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.

Autonomic Nervous System, Part II

All Autonomic impulses are afferent, meaning that they travel from the CNS to the PNS. The ANS can be broken down into two major divisions, the Parasympathetic and the Sympathetic divisions. The Parasympathetic division is responsible for all of the feed-and-breed or rest-and-digest functions of the body and is the restorer of homeostasis. The preganglionic axon is long and the post ganglionic axon is short. The Sympathetic division can be seen as the parasympathetic divisions opposite. The Sympathetic division carries out the fight-or-flight responses in our body. In this division, the preganglionic axon is shot and the post ganglionic axon is long. In both divisions, the target cells are smooth muscle, cardiac muscle and glands. Another commonality is that all preganglionic neurons release Ach and all receptors on the post ganglionic neurons are thus nicotinic.

There are two different categories of receptors for the ANS. Cholinergeric, which includes both Nicotinic and Muscarinic receptors and Adrenergic receptors. Nicotinic receptors always cause excitation or activation and perform as both the receptor and channel. They also only bind Ach. Muscarinic receptors can either cause excitation of inhibition and use either a PKA pathway or a PKC pathway to allow chemicals to enter the neuron. Both pathways utilize G-Proteins. Adrenergic receptors also utilize these pathways and are broken down into a1, a2, b1, b2, b3 receptors. The 1's refer to impulses that cause constriction or contraction and the 2's refer to impulses that cause dilation. B3 is the odd man out and its impulse causes heat production. Muscarinic and Adrenergic receptors are found on the cells of terminal targets.

I understood from lecture that the Adrenal gland, a gland that sits on top of the kidneys, is part of the sympathetic nervous system. This gland produces both epinephrine and norepinepherine by diffusing the hormones into the blood stream. This direct link into the blood stream allows for a fast regulation of the hormone throughout the body. That was as much as I was able to retain from lecture, so I researched a little more on the Internet. I learned that adrenal medulla is the central core of the Adrenal gland. The neurons within it (called Chromaffin cells) produce the hormones that are released into the blood stream instead of producing an impulse as all of the other neurons that we have learned about do. These hormones aid in the fight-or-flight response by increasing blood pressure, metabolic rate and or glucose concentration. The neurons in the Adrenal Medulla also produce dopamine, which low-levels of this hormone has been linked to Parkinson's diseases.

Automonic Nervous System

There are two motor neurons in an autonomic motor pathway. The first neuron is called a preganglionic neuron and its cell body is located in the brain or spinal chord. Its axon (very long) leaves the CNS and extends (as part of a spinal or cranial nerve) to an autonomic ganglion. The second neuron is called the post ganglionic neuron and its axon is short. The preganglionic neurons pass along nerve impulses from the CNS to the autonomic ganglia and the postganglionic neurons relay the impulse from the autonomic ganglia to the terminal target, which could be smooth muscle, cardiac muscle or a gland. The neurotransmitter that is released is always excitatory and is always Ach. The #2 neuron always produces an action potential. Wether the terminal target becomes excited depends on its receptors. They are usually cholinergeric and thus are either Nicotinic (excitatory) or muscarinic (inhibitory).

After browsing the internet, I learned that a malfunction in the autonimic system is called autonomic failure and is a result of the imbalance between the sympathetic and parasympathetic divisions of the autonomic nervous system. Signs that there is an imbalance include orthostatic hypotension and postprandial hypotension. These can cause dizzyness or lightheadedness. Elderly people are most likely to suffer from this condition and the drop in blood pressure is usually a result of the onset of a disease (diabetes, stroke) and the medications that are used to treat them. There is no cure for autonomic disorders, however there are medications that can treat the low blood pressure and the uncomfortableness that accompanies the episodes.

The Thalamus and Hypothalamus

All incoming sensory information from periphery is relayed through the thalamus to an appropriate higher processing center. The Thalamus is segregated into several regions each pertaining to its nuclei and associated functions. The Anterior Group is part of the limbic system, the regulator of emotion. The Medial Group integrates sensory information and relays it to the frontal lobes. The Ventral Group is responsible for passing along information from the basal nuclei of the cerebrum and the cerebellum to the somatic motor areas of the cerebral cortex. It also passes along sensory information to the sensory areas of the cerebral cortex. The Posterior Group includes the Pulvinar, and the lateral and medial geniculate nuclei. The function of the Pulvinar is to process sensory information for projection to the cerebral cortex. The lateral geniculate nucleus passes along visual information to the visual cortex and the medial geniculate nuclei passes along auditory information to the auditory cortex. Lastly, the lateral group processes sensory information as well as effects emotional states.

I am particularly intrigued by mood disorders and the effect they have on the brain. I have a relative with Bi-Polar disorder and although I know what the definition is and how it is treated, I did not really understand physiologically how Bi-Polar Disorder interrupts normal brain activity. I learned that through structural imaging studies, scientist have found a decrease in overall brain volume in patients with Bi-Polar Disorder. They believe that this is in part due to the decreased number of neurons and glial cells in layers II and III (are they referring to the meninges?) in the forebrain. They also know that the frontal and temporal lobes, the pre-frontal cortex, basal ganlia and parts of the limbic system are all involved and effected by this disorder. Some scientist also believe that since the cerebral cortex is responsible for some thought process that it may also be involved in the negative thinking that are part of the negative episodes of the disorder. Some websites offered that it was an excess of neurotransmitters that causes the manic episodes and a decrease in neurotransmitters that causes the depressive episodes, while other websites claimed that it was not the amount of neurotransmitters but the "effectiveness of the cell's functioning" that was to blame.

Ion channels

We learned that there are two different types of ion channels: chemically regulated and voltage regulated. Chemically Regulated Ion Channels open when a Neurotransmitter binds to a receptor in the membrane of the cell. and allow a chemical, such as a Na+ to pass through the membrane. In the case of Ach, the receptor is also the channel. These channels are much slower and much more controlled compared to voltage regulated channels. This is due to the need for each channel to be opened separately when a NT binds to a receptor instead of the gate/door effect for voltage channels. It is more of a trickle than a flood. Voltage Regulated Ion Channels are activated when a certain voltage threshold is reached and then all gates/doors are open and a surge of charge is released.

The topic that intrigued me the most during the lecture was the possibility of using an inhibitor drug to decrease stimulation or sensory information in patients who are hypersensitive to stimuli. At least for those who do not have triggers and for whom continual sensory overload is a problem. My brother is one of these people. He does not have certain tones or sensations that bother him, instead it is the multitude of sensory information that seems to attack him and gets worse in crowded rooms and such. It is though his brain does not have a filter. If it can work for schizophrenics why can't it work for PDD and autistic patients with this problem? Well, I googled and found no answers to my questions. I found sites discussing the use of inhibitors for heart failure and schizophrenia but nothing about its use for sensory integration. I think it is a problem of me knowing just enough to be dangerous.