Some curious facts about human body........

• Your heart beats around 100000 times a day, 36500000 times a year and over a billion times if you live beyond 30
• The lightest organ in the human body is the lung. Adult lungs have a surface area of around 70 square metres! 
• The brain uses over a quarter of the oxygen used by the human body
• Humans have a stage of sleep that features rapid eye movement (REM). REM sleep makes up around 25% of total sleep time and is often when you have your most vivid dreams
• The smallest bone found in the human body is located in the middle ear. The staples (or stirrup) bone is only 2.8 millimetres long
• Infants blink only once or twice a minute while adults average around 10
• As well as having unique fingerprints, humans also have unique tongue prints
• Your sense of smell is around 10000 times more sensitive than your sense of taste
• If you fully stretch your arms out, the fingertip to fingertip length is almost exactly your body height
• The length between your elbow and hand (forearm) equals the length of your foot
• Corneas are the only tissues that don't require blood.
• There's about 1.8m (6 feet) long DNA inside every cell nucleus in our body, and an average adult body contains around 50 trillion (million million) cells.
• The nails on long fingers grow faster than short fingers; and fingernails grow four times faster than toenails.
• The jaw is the strongest muscle in the human body in terms of exerting force.

How does blood circulate in the fetus?

Fetal circulation differs from circulation after birth because the lungs of the fetus are nonfunctional. Therefore, blood circulation essentially bypasses the lungs in the fetus. The umbilical vein carries oxygenated blood from the placenta to the fetus. About half of the blood from the umbilical vein enters the liver, while the rest of the blood bypasses the liver and enters the ductus venosus. The ductus venosus joins the inferior vena cava. Blood enters the right atrium of the heart and then flows through the foramen ovale to the left atrium. Blood then passes into the left ventricle (lower portion of the heart) and then to the aorta. From the aorta, blood is sent to the head and upper extremities. It returns to the right atrium of the heart through the superior vena cava. Some blood stays in the pulmonary trunk to reach the developing lung tissues.

Why is a man’s voice usually lower than a woman’s voice?

The pitch of the voice—how high or low it sounds—depends on the length, tension, and thickness of the vocal cords. Because males have longer vocal cords of up to 1 inch (2.54 centimeters) in length, the male voice is deeper in pitch, while women and children with shorter cords have higher-pitched voices. Vocal cords in women average 0.167 inches (0.42 centimeters) in length. Testosterone is the hormone that is responsible for the increase of length of male vocal cords during puberty.

Does your heart stop beating when you sneeze?

The heart does not stop beating when you sneeze. Sneezing, however, does affect the cardiovascular system. It causes a change in pressure inside the chest. This change in pressure affects the blood flow to the heart, which in turn affects the heart’s rhythm. Therefore, a sneeze does produce a harmless delay between one heartbeat and the next, often misinterpreted as a “skipped beat.”

How is the skin involved in the regulation of body temperature?

The skin is one of several organ systems participating in maintaining a core temperature, meaning the temperature near the center of someone’s body. Temperature sensors in the skin and internal organs monitor core temperature and transmit signals to the control center located in the hypothalamus, a region of the brain. When the core temperature falls below its set point, the hypothalamus: 1. Sends more nerve impulses to blood vessels in the skin that cause the vessels to narrow, which restricts blood flow to the skin, reducing heat loss. 2. Stimulates the skeletal muscles, causing brief bursts of muscular contraction, known as shivering, which generates heat. When the core temperature rises above its set point, the hypothalamus: 1. Sends fewer nerve impulses to blood vessels in the skin, causing them to dilate, which increases blood flow to the skin and promotes heat loss. 2. Activates the sweat glands, and when sweat evaporates off the skin surface it carries a large amount of body heat with it.

Is all the cartilage in the body the same?

There are three types of cartilage in the human body: 1) hyaline cartilage; 2) elastic cartilage; and 3)fibrocartilage. Hyaline cartilage (from the Greek hyalos, meaning “glass”) is the most common type of cartilage in the body. It has a translucent, pearly, blue-white appearance resembling glass. Hyaline cartilage provides stiff but flexible support and reduces friction between bony surfaces. It is found between the tips of the ribs and the bones of the sternum, at the end of the long bones, at the tip of the nose, and throughout the respiratory passages. Elastic cartilage is similar to hyaline cartilage except it is very flexible and resilient. It is ideal for areas that need repeated bending and stretching. Elastic cartilage forms the external flap of the outer ear and is found in the auditory canal and epiglottis. Fibrocartilage is often found where hyaline cartilage meets a ligament or tendon. It is found in the pads of the knees, between the pubic bones of the pelvis, and between the spinal vertebrae. It prevents bone-to-bone contact.

