Red Blood Cell Formation and Destruction

Red blood cells live approximately 120 days and then die and then pieces are recycled. Since red blood cells dispose of their nucleus while a reticulocyte and have no organelles, the RBCs cannot repair themselves or undergo mitosis. This is not inhibitory to their function, however, since their main job is to transport oxygen. Red blood cells are very efficient at this job since they produce ATP anaerobically and thus do not use oxygen in this process. RBC's bind or hold an oxygen molecule to each Iron which is at the center of each porphyrine ring (part of the hemoglobin molecule).

RBC's are phagosized in either the spleen, liver or red bone marrow. The RBC is first most broken down by macrophages into globin and heme. The globin is further broken down into amino acids and are reused for protein synthesis. The iron in the heme is then transported in the blood by a transport protein called transferrin, to the red bone marrow, where it binds to the transferritin and is stored (until used as part of Erythropoiesis). The rest of the heme is converted into biliverdin and then biliruben, enters the blood stream and travels to the liver. It is then secreted into the small intestine as bile. While in the small and large intestines, bile helps to break down large fat molecules. In the large intestine the bilirubin is converted by bacteria into urobilinogen. Some of this is converted into urobilin in the kidney and leaves the body as urine. Most of the urobilinogen is excreted in feces in the form of stercobilin.

I think the most worrisome part of this process for me is that there are some many players or places in this process where things can go awry and cause major problems for the body. And, if the body already has a disease or disorder that effects any of these elements, it becomes an even more compounded problem for the body, bringing it further and further from homeostasis. It seems like there are some naturally built in back-up systems to prepare in a way for such events. For example, if the body is suffering from liver disease and has lost some of its functioning, the macrophages can still phagosize RBCs in the spleen or red bone marrow. The liver however is still engaged in other parts of the process and I am not sure how the body adapts to this malfunction. The disfunction of one part or player in the process produces a domino effect on the rest of process, which, if I understand correctly, continues beyond just this process, effecting possibly many other processes and systems.

2nd Messanger Systems- cAMP

This messenger system begins with a hormone such as GH binding to a membrane bound receptor. Since the hormone is a protein the binding event causes a shape change in the receptor, which causes a shape change in the G-Protein complex. The G-Protein complex includes alpha, beta and gamma units, as well as an attached GDP, a low energy molecule. This shape change causes the G-Protein complex to remove the attached GDP and allows a molecule of GTP to bind. The alpha subunit and attached GTP then break away and bind to the Adenylate Cyclase. This then induces a shape change in the AC. A molecule of ATP is then recruited to the AC and is adapted into cAMP by the removal of 2 of its phosphates. It is now a 2nd messenger. The cAMP then binds to a PKA causing a shape change in the PKA which changes ATP into ADP leaving a phosphate attached to the PKA. The PKA is now able to transfer a phosphate to key enzymes. For example, in the case of GH, enzymes need the phosphate for mitosis.

Because I have a family member with liver cancer, I am interested in liver function and health. We learned that transfer proteins, specifically Albumin, transport steroidal hormones to target cells so that they can perform their function. I do not know if my family member has a low or high albumin count but I decided to read on-line to get some more information. I learned that in general, serum proteins are divided into two major categories, albumin and globulin and that the globulin can be broken down into 4 subdivisions. A general blood panel will test for the total protein, albumin. globulin and albumin/globulin ratio. I reviewed the causes for high and low amounts on all categories and it seems as if liver disfunction can cause it all. Total proteins may be increased due to liver disfunction or they may be lower than normal due to liver disease. The only category that liver disfunction did not seem to cause a change was in an increase in albumin. I did learn one interesting fact. Albumin levels can be used as strong predictors of health. Low levels of albumin suggests very poor health and a "predictor of bad outcome".

Pituitary Gland

The pituitary gland is divided into the posterior and anterior sections. The posterior pituitary releases the hormones oxytocin and ADH (Anti diuetic), however, it does not produce these hormones. The hormones are actually made in the hypothalamus and travel through a neuronal tract to the posterior pituitary gland, where it is released into the blood stream. Oxytocin stimulates mammery glands for milk secretion and stimulates the uterus for uterine contractions during child birth. ADH stimulates thirst and as a result less urine is produced to help rehydrate the body.

The Anterior Pituitary is composed of epithelial tissue and produces several different hormones. Growth hormone, prolactin and melanocyte-stimulating hormone work to stimulate a target organ directly. The others, Thyroid-stimulating hormone, ACTH, and Gonadotropin (FSH and LH) secrete hormones to effect other hormones which then stimulate a target organ or tissue. For example, Thyroid-stimulating hormone stimulates the Thyroid, triggering the release of Thyroxin, which regulates metabolic rate.

Many people in my family (including sibling and both parents) have hypothyroidism and so I decided to research this condition on-line. I learned that the disorder is a result of low levels of the hormones produced by the Thyroid gland, mostly, T3 and T4 and since most T4 is converted into T3 in the blood, this is the hormone of interest. The job of T3 is to regulate the metabolism of cells. The releases of thyroid hormones is regulated by a negative feedback system involving the hypothalamus, the pituitary gland and then the thyroid. The hypothalamus relases Thyrotropin releasing hormone which triggers the release of Thyroid-Stimulating hormone from the Pituitary Gland, which in turn sends a signal for the Thyroid gland to release its hormones. A disruption in any of these levels can result in a low production of Thyroid hormones.

The most common cause of this disorder is Hoshimoto's Thyroiditis Disease, an inherited disease, marked by an enlarged Thyroid gland that has difficulty producing its hormones. It is an autoimmune disease in which the body attacks the tissue of the gland. Other causes include a severe iodine difficiency or medications. Some medications used to treat hyperthyroidism actually have a dramatic effect by causing hypothyroidism. The treatment includes taking synthetic T-4 for the length of life of the patient. T4 is used instead of T3 because it effect is longer lasting and is converted into T3 easily.