1. Pima Medical Institute
Introduction to Human Anatomy & Physiology
Cell Movement
Cell Movement

2. Cell Membrane
The cell membrane controls which substances enter and leave the cell
PASSIVE MECHANISMS
do not use cellular energy
Diffusion
Facilitated diffusion
Osmosis
Filtration
ACTIVE MECHANISMS
use cellular energy
Active transport
Endocytosis
Exocytosis
The cell membrane is a selective barrier that controls which substances enter and leave the cell. Movements of substances into and out of cells include passive mechanisms that do not required cellular energy (diffusion, facilitated diffusion, osmosis, and filtration) and active mechanisms that use cellular energy (active transport, endocytosis, and exocytosis).

3. Diffusion is the process by which molecules or ions scatter
passive
Diffusion
Diffusion is the process by which molecules or ions scatter
from regions of higher concentration toward regions of lower concentrations
Higher concentration
Lower concentration
Atoms, molecules and ions diffuse “down” their concentration gradients
Diffusion, also called simple diffusion, is the process by which molecules or ions scatter or spread spontaneously from regions where they are higher in concentration toward regions where they are in lower concentration. This difference in concentration is called a concentration gradient. Atoms, molecules and ions are said to diffuse “down” their concentration gradients.
Concentration gradient: The difference in concentration

4. Diffusion
Under natural conditions, molecules and ions constantly move at high speeds
A single molecule may collide with other mollecules a million times each second
Under natural conditions, molecules and ions constantly move at high speeds. From a molecule’s point of view, the internal environment is crowded; a single molecule may collide with other molecules a million times each second. At body temperature, small molecules such as water move more than a thousand miles per hour.
At body temperature, small molecules such as water move more than a thousand miles per hour

5. The sugar molecules are distributed evenly
Diffusion
The sugar molecules are distributed evenly
solute
solvent
The sugar molecules dissolve then diffuse “down” the concentration gradient
Consider how molecules of sugar (a solute) distribute by diffusion in a glass of water (a solvent). At first the sugar remains highly concentrated at the bottom of the glass then it slowly disappears as the sugar molecules dissolve and then diffuse from regions where they are more concentrated toward regions where they are less concentrated. Eventually, the sugar molecules are distributed evenly throughout the water.

6. Diffusion O In the body, diffusion is the process whereby:
Oxygen enters cells
Carbon dioxide leaves cells
Equilibrium is never reached O C
Diffusion of a substance into or out of a cell can only occur if:
1.The cell membrane is permeable to the substance
2. A concentration gradient exists such that the substance is at a higher concentration on one side of the membrane than the other.
Consider oxygen and carbon dioxide—two substances to which cell membranes are permeable. In the body, diffusion is the process whereby oxygen enters cells and carbon dioxide leaves cells, but equilibrium is never reached.
Diffusion of a substance into or out of a cell can only occur if:
The cell membrane is permeable to the substance
A concentration gradient exists

7. Diffusion
A concentration gradient always allows oxygen to diffuse into cells
Dialysis separates small molecules from larger ones in a liquid O O
Intracellular oxygen is always low because oxygen is constantly used up in metabolic reactions. Extracellular oxygen is maintained at a high level by homeostatic mechanisms in respiratory and cardiovascular systems. Thus, a concentration gradient always allows oxygen to diffuse into cells.
Dialysis is a chemical technique that uses diffusion to separate small molecules from larger ones in a liquid.
Extracellular oxygen is maintained at a high level by homeostatic mechanisms
Intracellular oxygen is always low because it is constantly used up in metabolic reactions

8. Facilitated Diffusion
passive
Facilitated Diffusion
Protein carrier
Glucose
Insulin promotes facilitated diffusion of glucose through the membrane of certain cells
Substances that are not able to pass through the lipid bilayer (such as glucose and amino acids) need the help of membrane proteins to get across, a process known as facilitated diffusion. Facilitated diffusion is similar to simple diffusion in that it only moves molecules from regions of higher concentration toward regions of lower concentration.
In this process, a glucose molecule combines with a special protein carrier molecule at the surface of the cell membrane. This union changes the shape of the carrier, enabling it to move glucose to the other side of the membrane. Then the carrier releases the glucose and returns to its original shape to pick up another glucose molecule.
The hormone insulin, for example, promotes facilitated diffusion of glucose through the membrane of certain cells.
Glucose and amino acids need the help of membrane proteins to pass the lipid bilayer

