Histology, Pathology, and Physiology

• Here are notes on histology, pathology and the human body

Histology vs. Pathology vs. Physiology

• Histology studies morphological features of normal cells and tissues mainly via light microscope, examining structure-function correlation.
• Histology helps in understanding body functions and recognizing abnormalities by understanding normal conditions.
• Pathology studies and diagnoses diseases through examining surgically removed organs, tissues (biopsy samples), bodily fluids, and sometimes entire bodies (autopsy).
• Physiology aims to understand the mechanisms of living things from cellular ionic and molecular bases to whole-body behavior and external influences.

Cells, Tissues, Organs and Systems

• Tissue consists of cells with similar structure (morphology) and function.
• The five types of tissue are blood, supporting or connective tissue, nervous tissue, muscle, and epithelia.
• Organs are anatomically discrete collections of tissues performing specific functions, like a heart composed of muscle, nerve, connective, and epithelial tissues.
• A system comprises organs working together for a function, like the digestive system with the mouth, oesophagus, stomach, and intestines to absorb nutrients and eliminate solid waste.
• There are an estimated 30 trillion cells in the human body.
• There are over 200 different types of cells in the human body, each with a specialized function.
• Red blood cells are the most common cell type, accounting for about 84% of all cells.

Systems of the Human Body

• The 10 systems responsible for the body's functions are skeletal, muscular, cardiovascular, nervous, endocrine, lymphatic, respiratory, digestive, reproductive, and urinary.
• Skeletal, muscular, cardiovascular, and nervous systems create an infrastructure that facilitates the other systems.
• The skeletal system includes 206 bones to hold the body together, give shape, protect organs and tissues, and provide anchor points for the 3 types of muscles
• The cardiovascular system delivers O2, WBCs, hormones, and nutrients.
• The nervous system includes the brain, spinal cord, and spinal nerves.
• The endocrine, lymphatic, and urinary systems regulate the body's environment
• The endocrine system uses information from the nervous system to regulate body processes, distributing chemicals via the cardiovascular system.
• The lymphatic system, with lymph nodes and vessels, regulates the body's defense system, using neural pathways and WBCs delivered through the bloodstream.
• The urinary system sends waste through blood vessels into the kidneys for expulsion.
• All systems require energy from respiratory and digestive systems.
• Reproduction system - fertilization and life

Tissue Processing Steps

• Tissue processing involves fixation, dehydration, clearing, infiltration, and embedding.
• Fixation preserves tissue samples to prevent decay and maintain structure, typically using formalin to cross-link proteins.
• Dehydration removes water by passing the tissue through increasing alcohol concentrations (e.g., 70%, 95%, 100%).
• Clearing replaces alcohol with a solvent miscible with both alcohol and paraffin wax, like xylene.
• Infiltration immerses the tissue in molten paraffin wax, which penetrates and replaces the clearing agent.
• Embedding places paraffin-infiltrated tissue in a mold surrounded by molten paraffin wax, forming a block containing the embedded tissue once solidified.

Sectioning and Staining

• Sectioning involves trimming the paraffin block to expose the tissue of interest.
• Thin sections (4-6 micrometers thick) are cut using a microtome, a specialized instrument with a sharp blade.
• Tissue sections are mounted on glass slides and stained to enhance contrast and visualize different cellular components.
• Hematoxylin and Eosin (H&E) staining is common in pathology, where hematoxylin stains nuclei blue, and eosin stains cytoplasm and extracellular matrix pink.
• Basic dyes have positive charges and bind to negatively charged tissue components such as haematoxylin.
• Basophilia stains blue.
• Acidic dyes have negative charges and bind to positively charged tissue components such as eosin.
• Acidophilia stains pink.

Immunohistochemistry (IHC)

• Immunohistochemistry (IHC) visualizes specific proteins within cells and tissues using antibody-antigen interactions.
• Tissue Preparation: The tissue sample is carefully prepared and sectioned to expose the cells of interest.
• Antibody Binding: A primary antibody, specifically designed to recognize the target protein, is applied to the tissue section. This antibody binds to the protein of interest.
• Visualization: A secondary antibody linked to a detectable marker, such as an enzyme or a fluorescent dye, is used to visualize the antibody-antigen binding. When the secondary antibody binds to the primary antibody, it reveals the location of the target protein.
• Staining: A chromogen is added, reacting with the enzyme on the secondary antibody to produce a visible color at the site of the target protein.

