histology lec- 13 gi accessory glands

7/25/2019 HIstology Lec- 13 GI Accessory Glands

1/6

Histology (Module 3 Lecture 4)

DATE 11.10.2015Accessory Digestive System

Dr. Reginette Villoria

OUTLINE

A. Salivary Glandsa. Duct Systemsb. Parotid Glandc. Submandibular Glandd. Sublingual Gland

e. Minor Salivary GlandsB. LiverC. PancreasD. Gall Bladder

DIGESTIVESYSTEM

SALIVARY GLANDS Branched tubulo-alveolar/acinar glands

Secretes saliva into the oral cavity

colorless liquid ( H2O, CHO, CHON, mucin,

mineral salts and enzymes/lysozymes)

Saliva is a hypotonic watery secretion containing

variable amounts of mucus, enzymes (principally

amylase and the antibacterial enzymelysozyme), antibodies and inorganic ions.

Two types of secretory cells are found in the

salivary glands: serous cells and mucous cells.

It is usually acidic, below pH 7 (pH6.7-7.4).

CLASSIFICATIONS

1. Size

A. Small: Lingual Glands

Von Ebners gland (posterior lingual)

-Found underneath the circumvallate

-mixed (serous and mucous)

Blandins gland (anterior lingual)

-mucous

B. Large Parotid, Submandibular, Sublingual

2. Secretions - serous, mucous or mixed

Serous watery, basophilic (dark)

Mucous lipid, lightly stained

Mixed serous demilunes can be seen

3. Site of opening of duct oral vestibule or oral

cavity proper

Communication between oral vestibule and oral

cavity: last molar

SALIVARY SECRETORY UNIT

The salivary secretory unit consists of a terminal

branched tubuloacinar structure composed

exclusively of either serous or mucous secretory

cells or a mixture of both types.

In mixed secretory units where mucous cells

predominate, serous cells often form semilunar

caps called serous demilunes surrounding the

terminal part of the mucous acini.

Myoepithelial cells embrace the secretory units,

their contraction helping to expel the secretory

product.

The terminal secretory units merge to form small

intercalated ducts which are also lined by

secretory cells.

They drain into larger ducts called striated ducts,

so named because of their striated appearance by

light microscopy. The striations result from the

presence of numerous inter-digitations of thebasal cytoplasmic processes of adjacent columnar

lining cells.

The gland is divided into numerous lobules L,

each containing many secretory units. Connective

tissue septa radiate between the lobules from an

outer capsule and convey blood vessels, nerves

and large excretory/ interlobular ducts E.

Serous Acinus Mucous Acinus

Acinus / Tubule

Dark basophilic stain Lightly Stained

Round nucleus Flattened, Basal nucleus

With a lumen

Columnar / cuboidal

DUCT SYSTEM OF LARGE SALIVARY GLANDSA. INTERCALATED DUCT

o Lined by cuboidal cells

o Round nucleuso Intralobular

B. SECRETORY/STRIATED DUCTS

Lined by columnar cells, eosinophilic

cytoplasm and basal striations

The basal cytoplasm appears striated,

reflecting the presence of basal

interdigitations of cytoplasmic processes of

adjacent cells and associated columns of

mitochondria.


2/6

22019A BAGSIT, CEREZO, CORTEZ, FLORALDE

It lined by tall columnar eithelium

It has an apical nuclei

The duct epithelium also secretes lysozyme

and immunoglobulin (Ig) A. In predominantly

serous salivary glands, the striated ducts are

larger than in predominantly mucous glands,

a feature associated with the role of the

striated duct in modifying isotonic basic

saliva to produce hypotonic saliva.

It has a big lumen, round nucleus, tall

columnar cells. It has basal striations.

C. EXCRETORY DUCTS/INTERLOBULAR DUCTS

Stratified columnar

I. PAROTID GLAND

o Largest

o Main ductStensens duct

o Purely serous gland

o It divides into lobules with the septa

radiating between lobules

o It carries BV, nerves & excretory

duct

o The parotid gland consists mainly of serous

secretory units which are darkly stained in

H&E preparations. The serous cells (SC) have

numerouszymogen granules.

o These are strongly stained cytoplasmic

granules containing proteins. Their nuclei

are rounded with dispersed chromatin and

they usually occupy a more central position

within the cell (compared to mucus secreting

cell.)

o An intercalated duct (ID) with a lining of

cuboidal secretory cells can be seen.

