Lecture

DIGESTIVE SYSTEM part 2

INTESTINE

LIVER

PANCREAS

Department of histology, cytology andembryology KhNMU

Small intestine

• Functions:

• digestion – liver, pancreas, enterocytes

• absorption – enterocytes

• STRUCTURE: 4 membranes

Intestinal lining:

1) plicae circularis: mucosa + submucosa

2) villi - consist of:

epithelium, lamina propria, mm

3) crypts: invaginations of epithelium in the lamina propria

simple columnar epithelium: absorptive enterocytes, goblet, endocrine, Paneth cells and stem cells

fenestrated capillaries and central lacteal

IleumDuodenum

Villus

lacteal

serosa

Epithelium(villus)

• high mag.1). Enterocytes = Columnar absorptive cells (a) have microvilli = brush border

(bb) for absorption of digested food.

Membrane and luminal digestion

2). Mucus-secreting goblet cells (gc) produce a protective mucus. Lymphocytes and plasma cells (L) are numerous in the lamina propria of the villus.

a

bb

gc

L

• high mag

At the bottom of intestinal glands (crypts) are

3). the granule-containing Paneth cells (p). Lysozyme.

Goblet (g) and absorptive (a) cells.

p

g

a

Epithelium(crypt)

3. Paneth cells, 4. enteroendocrine cells (CCK, secretin, GIP),

5.undifferentiated cells=stem, at the bottom of crypt

3

4

5

Villus,lacteal

The lamina propria (lp) contains blood-filled capillaries c, and lacteal –lymphatic capillary l,smooth muscle cells (sm),(krok – villus shortens); GALT

v

gc

ivs

ivs

llp

csm

GALT

low

• Mm – 2 layers of sm.m.• Submucosa is usual. Only in the duodenum it is

filled with Brunner’s mucous glands (bg), around which - 2 layers of smooth muscle of the muscularis externa (me) surrounded by the serosa (s).

Duodenum

v

v

m

m

ig

sm

sm

lpmm

bg

me

s

low

med

v

Duodenum

• low & med mag.Ducts (d) from Brunner’s glands (Bg) (s) pass through

the muscularis mucosa (mm) to empty their alkaline mucus in or between the crypts (c).

d

sBg

mm mm

c

med

low

villi

intestinalglands

Duodenum

• nerve supply - submucosal (s) and myenteric (m) nerve plexuses.

med

high

high

s

m

crypts

muscul.mucosa

submucosa muscularisexterna

Brunner’s glands

medlow

Jejunum

• low & med. mag.The jejunum is like the duodenum & ileum

but has no submucosal glands and Peyer’s patches.

Contains bigger amount of goblet cells

v

ig

ig

g

a

P

• low & med. mag. The major distinguishing feature is the aggregated lymphatic

nodules (ln) called Peyer’s patches in the mucosa or submucosa

Ileum

medlow

v

v cr.

sm sm ln

ln

muscul.mucosa

IleumDuodenum

Villus

lacteal

COMPARE !

Large intestine (bowel) - general

• Reabsorption of water, electrolytes, cellulous• Elimination of wastes

• Inner lining - permanent internal folds of its mucosa & submucosa called plicae circulares and crypts.

• Its mucosa lacks of villi.• The submucosa is usual

• Circular & longitudinal smooth muscle form the muscularis externa. The inner circular layer is uniform but the outer longitudinal layer has 3 thicker bands, the taenia coli.

• where the colon faces the abdominal cavity there is a serosa.

Taenia coli

Colon

• low & med mag. Plicae circulares (pc) . Unlike the small intestine there are no mucosal villi.

There are straight intestinal glands – crypts (cr) composed mainly of

1. Goblet cells – the most numerous .

2. Columnar absorptive cells

3. Enteroendocrine cells

4. Undifferentiated cells

pc

cr

low

med

muscularismucosa

submucosa

musc. ext.

High.Magn.

Large intestineCOMPARE !

