Digestive and Respiratory Systems PDF

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Summary

Digestive SystemOral Cavity- Oral Mucosa, the mucous membrane lining the oral cavity. Made of stratified squamous non-keratinized epithelium over connective tissue (lamina propria). The lamina propria is a thin layer of areolar connective tissue. - Lip, the outer lip has a top layer of stratified sq...

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MLSC-3230, Microanatomy and Histotechnology Digestive System Oral Cavity -

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Oral Mucosa, the mucous membrane lining the oral cavity. Made of stratified squamous non-keratinized epithelium over connective tissue (lamina propria). The lamina propria is a thin layer of areolar connective tissue. Lip, the outer lip has a top layer of stratified squamous keratinized epithelium and hair follicles. This transitions into the red margin that is very vascularized (Vermillion zone). The red free margin transitions into non-keratinized squamous cells. The interior surface of the lip has mucous glands and the centre of the lip has skeletal muscle. Cheek, interior surface is made of stratified squamous non-keratinized with the lamina propria underneath. Mucous glands are also found below the squamous epithelium. Tongue, has a roughed surface due to papillae. There are 4 types of papillae and distribution of papillae varies per region of the tongue. o Circumvallate, large extensions found on the back of the tongue. Have taste buds and made of non-keratinized squamous epithelium. o Filiform, found on the main surface of the tongue. Pointy, horn shaped and made of stratified squamous keratinized epithelium without taste buds. Holds food. o Fungiform, found on the main surface of the tongue. Flatter on microscopy. Have taste buds and made of non-keratinized squamous epithelium. o Foliate, found along the sides of the tongue and are not very developed in humans. Have taste buds and made of non-keratinized squamous epithelium. Taste buds have sensory receptors to sense taste.

GI Tract -

This is essentially a muscular tube lined with a mucous membrane. Made of four layers. o Mucosa, has three sub layers.  Epithelium, made of epithelium with varying composition per location.  Lamina Propria, loose connective tissue underneath epithelium.  Muscularis mucosa, smooth muscle and a boundary between mucosa and submucosa. o Submucosa, made of a layer of LOCT with elastic fibres, nerves, blood and lymphatic vessels. Varies based on the presence of glands and their types. Has a nerve supply called the plexus of Meissner’s (submucosal plexus). o Muscularis Externa, typically made of smooth muscle organized into an inner circular layer and an outer longitudinal layer.  Mesenteric Plexus (Auerbach Plexus), the nerve supply for the GI muscle to allow peristalsis to happen. o Serosa/Adventitia, the outer surface of the GI tract. This is also called the adventitia if it does not open to a cavity. Serosa ends with a single layer of simple

MLSC-3230, Microanatomy and Histotechnology

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squamous epithelium (mesothelium), like in the stomach. Adventitia runs into another organ and attaches to another organ. Basic GI Tract Mucosal Forms, there are four basic types of GI mucosa classified by their function. o Protective, found in the oral cavity. Made of stratified squamous non-keratinized epithelium. o Secretory, found in the stomach and consists of long closely packed tubular glands of the stomach. o Absorptive, found in the small intestine. Uses microvilli to absorb nutrients and contains crypts to increase surface area. The duodenum has very deep crypts that go past the muscularis that form Brunner’s glands (neutralizes the low pH stomach contents to protect the small intestine). These glands are only found in the duodenum. o Absorptive/Protective, found in the large intestine. Protection increases the closer the mucosa gets to the anus. Contains straight tubular glands for water reabsorption. Esophagus, the top third of the muscularis propria is skeletal muscle, the third is skeletal and smooth muscle, and the bottom third is just smooth muscle. The muscle contains Auerbach Plexus’. Gastroesophageal Junction, found at the junction between the esophagus and the stomach. Seen as an abrupt change from stratified squamous to simple columnar epithelium (gastric mucosa). Stomach, consists of three regions. o Cardiac, contains secreting glands and is the closest area to the esophagus. o Fundus, the main body of the stomach that contains the gastric glands. o Pylorus, secretes two types of mucus as well as gastrin.  Pyloric Sphincter, found at the end of the stomach/pylorus separates the stomach from the duodenum. Allows controlled release of chyme into the duodenum. The stomach is lined with a layer of simple columnar epithelium. It has gastric pits with secretory cells formed in folds known as rugae. The muscularis of the stomach has three layers of smooth muscle going in three different directions. o Gastric Glands, secretory cells found in the gastric pits.  Parietal Cells, secrete HCl and intrinsic factor. Appear eosinophilic.  Chief Cells, secrete pepsinogen and located closer to the base of the gastric pit. Appear basophilic. Small Intestine, has an absorptive function and consists of three parts. o Duodenum, closest to the stomach and receives secretions liver/gall bladder/pancreas and chyme from the stomach. Only place where Brunner’s glands are found.

