Anatomy & Physiology

1. Anatomy & Physiology Lesson 4

2. HISTOLOGY • Histology is the study of the structure of tissues. • A tissue is a group of similar cells and their intercellular substance, function together to perform a specialized activity. • Tissues in the body can be classified into four principle types, according to their structure and function.

3. TYPES OF TISSUES • Epithelial tissue—covers body surfaces, lines hollow organs, body cavities, and ducts, and forms glands. • Connective tissue—protects and supports the body and its organs, binds organs together, stores energy reserves as fat, and provides immunity. • Muscle tissue—responsible for movement and generation of force. • Nervous tissue—initiates and transmits action potentials (nerve impulses) that help coordinate body activities.

4. EPITHELIAL TISSUE • Epithelial tissue (or epithelium) can be divided into two types: • Covering and lining epithelium—forms skin, outer covering of some organs, lines body cavities and the inside of the respiratory and digestive tracts, blood vessels, and ducts. • Glandular epithelium—forms the secreting portion of glands.

5. GENERAL FEATURES OF EPITHELIAL TISSUES • Consist of mostly or entirely tightly packed cells with little or no extracellular material between cells. • Cells are arranged in continuous sheets, in either single or multiple layers. • Cell layers have an apical (free) surface, which is exposed to a body cavity, lining of an internal organ, or the exterior of the body, and a basal surface, which is attaced to the basement membrane. • Cells have many junctions, providing secure attachments between cells. • Tissues are avascular—blood vessels that supply nutrients and remove wastes are located in the adjacent connective tissue. Materials move between epithelium and connective tissue by diffusion. • Have a nerve supply. • Diverse in origin—are derived from all three primary germ layers.

6. GENERAL FEATURES OF EPITHELIAL TISSUES • Adhere firmly to adjacent connective tissue, which holds the epithelium in place and prevents it from tearing. Connection between the epithelium and the connective tissue is via a thin basement membrane, which is composed of the basal lamina (collagen, laminin, and proteoglycans) and the reticular lamina (reticular fibers, fibroconectin, and glycoproteins). The basement membrane provides cell attachment and physical support for the epithelium, acts a filter in the kidneys, and guides cell migration during development and tissue repair. • Have a high capacity for renewal (high mitotic rate) because they are subject to wear and tear and injury. • Functions include: protection, filtration, lubrication, secretion, digestion, absorption, transportation, excretion, sensory reception, and reproduction.

7. EPITHELIAL TISSUE

8. TYPES OF EPITHELIAL TISSUE • Simple squamous epithelium • Description: Single layer of flat cells. • Location: Lines heart, blood vessels, lymphatic vessels, air sacs of lungs, glomerular capsule of kidneys, and inner surface of the eardrum. Forms epithelial layer of serous membranes. • Function: Filtration, diffusion, osmosis, and secretion in serous membranes.

9. TYPES OF EPITHELIAL TISSUE • Simple cuboidal epithelium: • Description: Single layer of cube-shaped cells. • Location: Covers surface of ovary, lines anterior surface of eye lens capsule, forms pigmented epithelium at back of eye, lines kidney tubules and smaller ducts of many glands. • Function: Secretion and absorption.

10. TYPES OF EPITHELIAL TISSUE • Nonciliated simple columnar epithelium: • Description: Single layer of nonciliated rectangular cells. Contains goblet cells (secrete mucus) and microvilli (fingerlike projections that increase the plasma membrane surface area) in some locations. • Location: Lines GI tract from the stomach to the anus, ducts of many glands, and gallbladder. • Function: Secretion and absorption.

11. TYPES OF EPITHELIAL TISSUE • Ciliated simple columnar epithelium: • Description: Single layer of ciliated rectangular cells. Contains goblet cells in some locations. • Location: Lines a few portions of upper respiratory tract, Fallopian tubes, uterus, some paranasal sinuses, and central canal of spinal cord. • Function: Moves fluids or particles along a passageway by ciliary action.

