Human Anatomy and Physiology - Human Cells
Cytology: - It is a branch of science concerned with a study of cells.
Cell- is the basic living structural and functional unit of the body.
Cell Theory
1. All living organisms are composed of cell and cell products.
2. Cells are the basic unit of structure & function of all living organisms.
3. All cells come from the division of pre-existing cells.
4. An organism as a whole can be understood through the collective activities & interactions of
its cells.
Four Principal Parts of Cell
1. Plasma (cell) membrane - it is the outer lining, limiting membrane separating the cell internal
parts from extracellular materials & external environment.
2. Cytoplasm - It is the substance that surrounds organelles and is located between the nucleus
and plasma membrane.
3. Organelles - these are permanent structures with characteristic morphology that are highly
specialized in specific cellular activity. (e.g. ribosomes, nuclei, and mitochondria)
4. Inclusions- they are the secretions and storage products of cells. (e.g. glycogen, lipids, and
pigments)
Extracellular materials - are also referred to as the matrix, which are substances external to the
cell surface.
, 1. Plasma Membrane
Plasma membrane is a thin outer membrane, which maintains the integrity of the cell.
It keeps the cell and its contents separate and distinct from the surrounding.
It is double layered (bi-layer) measuring about 4.5 nm and made of phospholipids, cholesterol,
glyco-lipid, & carbohydrate (oligosaccharides).
It is self-sealing. If a needle is injected and pulled out, it automatically seals.
Functions of Plasma Membrane
1. Separate the cytoplasm inside a cell from extracellular fluid.
2. Separate cells from one another.
3. Provide an abundant surface on which chemical reactions can occur.
4. Regulate the passage of materials into and out of cells. It also lets some things in and keeps
others out.
Movement across-cell membrane takes place in two ways (passive and active movements.)
Passive movement uses energy whereas active movement consumes energy in the form of
ATP. (adenosine triphosphate)
Passive movement includes;
a. Simple diffusion - the random movements of molecules from areas of high concentration to
areas of low concentration.
e.g air in alveoli of lungs
b. Facilitated diffusion - larger molecules, which are not soluble in lipid need protein channel to
pass through the plasma membrane. No direct energy needed.
e.g. Amino acid passes through the cell membrane.
c. Osmosis - a special type of diffusion referring to the passage of water through a selectively
permeable membrane from an area of high water concentration to lower water concentration.
d. Filtration - small molecules pass through selectively permeable membranes in response to
force of pressure.
e.g. filtration in the kidney in the process of urine formation.
Active movements across membranes Substances move through a selectively permeable
membrane from areas of low concentration on one side of a membrane to an area of higher
concentration on the other side. This is against the concentration gradient. Therefore, it requires
energy.
a. Active Transport: till equilibrium substances could move by passive movement.
But if equilibrium is reached and still more molecules are needed, they must be pumped
through the membrane against concentration gradient.
Cytology: - It is a branch of science concerned with a study of cells.
Cell- is the basic living structural and functional unit of the body.
Cell Theory
1. All living organisms are composed of cell and cell products.
2. Cells are the basic unit of structure & function of all living organisms.
3. All cells come from the division of pre-existing cells.
4. An organism as a whole can be understood through the collective activities & interactions of
its cells.
Four Principal Parts of Cell
1. Plasma (cell) membrane - it is the outer lining, limiting membrane separating the cell internal
parts from extracellular materials & external environment.
2. Cytoplasm - It is the substance that surrounds organelles and is located between the nucleus
and plasma membrane.
3. Organelles - these are permanent structures with characteristic morphology that are highly
specialized in specific cellular activity. (e.g. ribosomes, nuclei, and mitochondria)
4. Inclusions- they are the secretions and storage products of cells. (e.g. glycogen, lipids, and
pigments)
Extracellular materials - are also referred to as the matrix, which are substances external to the
cell surface.
, 1. Plasma Membrane
Plasma membrane is a thin outer membrane, which maintains the integrity of the cell.
It keeps the cell and its contents separate and distinct from the surrounding.
It is double layered (bi-layer) measuring about 4.5 nm and made of phospholipids, cholesterol,
glyco-lipid, & carbohydrate (oligosaccharides).
It is self-sealing. If a needle is injected and pulled out, it automatically seals.
Functions of Plasma Membrane
1. Separate the cytoplasm inside a cell from extracellular fluid.
2. Separate cells from one another.
3. Provide an abundant surface on which chemical reactions can occur.
4. Regulate the passage of materials into and out of cells. It also lets some things in and keeps
others out.
Movement across-cell membrane takes place in two ways (passive and active movements.)
Passive movement uses energy whereas active movement consumes energy in the form of
ATP. (adenosine triphosphate)
Passive movement includes;
a. Simple diffusion - the random movements of molecules from areas of high concentration to
areas of low concentration.
e.g air in alveoli of lungs
b. Facilitated diffusion - larger molecules, which are not soluble in lipid need protein channel to
pass through the plasma membrane. No direct energy needed.
e.g. Amino acid passes through the cell membrane.
c. Osmosis - a special type of diffusion referring to the passage of water through a selectively
permeable membrane from an area of high water concentration to lower water concentration.
d. Filtration - small molecules pass through selectively permeable membranes in response to
force of pressure.
e.g. filtration in the kidney in the process of urine formation.
Active movements across membranes Substances move through a selectively permeable
membrane from areas of low concentration on one side of a membrane to an area of higher
concentration on the other side. This is against the concentration gradient. Therefore, it requires
energy.
a. Active Transport: till equilibrium substances could move by passive movement.
But if equilibrium is reached and still more molecules are needed, they must be pumped
through the membrane against concentration gradient.
