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Home , Esophageal gland

Anhui Medical University

Chapter 11 Digestive tract

Lyu Zhengmei Department of Histology and Embryology, Anhui Medical University Anhui Medical University introdction

Digestive tract (DT) and Digestive glands ===Digestive system:

Functions of DT: Obtain molecules from ingested food. A protective barrier for the body. Anhui Medical University

Functions

Oral cavity Ingestion and Initial fragmentation

Conduct food from oral to

Stomach Complete fragmentation and initial digestion

Duodenum Get enzymes from pancreas and liver

Jejunum and Complete digestion and main absorption

Large intestine Absorption of Water and ions

Elimination of waste products Anhui Medical University Anhui Medical University

Part One Oral Cavity and Related structures Anhui Medical University Oral cavity

 The oral cavity extend from lips to .  lined by nonkeratinized stratified squamous epi., except the gum and hard palate (keratinized).  The wall of the oral cavity is made up of CT, muscles and bone.  The oral cavity contains the lips, the teeth, the tongue and salivary glands. Anhui Medical University

Papillae CV

Foliate  Filiform papillae  Fungiform papillae  Circumvallate Fg papillae FL

a). Filiform papillae: The most numerous. Present over entire surface. small and conical in shape. b). Fungiform papillae: resemble mushrooms, a narrow stalk and a dilated upper part. Anhui Medical University c). Circumvallate papillae: The largest papillae. CV is encircled by a deep cleft.  The epthelium contains numerous of taste buds.  Underlying of the mucosa, there are serous glands

CV

Foliate

Fg

FL

VE: serous glands(von Ebner’s) Anhui Medical University Taste bud 10,000 TBs in your mouth, present in the epi. of fungiform papillae, circumvallate papillae, etc.

 a onion-shaped structure made up of modified epithelial cells.  a small cavity that opens to the surface through a taste pore.

 The cells in TB are of 3 basic types. Receptor cells or taste cells, supporting cells, which have microvilli on the tip of the cells and basal cells. Anhui Medical University

 The same taste bud can respond to 4 types of taste (sweet, sour, salty and bitter). The sweet and salty is less sensitive, but bitter is most sensitive. Anhui Medical University

Part two

Esophagus, Stomach and Intestine Anhui Medical University

1. Components of digestive tract

mucosa

muscularis

share a similar histological plan: a hollow tube composed of a lumen surrounded by a wall. The wall includes: mucosa, submucosa, muscularis and . Anhui Medical University

2. General structural details of the wall 1) Mucosa () ------Three sublayers  Epithelium : stratified squamous epi. simple columnar epi. FUNCTION: A selectively permeable barrier. • Facilitate the transport and digestion. • Promote the absorption •Produce the hormone •Secret for lubrication and protection. Anhui Medical University

: LCT rich in BV, LV and LP nerves ,lymphoid tissues, glands

: Except esophagus, 2 sublayers (Inner circular and outer longitudinal of ).

Function: Promote the movements LP of the mucosa and increase its contact with the food. Anhui Medical University

2) Submucosa: CT . Submucosa nerve plexus. 3) Muscularis : Smooth muscle cells and less skeletal muscle cells. inner circular and outer longitudinal sublayer  Myenteric nerve plexus mucosa Function: The contraction of muscularis propel and mix the food in digestive tracts. 4) Adventitia submucosa Serosa: LCT + mesothelium Fibrosa: LCT muscularis Anhui Medical University Part 3 Esophagus 1) Mucosa: stratified squamous epi lamina propria muscularis mucosa: only a layer of longitudinal arranged SM 2) Submucosa: CT esophageal gland: Anhui Medical University

3) Muscularis: inner circular and outer longitudinal  upper portion: only skeletal muscle  middle portion: mixture of skeletal and smooth muscle  lower end: only smooth muscle 4) Adventitia: fibrosa

Functions:

 Transport food from the mouth to the stomach. Anhui Medical University Stomach Functions:  store food temporarily  initial digestion  absorb part of water and ion

 Structures: Gross inspection reveals 4 regions:  fundus,  cardia,  body, 

 Folds or rugae. Anhui Medical University

 The wall is composed of 4 layers: Mucosa, submucosa, muscularis adventitia.  Mucosa have some special features .

Mucosa muscularis Anhui Medical University

Regions of the stomach and their histological structure Anhui Medical University I. Mucosa of stomach

① Epithelium: Gastric pit Surface mucous cell: Structures: LM: Tall columnar, ovoid and basally- located nucleus. with mucin granules, so cells look empty with HE staining.

gastric pit: formed by epithelium invaginates into lamina propria Functions: Secreting mucus, which form mucous barrier Anhui Medical University

② lamina propria: Gastric pit Deep to , packed with and scanty CT.  Here’re 3 types of gastric gland: Main gastric gland cardiac gland pyloric gland.

muscularis mucosa Anhui Medical University

Main gastric glands

Distribution:

Most of the stomach (present in the body and fundus) except pylorus and cardia.

