DIGESTIVE SYSTEM 1 -st part General description

DIGESTIVE SYSTEM 1 -st part

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

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: a- Epithelium b- Lamina propria c -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 – different

2. lamina propria – connective tissue – has glands, lymphatic nodules, form core of villi 3. muscularis mucosae muscle tis. n Submucosa - con. t. – smooth - big blood vessels, glands, nerve plexuses, lymphatic nodules, n provides motility of mucosa, form FOLDS n Muscularis externa – circular, longitudinal layers n Serosa – peritoneum n or adventitia – con. Tis.

Lip The outer surface of the lip is covered by thin skin. The inner surface (oral) is lined by a thick stratified squamous nonkeratinized epithelium. In the submucosal connective tissue lie minor salivary glands The transitional zone - red

oral side Lip ss skin side skin oral ts ts lp bv sk sg sk ss sk low mag.

The cheek is similar to the lip.

Tongue f C G E SM

The mucosa consists of epithelium underlying c. t. Skeletal muscle (SM) runs in 3 planes. Embedded in the skeletal muscle lie glands (G).

Papillae. 1. filiform papillae : Most numerous , conical, keratinized 2. fungiform and 3. foliate papillae are scattered. 4. At the sulcus terminalis, lie 8 -12 large circumvallate papillae (C).

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

Tongue fp tb high med In the epithelium of the lateral surfaces of papillae there are many taste buds.

c ss Lingual Tonsil T mg sk Lingual tonsil locates on the dorsum of the tongue behind the circumvallate papillae.

Maxilla Hard Palate unerupted tooth b hard palate epithelium ss med n m low The mucosa is tightly bound to the bone.

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

TOOTH

TOOTH • Enamel • Dentine • Cementum • Pulp • Periodontal ligament

SALIVARY GLANDS n Saliva: water, mucus, amylase, lysozyme, antibodies, ions 2 groups: n I. Large salivary glands 3 pairs: parotid, submandibular, sublingual n n II. Minor salivary glands

General structure Compound branched acinar or acino-tubular glands n Connective tissue capsule send septae and divide on Lobules contain secretory units and small ducts n n Interlobular connective tissue has 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. Secretory unit is acinar, cells have abundant basal RER se RER n low high

Submandibular gland lobule m/s low id ed sa high med It has 1) serous acini (blue) and 2) pale mucous and 3) mixed - mucous with serous demilunes (m/s).

itd Sublingual gland id med low msu sd This gland has mucous and mixed secretory units but mostly mucous. n me me d id high msu

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

Esophagus

Esophagus The esophagus has all main features of the GI tubular organs: 1) Mucosa-epithelium, lamina propria & muscularis mucosae, 2) Submucosa, 3) Muscularis externa 4) Adventitia

Esophagus 1. Epithelium is stratified squamous nonkeratinized 2. 6 -7 longitudinal folds. 3. 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.

Glands ss mg lp mm sm me n 1. Mucosal cardiac glands are found in the lamina propria in the upper and lower thirds of the esophagus.

glands mm mg s me 2. A mucous esophagel glands proper in the submucosa (s). lie

m L Esophagus, sub middle 1/3 rd med. mag. . sm me sk

Nerve supply The enteric nervous system lie in 1 submucosa (Meissner’s plexus) and 2 - in the muscularis externa (Auerbach’s plexus)

Esophagus submucosal gl. med lymphatic nodule M' high lumen muscul. externa. str. sq. epi musc. muc. submuc. A' high

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

Stomach - general n n The process of digestion essentially begins in the stomach; little absorption and excretion also occur here. The stomach is composed of a mucosa, submucosa, muscularis externa & serosa. n The mucosal lining is a simple columnar secretory epithelium – produce viscous mucous. The mucus protects the lining from stomach acids. n Folds (rugae), gastric pits (invaginations lined by epithelium), mammilated areas.

look: mucosa: epithelium: simple columnar mucous- secreting cells; lamina propria: gastric glands ; muscularis mucosae: SM. submucosa: muscularis: an inner oblique layer, a middle circular layer and an outer longitudinal layer of SM. serosa

gp sc Gastric pits are invaginations of a simple columnar epithelium

n Lamina propria contains glands n Glands vary in different regions of the stomach. n Gastric glands were named for the region of the stomach, but glands of the fundus and body are generally called fundic glands, which secrete the enzymes and acid of the stomach. n While cardiac and pyloric glands predominantly secrete mucus.

• The fundic glands are simple tubular. They contain 4 cell types: • chief, • • parietal, mucous neck cells (stem), • endocrine cells

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

3. Enteroendocrine cells (APUD) 20 different types n 4 principal hormones: n Gastrin n Secretin, cholecystokinin (CCK), gastric inhibitory peptide (GIP) n

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

Stomach, pyloric gastric pit gastric gland mn low In the pylorus, 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.