Biology Chapter: Tissue and Germ Layers

Tissue Basics

• Tissue consists of groups of similar cells working together for a common purpose.
• The matrix is the nonliving material found between cells in tissues.

Primary Germ Layers

Ectoderm

• Forms the epidermis (skin) and linings of the mouth, anus, and nostrils.
• Produces sweat, sebaceous glands, hair, and enamel of teeth.
• Develops the nervous system, including the brain and spinal cord.
• Forms sensory parts of the eyes, nose, and ear.

Mesoderm

• Leads to the formation of muscles and skeletal structures (bones and cartilage).
• Develops blood and the epithelial lining of blood vessels.
• Gives rise to dermis of skin and organizational components in excretory and reproductive systems.
• Forms connective tissues.

Endoderm

• Creates the epithelial lining of the digestive and respiratory systems.
• Generates secretory parts of the liver and pancreas, urinary bladder, and epithelial lining of the urethra.
• Contributes to thyroid, parathyroid, and thymus tissues.

Epithelial Tissue

• Covers surfaces, lines cavities, and forms glands in the body.
• Two subdivisions: membranous (covers and lines) and glandular (forms glands).

Functions

• Protection from injury and pathogens.
• Sensory functions, especially in skin and sensory organs.
• Responsible for secretion (e.g., hormones and mucus) and absorption of nutrients.
• Assists in excretion in organs like kidneys.

Characteristics

• Contains limited matrix material; closely packed cells with desmosomes and tight junctions.
• Avascular - relies on diffusion for nourishment.
• Capable of regeneration.

Classification of Epithelial Tissue

By Shape

• Squamous: flat cells, scaly appearance.
• Cuboidal: cube-shaped, more cytoplasm.
• Columnar: taller than wide, cylindrical shape.
• Pseudostratified columnar: single layer of varied heights.

By Layers

• Simple epithelium: one cell layer (e.g., simple squamous, cuboidal, columnar).
• Stratified epithelium: multiple cell layers (e.g., keratinized, nonkeratinized, cuboidal, columnar, transitional).

Glandular Epithelium

• Specializes in secretions.
• Exocrine glands have ducts (e.g., sweat glands), while endocrine glands are ductless (e.g., hormones).

Connective Tissue

• Supports, connects, and protects other tissues.
• Main types include fibrous, bone, cartilage, and blood.

Fibrous Connective Tissue

• Loose connective tissue is widely distributed, consists of collagenous and elastic fibers, and includes various cell types.
• Adipose tissue primarily contains fat cells; functions include protection and energy reserves.
• Dense connective tissue has tightly packed fibers for strength (regular and irregular types).

Bone Tissue

• Highly specialized, consisting of osteocytes in a calcified matrix.
• Functions include support, protection, and mineral storage.
• Structural unit called the osteon contains lacunae, lamellae, and canaliculi.

Cartilage

• Contains chondrocytes, avascular, and heals slowly after injuries.
• Types include hyaline (smooth, translucent), fibrocartilage (durable, shock-absorbing), and elastic (flexible).

Blood

• A liquid tissue comprising plasma (55% of volume) and formed elements (45%).
• Functions include transportation and immune response.

Muscle Tissue

• Types include skeletal (voluntary, striated), smooth (involuntary, non-striated), and cardiac (involuntary, striated).
• Skeletal muscle has multiple nuclei; smooth muscle features single nuclei; cardiac muscle has intercalated discs.

Nervous Tissue

• Composed of neurons for conducting nerve impulses and neuroglia for support.
• Major organs include the brain, spinal cord, and nerves.

Tissue Repair

• Regeneration capabilities differ among tissue types; epithelial and connective tissues regenerate well, while muscle and nervous tissues have limited capacity.

Body Membranes

• Thin layers that cover surfaces and line cavities; include epithelial and connective tissue membranes.

Epithelial Membranes

• Cutaneous membrane: skin, accounts for ~16% body weight.
• Serous membrane: includes parietal and visceral layers for organs.
• Mucous membrane: protects and lines openings to the exterior (e.g., respiratory, digestive tracts).

Connective Tissue Membranes

• Lack epithelial components; include synovial membranes that reduce friction in joints.

Explore the fascinating world of tissues and their functions in this quiz focused on primary germ layers. Learn about ectoderm, mesoderm, and the various structures derived from these layers. Test your knowledge on how cells come together to perform specific functions in the body.