Tissue (nursing lavel answer)
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Tissue - Nursing Level Notes
Definition
A tissue is a group of similar cells that work together to perform a specific function. The study of tissues is called histology. All body tissues arise from three embryonic germ layers: ectoderm, mesoderm, and endoderm.
The human body has four basic tissue types:
| Tissue | Cells | Extracellular Matrix | Main Functions |
|---|---|---|---|
| Epithelial | Closely aggregated polyhedral cells | Small amount | Lining surfaces, glandular secretion |
| Connective | Several fixed and wandering cell types | Abundant | Support and protection of organs |
| Muscle | Elongated contractile cells | Moderate | Body movement, contraction |
| Nervous | Elongated cells with fine processes | Very small | Transmission of nerve impulses |
- Junqueira's Basic Histology, 17e, p. 194
1. Epithelial Tissue
Definition
Epithelium covers body surfaces, lines body cavities, and constitutes glands. All substances entering or leaving an organ must cross this tissue.
Key Features
- Avascular - no blood vessels; receives nutrients by diffusion from underlying connective tissue
- Highly cellular - cells are closely packed with minimal extracellular matrix
- Sits on a basement membrane (basal lamina) that anchors it to underlying connective tissue
- Has three domains: apical (free surface), lateral (cell-to-cell), and basal (anchoring)
Functions
- Covering and protection - e.g., skin (epidermis)
- Absorption - e.g., intestinal lining
- Secretion - e.g., glands
- Filtration - e.g., kidney glomerulus
- Special senses - taste buds, olfactory epithelium
Classification
By number of layers:
| Type | Description | Example |
|---|---|---|
| Simple | One cell layer | Alveoli, kidney tubules |
| Stratified | Multiple layers | Skin, esophagus |
| Pseudostratified | Appears layered but is one layer | Trachea, bronchi |
By cell shape:
| Shape | Appearance | Example |
|---|---|---|
| Squamous | Flat, scale-like | Blood vessels (endothelium) |
| Cuboidal | Cube-shaped, round nucleus | Kidney tubules |
| Columnar | Tall, elongated nucleus | Small intestine |
| Transitional | Changes shape with stretch | Urinary bladder |
Apical Surface Modifications
- Microvilli - finger-like projections; increase absorption surface area (e.g., intestinal brush border)
- Stereocilia - long, non-motile microvilli (e.g., inner ear, epididymis)
- Cilia - motile hair-like projections that move substances along the surface (e.g., respiratory tract)
Nursing Significance
- Damaged epithelium = entry point for infection
- Metaplasia (change in cell type under chronic irritation, e.g., smoking changes respiratory epithelium) can be a precancerous sign
- Wound healing depends on epithelial regeneration
- Histology: A Text and Atlas, p. 318-319; Junqueira's Basic Histology, 17e, p. 194-196
2. Connective Tissue
Definition
Connective tissue supports, binds, and protects all other tissues and organs. It is characterized by its extracellular matrix (ECM), which is more abundant than the cells themselves.
Key Features
- Derived from mesoderm (embryonic mesenchyme)
- Contains cells + fibers + ground substance (the ECM)
- Well vascularized (except cartilage and tendons)
ECM Components
| Component | Function |
|---|---|
| Collagen fibers | Strength and resistance to tension |
| Elastic fibers | Recoil and flexibility (e.g., lungs, blood vessels) |
| Reticular fibers | Fine network supporting soft organs (liver, spleen) |
| Ground substance | Gel-like; facilitates diffusion of nutrients/wastes |
Classification
A. Connective Tissue Proper
| Type | Structure | Location |
|---|---|---|
| Loose (areolar) | Loosely arranged fibers, many cell types | Under skin, around organs |
| Dense regular | Parallel collagen fibers | Tendons, ligaments |
| Dense irregular | Randomly arranged fibers | Dermis, joint capsules |
| Adipose | Fat-storing cells (adipocytes) | Under skin, around kidneys |
| Reticular | Reticular fibers forming networks | Lymph nodes, bone marrow |
B. Specialized Connective Tissue
| Type | Key Feature |
|---|---|
| Bone | Mineralized matrix (hydroxyapatite); rigid support |
| Cartilage | Firm but flexible; avascular |
| Blood | Fluid matrix (plasma); transport |
| Lymph | Fluid; immune surveillance |
Cells of Connective Tissue
- Fibroblasts - synthesize fibers and ground substance; key in wound healing
- Macrophages - phagocytosis; immune defense
- Mast cells - release histamine; allergic/inflammatory responses
- Plasma cells - produce antibodies
- Adipocytes - store energy as fat
Nursing Significance
- Collagen is the most abundant protein in the body; vitamin C is essential for collagen synthesis (deficiency = scurvy)
- Edema occurs in loose connective tissue spaces
- Inflammation is largely a connective tissue response
- Histology: A Text and Atlas, p. 314-315; Junqueira's Basic Histology, 17e, p. 194
3. Muscle Tissue
Definition
Muscle tissue is specialized for contraction. All muscle cells contain the contractile proteins actin and myosin arranged into myofilaments.
