Physiology 221: Cell and Blood Properties

Study Notes

Cell Structure and Function

The cell is the basic living unit of the body, with approximately 100 trillion cells in the human body.
Cells are capable of reproducing, and almost all have the ability to perform specific functions.
The cell is surrounded by a plasma membrane, which separates the cell's internal structures from the extracellular environment.

Cell Organisation

A typical cell has two major parts: the nucleus and the cytoplasm.
The nucleus is separated from the cytoplasm by the nuclear membrane.
The cytoplasm is separated from the surrounding fluid by the plasma membrane.

Cell Components

Protoplasm is a collective term for the different substances that make up the cell, including:
- Water
- Ions
- Proteins
- Carbohydrates
- Lipids

Cell Membrane

The cell membrane is a selectively permeable structure that:
- Surrounds the cell and gives it form
- Separates the cell's internal structures from the extracellular environment
- Participates in intercellular communication
The cell membrane is composed primarily of phospholipids and proteins.
Phospholipids are polar (hydrophilic) and nonpolar (hydrophobic).
The hydrophobic parts of the molecules are packed in the center of the membrane, leaving the polar parts exposed to water on both surfaces, resulting in the formation of a double layer of phospholipids.

Cytoplasm and Organelles

The cytoplasm is the aqueous content of a cell.
Organelles are subcellular structures within the cytoplasm that perform specific functions.
The cytosol is the fluid portion of the cytoplasm.
The cytosol is a highly organized structure in which protein fibers are arranged in a complex latticework surrounding the membrane-bound organelles.

Organelles

Endoplasmic Reticulum (ER):
- A system of membranes that performs specific functions
- Two types: granular (rough) and agranular (smooth)
- Granular ER bears ribosomes on its surface and is involved in protein synthesis and secretion
- Agranular ER is involved in lipid synthesis, Ca2+ regulation, and detoxification
Golgi Complex:
- A stack of flattened sacs with cavities called cisternae
- One side of the stack faces the ER, and the other side faces the plasma membrane
- Involved in the modification and packaging of cellular products
Lysosomes:
- Membrane-bound organelles that contain digestive enzymes
- Primary lysosomes contain only digestive enzymes
- Secondary lysosomes contain partially digested remnants of other organelles and ingested organic material
- Residual bodies contain undigested wastes
Peroxisomes:
- Membrane-enclosed organelles that contain specific enzymes that promote oxidative reactions
- Involved in lipid metabolism, chemical detoxification, and the breakdown of toxic molecules
Mitochondria:
- Organelles that serve as sites for energy production
- Vary in size and shape, but have the same basic structure
- Contain their own DNA and are able to reproduce themselves
- Have a double membrane with the inner membrane folded into cristae
Ribosomes:
- The site of protein synthesis
- Consist of two subunits that are designated 30S and 50S
- Contain ribosomal RNA and proteins
Nucleus:
- The largest organelle in the cell
- Contains the DNA that directs the cell's activities
- Has one or more nucleoli that are centers for the production of ribosomes
Chromatin:
- The DNA within the cell nucleus is combined with protein to form chromatin
- The threadlike material that makes up the chromosomes
- Histone proteins are positively charged and organized to form spools, about which the negatively charged strands of DNA are wound
Cytoskeleton:
- A group of fibrous proteins that provide structural support for cells
- Consists of microfilaments, intermediate filaments, and microtubules
- Important for cell motility, cell reproduction, and transportation of substances within the cell