Human Anatomy and Physiology Histology Human Anatomy and Physiology

What Is a Tissue? Tissue = cells organized into layer or groups Cells separated by nonliving, intercellular materials Solid minerals in bone Liquid plasma in blood

How Are Tissues Maintained? Stem cells = cells that have the ability to divide many times and yield new cells that then specialize Groups of stem cells set aside in tissues to replace worn or damaged parts

4 Major Types of Tissues

Embryonic Germ Layers

General Characteristics of Epithelial Tissue Widespread throughout the body Basement membrane Lacks blood vessels Divides readily Tightly packed Classified according to shape and number of layers Widespread - Covers organs, forms inner lining of body cavities, and lines hollow organs Basement membrane - Always has a free surface exposed to outside of body or an internal open space – basement membrane anchors underside of epithelial tissue to connective tissue No blood vessels – nutrients diffuse to epithelium from underlying connective tissue Divide readily – some epithelial tissues are constantly damaged and replaced (skin, stomach lining) Tightly packed – little intracellular material, many desmosomes, effective barriers Classification – squamous, cuboidal, and columnar; simple and stratified

Simple Squamous Epithelium Single layer of thin, flattened cells that fit tightly together; broad and thin nuclei Damaged easily because of thinness

Simple Squamous continued… Functions: Allows substances to pass easily Forms walls of capillaries Lines air sacs (alveoli) of lungs Lines insides of blood and lymph vessels Covers membranes that line body cavities

Simple Cuboidal Epithelium Single layer of cube-shaped cells; centrally located and spherical nucleus

Simple Cuboidal continued… Functions: Covers the ovaries Lines the kidney tubules Lines ducts of the salivary glands, pancreas, and liver Secretion and absorption In kidneys, functions in secretion and absorption In glands, secretes glandular products

Simple Columnar Epithelium May be ciliated or nonciliated Goblet cells Microvilli Functions: Absorption Movement of substances Secretion Single layer of elongated cells; nuclei usually at same level near basement membrane May be ciliated or nonciliated May have goblet cells between columnar epithelial cells; goblet cells – flask shaped, glandular cells that secrete mucus (protective fluid) If specialized for absorption, may have microvilli on surface to increase surface area; cylinder shaped processes

Nonciliated Simple Columnar Epithelium Lines uterus and parts of the digestive tract (stomach, small intestines, large intestine, galbladder) Elongated cells form thick tissue that provides protection to underlying tissue Secretes digestive fluids and absorbs nutrients from digested foods

Ciliated Simple Columnar Epithelium Cilia used to move substances (egg cells through oviducts) Lines oviducts, small bronchi

Pseudostratified Columnar Epithelium Appear stratified but all cells reach the basement membrane Appear layered because nuclei are at two or more levels Cells often fringed with cilia Goblet cells scattered throughout

Pseudostratified Columnar continued… Functions: Lines the passages of the respiratory system Lines ducts of glands and sperm-carrying ducts In respiratory tract, mucus traps dust and microorganisms that enter with air and cilia move mucus up and out of airways

Stratified Squamous Epithelium Stratified epithelium is named for the shape of the cells on the outermost layers Stratified squamous is made of many layers, so it’s relatively thick Deeper cells tend to be more cuboidal or columnar Stratified layers grow from the basement membrane Keratinized or nonkeratinized – keratinized contains keratin and produces a dry, tough, protective material and outer layer is dead; nonkeratinized stays soft and moist

Stratified Squamous continued… Functions: Keratinized form makes up the epidermis Nonkeratinized lines the oral cavity, throat, vagina, and anal canal

Stratified Cuboidal Epithelium Functions: Lines larger ducts of mammary glands, sweat glands, salivary glands, and pancreas Forms lining of developing ovarian follicles and seminiferous tubules Consists of 2-3 layers of cuboidal cells

Stratified Columnar Epithelium Functions: Lines vas deferens and some parts of the pharynx Protection Secretion Basal cells are usually cuboidal, but superficial cells are columnar Rare in the body

Transitional Epithelium Specialized to change in response to increased tension; appears thinner when stretched Resembles both stratified squamous and stratified cuboidal Basal cells are usually columnar and superficial cells are squamous or dome-shaped depending on the degree of stretch

