Five Flashcards
What are some functions of saliva? How much saliva is secreted per day? What are the major salivary glands and where are the located?
Salivary Glands: There are two types of salivary glands, major and minor. Saliva has
numerous functions, including wetting food, initiating digestion to a limited extent
(contains digestive enzymes, i.e. salivary amylase and lipase), provides an antimicrobial
function (i.e., contains secretory IgA), and is an important source for growth factors (i.e.,
epidermal growth factor), designated for the gastrointestinal tract.
Major Salivary Glands are branched and paired structures which secrete approximately
1L of saliva/day. They include:
- Parotid (located anterior and below the pinna of the ear).
- Sublingual (located in the floor of the mouth, on either side of the frenulum of the tongue).
- Submandibular (located on either side of the neck, just below the mandible).
What are the 3 types of salivary acini? What are their functions? How are their histological characteristics?
Salivary glands can be identified by their location and their secretory morphology. As such, salivary glands have three types of secretory components. They can be composed of serous, mucous, or seromucous acini. Serous salivary glands secrete primarily zymogen
(amylase and lipase), mucous acini secrete mucus, and seromucous salivary glands secrete both zymogen and mucus.
Serous acini are comprised of pyramidal cells arranged in circular groups around a central lumen. Each cell has a single basal nucleus, well developed rough endoplasmic
reticulum and Golgi apparatus. Numerous apical secretary granules and basal mitochondria are other common findings. Located between these cells and the basal lamina are specialized smooth muscle cells called “myoepithelial” cells. As a rule this type of acinus tend to stain homogenously dark with standard H and E stains, as they are comprised solely of one type of acinus (i.e. all serous)
Mucous acini are larger than the serous acini. Their cells are also pyramidal in shape and arranged in circular patterns around a central lumen. Their nuclei tend to be flattened and located in the basal aspect of the cell. A typical cell will have fewer mitochondria and less well-developed rough endoplasmic reticulum and Golgi apparatus. The apical aspect of these cells contains abundant clear cytoplasm. Myoepithelial cells are also associated with these acini. As a rule, this type of acinus stains uniformly “light” with standard H and E stains, as the mucus within the cells is extracted during processing, leaving a very white appearance of the apical cytosol.
Seromucous acini represent a blend of both serous and mucous acini. An important histologic feature of seromucous acini is the presence of serous “demilunes.” The serous demilune arises when a few serous secreting cells “cap” an acinus, which is composed of predominantly mucous element. The serous cells in this state look like half moons sitting on the edges of the mucous semi acini). Myoepithelial cells are also present. These mixed acini stain heterogeneously with standard H and E stains because they are comprised of two distinct types of acini (dark staining serous acini and lighter staining mucus secreting acine) .
What are the stroma of salivary glands like? How can the three major salivary glands be differentiated?
The stroma of salivary glands includes blood vessels, nerves, lymphatics, and ducts. The
connective tissue forms “septae,” which ramify throughout the parenchyma of the gland.
*For the major salivary glands your ability to identify parotid, submandibular, or
sublingual glands, will hinge on your ability to discriminate relative amounts of serous
and mucous acini. As a rule, parotid salivary glands are all serous secreting (Ross figure
15.28a, page 460)(Ross figure 16.28a, page 502). For the submandibular salivary gland,
serous acini predominate although some acini are mucus secreting (Ross figure 15.28b,
page 460)(Ross figure 16.28b, page 502). The sublingual glands are mixed as well, but
the mucous acini predominate in number over the serous acini (Ross figure 15.28c, page
460)(Ross figure 16.28c, page 502).
What are the main types of salivary gland ducts? What is their function? What are they like histologically? Which duct is associated with the 3 major salivary glands?
The major salivary glands discharge their secretions into a system of ducts, which
eventually drain into the oral cavity. The first duct, which communicates with the
secretory acinus, is referred to as an intercalated duct. Intercalated ducts are not easy to
see with microscopy, but are lined with a low cuboidal to squamous epithelium. Scattered
myoepithelial cells may be present, but otherwise the histoarchitecture of this duct is
rather unremarkable. Intercalated ducts then drain secretions into striated ducts. These
ducts are much more pronounced morphologically. They have a well developed columnar
lining. The histologic hallmark for this duct is numerous basolateral interdigitations that
run along the basal side of the epithelial lining (Ross plate 48, figure 2, page 471)(Ross
figure 2, page 514). These interdigitations appear as pale pink lines running parallel to
the long axis of the cell. The function of these interdigitations is to provide additional
surface area to house both mitochondria and ion pumps. These particular ducts play an
important role in controlling the osmotic content of saliva. As such, sodium and chloride
are removed from saliva and are reabsorbed, in exchange for potassium and bicarbonate,
which are released. A single euchromatic nucleus is generally located just above these
interdigitations. The high mitochondrial content in these cells imparts eosinophilic
staining with standard hematoxylin and eosin preparations. Both the intercalated ducts
and the striated ducts represent intralobular ducts. Intralobular ducts eventually fuse to
form interlobular ducts found in connective tissue septae separating individual lobes.
