Introduction to Human Physiology

Homeostasis refers to the ability of an organism to maintain a stable internal environment despite external changes.
- Critical for optimal cell function, as many enzymatic reactions depend on stable conditions.

Optimal temperature range is typically between $36$ to $37.5$ degrees Celsius.
- Deviations from this range impair cellular functions and enzymatic reactions.
- High temperatures can degrade proteins, while low temperatures may also disrupt normal function.

Fluid Levels:
- Concentration of solutes including glucose and ions needs stability (calcium, sodium, potassium).
Blood pH:
- Necessary for biochemical processes, should be maintained within a specific range.

Thick layer of fat to reduce heat loss in cold environments.
Mechanisms for heat production:
- Shivering: Involuntary muscle contractions generating heat from increased metabolism.
- Behavioral Adaptations: Penguins pack together to minimize heat loss.
Remarkable ability to maintain body temperatures even in extreme cold (e.g., $-40$ degrees Celsius).

Anatomy refers to the structure or form of organisms.
Physiology involves the functions of these structures.
Close correlation between structure and function at cellular, tissue, and organ levels.

Cells: Basic unit of life.
Tissues: Groups of similar cells working together.
- Four main types:
  - Epithelial Tissue: Covers surfaces, provides barriers against pathogens, aids in exchange (gas, nutrients).
  - Connective Tissue: Provides support and binds other tissues (e.g., blood, bone, cartilage).
  - Muscle Tissue: Specialized for movement (skeletal, smooth, cardiac).
  - Nervous Tissue: Comprises neurons and glial cells, specialized for signal transmission.
Organs: Structures composed of multiple tissue types working together.
Organ Systems: Groups of organs that perform related functions (e.g., respiratory system, digestive system).

Forms barriers, covers surfaces (both external and internal).
Types based on layers and shapes:
- Simple Epithelia: Single layer (e.g., simple squamous).
- Stratified Epithelia: Multiple layers (e.g., stratified squamous).
- Cuboidal and Columnar Epithelia: Found in glands and airways (e.g., pseudostratified columnar epithelium).
Cilia: Present on epithelial cells in airways, help clear debris through movement of mucus.

Variety of types including:
- Loose Connective Tissue: Contains fibers (collagen, elastin) and fibroblasts, provides support and holds organs in place.
- Dense Connective Tissue: Rich in collagen (e.g., tendons, ligaments).
- Bone and Cartilage: Supportive structures, characterized by rigidity and flexibility, respectively.
- Adipose Tissue: Stores energy, cushioning.
- Blood: Unique connective tissue, comprising red blood cells, white blood cells, and plasma.
Red Blood Cells (RBCs): Carry oxygen via hemoglobin.
White Blood Cells (WBCs): Immune function; different types respond to various infections.
- Neutrophils: Bacterial infections; Lymphocytes: Viral infections; Eosinophils: Parasites.

Three types:
1. Skeletal Muscle: Voluntary, striated, multi-nucleated.
2. Smooth Muscle: Involuntary, non-striated, found in internal organs, helps move substances.
3. Cardiac Muscle: Involuntary, striated, single nucleus, intercalated discs promote synchronized contractions for pumping blood.

Composed of neurons and supporting glial cells:
- Neurons: Generate and transmit action potentials (electrical signals).
- Dendrites: Receive signals.
- Axon: Conducts impulses away from the neuron, releases neurotransmitters at synaptic terminals to communicate with other neurons or target cells.
- Glial Cells: Supportive functions (e.g., oligodendrocytes create myelin sheaths for axons, astrocytes provide nourishment).
Multiple Sclerosis: An autoimmune disorder affecting myelin sheaths, leading to disrupted signal transmission.

Digestive System: Includes mouth, esophagus, stomach, intestines, pancreas, liver.
- Function: Breakdown nutrients and facilitate absorption into the bloodstream.
Circulatory System: Comprises heart and blood vessels.
- Function: Transports nutrients, gases, hormones, and waste products.
Respiratory System: Composed of lungs and airways.
- Function: Facilitates gas exchange (oxygen in, carbon dioxide out).
Renal System: Functions to filter blood, maintain fluid balance, and regulate solute concentrations.
- Kidneys produce urine, crucial in waste elimination and homeostasis.
- Hormonal regulation (e.g., Anti-Diuretic Hormone - ADH) affects water re-absorption.
Endocrine System: Includes glands such as pancreas (insulin production).
- Hormonal balance crucial for glucose metabolism.

Hormones help adjust bodily functions. Examples include Hormones affecting sodium levels and glucose concentration:
- Insulin: Regulates blood sugar by promoting uptake into cells.
- Anti-Diuretic Hormone (ADH): Promotes water reabsorption in kidneys, affecting urine concentration.
- Adrenaline (Epinephrine): Released during stress, increases blood pressure and energy availability.

Animals can be Conformers or Regulators:
- Conformers: Internal conditions change with the environment (e.g., some fish).
- Regulators: Maintain stable internal conditions regardless of external changes (e.g., mammals).

Primarily relies on Negative Feedback loops.
- Example: Thermostat analogy for temperature regulation.
- If temperature rises, cooling system activates; if temperature drops, heating system activates.
Components of negative feedback:
- Sensor: Detects changes, e.g., thermoreceptors.
- Effector: Executes responses, e.g., sweat glands or muscles adjusting body temperature.

Homeostasis is essential for cellular and organismal function.
Involves complex networks integrating various physiological systems to maintain stability in the internal environment.
Next session will cover the remaining details on hormonal interactions and physiological mechanisms involved in homeostasis.