Human Anatomy & Physiology, Sixth Edition 4 Tissue: The Living Fabric

Tissues  Groups of cells similar in structure and function  Four major types  Epithelial  Lining & secretory functions  Connective  Structural and dispersal functions  Muscle  movement  Nerve  Rapid coordination of muscles, cognitive and homeostatic functions

Epithelial Tissue  Tightly connected by cell-cell adhesions – desomosomes, tight junctions & adherins junctions  Form continuous sheets  Adherent to and supported by underlying basal laminae  Cells are polarized – apical and basal surfaces  Avascular but innervated  Regenerative

Classification of Epithelia  Layering  Shape

Epithelia: Tissues composed of epithelial cells  Lining  Skin  Digestive tract  Exocrine glands  Epithelial organs  Lung  kidney

Epithelia: Simple Squamous Figure 4.2a

Epithelia: Stratified Squamous Figure 4.2e  Thick membrane composed of several layers of cells  Function in protection of underlying areas subjected to abrasion  Forms the external part of the skin’s epidermis (keratinized cells), and linings of the esophagus, mouth, and vagina (nonkeratinized cells)

Epithelia: Simple Cuboidal Figure 4.2b  Single layer of cubelike cells with large, spherical central nuclei  Function in secretion and absorption  Present in kidney tubules, ducts and secretory portions of small glands, and ovary surface

Epithelia: Transitional Figure 4.2f  Several cell layers, basal cells are cuboidal, surface cells are dome shaped  Stretches to permit the distension of the urinary bladder  Lines the urinary bladder, ureters, and part of the urethra

Epithelia: Simple Columnar Figure 4.2c

Epithelia: Pseudostratified Columnar Figure 4.2d  Single layer of cells with different heights; some do not reach the free surface  Nuclei are seen at different layers  Function in secretion and propulsion of mucus  Present in the male sperm-carrying ducts (nonciliated) and trachea (ciliated)

Glands  1 or more cells that makes and secretes an aqueous fluid  Endocrine  Release material into blood stream  Secretions include amino acids, proteins, glycoproteins, and steroids (hormones)  Exocrine  Secrete products into a duct of epithelial cells or directly into target organ (stomach, intestine etc…)  mucous, sweat, oil, and salivary glands

Exocrine Glands  Unicellular gland  goblet cells in stomach  Multicellular  composed of a duct and secretory unit  Classified according to:  Simple or compound duct type  Structure of their secretory units

Figure 4.3a-d Multicellular Exocrine Glands

Modes of Secretion Merocrine - exocytosis (e.g., pancreas, sweat, and salivary glands) Holocrine – fragmentation of cells (e.g., sebaceous glands)

Connective Tissue  4 subcategories  Fibrous  Cartilagenous  Osseous  Hematopoietic  Extracellular matrix  Proteins secreted by connective tissue cells  Fluid

Connective Tissue Types & Derivation Figure 4.5 Fibrous

Extracellular Matrices  Ground substance – unstructured material between cells  Proteins  proteoglycans – protein core with glycosaminoglycans (GAGs) attached  GAGs – chondroitin sulfate, keratin sulfate, heparin, hyaluronic acid  fibronectin, laminin – attachement network for cells  Fluid  Structural protein fibers – collagen, elastin

Connective Tissue: Loose Figure 4.8b

Connective Tissue: Loose Figure 4.8c

Connective Tissue: Loose Figure 4.8d

Connective Tissue: Dense Regular Figure 4.8e

Connective Tissue: Dense Irregular Figure 4.8f

Connective Tissue: Hyaline Cartilage Figure 4.8g

Connective Tissue: Fibrocartilage Figure 4.8i  Matrix similar to hyaline cartilage but less firm with thick collagen fibers  Provides tensile strength and absorbs compression shock  Found in intervertebral discs, the pubic symphysis, and in discs of the knee joint

Connective Tissue: Elastic Cartilage Figure 4.8h  Similar to hyaline cartilage but with more elastic fibers  Maintains shape and structure while allowing flexibility  Supports external ear (pinna) and the epiglottis

Connective Tissue: Bone (Osseous Tissue) Figure 4.8j

Connective Tissue: Blood Figure 4.8k

Blood Extracellular Matrix Components H2OH2O  Proteins  Serum albumin  Apolipoproteins, HDL, & LDL  Complement proteins  Immunoglobulins (antibodies)  Clotting factors

Neural Tissue  Neurons  Conductive cells  Soma, Axon, Dentrites  Schwann cells  Insulating cells  Glia  Supporting cells

Nervous (Neural) Tissue Figure 4.10 glial cells

Muscle Tissue  Striated (skeletal)  Long, cylindrical, multinucleate cells  Striations due to alignment of contractile proteins  Cardiac  Branching, striated, uninucleate cells that interlock  Smooth  Sheets of spindle-shaped, uninucleate cells without visible striations

Muscle Tissue: Skeletal Figure 4.11a  Long, cylindrical, multinucleate cells with obvious striations  Initiates and controls voluntary movement  Found in skeletal muscles that attach to bones or skin

Muscle Tissue: Cardiac Figure 4.11b  Branching, striated, uninucleate cells interdigitating at intercalated discs  Propels blood into the circulation  Found in the walls of the heart

Muscle Tissue: Smooth Figure 4.11c

Developmental Aspects  Cellular differentiation  Primary germ layers  ectoderm  mesoderm  endoderm  Primary cell types interact - induction  1 st Ectoderm + Endoderm  mesoderm  2 nd Mesoderm + Ectoderm  neural tissue  Subsequent inductions give rise to all other tissue types

Developmental Aspects Figure 4.13 Ectoderm Mesoderm Endoderm & Endothelium