Structures:  Simple or branched tubular glands. The glands open into gastric pits. The epithelium of the glands includes chief cells, parietal cells, neck mucous cells, undifferentiated cells and endocrine cells. Their distribution is not uniform. Anhui Medical University

1. or oxyntic cell  Distribution: more numerous in the upper half of the gland.  Structures: LM: rounded or pyramidal with round and centrally-located nucleus. The cytoplasm is strongly acidophilic. Anhui Medical University

EM: Active cell Intracellular canaliculus (IC), which bear microvilli in the wall. Tubulovesicles (TV) and Abundant Resting cell Mitochondria

Functions: secrete hydrochloric acid and produce intrinsic factor. Anhui Medical University

Active ce

Resting cell EM of Parietal cell Anhui Medical University

1 Function of Hydrochloric acids Pepsinogen (chief cells)

hydrochloric acids Proteins

Pepsin pH0.9-1.5 Peptides 2 Function of intrinsic factor

Intrinsic factor Complex production of erythrocytes

Vitamin B12 Anhui Medical University

Gastric ulcer Anhui Medical University 2. Chief cell, zymogenic cell  Distribution: numerous in the basal part of the glands.

 Structures: LM: Low columnar, A round and basally-located nucleus. Basal cytoplasm is basophilic and apical is light-stained Anhui Medical University

EM: RER, Golgi apparatus and apical granules (pepsinogen).

 Functions: secrete pepsinogen

Pepsin can break down proteins into peptides and solid food become liquefied.

Highly active Inactive HCl pepsinogen pepsin digest proteins Anhui Medical University

3. Mucous neck cell Distribution: neck part of the gland. Structures: Columnar cells, A flattened and basally-located Nucleus The cytoplasm is pale-stained in HE stain. Functions: mucus secretion. 4. undifferentiated cell : can multiply to replace other cells and play an important role in healing.

5. Endocrine cell: Anhui Medical University

Cardiac glands and pyloric glands

Distribution: The mucosa of cardia and pylorus respectively.  Function: Mucous secreting glands.  Structure: The majority of cells is mucous cells. Occasionally, parietal cells, chief cells and endocrine cells is present. Anhui Medical University

③ muscularis mucosa: 2 sublayers of SM: inner circular and outer longitudinal

other layers of stomach

Muscularis is well developed

------three sublayers:

oblique, circular

and longitudinal

serosa Anhui Medical University

Small intestines Components: is a tube, 5 meters long. It is composed of 3 parts: : 25 cm long : 2 meters long Ileum: 3 meters long Functions:  The small intestine is the site of terminal food digestion, nutrient absorption and endocrine secretion. The nutrients are absorbed by the epithelial cells. Anhui Medical University General Structure: The wall of the small intestine includes 4 layers:  Serosa similar to other segments  Muscularis  Submucosa:  Mucosa exhibit several special features, will be described below.

Mucosa

Lamina propria

Submucosa

Muscularis Anhui Medical University Mucosa

The surface area is 600-fold(200m2) increased. Three special fetures as following: 1.Plicae circulares(3-fold) →2. Villi(10-fold)→3. Microvilli(20-fold)

Gross inspection Anhui Medical University

1. Plicae circulares ()  Structure : Mucosa and part of submucosa project into the lumen, which is so large that be readily seen with naked eye.  Distribution: most develped in the jejunum. Become fewer and less in the ileum.  Function: increase the surface area and slow down the passage of the contents to facilitate absorption.

Gross inspection Tissue section Anhui Medical University 2.Intestinal Villi:  Structure: finger like projections, 0.5-1.5mm long ,consisting of a core of connective tissue covered by a surface epithelium . The CT core contains 3 important structures:  Numerous fenestrated Cap., which allow rapid absorption of nutrients into the blood.  A central lymphatic Cap. called a central lacteal. Distal ends blindly and proximal ends in a plexus of lymphatic V.  Some smooth muscle cells Anhui Medical University

intestinal villi under SEM intestinal villi under LM

Distribution: most developed in the duodenum, decrease along SI. Function : villi can increase the surface areas 10-fold. Anhui Medical University

3. intestinal glands(Crypts):  The invagination of epithelium into lamina propria.  Really simple tubular glands.  They are lined by epithelium continuous with that of the villi. Anhui Medical University

The epithelium Epithelial lining is simple columnar epi. Epithelium of villi contains columnar cells, goblet cells, endocrine cells . Epithelium of Crypts are also lined by undifferentiated cells and Paneth cells except for the above three .

