LECTURE DIGESTIVE SYSTEM part 1 Oral cavity esophagus

LECTURE DIGESTIVE SYSTEM part 1 Oral cavity, esophagus & stomach Department of histology, cytology and embryology Kh. NMU

General description and significance n The digestive tract is: n a long tube extending from oral cavity to the anus and n associated glands. n Main functions are: ingestion, fragmentation, digestion, absorption of nutrients and elimination of waste products.

Classification and embryogenesis 3 compartments: n Anterior Oral cavity, pharynx, esophagus n Middle Gastrointestinal tract n Posterior Last 1/3 rectum, anus

Embryogenesis

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

Embryogenesis foregut hindgut midgut Cloacal Plate Oral Plate Allantois Heart Yolk Sac

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

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

Mucosa: 1. epithelium (buccal)

Mucosa: n n n 2. lamina propria – con. t. – nutrition, support, protection (GALT), absorption, secrition (glands), villi 3. muscularis mucosae Submucosa - con. t. - big bl. vessels, glands, nerve plexuses, lymphatic nodules, n provides motility of mucosa Muscularis externa – circular, longitudinal layers Serosa or adventitia

Oral Cavity consists of a number of suborgans Functions: Ingestion, STRUCTURE: Fragmentation 1. Mucosa Moistening 2. Submucosa Speech (not always present ! ) Facial expression 3. Muscularis ext. Sensory reception (facial muscles) Breathing 4. Adventitia (absent)

oral side Lip ss skin side skin oral ts ts lp bv sk sg sk ss sk low mag. The outer surface (skin) of the lip is covered by thin skin (ts). The inner surface (oral) is lined by a mucosa The transitional zone

ss Lip red area p bv Vermilion - “red” transitional zone In newborn there are small villi for sucking The cheek is similar to the lip. (Krok).

Tongue f C G E SM Epithelium (E) & underlying ct. Skeletal muscle (SM) runs in 3 planes. Embedded in the skeletal muscle lie glands (G). Papillae. Most numerous are conical, keratinized filiform (f) papillae; function – general sensation fungiform and foliate papillae are scattered. At the sulcus terminalis, lie 8 -12 large circumvallate papillae (C). - Taste sensation

Tongue, filiform & fungiform papillae ss ss fili ct Circumvallate papilla ct fili fungi nss

Tongue fp tb high med n papilla with taste buds

Maxilla Hard Palate unerupted tooth b hard palate epithelium ss med n m low The mucosa (m) is tightly bound to the bone (b). The epithelium (ss) is disturbed in chewing and swallowing and so tends to be keratinized, and lamina propria forms deep papillae, protruding in the epithelium.

Soft palate Epithelium sg sm oral cavity Its upper surfaces the respiratory passages pseudostratified epithelium. Facing oral cavity epithelium is stratified squamous. Krok !

c ss Lingual Tonsil T mg sk Lingual tonsil (T) locates on the dorsum of the tongue. Together with palatine, pharyngeal tonsils form "ring". At time of chronic inflammation may undergo tonsilectomy.

TOOTH

Tooth development n n n n Enamel organ (epith) Ameloblasts Enamel Dental papilla Odontoblasts Dentine Dental sac – cementum, pulp

SALIVARY GLANDS n Saliva: water, mucus, amylase, lysozyme, a/b, ions n I. Large salivary glands 3 pairs: parotid, submandibular, sublingual function IN RESPONce TO PARASYMPATHETIC ACTIVITY n II. Minor salivary glands function CONTINUOUSLY

General structure Compound branched acinar or acino-tubular glands n Connective tissue capsule n Lobulated structure n Lobules contain secretory units and small ducts n n Interlobular connective tissue with ducts and vessels

