Kharkov National Medical University Department of Histology, cytology and embryology LECTURE for dentistry students

DIGESTIVE SYSTEM

The digestive tract is a long tube and associated glands. The digestive tract is a long tube and associated glands. Main functions are: ingestion, fragmentation, digestion, absorption of nutrients and elimination of waste products. Main functions are: ingestion, fragmentation, digestion, absorption of nutrients and elimination of waste products.

Embryogenesis Gut – from endoderm, stomatodaeum, proctodaeum – from ectoderm Connective tissue, muscles are from mesoderm amnion yolk sac

General plan of structure FOUR membranes: FOUR membranes: Mucosa: Epithelium Mucosa: Epithelium Lamina propria Lamina propria Muscularis mucosae Muscularis mucosae Submucosa Submucosa Muscularis externa Muscularis externa Serosa or adventitia Serosa or adventitia

1c 2 4 3a 2a 2b 3b 1a 1b

Mucosa: 1.epithelium

Mucosa: 2. lamina propria – c.t. – nutrition, support, 3. muscularis mucosae Submucosa - Submucosa - c.t. - big bl.vessels, glands, nerve plexuses, lymphatic nodules, provides motility of mucosa Muscularis externa – circular, longitudinal layers Serosa or adventitia Serosa or adventitia

Esophagus 6-7 longitudinal folds. Epithelium is stratified squamous nonkeratinized The muscularis externa is composed of skeletal and smooth muscle.

HEsophagus 1)Mucosa- 2) Submucosa, 3) Muscularis externa 4) Adventitia

Esophagus Mucosal cardiac glands (mg) are found in the lamina propria (lp) (mm) in the upper and lower thirds of the esophagus. If they are not fully effective, the excessive reflux results in pyrosis (heartburn) – tending to rise of the gastric contents upward toward the neck. Mucosal cardiac glands (mg) are found in the lamina propria (lp) (mm) in the upper and lower thirds of the esophagus. If they are not fully effective, the excessive reflux results in pyrosis (heartburn) – tending to rise of the gastric contents upward toward the neck. mg lp ss mm sm me

Esophagus A mucous esophagel glands proper (mg) lie in the submucosa (s). lie in the submucosa (s). mg s mm me

The muscularis externa (me). smooth (sm) & skeletal muscle (sk). Accumulations of lymphocytes (L), called lymphatic nodules are common in the mucosa (m) along the GI tract. L sub me sm sk m HEsophagus, H middle 1/3rd - med. mag..

Esophagus nerve supply nerve supply The gut nervous system is extensive. In the submucosa (Meissner’s plexus) (M') and in the muscularis externa (Auerbach’s plexus) (A'). M' A' str.sq.epi musc. muc. submuc.muscul. externa. submucosal gl. lymphatic nodule lumen med high

H Esophagus/Stomach junction. - low, med. & high mag. Epithelium is changed from stratified squamous to simple columnar (sc) E E S S sc low medhigh

Stomach The process of digestion essentially begins in the stomach; little absorption and excretion. The process of digestion essentially begins in the stomach; little absorption and excretion. The mucosal lining is a simple columnar secretory epithelium (mucous). The mucosal lining is a simple columnar secretory epithelium (mucous). Folds (rugae), gastric pits, mammilated areas. Folds (rugae), gastric pits, mammilated areas. Glands vary in different regions of the stomach. Glands vary in different regions of the stomach.

Gastric pits (gp) are invaginations of a simple columnar epithelium The mucus layer protects the stomach. gp sc

Lamina propria contains glands: Lamina propria contains glands: fundic glands secrete enzymes and acid of the stomach. fundic glands secrete enzymes and acid of the stomach. While cardiac and pyloric glands predominantly secrete mucus. While cardiac and pyloric glands predominantly secrete mucus. The fundic glands are simple tubular. The fundic glands are simple tubular. They contain 4 cell types: They contain 4 cell types:

1. Chief cells form the body of the glands. form the body of the glands. produce pepsinogen and lipase. produce pepsinogen and lipase Parietal cells secrete hydrochloric acid ( HCL ) and intrinsic factor is necessary for absorption of vitamin B 12

3. Enteroendocrine cells (APUD) 20 different types 20 different types 4 principal hormones 4 principal hormones 4. mucous neck cells - stem 4. mucous neck cells - stem

Fundic stomach mucosa In fundic stomach, gastric pits occupy 1/4 the mucosa; fundic glands comprise the remaining 3/4ths. gastric pit fundic gland Isthmus Neck Base

Cardiac Stomach, Cardiac Stomach, Gastric pits occupy ½ of mucosa. Gastric glands are simple tubular and slightly branched Cells are mucus-secreting and occational endocrine gastric pit cardiac glands sc mm

