CHAPTER 13 Test Your Knowledge
Driving Question 1
What is the structure of tissues and organs, and how can organs be repaired or replaced?
By answering the questions below and studying Infographics 13.1, 13.2, 13.3, and 13.5, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Which of the following statements applies to tissues?
a. Only one cell type is present.
b. Multiple cell types are present.
c. Each tissue has a specific function.
d. Cells within a tissue cooperate.
e. all of the above
f. b, c, and d
f
The brain and spinal cord are made up of nervous tissue. This tissue includes neurons–cells that fire electrical impulses that communicate information–as well as glial cells. Some glial cells enable the electrical impulse to travel faster in a neuron. How are the roles of neurons and glial cells consistent with a functional tissue?
Tissues are made up of different cell types that work together. Neurons and glial cells are different cell types that work together to allow electrical impulses to travel faster through the nervous system.
You shed skin cells every day. How are those cells replaced?
a. by mitotic division and specialization of embryonic stem cells
b. by differentiation of neighboring neurons into skin cells
c. by differentiation of red blood cells that leave the circulation and migrate into deeper layers of the skin
d. by mitotic division and differentiation of tissue stem cells
e. all of the above
d
USE IT
What are the pros and cons of receiving an organ transplant versus growing a replacement organ from one’s own cells?
Pro: if a donor organ is available, it can be transplanted immediately, without having to wait for an organ to be grown from one’s own cells. Con: often very long wait time to receive a matching organ; the possibility of immune rejection (even “matched” organs are not in fact a perfect match); the need for long-term immunosuppressive drugs that can leave a person vulnerable to infections (organs grown from a person’s own cells will be a perfect match, so there is no concern about rejection and no need for immunosuppressive drugs).
Why does a recipient of a liver transplant have a high risk of bacterial infections?
a. because the liver plays a critical role in the immune response
b. because donor livers are often contaminated with disease-causing bacteria
c. because transplant recipients have to take drugs that suppress their immune system
d. because the surgery poses a high risk for introducing bacteria into the recipient
e. because the immune system may reject the liver
c
From the information provided in Question 2, would it be sufficient to just replace the neurons in someone who suffered nervous tissue damage? Why or why not?
Replacing only the neurons would not be sufficient, as the glial cells are also critical for normal function of the nervous system.
Why is engineering a bladder more challenging than engineering skin?
There are more tissue and cell types in a bladder, and a bladder has to have a specific three-dimensional shape (as compared to skin, which lies on underlying supporting tissue).
Driving Question 2
What are the properties of specialized cells in tissues, and how do stem cells differentiate into these specialized cells?
By answering the questions below and studying Infographic 13.4, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Relative to one of your liver cells, one of your skin cells
a. has the same genome (that is, the same genetic material).
b. has the same function.
c. has a different pattern of gene expression.
d. a and c
e. b and c
d
A muscle cell does not have keratin--the protein that gives skin its elasticity and “waterproofing.” Why would muscle cells not have keratin?
Muscle cells and skin cells have different functions. Keratin is not necessary for muscle cell function, so muscle cells do not express the keratin gene (and so do not have the keratin protein).
Is the genome of stem cells larger than that of specialized cells?
a. yes, because they need the genes found in every cell type, whereas specialized cells need only a subset of all the genes
b. yes, because they express more genes than do specialized cells
c. no, because all cells in a person have the identical set of genes in their genome
d. no; they have a smaller genome, because stem cells are equivalent to gametes (which are haploid) in that they can potentially create an entire individual
e. no; they have a smaller genome because stem cells express only a subset of genes
c
300
USE IT
Different cells have different functions. Muscle cells contract because of the sliding action of actin and myosin proteins in muscle cells; a protein called retinal is important for the function of the light-detecting photoreceptor cells in the retina of the eye; helper T cells of the immune system have a protein on their surface called CD4 that participates in the immune response. From this information, complete the following table.
| Photoreceptors of the Retina | Muscle Cells of the Heart | T Cells | |
| Myosin gene present? | Yes | Yes | Yes |
| Myosin protein present? | No | Yes | No |
| Retinal gene present? | Yes | Yes | Yes |
| Retinal mRNA present? | Yes | No | No |
| Retinal protein present? | Yes | No | No |
| CD4 gene present? | Yes | Yes | Yes |
| CD4 mRNA present? | No | No | Yes |
| CD4 protein present? | No | No | Yes |
A woman has had a heart attack, and her heart muscle is damaged. What genes would a possible replacement cell have to express in order to begin to take over the function of cardiac muscle? For each gene, explain briefly why its expression would be important in this situation.
At the least, the replacement cells would have to express actin and myosin genes, as the actin and myosin proteins are important for muscle contraction.
Driving Question 3
How do stem cells contribute to regenerative medicine, and how can we obtain or produce stem cells for this purpose?
By answering the questions below and studying Infographics 13.3, 13.5, 13.6, 13.7, and 13.8, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Compare and contrast embryonic stem cells and somatic (that is, adult) stem cells in regard to at least two features.
Embryonic stem cells can differentiate into almost any cell type and are found in early embryos. Somatic stem cells are more limited with respect to the cell types they can differentiate into, and are found in tissues in the body.
