ncarbone's blog

It is often assumed that oxygen consumption or metabolic rate occurs independently of the amount of oxygen available. However, this is not always the case. Invertebrates will sometimes increase their oxygen consumption as a function of different oxygen amounts. For some animals oxygen consumption is positively and linearly related to oxygen levels when levels are low. However, oxygen consumption obtains a plateau once levels reach a certain amount. Speckled trout are able to acclimate to low oxygen levels when maintained in low oxygen rich water. This proves that fish are able to extract oxygen from water better than most other organisms. Anaerobic metabolism is oxygen consumption without oxygen. Some organisms like internal parasites and bivalves survive only by anaerobic metabolism. Anaerobic metabolism is often associated with burst locomotion.

Cardiovascular disease in diabetics is caused by a combination of three factors including lipid control, glucose control, and blood pressure. Lipid control is thought to be the most influential in contributing to cardiovascular disease. Often, cardiovascular problems can arise from the development of atherosclerosis which is at an increased risk in diabetics. Atherosclerosis is the hardening and narrowing of blood vessels which leads to increased blood pressure. Poor glucose control or resistance to insulin causes a lack of nitric oxide production which is important in maintaining vascular flow. The lack of sufficient nitric oxide leads to an increase in plaque formation within the blood vessels. This increase in plaque buildup prohibits smooth blood flow through the vessels. Another diabetic complication is neuropathy. Neuropathy is caused by a metabolic cascade resulting from a lack of glycemic control, a long duration of diabetes, and potentially vascular abnormalities. Hyperglycemia causes the polyol pathway to produce more sorbitol from glucose, but at the same time this process consumes NADPH which results in less cofactor available for glutathione reductase. This inhibits the cells’ ability to respond to oxidative stress or the imbalance between antioxidants and free radicals in one’s body. Too many free radicals cause chemical chain reactions due to their high reactivity. Conversely, anti-oxidants have been proposed to prevent generation of free radicals (or reduce the impact of free radicals). Oxidative stress can alter nerve blood supply, nerve structure, and endoneural metabolism. High glucose levels also are found to be directly correlated with the production of advanced glycation end-products (AGE). AGE’s are produced by a chemical transformation of sugars binding to amino acids or fats. High blood glucose levels and increased fat/lipid levels can lead to the production of AGE’s. When AGE interacts with receptors (RAGE) it can further lead to oxidative stress. A test was run with rats where RAGE is expressed in endothelial and Schwann cells. Incubation of these neuronal and Schwann cells with AGE’s leads to cell death. Vascular complications can also lead to neuropathy through poor glycemic control. Similar to cardiovascular disease, the lack of glycemic control results in a buildup of plaque in the blood vessels ultimately ending in atherosclerosis. The lack of blood flow causes damage to the peripheral nervous system thus leading to complications such as neuropathy and foot ulcers.

Exercising on a regular basis can help maintain low blood sugars for type 1 and type 2 diabetics. When exercising insulin sensitivity increases which allows cells in the body to take up insulin in order to break down glucose. Sometimes there is a delayed effect on blood glucose when exercising. It can take up to 24 hours after physical activity for blood glucose levels to be affected. This is important especially if blood glucose levels are already low as physical activity can lead to hypoglycemia. Keeping a healthy blood glucose level due to exercise can help benefit the long-term effects of diabetes. It can surpass the chance of developing complications such as neuropathy, hyperglycemia, and retinopathy.

This study examines the long-term effects of exercise treatment in both type 1 and 2 diabetics. The 78 subjects had no signs or symptoms of diabetic neuropathy and their duration of diabetes averaged at 8.7 years. They were randomized into two groups; one group performed a supervised 4 hour per week treadmill session. The other group did not perform any supervised activity for the entire 4 year period of the study. Neurophysiological measurements were taken throughout the study. The exercise group was enrolled in a treadmill walking program. After 4 years there the investigators found specific changes in some, but not all, parameters in clinical characteristics between the two groups. Although the A1C of the exercise group dropped 0.42 points, meanwhile the control group increased 0.14 points. The nerve conduction velocity of the peroneal motor nerve increased significantly in the exercise group. There was no significant increase in nerve conduction velocity for the sural sensory nerve in the exercise group but there was a significant decrease in the control group. In the exercise group, 0% of the participants developed motor neuropathy at the end of the study while 17% of the control group developed motor neuropathy. Meanwhile 6.45% of the exercise group developed sensory neuropathy compared to 29.8% in the control group.

