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Showing posts from December, 2011

Regulation of body temperature

The thermostat for body temperature is located in the hypothalamus. When the body temperature falls below normal, the posterior hypothalamic sympathetic centre directs via nerve impulses the blood vessels of the skin to constrict. This conserves heat.  Sympathetic stimulation also causes piloerection i.e. hair to stand erect and trap a layer of air that act as an insulator. However, this does not play a great role in humans. If body temperature falls even lower, the regulatory centre sends nerve impulses to the skeletal muscles, and shivering occurs. Shivering generates heat, and gradually body temperature rises to 37°C. Metabolic systems are also activated to produce more heat. When the temperature rises to normal, the regulatory centre is inactivated. When the body temperature is higher than normal, the regulatory centre directs the blood vessels of the skin to dilate. This allows more blood to flow near the surface of the body, where heat can be lost to the environmen

Skin - structure

The skin is sometimes called the cutaneous membrane or the integument. It has 2 regions notably the epidermis and the dermis. The hypodermis is a subcutaneous tissue and is found between the dermis and any underlying structure like muscles.  Epidermis It is the outer and thinner layer of the skin.  It is made up of stratified squamous epithelium divided into several layers; the deepest layer is the stratum basale, and the most superficial layer is the stratum corneum. The deepest layer is constantly producing new cells and pushing them to the surface. The stratum corneum, on the other hand, gets keratinised to form a waterproof layer and also acts as a mechanical barrier.  Dermis It is a thicker and denser region than the epidermis. It is composed of dense and irregular connective tissues. Its upper layer has structures called as dermal papillae that project into the epidermis to cause ridges. These form unique patterns and give the characteristic fingerprint to all indi

Subcutaneous injection - Insulin / Heparin

Definition: It is defined as the introduction of a fluid drug under pressure using a syringe equipped with a hollow needle into the loose connective tissue below the dermis i.e. into the hypodermis. It has a low absorption there because of the low vascularisation but since it contains pain receptors, injection can be painful depending on the volume administered. For structure of skin, consider this page :  Skin structure Sites: 1) outer sides of arm, 2) front of upper outer thigh, 3) above and below the spine of scapula, 4) abdomen extending from the costal margin to the iliac crest except 5 cm all around the umbilicus. Angle of insertion of needle: 1) 90 degrees with a short needle, 2) 45 degrees with a longer needle. Techniques: 1) Pinch skin slightly to make 3 cm fold, 2) Insert needle quickly and firmly, 3) Release skin, 4) Aspirate and make sure that needle is not in a vessel, 5) Remove needle by gentle pressure with antiseptic swab, 6) Massage

Allergy symptoms more at start of season

Recent studies have found that allergic people tend to have more symptoms at the beginning of the season. This is regardless of the medications taken. The following are the proposed explanations: 1) Sufferers get used to the symptoms and are therefore not bothered by them. So they did not report the symptoms. 2) Allergen-specific regulatory T cells may down regulate the inflammatory response after high exposure to the pollen at the beginning of the season. 3) Pollen at the later part of the season are less allergenic.


Erythropoiesis refers to the formation of erythrocytes. Tissue oxygenation is the most essential regulator for this continuous process. Thus conditions like anemia, high altitudes, pulmonary disorders or heart failure cause tissue hypoxia. As a result of this, erythropoietin (EPO) is released from kidneys. It is glycoprotein in nature and 90% of it is produced in the kidneys. The remaining 10% is produced in the liver. This is why in cases where the kidneys have been removed or damaged by diseases, anemia results. The hypoxic sensor is believed to be the high oxygen-consuming renal tubular cells. If the hypoxic blood is unable to deliver enough oxygen from the peritubular capillaries, then the renal tubular epithelial cells are thought to release the erythropoietin. There may also be a non renal sensor because at times localised hypoxia elsewhere in the body can also lead to erythropoietin secretion. The effect of EPO is that it stimulates the production of proerythroblasts from

Post MI - wait how much before elective surgery

After a myocardial infarction, the longer we wait, the better it is to decrease the risk of post operative attack. But unfortunately we cannot delay the surgery indefinitely. We have to balance the risk for a post-op heart attack versus the risk of delaying the surgery. Studies have shown that for: 1) 0-30 days, risk is around 33%, 2) 31-60 days, risk is around 19%, 3) 61-90 days, risk is around 8% and 4) 92-180 days, risk is around 6%. So waiting for at least 2 months after an M.I decreases the risk for post-op heart attack.

CSF rhinorrhea - Double-ring sign / ring sign / halo sign

The double-ring test is clearly shown in this photo. It is also known as the ring sign or halo sign. The patient was brought following an injury to the head and was bleeding moderately from the nose but the blood was more watery than normal. CSF rhinorrhea was suspected. The dextrose stick test was positive to the sample and when placed on a filter paper, we got an inner ring of blood and a halo, followed by an outer ring of CSF. Though this has been a classical medical test, it is not 100% reliable.

Battle sign / Battle's sign

Battle sign refers to the post auricular ecchymosis that occurs following trauma to the middle cranial fossa of the skull. It may indicate underlying brain trauma. The picture above shows one patient who came to the emergencies few hours after the head injury while in the one below it, patient was brought in a confused state few days after trauma to his head. The sign was named after William Henry Battle, who was a English professor of surgery and pathology.