An adult stem cell from bone marrow is most useful in treating
a. a heart attack.
b. a large burn on the upper thigh.
c. a disorder affecting the development of white blood cells.
d. a degenerative eye disease affecting the retina.
e. a degenerative nervous system disease such as Alzheimer disease.
c
USE IT
List and then describe some of the successes and challenges associated with using adult stem cells for stem cell therapy in comparison with embryonic stem cells.
Embryonic stem cells have the potential to differentiate into almost any cell type in the body and so can be used to engineer and repair a wide array of tissues. Somatic stem cells have more limited differentiation capabilities, so a particular somatic stem cell type has to be chosen depending on the desired treatment. There is controversy and ethical discussion about the use of stem cells derived from embryos, and legislation can dictate research into and applications of embryonic stem cells. Somatic stem cells come from body tissues and are generally easy to obtain from a patient.
MINI CASE
History was made in 2008 when a 30-year-old woman whose airway was severely damaged from tuberculosis was treated with an engineered trachea that was a perfect match. A trachea consists of a cartilage tube, chondrocytes (cells that help maintain the cartilage by producing proteins that make up cartilage), and an epithelial lining. Physicians used the following components in order to accomplish the procedure: an intact donor trachea (from a woman who had died from cardiac complications); the patient’s own bone marrow stem cells; and the patient’s own airway epithelial cells.
The engineered trachea was surgically implanted in the patient. She did not take any drugs to suppress her immune system, and after 3 months, she had normal airway function, no evidence of rejection of the engineered trachea, and a much improved quality of life.
From the information provided, describe the steps that the physicians must have followed in order to accomplish this successful procedure.
(1) Remove all donor cells from the donor trachea, leaving just a tube. (2) Induce the patient’s multipotent bone marrow stem cells to differentiate into cartilage cells (which will be a perfect match to her own cartilage cells before damage by tuberculosis). Obtain airway epithelial cells and let them divide in culture to have sufficient airway cells to attach to the inside of the new trachea. (3) Seed the new, matching cartilage cells onto the outside of the trachea tube and let them attach and start to divide (in a tissue reactor). At the same time, add airway epithelial cells to the inside of the tube, so that they can attach and start to form a lining in the new trachea. (4) Transplant that trachea (coated with perfectly matched cartilage cells and lined with the patient’s own epithelial cells) into her respiratory system.
SOURCE: Macchiarini, P., et al. (2008) Clinical transplantation of a tissue-engineered airway. The Lancet 372:2023–2030.
301
INTERPRETING DATA
Specific proteins expressed by specific cell types can be used as markers to both identify and isolate specific cell types from a population of cells. The table at the right provides a list of markers specifically associated with different cell types.
(i) A scientist has isolated a population of cells that express telomerase.
a. Can these cells differentiate into neurons? What marker would you look for to determine if they had differentiated into neurons?
b. Can these cells differentiate into white blood cells? What marker would you look for to determine if they had differentiated into white blood cells?
(ii) Experiments in mice have shown that hematopoietic stem cells can be coaxed out of the bone marrow and into the circulation and then differentiate into cardiac muscle in mice that have experienced a heart attack. What markers must the scientists have followed to confirm this result?
(iii) In the Mini Case of the engineered trachea (Question 16), what marker was most likely on the bone marrow stem cells isolated from the patient? What marker would the scientists have looked for to confirm that the cells were differentiating into cartilage cells?
(i) a: As telomerase is a marker of embryonic stem cells, which can differentiate into almost any cell type. These cells can therefore differentiate into neurons. A marker for neurons is MAP2. b: As telomerase is a marker of embryonic stem cells, which can differentiate into almost any cell type, these cells can therefore differentiate into white blood cells. If the differentiated cells express CD8, that would indicate that the cells are white blood cells.
(ii) To identify bone marrow hematopoietic stem cells in the circulation, the scientists could look for cells with CD34 markers on their surface. Cells that have differentiated into cardiac muscle cells will express myosin heavy chain.
(iii) Bone marrow cells will have the CD34 marker, while cartilage cells will express collagen type II.
BRING IT HOME
Your roommate’s best (dog) friend recently died. This beloved pet had been with your roommate since she was in the second grade, and she is very upset about the loss. She has stated that she is going to try and have her pet cloned. You have heard about cloning, and that many pets have been cloned. But you have also heard that cloning is controversial. You decide to do some research. What can you find out about the differences between reproductive and therapeutic cloning? Do you think that reproductive cloning should be allowed? Does your opinion differ for pets vs. humans?
Reproductive cloning is cloning with the intent of creating a cloned organism (a duplicate of an organism). In reproductive cloning, a nucleus from a somatic cell from the organism to be cloned is inserted into an egg from which its own nucleus has been removed. The egg is allowed to divide into an embryo, which is inserted into a surrogate mother to carry the embryo and fetus to term (see Infographic 13.7). Therapeutic cloning is a way to produce embryonic stem cells that are identical to the cells of a given patient. These genetically identical embryonic stem cells can be used to treat almost any tissue damage or loss in that patient. In therapeutic cloning, a nucleus is removed from a somatic cell from the person to be treated. The nucleus is inserted into an egg from which its own nucleus has been removed, and the egg is allowed to divide into an embryo. At this point, the embryo is destroyed to obtain the embryonic stem cells to treat the patient. Opinions will vary regarding whether reproductive cloning should be allowed for humans, for their pets, for neither, or for both.