Vertebrates and invertebrates have different structures that allow them to respire in water. Gills are a common structure that help an organism respire. Gills are respiratory sturctures that are fan like shapes with thin cuticular walls. Both vertebrates and invertebrates have gill like structures. Mostly all of the fish in the ocean are equipped with gills. As for invertebrates, many marine worms have gill like structures. As for other marine invertebrates, Echinoderms have thin walled gills that are extensions of body cavities. Sea cucumbers have respiratory trees and clams have gills that are aided by flagella. Some of these structures are much more efficeint than others. The more active the organism typically the more effiecnt the respiratory system is. Marine vertebrates typically have a set of structures that include an operculum, gill arches, filaments, and lamella. The operculum is the gill cover which provides protection. The lamella help with the diffusion of oxygen between water and blood.  

Figure 1. Red Eyed Tree Frog. Red Eyed Tree Frogs are very adapt climbers due to their sticky hands and feet. Their vibrant colors help them blend in with the color of the tropical rainforests. They feed on insects and live in trees. They also have strong hind legs which make them excellent leapers. They are found in Mexico and Central America. Photo by Ralph Earlandson https://farm8.staticflickr.com/7374/9754481823_b0114636a1_z_d.jpg.

A proposed study with subjects experiencing some degree of neuropathy may require a smaller sample size. This study did not have a supervised control group meaning that the exercise group received more face to face time with the investigators and they received information from a qualified physical education instructor. The study also did not include any resistance exercise and the subjects that were tested showed no signs or symptoms of DPN. Measured motor and sural sensory nerves using a Medelec MS 928 Neurostar. Measured the nerve conduction velocity as well as the nerve action potential amplitude. Vibration perception threshold was tested by using a Biothesiometer and the vibration amplitude was increased until the patient could feel it.

Today in comparitve physiology we learned about how different animals respire in various ways. Most animals in the water breathe via gills. Gills are not well designed for respiration in air, but there are a few terrestrial organisms which breath through gills. One of these organsims is the coconut crab. Gills are essentially lungs that are not invaginated into the body. Instead they project into the environmental medium. There are both external and internal gills. Internal gills have a protective coating over them. There are also different typed of lungs. One type of lungs are diffusion lungs which respire air via diffusion and ventilation liungs which respire via tidal flow of air.

Despite the study having many positive findings it is lacking many important aspects. These gaps are important to the study and can make it unreliable. First, there are no control subjects to compare the DPN subjects to (no non-diabetic subjects or diabetic subjects without DPN). Therefore it is not a randomized study with a placebo present. The participants are all older individuals with a wide range of diabetes duration (12.2 years). The authors also do not define what stage of neuropathy the patients are experiencing at any point in the study. Also, there is no specific regimen on what equipment is used for exercise training. Although it is a supervised exercise intervention, the subjects are allowed to choose from a variety of options and are only encouraged to utilize different equipment. A nerve conduction study is used to test conduction velocity, motor action potential, and amplitude, but no significant changes were found. Lastly, skin biopsies are used to test intraepidermal nerve fiber density and epidermal axon branching. 

Despite some of the positive findings in this study there were a few important gaps. There were no control subjects to compare the DPN subjects to (no non-diabetic subjects or diabetic subjects without DPN). Therefore it was not a randomized study and there was no placebo. The participants were all older individuals with a wide range of a duration of diabetes (12.2 years). They also did not define what stage of neuropathy the patients were experiencing. Also, there was no specific regimen on what equipment was used for exercise training. Although it was a supervised exercise intervention, the subjects were allowed to choose from a variety of options and were only encourages to utilize different equipment. Nerve conduction study was used to test conduction velocity, motor action potential, and amplitude but not significant changes were found. Lastly, skin biopsies were used to test intraepidermal nerve fiber density and epidermal axon branching. There was only a significant difference in nerve fiber branching at the proximal biopsy site.