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Animal Tissues Overview

• There are four primary types of animal tissues: epithelial, connective, muscular, and nervous.

Structure and Function

• Anatomy is the study of the form of an organism's structures, focusing on arrangement.
• Physiology is the study of the functions of organisms and their structures.
• A tissue is a group of closely associated, similar cells carrying out specific functions.

Types of Animal Tissues

• Epithelial Tissue
• Connective Tissue
• Muscular Tissue
• Nervous Tissue

Epithelial Tissue

• Forms the covering or lining of free body surfaces both internally and externally.
• The outer layer of the skin is epithelial tissue
• The inner lining of the digestive tract and blood vessels is also epithelial tissue.
• Epithelium gets nourished through diffusion, as it is an avascular tissue.
• Gases and nutrients diffuse across the basement membrane from underlying tissues to reach the epithelium.
• Functions include protection, absorption, excretion, secretion, and lubrication.
• Features include the basement membrane, which separates epithelium from underlying connective tissue
  • It is a non-cellular, polysaccharide-rich membrane.

Epithelial Tissue Types Based on Cell Layers:

• Simple epithelium: single layer
• Stratified epithelium: multi-layered
• Pseudostratified epithelium
• Transitional epithelium

Epithelial Tissue Types Based on Cell Shape:

• Squamous: flat cells
• Cuboidal: cube-shaped cells
• Columnar: column-shaped cells

Simple Squamous Epithelium

• The structure consists of a single layer of thin, flat cells.
• Allows passage of materials via diffusion and filtration in areas where protection is not crucial.
• It secretes lubricating substances in serosae.
• It can be found in kidney tubules, the air sacs of lungs, the lining of the heart, blood/lymphatic vessels, and the lining of the ventral body cavity (serosae).

Simple Cuboidal Epithelium

• Structure includes a single layer of cube-shaped cells.
• Some cells feature microvilli (kidney tubules) or cilia (terminal bronchioles of lungs).
• The cells provide secretion and absorption in kidney tubules.
• It allows movement of mucus-containing particles out of the terminal bronchioles by ciliated cells.
• Location includes kidney tubules, glands and their ducts, choroid plexus of the brain, terminal bronchioles of lungs, and the surface of ovaries and retina.

Simple Columnar Epithelium

• Is made of a single layer of tall, narrow cells.
• Some cells may have microvilli and/or cilia.
• Secretion occurs by cells of the stomach, intestines, and glands.
• Absorption occurs by cells of the intestine.
• Ciliated cells facilitate movement of mucus to clear the lungs
• It also aids movement of the egg through the uterine tubes.
• Found in the stomach, intestines, glands, some ducts, bronchioles of the lungs, auditory tubes, uterus, and uterine tube.

Stratified Squamous Epithelium

• Is made of many layers of cells.
  • The basal layer includes cuboidal cells that become flattened at the free surface.
• Protection against abrasion and infection.
• It is located in the skin, mouth, throat, esophagus, anus, vagina, and cornea.

Stratified Cuboidal Epithelium

• It is made of generally two layers of cubelike cells.
• Functions as protective tissue.
• Location includes the largest ducts of sweat glands, mammary glands, and salivary glands.

Stratified Columnar Epithelium

• Includes a top layer of elongated cells, and lower layers of cubeshaped cells
• Functions for both protection and secretion.

Pseudo Stratified Epithelium

• It is comprised of a single layer of cells
  • Some tall, some thin.
• The nuclei at different levels gives a stratified appearance.
• Allows movement of mucus (or fluid) that contains foreign particles.
• It is located in the nasal cavity, nasal sinuses, auditory tubes, pharynx, larynx, trachea, and bronchi of lungs.

Transitional Epithelium

• Structure: Stratified cells that appear cube-like when the organ or tube is relaxed
  • Appear squamous when the organ or tube is distended by fluid.
• Allows for accommodation by fluid fluctuation in an organ or tube
  • Provides protection against the caustic effects of urine.
• It can be found in the urinary bladder, ureters, and superior urethra.

Connective Tissue

• Fibrous tissue that surrounds cells with large amounts of extracellular material.
• Functions include holding tissues together, providing a supporting framework for the body, and transporting substances (e.g., blood).

Types of Connective Tissue

• Reticular
• Elastic
• Blood
• Loose or areolar
• Dense
• Adipose
• Cartilage
• Bone tissue

Loose (Areolar) Connective Tissue:

• Consists of fibroblast, macrophages, and lymphocytes.
• Contains a fine network of collagen fibers; the cells and fibers are separated by fluid-filled spaces.
• Provides loose packing, support, and nourishment for associated structures.
• Widely distributed throughout the body, serving as the substance on which most epithelial tissue rests.
• It is the packing between glands, muscles, nerves, and attaches the skin (dermis) to underlying tissues.

Dense Connective Tissue

• Matrix is composed entirely of collagen fibers produced by fibroblasts.
• Fibers oriented in the same direction (tendons and ligaments) or in many different directions (dermis and capsules).
• It can withstand great pulling forces in the direction of fiber orientation.
• Location: Tendons (attach muscle to bones), ligaments (attach bone to bones), dermis of skin, and organ capsules.

