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Digestive System Digestive Glands. Components of Digestive Glands. ◇ small digestive glands: found in the wall of digestive tract. ◇ accessory glands (large digestive glands):. salivary glands pancreas liver. General Structure of Digestive Glands.

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Digestive System

Digestive Glands


Components of Digestive Glands

◇small digestive glands:

found in the wall of digestive tract.

◇accessory glands (large digestive glands):

salivary glands

pancreas

liver


General Structure of Digestive Glands

◇Parenchyma: ( functional portion of an organ )

acini / gland cells

ducts

◇Stroma: ( non-functional portion of an organ )

capsule

CT inside the organ.



Salivary Glands

General structure of the large salivary glands

serous acinus

mucous acinus

seromucous / mixed acinus

acinus

types

of acinus

Parenchyma

intercalated duct

striated/secretory duct

interlobular duct

excretory duct

duct


serous acinus

seromucous

/ mixed acinus

mucous acinus

intercalated duct

striated

/secretory duct

demilume

Model ( structure of the large salivary glands)


seromucous /mixed acinus

mucous acinus

serous acinus

Model

Section (H&E)


Salivary Glands

Structural Characteristic of gland Cell:

serous acinus:comprised by serous cells.

*zymogen granules in apical cytoplasm.

mucous acinus:comprised by serous cells.

*mucinogen granules in cytoplasm.

seromucous acinus:comprised by both cells.

/ mixed acinus*demilume


serous acinus:

*zymogen granules in apical cytoplasm.


Serous cell:

basal lamina (bl);

connective tissue (ct);

desmosome (d);

endothelium (en);

Golgi complex (g);

intercellular space (is);

lumen (l);

microvilli (mi);

mitochondria (m);

nucleus (nu);

RER (re);

secretion granule (sg).

10.000x.


mucous acinus:

*mucinogen granules in cytoplasm.

n


Detail of mucous cell:

Sero-mucous cell (sc);

Golgi complex (gc);

intercellular space (is);

secretion granule (sg);

lumen (l);

nucleus (n);

RER (re).

10000x.

sg

is

re

n


seromucous acinus

/ mixed acinus

demilume


Salivary Glands

acinus

duct

intercalated duct:

simple squamous/cuboidal epith.

striated/secretory duct:

simple tall columnar epith.

interlobular duct:

pseudostratified columnar epith.

excretory duct:

stratified squamous epith.


Salivary Glands

intercalated duct:

simple squamous

or cuboidal epith.


Salivary Glands

intercalated duct: simple squamous or cuboidal epith.


LM

EM


Detail ofintercalated duct cell

basal lamina (bl);

desmosome (d);

nerve fibers (nf);

Golgi complex (g);

intercellular space (is);

mitochondria (m);

nucleus (nu);

RER (re).

13.000x.

g

m

re

nu

bl

EM


Salivary Glands

striated/secretory duct:simple tall columnar epith.


Salivary Glands

striated/secretory duct

Note: the basal striations


Striated duct:

blood vessel (bv);

connective tissue (ct);

lumen (l);

nucleus (nu).

×2750.


Basal portion of striated duct cell:

basal lamina (bl);

basal membrane pleat (bmp);

collagen fiber (cf);

mitochondria (m);

nucleus (nu).

×16.500 .


Salivary Glands

striated/secretory duct

The secretory ducts,which are continuous with the intercalated ducts,are wider and lined with a simple columnar epithelium. As the secretion from the acini passes through the secretory ducts,the epithelium can re-absorb sodium(Na+) and water from the lumen to the interstitium(间质)and transport potassium (K+) into the saliva,thus changing the consistency of the saliva. The secretory ducts drain into interlobular ducts which run between lobules.


Salivary Glands

interlobular duct:

pseudostratified columnar epith.

excretory duct:

stratified squamous epith.


Salivary glands

include

*Parotid G.

*Submandibular G.

* Sublingual G.

Function:

* moistening food.

* carbohydrate digestion.

