8.2
Epithelgewebe und ihre Funktionen
Epithelgewebe sind große Zellverbände, die alle Oberflächen des Körpers bedecken. Diese Oberflächen können intern oder extern sein, zum Beispiel Haut,…
Epithelgewebe sind Schichten aus dicht gepackten Zellen, die den Körper bedecken und bestimmte Umgebungen unterteilen, um den Körper vor pathogenen Invasionen, Flüssigkeitsverlust oder mechanischen Verletzungen zu schützen.
Sie treten in zwei Formen auf, nämlich in den Epithelien, die die Epithelien bedecken oder auskleiden, und in den Drüsenepithelien.
Abdeckende oder auskleidende Epithelien fungieren als Torwächter. Sie bedecken freiliegende Körperoberflächen und säumen die inneren Trakte der Organe, so dass selektive Substanzen in den Körper ein- und austreten können.
So ermöglicht die epitheliale Auskleidung der Nierentubuli die Rückresorption von Nährstoffen aus dem Urin und die Freisetzung von Abfallprodukten aus den nahe gelegenen Kapillaren.
Drüsenepithelien sind in spezialisierten Strukturen oder Drüsen angeordnet, die eine einzelne Zelle oder eine Gruppe von Zellen sein können. Sie produzieren und setzen verschiedene sekretorische Substanzen wie Schleim, Schweiß und Hormone frei.
Epithelgewebe sind reich an sensorischen Nerven ausgestattet, die Informationen schnell zwischen der äußeren und inneren Umgebung weiterleiten und eine sofortige Reaktion hervorrufen.
Zum Beispiel stimuliert ein Mückenstich sofort die Nerven unter dem Hautepithel und veranlasst den Körper, an der Stelle zu schlagen.
Q1: What are the two main types of epithelial tissues and how do they differ?
Epithelial tissues exist as covering or lining epithelia and glandular epithelia. Covering or lining epithelia function as gatekeepers, covering exposed body surfaces and lining internal organ tracts while allowing selective substances to enter and exit. Glandular epithelia are specialized structures arranged into glands that produce and release secretory substances like mucus, sweat, and hormones.
Q2: How do epithelial tissues protect the body from harm?
Epithelial tissues form protective sheets of closely-packed cells covering body surfaces and lining internal tracts, shielding the body from pathogenic invasion, fluid loss, and mechanical injuries. They act as the body's first line of defense against physical, chemical, and biological wear and tear. All substances entering the body must cross an epithelium, making it a critical barrier.
Q3: What role do sensory nerves play in epithelial tissue function?
Epithelial tissues are richly supplied with sensory nerves that quickly relay information between external and internal environments, producing immediate responses. For example, a mosquito bite instantly stimulates nerves under the skin epithelium, triggering the body to swat at the location. This rapid sensory feedback helps protect the body from threats.
Q4: How do epithelial cells contribute to digestion and respiratory defense?
Many epithelial cells secrete mucus or other chemical compounds with specific functions. The intestinal epithelium releases digestive enzymes to help break down food, while the respiratory tract lining secretes mucus to trap incoming microorganisms and particles. These secretions support both nutrient processing and pathogen defense.
Q5: What is selective transport and why is it important in epithelial tissues?
Epithelial tissues act as gatekeepers by allowing selective transfer of materials across a physical barrier. For instance, the epithelial lining of kidney tubules allows reabsorption of nutrients from urine while releasing waste products from nearby capillaries. This selective permeability ensures the body retains essential substances while eliminating waste.
Q6: How are glands structured and what do they produce?
Glandular tissue consists of single or multiple secretory cells that yield a variety of secretions. These glands can be unicellular or multicellular structures that discharge secretions either on the epithelial surface or into the bloodstream to reach target cells. Common secretions include mucus, sweat, digestive enzymes, and hormones.
Q7: Where are epithelial tissues found throughout the body?
Epithelial tissues cover all body surfaces, both internal and external, including skin, airways, the digestive tract, urinary system, and reproductive system. Hollow organs and body cavities not connected to the exterior, such as blood vessels and serous membranes, are lined by specialized epithelial tissue called the endothelium. This extensive coverage ensures comprehensive protection and selective transport.