9. Osmosis OSMOTIC PRESSURE A B
passive
Osmosis
Osmosis occurs when water molecules diffuse from
a region of higher water concentration to
a region of lower water concentration
across a selectively permeable membrane
Selectively permeable membrane
OSMOTIC PRESSURE A B
Higher water concentration
Lower water concentration
H2O
Osmosis is a special case of diffusion that occurs whenever water molecules diffuse from a region of higher water concentration to a region of lower water concentration across a selectively permeable membrane, such as a cell membrane.
Assume that the selectively permeable membrane is permeable to water molecules (the solvent), but impermeable to protein molecules (the solute). This selectively permeable membrane separates a container into two compartments. At first, compartment A contains a higher concentration of protein and a lower concentration of water than compartment B. Because the membrane is impermeable to proteins, equilibrium can only be reached by diffusion of water. As a result of molecular motion, water diffuses by osmosis from compartment B into compartment A. This is because solute molecules take up space that water molecules would otherwise occupy causing the water level in compartment A to rise.
This ability of osmosis to generate enough pressure to lift a volume of water is called osmotic pressure.
H2O
H2O
H2O
Equilibrium can only be reached by the diffusion of water
H2O
H2O
H2O
H2O
H2O
Solvent: Water
Solute: Protein

10. Osmotic Pressure
Water always tends to diffuse toward solutions of greater osmotic pressure A B
Water always tends to diffuse toward solutions of greater osmotic pressure. The higher the concentration of impermeant solute particles in a solution, the lower the water concentration of that solution and the higher the osmotic pressure.
Low water concentration =
High osmotic pressure
High water concentration =
Low osmotic pressure

11. Osmotic Pressure
Hypertonic: Osmotic pressure is higher than body fluids
Isotonic: Osmotic pressure is the same as body fluids
Osmotic pressure of the intracellular and extracellular fluids is the same
Cell membranes are permeable to water
Water equilibrates by osmosis throughout the body
Water concentration of intracellular and extracellular fluids is the same
Extracellular fluid
Intracellular fluid
Hypotonic: Osmotic pressure is lower than body fluids
Since cell membranes are generally permeable to water, water equilibrates by osmosis throughout the body, and the concentration of water and solutes everywhere in the intracellular and extracellular fluids is essentially the same. Therefore, the osmotic pressure of the intracellular and extracellular fluids is the same.
Any solution that has the same osmotic pressure as body fluids is called isotonic. Hypertonic refers to a solution that has a higher osmotic pressure than the body fluids. This causes the cell to shrink as water moves out of the cell. Hypotonic refers to a solution that has a lower osmotic pressure than the body fluids. This causes the cell to swell and possibly burst as water moves into it.

12. Filtration Filtration is used to separate solids from water
passive
Filtration
Filtration is used to separate solids from water
Blood pressure forces smaller molecules through the capillary wall while larger molecules remain inside
Hydrostatic pressure is created by the weight of water on the paper due to gravity
Filter paper
Heart action is greater within the vessel than outside
One example of filtration is making coffee by the drip method
Filtration is commonly used to separate solids from water. One method is to pour a mixture of solids and water onto filter paper in a funnel. The paper is a porous membrane through which the small water molecules can pass, leaving behind the larger solid particles. Hydrostatic pressure, which is created by the weight of water on the paper due to gravity, forces the water molecules through to the other side. A familiar example of filtration is making coffee by the drip method.
Another example of filtration is when blood pressure forces smaller molecules through tiny openings in the capillary wall while the larger molecules remain inside. The force of this movement comes from blood pressure, generated mostly by heart action, which is greater within the vessel than outside it. However, the impermeable proteins tend to hold water in blood vessels by osmosis, thus preventing the formation of excess tissue fluid, a condition called edema. Filtration also occurs as the kidneys cleanse blood.
Impermeable proteins tend to hold water in blood vessels by omosis
to prevent excess tissue fluid from forming

13. FACILITATED DIFFUSION
Active Transport
active
DIFFUSION
FACILITATED DIFFUSION
OSMOSIS
Higher concentration
Lower concentration
When molecules or ions pass through cell membranes by diffusion, facilitated diffusion, or osmosis, their net movements are from regions of higher concentration toward regions of lower concentration. Sometimes, however, particles do move from a region of lower concentration to one of higher concentration. This process is called active transport and it requires energy which comes from adenosine triphosphate molecules.
ATP
ACTIVE TRANSPORT
Higher concentration
Lower concentration