5 Intercalated duct Striated duct, Serous acinus Mucous acinus Next are interlobular and general

Secretory unit Myoepithelial cells (contractile) surround secretory portions and small ducts – intercalated and striated Nucleus Myoepithelial cells

sd Parotid The parotid is a serous gland secreting amylase. su RER n Secretory unit (su) is acinar. Pyramidal acinar cells have round basally-placed nuclei (n) with abundant basal RER low high

itd Sublingual gland id med low msu sd This gland has mucous & mixed secretory units but mostly mucous. n. Mixed acinus with a n. Serous demilune n me me d id high msu

lobule Submandibular gland m/s low id ed sa high It is predominantly serous gland shows blue, pure serous acini (sa) & pale, mucous and mixed with serous demilunes (m/s). med

Intercalated duct Demilune demilune Parotid gland sublingual gland Striated duct Sublingual gland Demilune Striated duct Submandibular gland Compare

Esophagus (= Pharynx) 6 -7 longitudinal folds. The muscularis externa. The upper 1/3 rd is composed of skeletal muscle; the lower 1/3 rd - smooth muscle; the middle 1/3 rd shows a blending of the two varieties of muscle. Epithelium is stratified squamous nonkeratinized

HEsophagus 1) Mucosa- epithelium, lamina propria & muscularis mucosae, 2) Submucosa, 3) Muscularis externa 4) Adventitia

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

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

HEsophagus, m H middle 1/3 rd med. mag. . L sub sm me sk muscularis externa (me). = smooth (sm) & skeletal muscle (sk). lymphatic nodules (L) are in the mucosa (m).

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

E sc 1 S gp 2 low sc 3 E S gp med H high Esophagus/Stomach junction. - Epithelium is changed from stratified squamous to simple columnar (sc).

Stomach - general n The process of digestion essentially begins in the stomach; little absorption and excretion also occur here. n The stomach is composed of a mucosa, submucosa, muscularis externa & serosa. n The mucosal lining is a simple columnar secretory epithelium (mucous). n Folds (rugae), gastric pits, mammilated areas. n Glands vary in different regions of the stomach.

Stomach mucosa: ```epithelium lamina propria: gastric glands ; muscularis mucosae: both circular and longitudinal layers of SM. submucosa: muscularis: the inner oblique layer, circular layer and longitudinal layer of SM. serosa

gp n sc Stomach, mucosal lining & gastric pits Gastric pits (gp) are invaginations of a simple columnar epithelium The mucus blanket which protects the lining from stomach acids is present here.

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

1. Mucous neck cells 2. Chief cells , or zymogenic cells n columnar and basophilic cells - in the body of the glands. n produce pepsinogen and lipase. 3. Parietal cells secrete hydrochloric acid ( HCL ) and intrinsic factor. The latter is necessary for absorption of vitamin B 12 in the ileum

4. Enteroendocrine cells (APUD) 20 different types n 4 principal hormones: n Gastrin Hcl secretion n Secretin, cholecystokinin (CCK), gastric inhibitory peptide (GIP) pancreatic and gallblader activity and gastric secretion n

Pernicious anemia follows the absence of parietal cells (i. e. loss of epithelium due to gastric ulcer) n Disturbance of different cells may call the different pathology. n Digestion of different substances begins in different regions.

Fundic stomach r gp m sm fg low mm me sm 2 me med The lowest mag. shows the mucosa (m), submucosa (sm) with folds called rugae (r) & the muscularis externa (me). At higher mag. gastric pits (gp), fundic glands (fg), & muscularis mucosa (mm) comprises the mucosa. Outside is the submucosa (sm) and muscularis externa (me).

Fundic stomach mucosa gastric pit Isthmus n In fundic stomach, gastric pits occupy about 1/5 the mucosa; fundic glands comprise the remaining 3/4 ths. fundic gland Neck Base

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

Stomach, pyloric gastric pit gastric gland mn low Gastric pits occupy 3/4 ths the depth of the mucosa; the remaining 1/4 th are pyloric glands – short and branched. The major cell of the gland is the pale mucous (mn); parietal cells are absent as the pyloric stomach nears the intestine.

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