Zoo 115: Animal Histology Lecture Notes PDF

**MODULE 10: RESPIRATORY SYSTEM** - Consists of organs that serve as avenues of air to and from the lungs - **Main function**: avenue for intake of oxygen and removal of carbon dioxide, which is a byproduct of metabolism among aerobic animals including humans, from the body - Ha...

**MODULE 10: RESPIRATORY SYSTEM** - Consists of organs that serve as avenues of air to and from the lungs - **Main function**: avenue for intake of oxygen and removal of carbon dioxide, which is a byproduct of metabolism among aerobic animals including humans, from the body - Has conducting portion and respiratory portion - The **conducting portion** is dedicated to passageway of inhaled and exhaled air. - This consists of the nose, the pharynx, larynx, trachea and branching system of bronchi. - The **respiratory portion** is involved in exchange of gases between inhaled air and the blood. - This begins with respiratory bronchioles to the alveolar ducts and alveoli. **Functions of the Respiratory System** 1. Filtration of air 2. Conduction of air 3. Exchange of gases (respiration) **Conducting Portion of the Respiratory System** **Nasal Cavity** - are paired chambers separated by bony and cartilaginous septum. - opens anteriorly through the [anterior] nares, [posteriorly] through the choanae into the pharynx, and laterally to the paranasal sinuses and nasolacrimal duct. **NOSE** - Bounded anteriorly by external or anterior nares and posteriorly by choanae into the pharynx - **Nasal vestibule** - area just inside the external nares leading to the nasal cavity - **Nasal cavity** - divided into 3 segments: vestibule, respiratory segment, and olfactory segment - **Right and left nasal cavities** - paired chambers separated by bony and cartilaginous septum - open laterally through the paranasal sinuses and lacrimal duct **[Chambers of the Nasal Cavity]**  **Nasal vestibule** - is the dilated space just inside the nostril. - This has vibrissae, which are large stiff hairs, and sebaceous glands. - Stratified squamous epithelium continues through the nares into the vestibule. Inside the vestibule the lining epithelium becomes a transition band of ciliated cuboidal or columnar epithelium. **Respiratory region** - is largest part comprising two-thirds of the nasal cavity. - Ciliated pseudostratified columnar epithelium lines its mucosa. - Its lamina propria is firmly attached to the periosteum and perichondrium, and contains mucous glands. Its mucosa warms, moistens and filters air. **Olfactory region** - is located at the roof or apex of the nasal cavity. - This occupies almost one third of the cavity and is lined by specialized olfactory mucosa, which is lined with olfactory epithelium. - This olfactory epithelium is capable of regeneration following partial destruction. - The lamina propria of the olfactory mucosa contains olfactory glands of Bowman. - This lamina propria covers a dense connective tissue that forms the periosteum of the cribriform plate of the ethmoid bone of the skull. **Cells in the Respiratory Epithelium** **[Olfactory Epithelium]** - Specialized respiratory epitheliu - Lined with ciliated pseudostratified columnar epithelium. - Thicker with numerous nuclei than ordinary respiratory epithelium - Most nuclei belong to olfactory cells - Overlies a lamina propria with Bowman's glands **[Cells of the Olfactory Epithelium]** **Olfactory Cells** - are **bipolar** neurons. - Each cell has a round nucleus with the apical portion narrowed to a thin cylindrical process, which extends to the surface of the epithelium where it terminates into an expansion called olfactory bulb. - This has 6 to 8 nonmotile olfactory cilia. **Sustentacular cells** - are tall columnar cells that possess closely packed microvilli projecting into a blanket of mucus. - Each cell has a pale- staining nucleus and its apical cytoplasm has few pigment granules that confers yellowish- brown color to the olfactory epithelium. - These cells provide mechanical and metabolic support, and synthesize and secrete odorant- binding proteins. **Brush cells** - are cells with short blunt microvilli. Its basal surface is in contact with afferent nerve endings of C.N. V trigeminal nerve. **Basal cells** - are stem cells that appear small and deeply basophilic. +-----------------------------------------------------------------------+ | **Paranasal Sinuses** | | | | - are air-filled spaces in the bones of the walls of the nasal | | cavity. These