Microscopy

• Light microscopes can magnify up to X1000.
• Electron microscopes can magnify up to X100,000.
• Fluorescence microscopes use antibodies or probes with fluorescent tags.
• Electron microscopy provides higher resolution than light microscopy, allowing visualization of cellular organelles and subcellular structures.
• Transmission Electron Microscopy (TEM) provides 2D images of thin tissue sections.
• Scanning Electron Microscopy (SEM) provides 3D images of the tissue's surface.

Interpreting Electron Micrographs

• Interpreting electron micrographs involves identifying cellular organelles like mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes.
• Examining subcellular structures like cell membranes and the cytoskeleton is important when interpreting electron micrographs
• Pathological Changes: Pathological changes can be observed, such as abnormalities in cancer cells.

Tissue Processing and Staining

• Formalin is used to fix paraffin-embedded samples, while epoxy resin is used to fix samples for electron microscopy.
• Epoxy resin is a harder fixative that provides better preservation of ultrastructural details, such as cell organelles. It is often used for electron microscopy, but it can also be used for light microscopy. Epoxy resin is less commonly used than formalin because it is more difficult to work with and requires special processing techniques.
• Epoxy resins penetrate and preserve fine cellular and subcellular structures well, making them ideal for studying the stratum spinosum's intricate details.
• Toluidine blue is a metachromatic dye that stains acidic tissue components like nucleic acids and glycosaminoglycans, highlighting keratinocyte nuclei in the stratum spinosum.
• Epoxy resin embedding provides excellent tissue support for preparing thin sections for light microscopy
• Clarity is combined with the staining specificity of toluidine blue, enables clear visualization of the stratum spinosum's cellular architecture.
• Toluidine blue stains different cellular components with varying intensities for contrast, making it easier to distinguish between different structures within the stratum spinosum.

Histological Staining

• Tinctorial staining is based on the physical and chemical properties of tissue components
• Dyes are used to stain different cellular structures based on their affinity for the dye.
• Histochemical staining detects specific chemical substances within tissues, identifying substances like carbohydrates, lipids, and enzymes.
• Immunohistochemical staining uses antibodies to detect specific proteins or other antigens within tissues.
• Nucleic acid staining specifically visualizes DNA and RNA within cells.
• Routine Hematoxylin and Eosin (H&E) provides a general overview of tissue architecture
  • Hematoxylin stains nuclei (containing DNA) a deep blue or purple and highlights the nuclear structure, important for identifying cell types and detecting abnormalities.
  • Eosin stains the cytoplasm and extracellular matrix various shades of pink or red.
• Special-ellastin EVG highlights elastic fibers in tissues
  • Elastic fibers, crucial components of the extracellular matrix, provide elasticity and resilience to tissues
  • Elastin stains elastic fibers a dark brown or black color, visualizing their distribution and integrity,
  • Van Gieson stains collagen fibers pink or red and other tissue components yellow, providing contrast to the elastin fibers.
• Staining is used in lung conditions to diagnose and study various lung conditions because it helps visualize changes in the elastic fibre network: -Emphysema: In emphysema, the elastic fibers in the lung's alveolar walls are damaged and destroyed, leading to a loss of lung elasticity. EVG staining can demonstrate this loss and disruption of elastic fibers. -Chronic Obstructive Pulmonary Disease (COPD): Similar to emphysema, COPD often involves damage to elastic fibers, which contributes to the disease's progression.

Microscopy Parts and Functions

• Coarse adjustment knob: Knob makes large adjustments to the distance between the objective lens and the specimen. It's used for initial focusing and to get the specimen into the general field of view.
• Fine adjustment knob: This knob makes small, precise adjustments to the focus. It's used to sharpen the image and bring out fine details once the specimen is already in the field of view.

Magnification

• Total Magnification: Multiply the objective lens magnification by the eyepiece (ocular lens) magnification (e.g., 10x eyepiece + 40x objective lens = 400x total magnification).