Stomach, pyloric In the pylorus, gastric pits occupy 3/4ths, pyloric glands – short and branched. The major cell of the gland is the pale mucous (mn); parietal cells are absent - pyloric stomach nears the intestine. gastric pit gastric gland mn low

Fundic Stomach, nerve supply, - med & high mag Fundic Stomach, nerve supply, - med & high mag Elements of the submucosal (s) and myenteric (m) nerve plexuses are present. fundic glands musc. mucosa submucosamuscularis externa inner middle outer s m smooth muscle artery vein

Small intestine Functions: Functions: digestion – liver, pancreas, enterocytes digestion – liver, pancreas, enterocytes absorption - enterocytes absorption - enterocytes

Intestinal lining: plicae circularis: mucosa + submucosa intestinal villi: epithelium, lamina propria, mm epithelium, lamina propria, mm crypts: invaginations of epithelium in the lamina propria

Ileum Duodenum Villus lacteal serosa

Epithelium (villus) 1. Enterocytes = Columnar absorptive cells (a) have microvilli = brush border (bb) for absorption of digested food. 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

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 3 4 5

Villus, lacteal The lamina propria (lp) contains blood-filled capillaries ©, and lacteal (l), and lacteal (l), smooth muscle cells (sm),(krok – villus shortens GALT v gc ivs l lp c sm GALT low

Lamina propria, mm Lamina propria, mm Submucosa filled with Brunner’s mucous glands (bg), around which - 2 layers of smooth muscle the muscularis externa (me) surrounded by the serosa (s). Duodenum v v m m ig sm lp mm bg me s low med v

lowJejunum low & med. mag. low & med. mag. The jejunum is like the duodenum but has no submucosal glands and Peyer’s patches. Contains bigger amount of goblet cells v ig g a P

low & med. mag. low & med. mag. The major distinguishing feature is the aggregated lymphatic nodules (ln) called Peyer’s patches in the mucosa or submucosa The major distinguishing feature is the aggregated lymphatic nodules (ln) called Peyer’s patches in the mucosa or submucosaIleum med low v v cr. sm ln muscul. mucosa

Large intestine Reabsorbtion of water & electrolytes Reabsorbtion of water & electrolytes Elimination of wastes Elimination of wastes Inner lining - permanent internal folds of its mucosa & submucosa called plicae circulares and crypts. Inner lining - permanent internal folds of its mucosa & submucosa called plicae circulares and crypts. muscularis externa. The inner circular layer is uniform but the outer longitudinal layer has 3 thicker bands, the taenia coli. muscularis externa. The inner circular layer is uniform but the outer longitudinal layer has 3 thicker bands, the taenia coli.

Taenia coli

Colon Plicae circulares (pc). Unlike the small intestine there are no villi. Plicae circulares (pc). Unlike the small intestine there are no 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 muscularis mucosa submucosa musc. ext.

Large intestineCOMPARE ! Large intestineCOMPARE ! Appendix Appendix

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

Liver has lobulated structure

Liver lobule is hexagonal in shape 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

Hepatic plate(cord)is one or two cells thick Hepatic plate(cord)is one or two cells thick Between cells the bile canaliculi locate Between cells the bile canaliculi locate The bile canaliculus wall is made up of hepatocytes hepatocyte sinusoid Kupffer cell Bile canaliculus

Blood circulation of the liver Hepatic artery interlobular artery Hepatic artery interlobular artery Portal vein interlobular vein Portal vein interlobular vein hepatic sinusoid hepatic sinusoid central vein central vein cv cv sublobular vein sublobular vein hepatic vein hepatic vein The way of bile draining The way of bile draining v a d s cv

At the lobule coners the portal triads are found:

Pancreas.Mixed gland Functions: Functions: –Exocrine Trypsinogen, pepsinogen, peptidase Trypsinogen, pepsinogen, peptidase Amylase Amylase Lipase Lipase Deoxyribonuclease, ribonuclease Deoxyribonuclease, ribonuclease –Endocrine

Pancreas – compound acinar serous gland Exocrine – 98-99% Exocrine – 98-99% Endocrine – 1-2% Endocrine – 1-2% Capsule Capsule Septa Septa Lobules Lobules Interlobular duct Interlobular duct Serous secretory units Serous secretory units low med lobule id lobule

Exocrine part Exocrine part Structural 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. 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: islets of Langerhans: 1. B cell 1. B cell 2. A cell 2. A cell 3. D cell 3. D cell 4. minor cells: 4. minor cells: PP, D 1, EC,

Islets of Langerhans B - insulin blood glucose B - insulin blood glucose 70% 70% A – glucagon blood glucose A – glucagon blood glucose 15-20% 15-20% D – somatostatin insulin D – somatostatin insulin 5-10% glucagon 5-10% glucagon PP – PP, PP – PP, D 1 – VIP, D 1 – VIP, EC – secretin, motilin EC – secretin, motilin