* Secrete IgA.


Structural Features of Salivary Glands

Parotid G.

Submandibular G.

Sublingual G.

Serous A.

+++

+++++

+

Mucous A.

none

+

+++

Mixed A.

none

+

+

Inter-

calated D

none

short

long

few

long

short

Striated D


Pancreas

The pancreas is a lobular organ.

The pancreas has both exocrine functions (releases digestive enzyme secretions into the intestines) and endocrine functions (releases hormones into the blood).


Pancreas

Parenchyma

endocrine gland

exocrine gland

produces

hormones

produces

pancreatic juice


Parenchyma

make section


Parenchyma

endocrine

gland

endocrine

gland

exocrine

gland

exocrine

gland

exocrine

gland


Parenchyma

exocrine

gland

endocrine

gland


Pancreas

Exocrine Pancreas

Acini

Ducts

intercalated ducts

interlobular ducts

main pancreatic ducts

  • wholly consists of serous acini.

  • small centroacinar cells in the lumen.

major duodenal papilla


Exocrine Pancreas

Here is another look at the Exocrine Pancreas and the Acini (white dotted lines) which make it up.

Central

Acinar Cells

The yellow arrows are pointing to the characteristic centroacinar cells

which are the key to identifying the pancreas. Notice how they stand out against the dark cells of the acini.

Pancreas Acinus


Exocrine Pancreas

Centroacinar Cell

Pancreas Acinus

Acinar

Cell

Low power

(LM)

high power

(LM)


Exocrine Pancreas

  • Ducts

  • Intercalated ducts: simple squamous

  • or cuboidal epith.

  • Interlobular ducts:columnar epith.

  • pancreatic ducts: tall columanr epth.

(similar to salivary glands. REMEMBER: there are no striated ducts in the pancreas. )

major duodenal papilla


Exocrine Pancreas

It releases the pancreatic juice.

pancreatic juice contain many kinds of enzyme:

* amylase(胰淀粉酶):hydrolyses starch & glycogen .

* lipase(胰脂肪酶):hydrolyzes triglycerides(甘油三酯).

into fattyacids and mono-glycerides(甘油单酯).

* cholesterol esterase(胆固醇酯酶) :breaks down

cholesterol esters(酯)into cholesterol and a fatty acid.

* trypsin( 胰蛋白酶)and chymotrypsin(糜蛋白酶) :

hydrolyze proteins.

* ribonuclease(核糖核酸酶)& deoxyribonuclease(脱氧核

糖核酸酶):split nucleic acids.


Pancreas

Endocrine Pancreas

  • Islets of Langerhansscatter throughout the exocrine pancreas.

  • Three types of cells :

  • A-cells(20%) glucagon

  • B-cells(75%) insulin

  • D-cells( 5% ) somatostatin

  • Capillaries:each islet is richly supplied with blood vessels.


Pancreas

Endocrine Pancreas

D-cells

A-cells

B-cells

A-cells

A-cells

B-cells




Liver

General Introduction

*The largest gland (~ 2% of body weight in adult).

* Respectively receives both venous & arterial blood

through the portal V. (~75%) & hepatic A (~25%). * CT of capsule extended into the parenchyma,

forming “classical” liver loblules.

* Functions as an exocrine gland (secreting bile)

and other very important roles.


Liver

liver loblules

section


Liver

Structures of Liver Lobule


Liver

Structures of Liver Lobule


Model ofLiver Lobule


Liver

Structures of Liver Lobule

*six-sided prism

with a central V. at its center.

*sheets of hepatocytes( orhepatic plates)

extend radially from the central V.

* sinusoids between hepatic plates.

portal triads ( or portal area):

in the corner of lobules.


Liver

Structures of Liver Lobule

hepatic plates


Liver

Portal Triads (or Portal Area)

* Definition:

The area of CT found in the angles

where adjacent hepatic lobules meet.

