Tissues

Groups of similar cells organized to perform the same function.

Histology

Study of tissues.

Organs

Composed of different tissues to form a unit with specific functions.

Organ Systems

Organs working together for a specific function.

Cells are recognized and bound by

Extracellular Matrix (mostly glycoproteins, secreted by fibroblasts in connective tissue). Carbohydrate Markers on cell membranes.

Desmosomes

Weld cells into a strong sheet, allowing free passage of substances; found in tissues under stress (e.g., heart muscle).

Tight Junctions

Form a barrier to block transport between cells; found in epithelial layers (e.g., intestines).

Gap Junctions

Channels for electrical and ion communication; found in areas requiring rapid communication (e.g., heart).

Epithelial

Covers/lines surfaces.

Connective

Binds tissues (e.g., connects skin layers).

Muscle

Enables movement.

Nervous

Facilitates communication.

Epithelial Tissue Overview

• Definition: Tightly packed cells forming continuous sheets, covering surfaces or lining cavities.
• Polarity: Cells have an apical side (exposed to fluid/air) and a basal side (attached to connective tissue via the basement membrane made of collagen).
• Functions: Protection, secretion, sensation.

Locations of epithelial

1. Epidermis (skin).
2. Digestive tract.
3. Respiratory tract (windpipe, lungs).
4. Kidney tubules.

Types of Epithelial Arrangements:

1. Simple: One cell layer.
2. Stratified: Multiple layers, only the bottom layer attached to the basement membrane.
3. Pseudostratified: Appears layered but isn’t; all cells touch the basement membrane.

Cell Shapes:

1. Squamous: Flat, ideal for diffusion (e.g., alveoli, blood vessels).
2. Columnar: Tall, aids in absorption/secretion (e.g., intestines, with villi/microvilli).
3. Cuboidal: Cube-like, often for secretion (e.g., thyroid, kidney tubules).

Simple Squamous

Single layer, flat, found in diffusion areas.

Stratified Squamous

Multiple layers, flat, for protection (e.g., skin, mouth).

Simple Columnar

Single layer, tall, for absorption/secretion (e.g., intestines).

Simple Cuboidal

Single layer, cube-shaped, common in glands (e.g., thyroid).

Pseudostratified Ciliated Columnar

Appears layered, ciliated, found in respiratory tract, with goblet cells producing mucus to trap debris.

Glandular Epithelium

Specialized for secretion.

Exocrine Glands

Secrete into ducts (e.g., sweat glands).

Endocrine Glands

Ductless, secrete hormones into the bloodstream.

Connective Tissue Overview

• Function: Supports and binds other cells.
• Matrix: Non-living material that can be solid, liquid, or semi-liquid; contains fibers (collagen, elastic, reticular).
• Fiber Types:
• Collagen
• Elastic
• Reticular

Collagen

Strong, not elastic, for support.

Elastic

Stretchy, allows tissues to "snap back."

Reticular

Thin, branched, supports other tissues.

Types of Connective Tissue

1. Loose (Areolar
2. Adipose (Fat):
3. Fibrous/Dense:
4. Cartilage:
5. Bone:

Loose (Areolar):

• Holds organs in place, binds epithelium to underlying tissue.
• Contains all three fiber types.
• Cells: Fibroblasts (produce matrix), macrophages (immune).

1. Adipose (Fat):

• Specialized for lipid storage, insulation, and cushioning.
• Cells: Adipocytes (fat cells).

1. Fibrous/Dense:

• Dense Regular: Parallel collagen fibers, strong (e.g., tendons, ligaments).
• Dense Irregular: Interwoven collagen, in areas with stress from multiple directions (e.g., skin dermis).

1. Cartilage:

• Matrix: Dense with collagen, embedded in chondroitin sulfate.
• Cells: Chondrocytes in lacuna.
• Types:
• Elastic
• Hyaline
• Fibrocartilage

Elastic

High elastin, flexible (e.g., ear).

