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O1. There is a hierarchical structure within multicellular organisms.


This is not a bad summary of the Key Idea overall. However, just skim through it as much of it is too detailed.


Student Outcome: O1.1

Give examples of cells with identical genetic information that differentiate to produce cells with specialised structures and functions.


Stem cells can give rise to specialized cells.

When unspecialized stem cells give rise to specialized cells, the process is called differentiation. Scientists are just beginning to understand the signals inside and outside cells that trigger stem cell differentiation. The internal signals are controlled by a cell's genes, which are interspersed across long strands of DNA, and carry coded instructions for all the structures and functions of a cell. The external signals for cell differentiation include chemicals secreted by other cells, physical contact with neighboring cells, and certain molecules in the microenvironment.

Here is a picture of a stem cell that can differentiate into many different types of blood cells:

[Original beautiful image removed at the request of the author.]

Here is another showing the types of cells that an undifferentiated zygote can differentiate into. (Source:  http://stemcells.nih.gov/info/scireport/chapter1.asp)


Therefore, many questions about stem cell differentiation remain. For example, are the internal and external signals for cell differentiation similar for all kinds of stem cells? Can specific sets of signals be identified that promote differentiation into specific cell types? Addressing these questions is critical because the answers may lead scientists to find new ways of controlling stem cell differentiation in the laboratory, thereby growing cells or tissues that can be used for specific purposes including cell-based therapies.


Image removed at the request of the author. Adult stem cells typically generate the cell types of the tissue in which they reside. A blood-forming adult stem cell in the bone marrow, for example, normally gives rise to the many types of blood cells such as red blood cells, white blood cells and platelets. Until recently, it had been thought that a blood-forming cell in the bone marrow—which is called a hematopoietic stem cell—could not give rise to the cells of a very different tissue, such as nerve cells in the brain. However, a number of experiments over the last several years have raised the possibility that stem cells from one tissue may be able to give rise to cell types of a completely different tissue, a phenomenon known as plasticity. Examples of such plasticity include blood cells becoming neurons, liver cells that can be made to produce insulin, and hematopoietic stem cells that can develop into heart muscle. Therefore, exploring the possibility of using adult stem cells for cell-based therapies has become a very active area of investigation by researchers.


Source: http://stemcells.nih.gov/info/basics/basics2.asp

This video shows how all the layers of the cells in the body are formed from the embryo.


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Student Outcome: O1.2

Give examples of cells of like form and function that aggregate as tissue.


The human body is a complex machine made up of many parts. Although diverse in structure and function, all body parts are constructed of four basic tissue types: 1) epithelia, 2) connective, 3) muscle, and 4) nervous tissues. Consider these basic tissue types as the "lego building blocks" of the human body. During development, these building blocks are put together in many different ways to build the anatomical elements of the body.


Tissue Types Broad Function  
Epithelia Act as protective linings and coverings. In some locales, absorption and secretion are important functions of these lining and covering cells. As secretory cells, epithelia form most glandular structures of the body.
Connective Serve as connective and supportive tissues that bind and hold body structures together. Specialized fluid connective tissue types serve as liquid media important in transport, exchange, and body defense.  
Muscle Tissues with the unique capability to contract or shorten. This enables muscle types to be involved in functions of support and movement.  
Nervous Nerve cells are specialized for conduction. Nervous tissues therefore serve as the complex telecommunications network of the body. These tissues act in a sensory capacity, to receive, disseminate, and store information collected from receptors. In a motor capacity, nervous tissues provide response potential by controlling effectors such as muscles or glands.  


Source: http://www.mhhe.com/biosci/ap/histology_mh/tis1.html



Student Outcome: O1.3

Give examples of organs that contain several types of tissue.


Organs are the next level of organization in the body. An organ is a structure that contains at least two different types of tissue functioning together for a common purpose. There are many different organs in the body: the liver, kidneys, heart, even your skin is an organ. In fact, the skin is the largest organ in the human body and provides us with an excellent example for explanation purposes. The skin is composed of three layers: the epidermis, dermis and subcutaneous layer.

  • The epidermis is the outermost layer of skin. It consists of epithelial tissue in which the cells are tightly packed together providing a barrier between the inside of the body and the outside world.
  • Below the epidermis lies a layer of connective tissue called the dermis. In addition to providing support for the skin, the dermis has many other purposes. The dermis contains blood vessels that nourish skin cells. It contains nerve tissue that provides feeling in the skin. And it contains muscle tissue that is responsible for giving you 'goosebumps' when you get cold or frightened.
  • The subcutaneous layer is beneath the dermis and consists mainly of a type of connective tissue called adipose tissue. Adipose tissue is more commonly known as fat and it helps cushion the skin and provide protection from cold temperatures.

Below are pictures of the skin, heart and the brain showing the different types of tissue found in each organ.


Source: http://web.jjay.cuny.edu/~acarpi/NSC/14-anatomy.htm


Student Outcome: O1.4

List the organ systems that constitute the human body.


  • Circulatory system: blood circulations with heart and blood vessels
  • Digestive system: processing food with mouth, stomach and intestines
  • Endocrine system: communicating within the body using hormones
  • Immune system: defending against disease-causing agents
  • Integumentary system: skin, hair and nails
  • Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream
  • Muscular system: moving the body
  • Nervous system: collecting, transferring and processing information with brain and nerves
  • Reproductive system: the sex organs
  • Respiratory system: the organs used for breathing, the lungs
  • Skeletal system: structural support and protection through bones
  • Urinary system: the kidneys and associated structures involved in the production and excretion of urine


Source: http://en.wikipedia.org/wiki/Human_anatomy


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Go here for a slideshow which introduces the body systems.


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