appearance of stratified squamous epithelium • Location: • Lines the urinary bladder and parts of the ureters and urethra • Function: • Allows urinary organs to stretch as they fill with wastes while maintaining protective lining 39
Transitional epithelium 40
Glandular epithelium • Glandular epithelium is responsible for secretion • Accomplished through clusters of glandular cells that usually are deep to the covering and lining epithelium • A gland may consist of one or more cells that secrete substances into ducts (hollow tubes) onto a surface, or directly into the bloodstream if no duct is present • All glands are divided into two groups • Endocrine glands • Secrete substances called hormones into the interstitial fluid where they diffuse into the blood stream • These secretions have far reaching effects (discussed in chapter 18) • Exocrine glands • Secrete products into ducts that empty onto the surface of covering and lining epithelium, such as the surface of the skin or into the lumen of the intestine • The secretions have limited effect, and may even be harmful if they gained access to the blood • Note that some glands like the pancreas have both endocrine and exocrine functions 41
Endocrine glands 42
Exocrine glands 43
Classification of exocrine glands • Exocrine glands can be unicellular or multicellular • Unicellular glands consist on one cell that secretes their products directly onto the apical surface of a covering and lining epithelium • Most exocrine glands are multicellular glands, composed of many cells arranged into distinctive microscopic structures • Multicellular glands are divided based on two criteria • Does the duct branch • Simple glands do not branch • Compound glands have branching • The shape of the secretory portion of the gland • Tubular – secretory portion resembles a tube • Acinar- the secretory portion have a more rounded appearance • Tubuloacinar – have both tubular and rounded secretory portions 44
Simple exocrine glands 45
Compound exocrine glands 46
Functional classification of exocrine glands • Functional classification of exocrine glands is based on how their secretions are released • All forms begin with the endoplasmic reticulum and Golgi forming intracellular secretory vesicles containing the product • Merocrine gland secretions are packaged by the Golgi and released from the cell in secretory vesicles via exocytosis • Most common form of gland • Apocrine gland secretions accumulate at the apical surface of the secreting cell; that portion of the cell then pinches off, releasing the secretion • Holocrine gland secretions accumulates secretory product in the cytoplasm of the cell; when mature, the cell ruptures, releasing the secretory product 47
Connective tissue • One of the most abundant and widely distributed tissues in the body • Functions: • Binds, supports and strengthens other tissues • Compartmentalizes other tissues • Transport throughout the body
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- Anatomy, cells