Organization of the Body and Cellular Anatomy
Organization of the body
Cells
The body is foremost organized into cells, which are the basic structural unit of life. In the human body, there is a plethora of specialized and differentiated cell types that serve to perform specialized functions necessary for life.
Tissues
Cells are organized into communities known as tissues. Tissues themselves have very specialized functions; there is even an entire chapter introducing the many types and purposes of tissues in the human body.
Organs
Tissues compose of structures that are known as organs. Organs carry out particular functions and are very diverse. For example, your skin (integument) is an organ, as is your spleen. These organs differ greatly in size and function, but they are both considered organs of the human body.
Organ systems
Organ systems are the basis of this course. Most of the topics covered in anatomy and physiology are about particular organ systems, and by the end of this course, you will (hopefully) be able to see how each system functions together to create the phenomenon that is human life.
Organisms
The organ systems that work together to create life can be organized into a “macro”-unit known as an organism. In the scope of this class, we are concerned with humans as the organism of study (as well as domesticated cats as our mammalian model organism). Organisms, like organs, have a complex diversity; organisms can range from a prokaryotic bacterium to something as complex as a whale.
Overview of systems
Integumentary
Commonly known as the skin, this system is considered the largest human organ. The integument is the outer covering of the body, which contains the layers of the skin, the hair, and the nails. The skin is relevant when working with the immune system (as a first layer of defense) and the nervous system (cutaneous receptors). Logically, it makes sense to start with the skin because this is the most superficial aspect of human anatomy!
Skeletal
The skeletal system is composed of all of the 206 adult bones found in the human body. While they might not seem interesting at first, you will find that the cavities in the bone are useful for production of red blood cells and immune cells. This system operates with the muscular system to produce the phenomenon of movement, while on its own works as a framework for the resting body.
Muscular
The muscular system is composed of the muscles and the joints. You will learn there are several types of muscle tissue based on which organs they muscularize. With the principles of tension in mind, the muscular system results in coordinated movements, involuntary movements, and so many fascinating things. This system is also your first introduction to how the nervous system operates and controls the way the human body works.
Nervous
The nervous system is ultimately “the big bad” of the human anatomy. This system contains the central nervous system, the peripheral nervous system, and the autonomic nervous system which altogether exert control on the human body through electrochemical stimulation.
Endocrine
While the nervous system is the boss of the human anatomy, the endocrine system is the contractor that actually gets the work done. Ultimately, this system is composed of glands that secrete hormones that will influence the cells of another organ system.
Cardiovascular
The cardiovascular system contains the heart and the vasculature of the entire body. The heart pumps blood through the systemic (body) circuit and the pulmonary (lungs) circuit to maintain that cells stay oxygenated. Solutes move through the circulatory system, which makes this system relevant to the endocrine and urinary systems.
Lymphatic
The lymphatic system is a sort of secondary circulatory system in which reclaimed cellular fluid circulates through sites in the body in which debris can be screened for dangerous pathogens. This system is related to immunity, which is the body’s response to a foreign material.
Respiratory
The respiratory system contains the organs in which humans do gas exchange with the atmospheric air. The human body is essentially a chemical pump with gaseous substances that will be transported through a liquid medium, and the respiratory system is where oxygenation happens to the blood and then the tissues of the body, as well as the transport of carbon dioxide out of the body.
Digestive
Humans need nutrients to build the systems you will study in anatomy and physiology, which will be chemically broken down in an alimentary canal which is technically continuous with the atmosphere. This canal and its accessory organs will break down the substances that pass through this canal in order to absorb the necessary compounds and excrete the unnecessary solid waste.
Urinary
Like the digestive system excretes liquid waste, which is in solution of the blood. The circulation of the body passes through the kidneys so that cellular transport can filter the solutes for optimal conditions. Metabolites and ions are concentrated and secreted through the kidneys in order to maintain a chemical balance within the human body.
Reproductive
The reproductive system is the body system with which humans can copulate and reproduce.
