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General Histology Lecture 9 Integumentary system 1 Reference : Anthony L. MESCHER, Jonquiere's Basic Histology TEXT & ATLAS  Function of skin Serves as a barrier protecting against physical and chemical injury and infection. Prevents...

General Histology Lecture 9 Integumentary system 1 Reference : Anthony L. MESCHER, Jonquiere's Basic Histology TEXT & ATLAS  Function of skin Serves as a barrier protecting against physical and chemical injury and infection. Prevents water entry and loss. Helps regulate body temperature. Receptor organ for sensory stimuli. Involved in synthesis of vitamin D3 from precursors in skin. Excretion of substances produced by glands.  Embryologic Origins of Skin Epidermis (the surface layer of skin) arises from ectoderm. Dermis (the connective tissue component of skin) arises from somites of the paraxial mesoderm.  Skin is composed of: Epidermis: a surface of keratinized stratified squamous epithelium Dermis: connective tissue Skin appendages: Merocrine (eccrine) sweat glands, apocrine sweat glands, sebaceous glands, hair follicles, nails. Layers of the skin  The Five Layers of Epidermis 1. Stratum Corneum 2. Stratum Lucidum 3. Stratum Granulosum 4. Stratum Spinosum 5. Stratum Basale  Stratum Basale (Basalis) Bottom layer; just above basal lamina. Cuboidal to columnar keratinocytes one layer thick. Cells attached to each other by spot desmosomes and to basal lamina by hemidesmosomes. Mitoses renew epidermis every 15-30 days. Contains melanocytes and Merkel cells.  Stratum Spinosum Thick layer directly above stratum basale. Spot desmosomes connect cells. Cells shrink during processing but remain attached at desmosomes, and look “spiny” or prickly. Areas of skin subject to more mechanical pressure have more spot desmosomes.  Stratum Granulosum Just above stratum spinosum. Cells contain two types of granules. Keratohyaline granules: large, basophilic; bind cytokeratin molecules together to make keratin. Lamellar granules: small; contain lipid that is released into intercellular spaces (acts as a cement to prevent penetration of water and other materials).  Stratum Lucidum Above stratum granulosum. Keratinocytes have lost nuclei and organelles and appear as homogeneous, translucent cells. Cells contain keratin. Present only in very thick skin.  Stratum Corneum Most superficial layer. Consists of flat, dead cells – basically keratin scales - that are continuously shed. Keratin is composed of cytokeratin filaments (long intertwined protein chains) and keratohyalin (a substance that helps hold cytokeratin filaments together).  Four Types of Cells in Epidermis Keratinocytes are stratified squamous epithelial cells. Most of the epidermis is composed of keratinocytes. Function is to produce intermediate filaments called cytokeratins. Amount of cytokeratins increases as the cells move upward. Melanocytes produce melanin. Langerhans cells process antigen. Merkel cells are involved in sensation. keratinocyte melanocyte  Dermis Papillary dermis Loose connective tissue with lots of capillary loops and thin elastic fibers Reticular dermis Dense connective tissue with thick collagen bundles and elastic fibers, larger blood vessels and glands.  Subcutaneous tissue Also called hypodermis NOT considered part of the skin! Consists of loose connective tissue and adipose tissue Function: loosely binds the skin to underlying structures 16 Layers of the skin  Questions Respiratory system Components of respiratory system ? Pleuro in respiratory system is one of the conducting portion. True or false Hematopiosis of the lung > in breif Embryonic origin of the respiratory system is mesodermal only.. True or false Mesoderm in respiratory gives rise to >>>  Endoderm in respiratory gives rise to >>>> The walls of the conducting system in res. system did not changed in thickness and composition from region to region. Cartilage is always exist in all parts of the respirator tract. True or false Four types of cells exist in respiratory system Function of goblet cells and basal cells in respirator system..  The type of cells in the nasal cavity> 3types ? Identify nasal septa and nasal fossa Type of cartilage in epiglottis and trachea ? Cartilage in bronchi is hyaline cartilage.. True or false Larger bronchioles have respiratory epithelium. Smaller bronchioles have …..  Clara cells is (non-ciliated epithelial cells with secretory granules) Function is ? Respiratory bronchioles are lined with cuboidal epithelial, Alveolar Duct is Lined by simple squamous epithelium Alveolar sac Composed of squamous epithelial cells, basement membrane and capillaries.. Types of fibers in alveolar sac and the function ? Elastic and reticultur  the interstitium of the interalveolar septum is found the richest capillary network in the body. alveolar epithelial cells are 3 types ……. Function is mesothelial cells resting on a fine connective tissue layer that contains collagen and elastic fibers found mainly in The layers of pleura includes parietal and vesceral