adipose, areolar, and reticular.
Dense connective tissue
is composed primarily of protein fibers and has proportionately less ground substance than loose connective tissue. There are three types dense regular tissue, dense irregular connective tissue, and elastic connective tissue.
has a firm semisolid extracellular matrix that contains variable amounts of collagen and elastic protein fibers. Most is surrounded by a dense irregular connective tissue covering called perichondrium which has two parts an outer fibrous layer and an inner cellular layer. (tip of the nose or the auricle of the ear)
this is called osseous connective tissue and makes up the mass of most of the structure referred to as bone. The extracellular matrix of bone consists of organic components and inorganic components composed of the mixture of calcium salts, primarily calcium phosphate.
almost all of the external bone surface, except of for those surfaces that participate in joints, are covered by a dense irregular connective tissue.
appears completely solid but is in fact perforated by a numer of neurovascular canals. It is formed from cylindrical structures called osteons, which display concentric rings of bone connective tissue called lamellae.
- is located within the interior of a bone, and it
- contains a latticework structure of bone connective tissue that is very strong,
- yet light weight. Houses hemopoietic cells, which form a type of reticular connective tissue that makes blood cells.
Blood (fluid connective tissue)
composed of formed elements, which includes cells, both erythrocytes and leukocytes, and cellular fragments called platelets. It has numerous functions such as, erythrocytes transport respiratory gases, while the leukocytes mount an immune response. Platelets and the protein fibers help clot the blood. Plasma transports nutrients, wastes, and hormones throughout the body.
is derived from blood plasma and ultimately is returned to the bloodstream
are stem cells derived from mesenchyme. They are derived through the process of mitosis; another stem cell is produced along with a “committed cell” that matures to become an osteoblast.
are formed from Osteoprogenitor stem cells. These are often positioned side by side on bone surfaces. Active ones exhibit a somewhat cuboidal shape and have abundant rough ER and Golgi apparatus. It performs the important function of synthesizing and secreting the initial semisolid organic form of bone matrix called osteoid.
are mature bone cells derived from osteoblasts that have lost their bone-forming ability when enveloped by calcified osteoid. Connects between the original neighboring osteoblasts are maintained as they become osteocytes. Osteocytes maintain the bone matrix and detect mechanical stress on a bone
are large, multinuclear, phagocytic cells. They are derived from fused bone marrow cells similar to those that produce monocytes. An osteoclast is often located within or adjacent to a depression or pit on the bone surface which is called a resorption lacuna. They are also involved in breaking down bone in an important process called bone resorption
is composed of specialized cells that can contract when stimulated by the nervous system. When this tissue contracts, it produces movement, such as the voluntary motion of body parts, contraction of the heart, and propulsion of materials through the digestive and urinary tracts
Skeletal muscle tissue
is primarily responsible for movement of the skeleton and is composed of long cylindrical cells called skeletal muscle fibers. They are considered voluntary.
Cardiac muscle tissue
is confined to the thick middle layer of the heart wall, called the myocardium; it is responsible for the contraction of the heart to pump blood. This type of tissue is involuntary because it does not require nervous system activity to start a contraction.
Smooth muscle tissue
these cells are fusiform, which means they are thick in the middle and tapered at their ends. It is found in the walls of most viscera, such as the intestines, stomach, airways, urinary bladder, uterus, and blood vessels. It is considered involuntary
is located within the brain, spinal cord, and the nerves that travers through the body. The major functions are neurons, glial cells, cell body, dendrites, and axons.
lines body cavities that typically do not open to the external environment. The membrane is composed of a simple squamous epithelium called mesothelium. It produces a thin, watery serous fluid and examples of this are part of the pericardium, the pleura, and the peritoneum.
Major functions of the Integumentary system
- Provides protection
- regulates body temperature
- synthesizes vitamin D
- Prevents water loss
- Cite of cutaneous receptors
it is the epithelium of the integument and is a keritinized stratified squamous epithelium.
Most superficial layer of epidermis; 20-30 layers of dead, flattened, anucleate, keratin-filled keratinocytes
2-3 layers of anucleate, dead cells; seen only in thick skin
3-5 layers of keratinocytes with distinct granules in cytoplasm; keratinization begins in this layer
Several layers of keratinocytes with distinct granules in cytoplasm; epidermal dendritic cells present
- Deepest, single layer of cuboidal to low columnar cells in contact with basement membrane; mitosis occurs here; contains
- keratinocytes, melanocytes, and a tactile cells
- is deep to the epidermis and ranges in thickness from 0.5 to 3.0mm. this layer of the integument is composed of connective tissue proper, and contains primarily collagen fibers, although both elastic and
- reticular fibers also are found within the dermis. (Blood vessels, sweat glands, sebaceous glands, hair follicles, nail roots, sensory nerve endings, and arrector pili).
More superficial layer of dermis; composed of areolar connective tissue; forms dermal papillae
- Deeper layer of dermis; dense irregular connective tissue surrounding hair follicles, sebaceous glands and sweat glands, nerves,
- and blood vessels.
is an oxygen-binding protein present in red blood cells. It exhibits a bright red color upon binding oxygen, thus giving blood vessels in the dermis a reddish tint that is seen most easily in lightly pigmented individuals. (determine skin color)
- is a pigment produced and stored in melanocytes, and occurs in a variety of black, brown, tan, and yellow-brown shades. It is transferred in vesicles from
- melanocytes to keratinocytes are displaced toward the stratum corneum, melanocyte activity affects the color of the entire epidermis. (determine skin color)
is a yellow-orange pigment that is acquired from various yellow-orange vegetables, such as carrots, corn, and squashes. Usually it accumulates inside keratinocytes of the stratum corneum and in the subcutaneous fat. (determine skin color)
Merocrine sweat glands
- are the most numerous and widely distributed sweat glands. There are between 3-4 million Merocrine sweat glands in the adult integument. Sweat is the clear secretion that is released by exocytosis which consists of approximately 99% water and 1% other chemicals that include electrolytes, metabolites, and waste
- products. The major function is thermoregulation- which is the regulation of body temperature by evaporation of fluid from the skin.
Apocrine sweat glands
- are coilded, tubular glands that release their secretion into hair follicles in the axillae, around the nipples, in the pubic region,
- and in the anal region. The secretion they produce is viscous and cloudy, and it contains both proteins and lipids that are acted upon by bacteria to produce a distinct, noticeable odor
- are Holocrine glands that produce an oily, waxy secretion called sebum that is usually discharged into a hair follicle and onto the hair itself. It acts as a lubricant to keep the skin and hair from becoming dry, brittle, and cracked. Secretion of sebum is stimulated by hormones, especially androgens and are inactive during childhood, but are activated
- during puberty
- are modified apocrine sweat glands located only in the external acoustic meatus (ear canal), where their secretion from a waterproof earwax called cerumen. They help trap foreign particles or small insects and
- keeps them from reaching the eardrum
of the breasts are modified apocrine sweat glands. Both males and females have mammary glands, but these glands only become functional in pregnant and lactating females, when they produce milk, a secretion that nourishes offspring