12. TYPES OF EPITHELIAL TISSUE • Stratified squamous epithelium: • Description: Multiple cell layers. Deep layers are cuboidal to columnar in shape. Superficial layers consist of squamous cells. As surface cells are lost, they are replaced by basal cells. • Location: Keratinizing variety forms superficial layer of skin. Nonkeratinizing variety lines wet surfaces, such as lining of the mouth, esophagus, part of epiglottis, vagina, and covers tongue. • Function: Protection.

13. TYPES OF EPITHELIAL TISSUE • Stratified cuboidal epithelium: • Description: Two or more layers of cells in which the superficial cells are cube-shaped. • Location: Ducts of adult sweat glands and part of male urethra. • Function: Protection.

14. TYPES OF EPITHELIAL TISSUE • Stratified columnar epithelium: • Description: Several layers of polyhedral cells. Columnar cells are only in the superficial layer. • Location: Lines part of urethra, large excretory ducts of some glands, small areas in anal mucus membrane, and part of the conjuctiva of the eye. • Function: Protection and secretion.

15. TYPES OF EPITHELIAL TISSUE • Transitional epithelium • Description: Appearance is variable. Shape of superficial cells ranges from squamous to cuboidal, depending on the degree of distention (stretching). • Location: Lines urinary bladder and portions of ureters and urethra. • Function: Permits distention.

16. TYPES OF EPITHELIAL TISSUE • Pseudostratified columnar epithelium: • Description: Not a true stratified tissue. Nuclei of cells are at different levels. All cells are attached to the basement membrane, but not all reach the free surface. • Location: Ciliated lines most of upper respiratory tract. Nonciliated lines larger ducts of many glands, epididymis, and part of male urethra. • Funtion: Secretion and movement of mucus by ciliary action.

17. TYPES OF EPITHELIAL TISSUE (GLANDULAR) • Exocrine glands: • Description: Secretory products released into ducts. • Location: Sweat, oil, ear wax, and mammary glands of the skin, digestive glands (like salivary glands and pancreas). • Function: Produce mucus, perspiration, oil, ear wax, milk, or digestive enzymes. • Endocrine glands: • Description: Secretory products (hormones) diffuse into blood after passing through extracellular fluid. • Location: Pituitary gland, pineal gland, thyroid and parathyroid glands, adrenal glands, pancreas, ovaries, testes, thymus gland, etc. • Function: Produce hormones that regulate various body activities.

18. CONNECTIVE TISSUE • Connective tissue is the most abundant, widely distributed (and diverse) tissue in the body. It can be divided into two classifications, with several subclasses: • Embryonic connective tissue • Mesenchyme • Mucous connective tissue • Mature connective tissue • Loose connective tissue • Areolar connective tissue • Adipose connective tissue • Reticular connective tissue • Dense connective tissue • Dense regular connective tissue • Dense irregular connective tissue • Elastic connective tissue • Cartilage • Hyaline cartilage • Fibrocartilage • Elastic cartilage • Bone (osseous) tissue • Blood (vascular tissue)

19. GENERAL FEATURES OF CONNECTIVE TISSUE • Consists of three basic elements: Cells, ground substance, and fibers. Together, the ground substance and fibers form the extracellular matrix. Connective tissue cells are surrounded by large amounts of matrix, so they seldom touch eachother. • Connective tissues usually do not occur on free surfaces. However, joint cavities are lined by areolar connective tissue. • Except for cartilage, connective tissue has a nerve supply. • Usually is highly vascular (has a rich blood supply). Exceptions are cartilage (no blood supply) and tendons (scant blood supply). • The matrix, which may be fluid, semifluid, gelatinous, fibrous, or calcified, is usually secreted by the connective tissue cells and adjacent cells and determines the tissue’s physical qualities.

20. CONNECTIVE TISSUE CELLS • Derived from embryonic mesodermal cells (mesenchymal cells). • The immature cells have names that end in –blast (fibroblasts, chondroblasts, osteoblasts). These cells retain the ability to undergo mitosis and produce matrix. • The mature cells have names that end in –cyte (chondrocyte, osteocyte). Mature cells have decreased capacity for cell division and matrix formation. They are mostly responsible for maintaining the matrix.