Epithelial Cells

• Epithelial cells are bound to adjacent cells via cell junctions, are supported by an underlying thin basement membrane, and never have blood vessels crossing the basement membranes
• Classification by number of cell layers, cell type, and special features like goblet cells or cilia.
• Glandular epithelia - a type of epithelial tissue that is specialized for producing and secreting substances-essentially the lining tissue of glands.

Simple Epithelia

• In simple columnar epithelium, nuclei are elongated and located towards the base, known as polarity of the nucleus
  • ciliated version is mainly found in the female reproductive tract
  • pseudostratified which has cilia as it looks that it has more than one layer of cells,this is due to the nuclei being at different levels positioned.
• Cilia are never present on true stratified epithelia.

Stratified Epithelia

• Cell layers exhibit maturation from a cuboidal basal layer to a flattened surface layer.
• Cells migrate towards the surface where they are shed as anucleate squames.
• Have cell junctions and keratin cytoskeleton.

Epithelium Types

• Simple Squamous: Single layer of flattened cells
  • Lining blood vessels (endothelium) and air sacs of lungs
  • Function: diffusion, filtration.
• Simple Cuboidal: Single layer of cube-shaped cells. May have microvilli in PCT.
  • Locations: kidney tubules, glands
  • Function: secretion, absorption.
• Simple Columnar: Single layer of tall, cylindrical cells. May have microvilli in the small intestine, cilia in the fallopian tube, pseudostratifications in the respiratory tract, goblet cells in the bowels and stereocilia(long microvilli) in the vas deferens.
  • Locations: lining of the digestive tract
  • Function: absorption, secretion.
• Stratified Squamous: Multiple layers of cells, with the outermost layers being flattened.
  • Locations: skin (keratinized) and lining of the oral cavity, esophagus, and vagina (non-keratinized)
  • Function: protection against abrasion.
• Stratified Cuboidal / Columnar: Less common, found in exocrine glands and ducts.
  • Function: protection, secretion.
• Transitional: Specialized epithelium that can stretch.
  • Locations: lining of the urinary bladder
  • Function: allows for distension.
• Pseudostratified Columnar looks stratified, but is a single layer
  • Location lining of the trachea
  • Function secretion, movement of mucus (often ciliated).

Supporting cells

• Fibroblasts: Produce and maintain the extracellular matrix (fibers and ground substance) in connective tissue proper.
• Chondrocytes: Cartilage cells, located in lacunae within the cartilage matrix.
• Osteocytes: Bone cells, located in lacunae within the bone matrix.
• Adipocytes: Fat cells.
• Blood cells: Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).
• Mesenchymal cells: Embryonic connective tissue cells that can differentiate into other connective tissue cell types.

Mesenchymal Tissue

• Mesenchymal tissue is embryonic connective tissue that gives rise to all other connective tissues.
• Composed of loosely arranged, star-shaped cells in a gel-like matrix.
• Mesenchymal cells differentiate into fibroblasts, chondrocytes, and osteoblasts.

Skin Layers

• Skin composed of three main layers: the epidermis, the dermis, and the hypodermis.
• Epidermis: The outermost layer, derived from ectoderm, It's stratified squamous epithelium containing keratinocytes, melanocytes, Langerhans cells (immune cell:) and Merkel cells(sensory cells.)
  • Stratified into stratum corneum (dead, keratinized cells), stratum lucidum (only in thick skin), stratum granulosum, stratum spinosum, and stratum basale (where new cells are generated) and produces a surface layer of keratin.
• Dermis: The middle layer, derived from mesoderm containing connective tissue, blood vessels, nerves, hair follicles, and glands.
  • Consists of two layers: papillary dermis (superficial) and reticular dermis (deep). Contains collagen and elastic fibres.
• The deepest layer in the hypodermis (Subcutaneous Tissue) is located beneath the dermis.
  • It's composed mainly of adipose tissue and fibrous bands called septa, and connects the skin to underlying tissues, muscules and bones and provides insulation and cushioning.