Transitional Epithelium continued… Functions: Forms the inner lining of the urinary bladder Lines the ureters and part of the urethra Expandable lining Blocks urine from diffusing back into the body

Glandular Epithelium Specialized to produce and secrete substances into ducts or into body fluids Glands classified as endocrine or exocrine Glandular cells usually found within cuboidal or columnar epithelium Gland = one or more glandular cells Exocrine glands can also be classified according to their structure: unicellular, simple, compound Simple gland – unbranched duct Compound gland – branched duct Tubular gland – epithelial-lined tubes Alveolar glands – saclike portions on ends Most exocrine glands are merocrine: cells glands – watery secretion, mucous cells – thicker fluid

Endocrine Glands Pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas Will be discussed in more detail later

Exocrine Glands Goblet cells Intestinal glands, sweat glands, mucous glands in small intestine, sebaceous glands, bulbourethral glands of male, salivary glands

Classification of Connective Tissue

Mesenchyme Embryonic connective tissue that gives rise to all connective tissues Consists of ground substance (gel-like), fibers, and star-shaped mesenchymal cells

General Characteristics of Connective Tissue Most abundant type of tissue by weight Large amounts of matrix between cells Matrix contains fibers and ground substance Vascularity Major cell types: Fibroblast Macrophage Mast Cell Fiber types: Collagenous Elastic Reticular Connective tissue proper and specialized connective tissues Functions: bind structures, provide support and protection, frameworks, fill spaces, store fat, produce blood cells, protext against infections, help repair tissue damage Ground substance consistency varies from fluid to semisolid to solid; ground substance binds, supports, and provides a medium through which substances may be transferred between the blood and tissue cells Generally have good blood supplies Fibroblast – most common kind of fixed cell in connective tissues; large, star-shaped; produce fibers by secreting protein into the matrix of connective tissues Macrophage – usually attached to fibers but may move around; specialized to carry on phagocytosis; role in immunity Mast cells – large and widely distributed; usually located near blood vessels; release heparin (prevents blood clotting) and histamine (promotes reactions associated with inflammation and allergies) Collagenous fibers – thick threads of collagen; grouped in long, parallel bundles; dense and loose connective tissue classified according to amounts of collagenous fibers; sometimes called white fibers Elastic fibers – bundles of microfibrils embedded in elastin (protein); fibers branch and form complex networks; weaker than collagenous fibers but very elastic; common in body parts that stretch; sometimes called yellow fibers Reticular fibers – very thin collagenous fibers; highly branched and form delicate supporting networks

Areolar Connective Tissue Also known as loose connective tissue Mainly fibroblasts Collagenous and elastic fibers

Areolar Connective Tissue continued…

More Areolar Connective Tissue Functions: Binds the skin to underlying organs Fills spaces between muscles Lies beneath most epithelium layers Blood vessels nourish epithelial cells

Adipose Tissue Also known as fat Adipocytes store fat in their cytoplasm Amount in the body reflects diet or endocrine disorder Adipocytes resemble fibroblasts until they accumulate fat and swell; nucleus is pushed to the side Adipose tissue forms when adipocytes crowd out other cells A person is born with a certain number of fat cells Fasting causes adipocytes to lose fat droplets and shrink

Adipose Tissue continued… Functions: Lies beneath skin, in spaces between muscles, around the kidneys, behind the eyeballs, in some abdominal membranes, on the surface of the heart, in breasts, and around some joints Cushions joints and some organs Insulation Stores energy

Reticular Connective Tissue Reticular fibers Numerous fibroblasts and white blood cells

Reticular Tissue continued… Function: Provides supportive framework in walls of certain internal organs, such as the liver, spleen, and lymphatic organs

Regular Dense Connective Tissue Closely packed collagenous fibers, fine network of elastic fibers Few cells, mostly fibroblasts Regular dense connective tissue – very organized fibers

Regular Dense continued… Functions: Attaches muscles to bones or to other muscles Attaches bones to bones Withstands great tensile stress when pulling force is applied in one direction Makes up tendons and most ligaments Poor blood supply, so tissue repair takes longer – sprains take considerable amount of time to heal

Irregular Dense Connective Tissue Thicker, interwoven, and more randomly organized fibers Same fiber types and cell types as regular dense connective tissue