MLSC-3230, Microanatomy and Histotechnology

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o Jejunum, responsible for most of the absorption of nutrients. Contains Peyer’s patches which are lymphoid aggregates of the mucosa that may extend into the submucosa (provide immune function). o Ileum, connects the cecum to of the large intestine at the ileocecal sphincter. Also contain Payer’s patches. The small intestine has circular folds called Plica Circulares (most abundant in the jejunum). Villi, projections that stick out into the lumen of the intestine to increase surface are for absorption. Microvilli are found on villi to further absorb nutrients and increase surface area. Lacteals, blood vessels that go into the lamina propria and the microvilli to absorb nutrients. Originate from the submucosa. The mucosa has simple columnar epithelium with goblet cells and microvilli. It forms the crypts of Lieberkühn. The muscularis propria is made of two layers that sandwich an Auerbach plexus. Outer layer is surrounded by mesothelial serosa. Intestinal Mucosal Cells o Absorptive cells, enterocytes. o Goblet Cells, secrete mucin. o Enteroendocrine Cells, synthesize and secrete hormones. o Paneth Cells, found in crypts and protect against pathogenic bacteria. o Stem Cells, found in crypts and serve to replenish old cells in turn over. The large intestine does not contain villi or Paneth cells compared to the small intestine that does. Large Intestine, serves to absorb water and electrolytes. Contain the most goblet cells and lined with simple columnar epithelium. Does not contain Paneth cells or villi. Contains the deep intestinal glands. Recto-anal Junction, found at the abrupt transition between the large intestine (simple columnar) and the anus (stratified squamous non-keratinizing). Accessory Digestive Organs o Pancreas, localized posteriorly to the stomach. Contains the Islets of Langerhans that make up around 2% of the pancreas and secrete insulin and glucagon. Also contain Acini exocrine glands made of simple cuboidal epithelium and are help food digestion by secreting digestive enzymes into a duct. o Liver, serves to make bile, lipids, proteins and detoxifies the body. Bile is produced by hepatocytes and secreted into the gall bladder for storage via the bile canaliculi. o The bile canaliculi merge with each other to form bile ducts which will go on to form the left and right hepatic ducts. The hepatic lobule is the functional unit of the liver.  Portal Triads, join the hepatic lobule together and contain a bile duct, portal vein and a hepatic artery.

MLSC-3230, Microanatomy and Histotechnology o Gall Bladder, serve as a storage gland for bile. Releases bile from the liver into the smaller intestine via the bile duct. Has no distinctly defined submucosa and is lined with tall, simple columnar epithelium.

Respiratory System -

The respiratory system is typically lined with pseudostratified columnar epithelium with goblet cells. Upper Respiratory Tract, include the nasal cavity, para-nasal sinuses, and nasopharynx. Lower RT, includes the larynx, trachea, and lungs. The respiratory system is divided into the conductive and respiratory portion. o Conducting Portion, consist of all components that are not involved in gas exchange. Serves in air warming, humidifying, and filtering. Warming is done using an extensive venous plexus in the tissue. Made of pseudostratified columnar epithelium with goblet cells and cilia. o The epithelium transitions to the cuboidal epithelium of the respiratory portion in the small bronchioles o Respiratory Portion, consist of all components that are involved in gas exchange. Goblet cells are absent in the alveoli as they are lined with a thin layer of simple squamous epithelium.

Trachea -

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Lined with typical respiratory epithelium (pseudostratified columnar with goblet cells). Support by 16-20 C-shaped rings of cartilage. Contains glands to moisten the lining and blood vessels to facilitate heat exchange with air. Mucosa, made of the epithelium and a lamina propria. Submucosa, the serous portion that humidifies the air. Adventitia, made of dense connective tissue containing hyaline cartilage. This adventitia is shared with the esophagus. The hyaline cartilage provides structural support to the trachea. The amount of cartilage will decrease as you get deeper into the respiratory tract. Irregular cartilage plates support the walls of the primary bronchi to ensure they remain open.

Bronchi -

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The trachea divides into the primary bronchi (pseudostratified ciliated epithelium with goblet cells), which further branch into smaller bronchi, which will branch even further into bronchioles. The bronchioles branch into the terminal bronchioles (simple ciliated columnar) which is the end of the conductive portion. Terminal bronchioles begin the respiratory section

MLSC-3230, Microanatomy and Histotechnology and branch into respiratory bronchioles (simple ciliated cuboidal with cilia disappearing distally) which end in alveoli (simple squamous).

Bronchioles -

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The epithelium in the bronchioles is made of ciliated columnar epithelium and the cartilage and glands disappear. Goblet cells completely disappear at the terminal bronchioles. The conduction part of the respiratory tract also ends here. Gas exchange (respiratory portion) begins at the respiratory bronchioles. The epithelium transitions into non-ciliated cuboidal until the become simple squamous cells in the alveoli. Clara Cells, gradually replace disappearing goblet cells in the bronchioles. They are dome shaped non-ciliated cells. Serve to secrete surfactants, detoxify and secrete antimicrobial peptides.

Alveoli -

The alveoli are the functional unit of the lung and the site of gas exchange. Lined with simple squamous epithelium. Contain type I and II pneumocytes. Type I, typical simple squamous cells covering most of the alveoli surface. Type II, secrete surfactant into alveoli to reduce alveolar surface tension to inhibit alveolar collapse....