Cartilage does not contain blood vessels. Oxygen, nutrients, and cellular wastes diffuse through the selectively permeable matrix. Cartilage transplants are successful because foreign proteins in the transplanted cells do not have a way to enter the host body’s circulation and cause an immune response. However, since there are no blood vessels in cartilage, the healing process is slower than for other tissues

Which types of tissue have the greatest capacity to regenerate?

Epithelial and connective tissues have the greatest capacity to regenerate. In small wounds and injuries, the epithelial and connective tissues often heal with normal tissue. The ability of muscle tissue to regenerate is very limited. Fibrous connective tissue often replaces damaged muscle tissue. As a consequence, the organ involved loses all or part of its ability to function. Nerve tissue has even less capacity to regenerate. Although neurons outside the brain and spinal cord sometimes regenerate at a very slow pace, most brain and spinal cord injuries result in permanent damage.

What are the effects of Ageing on respiratory system?

There is a decline in the efficiency of the respiratory system with ageing. There is a gradual loss of elastic tissue & the chest wall becomes less capable of expansion. These changes show up as a reduction in vital capacity (The maximum volume of air that can be expired after a maximum inspiration). This may decrease by as much as 35% by the age of 70. All other aspects of function decline in performance notably, the action of cilia & protective activity of white blood cells. This leaves the system more prone to disease like pneumonia, bronchitis & emphysema.

How the Urinary tract infections are differentiating?

Urinary tract infections may occur in the urethra, where they are called urethritis; if they occur in the bladder, they are referred to as cystitis; and if they develop in the ureters, they are called ureteritis. Infection of the kidney is generally called pyelonephritis. In males, inflammation of the prostate gland, called prostatitis, often accompanies urinary tract infection. It often happens that blood infection with beta- hemolytic streptococci, Streptococcus pyogenes, leads to inflammation in the kidney. This inflammation is known as glomerulonephritis (also called Bright’s disease). The disease reflects an immune complex reaction resulting from activity of the immune system and type III hypersensitivity. Fever and high blood pressure accompany the disease.

What is rigor mortis?

Dead bodies are at first limp. Several hours after death, the skeletal muscles undergo a partial contraction that fixes the joints. This condition, known as rigor mortis, may continue for 72 hours or more. When neurons signal living muscle fibers to contract, they do so with a neurotransmitter that is received at the surface of the muscle fiber. The signal makes the fiber open calcium ion channels, and it is the calcium that causes the contraction. The muscle then removes the calcium in two ways: it stores some in its mitochondria, and it pumps out the rest. When a body dies, stored calcium leaks and calcium pumps no longer function. The excess calcium causes the actin and myosin filaments of the muscle fibers to remain linked, stiffening the whole body until the muscles begin to decompose.

How does the endocrine system differ from the nervous system?

Both the endocrine and nervous are regulatory systems that permit communication between cells, tissues, and organs. A major difference between the endocrine system and nervous system is the rate of response to a stimulus. In general, the nervous system responds to a stimulus very rapidly, often within a few milliseconds, while it may take the endocrine system seconds and sometimes hours or even days to offer a response. Furthermore, the chemical signals released by the nervous system typically act over very short distances (a synapse), while hormones in the endocrine system are generally carried by the blood to target organs. Finally, the effects of the nervous system generally last only a brief amount of time, while those of the endocrine system are longer lasting. Examples of endocrine control are growth and reproductive ability.

Which is the only bone that does not touch another bone?

The hyoid bone is the only bone that does not touch another bone. Located above the larynx, it supports the tongue and provides attachment sites for the muscles of the neck and pharynx used in speaking and swallowing. The hyoid is carefully examined when there is a suspicion of strangulation, since it is often fractured from such trauma.

Are smooth muscle contractions the same as skeletal muscle contractions?