II. SUBMANDIBULAR GLAND

o

Second largesto Main ductWhartons duct

o Mixed gland, predominantly serous

o With Serous demilunes of Gianuzzi

o The submandibular gland consists of a

mixture of serous and mucous secretory

units which are often found in the form of

mixed Sero-mucous secretory units.

o The mixed secretory units consist of mucous

acini M with serous demilunes (SD).

III. SUBLINGUAL GLAND

o Under the tongue

o Major ductBartholins duct

o Minor ductRivinus

o Mixed gland, predominantly mucous

o With serous demilunes of Gianuzzi

o No fibrous capsule

o Mucous acini predominate in the sublingual

glands, making them stain very poorly with

H&E, in contrast to the serous acini shown in

the parotid.

o A large excretory duct lined by a stratified

cuboidal epithelium is present in the fibrous

tissue septum. The duct is accompanied by

blood vessels and nerves.

o Contains occasional adipocytes

o Proportion of adipose tissue

increases with age

IV. MINOR SALIVARY GLANDS

o Seen in the buccal mucosa layer, in the tongue

and lips

o Von Ebners Gland watery secretions

o Lingual mucous glands

LIVER

o GENERAL INFORMATION

Largest internal organ;

Derived from foregut


3/6


o HEPATOCYTES: Key cells of this organ & arranged in

rows/cords separated by sinusoids with 1-2 centrally

located nucleus;

Main Digestive Function: BILE PRODUCTION for

fat

liver parenchyma

o emulsification (Exocrine Function);

Other Functions:o Plasma protein synthesis like

fibrinogen, prothrombin, albumin,

o apolipoproteins & transferring

(Endocrine Function);

o Gluconeogenesis;

o Detoxification;

o Deamination;

o Glucose storage in the form of glycogen

& triglycerides;

o Fat-soluble vitamin storage especially

Vit. A;

o Removal of effete RBC;

o Storage of Iron

o Blood flow

o Hepatic portal vein

o Hepatic artery

HEPATOCYTES & HEPATIC LOBULES

o Polyhedral cells with round nuclei, peripherally

dispersed chromatin

o Strongly eosinophilic cytoplasm due to numerous

mitochondria

o Lipofuscin

o Present in variable amounts

o Fine brown granules (wear and tear

pigment)

HEPATIC LOBULES: Basic functional unit of the

liver & these are polygonal in shape;

TIGHT JUNCTIONS: Connects hepatocytes

together;

DESMESOMES: Structure where the basal lamina

is attached;

CENTRAL VEIN: Center of a hepatic lobule;

o Flow of blood: TOWARDS central vein;

o Flow of bile: AWAY from central vein;

PORTAL TRIAD: Peripherally located vessels of a

hepatic lobule; contains:

o PORTAL VEIN (Venule): Rich in nutrient

but low in oxygen;

o HEPATIC ARTERY (Arteriole): Supplies

oxygen into the hepatic lobule

o BILE DUCTULES: Cuboidal Epithelium &

branches of the biliary system.

o Bordered by a layer of

hepatocytes known as the

limiting plate SINUSOIDS: Between all the plates of

hepatocytes of a hepatic lobule & contains mixed

type of blood. SINUSOIDAL BV:

Discontinuous linings of fenestrated endothelial

cells;

LE of simple squamous cells;

Why discontinued & fenestrated?

It allows to fill the SPACE OF DISSE

(Perisinusoidal space) and directly bathes

the many microvilli projections from the

hepatocytes;

SPACE OF DISSE: narrow space which

separates the hepatocytes from the

sinusoids

Hepatic lobule microvasculature(a) Hepatocytes (H) are polygonal epithelial cells that

form branching, irregular plates separated by

venous sinusoids (S). (b) Reticulin (collagen type

III) fibers (R) running along the plates of

hepatocytes (H), supporting these and the

intervening sinusoids. Most connective tissue in

the liver is found in the septa and portal tracts. (c)

With plates of hepatocytes (H) appearing to

radiate from it, the central vein (C) of the lobule

has more collagen than the smaller sinusoids (S)

that drain into it from all directions (d) Peripheral

portal areas contain more connective tissue and

are the sites of the portal triad: a portal venule

(PV), an arteriole branching off the hepatic artery(HA), and one or two bile ductules (BD).