include accessory nasal sinuses such as frontal, | | sphenoidal, ethmoidal, and maxillary sinuses. | | | | - The paranasal sinuses are connected with the nasal cavity. These | | are lined with ciliated pseudostratified columnar epithelium. The | | cilia present in the epithelium sweep the mucus towards the nasal | | cavity. | | | | - Inflammation of its lining epithelium is called | | **sinusitis**. | +-----------------------------------------------------------------------+ **Pharynx** - Common path of air and food - serves as a resonating chamber of speech. **Divisions**: a. **Nasopharynx** -- - lined with ciliated pseudostratified columnar epithelium overlying a submucosa with mucous-secreting glands - Connected to middle ear through Eustachian tube - nasopharynx is connected to the middle ear through the auditory tube or Eustachian tube. This has pharyngeal tonsils at its superior and posterior walls. b. **Oropharynx** - lined with nonkeratinized stratified squamous epithelium; - lacks both muscularis mucosae and submucosa c. **Laryngopharynx** - a.k.a. hypo pharynx **Epiglottis** - at the superior end of the larynx, which has both lingual and a laryngeal surface - **Lingual surface** (mucosa) - covered with nonkeratinized stratified squamous epithelium - **Laryngeal surface** - covered with ciliated pseudostratified columnar epithelium With central elastic cartilage Towards the base of the epiglottis at the laryngeal mucosa it is covered with ciliated pseudostratified columnar epithelium. There may be some taste buds and solitary lymphoid nodules in the epithelial covering at its lingual or laryngeal surfaces. **Larynx** - is a hollow organ located between the pharynx and trachea. This produces sound and closes the trachea during swallowing through the epiglottis. - With two pairs of folds that project into the lumen of the larynx: a. **Vestibular folds or false vocal cords** - continuous with posterior surface of epiglottis - Lined with ciliated pseudostratified columnar epithelium with goblet cells - Present in lamina propria are seromucous glands, lymphatic nodules, blood vessels and adipose cells - Underneath the vestibular folds is the **ventricle**, which is a deep indentation. - The lower pair of mucosal folds are the: b. **Vocal folds or true vocal cords** - Lined with nonkeratinized stratified squamous epithelium - Lamina propria has no glands, blood vessels or lymphoid tissue - Has **vocalis ligament** made of dense elastic fibers at its apex and **vocalis muscle,** which consists of striated or skeletal muscles. 1. **Vestibule** 2. **Ventricular fold** or **vestibular fold** - With prominent mucous glands - Covered with pseudostratified 3. **columnar epithelium** 4. **Ventricle** - deep indentation 5. **Vocal fold** - Has vocalis ligament and underlying vocalis muscle 6. **Infraglottic cavity** **Trachea** - 10 cm long and 2 cm wide flexible tube - Its lumen remains open or patent because of its cartilaginous rings. - With C-shaped hyaline cartilage rings - Prevent the tracheal mucosa from collapsing after inspiration - Posterior gap closed by trachealis muscle, which is made of smooth muscles ***[Layers:]*** a. **Mucosa** - Lined with ciliated pseudostratified columnar epithelium - These ciliated cells have microvilli projecting into the lumen - The tracheal epithelium has a thick basement membrane. - Its lamina propria is separated from the submucosa by a band of elastic membrane. - Lacks muscularis mucosae - Lamina propria separated from submucosa by a band of elastic membrane b. **Submucosa** - Layer of dense connective tissue - Has numerous glands c. **Cartilaginous layer** - Is made of C-shaped hyaline cartilage d. **Adventitia** - is the external connective tissue covering that binds the trachea to adjacent structures. ***[Cells in Mucosa]*** i. **Goblet cells** - produce mucus ii. **Brush cells** - with microvilli at its luminal border; believed to be depleted goblet cell or cell at its intermediate stage of differentiation iii. **Serous cells** - produce less viscous secretions than mucus iv. **Basal cells** - pyramidal cells between bases of columnar cells **Bronchus** - trachea divides into right and left primary bronchi. - Right and left bronchi divide into secondary bronchi that continue to divide into smaller bronchi - right primary bronchus is shorter and more aligned with the trachea than the left primary bronchus. - primary bronchi enter the lung parenchyma where each divides into