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

Salivary GlandsGeneral structure of the large salivary glands

Parenchyma

acinus

duct

Serous acinus

Mucous acinus

Seromucous/mixed acinus

Intercalated duct

Striated/secretory duct

Interlobular duct

Excretory duct

Model (structure of the large salivary glands)

Salivary GlandsStructural characteristic of gland cell:

Serous acinus: comprised by serous cells.

﹡zymogen granules in apical cytoplasm.

Mucous acinus: comprised by mucous 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 comples (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.

Detail of mucous cells:

mucous cell (sc);

Golgi complex (gc);

Intercellular space (is);

Secretion granule (sg);

Lumen (l);

Nucleus (n);

RER (re).

10000x.

Seromucous acinus

/mixed acinus

demilume

Salivary GlandsAcinus

Duct

Intercalated duct:

Simple squamous/cuboidal epith.

Striated/secretory ducts:

simple tall columnar epith.

Interlobular duct:

pseudostratified columnar epith.

Excretory ducts:

stratified squamous epith.

Salivary Glands

Intercalated duct:

Simple squamous

or cuboidal epith.

Salivary GlandsIntercalated duct: simple squamous or cuboidal epith.

Detail of intercalated duct cell

Basal laminar (bl);

Desmosome (d);

Nerve fibers (nf);

Golgi complex (g);

Intercellular space (is);

Mitochondria (m);

Nucleus (nu);

RER (re).

13.000x

Salivary Glands

Striated/secretory duct: simple tall columnar epith.

Salivary GlandsStriated /secretory duct

Salivary Glands

Striated/secretory duct

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

Salivary GlandsInterlobular duct: excretory duct:

Pseudostratified columnar epith. Stratified squamous epith.

Salivary glands

Include

﹡Parotid G.

﹡Submandibular G.

﹡Sublingual G.

Function:

﹡Moistening food.

﹡Carbohydrate digestion.

﹡Secrete IgA.

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

exocrine gland endocrine gland

produces produces

pancreatic juice hormones

Parenchyma

Parenchyma

Pancreas

Exocrine pancreas

Acini Ducts

Wholly consists of serous acini.

Small centroacinar cells in the lumen

Intercalated ducts

Interlobular ducts

Main pancreatic ducts

Major duodenal papilla

Exocrine Pancreas

Exocrine Pancreas

It releases the pancreatic juice.

Pancreatic juice contain many kinds of enzyme:

﹡amylase: hydrolyses starch & glycogen.

﹡lipase: hydrolyzes triglycerides

into fatty acids and mono-glycerides

﹡cholesterol esterase: breaks down

﹡trypsin and chymotrypsin:

hydrolyze proteins.

﹡ribonuclease & deoxyribonuclease:

split nucleic acids.

PancreasEndocrine pancreas

﹡Islets of Langerhans

Scatter throughout the exocrine pancreas.

﹡Three types of cells:

A-cells (20%) glucagon (glycogen→ glucose)

B-cells (75%) insulin

D-cells (5%) somatostatin

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

PancreasEndocrine pancreas

GlucagonPurpose: Assist insulin in regulating blood glucose (sugar) in the normal rangeAction:    Forces many cells of the body to release (or produce) glucose (increasing blood sugar)Secreted in response to:     Low blood glucoseSecretion inhibited by:     High blood glucoseDisease due to deficient action: Some times nothing, sometimes hypoglycemiaDisease due to excess action: HyperglycemiaTumor called: Glucagonoma

InsulinPurpose: Regulate blood glucose (sugar) in the normal range Action: Forces many cells of the body to absorb and use glucose thereby decreasing blood sugar levelsSecreted in response to: High blood glucoseSecretion inhibited by: Low blood glucoseDisease due to deficient action: Diabetes   Disease due to excess action: HypoglycemiaTumor called: Insulinoma. 

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 lobules.

﹡Functions as an exocrine gland (secreting bile) and other very important roles.

Liver

LiverStructrues of Liver lobule

LiverStructures of Liver lobule

Model of Liver Lobule

LiverStructures of Liver lobule

﹡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.

Structures of Liver lobule

Liver

Portal Triads (or Portal Area)

Liver

﹡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

Portal Triads (or Portal Area)

Liver

Portal Triads (or Portal Area)

Liver

Sinusoids

Liver

﹡Dilated anastomosing venules between the hepatic plates.

﹡Blood pathway: periphery→central V.

﹡Kupffer cells line in the wall of sinusoids.

﹡EM (endothelium of sinusoid)

significant gaps;

numerous fenestration;

incomplete basal lamina.

Sinusoids

Liver

TEM

Sinusoids

Sinusoids

HepatocyteLiver

﹡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.

Hepatocyte

Liver

Functions of Hepatocyte

Liver

﹡Produce bile.

﹡Degrade glycogen to glucose under regulation of hormones.

﹡Involve the blood lipid metabolism.

﹡Synthesize the blood plasma proteins: albumin;fibrinogen, and so on

﹡Detoxification

Bile Canaliculus

Liver

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

Bile Canaliculus

Perisinusoidal space (Disse’s Spaces)

Liver

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.

Perisinusoidal space (Disse’s Space)

Perisinusoidal space (Disse’s Space)

Sinusoids

LiverThree functional surface on the surface of hepatocyte

LiverBlood Supply

Liver

Liver

Liver

Liver