At the end of this session, the student should be able to: a. Describe the representative functional systems of the cell and discuss their potential roles. b. Describe the types of locomotion in non-muscle cells and discuss their mechanisms. med_students0

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Cells and Organelles II
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2. At the end of this session, the student should be able to:
a. Describe the representative functional systems of the cell and
discuss their potential roles.
b. Describe the types of locomotion in non-muscle cells and
discuss their mechanisms.
GUYTON & HALL Textbook of Medical Physiology, 12th edition,
page: 18-25.
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3. Functional Systems of the Cell
Ingestion (Cell Endocytosis):
- This is a function by which the cell obtains very large particles (as
nutrients and other substances) from the surrounding fluids.
N.B.: the small molecules can pass the cell membrane without
energy (diffusion) or with energy (active transport)
- Endocytosis may be:
1) Pinocytosis (ingestion of extracellular fluid with dissolved
substances into it).
2) Phagocytosis (ingestion of large particles such as bacteria, whole
cells, or portions of degenerating tissue).

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5. - Occurs in most cell but at a variable rate.
-The successive steps of pinocytosis are:
1) Molecules of protein attach to specialized protein receptors on
the surface of the membrane. These receptors are
concentrated in small pits on the outer surface of the cell
membrane, called coated pits.
2) On the inside of the cell membrane beneath these pits is a
meshwork of fibrillar protein called clathrin, as well as other
proteins, perhaps including contractile filaments of actin and
myosin.
Pinocytosis:

6. 3) Once the protein molecules have bound with the receptors, the
entire pit invaginates inward and the fibrillar proteins
surrounding the invaginating pit cause its borders to close over
the attached proteins, as well as over a small amount of
extracellular fluid.
4) Immediately, the invaginated portion of the membrane breaks
away from the surface of the cell, forming a pinocytotic vesicle
inside the cytoplasm of the cell.
 This process requires energy (in the form of ATP) and also the
presence of calcium ions in the extracellular fluid.
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7.  It occurs in much the same way as pinocytosis, except:
1) It involves large particles.
2) Occurs only in certain cells (most notably the tissue
macrophages and some of the white blood cells)
Phagocytosis:
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9. Digestion (Function of the Lysosomes)
 Almost immediately after a pinocytotic or phagocytic vesicle
appears inside a cell, one or more lysosomes become attached to
the vesicle and empty their acid hydrolases to the inside of the
vesicle.
 Thus, a digestive vesicle is formed inside the cell cytoplasm in
which the vesicular hydrolases begin hydrolyzing the proteins,
carbohydrates, lipids, and other substances in the vesicle.
 The products of digestion are small molecules of amino acids,
glucose, phosphates, and so forth that can diffuse through the
membrane of the vesicle into the cytoplasm.
Thus, the pinocytotic and phagocytic vesicles containing
lysosomes can be called the digestive organs of the cells.

10.  What is left of the digestive vesicle, called the residual body,
represents indigestible substances.
 In most instances, this is finally excreted through the cell
membrane by a process called exocytosis, which is essentially the
opposite of endocytosis.
Excretion (Exocytosis):

11. Synthesis and Formation of Cellular Structures (Function of
endoplasmic reticulum and Golgi apparatus):
Remember that:
1) Proteins are formed by ribosomes on the surface of rough
endoplasmic reticulum.
2) Lipids may be perioxisomes are formed by smooth
endoplasmic reticulum.
3) Glogi apparatus forms 2 types of vesicles:
a) Lysosomes. b) Secretory vesicles.
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12.  The most important type of movement that occurs in the body
is contraction of the muscle cells in skeletal, cardiac, and smooth
muscle (later).
 Two other types of movement occurs in other cells:
1) Amoeboid movement.
2) Ciliary movement.
Locomotion of Cells
It is the movement of an entire cell in relation to its
surroundings.
Example: movement of white blood cells through tissues.
Amoeboid Movement

13. It begins with protrusion of a pseudopodium from one end of the
cell. The pseudopodium projects far out, away from the cell body.
The remainder of the cell is pulled toward the pseudopodium.
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14.  The most common cells are the white blood cells when they
move out of the blood into the tissues to form tissue macrophages.
 Other types of cells can also move by amoeboid movement
under certain circumstances.
Example:
fibroblasts move into a damaged area to help repair the damage of
the skin.
Cells That show amoeboid movement:

15.  It results from continuous formation of new cell membrane at
the leading edge of the pseudopodium and continuous absorption
of the membrane in mid and rear portions of the cell.
 This requires:
1) Attachment of the pseudopodium to surrounding tissues so that
it becomes fixed in its leading position. This attachment is effected
by receptor proteins that line the insides of exocytotic vesicles.
- When the vesicles become part of the pseudopodial membrane,
they open, and the receptors now protrude to the outside and
attach to ligands in the surrounding tissues.
Mechanism

16. 2) Energy: Why?
In the cytoplasm of all cells is a moderate to large amount of the
protein actin. Much of the actin is in the form of single molecules
that do not provide any movement.
When energy (in form of ATP) is available, these polymerize to form
a filamentous network, and binds with another protein such as
myosin then it contracts. This helps the movement of
pseudopodium and retraction of cell body towards it.

17.  The most important initiator of amoeboid locomotion is the
process called chemotaxis.
 This results from the appearance of certain chemical
substances in the tissues. Any chemical substance that causes
chemotaxis to occur is called a chemotactic substance.
 If cells move toward the source of a chemotactic substance,
This is called positive chemotaxis.
 If cells move away from the source, this is called negative
chemotaxis.
Control of Amoeboid movement:

18. Cilia and Ciliary Movements
 It is a whip-like movement of cilia on the surfaces of cells.
 This occurs in only two places in the human body:
1) on the surfaces of the respiratory airways to move mucus
toward the pharynx and thus clear the airways.
2) on the inside surfaces of the uterine tubes (fallopian tubes) of
the reproductive tract to move fluid towards the uterus carrying
with it the ovum.

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20.  A cilium has the appearance of a sharp-pointed straight or curved
hair that projects 2 to 4 micrometers from the surface of the cell.
 The cilium is covered by a cell membrane.
 It is supported by 11 microtubules (9 double tubules around the
periphery +2 single tubules down the center).
 Flagellum:
- It is present in the sperm & is similar to a cilium (in structure &
contraction mechanism).
- But; The flagellum is:
1) much longer and
2) moves in quasi-sinusoidal waves instead of whip-like
movements.
Structure of the cilia:

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