14. Active Transport
Carrier protein combines with particle to be transported
This union triggers a release of energy altering the carrier protein’s shape
“Passenger” particle moves through the membrane
The carrier molecules in active transport are proteins with binding sites that combine with the particles being transported. Such a union triggers the release of energy altering the shape of the carrier protein. As a result, the “passenger” particle moves through the membrane. Once on the other side, the transported particles are released and the carriers can accept other passenger molecules at that binding site.
“Passenger” particle is released
Protein carrier can accept other passengers

15. Other particles that are actively transported across
Active Transport
Up to 40% of a cell’s energy supply may be used to actively transport particles through cell membranes
The concentration of sodium ions remains greater outside the cell than inside
Sodium ion
Sodium ions, for example, diffuse passively into cells through protein channels but their concentration typically remains much greater outside cells than inside; equilibrium is never reached. Up to 40% of a cell’s energy supply may be used to actively transport particles through cell membranes. Other particles that are actively transported across cell membranes include sugars and amino acids, potassium, calcium, and hydrogen ions.
Protein channel
Other particles that are actively transported across
cell membranes:
Sugars and amino acids
Potassium
Calcium
Hydrogen ions

16. Endocytosis & Exocytosis
active
ENDOCYTOSIS
EXOCYTOSIS
Large molecules are conveyed (transported) into a cell with a vesicle formed from the cell membrane
Large molecules are conveyed (transported) out of a cell with a vesicle formed from the cell membrane
Endocytosis and exocytosis
use cellular energy to move substances into or out of a cell without crossing the
cell membrane
Endocytosis and exocytosis are two processes that use cellular energy to move substances into or out of a cell without actually crossing the cell membrane.
In endocytosis, molecules or other particles that are too large to enter a cell by diffusion, facilitated diffusion, or active transport are conveyed (transported) with a vesicle formed from a section of the cell membrane.
In exocytosis, the reverse process secretes a substance stored in a vesicle from the cell. Nerve cells use exocytosis to release the neurotransmitter chemicals that signal other nerve cells, muscle cells, or glands.
Nerve cells use exocytosis to release neurotransmitters

17. Pinocytosis & Phagocytosis
Particle attaches to the cell membrane 
Part of the membrane surrounds the particle 
White blood cells are phagocytes
PINOCYTOSIS
(type of endocytosis)
Cells engulf tiny droplets of liquid
PHAGOCYTOSIS
(type of endocytosis)
Cells engulf solid particles
Membrane detaches and forms a vesicle 
Pinocytosis (pin-uh-cy-toh-sis) means “cell drinking.” Cells engulf tiny droplets of liquid from their surroundings as a small portion of the cell membrane indents. Phagocytosis (fag-uh-cy-toh-sis) means“cell eating.” This process is similar to pinocytosis but the cell takes in solids rather than liquids. Certain kinds of white blood cells are called phagocytes because they can take in solid particles such as bacteria and cellular debris.
When a phagocyte first encounters a particle, the particle attaches to the phagocyte’s cell membrane. This stimulates a portion of the membrane to project outward, surround the particle, and slowly draw it inside the cell. The part of the membrane surrounding the particle detaches from the cell’s surface, forming a vesicle that contains the particle.

18. Receptor-Mediated Endocytosis & Transcytosis
Pinocytosis & phagocytosis
Engulf a variety of particles
Receptor-mediated endocytosis
Engulf specific particles
Example: Cholesterol molecules
Pinocytosis and phagocytosis engulf a variety of molecules in the vicinity of the cell membrane. In contrast, receptor-mediated endocytosis moves very specific kinds of particles into the cell.
In this process, protein molecules extend through a portion of the cell membrane to the outer surface, where they form receptors to which only specific molecules from outside the cell, called their ligands, can bind. Continued indentation forms a vesicle, which transports the molecule into the cytoplasm. Cholesterol molecules, for example, enter cells by receptor-mediated endocytosis.
A process called transcytosis combines endocytosis and exocytosis to transport a particle or structure across a cell.
TRANSCYTOSIS
Combines endocytosis and exocytosis to transport a particle
or structure across a cell

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