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Histology. Objectives Define histology Describe the four main tissue types Identify the various tissues that fall under the four main tissues types, their.

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Presentation on theme: "Histology. Objectives Define histology Describe the four main tissue types Identify the various tissues that fall under the four main tissues types, their."— Presentation transcript:

1 Histology

2 Objectives Define histology Describe the four main tissue types Identify the various tissues that fall under the four main tissues types, their functions and composition Be able to describe the types of glands, membranes, and cellular junctions Know how tissue growth and repair occur

3 Histology The study of tissues and their arrangement into organs Tissues – Group of cells that are similar in structure and perform a common or related function – Four main types Differ by type of cells and characteristics of matrix

4 How We Study Tissues Tissues are cut into various sections – Cross section (c. s.) – Longitudinal section (l. s.) – Oblique section Tissues can also be mounted as smears – Blood, spinal cord

5 Four Main Tissue Types Epithelial Connective Muscle Nervous

6 Epithelial Tissue Sheet of cells that covers a body surface or lines a body cavity – Covering and lining epithelium Cells that compose glands of the body – Glandular epithelium Functions – Protection, absorption, filtration, secretion, excretion, sensory reception

7 Characteristics of Epithelium Cellularity – Almost entirely composed of closely-packed cells Minimal ECF Specialized connections – Continuous sheet of cells – Tight junctions and desmosomes Polarity – Apical surface and basal surface – Basal lamina Connective tissue support – All epithelium supported by connective tissue – Reticular lamina – Basal lamina + reticular lamina = basement membrane Avascular – No blood vessels within epithelium – Is innervated Regeneration – high regenerative capacity

8 Classification of Epithelium Based on number of cell layers and on cell shape Cell layers – Simple – refers to one layer of cells – Stratified – refers to two or more layers of cells Cell shape – Squamous – flat, scale-like cells – Cuboidal – cube shaped cells – Columnar – column shaped cells How is pseudostratified columnar classified?

9 Simple Squamous Epithelium Thin and permeable – Found where rapid filtration and diffusion is desired Kidneys, lungs

10 Simple Cuboidal and Columnar Function in secretion and absorption Found in tubules of the kidneys and in ducts of glands Function in absorption and secretion Found in stomach, intestines, uterus, uterine tubes

11 Pseudostratified Columnar Epithelium Function in secretion, absorption, and motility of mucus Cells vary in height, but all cells touch the basement membrane Found in the respiratory tract and male urethra

12 Stratified Squamous Most abundant stratified epithelium Functions in protection against abrasion Found on outer layer of skin and extend a short way into every body opening that is continuous with the skin – Keratinized and non-keratinized

13 Stratified Cuboidal and Columnar Functions in secretion and sperm production Found in sweat gland, ovaries, seminiferous tubules Function in protection and secretion Rare, found in ducts of large glands, male urethra

14 Transitional Epithelium Functions to allow distention of the urinary bladdery Found in the bladder Basal cells are typically cuboidal Apical cells vary in shape

15 Glandular Epithelia Glands are cells or organs that secrete a substance for use or elimination – Originate from invagination of epithelial tissue Classified into two categories – Endocrine – Exocrine Unicellular glands – Composed of one cell that secretes its products into its surroundings

16 Exocrine Glands Typically enclosed by fibrous capsule – Septa – capsular extension that divide gland into lobes – Parenchyma – cells that synthesis and secrete Classified based on the duct – Simple – single unbranched duct – Compound – branching ducts

17 Exocrine Glands

18 Types of Secretions Serous glands – Thin watery fluids Mucus glands – Secrete mucin that is converted into mucus upon absorption of water Cytogenic glands – Secrete whole cells Testes and ovaries

19 Method of Secretion Merocrine (eccrine) – vessicles release secretion via exocytosis – Apocrine Sweat and mammary glands Holocrine – cell accumulates a product and then the cell disintegrates

20 Connective Tissue Found everywhere in the body and most widely distributed Functions – Connects, supports, protection, insulation, and transportation Four main classes – Fibrous tissue and fat – Cartilage – Bone – Blood

21 Characteristics of Connective Tissue Common origin – All arise from mesenchyme Degree of vascularity – Some avascular, while others highly vascular Extracellular Matrix – Tissue made up mostly of matrix Ground substance

22 Structural Elements of CT Ground substance – Interstitial fluid between the cells allows for diffusion between blood vessels and cells – CAP, GAG, Proteoglycans Fibers – Provide support Collagen Elastic Reticular Cells – Fibroblasts, macrophages, leukocytes, plasma cells, mast cells, adipocytes

23 Fibrous Connective Tissue Loose connective tissue – Areolar Serves to support most epithelium Very loose fibers run in various directions – Reticular Framework of “soft organs” Dense connective tissue – Dense regular Composed of closely packed parallel collagen fibers Fibroblast only type of cell Tendons and ligaments – Dense Irregular Thick collagen fibers running in various direction Compose the dermis, and fibrous sheaths around various organs



26 Fibrous Connective Tissue Adipose tissue – Composed of adipocytes that store fat – Functions as insulation and support – Most fat is white fat – Children also produce brown fat Heat production

27 Cartilage Supportive connective tissue with flexible rubbery matrix Chondroblasts secrete matrix until they are trapped. – Chondrocytes Avascular – Dependent on diffusion – Slow metabolism, slow to heal

28 Cartilage Three types – Hyaline Clear glassy matrix with collagen fiber Found at the ends of bones, larynx, trachea, and chest Composes fetal skeleton – Elastic Matrix composed of elastic fibers Perichondrium sheath Ear, epiglottis – Fibrocartilage Matrix composed of thick parallel collagen bundles No perichondrium sheath Pubic symphysis, intervertebral discs, menisci Compression and shock absorption Sometimes transition between dense connective tissue and hyaline




32 Bone Osseous Tissue – Spongy – Compact Hard calcified matrix containing collagen fibers – Deposited in concentric lamellae around central canal Blood vessels and nerves – Osteoblasts, osteocytes, osteoclasts Support, protection, movement, mineral and fat storage, blood production

33 Blood Fluid connective tissue – Formed elements in a fluid matrix (plasma) Transport nutrients, wastes, gases... Found within blood vessels

34 Muscle Tissue Highly cellular, well vascularized tissues responsible for movement Capable of contraction and producing tension Three types – Skeletal – Smooth – Cardiac

35 Nervous Tissue Main component of nervous system – Regulates and controls various functions Capable of transmitting electrical impulses Two cell types – Neurons Conduct impulse – Supporting cells Nonconducting, insulate and protect neurons

36 Cell Junctions Extra cellular matrix – The “glue” that holds the cells together – Network of fibrous proteins embedded in gel-like fluid Collagen, elastin, fibronectin – Secreted by fibroblasts Specilaized junctions – Desmosomes – Tight junctions – Gap junctions

37 Cell Junctions Tight junctions Gap junctions

38 Please read section 5.6 on tissue growth, repair and death

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