Online lecture material to correspond to Chapter 3: The Cellular Level of Organization from OpenStax Anatomy & Physiology textbook for Dr. Poe’s A&P1 class.
This is the Second Part of The Cellular Level Organization Chapter Material Focusing on the Cytoplasm and Organelles
The cytoplasm Is
usually thought of as the space between the nucleus and the cell membrane. The
word itself basically means the stuff in the cell. Plasma is a very old term
coming from a Greek word that means to form or mold,
and it's just what takes up the space
between
the nucleus and the cell membrane.
Within the cytoplasm, we find a number of major organelles that are important to the functioning of any cell.
The cytoskeleton isn't really an organelle, it's the protein
skeleton of the cell it gives the cell its structure and has a lot to do with movement of cells
sometimes only internal movement as many cells don't have motility
functions with them. The cytoskeleton is composed of a number of different proteins
classified into three different types.
The smallest of those Is
the
micro-filament
which is made up of a
protein called actin
the largest is the microtubule made up a
protein called tubulin.
Those are found in all different types of cells and then each cell
type has its own
particular Iitermediates fiber,
and oftentimes those are named
in relation to the cell, such as neurons have neurofilaments,
While other cells have
proteins with unique names, such as
the
epithelial cells in the skin have keratin, the
cells are actually named after those as keratinocytes.
The main point of the cytoskeleton as a whole is to give cells their
structure and
there are many processes that make use of the
microtubules especially to move structures around within the cell and for motile cells like white
blood cells, actin can be important in how it extends portions of the cell membrane out.
As far as the cells that we're going to pay the most attention to the cytoskeleton in
it is in fact the epithelial cells and the neurons. When, we get to talking about the white blood cells
in A&P2
we won't necessarily talk about the cytoskeleton
itself. And then in muscle cells, the
cytoskeleton Is
adapted to a very specialized function which allows for contraction of the muscle tissue itself.
Mitochondria is
possibly one of the better-known organelles in cells. You'll often hear reference to the mitochondria being the powerhouse of the cell.
That's become such a
trite expression,
it's lost a lot of meaning a
powerhouse is referring to
part of a
dam or some sort of structure that generates energy and the powerhouse Is part of that generation of energy,
and in fact, that is what mitochondria are for.
They take
carbohydrates primarily, although
lipids and amino acids can work into the system too,
break them down and
harvest
energy out of them in the form mostly of
electrons that's then used to produce the
energy rich molecule ATP.
The process of taking the
electrons and
making ATP goes through a process called the electron transport chain which is a series of
proteins embedded in the inner membrane
which
pump hydrogen ions, or protons,
from the matrix, the central part of the mitochondria, into the space between the inner and outer membranes,
building up a concentration gradient, and
the protons can only get out of that space and
go down their concentration gradient
when they move through the ATP synthase
molecule which makes use of the physical movement of those protons
to
attach a third phosphate group on to ADP, therefore making ATP.
Muscle cells, as we talked about in A&P1,
use
quite a bit of ATP, so we will be considering that
this semester.
Neurons will also
be important as there are many energy dependent processes there that
we're interested in, but really all cells have a need for ATP.
The one
significant exception to that is
Red Blood Cells. Mitochondria need oxygen to do their job and so red blood cells which carry oxygen
do not have mitochondria,
therefore they won't be using up the oxygen they carry for their own purposes.
Endoplasmic reticulum is an organelle which is really just an internal
network of membrane enclosed spaces.
To some degree, that's pretty much what endoplasmic reticulum means.
There are two types of endoplasmic reticulum: rough and smooth. The rough ER is
associated with
protein synthesis because what makes it rough is that it has
ribosomes embedded into its
membrane. The smooth ER or SER is
mostly concerned with storage, and calcium ions is a common thing to be stored in the smooth ER.
We'll be considering the rough ER as part of the secretory pathway in cells
such as for the endocrine system and the smooth ER
will be important in muscle cells, it has a special name there, but it is the smooth ER.
With the rough ER
protein synthesis and secretion is
also dependent on the golgi apparatus.
The golgi apparatus is another membrane enclosed space. It's a series of disks that are
separate from each other, but they make up one integrated whole in how they work together.
Vesicles that leave the rough ER with synthesized proteins
merge into the golgi apparatus and then those proteins are processed in preparation before
secretion mainly
to be released from the cells.
There are some things that are released from the golgi apparatus that remain in the cell but they're going to be
transported to another part of the cell usually and those transport vesicles from the golgi apparatus will associate with the
microtubule system in the cytoskeleton to move those vesicles to their eventual
location. The most important aspect of secretion that
we're Going to be considering is either endocrine or exocrine functions,
hormones being released, or sweat oils that are released,
digestive enzymes those sorts of things.
There are two membrane-bound, organelles that are important for clearing
toxins and waste products out of the cell. The one pictured here is the peroxisome,
which is important for reducing reactive oxygen species in the cell, and it's called a peroxisome because
oxygen which is
possibly toxic in its chemical reaction with a number of things in
the cell is
modified into hydrogen peroxide
to become less reactive.
The other organelle which isn't pictured here is the lysosome. The name
really means "eating body" or "breaking down body" and it's important as sort of the
internal stomach of the cell. It has a lower pH,
similar to the stomach, though not as low, and it has a
number of
digestive enzymes
that can break down things. One important thing that a lysosome does is that it will merge with
vacuoles that debris or pathogens have been pulled into a cell like a white blood cell and
destroy them by digesting them.
The peroxisomes are mostly associated with the liver where detoxification takes place,
and the lysosomes, like I said, are an important part of how white blood cells work.

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