Paneth cells Anhui Medical University

1. Absorptive columnar cells  Function: digestion and absorption of nutrients LM: tall columnar cells, an oval nucleus located in basal part. Free surface have striated border . EM: microvilli arranged in regular manner. Usual organelles, such as lysosomes, smooth ER, and mitochondria. Anhui Medical University & Free surface : microvilli. Each is composed of a wall of cell membrane and central cytoplasm with microfilaments. The microfilaments are continuous with terminal web. Digestive and absorptive processes take place. & Lateral sides: junctional complexes Anhui Medical University

2. Goblet cells Like a drinking glass, broad above and narrow stem attach to a base. LM: It is pale by HE staining. The nucleus is flattened or triangular and located near the base of cells. EM: An expanded upper part with mucin granules. well developed Golgi complex and RER. Function: secret mucous for lubrication. Anhui Medical University

3. Distribution: at the base of intestinal glands. LM: Pyramidal and present in groups. And contains acidophilic granules in the apical region.  EM: considerable RER, usual organelles, and large granules. Function: produce lysozyme and defensin.

EM

LM Anhui Medical University

4. Undifferentiated cells

LM: Columnar cells in the epithelium of the crypts. The structure is similar to absorptive cells. In mitosis.

EM: Cytoplasm contains secretory granules.

Function: Proliferate by mitosis to form new cells and migrate to reach the wall of villi.

5. Endocrine cells (described later)

It is difficult to identify with HE staining. Anhui Medical University

 Duodenum ---Brunner’s glands=duodenal glands

Function: produce alkaline mucus to neutralize gastric acid Anhui Medical University

 Ileum  ---Peyer’s patches aggregated lymphoid nodules Anhui Medical University

Distinguish features of small intestines

 Villi are important characterization for identification of small intestine,most well-developed in jejunum.  Duodenum has duodenal glands in the submucosa.  There is not hard and fast line of distribution between jejunum and ileum.  Jejunum has fewer solitary lymphoid nodules and greater vascularity.  Ileum has abundant aggregated lymphoid nodules. Anhui Medical University

Large intestines

 Mucosa: no villus and no circular folds. Well-developed large intestinal mucosa glands, numerous goblet cells.

 Submucosa: CT with fat cells. submucosa  Muscularis: 2 sublayers SM. Inner circular layer, Outer longitudinal layer muscularis

 Adventitia: Serosa, except posterior ascending and . Anhui Medical University Mucosa  structure: Lined by simple columnar epi. and the lamina propria is filled with tubular . 4 types of cells.  Columnar cells: absorb water and Ions, secrete mucus  Goblet cells: secrete mucus.  Endocrine cells (describe below)  Stem cells: renew other cells.

 Functions: absorb water and ions Anhui Medical University

Appendix

The structure of the resembles that of the colon with following differences.

1. The appendix is the narrowest part of the gut and is a blind- ended tubule.

2. The crypts are poorly formed.

3. The mucosa and submucosa contains abundant lymphoid tissue. Anhui Medical University Gut-associated lymphoid tissue (GALT)

 Lymphoid nodules • Solitary (jejunum) and aggregated (ileum) lymphoid nodules. • Most prominent in ileum, forming Peyer’s patches.  Immune cells Eosinophil, Lymphocytes, Macrophages, Mast cells and Plasma cells Function: protection Anhui Medical University

M (microfolds)-cells: is specialized epithelial cells overlying Peyer’s patches. M-cells can capture antigen and present it to immune cells. Anhui Medical University

The endocrine cells of the guts

 The epithelium contains scattered cells that have an endocrine function (enteroendocrine).  The cells can be identified by the presence of granules that is blackened with silver stain--- argentaffin cells Anhui Medical University

some biologically active substances (amines or polypeptides) have been located in these cell, which can be found in nerve system.  Gastro-entero-pancreatic endocrine system  The action affects neighboring cells (paracrine effect) and/or cells at distant sites through the blood (endocrine).

Hormones include: glucagon, gastrin, secretin, gastric inhibitory peptide, cholecystokinin, somatostatin, motilin, serotonin, substance P, vasoactive intestinal peptide Anhui Medical University Quiz

Fig1 Fig2 Fig3 Anhui Medical University

Fig 4 Fig 5 Fig 6

Fig 7 Fig 8 Fig 9 Anhui Medical University Key points

 General structure of the wall of digestive tract The wall includes: mucosa, submucosa, muscularis and adventitia  Mucosa of stomach------epithelium, gastric gland: cell components and function  3 types of features to greatly increase luminal surface of small intestines : Plicae circulares、 villi 、 Microvilli----components and function  Cell components of intestinal epithelial lining and small  Esophageal gland and duodenal gland Anhui Medical University

ASSIGNMENTS:

1. Describe four layers of the wall of digestive tracts.

2. Compare structural features and function of parietal cells and chief cells. 3. Describe 3 types of features which greatly increase luminal surface of small intestines .