Feedback
Positive feedback
Result enhances the original stimulus.
Negative feedback
Result shuts off the original stimulus.
Cell junctions
Gap junctions
Gap junctions allow transport of ions and small ions. The linked article goes in great depth about the mechanics of gap junctions; however, this knowledge is beyond the scope of this course. These sort of connections are important for cellular transport.
Desmosomes
Desmosomes distribute tension within high-working cellular connections. The linked article describes the mechanics of the desmosomes. Desmosomes are an important intercellular connection in tissues that have a high magnitude of tension exerted on them. Desmosomes are not particulary used for transport.
Tight junctions
Tight junctions are impermeable for the passage of any materials and promote cell adhesion. These junctions do not enhance structural support in the way that desmosomes do, but they are important for local cellular boundaries.
Cell transport
The intercellular and extracellular environments are very different in terms of chemical concentrations and electric potential. This is the driving force for cellular transport and stimulation, which will be particularly relevant in the scope of this class when action potentials are studied. Chemical substances can move with or against the concentration gradient based on the type of transport this material will undergo. It is important to remember that the cellular membrane is selectively permeable based on protein channels, and it is composed of a phospholipid bilayer that has hydrophilic (water-permeable) and hydrophobic (water-resistant) parts.
Here is a basic review of the four major cellular transport mechanisms relevant to this class:
Simple diffusion
Simple diffusion is passive transport mechanism through the phospholipid membrane that surrounds the cellular cytosol. Because the cell membrane has a hydrophobic region, only nonpolar molecules can move through the cellular membrane. This mechanism requires no ATP.
Carrier-mediated facilitated diffusion
An extracellular substance binds to an region of a membrane protein to cause a conformational change to allow this substance through.
Channel-mediated facilitated diffusion
An extracellular substance is allowed selective transport through the membrane.
Osmosis
A solvent can flow through the lipid bilayer, which is analogous to simple diffusion. This is exemplified by the transport of liquid water, which moves through aquaporin proteins.
Important cellular anatomy
Cilia
Cilia are specialized cellular structures that aid in the propulsion of materials. You can find cilia in many different structures of the body, particularly ciliated epithelia in areas of the body that transport important materials. An important area in which you may find cilia is the columnar epithelia in the esophagus. Structurally, cilia are protrusions of the cell membrane, and you can read more about them in this Molecular Biology excerpt if you are interested (although this in depth knowledge is beyond the scope of this class).
Here is a histological example of what a cilium is for the purposes of this course:*
Endoplasmic reticulum
This organelle is a continuation of a rough and smooth aspect. It is system of tubes with cisterns through which proteins move, beginning at the rough ER, which synthesizes all cellular proteins with their adjacent (“rough”) ribosomes. Then, enzymes in the endoplasmic reticulum perform metabolic functions on proteins as they are transported from the smooth ER to the Golgi body. The focus in this course is on the smooth ER of skeletal and cardiac muscle cells, which has important specializations that aid their electrical/chemical stimulation that produces muscular contraction.
This micrograph has captured the specialized smooth ER for the purposes of this class.
Mitochondria
Mitochondria, as many of you may call it, it the “powerhouse of the cell”. But what exacty does this mean? Mitochondria is an important organelle for carbohydrate metabolism, and from this biochemical process, there is a net ATP gain which is used as cellular energy. This organelle is not necessarily the centerpiece of anatomy and physiology, but it is important to recognize this when studying sources of cellular energy when muscular tissues are stimulated.
This muscular micrograph also displays mitochondria in the context of BIO-203/L203:
Interstitial fluid
Some publicized news sources claim that the interstitium is a new organ, which is up for debate, but is entirely not new at all. Interstitium is the extracellular fluid found in the body, and the relations between extracellular fluid and intracellular fluid will become a prominent theme in A&P, particularly with the circulation and the pressure associated with this fluid. The chemical compositon of the interstitial fluid is similar to the blood plasma, but filtered quite immensely.
Copyright: Pearson Education