Skin Functions

• Protection: Barrier against physical damage, UV radiation, and microorganisms.
• Thermoregulation: Helps regulate body temperature through sweating and blood vessel dilation/constriction.
• Sensation: Contains sensory receptors for touch, pain, temperature, and pressure.
• Vitamin D Synthesis: Synthesizes vitamin D from sunlight exposure.
• Excretion: Small amounts of waste products are excreted through sweat.

Skin Cells and Appendages

• Keratinocytes are the most abundant cell type in the epidermis and produce keratin for strength and waterproofing.
• Melanocytes produce melanin, which protects against UV radiation.
• Langerhans cells are immune cells that protect against infection.
• Merkel cells are sensory cells involved in touch sensation.
• Hair follicles produce hair.
• Sebaceous glands produce sebum (oil), which lubricates the skin and hair.
• Sweat glands produce sweat, which helps regulate body temperature.
• Nails are protective plates of keratin.

Skin Structure-Function Relationships

• Stratified squamous epithelium provides a tough, protective barrier.
• Melanin protects against UV damage.
• Dermis's rich network of blood vessels helps regulate temperature.
• Sensory receptors allow interaction with the environment.
• Hypodermis's adipose tissue provides insulation and cushioning.

Four Basic Tissues

• Muscle, nervous, epithelial and connective
  • Surface epithelia cover and line all body surfaces, cavities, tubes-interference between different compartments.
  • All epithelia are supported by a basement membrane that separates the epithelium from the underlying surface.
  • They are classified by number of cell layers, shape ( based on appearance at right angles to the epithelial surface -cells are squamous, cuboidal, columnar), specialisations.
• Simple epithelia
  • Flat, thin, pavement that is supported by a delicate basement membrane
• Simple cuboidal
  • Lines the small ducts, with a round nucleus in the middle.
• Simple columnar
  • The cells are thinner, taller than cuboidal
  • The are Found on absorptive surfaces:small intestine, gall bladder
• Pseudostratified
  • Rests on basement membrane, with nuclei at illusions that create the layers as if they are confined to airways and are ciliated
• Stratified epithelia have two or more layers and a protective function.
• Stratified squamous has flattened cells and more layers Cells that sit on the basement membrane are stem cells that as they mature, cells become squamous with keratin that helps against abrasion
• Stratified cuboidal has 2 to 3 layers, lines excretory ducts, is not involved in important secretory roles
• Transitional (urothelium) is only found in the urinary tract of mammals, accommodate stretch and toxicity and when relaxed their surface cells are large and rounded

Cilia

• Cilia is mainly found in the respiratory tract and female reproductive tract, 10 micrometers long with 300 cilia
• Microvilli consist of finger like projections of the plasma membrane that are found in epithelia specialized for absorption-in the small intestine, only 1 micrometer in length and are seen as brush border
• Goblet cells consist of modified columnar epithelial cells that have periodic acid stain and are Scattered in many simple epithelia in the gastrointestinal tract
• Glandular epithelium is a specialized type of epithelium that is adapted for secretion and consists of glands that are the organs or structures that are primarily composed of this specialized epithelium
  • Two main types:

Glands

• Exocrine glandsMaintain connection to epithelial surface via ducts with secretions released onto the surface (e.g., skin, digestive tract lumen) with a structure of solid organs of epithelial cells with branching ducts.
  • Types (based on duct structure):
    • Simple Tubular: Straight, unbranched duct (e.g., large intestine).
    • Simple Coiled: Coiled duct (e.g., sweat glands).
    • Simple Branched Tubular: Branched duct (e.g., stomach mucus glands).
• Endocrine Glands lose connection to epithelial surface during development. Secretions (hormones) released directly into bloodstream. Highly vascularized. The hormones travel through intercellular space to reach blood vessels.
• Supporting tissues of Mesodermal origin provide structural and metabolic support
  • Mediates exchange of nutrients, gases and metabolites and has blood and lymphatic vessels that is Composed of specialized cells,extracellular matrix(fibres and substances)
    • Collagen for tensile strength secreted as tropocollagen which polymerases in the extracellular matrix to form collagen. -Type 1 collagen found in the dermis and tendons -Type 2 collagen found in hyaline cartilage and Type 3 f(reticulum) delicate branching surrounds individual cells in the liver, absorbs silver -Type 4 collagen, mesh membrane in the basement membrane and Type 7 collagen anchoring fibrils that link to the basement membrane.
    • Fibroblasts-secrete extracellular matrix,Myofibroblasts, chondrocytes/osteocytes, adipocytes that have Mast cells, macrophages and plasma cells