* Components:

CT. + portal triad

interlobularA

interlobularV

interlobularbile duct


Liver

Portal Triads (or Portal Area)


Liver

Portal Triads (or Portal Area)

interlobularV

interlobular bile duct

interlobularA


Liver

Sinusoids

* Dilated anastomosing(吻合) venules

between the hepatic plates.

* Blood pathway: periphery central V.

* Kupffer cells line in the wall of sinusoids.

* EM ( endothilium of sinusoid )

significant gaps;

numerous fenestration;

incomplete basal lamina.


Liver

Sinusoids

Model


Sinusoids

Sinusoids

SEM


Scanning Electron M.(SEM)

Ec: Erythrocyte; BC: Bile Canaliculus

DS: Disse’s Space S: Sinusoid

H: Hepatocyte Mv: Microvili


Sinusoids

fenestration

endothilium

SD: Space of Disse

TEM


Sinusoids

Kupffer Cell

(LM)

Kupffer Cell

(TEM)


Liver

Hepatocyte

* typically large polyhedral cells with large round

centrally located nucleus.

* abundance of organelles relates to its functions:

Mitochondria: provide energy

RER:protein synthesis

SER:bile formation / metabolism of lipids and

hormones / detoxification.

Lysosome:defence

Microbody:detoxification.

Inclusions:glcogen particles, lipid droplets

and pigments.


Liver

Hepatocyte

MODEL


Model of Hepatocyte



Liver

Functions of Hepatocyte

* Produce bile.

* Degrade glycogen to glucose

under regulation of hormones.

* Involve the blood lipid metabolism.

* Synthesize the blood plasma proteins:

Albumin: major plasma protein;

Fibrinogen;thrombin(凝血酶);

Clotting(凝结)factor III.

* Detoxification


Liver

Bile Canaliculus

Definition:

the tubular space limited by plasma membrane

of two adjacent hepatocytes.

Structure:

LM: network-like structures are seen

by silver impregnation.

EM: *plasma membrane of adjacent hepatocytes

forms the wall of bile canaliculi.

* tight junctions form seals.


Bile Canaliculus

Blie canaliculi stained

by silver impregnation

(LM)




Bile Canaliculus

Bile Canaliculus

Freeze Fracture SEM


Liver

Perisinusoidal space (Disse’s Space)

  • A space between endothelium & hepatocyte.

  • Bevisible under EM.

  • Occupy by numerousmicrovilliof hepatocytes.

  • Fill with blood plasma.

  • have fat-storing cells (storing fat & vitamin a)

  • A site for substance exchange

  • between the blood & the hepatocytes.



Scanning Electron M.(SEM)

Ec: Erythrocyte; BC: Bile Canaliculus

DS: Disse’s Space S: Sinusoid

H: Hepatocyte Mv: Microvili



Sinusoids

fenestration

endothilium

SD: Space of Disse

TEM


TEM

E: Erythrocyte S: Nucleus of Endothelial Cell

D: Disse’s Space BC: Bile Canaliculus


Liver

Three functional surface

on the surface of hepatocyte

*Perisinusoidal surface:

face to perisinusoidal space

*bile canalicular surface:

face into the bile canaliculus

*cell junction surface


Liver

Blood Supply

Portal V→ interlobular V → →

(75%)

sinusoids

Hepatic A→interlobular A → →

(25%)

central V

hepatic V

sublobular V

Inferior vena cava


Biliary Passages

Bile canaliculi →periperal bile ductules ( Hering’s )

interlobular bile duct

Left & right hepatic ducts

Common hepatic duct

Common bile duct

Duodenum papilla

Cystic duct

Gall bladder


Liver

Classification of Lobules

Portal lobule

Liver acinus

Classic lobule


Liver

Classic lobule

A hexagonal structure with the central vein at its center; at the six corners of the lobule are hepatic triads.


Liver

Portal lobule

A triangular structure with the portal area at its center.

Three central veins are found at the peripheral boundary points.


Liver

Liver acinus

An elongate olive-shaped lobule; a central vein is at the ends of the two elongated points of the olive.



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