Hyaline

Rigid support, low elastin (e.g., trachea rings).

Fibrocartilage

Wavy collagen, absorbs shock (e.g., intervertebral discs).

1. Bone:

• Matrix: Rigid, mineralized (hydroxyapatite with calcium, phosphate, and magnesium).

compact bone

• Contains osteons (Haversian canal + lamella rings).

spongy bone

• Lattice-like (trabeculae) with spaces filled with red marrow for blood cell production.

Osteoblasts

Build bone.

Osteoclasts

Break down bone.

Osteocytes

Maintain bone tissue, connected by canaliculi.

Classification of blood

Connective tissue with a liquid extracellular matrix called plasma.

Plasma

Mainly water with dissolved substances (hormones, gases, nutrients, enzymes).

Function of blood

Transports substances and cells throughout the body.

Liquid Component of blood(55%)

Plasma

Cellular Component of blood(45%)

Includes red blood cells, white blood cells, and platelets.

• Erythrocytes (Red Blood Cells):

• Function: Transport oxygen (via hemoglobin) and assist in carbon dioxide transport.
• Structure: Biconcave shape without nuclei/mitochondria (in mammals); lifespan of a few weeks.
• Deficiency Condition : Low RBCs or hemoglobin causes anemia.

• Leukocytes (White Blood Cells):

• Movement: Amoeboid movement to traverse capillary walls.
• Types:
• Granulocytes:
  • Neutrophils
  • Eosinophils
  • Basophils
• Agranulocytes:
• • Monocytes
  • Lymphocytes

Neutrophils

Most common (65-75%), with multi-lobed nuclei; perform phagocytosis.

Eosinophils

Bilobed nuclei, red-staining; combat parasitic infections and respond to allergies.

Basophils

Rarest (<0.5%), with “s”-shaped nucleus and dark granules; release histamine in allergic reactions.

Monocytes

Largest, with crescent-shaped nuclei; transform into macrophages for immune defense.

Lymphocytes

Smallest WBCs, important for immune memory, with a large dark nucleus.

• Platelets (Thrombocytes):

• Description: Not full cells, but fragments.
• Function: Essential for blood clotting to prevent excessive blood loss.

Characteristics of skeletal muscle

(voluntary, attached to bones)

• Appearance: Cylindrical, striated (alternating light and dark bands).
• Structure: Multinucleated (coenocytic) with peripheral nuclei.
• Components: Contains myofibrils composed of actin and myosin proteins.
• Contraction: Fastest type; exercise increases cell size, not number.

Characteristics of cardiac muscle

(involuntary, heart walls)

• Appearance: Cylindrical with faint striations and branching fibers.
• Structure: Single, centrally located nucleus in each cell.
• Unique Feature: Intercalated discs join cells, aiding in rapid transmission of contraction signals.
• Contraction: Moderate speed and rhythmically self-regulated.

Characteristics of smooth muscle

(involuntary, digestive, genital, urinary, veins)

• Appearance: Spindle-shaped (tapered ends) without striations.
• Structure: Single, centrally located elongated nucleus.
• Arrangement: Cells overlap, forming sheets of muscle.
• Contraction: Slowest of the three but able to maintain contraction for extended periods.

Neuron Structure and Components

Soma (Cell Body)

Dendrites

Axon

Soma (Cell Body)

Contains nucleus and most organelles. Serves as the central part of the neuron, supporting cellular processes.

Dendrites

Cytoplasmic extensions from the soma. Conduct impulses into the cell body.

Axon

Long cytoplasmic extension that conducts impulses away from the cell body. Often bundled with dendrites to form nerve fibers.

Nerves

Composed of bundled axons and dendrites outside the central nervous system (CNS), bound by connective tissue.

Function of Nerves

• Transmit sensory information from sense organs to the CNS.
• Relay motor commands from the CNS to muscles, initiating contraction