Types of Muscle
| Feature | Skeletal | Cardiac | Smooth |
|---|---|---|---|
| Location | Attached to bones | Heart | Walls of hollow organs (GIT, blood vessels, uterus) |
| Shape | Long, cylindrical fibers | Branched, cylindrical | Spindle-shaped |
| Striations | Yes | Yes | No |
| Nuclei | Multiple, peripheral | Single, central | Single, central |
| Control | Voluntary | Involuntary | Involuntary |
| Intercalated discs | No | Yes | No |
| Speed of contraction | Fast | Rhythmic | Slow, sustained |
Nursing Significance
- Skeletal muscle atrophy occurs with immobility - early mobilization is key in nursing care
- Cardiac muscle has intercalated discs that allow coordinated electrical impulses (disruption = arrhythmias)
- Smooth muscle spasm causes conditions like asthma (bronchospasm), hypertension (vascular smooth muscle), and colic
- Histology: A Text and Atlas, p. 314
4. Nervous Tissue
Definition
Nervous tissue receives, transmits, and integrates information from inside and outside the body.
Two Main Cell Types
A. Neurons (nerve cells)
- Highly specialized to transmit electrical impulses
- Parts of a neuron:
- Cell body (soma) - contains nucleus and organelles
- Axon - single, long process; carries impulses AWAY from cell body
- Dendrites - multiple short processes; receive impulses and carry them TOWARD cell body
- Found in the CNS (brain, spinal cord) and PNS (nerves and ganglia)
B. Supporting (Glial) Cells
| Cell | Location | Function |
|---|---|---|
| Neuroglial cells (astrocytes, oligodendrocytes, microglia, ependymal cells) | CNS | Support, protection, myelination |
| Schwann cells | PNS | Form myelin sheath around peripheral nerves |
| Satellite cells | PNS ganglia | Support and protect neuron cell bodies |
Impulse Transmission
- Myelinated fibers - faster conduction (insulation by myelin)
- Unmyelinated fibers - slower conduction
- Synapse - junction between neurons or neuron and effector
Nursing Significance
- Neurons cannot regenerate effectively after injury (CNS) - neurological deficits from strokes may be permanent
- Peripheral nerves have limited regeneration capacity
- Demyelinating diseases (e.g., multiple sclerosis) impair nerve conduction
- Neuromuscular blocking agents and anesthetics act at neuromuscular junctions
- Histology: A Text and Atlas, p. 315
Embryonic Origin of Tissues (Summary)
| Germ Layer | Tissues Derived |
|---|---|
| Ectoderm | Epidermis, nervous system, sense organs, tooth enamel |
| Mesoderm | Connective tissue, muscle, bone, blood, kidneys, gonads |
| Endoderm | GIT epithelium, liver, pancreas, respiratory epithelium, thyroid, thymus |
- Histology: A Text and Atlas, p. 315-316
Quick Memory Aid: "ECM N"
| Letter | Tissue | Key Word |
|---|---|---|
| E | Epithelial | External surface / Lining |
| C | Connective | Connects and supports |
| M | Muscle | Movement |
| N | Nervous | Nerve impulses |
Clinical Nursing Notes - Tissue Integrity
- Pressure injuries (pressure ulcers) progress through tissue layers: skin (epithelial) → subcutaneous (connective) → muscle → bone
- Wound healing involves all four tissue types - epithelium regrows, connective tissue lays collagen (scar), blood vessels regrow, nerves regenerate partially
- Cancer is often classified by tissue of origin: carcinoma (epithelial), sarcoma (connective/muscle), lymphoma (lymphoid connective), glioma (glial/nervous)
- Inflammation primarily involves connective tissue - the classic signs (redness, heat, swelling, pain) reflect vascular and cellular events in connective tissue
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