The pancreas
Professor Sir Norman Williams, Professor P. Ronan O’Connell, Professor Andrew W. McCaskie in Bailey & Love's Short Practice of Surgery, 2018
The pancreas weighs approximately 80 g. Of this, 80-90% is composed of exocrine acinar tissue, which is organised into lobules. The main pancreatic duct branches into interlobular and intralobular ducts, ductules and, finally, acini. The main duct is lined by columnar epithelium, which becomes cuboi- dal in the ductules. Acinar cells are clumped around a central lumen, which communicates with the duct system. Clusters of endocrine cells, known as islets of Langerhans, are distributed throughout the pancreas. Islets consist of different cell types: 75% are B cells (producing insulin); 20% are A cells (producing glucagon); and the remainder are D cells (producing somatostatin) and a small number of pancreatic polypeptide cells. Within an islet, the B cells form an inner core surrounded by the other cells. Capillaries draining the islet cells drain into the portal vein, forming a pancreatic portal system.
Structure and function of skin
Roger L. McMullen in Antioxidants and the Skin, 2018
The duct of the eccrine gland is a tubular structure that begins in the coiled region, followed by a straight, long portion that extends to the surface of the skin. One of the most important functions of the duct is the re-absorption of NaCl and HCO3– that is secreted from the lower secretory tubule. This key mechanism prevents the body from entering a state of electrolyte imbalance. Ion recuperation is most effective during slow rates of perspiration and less efficient when the rate of perspiration is high. The duct of the eccrine gland contains two cell types, basal and luminal cells. The luminal cells are located closest to the lumen, while the basal cells provide underlying support. The basal cells are very metabolically active (they have many mitochondria) and contain a cell membrane abundant with Na+/K+-ATPase (responsible for the re-adsorption of NaCl). Luminal cells, on the other hand, contain less mitochondria and ATPase. It is believed that luminal cells serve more of a structural role by providing integrity to the duct, which is likely due to the presence of tonofilaments in the region next to the cell membrane closest to the lumen.
Miscellaneous
Joseph Kovi, Hung Dinh Duong in Frozen Section In Surgical Pathology: An Atlas, 2019
The growth is surrounded by an incomplete capsule, and if enucleated small nests of neoplastic cells may be left behind, resulting in recurrence of the tumor. As Thackray and Lucas292 have emphasized, tumors that are completely removed do not recur and the patient is cured. With en bloc excision of the tumor, recurrence is exceptional.291 Microscopically, a wide variety of morphologic patterns can be found in the tumor. Well differentiated ductlike structures which faithfully copy the ducts found in the normal salivary gland are present. The duct-like structures are lined by two types of epithelial cells: the inner layer is composed of low columnar or cuboid cells, the outer layer is made up of myoepithelial elements. Some ducts are cystically dilated and may contain pale colloid- or mucin-like substance. The small, dark myoepithelial cells are arranged in cords, nests, and sheets and seem to infiltrate the surrounding stroma. This stroma is rich in myxochondroid (mucoid) substances and stains deeply with hematoxylin. Occasionally, the myoepithelial cells produce islands of cartilage. Mitotic activity is virtually never encountered in the tumor (Figures 131 and 132).
Oral mucosa grafting in periorbital reconstruction
Published in Orbit, 2018
Andre Grixti, Raman Malhotra
MSGs ranging from 1 to 5 mm in size, are predominantly present in the labial and buccal mucosa as well as the tongue base and posterior hard palate.80 In the lips, MSGs form a tightly packed continuous layer of single lobules between the quadratus labii and the labial mucosa.71 Labial MSGs are more numerous and surgically accessible than at other sites.72 MSGs develop from the upper respiratory ectoderm during the 12th gestational week as simple tubuloacinar units and are classified as exocrine glands. Compared to major salivary glands, the duct system of MSGs is less developed. The intercalated duct arising from the gland acinus tends to be longer, while the next segment of the duct system leading to the interlobular excretory duct, known as the striated duct is often absent. The short excretory duct transports saliva to the oral mucosa. MSGs secretions are mainly mucinous or seromucinous.80,81 MSGs have minimal or no sympathetic innervation and postganglionic parasympathetic innervation to the MSGs derived mainly from the lingual nerve, is primarily responsible for stimulating secretion.80
Physiology of sweat gland function: The roles of sweating and sweat composition in human health
Published in Temperature, 2019
Lindsay B. Baker
The anatomical structure of the eccrine sweat gland, illustrated in Figure 2, consists of a secretory coil and duct made up of a simple tubular epithelium. The secretory tubule is continuous with and tightly coiled with the proximal duct. The distal segment of the duct is relatively straight and connects with the acrosyringium in the epidermis [5]. The secretory coil has three types of cells: clear, dark, and myoepithelial. As shown in Figure 2(c), clear cells are responsible for the secretion of primary sweat, which is nearly isotonic with blood plasma [6–8]. The clear cells contain a system of intercellular canaliculi, glycogen, and a large amount of mitochondria and Na-K-ATPase activity [5]. The dark cells are distinguishable by the abundance of dark cell granules in the cytoplasm. Their function is poorly understood, but thought to potentially act as a repository for various bioactive materials involved in regulation of clear cell and duct cell function [9,10]. The function of the myoepithelial cells is provision of structural support for the gland against the hydrostatic pressure generated during sweat production [5]. The duct has two cell layers: basal and luminal cells. Its primary function is reabsorption of Na and Cl ions as sweat flows through the duct, as shown in Figure 2(d). Most of the NaCl reabsorption occurs in the proximal duct, as these cells contain more mitochondria and Na-K-ATPase activity than that of the distal segment of the eccrine duct [5]. The result is a hypotonic final sweat excreted onto the skin surface [6,9].
The byssal-producing glands and proteins of the silverlip pearl oyster Pinctada maxima (Jameson, 1901)
Published in Biofouling, 2022
Alessandra Whaite, Anne Klein, Shahida Mitu, Tianfang Wang, Abigail Elizur, Scott Cummins
At their origin in the byssal gland, the byssal threads appear as either long connected strands proximal to the crypt base, or more distally as thread lamellae. This may be due to the axis of the tissue section, although the neatly stacked alignment of the lamellae is curious. It is unclear from this study what form the proteins take (connected or lamellar strands) upon entry into the byssal duct and duct branches. It is within the duct branches, ubiquitous at the highly ciliated epithelial layer, that the GRT is detected. Perhaps, the GRT is being cleaved for processing into the thread at this point or acting to draw and anchor proteins directed from the byssal gland to this epithelial surface for the inclusion of further proteins specifically secreted by the duct gland (see Figure 6A). GRT is rich in tyrosine residues which could be converted to DOPA by the tyrosinase found in the P. maxima proteome, suggesting a role in covalent cross-linking associated with the oxidation of DOPA in the duct gland. It would be of interest in future studies to see if the byssal thread tyrosinase and the peroxidase reported above could be detected in the vicinity of the duct gland.
Related Knowledge Centers
- Acinus
- Anatomy
- Breast
- Exocrine Gland
- Pancreas
- Physiology
- Pseudostratified Columnar Epithelium
- Simple Columnar Epithelium
- Submandibular Gland
- Simple Cuboidal Epithelium