chapter 14 p4 Flashcards
Potential use of stem cells in diabetes treatment:
p1
- For decades, diabetes researchers have been searching for ways to replace the faulty B cells in the pancreatic islets of diabetic sufferers.
- Each year, over 1000 people with type 1 diabetes receive a pancreas transplant.
- After a year, over 80% of these patients have no symptoms of diabetes and do not have to take insulin.
- However, the demand for transplantable pancreases far outweighs their availability.
- The risk of having a transplant can also be a greater health risk than the diabetes itself - immunosuppressant drugs are required to ensure the body accepts the transplanted pancreas, which can leave a person susceptible to infection.
Potential use of stem cells in diabetes treatment:
p2
- Doctors have attempted to cure diabetes by injecting patients with pancreatic B islet cells, but fewer than 8% of cell transplants performed have been successful.
- The immunosuppressant drugs used to prevent rejection of these cells increases the metabolic demand on insulin-producing cells.
- Eventually this exhausts their capacity to produce insulin.
- As type 1 diabetes results from the loss of a single cell type, and there is evidence that a relatively small number of islet cells can restore insulin production, the disease is a perfect candidate for stem cell therapy.
- Totipotent stem cells have the potential to grow into any of the body’s cell types.
- Scientists have been researching the best type of stem cells and the signals required to promote their differentiation into B cells, either directly in the patient or in the laboratory before being transplanted.
Potential use of stem cells in diabetes treatment:
p3
- It is likely that the stem cells used in diabetes treatment would be taken from embryos.
- To obtain the stem cells, the early embryo has to be destroyed.
- This means destroying a potential human life.
- However, the embryos used as a source for these stem cells would usually be destroyed anyway - they are ‘spare’ embryos from infertility treatments or from terminated pregnancies.
- Stem cells lines formed from a small number of embryos can be used to treat many patients - each treatment does not require a separate embryo.
- An alternative to using embryonic matter is that of using preserved umbilical stem cells.
Stem cells offer many advantages over current therapies:
- donor availability would not be an issue - stem cells could produce an unlimited source of new B cells
- reduced likelihood of rejection problems as embryonic stem cells are generally not rejected by the body (although some evidence contradicts this).
- Stem cells can also be made by somatic cell nuclear transfer (SCNT)
- people no longer have to inject themselves with insulin.
however… stem cells have disadvantages over current therapies:
because our ability to control growth and differentiation in stem cells is still limited, a major consideration is whether any precursor or stem-like cells transplanted into the body might induce the formation of tumours as a result of unlimited cell growth.
- Coordinated responses
On many occasions the body responds to changes in its internal and external environment through a coordinated response.
The nervous and endocrine systems work together to detect and respond appropriately to stimuli.
One example of coordination between these two systems is the mammalian ‘fight or flight’ response.
Fight or flight response: p1
- The fight or flight response is an instinct that all mammals possess.
- When a potentially dangerous situation is detected, the body automatically triggers a series of physical responses.
- These are intended to help mammals survive by preparing the body to either run or fight for life, hence the name of the response.
- Once a threat is detected by the autonomic nervous system, the hypothalamus communicates with the sympathetic nervous system and the adrenal-cortical system.
- The sympathetic nervous system uses neuronal pathways to initiate body reactions whereas the adrenal-cortical system uses hormones in the bloodstream.
- The combined effects of these two systems results in the fight or flight response.
coordination of the fight or flight response diagram
Fight or flight response: p2
- The sympathetic nervous system sends out impulses to glands and smooth muscles and tells the adrenal medulla to release adrenaline and noradrenaline into the bloodstream.
- These ‘stress hormones’ cause several changes in the body, including an increased heart rate.
- The release of other stress hormones which have a longer-term action from the adrenal cortex is controlled by hormones produced by the pituitary gland in the brain.
- The hypothalamus stimulates the pituitary gland to secrete adrenocorticotropic hormone (ACTH).
- This travels in the bloodstream to the adrenal cortex, where it activates the release of many hormones that prepare the body to deal with a threat.
The physiological responses which occur as part of the fight or flight response:
Action of adrenaline:
One of adrenaline’s main functions during the fight and flight response is to trigger the liver cells to undergo glycogenolysis so that glucose is released into the bloodstream.
This allows respiration to increase so more energy is available for muscle contraction.
Adrenaline is a hormone.
It is hydrophilic therefore cannot pass through cell membranes.
Adrenaline binds with receptors on the surface of a liver cell membrane and triggers a chain reaction inside the cell
When adrenaline binds to its receptor:
the enzyme adenylyl cyclase (which is also present in the cell membrane) is activated.
Adenylyl cyclase triggers the conversion of ATP into cyclic adenosine mono-phosphate (cAMP) on the inner surface of the cell membrane in the cytoplasm.
The increase in CAMP levels activates specific enzymes called protein kinases which phosphorylate, and hence activate, other enzymes. In this example, enzymes are activated which trigger the conversion of glycogen into glucose.
This model of hormone action is known as
the second messenger model.
The hormone is known as the first messenger (in this example, adrenaline) and CAMP is the second messenger.
One hormone molecule can cause many cAMP molecules to be formed.
At each stage, the number of molecules involved increases so the process is said to have a cascade effect (Figure 3).
The human heart beats at
approximately 70 beats per minute at rest.
However, when you exercise, or in times of danger, it is essential that the heart rate increases to provide the extra oxygen required for increased respiration.
Controlling heart rate:
Heart rate is involuntary and controlled by the autonomic nervous system.
The medulla oblongata in the brain is responsible for controlling heart rate and making any necessary changes.
two centres within the medulla oblongata, linked to the sinoatrial node (SAN) in the heart by motor neurones:
diagram of control of heart rate
effect of excersize on cardiac output