lobar or secondary bronchi. - Each lobe of the lungs receive a lobar bronchus. - There are **two lobar bronchi on the left** lung while there are **three lobar bronchi on the right** lunch. - Each lobar bronchus divides into segmental or tertiary bronchi, which in turn divide into subsegmental bronchi. ***Histologic Features of the Bronchus*** - Has the same histologic features as the trachea - Once these enter the lungs as intrapulmonary bronchi, the bronchial wall changes. ***[Layers of bronchus ]*** a. **Mucosa** - Lined with ciliated pseudostratified columnar epithelium - With goblet cells and submucosal glands that diminish in number as bronchus further divides to form bronchioles b. **Muscularis** - Continuous circumferential layer of smooth muscle in larger bronchi - Becomes loose and disorganized in smaller bronchi c. **Submucosa** - Consists of loose connective tissue - In larger bronchi, this layer has adipose tissue and glands d. **Cartilage layer** - With discontinuous plates of hyaline cartilage - Cartilage plates reduce in size and eventually disappear at the subsegmental bronchi e. **Adventitia** - dense external covering of the bronchus and is continuous with nearby structures - Made of dense connective tissue **Bronchioles** - Measures 1 mm or less in diameter - Segmental bronchi divides into larger bronchioles, which divides to form terminal bronchioles - Terminal bronchioles give rise to **respiratory bronchioles** - **In larger-diameter bronchioles,** the mucosa is lined with ciliated pseudostratified columnar epithelium. - May contain goblet cells but subepithelial glands are absent - Lining epithelium becomes ciliated simple columnar epithelium as its diameter narrows - **Small bronchioles** - lined with simple cuboidal epithelium - **Terminal bronchioles** - lined with simple cuboidal epithelium with Clara cells - **Clara cells** - secrete component of **surfactant**, a surface-active agent that prevents walls of airway from collapsing during exhalation - Bronchioles [do not have cartilage plates]. However, bronchioles have thick layer of smooth muscle. **Terminal bronchiole** - Terminal end of the conducting airway - With layer of smooth muscles surrounding the lumen **Respiratory bronchiole** - With presence of alveoli or air sacs in the walls which are sites for gas exchange. - Lined with simple cuboidal epithelium with **Clara cells** - Only some epithelial cells are ciliated - **function** for air conduction and gas exchange - Walls are discontinuous that opens into a number of alveolar ducts **Alveolar Duct and Alveoli** **Alveoli** - are terminal air spaces for gas exchange. Each alveolus is surrounded by capillaries. **Alveolar Duct** - Elongated airways with walls made of alveoli - Terminate into alveolar sacs, **Alveolar Sac** - Space surrounded with cluster of several alveoli at the terminal end of an alveolar duct. ***Alveoli*** **[Cells in Alveolus]** a. **Type I pneumocyte** - or type I alveolar cells - Constitute 40% of cells lining the alveoli - Very thin squamous cells where gas exchange occurs between inhaled air and blood in capillaries. b. **Type II pneumocyte** - or type II alveolar cells - Constitute 60% of cells lining the alveoli - Cuboidal cells that secrete surfactant - Surfactant prevents collapse of alveolar walls during exhalation. In the event of injury, type II alveolar cells can give rise to type I alveolar cells. c. **Brush cells** - Present in small number - Receptors for monitoring air quality d. **Alveolar macrophage** - May move from connective tissue of the septum to lumen of alveolus - Removes or phagocytose inhaled particulate matter from air, erythrocytes in heart failure, or M. tuberculosis in tuberculosis infection - These remove inhaled particulate matter from air, and erythrocytes (RBCs) that may enter the alveoli in the event of a heart failure. These may also phagocytose Mycobacterium tuberculosis, the bacterium causing tuberculosis. **Air-Blood Barrier** - Cell and cell products through which gases must diffuse between alveoli and capillaries compartments **Consists of the following:** a. Thin layer of surfactant b. type I pneumocyte of alveolar wall c. endothelium of the capillary, and d. shared basement membrane of the type I pneumocyte and the capillary - The connective tissue between the two basal lamina of type I alveolar cell and endothelium can widen the air- blood barrier.
 - To allow efficient exchange of gases (O2 and CO2) between air and blood