Adipose Tissue

• Has little extracellular material between adipose cells.
• Cells contain lipids, pushing the cytoplasm to the periphery.
• Functions as energy storage, packing material/provides protection, and a heat insulator.
• Under the skin, around organs such as the heart and kidneys, in the breast, and in bones.
• Also referred to as "fat tissue".

Cartilage

• Characterized by a solid matrix with fibers dispersed throughout the ground substance.
• Chondrocytes are located within lacunae.
• Hyaline cartilage creates a smooth surface on joints, creates a site of bone growth, and forms the embryonic skeleton.
• Fibrocartilage can withstand high pressure
• Elastic cartilage returns to its original shape when bent.
• Location: Hyaline cartilage is found in ribs, the respiratory tract, the end of bones, and the embryonic skeleton.
• Location: Fibrocartilage is found in intervertebral disks, symphysis pubis, and the articular disk of the knees.
• Location: Elastic cartilage is found in the external ear.

Bone Tissue:

• Is made of a hard, mineralized matrix with osteocytes located within lacunae.
• Is surrounded by collagen and calcium.
• Provides great strength, support, and protects internal organs such as the brain.
• Location: Bones

Blood

• Blood cells are within a fluid matrix called plasma.
• Transports oxygen, carbon dioxide, hormones, nutrients, waste products, etc.
• Protects the body from infection and is involved in temperature regulation.
• Located within blood vessels and the heart

Elastic Connective Tissue

• Features branching elastic fibers interspersed with fibroblasts.
• Provides elasticity (allows stretching of the tissue).
• Location: Framework of the liver; lymph nodes; spleen.

Reticular Connective Tissue

• Composed of interlacing reticular fibers.
• Provides support.
• Location: Structures that must expand and return to their original size, such as lung tissue and large arteries.

Muscular Tissue

• Functions to produce force and cause motion, either locomotion or movement within internal organs.
• Composed of contractile proteins.
• Contractile proteins (actin and myosin) are found in cytoplasm of muscle cells.
• Muscle cells are aggregated into bundles and are elongated
• Cells run oriented with their long axes in the same direction.
• Cells’ nuclei are arranged in parallel to the elongation of these cells.
• Muscle tissue has the ability to contract or shorten, making movements possible.

Types of Muscular Tissue

• Cardiac
• Skeletal
• Smooth

Cardiac Muscle

• Structure involves cylindrical shaped, striated cells with a single nucleus.
• The cells are branched and are connected to each other by intercalated disks.
• It is responsible for the pumping of blood.
• Located in Muscle of the heart

Skeletal Muscle

• Cylindrical in shape and striated.
• Contains multiple nuclei.
• Attaches to bone.
• Usually thought of as regular meat comprised of 40% of a person's body weight.
• The skeletal muscle enables body movements (voluntary control).
• Located between skin and bones.

Smooth Muscle

• Also known as "visceral muscle tissue".
• Tapered at each end, not striated, and contains a single nucleus.
• Responsible for movement, as well as involuntary control.
• Responsible for movement of food through the digestive tract.
• Responsible for emptying the the urinary bladder
• It is located in the muscle of the heart, skin, eyes, and G.I. tract.

Nervous Tissue

• Forms the brain, spinal cord, and nerves
• Responsible for coordinating and controlling many of the body's activities.
• Conscious control of skeletal muscles and unconscious regulation of cardiac muscle.
• Includes awareness to external environment, emotions, reasoning skills, and memory.
• Action potential - the communication of nervous tissue to each other by electrical signals.
• Cells that comprise the central nervous system (CNS) and peripheral nervous system (PNS)
• CNS: brain and spinal cord
• PNS: cranial nerves and spinal nerves, inclusive the motor nerves
• Responsible for movement, sensing, and thinking (cells transmit messages between them)

Functions of Nervous Tissue

• Sensory input: nerve cells receive and process information from the external environment.
• Integration: neurons transmit electrical impulses from one site in the body to another and integrate those impulses.
• Homeostasis: body's ability to regulate its inner environment and ensure stability despite changes in the external environment.
• Mental Activity: brain is comprised of nervous tissue.

Nervous Tissue Details

• Contains neurons (nerve cells) responsible for action potential conduction and support cells.
• Has processes that communicate/interact with other nerve cells, or with epithelial and muscle cells.
• Has neuroglia, which support cells of the nervous system.
• It also functions to nourish, protect (surround the axon), and insulate neurons.

Types of Neurons by Function

• Sensory neurons (afferent): detect changes in the environment and transmit information to the brain and spinal cord.
• Motor neurons (efferent): send signals from CNS to muscles and glands (effectors).
  • Organs that carry out responses are called effectors.
• Interneurons lie between sensory and motor pathways in CNS.
  • They process, store, and retrieve information.
  • 90% of our neurons are interneurons.

Parts of Neurons

• Dendrite: nerve cell processes that receive action potential and conduct them toward the cell body.
• Cell body: contains the nucleus and is the site of general cell functions.
• Axon: nerve cell processes that conduct action potentials away from the cell body.
  • Only one axon per neuron is present.