General Histology Lecture 6: Respiratory System 2 PDF

Summary

This document is a lecture on general histology of the respiratory system. It discusses the structure of respiratory bronchioles, alveolar ducts, sacs, and alveoli, and explains their function in gas exchange. It also covers the pleura.

Full Transcript

General Histology Lecture 6 Respiratory System 2 Ahmed Abdul-Aziz Muhamed. PhD Reference : Anthony L. MESCHER, Jonquiere's Basic Histology TEXT & ATLAS 1 Respiratory portion Re...

General Histology Lecture 6 Respiratory System 2 Ahmed Abdul-Aziz Muhamed. PhD Reference : Anthony L. MESCHER, Jonquiere's Basic Histology TEXT & ATLAS 1 Respiratory portion Respiratory bronchioles Similar to the terminal bronchioles, except that the epithelium is interrupted by alveoli Epithelium consists almost entirely of clara cells Respiratory bronchioles are lined with cuboidal epithelial, alveolar ducts opened to the alveoli Respiratory bronchioles Primary, terminal respiratory bronchioles Alveolar Duct Elongate airways that have almost no walls, only alveoli, as its periphery boundary. Lined by simple squamous epithelium Terminate in clusters of alveolar sacs Alveolar ducts : arise by branching of respiratory bronchioles; walls made up of alveolar sacs and alveoli. Alveolar sac Alveolar sacs : cluster of alveoli that open into the lumen of the alveolar duct. Composed of squamous epithelial cells, basement membrane and capillaries.. Site of respiratory exchange. Alveolar sac Alveolar ducts open into atria that communicate with alveolar sacs, two or more of which arise from each. Elastic and reticular fibers form a complex network encircling the openings of atria, alveolar sacs, and alveoli. The elastic fibers enable the alveoli to expand with inspiration and to contract passively with expiration. The reticular fibers serve as a support that prevents over distention and damage to the delicate capillaries and thin alveolar septa. Alveolar sac Alveoli are responsible for the spongy structure of the lungs. Structurally, alveoli resemble small pockets that are open on one side, where O2 and CO2 are exchanged. An inter-alveolar septum consists of two thin squamous epithelial layers between which lie capillaries, elastic and reticular fibers, and connective tissue matrix and cells. The capillaries and connective tissue constitute the interstitium. Within the interstitium of the interalveolar septum is found the richest capillary network in the body. Mechanism Air in the alveoli is separated from capillary blood by three components referred to collectively as the blood- air barrier: 1. The surface lining and cytoplasm of the alveolar cells, 2. The fused basal laminae of the closely apposed alveolar and endothelial cells, 3. and the cytoplasm of the endothelial cells. The total thickness of these layers varies from 0.1 to 1.5 µm. alveolar epithelial cells are: Type 1 alveolar cells Simple squamous cells Adjacent cells joined by tight junction Type II cells Surfactant : cuboidal cells scattered among type 1, secrete pulmonary surfactant which lower the surface tension and prevent alveoli from collapsing Alveolar macrophage or dust cells > remove debris Pleura The pleura is the serous membrane covering the lung. It consists of two layers, parietal and visceral, that are continuous in the region of the hilum. Both membranes are composed of mesothelial cells resting on a fine connective tissue layer that contains collagen and elastic fibers. The elastic fibers of the visceral pleura are continuous with those of the pulmonary parenchyma

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