Types of bone marrow.
The two types of bone marrow are "red marrow" (Latin: medulla ossium rubra), which consists mainly ofhematopoietic tissue, and "yellow marrow" (Latin: medulla ossium flava), which is mainly made up of fat cells. Red blood cells, platelets, and most white blood cells arise in red marrow. Both types of bone marrow contain numerous blood vessels and capillaries. At birth, all bone marrow is red. With age, more and more of it is converted to the yellow type; only around half of adult bone marrow is red. Red marrow is found mainly in the flat bones, such as thepelvis, sternum, cranium, ribs, vertebrae and scapulae, and in the cancellous ("spongy") material at the epiphysealends of long bones such as the femur and humerus. Yellow marrow is found in the medullary cavity, the hollow interior of the middle portion of short bones. In cases of severe blood loss, the body can convert yellow marrow back to red marrow to increase blood cell production.
The pituitary gland
The pituitary glands are made of the anterior lobe and posterior lobe. The anterior lobe produces and releases hormones. The posterior lobe does not produce hormones per se—this is done by nerve cells in the hypothalamus—but it does release them into the circulation.
Hormones of the Pituitary Gland
The hormones of the pituitary gland send signals to other endocrine glands to stimulate or inhibit their own hormone production. For example, the anterior pituitary lobe will release adrenocorticotropic hormone (ACTH) to stimulate cortisol production in the adrenal glands when you’re stressed.
The anterior lobe releases hormones upon receiving releasing or inhibiting hormones from the hypothalamus. These hypothalamic hormones tell the anterior lobe whether to release more of a specific hormone or stop production of the hormone.
Anterior Lobe Hormones:
Adrenocorticotropic hormone (ACTH): ACTH stimulates the adrenal glands to produce hormones.
Follicle-stimulating hormone (FSH): FSH works with LH to ensure normal functioning of the ovaries and testes.
Growth hormone (GH): GH is essential in early years to maintaining a healthy body composition and for growth in children. In adults, it aids healthy bone and muscle mass and affects fat distribution.
Luteinizing hormone (LH): LH works with FSH to ensure normal functioning of the ovaries and testes.
Prolactin: Prolactin stimulates breast milk production.
Thyroid-stimulating hormone (TSH): TSH stimulates the thyroid gland to produce hormones.
The posterior lobe contains the ends of nerve cells coming from the hypothalamus. The hypothalamus sends hormones directly to the posterior lobe via these nerves, and then the pituitary gland releases them.
Posterior Lobe Hormones:
Anti-diuretic hormone (ADH): This hormone prompts the kidneys to increase water absorption in the blood.
Oxytocin: Oxytocin is involved in a variety of processes, such as contracting the uterus during childbirth and stimulating breast milk production.
Diseases and Disorders of the Pituitary Gland
Pituitary tumors are the most common pituitary disorder, and many adults have them. However, they are not, in the great majority of cases, life threatening. But that doesn’t mean they’re harmless—pituitary tumors can disrupt the gland’s normal ability to release hormones.
There are two types of pituitary tumors—secretory and non-secretory. Secretory tumors secrete too much of a hormone, and non-secretory tumors don’t secrete excess hormone.
These hormonal imbalances can cause problems in many different areas of the body. If you have a secretory tumor that is overproducing thyroid-stimulating hormone, for instance, you will experience hyperthyroidism.
Another pituitary disorder is known as pituitary apoplexy. In some cases, pituitary function can be suddenly disrupted (due to bleeding or trauma), creating a life-threatening shortage of vital hormones.
Pericardium
The pericardium is a tough double layered fibroserous sac which covers the heart. The space between the two layers of serous pericardium the pericardial cavity, is filled with serous fluid . There are two layers to the pericardial sac: the outermost fibrous pericardium and the inner serous pericardium.
Fibrous pericardium
The fibrous pericardium is the most superficial layer of the pericardium, preventing it from overfilling with blood.
Serous pericardium
The serous pericardium is divided into two layers, the parietal pericardium, which is fused to and inseparable from the fibrous pericardium, and the visceral pericardium, which is part of the epicardium. Both of these layers function in lubricating the heart to prevent friction during heart activity.
In between the parietal and visceral pericardial layers there is a potential space called the pericardial cavity, which contains a supply of lubricating serous fluid known as the pericardial fluid.
When the visceral layer comes into contact with heart it is known as the epicardium. The epicardium is the layer immediately outside of the heart muscle proper (the myocardium). The epicardium is largely made of connective tissue and functions as a protective layer.
