Membranes, Other Tissues and Tissue Homeostatis

Membranes are sheets of viable tissues that cover or line a part of the body.
Two main types of membranes:
- Epithelial membranes: mucous, serous, cutaneous.
- Synovial membranes.
Membranes cover organ systems and aid in their functionality, protection, isolation, and sliding against each other.

Composed of squamous epithelial cells.
Release a serous fluid (water-based with some protein).
Line cavities that do not open directly to the outside, such as the pleurae (covering the lungs).
The serous fluid helps the lungs remain expanded for oxygen absorption.

Line joints like those in the elbow or knee.
Produce a watery-based synovial fluid.
Synovial fluid acts as a hydraulic cushion, preventing bones from directly touching and causing damage during articulation.
Cartilage and synovial fluid work together to allow smooth joint movement.

Three types: skeletal, cardiac, and smooth.
- Skeletal: involved in body movement.
- Cardiac: found in the heart.
- Smooth: mediates involuntary contractions in organs (e.g., peristalsis in the intestine, blood pressure constriction).

Composed of two main cell types: neurons and neuroglia.
Neurons:
- Considered the primary functional cells.
- Composed of a big cell body.
- Transmit signals via axons.
- Carry sensory information (from senses) or motor information (for movement).
- Central nervous system neurons integrate and elaborate data.
- Neurons are excitable cells that generate and transmit electric signals called action potentials.
Neuroglia:
- Support neuron function.
- Play a key role in modulating neuron growth and interconnections.

Tissue damage disrupts homeostasis, necessitating tissue repair to restore balance.
Epithelial tissue cells:
- Have a high capacity for repair due to frequent mitosis and stem cells.
- Repair may result in fibrous tissues and scar formation.
Connective tissues:
- Vary in their ability to repair.
- Bones and blood can repair.
- Tendons have limited repair capabilities.
Muscle cells:
- Exhibit limited repair; tears can be repaired to some extent but may result in scar tissue.
Nervous tissue:
- Has very limited repair capabilities.
- Damaged axons in the peripheral nervous system may undergo some repair.
- Lost neurons cannot be replaced, as they do not duplicate.
- The number of neurons decreases with age after around 18 years old.
- Brain functionality can be maintained by training and increasing interconnections between remaining neurons.

The body's skeletal muscular system is at its peak around 18-20 years old, then declines.
Training helps slow the rate of decline, allowing for continued performance even in older age.
Younger bodies generally experience better nutrition, blood supply, metabolic rate, and tissue repair.
Young skin can often repair without scars due to specialized connective tissue.
Aging slows the tissue repair process.
Loss of water, elasticity, and key proteins in connective tissues impairs function and protection.
This makes maintaining homeostasis more challenging.

Epithelial tissues:
- Damage can lead to organ-specific issues.
- Example: damage to stomach lining can allow hydrochloric acid to contact and digest cells, leading to ulcers.
Connective tissues:
- Disorders can trigger inflammatory processes due to the presence of immune system cells.
- Autoimmune diseases such as lupus, gout, and arthritis may result.
Muscular/Nervous System: Imbalances will be discussed in detail in later lectures.