Absorbed food pass to the liver via the hepatic

portal vein.Oxygen required by the liver is supplied

via the hepatic artery. After passing through the

sinusoids, venous drainage occurs via the portal

vein.

Taken from the book

TANDAAN: Eto ang portal trial/portal tract. Portal vein

ang pinakamalaki. Yung maliliit na structures will be

hepatic artery and bile duct. Kapag makapal ang wall,

ARTERY yun. Yung bile duct yung may SIMPLE

CUBOIDAL EPITHELIUM.


4/6


KUPFFER CELLS:

o Stellate macrophages from monocytes;

o Within the sinusoidal linings;

o Phagocytose aged RBCs;o Antigen-presenting cells;

o Removes bacteria/debris in the portal

blood.

Hepatic sinusoids.

In the endothelial lining of the hepatic sinusoids

are numerous specialized stellate macrophages

or Kupffer cells that detect and phagocytose

effete erythrocytes. (a) Kupffer cells (K) are seen

as black cells in a liver lobule from a rat injected

with particulate India ink. (b) In a plastic section,

Kupffer cells (K) are seen in the sinusoid (S)

between two groups of hepatocytes (H). They are

larger than the flattened endothelial cells (E).

Between the endothelium and the hepatocytes isa very thin space called the perisinusoidal space

(PS) of Disse, in which are located small hepatic

stellate cells (HS), or Ito cells, that maintain the

very sparse ECM of this compartment and also

store vitamin A in small lipid droplets.

ITO CELLS:

o Hepatic stellate cells;

o Stores fat-soluble vitamins like Vit. A;

o Produces extracellular matrix and

cytokines.

BILE FLOW:

Hepatocytes >>> Bile Canaliculi (smallest branch

of the biliary tree) >>> Canals of Hering

(composed of cholangiocytes) >>> Bile ductules

(LE: simple cuboidal-columnar cells) >>> Hepatic

ducts

Bile ductules

Near the periphery of each hepatic

lobule, many bile canaliculi join with the

much larger bile canals of Hering, which

are lined by cuboidal epithelial cells

called cholangiocytes. These canals

soon join the bile ductules in the portal

areas and drain into the biliary tree.

STRUCTURAL & FUNCTIONAL COMPONENTS

CLASSICAL HEPATIC LOBULE

o Contains plenty of RER;

o For protein synthesis (Endocrine

functions);

o Blood flows past hepatocytes from theportal areas to a central venule.

Hepatic lobule.

In humans these lobules have much less

connective tissue and their boundaries are more

difficult to distinguish. In both cases peripheral

connective tissue of portal areas contains the

portal triad: small bile ductules (D), venule (V)

branches of the portal vein, and arteriole (A)

branches of the hepatic artery.

PORTAL LOBULE

o Contains plenty of peroxysomes;

o For detoxification and bile secretion

(Exocrine functions);

o From one portal area to another portal

area;

o Portal areas are rich in oxygen,

nutrients and connective tissue.

HEPATIC ACINUS

Emphasizes the nature of blood supply to the

hepatocytes and the oxygen gradient from the

hepatic artery to central vein;

For oxygen and nutrient supply;

From one central vein to another central vein

ZONE I

o For oxidative metabolism such as

protein synthesis;

o

1st to be affected during toxicity. ZONE II

o Intermediate metabolism between

Zone I & II.

ZONE III

o Anaerobic metabolism;

o Preferential sites for glycolysis, lipid

formation and drug

biotransformations;

o 1st to be affected during low oxygen

level;

o 1st to undergo fatty accumulation and

ischemic necrosis.

Concepts of structure-function relationships in

liver. The classic lobule concept offers a basic

understanding of the structure function

relationship in liver organization and emphasizes

the endocrine function of hepatocytes as blood

flows past them toward the central vein.

The portal lobule emphasizes the hepatocytes

exocrine function and the flow of bile from

regions of three classic lobules toward the bile

duct in the portal triad at the center here. The


5/6


area drained by each bile duct is roughly

triangular.

The hepatic acinus concept emphasizes the

different oxygen and nutrient contents of blood

at different distances along the sinusoids, with

blood from each portal area supplying cells in two

or more classic lobules.

Major activity of each hepatocyte is determinedby its location along the oxygen/nutrient

gradient: periportal cells of zone I get the most

oxygen and nutrients and show metabolic activity

generally different from the pericentral

hepatocytes of zone III, exposed to the lowest

oxygen and nutrient concentrations. Many

pathologic changes in the liver are best

understood from the point of view of liver acini.

