Microscopic Structures of the Lungs 2024-2025 PDF

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King Faisal University

2024

Maryam Alyahya

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lung anatomy pulmonary histology respiratory system medical education

Summary

These lecture notes cover the microscopic structures of the lungs, including alveoli, interalveolar septum, and the blood-air barrier. The materials detail the structure and function of these components.

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Block 1.3 lectures 2024-2025 lecture Highlighter key Writer Reviewer...

Block 1.3 lectures 2024-2025 lecture Highlighter key Writer Reviewer Doctor explanation Abbreviation Key information Book >> >> Maryam Alyahya Suaad aljumaiah Student explaintion 221-222-223 notes References Deleted ‫بسم هللا الرحمن الرحيم‬ Respiratory System II Dr. AsmaaFathi Assist.Prof. of Histology Reference JunqueiraBasic Histology Text and Atlas 14&15thedition Chapter 17 Learning objectives To Identify histological structure of: Alveoli/ types of alveolar cells Interalveolar septum Blood air barrier Bronchial tree -bronchi ? Primary bronchi 2ry bronchi/ pulmonary lobe 3ry bronchi/ broncho pulmonary segment Bronchiole-pulmonary lobule The histological structure of the respiratory bronchiole = terminal Respiratory zone ? bronchiole + few alveoli through the passage the epithelium in the terminal bronchiole was simple cuboidal ciliated, and it resides the same in the respiratory but: the cuboidal will turn into squamous and the cilia are going to be less other type of cells are present due to the fact that its the same as the terminal but with few alveoli the 5 cells are: ciliated, clara, basal, brush, small granule the new fact is that the epithelium bronchile is continuos with alveolar epithelium The lamina propria is also the same as the terminal, there are smooth muscle, MALT and elastic but with less number of cilia After the respiratory bronchiole we’re going to the alveolar duct which is a linear arrangement of alveoli ending with the alveolar sac (epithelium of the alveolar sac is an alveolar epithelium, simple squamous epithelium with few 2-3 cells of the cuboidal between the alveoli but disregard the cuboidal, just memorize that it is simple squamous) Going back to the supporting tissue: the elastic Respiratory zone fibers and MALT are there and increasing, no glands nor secretions, the smooth muscles are still present to the openings of the alveoli Simple cuboidal epithelium: cilia Alveolar duct/sac -Simple squamous “alveolar epithelium” -No cilia -“Bands of smooth muscle around alveolar openings” -Extremely thin lamina propria is rich in elastic and reticular fibers and capillaries Lung alveoli The structural unit which makes the alveolar duct / sac is the alveoli, summarized by 3S’s: — Shape: Sac like / Cup like / Honeycomb Saclike / cuplike / — Surrounding the bronchial tree and alveoli in specific: Spongy connective tissue called lung interstitium (also honeycomb called interalveolar septum) Spongy structure — Site of exchange of lung Site of gaseous exchange Interalveolar septum between the alveolous and the other, is there any connection ? Yes there are pores that * Just connective tissue rich in: 4. Alveolar pores ? connect the edges of the alveoli together called 5. Cells: -macrophage “ dust cells”/Heart failure cell ? pores of Kohn. Pores importance: (site/function/fate) - Leucocytes - Fibroblasts — to equalize the air pressure inside the alveoli — provide colateral pass of the air in case of bronchiolar obstruction What are the types of cells found in the lung interstitium ? — Fibroblasts secreting elastin and reticular fibers — Immune cells such as lymphocytes — Macrophages located in the septum & within the lumen of the alveoli, functioning in: —Phagocytosis of any foreign body, bacteria, dust and etc. —Phagocytosis of few RBCs that are released due to the mechanical stress of the capillaries —Help in turn over of surfactant how to identidy macrophages in light microscope? It appears dark, why? Because it accumulates dust particles, accumulate carbon (especially in smoker individuals), and accumulation of Hemosiderin Pigment (coming from the breakdown of RBC’s) How to get rid of macrophages? either drained by lymphatics, or remain in the lungs, or token upward by the mucociliary movement to be coughed or swallowed What structures are found among the alveoli Interalveolar septum — First is the interalveolar septum, the space between the alveoli that contains 2 types of fibers: Elastic & Reticular we said that the alveoli is like