Interlobular ducts are lined by pseudostratified columnar epithelium. As these become
larger, the epithelium changes again to a stratified columnar epithelium. Finally, as the
ducts get closer to the oral cavity, they change to a stratified squamous epithelium. The
main excretory duct of parotid salivary glands is Stenson’s duct. The major excretory
duct of submandibular salivary glands is Wharton’s duct. In contrast, sublingual salivary
glands drain directly into the floor of the mouth.
What is the innervation of the secretion of saliva like?
The secretion of saliva is governed by both sympathetic (more viscous) and parasympathetic innervation (more watery).
What are the parts of the pancreas grossly? What are the basic functions of the pancreas?
The pancreas is a complex gland divided grossly into a head (nearest the duodenum), a
body (located medially) and a tail which extends towards the hilum of the spleen. The
pancreas has both an endocrine function (i.e., delivery of insulin, somatostatin, and
glucagon into the blood stream), and an exocrine function (delivery of digestive enzymes
into the gastrointestinal tract). Here we will concentrate only on the exocrine component
of pancreatic morphology which accounts for about 1.2L of secretions/day.
Describe the histology of the parenchyma of the exocrine pancreas, including the acini and the ducts.
The parenchyma of the exocrine pancreas is comprised of pancreatic acini (Ross figure
17.20, page 553)(Ross figure 18.20, page 596). Pancreatic acini have a characteristic
morphology and are comprised of pyramidal shaped cells located in circular patterns
around a central lumen, which is often difficult to identify. These pyramidal shaped cells
synthesize and release digestive enzymes (pancreatic lipase and amylase). With standard
hematoxylin and eosin stains the basal component of these cells tends to stain basophilic.
This is due to the presence of numerous profiles of rough endoplasmic reticulum, which
are found oriented towards the base of the cells. The apical portion of these cells tends to
stain eosinophilic. This is due to the presence of numerous secretory vesicles containing
digestive enzymes. A euchromatic nucleus is generally found at the base of the cell
whereas a well developed Golgi apparatus is located in a supranuclear position.
Microvilli and tight junctions can also be found at the apical surface of the acinar cells.
Pancreatic ducts: The duct system of the pancreas is as follows. The acini are drained by intercalated ducts. These short ducts are lined by squamous to low cuboidal epithelium composed of centroacinar cells. These cells have a single basal nucleus and stain lightly eosinophilic. Intercalated ducts lead into intralobular ducts, which are lined by cuboidal or low columnar epithelial cells with single basal nuclei. The intralobular ducts then lead
into interlobular ducts, which are lined by a more defined columnar epithelium. A single basal nucleus also helps identify these cells. Finally, interlobular ducts then unite to form the major excretory ducts: the ducts of Santorini and Wirsung.
Describe the gross anatomy of the liver, its functions, and the cells that comprise it,
Liver: The liver is the largest gland in the body (2% of adult body weight) and is located
in the upper right quadrant of the abdominal cavity, where it lies protected by the rib
cage. It has both an endocrine function (i.e., delivery of albumin and fibrinogen into the
bloodstream) and an exocrine function (i.e., delivery of bile to the gastrointestinal tract).
The liver is traditionally divided in to four lobes: right, left, quadrate, and caudate, but is
homogenous on a microscopic level and, thus, these designations are mainly important in
gross anatomy. The hepatic artery perfuses the liver with oxygenated blood from the
celiac axis. The portal vein carries blood from the digestive tract and spleen. Although
deoxygenated, this blood is particularly rich in carbohydrates, amino acids, lipids, and
potential pathogens, such as bacteria. Thus, the liver is the first organ to be exposed to
potentially toxic compounds that have been ingested.
The liver is comprised of hepatocytes (parenchymal cells), connective tissue, blood
vessels, lymphatics, nerves, specialized capillaries called sinusoids, and a connective
tissue covering (Glisson’s capsule).
What are the major afferent vessels of the liver? Efferent vessels?
The major afferent vessels include:
- Hepatic artery (delivers one-third of blood flow to the liver, 70% of oxygen delivery)
- Portal vein (delivers two-thirds of blood flow to the liver, 30% of oxygen delivery)
- Lymphatics
The major efferent vessels include:
- Hepatic veins which empty into the inferior vena cava
- Common hepatic duct (right and left bile ducts)
- Lymphatics
Describe the portal triad including the microscopic histology of its components. Describe the liver lobule.
The portal vein, hepatic artery, and bile duct (and their branches) course throughout the
liver as a triad in the connective tissue stroma (Ross plate 61, figure 1, page 561) (Ross
figure 1, page 605). This is referred to as a portal triad. Since there are numerous
branchings, it is possible to see more than one of each component in a single triad. The
bile ducts are the easiest to discern by the presence of a cuboidal lining. Finally, the
portal triads can vary in size based upon their location within the liver.