OTHER NOTES

Notes

o Liver has a strong capacity for cell

regeneration unlike the salivary glands

and pancreas;

o Regeneration rate is slow;

o Liver stem cells had shown a role in

regeneration in some experimental

models like the oval cells;

o Oval cells are present among

cholangiocytes of bile canals near portal

are and produce progenator cells for both

cholangiocytes and hepatocytes.

PANCREAS (Exocrine part)o Compound tubo-acinar gland

o Derived from foregut

o Endocrine and exocrine- produces both

digestive enzymes and hormoneso ENDOCRINE FUNCTION

Islet of Langerhans cluster

of epithelial cells where

hormones are synthesized

o EXOCRINE FUNCTION

Functional unit- serous or

pancreatic acini (similar

structure to parotid gland,

can be distinguished by

absence of striated ducts and

presence of islets in

pancreas)

Secretes 1.5 to 2L of fluid/day

Encapsulated Consists of secretory acini

Secretions drain into the main pancreatic duct

Each acinus is made up of irregular cluster of

pyramidal secretory cells

o The apices of surround a central lumen

VISCID

o The smallest tributaries (of the duct

system) is known as intercalated ducts.

Pancreatic juice is rich in bicarbonate ions

o Digestive enzymes include:

o proteases

o proelastases

o protease E

o lipases

o a-amylase

o nucleases

The exocrine function secretes an enzyme-rich

alkaline fluid into the duodenum via the

pancreatic duct. The high pH of pancreatic

secretions is due to a high content of bicarbonate

ions and serves to neutralise the acidic chyme as

it enters the small intestine from the stomach.

The pancreatic enzymes degrade proteins,

carbohydrates, lipids and nucleic acids by the

process of luminal digestion. Like pepsin in the

stomach, the pancreatic proteolytic enzymes

trypsin and chymotrypsin are secreted in an

inactive form.

Enterokinase, an enzyme secreted by the

duodenal mucosa, activates protrypsin to form

trypsin. Trypsin then activates prochymotrypsin

to form chymotrypsin. This mechanism prevents

autodigestion of the pancreas. The other

main pancreaticduct

commonbile duct

ampulla ofVater

doudenum

intercalated ductintralobular

duct

interlobular

duct

Ganito ang drainage ng pancreatic secretion. Galing ng acinus magde-

drain sya sa intercalated duct hanggang mapunta sya sa interlobular

duct. So anong pinagkaiba ng itsura nila?

Ang IC duct ay may SIMPLE CUBOIDAL. Habang lumalaki yung duct,

nagiging stratified cuboidal na sya. Pano malalaman kapag

intralobular o interlobular na? Take note of the LOCATION. Ang

INTERLOBULAR DUCT ay makikita sa SEPTUM.

So kapag ka stratified cuboidal na sya pero wala sa septum,

INTRALOBULAR DUCT yun. Tingnan nyo yung pcture and identify.


6/6


pancreatic enzymes are secreted in the active

form.

Centroacinar cells

o small, pale-staining

Intercalated ducts

o merge to form to form larger interlobular ducts

lined by columnar epithelium

**No ducts in the pancreas are striated

GALL BLADDER Muscular sac lined by simple columnar

epithelium with basally located nuclei

Presence of lipid in the duodenum promotes

secretion of cholecystokinin-pancreozymin (CCK)

o CCK stimulates contraction of the gall

bladder, forcing bile into the duodenum

Mucosa is thrown into many folds

Submucosa is rich in elastic fbers

Muscularis layer is arranged in longitudinal,

transverse, and oblique orientations SPHINCTER OF ODDI

o The sphincter of ampulla or sphincter of

Oddi is a muscular valve that controls

the flow of digestive juices (bile and

pancreatic juice) through the ampulla

of Vater into the second part of the

duodenum

Consists of 4 muscles:

Sphincter choledochus

surrounds and controls

terminal region of common

bile duct, to stop flow into

duodenum

Sphincter pancreaticus

from pancreatic duct

Sphincter longitudinalis

triangular interval of ampulla

of Vater, pancreatic duct and

common bile duct

Sphincter ampullae from

ampulla of Vater

References:

Wheaters

Junqueiras

Trans of Upclass

histology lec- 13 gi accessory glands

Documents