Cell transportation

Fundamental concepts in understanding how substances cross the cell membrane.
Key focus on the structure and function of phospholipids in the membrane.
- Nonpolar nature keeps phospholipids apart at low temperatures, acting as a spacer.
- Unsaturated structures (due to carbon double bonds) contribute to the fluidity of the membrane.

Carbohydrates serve as markers for the immune system to distinguish between self and non-self.
- Important for preventing pathogen recognition and infection.
- Examples include blood types which are defined by specific carbohydrate receptors on red blood cells.

Types of Blood:
- A Type: Has A-type receptors; recognized as self.
- B Type: Has B-type receptors; recognized as self.
- AB Type: Has both A and B receptors; recognized as self.
- O Type: Lacks A and B receptors, hence universal donor (O negative is safest).
Immune System Response:
- If type A blood receives type B, immune system attacks due to non-recognition.
- Autoimmune disorders can occur if the immune system attacks its own body cells.

Rh factor: Refers to the presence of D antigens on blood cells.
- Positive: Presence of D marker; Negative: Absence of D marker.
- Risk during pregnancy: If a Rh-negative mother carries a Rh-positive child, potential immune reaction in subsequent pregnancies.
- Prevention with Rh immunoglobulin shots during pregnancy to minimize risks of hemolytic disease.

Initial immune response to foreign invaders takes time; the body learns to recognize pathogens over time.
Examples of pathogens include viruses like HIV and SARS-CoV-2 (COVID-19).
- HIV infects helper T cells, leading to AIDS; affects overall immune function.
- SARS-CoV-2 primarily affects respiratory systems but may have systemic effects.

Cell membranes are selectively permeable; they allow certain substances to enter while blocking others.
Example: Hormones (like insulin and estrogen) interact differently with cell membranes based on their structure.
- Insulin (protein hormone) does not pass through membranes easily; requires receptors for signaling.
- Estrogen (steroid hormone) can diffuse through membranes due to its lipid-based structure.

Diffusion: Movement of molecules from high concentration to low concentration.
Osmosis: Specialized diffusion referring to water movement through a semipermeable membrane.
- Water moves from areas of low solute concentration to high solute concentration to equalize concentrations.
- Example: Infusing pure water into a patient can be dangerous; causes cells to swell and can lead to catastrophic failures.

Relevance in medical situations:
- Why saltwater fish placed in freshwater face stress; osmosis causes drastic changes in their internal systems.
- Examples of solute concentration dynamics within cellular systems using semi-permeable membranes.