Wednesday, April 28, 2010

Thyroid Hormone, Thyroid Stimulating Hormone, and More...

I am particularly interested in the thyroid gland, since I have been diagnosed with hypothyroidism, which means my body is not making enough thyroid hormone. In Anatomy & Physiology, we have identified the thyroid gland on various models in lab, and we have also learned about the physiology of the thyroid gland. I am surprised to find out that many people I talk to are either being treated for hypothyroidism, or think they have it, so I thought I would share what I know here.

The first picture is a model of the larynx. The thyroid gland is the big yellow blob in the lower left corner of the picture. The second picture is the neck and chest of a torso model. The thyroid gland is the big yellow blob attached to the larynx!



Hormones made by the Thyroid Gland
Calcitonin works with Parathyroid Hormone (which is made by the Parathyroid Glands) to regulate calcium in the bloodstream and calcium in the bones. Calcitonin stimulates osteoblasts (causing bone formation by increasing calcium in the bone matrix and removing calcium from the bloodstream). In other words, irregular levels of these hormones could lead to osteoporosis.

What about other hormones made by the thyroid gland?
At the microscopic level, the thyroid gland has Thyroid Follicles surrounded by Follicular Cells. The Follicular Cells make Triiodothyronine (T3) and Tetraiodothyronine, also known as Thyroxine (T4). Together these 2 hormones are referred to as “Thyroid Hormone”.

These thyroid hormones are mainly regulated by Thyroid Stimulating Hormone (TSH), which is produced at the Anterior Pituitary Gland. In my case, my TSH was recently at 6.69, which is considered elevated. According to Medline, normal TSH values are .4 to 4.0. If your TSH is high, it means your thyroid hormones are low. Your doctor may prescribe a synthetic thyroid hormone known as Synthroid, which I had a bad reaction to, or a natural (but less used) thyroid hormone known as Armour Thyroid.

What do increases in “Thyroid Hormone” cause?
1. Nervous System – Increases activity and necessary also for proper fetal development of the nervous system (also necessary after birth for normal nervous system)

2. Skeletal System – Promotes normal bone growth while growing in height AND promotes remodeling of bone after a fracture or as a result of change in weight, etc.

3. Cardiovascular System - Increases Heart Rate, Force of contraction of cardiac muscle and blood pressure

4. Respiratory System – Increases respiratory rate and depth of respiration

5. Increases Metabolic Rate – Increases heat production AND Increases rate of catabolism of carbohydrates, proteins and lipids

Tuesday, April 13, 2010

Patent Foramen Ovale & Fetal Circulation

When my mom was in the hospital for four months, after having an ischemic stroke that blocked blood flow to the right side of her brain, I kept hearing doctors say things about the reasons for my mom’s stroke—things like, “she has a PFO.” I had no idea what this term meant, but I later found out that PFO stands for “patent foramen ovale.” It’s a hole between the right and left atrium in the heart, which allows blood to bypass the lungs during fetal development. The foramen ovale is supposed to close on its own at birth, when the baby begins to breathe on her own, but in 20% of the population, the hole never closes, resulting in a patent foramen ovale, a hole between the atria of the heart. Since it can be hereditary, doctors recommended that my sisters and I be evaluated for a PFO. A transthoracic echocardiogram with a bubble study confirmed that I do have a PFO, and neither of my sisters do. There is no treatment and usually no symptoms, although doctors suspect that a PFO can allow blood to pool and form clots, and therefore increase the risk of stroke.

Our method of studying this in A&P involved text and a couple heart models in lab (our class is pretty much devoid of technology), but as I suspected, a search of “fetal circulation” on YouTube reveals many creative approaches to understanding fetal circulation and the changes that occur at birth. The foramen ovale is supposed to close at birth and be replaced by a flap of tissue called the fossa ovalis. And there are several other unique characteristics of fetal circulation similar to the foramen ovale, such as the ductus arteriosus, which allows blood to bypass the lungs by shunting blood from the pulmonary trunk to the aorta, and on to systemic circulation. When the ductus arteriosus closes at birth, it becomes the ligamentum arteriosum. These videos also discuss the umbilical vein, ductus venosus, and the umbilical arteries.

The following YouTube clips show fetal circulation in a creative and interesting way. I think it also says a lot for how audio and images can be paired with text to demonstrate a process or complex concepts in ways that are easy to understand. These are relatively simple projects that involve still images and audio, and no actual video footage. It’s exciting to see that some educators are taking advantage of technology-based assignments that students will enjoy much more than sitting idly in a lab and identifying numbers on plastic models. These projects would also help students learn about processes and how different parts of anatomy are related, rather than just focusing on identification and rote memorization. Do you think my A&P teacher would be offended if I sent her links to these YouTube videos?! Probably.