21. CONNECTIVE TISSUE CELLS • Some connective tissue cells include: • Fibroblasts—Large, flat, spindle-shaped cells with branching processes. Secrete the molecules that form the matrix. • Macrophages (histiocytes)—Develop from monocytes (a type of white blood cell). Irregular shape with short, branching projections that engulf bacteria and cellular debris by phagocytosis, providing defense for the body. Wandering macrophages leave the blood and travel to infected tissues while fixed macrophages remain in certain tissues and organs. • Plasma cells—Small and either round or irregularly shaped. Develop from B lymphocytes (a type of white blood cell). Secrete antibodies and provide immunity. Found throughout the body, but mostly in connective tissues—especially in the GI tract and mammary glands. • Mast cells—Abundant alongside blood vessels. Produce histamine, which dilates small blood vessels during inflammation.

22. CONNECTIVE TISSUE MATRIX • Ground Substance: • Supports cells, binds them together, provides a medium for transport of substances between blood and cells, influences tissue development, migration, proliferation, shape, and metabolic functions of tissues. • Contains a variety of large, complex molecules, including: • Hyaluronic acid—viscous, slippery substance that binds cells together, lubricates joints, and help maintain shape of eyeball. • Chondroitin sulfate—jellylike substance that provides support and adhesiveness in cartilage, bone, skin, and blood vessels. • Dermatan sulfate—exists in skin, tendons, blood vessels, and heart valves. • Keratan sulfate—exists in bone, cartilage, and the cornea of the eye. • Adhesion proteins—(fibronectin, laminin, collagen, fibrinogen) interact with receptors on plasma membranes to anchor cells in position and provide traction for cell movement.

23. CONNECTIVE TISSUE MATRIX • Fibers • Synthesized by fibroblasts. Provide strength and support for tissues. • Collagen fibers—at least five different types. Very tough and resistant to pulling forces, yet allow some flexibility in the tissue. Often occur in bundles composed of many tiny fibrils lying parallel to each other. Bundle arrangement provides great strength. Composed of the protein collagen (most abundant protein in the body). Found in most CT types—especially bone, cartilage, tendons, and ligaments. • Elastic fibers—smaller diameter than collagen fibers. Branch and join together to form a network within a tissue. Composed of the protein elastin and the large glycoproteins (especially fibrillin). Provide strength. Can be stretched up to 150% of their relaxed length without breaking. Plentiful in skin, blood vessel walls, and lung tissue. • Reticular fibers—consist of collagen and a glycoprotein coating. Much thinner that collagen fibers and form a branching network. Provide support in blood vessel walls. Form a network around fat cells, nerve fibers, and skeletal and smooth muscle cells. Provide support and strength and form the stroma (supporting framework) of many soft organs (spleen, lymph nodes). Help form basement membrane.

24. TYPES OF CONNECTIVE TISSUE (EMBRYONIC) • Mesenchyme • Description: Irregularly shaped mesenchymal cells embedded in a semifluid ground substance that contain delicate reticular fibers. • Location: Deep to skin, along developing embryonic bones. Some mesenchymal cells found in adult CT—especially along blood vessels. • Function: Forms all other kinds of CT. • Mucous connective tissue • Description: Star-shaped cells embedded in a viscous, jellylike ground substance that contain fine collagen fibers. • Location: Umbilical cord. • Function: Support.

25. TYPES OF CONNECTIVE TISSUE • Areolar connective tissue • Description: Fibers (collagen, elastic, and reticular) and several kinds of cells (fibroblasts, macrophages, plasma cells, adipocytes, and mast cells) embedded in a semifluid ground substance. • Location: Subcutaneous layer of skin, papillary (superficial) region of dermis of skin, mucous membranes, blood vessels, nerves, and around body organs. • Function: Strength, elasticity, support.

26. TYPES OF CONNECTIVE TISSUE • Adipose tissue • Description: Consists of adipocytes, specialized cells that store triglycerides (fats and oils) in a large central area. Nuclei are peripherally located. • Location: Subcutaneous skin layer, around heart and kidneys, yellow bone marrow of long bones, padding around joints, and behind eyeball in eye socket. • Function: Heat regulation, energy reserve, support and protection. In newborns, brown fat generates heat to help maintain body temperature.