Primitive Mesenchyme

• Primitive mesenchyme consists of embryonic tissue from which all connective tissue is derived, stellate shaped, oval nuclei, and is mainly with ground substance with very few fibres Mature fibroblasts -dense, pink.
• Basement membrane sheet like arrangement of extracellular matrix proteins which act as interface between support tissue and is Made of collagen type 4,glycoproteins laminin,entactin and fibronectin with 3 layers-lamina lucida, lamina densa-electron dense layer, lamina fibroreticularis which interacts with the surrounding tissues.

Adipose Tissue

• Cells that are specialised for storage of fat that are rich in blood supply responsible for releasing proteins
• White adipose tissue-distributed in the dermis, a thermal insulator, pale staining as it is occupied by lipid, leaving the rim of cytoplasm, nucleus, which is pushed against the membrane to the side
• Brown adipose tissue is specialised, found in newborn mammals, for temperature regulation, arranged in lobules separated by fibrous septae
• Hypodermis/Subcutis Mature adipose tissue that is compartmentalised by fibrous septa with thickness & degree of compartmentalisation variable
• Dermis consists of bundles of collagen fibres and strands of elastic fibres in that is Small amount of acellular ground substance in 2 Layers - Reticular & Papillary
• Basal layer of keratinocytes, proliferates continuously-stratum basale

Cells of the Epidermis

• Characterised by basophilic cytoplasmic granules-stratum granulosum and Keratin flakes/plates attached at the edges-stratum coreneum.
• Keratinocytes produce the protective keratin layer
• Langerhans cells are antigen presentation-st spinosum
• Melanocytes contain melanin as UV protection-protects keratinocytes when they proliferate as the nuclei can get exposed-st basale
• merkel cell are the rare neuroendocrine cell that are sensory-st basale.

Hair Folicle

• The Hair Folicle is composed of several layers and associated with arrector pili muscle & sebaceous glands
• In dermis, reticular dermis

Glands

• Sebaceous Gland Secretes sebum (oily substance) via the holocrine mechanism of secretion-entire cells are released and travel up the duct, lubricates the hair and skin and is In dermis, reticular dermis
• Eccrine sweat glands & ducts have Secretory component (highly coiled) & duct (straight) with an outer layer of contractile cells (myoepithelial cells) which secrete sweat with mostly water, sodium, chloride ions, urea.

Skin Functions

• Skin functions include protection from multiple external threats - UV/mechanical/biological/chemical, moisture control, Immunological/Antigen presentation, Metabolic (eg vitamin D/lipid reservoir), Thermoregulation, Sensory, excretory.

GI Anatomy and Functions

• Mouth: The mouth is the beginning of the Gl tract which is where food is ingested and chewed
  • The teeth and tongue help break down food mechanically, and saliva helps to moisten food and begin the process of chemical digestion
• Pharynx: The pharynx is a common passageway for food and air and connects the mouth to the esophagus
• Esophagus: The esophagus transports food from the pharynx to the stomach
• Stomach: The stomach is a muscular sac that stores food and mixes it with gastric juices.
  • Gastric juices contain hydrochloric acid, which helps kill bacteria and break down food, and pepsin begins the digestion of proteins
• Small intestine: The small intestine is the longest part of the Gl tract and is where most of the digestion and absorption of nutrients occurs
  • It is divided into three parts: the duodenum, jejunum, and ileum
• Large intestine: The large intestine absorbs water and electrolytes from the remaining chyme and forms feces, and is divided into the cecum, colon, rectum, and anus.

GI Tract Functions

• The process of taking food into the mouth is ingestion.
• Mechanical digestion breaks down food into smaller pieces by chewing and churning.
• Chemical digestion breaks down food into its component molecules by enzymes.
• Absorption transports nutrients from the Gl tract into the bloodstream.
• Elimination removes waste products from the body.