a ball, each ball is surrounded by three networks, first is the elastic, second is the reticular and the last one is capillary network * Just connective tissue rich in: the importance of the elastic fibers is to assist the distention of the alveoli during inspiration, and 1. Elastic fibers ? the passive recoil during expiration 2. Reticular fibers ? the importance of the reticular is to prevent over inflation & rupture during inspiration, preventing 3. Capillaries “ the richest capillary network collapse of alveoli during expiration type of capillaries: continuous capillaries that prevent leakage in body” ? “continuous capillaries” why does the lung has too many capillaries? To assist rapid gas exchange question may come in the exam : what is the type of capillary in the Interalveolar septum ? continuous capillaries Respiratory membrane “blood air barrier” What structures that makes up this barrier? — alveolar epithelium type 1 (type 2 is not involved in gas exchange) — fused basal lamina of the capillary endothelium and alveoli — capillary endothelium it is a very thin membrane, 0.1-1.5 micrometer The main function of the lung is the exchange of gases — there is air in the lung alveoli and carbon dioxide and oxygen in the blood, to pass through there is a membrane called the blood-air membrane barrier Its a barrier between the air in the alveoli and the air in the capillaries, through gas exchange, the alveoli takes up carbon dioxide and gives oxygen Blood air barrier “structure/function” Its total thickness 0.1-1.5mμ fused basal laminae The alveoli are lined by simple squamous epithelium contains 2 types of Alveolar epithelium cells: — Type 1 pneumocytes / type 1 alveolar cells / squamous alveoli cells it is also the major cell type — 5% of the cells are the great alveolar cells / type 2 alveolar cell / type 2 Simple squamous epithelium pneumocytes Type I alveolar cell Type 1 alveolar cells are the major cells and makes 95% of the epithelium, its shape is squamous (flat), responsible for the contact with the blood (gas “type I pneumocyte” exchange is done through it) type 2, which makes up 5%, IS NOT involves in gas exchange - Squamous Types of junctions between the alveolar cells are 2: -95% — desmosome which is found where there is mechanical stress such as the -Occluding junctions/desmosome/pinocytotic vesicle skin and heart muscle these cells during inspiration and expiration must be strongly attached -Barrier of minimal thickness to gases together by desmosome to provide strong attachment — tight junction making barrier in the intercellular space, why? To prevent leakage of fluids into the alveolar sac & prevent any invasion to the lung interstitium The cytoplasm of the type 1 cells contain many pinocytotic vesicles (present in both 1&2), which means they both function in pinocytosis (taking up fluids such as the surfactant and abnormal fluids to the interstitial side ) Which cell is involved in the turn over of the alveolar surfactant? macrophages through phagocytosis and type 1&2 pneumocytes through pinocytosis Type II alveolar cell/Septal There are 2 functions of type 2 cells, First: secreting surfactant which coat the alveoli which reduces the surface tension within the alveoli “type II pneumocyte” leading to easy inflame during inspiration & recoil during expiration without collapse the surfactant also contains antimicrobial agent, involved in innate immunity - rounded/cuboidal Second: it is mitotically active, they can divide and replace themselves & type 1 pneumocytes - Lamellar bodies/tight junction/desmosome in other words, it helps in repare of lung tissue -Mitotically active about the surfactant, it is a mix of lipoprotein and phospholipids, secreted by this cell into the surface which organelles involved in producing the surfactant? -Synthesis of surfactant/its function? —RER, Golgi apparatus giving us secretions in form of droplets called lamellar bodies appearing as -Surfactant turnover/innate immunity vesicles with white & black lines in the light microscope in the human body there are 3 structures containing lamellar bodies: granular cell layer of the skin, type 2 pneumocytes and retina of the eye Always remember…… Maturation of the lung in pregnant women happens in the last 2 weeks of the 9th month, if the fetus were born earlier they get under a respiration machine because there lung cells are immature & there is no surfactant in their alveoli & the physician gives them cortisone injection that stimulate / induce the maturation of the fetal lung barrier team Wishes you the best

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