Introduction to Tissues, Organ Systems, and Homeostasis Chapter 4

Homeostasis Stable operating conditions in the internal environment Brought about by coordinated activities of cells, tissues, organs, and organ systems

Tissue A group of cells and intercellular substances that interact in one or more tasks Four types Epithelial tissue Muscle tissue Connective tissue Nervous tissue

Organs Group of tissues organized to perform a task or tasks Heart is an organ that pumps blood through body Heart consists of muscle tissue, nervous tissue, connective tissue, and epithelial tissue

Organ Systems Organs interact physically, chemically, or both to perform a common task Circulatory system includes the heart, the arteries, and other vessels that transport blood through the body

Epithelial Tissue Lines the body’s surface, cavities, ducts, and tubes One free surface faces a body fluid or the environment simple squamous epithelium basement membrane connective tissue

Simple Epithelium Consists of a single layer of cells Lines body ducts, cavities, and tubes Cell shapes: Squamous Cuboidal Columnar

Stratified Epithelium Two or more layers thick Functions in protection, as in skin Cells in the layers may be squamous, columnar, or cuboidal

Glands Secretory organs derived from epithelium Exocrine glands have ducts or tubes Endocrine glands are ductless

Cell Junctions Tight junctions prevent leaks Gap junctions connect abutting cytoplasms Adhering junctions cement cells together

Connective Tissue Most abundant tissue in the body Cells are scattered in an extracellular matrix Matrix is collagen and/or elastin fibers in a polysaccharide ground substance

Soft Connective Tissues Loose connective tissue Dense, irregular connective tissue Dense, regular connective tissue

Specialized Connective Tissues Cartilage Bone Adipose tissue

Blood Classified as a connective tissue because blood cells arise in bone Serves as the body’s transport medium Red cells, white cells, and platelets are dispersed in a fluid medium called plasma

Muscle Tissue Composed of cells that contract when stimulated Helps move the body and specific body parts

Three Types of Muscle Skeletal muscle Smooth muscle Cardiac muscle

Skeletal Muscle Located in muscles that attach to bones Long, cylindrical cells are striated Cells are bundled closely together in parallel arrays

Smooth Muscle In walls of many internal organs and some blood vessels Cells are not striped and taper at the ends

Cardiac Muscle Present only in the heart Cells are striated and branching Ends of cells are joined by communication junctions

Nervous Tissue Detects stimuli, integrates information, and relays commands for response Consists of excitable neurons and supporting neuroglial cells

Neurons Excitable cells When stimulated, an electrical impulse travels along the plasma membrane Arrival of the impulse at the neuron endings triggers events that stimulate or inhibit adjacent neurons or other cells

Neuroglia Constitute more than half of the nervous tissue Protect and support the neurons, both structurally and metabolically

Replacement Tissues Artificial skin Bioengineered cartilage and bone Organoapatites and coral to repair bone

Stem Cells Have the potential to develop into different kinds of mature cells Embryonic cells most useful but use of embryos as source is controversial Some adult tissues also may provide stem cells

Membranes Epithelial tissue membranes Connective tissue membranes Mucous membranes Serous membranes Cutaneous membrane Connective tissue membranes Synovial membranes

Major Organ Systems Integumentary Muscular Skeletal Nervous Endocrine Lymphatic Respiratory Urinary Circulatory Reproductive

Major Body Cavities Cranial cavity Spinal cavity Thoracic cavity Abdominal cavity Pelvic cavity

Planes of Symmetry Frontal plane (aqua) Transverse plane (yellow) Midsagittal plane (green)

Primary Tissues In vertebrate embryos, cells become arranged to form three primary tissues Ectoderm Mesoderm Endoderm These give rise to all adult tissues

Functions of Human Skin Protects the body from injury, dehydration, UV radiation, and some pathogens Helps control temperature Receives some external stimuli Produces vitamin D

Structure of Human Skin Part of body’s integument Two layers Outer epidermis Inner dermis Atop a layer of hypodermis

Epidermis Stratified epithelium Grows from bottom upward Most abundant cells are keratin-producing keratinocytes Melanocytes produce the brown pigment melanin

Dermis Dense connective tissue with many elastin and collagen fibers Includes blood vessels, lymph vessels, and receptor endings of sensory nerves

Sweat Glands Arise from epidermal cells Composition of sweat 99% water, with dissolved salts, trace of ammonia (waste product) Controlled by sympathetic nerves

Oil Glands Also called sebaceous glands Derived from epidermal cells Secretions lubricate and soften hair and skin; also kill many surface bacteria Acne occurs when bacteria infect oil-gland ducts

Hair Root is embedded in skin Cells near the base of root divide, push cells above them upward Hair follicles nourished by the dermis Shaft of dead cells extends above the skin surface

UV Damages Skin UV light stimulates melanin production in skin; produces a tan Tan is the body’s way of protecting itself against UV Prolonged sun exposure causes elastin fibers to clump, skin to age prematurely, increases risk of cancer

Body Fluids The human body contains about 15 liters of fluid Fluid outside of cells is extracellular fluid Interstitial fluid lies between cells Plasma is the fluid portion of the blood

Fluid Balance Changes in extracellular fluid cause changes in cells The component parts of every animal work to maintain a stable fluid environment for living cells

Homeostasis Stable operating conditions in the internal environment STIMULUS (input into the system) RECEPTOR (e.g., free nerve ending in the skin) INTEGRATOR (such as the brain) EFFECTOR (a muscle or a gland) RESPONSE (system’s output) Response to the stimulus leads to change. Change is “fed back” to the receptor.

Negative Feedback Some activity alters a condition in the internal environment Alteration triggers a response Response reverses the altered condition

Positive Feedback Some activity alters the internal environment The alteration triggers a response The response intensifies the change in the internal condition