There are a number of ways to describe liver morphology, but the classical functional
unit of the liver is described as the liver lobule, a portion of which is shown below. In
cross section the “perfect” liver lobule has six sides which are oriented around a single
blood vessel called the central vein, which runs along the long axis of the lobule. The
plates of hepatocytes radiate from the central vein toward the periphery, where they
communicate with the portal triads.
Describe the pattern of blood flow in the liver. Describe the histological characteristics of the various blood vessels.
The hepatic artery and portal vein are both afferent vessels, which branch to form smaller
interlobular vessels. The portal vein and its branches have the typical structure of veins.
The hepatic artery and its branches have the structure of normal arteries and can be
identified by the presence of a thicker muscular wall. The interlobular vessels themselves
branch further and further to produce very small vessels that deposit blood directly into
the hepatic sinusoids. The sinusoids are specialized capillaries that are lined by a thin,
discontinuous, and highly fenestrated endothelium (squamous cells), which rest upon an
incomplete basal lamina. Interposed between the endothelial lining and the underlying
hepatocytes is an area referred to as the Space of Disse (Ross figure 17.9, page 541)
(Ross figure 18.9 page 589). It is here that the hepatocytes gain access to the soluble
components of the blood. Blood exits the sinusoids and then flows towards small central
veins. These small veins can be detected by their irregular shape and thin walls (Ross
plate 61, figure 2, page 561)(Ross figure 2, page 605). Additionally, central veins are not
associated with components of the portal triad (i.e., bile ducts or branches of the portal vein or hepatic artery). The central veins course through the liver and increase in size to
form sublobular veins. Sublobular veins then converge to form hepatic veins which, in
turn, drain blood back into the inferior vena cava.
Describe the pattern of bile flow in the liver.
Bile Flow:
Hepatocytes secrete bile into apical bile canaliculi on the opposite side of the cell from
the basolateral sinusoids. Canaliculi are at right angles to the sinusoids. These canaliculi
anastomose with each other and near the portal triad, the bile is then deposited into
Canals of Hering. The Canals of Hering, in turn, empty into intralobular bile ducts
(commonly seen in the portal triads), which increase in size and finally unite to form the
right and left hepatic ducts and, finally, the common bile duct.
Describe the histology of hepatocytes.
Hepatocytes are the major parenchymal cell of the liver and are arranged in “plates” of
cells that are normally one cell layer thick and are separated from one another by
sinusoids. In the adult, the plates are usually comprised of one cell layer; in young
children the plates are arranged in 2 cell layers. Each hepatocyte is roughly polygonal and
may be uninucleate or binucleate with one or more prominent nucleoli being present.
Hepatocytes contain numerous mitochondria throughout the cell, and numerous profiles
of both rough and smooth endoplasmic reticulum. More than one Golgi apparatus may be
found. The hepatocyte also has bile canaliculi associated with its lateral sides. The
canaliculi arise from the fusion of adjoining plasma membranes that are sealed by tight
junctions. Microvilli are often seen in the lumen of the canaliculi
Describe the histology and function of kupffer cells. Describe the histology and function of hepatic stellate cells. Where are fibroblasts found?
Kupffer cells are liver macrophages, which are found within the liver sinusoids. These stellate shaped cells maybe found attached to the surface of the endothelium or often times spanning the lumen of the sinusoid. These uninucleated cells are phagocytic and help to eliminate particular matter which has entered the liver. They often will stain positively for the presence of iron with special stains, as these cells play a role in the breakdown of red blood cells (Ross plate 62, figure 2, page 563)(Ross figure 2, page 607).
Hepatic stellate cells are found within the Space of Disse. They were previously called fat storing cells (because they store vitamin A in droplets, Ito cells (after the pathologist who described them) or lipocytes, but are difficult to identify. They will not be seen in standard H and E preparations (Ross figure 17.9, page 541) (Ross figure 18.9, page 584). and they are the major source of collagen and other extracellular matrix components that
are deposited in excess during the development of cirrhosis.
Fibroblasts maybe found throughout the stoma of the organ and to a lesser extent in the Space of Disse.
Describe the function, microscopic histology, and gross histology of the gall bladder.
The gallbladder is a small pear shaped organ attached to the posterior aspect of the right
lobe of the liver. It receives dilute bile from the common hepatic duct and releases thick
concentrated bile into the common bile duct. The gallbladder is lined by a simple
columnar epithelium. These cells will display numerous microvilli, mitochondria, a
supranuclear Golgi apparatus, as well as rough endoplasmic reticulum and pinocytotic
vesicles. The epithelial cells are jointed by tight junctions at their apical surface. Situated
below the epithelial lining is a lamina propria containing loose connective tissue. Below
this layer is located a single coat of smooth muscle, which may also contain elastic fibers
and collagen. Finally, the gallbladder is lined on its external surface by a serosa except
where it attaches directly to the liver (Ross figure 17.16, page 549)(Ross figure 18.16,
page 592).
