HISTO LAB TOPICS

• The digestive system is responsible for obtaining molecules from ingested food for maintenance, growth, and energy needs of the body
• Digestion


  Dietary biomolecules (proteins, fats, carbohydrates, and nucleic acids) are broken down into smaller subunits
• Absorption


  Dietary biomolecules are broken down into smaller subunits that can be absorbed
• General structure of the digestive tract

  • Hollow tube with a lumen
  • Wall made up of mucosa, submucosa, muscularis, and an outermost serosa or adventitia in the esophagus
• Parts of the alimentary canal

  • Oral cavity
  • Esophagus
  • Stomach
  • Intestines
  • Anus
  • Accessory glands
• Oral cavity

  Lined with stratified squamous epithelium, which may be keratinized, partially keratinized, or nonkeratinized depending on the location
• Lips

  • Internal mucous surface has lining mucosa with a thick, nonkeratinized epithelium and many minor labial salivary glands
  • Red vermilion zone is covered by very thin keratinized stratified squamous epithelium and is transitional between the oral mucosa and skin
  • Outer surface has thin skin, consisting of epidermal and dermal layers, sweat glands, and many hair follicles with sebaceous glands
  • Well-developed core of striated muscle makes the lips highly mobile
• Tongue


  • A mass of striated muscle covered by mucous membrane whose structure varies according to the region
  • Lingual papillae are elevations of the mucous membrane that assume various forms and functions
• Types of lingual papillae

  • Filiform papillae
  • Fungiform papillae
  • Foliate papillae
  • Vallate (or circumvallate) papillae
• Taste buds


  Ovoid structures within the stratified epithelium on the tongue's surface, which sample the general chemical composition of ingested material
• Layers of the tongue

  • Mucosa (stratified squamous epithelium on both surfaces and the dorsal surface forms the papillae)
  • Submucosa (thin dense irregular connective tissue)
  • Muscularis (muscular layer)
• Teeth


  • Parts include enamel, dentin, cementum, periodontal ligament, root canal, gums, and alveolar bone
• Types of teeth


  • Primary teeth (baby teeth or deciduous teeth)
  • Permanent teeth (adult teeth or secondary teeth)
• Palate


  • Epithelial cells, mucous cells, goblet cells, fibroblasts, immune cells (lymphocytes, macrophages, dendritic cells)
• Esophagus


  • Muscular tube, 25 cm in length, that conveys bolus from the oropharynx to the stomach
  • Epithelium is thick protective stratified squamous (non-keratinized) epithelium
  • Lamina propria contains scattered lymphoid cells
  • Submucosa is loose connective tissue with many elastic fibres, allowing for distension during passage of a food bolus
  • Seromucous glands aid lubrication, most prominent in the upper and lower thirds
  • Muscularis propria has inner circular and outer longitudinal layers of muscle, with the superior third consisting of striated muscle, the inferior third of smooth muscle, and the middle third of both
• Stomach


  • Muscularis propria has the usual inner circular and outer longitudinal layers, but the inner circular layer is reinforced by a further innermost oblique layer
  • Mucosa consists of straight tubular gastric glands with gastric pits (foveoli) where the glands open
  • Cell types include mucous cells, parietal (oxyntic) cells, chief (peptic or zymogenic) cells, neuroendocrine cells, and stem cells
• Mucous cells


  Cover the luminal surface of the stomach and line the gastric pits, packed with cytoplasmic mucigen granules, secrete mucus and protective bicarbonate ions
• Parietal (oxyntic) cells


  Distributed along the length of the glands, large rounded cells with an extensive eosinophilic cytoplasm, secrete gastric acid and intrinsic factor
• Chief (peptic or zymogenic) cells

  Located towards the bases of the gastric glands, have a condensed, basally located nucleus and a basophilic granular cytoplasm, secrete pepsin
• Neuroendocrine and stem cells


  • Neuroendocrine cells are part of the diffuse neuroendocrine system, found in the base of the gastric glands, secrete histamine and other hormones
  • Stem cells are undifferentiated cells that divide continuously to replace worn out epithelial cells
• Parts of the small intestine

  • Duodenum
  • Jejunum
  • Ileum
• Small intestine


  • Chyme moves into the small intestine, where the majority of digestion and absorption of nutrients occur
  • Digestive enzymes from the pancreas and bile from the liver (stored in the gallbladder) further break down food particles into molecules that can be absorbed into the bloodstream
• Parts of the large intestine

  • Cecum
  • Ascending colon
  • Transverse colon
  • Descending colon
  • Sigmoid colon
  • Rectum
  • Anus
• Appendix


  • A vestigial organ located near the ileo-cecal junction, shows the same basic organization as the rest of the large intestine but has particularly abundant lymphatic nodules
• Large intestine


  • Responsible for the absorption of water and electrolytes, as well as the formation and elimination of feces
  • Rectum stores the feces and has a columnar epithelium with abundant goblet cells
  • Anus is characterized by a stratified squamous epithelium that undergoes a gradual transition to skin containing sebaceous and apocrine sweat glands
• Layers of the large intestine

  • Mucosa
  • Submucosa
  • Muscularis externa
• Respiratory System


  Group of organs responsible for gas exchange in the body
• Accessory digestive glands


  • Salivary glands
  • Pancreas
  • Liver
  • Gallbladder
• Salivary glands


  • Surround the oral cavity with adenomeres secreting saliva to moisten/lubricate food, aid enzymatic digestion, and provide immune defense
  • Cell types include serous cells, mucus cells, and myoepithelial cells
• Components of the Respiratory System

  • Trachea
  • Nasal Cavities
  • Pharynx
  • Larynx
  • Bronchi
  • Bronchioles
  • Terminal Bronchioles
  • Respiratory Bronchioles
  • Alveolar Ducts
  • Alveoli
• Pancreas


  • Located behind the stomach and surrounded by spleen, liver and small intestine, secretes digestive enzymes essential for digestion
  • Cell types include pancreatic acinar cells and centroacinar cells
• Type I pneumocytes


  • Extremely attenuated cells lining the alveolar surfaces, constitute 95% of the alveolar lining
• Liver


  • Hepatocytes are the key cells, secreting bile which is stored in the gallbladder
  • Hepatic lobules have stellate cells called Kupffer cells and Ito cells
  • Processes ingested food into smaller components which can be absorbed by the small intestine
• Type II pneumocytes


  • Cuboidal cells bulging into the air space, interspersed among the Type I
• Gallbladder


  • Stores bile produced from the liver, and releases it into the duodenum after a meal
  • Lined by simple columnar epithelium of cholangiocytes
• Alveolar macrophages


  • Collect inhaled particles from the environment, such as coal, silica, and microbes, including viruses, bacteria, and fungi
• Pulmonary surfactant


  • Vital substance that reduces surface tension, preventing alveoli from collapsing
• Olfactory neurons


  • Bipolar neurons present throughout the olfactory epithelium, form the olfactory nerve and synapse with neurons in the olfactory bulb
• Supporting cells


  • Columnar cells with narrow bases and broad, cylindrical apexes, express abundant ion channels that maintain a microenvironment conducive to olfactory function and survival
• Basal cells


  • Small, spherical, or cone-shaped cells near the basal lamina, stem cells for the other two types of olfactory epithelium cells