Welcome to lab classes in basic histology. Introducing lab class (in spanish)

The aim of these lab classes is to provide students with educational resources to acquire basic practical skills of each subject, recognize, locate and describe cell types and basic tissues.

Each of these practical sessions are structured around three main elements:
- Definition of learning objectives.
- Description of basic tissues and their cell types.
- Exercices location of cell types and basic tissues in virtual slides.

LEARNING OBJECTIVES
- Distinguish between endocrine glands and exocrine gland.
- Identify mucose glands.
- Identify serose glands.
- Identify seromucose glands.
- Identify the goblet cells.
- Identify glands according secretion type.
- Identify glands according secretory duct.

MAIN FEATURES EPITHELIAL GLANDS TISSUE
Epithelial gland tissue are composed of specialized cells to secrete molecules that are usually stored in small membrane-coated vesicles called secretory granules.

Glandular epithelial cells can synthesize, store and secrete proteins (eg. pancreas), lipids (eg. the adrenal glands and sebaceous glands) or complex carbohydrates and proteins (eg salivary glands). The cells of some glands show a low synthetic activity (sweat glands) and preferably secrete water and electrolytes from the blood transferred within gland.

Epithelial glands can be classified according to several criteria. Unicellular glands consist of large secretory cells isolated while multicellular glands present groups of cells. The classic unicellular gland is the goblet cell in the lining of the intestine or respiratory tract. The term "gland", but is used to designate large aggregates of secretory epithelial cells, as in the case of salivary glands and pancreas.

While the exocrine glands Compound tubular gland maintain their connection with the epithelial surface due to secretory ducts, the endocrine glands Structure of Thyroid follicles have lost their epithelial surface connection, which they are formed during fetal life. These glands flow into blood vessels directly and secretion product are transported around the body through the bloodstream. Multicellular glands, both exocrine and endocrine also present a capsule of connective tissue and sometimes divide the gland into lobes. These lobes can be subdivided, and thus the connective tissue separates and unites all glandular components.

TYPES OF SECRETION
On the basis of secretion mechanism, exocrine glands can be classified as mucus glands, with a secretion product rich in glycoproteins; serous glands, a protein-rich secretion; or mixed or seromucouses glands, which contain a mixture of both types of secretion.

SEROUS SECRETION Serose secretory cells
The serous-secreting cells have a large spherical nucleus, a basal region in wich the rough endoplasmic reticulum predominates, and an apical region with red-stained zymogen granules.
Zymogen granules represent secretory vesicles containing enzyme precursor.

MUCOUS SECRETION Mucose secretory cells
The mucus-secretory glands, which usually appear pale because of the high content of mucus-containing secretory vesicles. The nuclei generally lie flattened against the basal portion if the secretory cell. The secretory content can be demonstrated by the PAS reaction, which stains glycoproteins. Myoepithelial cells are also present around the mucouse secretory portion.

SEROMUCOUS SECRETION Types of secretion
These glands consist of both serous cells and mucous cells that produce a secretion seromucous secretion delivered into the same lumen. Mixed secretory units are made up of mucous cells and a small cap of serous cells on one side. The cap is called the serous demilune because of its crescent moon shape. Surrounding each secretory unit and the initial portion of the secretory duct are the myoepithelial cells. Myoepithelial cells are placed between the secretory cells and the basal lamina and their long and branched cytoplasmatic processes form a loose basket. Their function is to contract and squeeze the secretion out of the secretory portion and along the duct system.

MECHANISMS OF SECRETION
Furthermore, exocrine glands can also be classified according to the mechanism of secretion, finding merocrine glands, apocrine and holocrine glands.

MEROCRINE GLANDS Merocrine secretion
In merocrine secretion glands, the secretory vesicles approaches the apical domain of an epithelial cell. The vesicular membrane fuses with the plasma membrane to releases its content into the extracellular space. The fused plasma membrane can be taken back into the cell by endocytosis and recycled for further use by secretory vesicles.

APOCRINE GLANDS
In apocrine secretion glands, some of the apical cytoplasm is pinched off with the contained secretion. Mammary gland secretes milk lipids by apocrine secretion and milk protein casein by merocrine secretion.

HOLOCRINE GLANDS
In holocrine secretion glands, the cell produces and accumulates a secretory product in the cytoplasm, such as sebum in sebaceous glands and then disintegrates to release the secretory material.

TYPE OF SECRETORY DUCT
Another nomenclature used to classify exocrine glands is based on the secretion duct morphology.

UNICELLULAR GLANDS
- Goblet cells Goblet cells Goblet cells . Goblet cells are found among the columnar (small intestine) or pseudostratified (trachea wall) epithelial cells. They can be distingished by a dilated, goblet-like apical cytoplasm containing a light-stained mucus material. Mucus relased into the lumen and coats the epithelial cell surface.

TUBULAR GLANDS
- Simple tubular gland Simple tubular glands . This type of gland has no secretory duct or duct is very short. One example is the intestinal glands or crypts of Lieberkühn.
- Simple coiled tubular gland Simple tubular coiled gland Simple tubular coiled gland . This glands presents a glandular secretory coiled duct. One example is the sweat glands of the skin.
- Simple branched tubular gland Tubular branched gland . The secretory duct is divided into two portions. One example is the gastric glands in the mucosa of the stomach.
- Compound tubular gland Compound tubular gland . The gland is composed of several tubular secretory units to dump their contents through a single secretory duct. One example is the Brunner's glands of the duodenum.

ALVEOLAR GLANDS
- Simple alveolar gland Acinar simple glands . Simple alveolar glands have a tubular structure similar to the simple glands, but organized in the form of secretory alveoli. An example are the groups of chef cells present in the bottom of the gastric glands of the stomach.
- Aveolar branched gland Alveolar branched gland . Branched alveolar glands, as sebaceous glands of the skin, presents a series of acinar gland to dump its contents into a single secretory duct.
- Alveolar compound glands Alveolar compound gland . The compound alveolar gland consists of several units of acinar glands that dump the content to a single secretory duct.

TUBULOALVEOLAR GLANDS
These glands consist of a mixture of glandular morphologies, can be found tubular glands and alveolar gland.
- Tubuloalveolar compound glands Tubulo-acinar gland Tubulo-acinar gland . Tubuloalveolar glands are usually composed of large gland wrapped by a capsule and septed by connective tissue. Usually have a duct part, a secretory serous part and a mucous secetory part. Secretory portion dump its contents into ducts which were becoming of greater caliber. Examples of tubuloalveolar compound glands are the mammary glands and some of the human salivary glands, as submandivular glands.

EXERCICIES
- What kind of gland found in this digital slide? Compound alveolar gland H-E 1,5 um
- What kind of gland found in this digital slide? Simple tubular gland PAS-Hematoxylin 7 um
- What kind of gland found in this digital slide? Compound tubular gland H-E 1,5 um
- What kind of gland found in this digital slide? Simple coiled tubular gland H-E 7 um
- What kind of gland found in this digital slide? Compound tubulo-alveolar gland PAS-Hematoxylin 1,5 um
- What kind of gland found in these digital slides? Are the same gland? Mammary gland (resting / non-lactating) H-E 1,5um 1 Mammary gland (resting / non-lactating) H-E 1,5um 2 Mammary gland (lactating) H-E 1,5um