Endoscopy Notes

• The upper airway, the esophagus, the stomach, and the first part of the duodenum. The endoscopy is often called gastroscopy although that's less specific because gastro indicates stomach and we're scoping more than just the stomach.
• In England it's often called an OGD.
• Don't eat solid food for 8h before, allowed to have clear fluids for 2-3h before
• The epiglottis or flap will fold down and cover the vocal cords which is just below it so that when you swallow food the food doesn't go down the wrong way, the food will be guided into the esophagus
• The esophagus is 20 cm from the lips and it joins the stomach at 40 cm and has a 2 cm diameter.
• Peristaltic waves are waves of contraction.
• The Diaphragm has a diaphragmatic hiatus where the oesophagus goes through it.
• The end of the stomach is called the pylorus.
• CO2 in to distend the stomach
• 90% of the digestion absorption of food comes in through the small intestine.
• A tube should be placed between the 2 vocal cords
• Esophagitis can occur

Large Intestine Anatomy

• The anal canal measures 3 centimeters, while the rectum is approximately 15 centimeters long
• The Notable folds are known as the Babs of Houston. Sigmoid Colon can stretch up to 80 centimetres but may crumple to 30 centimetres when straightened, often forming a clockwise spiral loop.
• Colon Configuration Transverse colon has a triangular shape influenced by its degree of descent towards the pelvis, affecting bowel length and influencing the hepatic flexure angle.
• The Ileocecal Valve is crucial for navigation to the terminal ileum, which appears granular in air but displays floating villi underwater.
• Colonoscopy Techniques include a withdrawal technique that includes suctioning and careful reflection optimises lesion detection and enhances adenoma detection rates during colonoscopy.
• The Esophagus serves as the transport conduit for food.
• In the stomach, food is broken down into a liquid form through the action of stomach acid, digestive enzymes, and muscular contractions.
• Small Intestine plays a crucial role in nutrient absorption, aided by the pancreas, liver, and gallbladder.
• Large Intestine primarily focuses on water absorption and the formation of feces, supported by the action of bacteria that help break down undigested matter.

Stomach Sections

• Joins the oesophagus at GE junction.
• Cardia is the most primal part of the stomach.
• The fundus is the roof.
• The body makes up most of the stomach and secretes acid and pepsin
• The pylorus and antrum are the most distal parts of the
• Stomach that stores the food while it is broken down Rugae are mucosal folds that allow the stomach to expand with food

The Layers of the Stomach

• The Mucosa is the outer surface and includes up of 3 layers
• The Submucosa is a connective tissue that has major blood and lymph vessels, and nerves
• The Muscularis externa is made up of 3 smooth muscle layers
• The Serosa is a membrane outside of the stomach

Small Intestine Sections

• The Small Intestion consist of the duodenuum, the jejunum and the ileum
• Duodenum short, connected to the gallbladder, liver, pancreas via ducts
• Jejunum longest part of the SI and absorbs most nutrients, has a thick wall and has many folds
• Ileum long, absorbs B12, bile salt and anything not absorbed by the
• Jejunum containing Peyer's patches, Peyer's patches are located in the lamina propria and extend into the submucosa of the ileum. They play an important role in the immune system of the gut. responsible for sampling antigens from the intestinal lumen and initiating an immune response , and also help to maintain the balance of the gut microbiota.
• Layers of the SI :
  • Mucosa outer surface ,has the epithelium, lamina propria and muscularis mucosae
  • Submucosa is a connective tissue that containing major blood and lymph vessels, and nerves
  • Muscularis externa is made up of 3 smooth muscle layers
  • Serosa is a membrane outside of the stomach

Unique Structures of Small intestine

• Immune follicles, that are Present in the submucosa of the ileum more frequent in the distal ileum responsible for sensing bacteria -The parts of the large intestine consist of the Ileum joining the large intestine at the ileocaecal valve and the . -Caecum -evolutionary redundant that is merged with the colon.
• The Colon has 4 parts (ascending,transverse,descending and sigmoid and absorbs water Forms faeces. and the Retum expulses .

