Digestive System

Week of April 30th 2009 we are covering the digestive system. The alimentary canal (GI tract) extends from the mouth to the anus. 6 processes of the digestive system: ingestion, secretion, mix and propel, digestion, absorption and defecation. GI tract has 4 layers: 1. Mucosa-the inner most layer which is avascular. Compromised of simple columnar epithelial cells. 2. Submucosa-highly vascular, may contain glands and lymphatic tissue and is composed of areolar connective tissue. An extensive network of neurons known as the submucosal plexus is found in this layer. 3. Muscularis-consists of circular, long and oblique fibers and is smooth muscle. The myenteric plexus, a network of axons that branch from the Vagus nerve X, are found between the layers of the muscularis. Peristalsis, wave like contractions, occur in this layer. 4. Serosa-portions of the GI tract suspended in the abdominopelvic cavity. Secretes a slippery, watery fluid that allows the tract to slide against other organs. Serosa is composed of simple squamous epithelium and areolar connective tissue and is part of the visceral peritoneum. There is a mechanical and chemical digestion that occurs. By way of peristaltic movements food is mixed in the stomach (mixing bag), these contractions allow the contact with HCl(hydrochloric acid). Specialized parietal cells, located in the mucosa, are plentiful with the enzyme carbonic anhydrase, this enzyme catalyzes the formation of carbonic acid,H2CO3, from water, H2O, and carbon dioxide, CO2. As it dissociates it provides a source of the H+ for proton pumps and generates the bicarbonate ions, HCO3, which after it builds up in the cytosol, will exchange for Cl- in the exchanger. Pumps powered by ATP actively transport H+ and K+ into the lumen of the stomach from the mucosa. The K+ will diffuse back into the mucosa while the H+ will free float in the lumen, at the same time Cl - will diffuse through Cl channels in to the lumen and free float in the lumen. The free floating H+ and Cl- bind HCl. Chief Cells, located in the mucosa, secrete pepsinogen, which is inactive so it will not digest the proteins in the chief cells that produced it. Once the pepsinogen comes in contact with HCl in the gastric fluids it converts to active pepsin which break apart big proteins making them smaller fragments.
Many family members included myself are taking medication to reduce stomach acids. I take Pepcid AC daily. Pepcid AC works by blocking a specific histamine receptor in the stomach. In the stomach histamine can cause the production of more acid, Pepcid AC reduces the amount of acid produced.

Blood

The average adult male and pregnant females have 6 liters of blood, the average non pregnant female has 5 liters. Blood consists of Red Blood Cells(RBC), White Blood Cells(WBC), and Platelets. RBC’s transport oxygen atoms. The cycle of a RBC is 90-120 days. There are 5 categories of White Blood cells (WBC) aka Leukocytes: Neutrophils whose function is phagocytosis, make up 60-70% of all WBC’s, lymphocytes whose function mediate immune response make up 20-25% of all WBC’s, monocytes function is macrophage, they make up 3-8% of all WBC’s, eosinophils function is the combat the effects of histamine in allergic reactions and destroy certain parasitic worms they make up 2-4% of all WBC’s, and basophils which liberate heparin, histamine, and serotonin in allergic reactions, they make up .5-1% of all WBC’s. The WBC’s that end in -phil have granules in the cytoplasma, these granules are histamine. WBC’s that end in -cytes do not have granules. Platelets are cell fragments that live for 5-9days and they release chemicals that promote blood clotting. RBC’s and platelets do not have a nucleus, WBC’s have nucleus which may be multilobed, bilobed, round or kidney shaped.
Blood tests are used to determine how organs with in the body are functioning. Diabetes is monitored by the levels of glucose in the blood. I think of the bloodstream as a super highway in the human blood. This superhighway is transporting the gases essential to live, and it transports nutrients needed to sustain homeostasis.

Adrenal Cortex Layers

The 3 layers of the Adrenal Cortex are: zona glomerulosa, zona fasciculate, and the zona reticularis. Zona glomerulosa is the superficial layer. It primarily produces alderstone. Alderstone is a steroidal hormone that helps increase the volume of fluid in the body. The increase of fluid will increase the blood pressure. Zona fasciculate is the middle layer. It primarily produces cortisone. Cortisone is a immune suppressant. Prolonged stress will cause cortisone to increase and therefore the immune system will lower. Cortisone is non polar therefore it will not moving easily through the body. The zona reticularis is the deepest layer. It produces androgens. Androgens are steroidal hormones that aid in the development of masculine characteristics. The most well known androgen is testosterone, which is the male sex hormone. Androgens are also the precursor for estrogen, the female sex hormone. Cholesterol is the base for synthesis of these hormones produced in the adrenal cortex.
Upon researching cholesterol further to find out which foods are better for a person to consume. Animal fats have lower cholesterol and more triglycerides which may contribute to heart disease. Human breast milk has a high level of cholesterol and vegetables do not have any unless it is prepared with something that contains cholesterol. Limiting trans fats can help lower the risk of plaque build up in the walls of arteries.