Irregular Dense continued… Functions: Able to withstand tension exerted in many directions Provides structural strength Makes up dermis of skin, submucosa of digestive tract, fibrous capsules

Elastic Connective Tissue Elastic fibers in parallel strands or branching networks Collagenous fibers and fibroblasts between elastic fibers Found in ligamenta flava and within walls of some large arteries, some portions of the heart, and larger airways Ligamenta flava = attachments between vertebrae of the spinal column

Cartilage Rigid connective tissue Functions: Many collagenous fibers Provides support, frameworks, and attachments Protects underlying tissues Forms structural models for developing bones Many collagenous fibers Chondrocytes and lacunae Perichondrium Lacks direct blood supply Types distinguished by types of intercellular material Chondrocytes are cartilage cells that occupy small chambers called lacunae Perichondrium is connective tissue covering that encloses a cartilaginous structure; contains blood vessels Lack of direct blood supply means cartilage heals very slowly and chondrocytes divide infrequently

Hyaline Cartilage Most common type of cartilage Collagenous fibers form imperceptible network Chondroblasts form matrix and mature into chondrocytes

Hyaline Cartilage continued… Functions: Supports and reinforces Has resilient cushioning properties Resists compression stress Found on ends of bones in joints, soft part of nose, trachea, larynx, and costal cartilages of ribs Forms most of embryonic skeleton Important in bone growth and repair of fractures

Elastic Cartilage More flexible than hyaline cartilage Elastic fibers in matrix

Elastic Cartilage continued… Functions: Maintains the shape of a structure while allowing greater flexibility Provides the framework for the external ears and parts of the larynx

Fibrocartilage Very tough cartilage Many large collagenous fibers

Fibrocartilage continued… Functions: Tensile strength Shock absorber Forms intervertebral disks, disks in knee joint, and pubic symphysis

Compact Bone Also called osseous tissue Most rigid connective tissue Mineral salts in matrix Large amounts of collagen Osteocytes Hardness due to mineral salts in matrix – calcium phosphate and calcium carbonate Osteocytes are bone cells; deposit bone matrix in thin layers called lamellae which form rings around capillaries located within central (Haversian) canals Osteocytes located within lacunae Haversian system = osteocytes, lamellae, and central canal Each central canal contains a blood vessel – good blood supply Canaliculi = small tubes in matrix that contain cytoplasmic extensions of bone cells

Bone continued… Functions: Supports and protects by enclosing Provides levers for muscles to act on Stores calcium and other minerals Marrow inside bones is site of hematopoiesis

Blood Blood plasma Red blood cells, white blood cells, and platelets Most blood cells formed in red bone marrow Functions: transport gases, fight infection, clotting Will be discussed in more detail later Blood plasma = fluid matrix of blood tissue

General Characteristics of Muscle Tissues Contractile Elongated cells Three types classified according to striations and nuclei Will be discussed more later

Skeletal Muscle Long and narrow cells Striations Multinucleate cells Striations = alternating light and dark cross-markings on cells

Skeletal Muscle continued… Functions: Voluntary movement Locomotion Manipulation of the environment Facial expression Voluntary control Attached to bones and occasionally skin

Smooth Muscle No striations Spindle-shaped cells Single, centrally located nucleus

Smooth Muscle continued… Functions: Propels substances or objects along internal passageways Involuntary Found mostly in walls of hollow organs

Cardiac Muscle Striated cells joined end to end Cells form complex, branching network Intercalated disks Usually uninucleate Intercalated disks are specialized junctions between cardiac muscle cells

Cardiac Muscle continued… Functions: Involuntary Propels blood into the circulation Found only in the heart

General Characteristics of Nervous Tissue Neurons Neuroglia Will be discussed more later Neurons – nerve cells; highly specialized; sense changes in their surroundings and respond by transmitting nerve impulses to other neurons, muscles, or glands Neuroglia – cells that support and bind the components of nervous tissue, carry on phagocytosis, and help supply nutrients to neurons by connecting them to blood vessels

Nervous Tissue continued… Functions: Transmits electrical signals from sensory receptors and to effectors (muscles and glands) Found in brain, spinal cord, and nerves