The circulatory system delivers vital oxygen to the tissues in the body and carries wastes from the tissues to be excreted. The cycle of blood circulation begins in the heart. The heart pumps blood through the lungs to fill up with oxygen. From the lungs, oxygen-rich blood returns to the heart to be pumped out to the tissues. After delivery of oxygen the tissues, blood collects wastes (e.g.: carbon dioxide) from the tissues. Oxygen depleted blood, containing wastes, returns to the heart once again to be pumped to the lungs to rid itself of carbon dioxide while simultaneously acquiring more oxygen.
If your pet experiences heart problems, you may notice: coughing, exercise intolerance, pale gum color, cold extremities, weakness, lethargy, collapse, poor appetite, and/or labored breathing.
Common abnormalities of the heart include:
- Inability to effectively pump blood through the body as is seen with heart failure.
- Electrical disturbances within the heart. The heart possesses an entire electrical system to activate the heart muscle to pump blood. If there is a block in the circuit or an abnormal circuit develops, the heart cannot pump effectively. Examples include: atrial fibrillation and ventricular tachycardia.
- Incorrect plumbing pathways through the heart cause pumped blood to travel in uncoordinated directions. Some heart and blood vessel malformations develop in utero, before birth (e.g.: Patent Ductus Arteriosis, PDA and Subaortic Stenosis, SAS), while others develop as your pet ages (e.g.: Mitral Valve Insufficiency, MVI).
- Heart muscle abnormalities, known as cardiomyopathies.
- Heartworm infection
Blood, although a liquid, is a tissue: it is filled with cells. Blood carries red blood cells to deliver oxygen and white blood cells to ward off infection. The water portion of blood surrounding the cells contains nutrients, proteins, and hormones that are essential for life. Your pet may experience deficiencies and/or excesses of any of these blood components, leading to disease.
Nestled next to the kidneys are the adrenal glands. The adrenal glands develop from two distinct tissue types to form one organ. The outer portion (cortex) originates from glandular tissue, while the inner portion (medulla) originates from nerve tissue. These distinct layers also reflect different functions: 1) the cortex secretes sex hormones (e.g.: estrogens and androgens) and hormones that regulate salt (e.g.: aldosterone) and sugar (e.g.: cortisol) metabolism and 2) the medulla is under neurologic control releasing adrenaline during the “fight or flight” response. Adrenal gland abnormalities develop when there are excesses or deficiencies of any of these hormones. Treatment for deficiencies focuses on restoration of normal hormone levels by hormone replacement therapy. Excess hormone levels may be treated medically; rare cases require surgery to remove the affected adrenal gland to restore normal hormone levels
What makes your dog’s heart tick? A dog’s four-chambered heart is a complex, synchronized network of electrical circuits that weaves through the cardiac muscle. The heart is the pump at the center of the circulatory system. This system delivers vital oxygen to the tissues in the body and carries wastes from the tissues back to the lungs to be exhaled. Problems within the circulatory system may involve abnormal: 1)blood flow (heard as a murmur), as in congenital defects and valve degeneration; 2) heart muscle function, termed cardiomyopathies; and 3) electrical signals in the heart muscle (e.g.: ventricular tachycardia), causing uncoordinated contractions of the heart. Indications that your dog may have a heart problem include: coughing, exercise intolerance, cold extremities, weakness, collapse, and/or changes in breathing patterns.
Scattered throughout the body are numerous lymph nodes. The lymph nodes are immune centers that help to fight infection. When your veterinarian examines your pet, multiple lymph nodes will be felt to assess for normal size and texture. Enlarged lymph nodes can be caused by infections (viral, bacterial, and fungal), inflammation, and tumors. If your veterinarian finds an enlarged lymph node, a small sample of the lymph node can be aspirated and evaluated under the microscope. Under the microscope, inflammatory processes can be distinguished from cancer. Occasionally, lymph nodes need to be biopsied if the aspirate sample is not conclusive.
The thyroid glands rest on each side of the neck. These small glands secrete thyroid hormone to regulate the body’s metabolism. An excess of this hormone increases the metabolic rate (hyperthyroidism), while a deficiency slows down the metabolic rate (hypothyroidism). Hypothyroidism is much more common in dogs; hyperthyroidism is rare and often associated with thyroid cancer. Hypothyroidism tends to develop in middle aged dogs; certain breeds are predisposed (e.g.: Golden Retrievers, Doberman Pinschers). Symptoms of hypothyroidism demonstrate a declining metabolic rate: decreased energy level, weight gain. Other symptoms involve the skin: thinning of the hair coat, dry skin, skin infections, and ear infections. Treatment of hypothyroidism is simple: lifelong oral thyroid hormone supplementation. Dogs treated with thyroid hormone replacement live normal, active lives.
The tonsils lie within folds of tissue (crypts) on either side of the throat. The tonsils perform immune functions, helping to fight infection in the head region. Tonsillitis refers to inflammation of the tonsils; however, it does not refer to a specific cause. Anything that causes inflammation and/or infection in the head region may cause activation and enlargement of the tonsils. Tonsillitis rarely occurs without an underlying cause such as viral, bacterial, and fungal infections, tumors, chronic cough, and periodontal disease.
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