• Appendix

Anal canal

• low & high mag.Anal columns

Brunched tubular glands (g)

Stratified squmous epithelium (ss)

ig

gss

gca v

v

v

lowhigh

L

mm

Liver & Gall Bladder

Liver has specific location – on the way of absorbed material, that is why has

very original vasculature and functions

Functions:• Bile synthesis and secretion (emulsification)• Excretion of bilirubin• Protein synthesis• Gluconeogenesis• Storage• Detoxification• Protective• Hemopoietic organ• Endocrine

Liver has lobulated structure

Liver lobule is hexagonal in shape

① at its center - central

vein

② hepatic plates （ cords of cells - hepatocytes ） locate radially

③ hepatic sinusoids locate

between plates

Liver lobule

• Connective tissue poor develops

Central veins (cv) drain to a sublobular vein (sv). The portal triads (pt) locate at lobule coners.

pt

cv

sv

• Hepatic plate(cord)is one or two cells thick

• Inside the plate between cells the bile canaliculi locate

The bile canaliculus wall is made up of hepatocytes

hepatocyte

sinusoid

Kupffer cell

Bile canaliculus

• Hepatocytes：

Polyhedral6 surfaces

Vascular and bile surfaces

a. RERb. SERc. Golgi complexd. Mitochondriae. Inclusions

• Jaundice

• ①High regeneration

EM of Liver

LiverTwo hepatocytes (h) are seen.

The bile canaliculus form a network that eventually empty into bile duct at the periphery of the lobule.

Ultimately ducts will empty into the gall bladder.

h

h

b

Hepatic sinusoid

Lined by endothelium

Hepatic macrophages(Kupffer cell)

SSpace of Dissepace of Disse

sinusoidsinusoid

Kupffer cellKupffer cell

• high mag.Liver had been injected with carbon particles

Kupffer cells containing carbon (red arrows)

Sinusoids (s)

A flattened endothelial cell (e)

Space of Disse (d) between it and the hepatocytes

e d

s

Adipose cells storage vit. A

Blood circulation of the liver• Hepatic artery interlobular artery• Portal vein interlobular vein• hepatic sinusoid

• central vein• cv• sublobular vein• hepatic vein

• The way of bile draining

v

a

d

s

cv

At the lobule coners the portal triads are found:

• Liver, injectedwith red gelatin to demonstrate the abundant vasculature.

central vein (cv), the portal triad (pt)

hepatic sinusoids (hs).

cv

pt

hs

Liver lobules – 3 types

Gall bladder

Pancreas. Mixed gland

• Functions:–Exocrine

• Trypsinogen, pepsinogen, peptidase• Amylase• Lipase• Deoxyribonuclease, ribonuclease

–Endocrine

Pancreas – compound acinar serous gland

• Exocrine – 98-99%• Endocrine – 1-2%

• Capsule

• Septa

• Lobules

• Interlobular duct

• Serous secretory units

low

med

lobule id

lobule

• Septa (c.t.)

• Lobules

• Interlobular duct

• Serous secretory units

Pancreas. Exocrine secretory units

• Zymogen granules

• Intercalated duct is intercalated into the s.unit =

centroacinar cells

• Exocrine partStructural features of the acinus:

① Purely serous.

② the presence of centroacinar cells in the center of the acinus

Centroacinar cells

Serous cells

Intercalated duct

Pancreas. Endocrine

• Islets of Langerhans, - low & med. mag.

Scattered among exocrine secretory units spherical collections of light-staining cords of endocrine cells

.

low, H&E

med, trichrome

Pancreas. Endocrine

• islets of Langerhans:

• 1. B cell

• 2. A cell

• 3. D cell

• 4. minor cells:PP, D1, EC,

Islets of Langerhans• B - insulin blood glucose

70%

• A – glucagon blood glucose

15-20%

• D – somatostatin insulin

5-10% glucagon

• PP – PP,

• D1 – VIP,

• EC – secretin, motilin