There are similarities, as well as differences, in comparing smooth and skeletal muscle contractions. Both types of muscles include reactions involving actin and myosin, both are triggered by membrane impulses and an increase in intracellular calcium ions, and both use energy from ATP (adenosine triphosphate). One difference between smooth and skeletal muscle contractions is that smooth muscle is slower to contract and to relax than skeletal muscle. Smooth muscle can maintain a forceful contraction longer with a set amount of ATP. In addition, smooth muscle fibers can change length without changing tautness (as when the stomach is full), while this does not occur in skeletal muscles.

Which neurotransmitter is depleted in Parkinson’s disease?

Parkinson’s disease results from a deficiency of the neurotransmitter dopamine in certain brain neurons that regulate motor activity. Parkinson’s disease is characterized by stiff posture, tremors, slowness of movement, postural instability, and reduced spontaneity of facial expressions. There is no cure for Parkinson’s disease, but certain medications provide relief from the symptoms by increasing the amount of dopamine in the brain. Patients are usually given levodopa combined with carbidopa. Carbidopa delays the conversion of levodopa into dopamine until it reaches the brain. Nerve cells can use levodopa to make dopamine and replenish the brain’s dwindling supply.

Why is the blood-brain barrier important?

The blood-brain barrier is formed by the contacts of special glial cells, called astrocytes, with blood vessels. It is essential for maintaining homeostasis in the brain. In general, only lipid-soluble molecules, such as carbon dioxide, oxygen, steroids, and alcohols, can pass through the blood-brain barrier easily. Water-soluble molecules, such as sodium, potassium, and chloride ions can pass through the blood-brain barrier only with the assistance of specific carrier molecules. Some substances cannot pass through the barrier at all.

Do creatine supplements improve muscular performance?

Creatine phosphate (CP) is a molecule stored in muscle that yields energy when the creatine splits from the attached phosphate. This energy is used to resynthesize the small amount of ATP (adenosine triphosphate) that is available to the muscle in the initial seconds of high intensity work (think 100-yard dash or a power lift). Because greater amounts of CP in the muscle can potentially allow for those high intensity efforts to be sustained a bit longer or to be performed more effectively, creatine supplementation has become popular within the last 15 years. Some research indicates that such supplementation can improve performance in the short term and in high intensity activities, but for more sustained activities it has little or no effect because of the ATP’s great dependence on aerobic metabolism. The long-term effect of such supplementation on the human body is unknown.

Are there differences between the male and female skeletons?

Several general differences exist between the male and female skeletons. The male skeleton is generally larger and heavier than the female skeleton. The bones of the skull are generally more graceful and less angular in the female skeleton. A female also has a wider, shorter breastbone and slimmer wrists. There are significant differences between the pelvis of a female and a male, which are related to pregnancy and childbirth. The female pelvis is wider and shallower than the male pelvis. Females have an enlarged pelvic outlet and a wider, more circular pelvic inlet. The angle between the pubic bones is much sharper in males, resulting in a more circular, narrower, almost heart-shaped pelvis.

Is brain size an indication of intelligence? How the size changes from birth to adulthood?

There is no correlation between brain size and intelligence. Individuals with the smallest brains (as small as 46 cubic inches [750 cubic centimeters]) and the largest brains (as large as 128 cubic inches [2,100 cubic centimeters]) have the same functional intelligence.

Brain cells grow in size and degree of myelination as a child grows from birth to adulthood. Although the number of neurons does not increase after infancy, the number of glial cells does increase. An adult brain is approximately three times as heavy as it was at birth. Between ages 20 and 60, the brain loses approximately 0.033 to 0.10 ounces (1 to 3 grams) a year as neurons die and are not replaced. After age 60 the annual rate of shrinkage increases to 0.10 to 0.143 ounces (3 to 4 grams) per year.

Are cells in the nervous system replaced during an individual’s lifetime?

Neurons have a very limited capacity for regeneration. In general, they neither replicate themselves nor repair themselves. Axons and dendrites in the peripheral nervous system may undergo repair if the cell body is intact and if the Schwann cells are functional. In the central nervous system, however, a damaged or cut axon is usually not repaired even when the cell body is intact and undamaged. Scientists have discovered recently that there are a few small concentrations of neuronal stem cells that remain in adults that can produce a limited number of new neurons.