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Wednesday, October 15, 2008

HEART

The human embryonic heart begins beating around 21 days after conception, or five weeks after the last normal menstrual period (LMP), which is the date normally used to date pregnancy. It is unknown how blood in the human embryo circulates for the first 21 days in the absence of a functioning heart. The human heart begins beating at a rate near the mother’s, about 75-80 beats per minute (BPM). The embryonic heart rate (EHR) then accelerates linearly for the first month of beating, peaking at 165-185 BPM during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, an increase of 100 BPM in the first month.[3] After peaking at about 9.2 weeks after the LMP, it decelerates to about 152 BPM (+/-25 BPM) during the 15th week after the LMP. After the 15th week the deceleration slows reaching an average rate of about 145 (+/-25 BPM) BPM at term. The regression formula which describes this acceleration before the embryo reaches 25 mm in crown-rump length or 9.2 LMP weeks is Age in days = EHR(0.3)+6 There is no difference in male and female heart rates before birth.[4
At 21 days after conception, the human heart begins beating at 70 to 80 beats per minute and accelerates linearly for the first month of beating.

The heart is a muscular organ in all vertebrates responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods. The HEART beats about 72 times a minute. 100,000 times a day.

The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BC. However their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for transport of air. Philosophers distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Erasistratos observed that arteries that were cut during life bleed. He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood that entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood. The 2nd century AD, Greek physician Galenos (Galen) knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves. Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through 'pores' in the inter ventricular septum, air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created 'sooty' vapors were created and passed to the lungs also via the pulmonary artery to be exhaled.

HUMAN HEART WITH CORONARY ARTERIES

The muscular organ which propels the body throughout the body. The human heart lies in the thoracic or chest cavity, between the lungs. it is roughly conical in shape, about 5 inch. long, weighs 9 to 11 oz. This organ is enclosed in a protective sac called the pericardium. A thin lubricating fluid secreted between the pericardium and the heart's surface facilitates the beating of the heart within its enclosure. An impermeable fibrous partition divides the heart into two parts, each of which contains two chambers, an auricles and passes through valves into the ventricles, which force it into the arteries. the cardiac cycle consists of

(1) simultaneous contraction of both auricle

(2) simultaneous contraction of both ventricle

(3) a period of relaxation.

The first two are known as systole, the third one as diastole.The heart muscle is of the involuntary type, ie., not under control of the will. Heart action is regulated by two sets of nerves, one acting to inhibit, the other to accelerate its beating.

HEART REMOVED FROM A 64 year-old MALE: In humans, the function of the right side of the heart (see right heart) is to collect de-oxygenated blood, in the right atrium, from the body and pump it, via the right ventricle, into the lungs (pulmonary circulation) so that carbon dioxide can be dropped off and oxygen picked up (gas exchange). This happens through the passive process of diffusion. The left side (see left heart) collects oxygenated blood from the lungs into the left atrium. From the left atrium the blood moves to the left ventricle which pumps it out to the body. On both sides, the lower ventricles are thicker and stronger than the upper atria. The muscle wall surrounding the left ventricle is thicker than the wall surrounding the right ventricle due to the higher force needed to pump the blood through the systemic circulation. Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. Here it is pumped out the pulmonary semilunar valve and travels through the pulmonary artery to the lungs. From there, blood flows back through the pulmonary vein to the left atrium. It then travels through the mitral valve to the left ventricle, from where it is pumped through the aortic semilunar valve to the aorta. The aorta forks, and the blood is divided between major arteries which supply the upper and lower body. The blood travels in the arteries to the smaller arterioles, then finally to the tiny capillaries which feed each cell. The (relatively) deoxygenated blood then travels to the venules, which coalesce into veins, then to the inferior and superior venae cavae and finally back to the right atrium where the process began. The heart is effectively a syncytium, a meshwork of cardiac muscle cells interconnected by contiguous cytoplasmic bridges. This relates to electrical stimulation of one cell spreading to neighboring cells.












HUMAN HEART
The heart is one of the critical organs of an animal's body, as it pumps oxygenated blood to feed the body's biological functions. The cessation of the heartbeat, referred to as cardiac arrest, is a critical emergency. Without intervention, death can occur within minutes of cardiac arrest since the brain requires a continuous supply of oxygen and cannot survive for long if that supply is cut off.








HEART
Electrical innervation of the heart in health is supplied by two closely intertwined mechanisms. The first mechanism is well demonstrated in electrical coil systole (interpreted by the electrocardiogram as QRS) as an individualized myocardial electrical tree initiated by the sinoatrial node. Secondary diastolic electrical control is posited to represent autonomic recoil control from the vagus nerve and cardiac branches and the thoracic ganglia.




Posted by Bryan @ 3:23 PM 0 comments
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URINE

URINE
Low specific gravity of urine may be merely a temporary condition, the result of drinking large quantities of water or other liquids shortly before voiding the sample of urine submitted for examination. when more water is taken than the system requires, the excess is promptly excreted by the kidneys. the habit of drinking water freely may be beneficial for some persons, but it is not advisable as a steady practice. It throws extra work upon the heart and kidneys.the chemical and microscopic examination of urine of low specific gravity is not a fair test of condition of the kidneys.. Therefore, if you have been notified that a sample you submitted for laboratory examination had low specific gravity, an additional specimen should be taken. by restriction of liquids or water for several hours before voiding, your urine will become more concentrated and usually show a higher specific gravity.Persistent low specific gravity of the urine, not due to excessive water drinking, is not a normal condition and usually indicates a chronic form of kidney trouble or hardening of the arteries which occurs usually in very old people. such a condition should be investigated by your physician in order to determine the exact cause.
Posted by Bryan @ 3:19 PM 0 comments
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