The Eyeball

There are 3 layers to the eyeball: the sclera-the outer most layer, which is also known as the fibrous tunic, the choroid-the middle layer, which is also know as the pigmented tunic, and the retina-the inner layer, which also known as the visual tunic. The sclera is the white of the eye and is vascular. It is white in color because of collagen and is a continuous with the dura mater. The sclera is covered by a thin membrane called conjunctiva, the conjunctiva also lines inside of the eyelid. The choroid layer lies between the sclera and the retina. It is vascular and provides oxygen and nourishment to the retina. The retina is avascular. Light hitting the retina triggers nerve impulses which are sent to the brain via fibers of the optic nerve. Photoreceptors of the retina are rod cells-perceive light, and cone cells-perceive color. The Central fovea, a small indentation in the macula of the retina, is where cones are most concentrated and the area of most acute vision.
The eye has always been a wonder to me. Thanks to world of contacts I do not have to wear extremely heavy akward glasses. I was diagnosed with cataracts about 2 years ago. Cataracts are a clouding of the lens of the eye because of a build up of deposits. It is caused by a number of things-age, injury, congenital. I come from a long line of eye diseases and poor vision. I keep reading new ways that they treat this disease. From the advice of my Optometrist I look for the alternatives to laser surgery. I have thin corneas and he has advised that laser surgery would be dangerous. We are trying to hold off as long as possible before having the intraocular lens implanted because of my age and the likelihood of cataracts reoccurring. According to the Spokane Eye Clinic the cataract surgery has a 90% success rate of the patient recovering at least some of the lost vision. My optometrist says I should have vision in an eye that has never had anything other than a few shadows.

Spinal nerves within the Vertebral Column

There are 31 pairs of spinal nerves. They consist of 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves 5 pairs of sacral nerves and 1 coccyxgeal nerve. The spinal cord passes through the vertebral foramen, it comes to an end at the conus medullaris. The filum terminale comes off the end of the conus medullaris and is a anchoring strip of fibrous tissue that attaches the spinal cord to the interior surface of the pelvic girdle. The dura mater of the spinal cord has only 1 layer unlike the dura mater of the brain that has 2 layers, the periosteal and the meningeal. The gray matter, cell bodies of the neurons, in the brain is superficial where in the spinal cord it is deep and its counterpart the white matter, mostly myelinated axons, is superficial in the spinal cord and deep in the brain.
This relates to everyday living by giving us the map of the nerves through the spinal column. Understanding which nerve controls what muscles gives me a better concept of how injuries to certain parts of the spinal cord causes parylsis.

The Peripheral Nervous System

We had Brad Haskell for lecture. We learned that the spinal cord ends at L2 region of the vertebral column. Plexuses are a weaving or braiding of a nerve and the nerves that come off from it. The principal plexuses are cervical, brachial, lumbar, and sacral plexuses. The sciatic nerve is the longest and thickest nerve in the body. Phrenic nerve controls the diaphragm injury to C5 can be life threatening. We reviewed the cranial nerve names and a few of he foramen. We went over the central canal of the spinal column.
This relates to every day living for any human being because if some reason there is an injury or the neurons misfire it effects the way our bodies work. The sensory nerves have to get the impulse to the brain in order for an impulse to be sent to the motor nerves for movement to happen.

The Brain

Meninges are the 3 wrappings around the brain. 1. The outer most layer is the Dura Mater that consists of major blood vessels. The Dura Mater is 2 layers thick around the brain, inner called the Meningeal and outer called the Periosteal, and 1 layer thick around the spinal cord. 2. Arachnoid Mater is the middle most layer there are no blood vessels in this layer, CSF is located here. 3. Pia Mater is the inner most layer that contains capillary network. We are also working on the Circulatory Pathways. Venous Pathway or Venous drainage and the Arterial Pathway. Venous drainage, CSF drains from the Superior Sagittal Sinus through the Confluence of Sinuses (point where straight sinus, s sagittal sinus, & occiptal sinus meet) then to the transverse sinuses on to the sigmoid sinuses and into the 2 internal jugular veins. Arterial Pathway, oxygen rich blood from the left side of the heart is carried to the left Atrium it then reaches the left Ventricle via the Bicuspid valve, from the left Ventricle it travels through the Semilunas valve (Aortic valve) into the Ascending Aorta to the Aortic Arch. In the Aortic Arch it goes to the right Subclavian artery and right Common Carotid artery via the Brachiocephalic, the left Common Caroid artery which feeds the Circle of Willis, and to the left Subclavian artery. It also travels out the descending Aorta to suppply blood to the Thoracic and Abdomen.
We receive many patients that have suffered strokes and or blood clots to areas of their bodies. DVT's (deep vein thrombosis) are common with our elderly. I was once involved with a code on a patient that was having a Pulmonary Emblosism, I knew it was a blood clot that had traveled to the lungs but I did not understand it completely until I started to get more in detail with this weeks study of the Circulatory pathway of blood and CSF. That same patient also had a history of strokes.