Digestive System Digestive Glands

Digestive SystemDigestive System

Digestive GlandsDigestive Glands

◇ small digestive glands:

found in the wall of digestive tract.

◇ accessory glands (large digestive glands):

Components of Digestive GlandsComponents of Digestive Glands

salivary glands

pancreas

liver

◇ Parenchyma: ( functional portion of an organ )

acini / gland cells

ducts

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

capsule

CT inside the organ.

General Structure of Digestive GlandsGeneral Structure of Digestive Glands

Salivary GlandsSalivary Glands

serous acinus mucous acinus seromucous / mixed acinus

General structure of the large salivary glands

Parenchyma

acinus

duct

intercalated duct

striated/secretory ductinterlobular duct

excretory duct

types of acinus


Model ( structure of the large salivary glands)

serous acinus

seromucous / mixed acinus

mucous acinus

intercalated duct

striated/secretory duct

demilume

Model Section (H&E)

serous acinus

mucous acinusseromucous /mixed acinus

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

Structural Characteristic of gland Cell:


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

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.

re

is

sg

seromucous acinus

/ mixed acinus

demilume

acinusductintercalated duct: simple squamous/cuboidal epith.striated/secretory duct: simple tall columnar epith.interlobular duct: pseudostratified columnar epith.excretory duct: stratified squamous epith.


intercalated duct:

simple squamous

or cuboidal epith.


intercalated duct: simple squamous or cuboidal epith.


basal lamina (bl);

desmosome (d);

nerve fibers (nf);

Golgi complex (g);

intercellular space (is);

mitochondria (m);

nucleus (nu);

RER (re).

13.000x.

EM

nu

re

mg

bl

Detail of intercalated duct cell

striated/secretory duct: simple tall columnar epith.




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 .



The secretory ducts ， which are continuous with the i

ntercalated ducts ， are wider and lined with a simple

columnar epithelium. As the secretion from the acini p

asses 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 duct

s which run between lobules.

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.

Parotid G.

Mucous A.

+++++Serous A.

Mixed A.

Inter-calated D

Submandibular G. Sublingual G.

+++

+++

short

+

Structural Features of Salivary Glands

Striated D

+

+ +

long short

long

none

few

none

none

PancreasPancreas

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).

PancreasPancreas

Parenchyma

exocrine gland endocrine gland

produces pancreatic juice

produces hormones

Parenchyma

make section

Parenchyma

exocrine gland

endocrine gland endocrine

gland

exocrine gland

exocrine gland

Parenchyma

exocrine gland

endocrine gland

Acini

PancreasPancreas

Exocrine Pancreas

Ducts

• wholly consists of serous acini.

• small centroacinar cells in the lumen.

intercalated ducts

interlobular ducts

main pancreatic ducts

major duodenal papilla

Exocrine Pancreas

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.

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

Pancreas Acinus

Central Acinar Cells

Exocrine Pancreas

Pancreas Acinus

Centroacinar Cell

Acinar Cell

Low power(LM)

high power(LM)

Ducts • Intercalated ducts ： simple squamous or cuboidal epith.• Interlobular ducts ： columnar epith.• pancreatic ducts ： tall columanr epth.

Exocrine Pancreas

major duodenal papilla

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

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

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

into fatty acids 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.

Exocrine PancreasIt releases the pancreatic juice.

pancreatic juice contain many kinds of enzyme:

PancreasPancreasEndocrine Pancreas

• Islets of Langerhans scatter 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.

PancreasPancreas

Endocrine Pancreas

A-cells

B-cells

D-cells

A-cells B-cells A-cells

capillaries

Liver Liver

Liver 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

section

liver loblules

Liver Liver

Structures of Liver Lobule

Model of Liver Lobule

Liver Liver


* six-sided prism

with a central V. at its center.

* sheets of hepatocytes ( or hepatic plates )

extend radially from the central V.

* sinusoids between hepatic plates.

portal triads ( or portal area): in the corner of lobules.

Liver Liver


hepatic plates

Liver Liver

Portal Triads ( or Portal Area)

* Definition: The area of CT found in the angles

where adjacent hepatic lobules meet.* Components: CT. + portal triad

interlobular A interlobular V interlobular bile duct

Liver Liver


Liver Liver


interlobular A

interlobular bile duct

interlobular V

Liver 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 Liver

Sinusoids

Model

Sinusoids

SEM

Sinusoids

Scanning Electron M.(SEM)Ec: Erythrocyte; BC: Bile Canaliculus DS: Disse’s Space S: Sinusoid H: Hepatocyte Mv: Microvili

Sinusoids

TEM

SD: Space of Disse

fenestration

endothilium

SinusoidsKupffer Cell

(LM)

(TEM)Kupffer Cell

Liver Liver

Hepatocyte* typically large polyhedral cells with large round centrally located nucleus. * abundance of organelles relates to its functions:

Mitochondria: provide energyRER: protein synthesisSER: bile formation / metabolism of lipids and

hormones / detoxification.

Lysosome: defence

Microbody: detoxification.Inclusions: glcogen particles, lipid droplets

and pigments.

Liver Liver

Hepatocyte

MO

DE

L

Model of Hepatocyte

Hepatocyte(EM)

* 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

Functions of Hepatocyte

Liver Liver

Liver Liver

Bile CanaliculusDefinition: 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

BC

Bile Canaliculus

Bile Canaliculus

Bile Canaliculus Freeze Fracture SEM

Liver Liver

Perisinusoidal space (Disse’s Space)

A space between endothelium & hepatocyte.• Be visible under EM.• Occupy by numerous microvilli of hepatocytes.• Fill with blood plasma.• have fat-storing cells (storing fat & vitamin a)• A site for substance exchange between the blood & the hepatocytes.


Disse’s Space

Scanning Electron M.(SEM)Ec: Erythrocyte; BC: Bile Canaliculus DS: Disse’s Space S: Sinusoid H: Hepatocyte Mv: Microvili

Sinusoids

TEM

SD: Space of Disse

fenestration

endothilium

E: Erythrocyte S: Nucleus of Endothelial CellD: Disse’s Space BC: Bile Canaliculus

TEM

*cell junction surface

* Perisinusoidal surface: face to perisinusoidal space

* bile canalicular surface: face into the bile canaliculus

Liver Liver Three functional surface

on the surface of hepatocyte

Blood SupplyBlood Supply

Portal V→ interlobular V → →

Hepatic A→interlobular A → →

sublobular V

sinusoids

central Vhepatic V

Inferior vena cava

(75%)

(25%)

Liver Liver

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

Biliary PassagesBiliary Passages

Liver Liver

Classification of Lobules

Classic lobule Portal lobule Liver acinus

Liver Liver

Classic lobule

A hexagonal structure

with the central vein

at its center; at the six

corners of the lobule

are hepatic triads.

Liver Liver

A triangular structure

with the portal area at

its center.

Three central veins

are found at the

peripheral boundary

points.

Portal lobule

Liver Liver

An elongate olive-

shaped lobule; a central

vein is at the ends of

the two elongated

points of the olive.

Liver acinus

Digestive System Digestive Glands

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