27. TYPES OF CONNECTIVE TISSUE • Reticular connective tissue • Description: Network of interlacing reticular fibers and reticular cells. • Location: Stroma (framework) of liver, spleen, lymph nodes. Red bone marrow that gives rise to blood cells. Reticular lamina of basement membrane. • Function: Forms stroma of organs. Binds smooth muscle tissue cells together.

28. TYPES OF CONNECTIVE TISSUE • Dense regular connective tissue: • Description: Matrix has shiny white appearance. Mostly composed of collagen fibers arranged in parallel bundles. Fibroblasts present in rows between bundles. • Location: Tendons, most ligaments, and aponeuroses (sheetlike tendons that attach muscle to other muscle or bones). • Function: Provides strong attachment between various structures.

29. TYPES OF CONNECTIVE TISSUE • Dense irregular connective tissue • Description: Predominantly collagen fibers, randomly arranged, and a few fibroblasts. Usually forms a sheet. • Location: Fascia, reticular (deeper) region of dermis of skin, perichondrium (membrane around cartilage), periosteum (membrane around bone), joint capsules, dura mater (outer membrane around brain and spinal cord), membrane capsules around various organs, heart valves. • Function: Provides strength. • Elastic connective tissue • Description: Predominantly freely branching elastic fibers. Fibroblasts present in spaces between fibers. • Location: Lung tissue, walls of elastic arteries, trachea, bronchial tubes, true vocal cords, suspensory ligament of penis, and ligamenta flava of vertebrae (ligaments between vertebrae). • Function: Allows stretching of various organs.

30. TYPES OF CONNECTIVE TISSUE • Hyaline cartilage • Description: Bluish-white, shiny ground substance with fine collagen fibers. Contains numerous chondrocytes. Most abundant type of cartilage. • Location: Ends of long bones, anterior ends of ribs, nose, parts of larynx, trachea, bronchi, bronchial tubes, embryonic skeleton. • Function: Provides smooth surfaces for movement at joints, flexibility, and support.

31. TYPES OF CONNECTIVE TISSUE • Fibrocartilage • Description: Chondrocytes scattered among bundles of collagen fibers within the matrix. • Location: Pubic symphysis, intervertebral discs, menisci (cartilage pads) of knees. • Function: Support and fusion. • Elastic cartilage • Description: Chondrocytes located in a threadlike network of elastic fibers within the matrix. • Location: Epiglottis of larynx, external ear, auditory (Eustacian) tubes. • Function: Support and shape maintenance.

32. TYPES OF CONNECTIVE TISSUE • Bone (osseous) tissue • Description: Compact bone consists of osteons (Haversian systems) that contain lamellae, lacunae, osteocytes, canaliculi, and central (Haversian) canals. Spongy bone consists of thin plates called trabeculae with red bone marrow between the trabeculae. • Location: Both compact and spongy bone form the various parts of the body’s bones. • Function: Support, protection, storage, houses blood-forming tissue, serves as levers that act with muscles to provide body movement.

33. TYPES OF CONNECTIVE TISSUE • Bone (osseous) tissue

34. TYPES OF CONNECTIVE TISSUE • Blood (vascular tissue) • Description: Plasma and formed elements. Formed elements are erythrocytes (red blood cells), leukocytes (white blood cells), and platelets. • Location: Within blood vessels (arteries, arterioles, capillaries, venules, and veins). • Function: Erythrocytes transport oxygen and carbon dioxide. Leukocytes are involved in phagocytosis, allergic reactions, and immunity. Platelets are essential for blood clotting.

35. TYPES OF CONNECTIVE TISSUE • Blood (vascular tissue)

36. MEMBRANES • Epithelial membrane—The combination of an epithelial layer and the underlying connective tissue layer. Principal epithelial membranes are: • Mucous membrane • Serous membrane • Cutaneous membrane—Skin. An organ of the integumentary system. Will be discussed later. • Synovial membrane—Contains connective tissue only—no epithelium.

