Histology I. Dr. Carmen E. Rexach Anatomy 35 Mt San Antonio College

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1 Histology I Dr. Carmen E. Rexach Anatomy 35 Mt San Antonio College

2 Histology Study of tissues Tissues = a group of cells performing a common function Microscopic anatomy Includes how different tissues are arranged to form organs and other structures

3 Extracellular matrix: cell Composition surface Fibrous structural and adhesion proteins embedded in gelatinous polysaccharide ground substance Function Binds cells together to form tissues

4 Extracellular matrix: cell surface

5 Cell Junctions Tight junctions Near apical surface Adhering junctions Below tight junctions Desmosomes Sites that stretch Gap junctions Shared cytoplasm

6 Tissue sections Longitudinal sections Transverse or cross section

7 Tissue sections

8 Primary tissue classes Epithelial Connective Nervous Muscular Differences Matrix variation Primary constituents Fibrous proteins Ground substance Amount of cells vsmatrix

9 Epithelial tissue Composition One or more layers of closely adhering cells Apical surface and basal surface Rest on a basement membrane Avascular Supported by connective tissues Function Cover organ surfaces Form secretory tissue Form ducts of glands

10 Classification Criteria Number of cell layers Morphology of the surface cells Two major categories Simple(one layer) Stratified (two or more layers)

11 Cell shape Squamous Columnar Cuboidal Acinar

12 Simple Epithelia General All cells touch basement membrane Exception: Pseudostratified columnar Categories Simple squamous Simple cuboidal Simple columnar Pseudostratified columnar

13 Simple Epithelia

14 Microvilli vs. Cilia Microvilli are folds in the apical surface of the plasma membrane. They increase cell surface area. Cilia are composed of microtubules and project from the apical surface. Function: to move things across the cell surface

17 Acini Acinar cells are often arranged in a circle (acinus, acini), creating structures that resemble flowers or a pie that s been cut into slices. Many exocrine glands are composed of acini.

19 Stratified Epithelia General characteristics Up to 20 or more cell layers Named for shape of surface cells Exception: transitional epithelium Stratified squamous Most common Exfoliation Keratinized tissue (cornified) Nonkeratinized

20 Stratified epithelia

21 Transitional epithelium Note the dome cells at the apical surface

22 Connective Tissue Less cells, more ECF (ground substance) Variable, widely distributed, most abundant Three categories of mature tissue Fibrous CT Supportive CT (bone, cartilage) Fluid CT (blood)

23 Functions Binds organs Support Protection Physical Immune Movement Storage Heat production Transportation

24 Fibrous Connective Tissue: Components Cells Fibroblasts Macrophage Leukocytes Plasma Cells Mast Cells Adipocytes Fibers Collagenous Reticular Elastic Ground substance

25 Types of Fibrous CT Loose Lots of ground substance dissolves in vitro Types Areolar, reticular, adipose Dense Fiber is predominant component Types Dense regular, dense irregular

26 Loose CT Reticular connective tissue Areolar connective tissue Adipose connective tissue

27 Areolar Connective Tissue Cells All six types Matrix Predominately collagenous Some elastic/reticular General Very vascular Loosely organized Varied Underlies almost all epithelial tissue

28 Reticular Reticular fibers and fibroblasts Stroma of organs and tissues such as lymph nodes, spleen, thymus, bone marrow

29 Adipose Tissue Adipocytes most abundant cell type Supported by areolar CT, reticular CT, blood vessels Function: energy storage White fat vs. Brown fat

30 Dense Connective Tissue Dense Regular Closely packed parallel collagen fibers + fibroblasts Tendons and ligaments Yellow elastic tissue Elastic fibers Fibroblasts with larger nuclei Wavy elastic sheets in walls of medium/large arteries Dense Irregular Collagen fibers in random arrangement + fibroblasts Dermis, protective capsule around organs, fibrous sheet around bones, etc. Similar to areolar, but less open space

31 Dense Connective Tissue Dense Regular Dense Irregular

32 Cartilage Three types Hyaline Elastic Fibrocartilage Flexible matrix Avascular except when transforming to bone External ear, tip of nose, larynx Cells Chondroblasts secrete matrix Chondrocytes trapped in lacunae

33 Hyaline Cartilage Matrix smooth, frictionless mix of collagen, elastin, chondroitin (a glucosaminoglycan) Cells Cell nests Usually covered by perichondrium Dense irregular CT covering inner layer produces new chondrocytes Examples: Costal cartilage Nasal septum C-ring cartilage of trachea Fetal skeleton

34 Elastic Cartilage Matrix Web-like mesh of elastic fibers Appearance of fur Perichondrium always present Examples: Pinna Epiglottis

35 Characteristics Parallel collagen fibers Rows of chondrocytes in lacunae No perichondrium Examples Pubic symphysis Intervertebral discs Menisci of the synovial joints Fibrocartilage

36 Bone Two forms Spongy Heads of long bone Named for appearance Compact No visible spaces Dense calcified tissue External surface of all bone Structure of compact bone Haversiancanal Osteon Lamellae Lacunae Canaliculi Periosteum

37 Compact Bone

38 Blood Plasma + formed elements Erythrocytes Leukocytes Neutrophils Basophils Eosinophils Monocytes Lymphocytes

39 Hemopoiesis formation of formed elements

40 Nervous Tissue Excitable tissue Function Rapid communication Cell types Neurons Neuroglia

41 Neurons impulse: an all or none electrical event neurotransmitters: chemical messengers released by neurons

42 Neuron

43 Neuroglia (nerve glue) 6 subtypes highly branched like neurons not capable of impulses perform supportive (connective tissue type) functions astrocyte

44 Nerves: Cross section

45 Muscular Tissue Contracts when stimulated Three types Skeletal Striated, multinucleated, voluntary Muscle fibers Cardiac Striated, uninucleate, involuntary Short branching cells Intercalated discs gap junctions desmosomes Smooth No striations, uninucleate, involuntary Short fusiform cells Visceral muscle

46 Muscular Tissue Cardiac muscle Skeletal Muscle Smooth muscle

The Tissue Level of Organization

The Tissue Level of Organization Tissues A groups of similar cells, usually having similar embryonic origin and specialized function Histology: the study of tissues Four general types Epithelial Muscle