The layers of the large intestine consist of

• Epithelium -Crypts which is Mucosa that is the outer surface having the epithelium, lamina propria and muscularis mucosae and also the
• submucosa that is a connective tissue having major blood and lymph vessels, and nerve that have Muscularis externa made up of 3 smooth muscle layers Serosa/mesothelium
• Crypts are essentially test-tube-like invaginations or pockets in the mucosal lining of the large intestine and extend down into the lamina propria, the connective tissue layer beneath the epithelium used for cell renewal
  • New epithelial cells are generated at the base of the crypts, and they migrate upwards to replace older cells that are shed into the intestinal lumen
  • This constant renewal is essential for maintaining the integrity of the intestinal lining with Mucus secretion The crypts contain goblet cells, which produce mucus that is vital for protecting the intestinal lining.

Gut Epithelium

• In the Esophagus, the Mucosa consists of the Stratified squamous epithelium, which is non-keratinized, resists Abrasion, because the Esophagus is exposed to Friction from Food,.
• In the Stomach, the Mucosa consists of the a Simple columnar epithelium, specialized for secretion that contains cells secreting mucus, hydrochloric acid, and pepsin.
• the Small intestine has a Simple columnar epithelium mucosa is folded into villi and microvilli, ,which increases the surface area for absorption, contains cells that secrete enzymes and hormones.
• The large Intestine -has a Simple columnar epithelium, containing many Goblet cells but no Villi or Microvilli.

The Glycoprotein Functions

• GI Tract secretes;

1. Mucus; A Glycoprotein that lubricates and protects Tract;
2. Enzymes, Proteins, catalyze Chemical reactions, to Break down Food;
3. Hormones; Chemical messengers that regulate bodies, digestion and absorption

Intestinal Tract layers

• The gastrointestinal tract is a muscular tube lined with a mucous membrane
• It has four distinct layers including the mucosa, submucosa, muscularis propria, and adventitia
• The mucosa is the innermost layer made up of three components include the epithelium, the lamina propria, and the muscularis mucosa.
• The submucosa consists of a layer of loose connective tissue Supports the mucosa and contains blood vessels, lymphatics, and nerves
• The Submucosal Plexus is a Network of Nerves to Controls Secretion’s.
• The Muscularis Propria is the middle layer and made up of smooth muscle consisting of a wave-like structure called peristalsis
  • controls the inner lining of the tract and also supports the myentric Plexus a Network that controls Peristalsis
• Adventitia is the outermost layer of gastrointestinal tract and is made up of loose Connective Tissues
  • It contains the Blood vessels and Nerves and submucosal Plexus
• The Mucosa’ has an Innermost, outer, Middle and Loose Connective Tissues _The Submucosa the outermost Layer and Smooth Muscle _

Secretory Mucosal Epithelium

• Secretory, found in the Stomach, making acids
• Absorptive type found in the small intestine that absorb nutrients/water
• Protective, found in the mouth esophagus ,anal canal, resisting friction
• Absorptive Protective-Found, absorbing electrolytes

Gland Cell Components

• Mucus- cells secrete, lubricate
• Parietal Cells; secrete hydrochloric acid and enzymes, which help in making vitamin B12
• Chief cells; secrete pesinogen (converting into pesin) to break down, protiens peptide cell
• Endocrine- secrete, somatostatin, gastrin, and histamine
• Gastrin helps make hydrochloric and persinogen. Histamines help for the secretion of hydrochloric

Gastric Cell

Parietal Cells - have unique features such as the of numbers Mitochondria, and number or Microvilli in plasma Membrane.

• The vagus nerve releases acetylcholine that stimulates acid secretion
• Gastrins act upon theCCK2 to stimulate secretion

Hormones that Inhibit Acid Secretion Include

• Somatostatin and prostaglandins are hormones releases, to limit acid and histamine
• Acetyl choline helps inhibit acid and muscarinic secretin Mucous neck, Clustered around Gastric glands with secretion’s

Cells near Glands

• Inner part is more clustered
• Some glands produce mucus for the glands
• The Corpus; has both parts directional migration from both stem cells and common to all parts:
• Stem cells in theisthmus.
• some are replaced upwards
• Other; differentiates in the parietal and chief cells