37. MUCOUS MEMBRANES • Line body cavities that open directly to the exterior (entire digestive, respiratory, and reproductive systems, and much of the urinary system). • Consist of a lining layer of epithelium and an underlying layer of connective tissue • Epithelial layer provides barrier against microbes and other pathogens, secretes mucus (moisturizes body cavities, traps particles in the respiratory tract, and lubricates food), secretes enzymes digestive enzymes, and is the site for food and fluid absorption in the GI tract. • Connective tissue layer is called the lamina propria. It binds the epithelium to underlying structures while allowing some flexibility, holds blood vessels in place, and protects underlying muscles from abrasion or puncture. Oxygen and nutrients diffuse from the lamina propria to the epithelial layer while carbon dioxide and wastes diffuse in the opposite direction.

38. SEROUS MEMBRANES • Line body cavities that do not open to the exterior and cover the organs lying within those cavities. • Composed of two layers: • Parietal layer—attached to the cavity wall. • Visceral layer—attached to and covering the organs within the cavity. • Epithelial layer secretes a watery fluid called serous fluid, which allows organs to glide freely against each other and against the cavity wall. • Epithelial layer is composed of mesothelium (simple squamous epithelium). • Connective tissue layer is composed of a thin layer of areolar CT. • Serous membrane of the thoracic cavity is called the pleura, of the pericardial cavity is the pericardium, and of the abdominal cavity is the peritoneum.

39. SYNOVIAL MEMBRANES • Do not contain epithelium. • Line cavities that do not open to the exterior. • Line the cavities of freely movable joints, bursae (cushioning sacs), and tendon sheaths in our hands and feet. • Composed of areolar CT, with elastic fibers and varying amounts of fat. • Secrete synovial fluid, which lubricates the cartilage at the end of bones during movement and nourishes the cartilage at joints.

40. MUSCLE TISSUE • Muscle tissue consists of fibers (cells) that are designed to generate force for contraction. It provides motion, maintains posture, and generates heat. Muscle tissue is classified into three types, based on location, structure, and function: • Skeletal muscle tissue • Cardiac muscle tissue • Smooth muscle tissue

41. TYPES OF MUSCLE TISSUE • Skeletal muscle tissue • Description: Long, cylindrical, striated (having alternating light and dark bands) fibers with many peripherally located nuclei. Voluntary control (can be made to contract or relax by conscious control). • Location: Usually attached to bones by tendons. • Function: Motion, posture, heat production (thermogenesis).

42. TYPES OF MUSCLE TISSUE • Cardiac muscle tissue • Description: Branched, striated fibers with one or two centrally located nuclei. Contains intercalated discs (unique end-to-end attachments between muscle fibers). Involuntary control (contractions are usually not under conscious control). • Location: Heart wall. • Function: Pumps blood to all parts of the body.

43. TYPES OF MUSCLE TISSUE • Smooth muscle tissue • Description: Spindle-shaped, nonstriated (smooth) fibers with one centrally located nucleus. Usually involuntary control. • Location: Walls of hollow internal structures such as blood vessels, airways to the lungs, stomach, intestines, gallbladder, urinary bladder, and ureters. • Function: Motion (constriction of blood vessels/airways, propulsion of food through GI tract, contraction of urinary bladder/gallbladder).

44. NERVOUS TISSUE • Composed of only two principal cell types: • Neurons—Nerve cells. Convert stimuli into nerve impulses, which they conduct to other neurons, muscle tissue, or glands. Most neurons consist of: • Cell body—contains the nucleus and other typical organelles. • Dendrites—tapering, highly branched, usually short extensions that are the major input receiving portions of neurons. • Axon—single, thin, cylindrical process that may be very long. Output portion of a neuron—conducts nerve impulses toward another neuron or other tissue. • Neuroglia—Do not generate or conduct nerve impulses but do perform many important support functions in nervous tissue.

45. NERVOUS TISSUE • Description: Consists of neurons and neuroglia. • Location: Nervous system. • Function: Exhibits sensitivity to various stimuli, converts stimuli into nerve impulses, and conducts nerve impulses to other neurons, muscle fibers, or glands.