The amount of light entering the human eye is regulated by the diameter of the pupil. The pupil is the dark spot at the center of a healthy iris that, according to the National Institutes of Health, rests immediately in front of the eye's lens.
A:The amount of light entering the human eye is regulated by the diameter of the pupil. The pupil is the dark spot at the center of a healthy iris that, according to the National Institutes of Health, rests immediately in front of the eye's lens.
A:Caucasian babies are generally born with bluish-gray eyes, while babies of African-American or Asian descent usually have brown eyes at birth. Because the baby has just emerged from the dark, true eye color takes about a year to develop.
A:According to the New Health Guide Organization, the role the lungs play in the excretory system is to dispose of carbon dioxide through exhalation. This occurs when cells release carbon dioxide into the bloodstream. The blood then travels to the lungs where the carbon dioxide is transferred to the lungs.
A:The large and small intestines of the average adult human, when stretched, are only an average of 25 feet long and cannot stretch around the world. It would take the intestines of multiple humans to stretch the circumference of Earth.
A:Skin is considered an organ because it meets the definition of an organ, which is a group of related cells that combine together to perform one or more specific functions within the body. Skin performs several functions vital to the survival and health of the body, so deserves the label of organ.
A:According to About.com Biology, the corpus callosum connects the brain's two hemispheres. Innerbody.com reports that the corpus callosum is a broad arch that is divided into a curved front end called the genu and a backward-pointing portion called the rostrum, which tapers downward to connect with the lamina terminalis.
A:Humans lose between 30,000 and 40,000 skin cells every hour. During a 24-hour period, a person loses almost a million skin cells. The human body is made up of roughly 10 trillion cells in total, 1.6 trillion of which are skin cells.
A:Lymph nodes are tiny structures that help the body filter harmful and unhealthy substances, especially those that lead to infection. Cancer.org explains that each lymph node is packed with immune cells that help the body fight off infections by attacking germs carried to the nodes through lymph fluid.
A:The brain stem controls a number of basic bodily processes that are necessary for life. According to Brain-Guide.org, the brain stem functions as an autopilot for the human body, as it regulates such activities as breathing, digestion, heart rate, blood pressure and arousal. Additionally, the brain stem, which is located at the junction of the spinal cord, serves as a conduit through which information and instructions pass.
A:The upper epidermis, or stratum corneum, functions to protect the lower layers of skin and the tissues beneath from both physical and chemical damage. It is composed of plates made from dead skin cells, toughened against physical damage with protein envelopes, protected against chemicals with layers of special lipids, all held together by special protein bridges between the cells. While the protections the upper epidermis provides against direct damage are important, of perhaps even greater importance is its ability to block the entry of pathogenic organisms.
A:The University of Washington explains that the prefrontal cortex is responsible for activities that include problem solving, processing complex thoughts and causing emotions. The prefrontal cortex is located at the front of the brain, in the outer layer of structure called the cerebral cortex.
A:The human brain does not stop developing until around age 25. Parts of the brain that are involved in decision making do not fully develop until that age. However, female brains typically develop around two years earlier than male brains.
A:Dreams are controlled by a part of the brain called the cerebral cortex. During REM sleep, signals sent from another part of the brain, the pons, are relayed through the thalamus to the cerebral cortex, and it is the cerebral cortex's attempts to make sense of these signals that causes dreaming.
A:The part of the ear that contains the sensory organs for hearing and balance is the inner ear, says the American Speech-Language-Hearing Association. The cochlea is the inner ear’s hearing part, while the semicircular canals are part of the balance system.
A:Neuroscientists suggest that the brain is always firing or using its cells, the neurons, to perform functions. Over the course of a normal day, most people use all of their brain capacity. Previous myths stated that humans only used 10 percent of their brains.
A:The tears that keep the eyes moist are produced by the conjuctiva, while the tears produced by crying come from the lachrymal glands located in the eyelids. According to Moment of Science, the chemical composition of tears from the lachrymal glands leads to puffiness in the eyelids.
A:According to Scientific American, kids can hear sounds above about 16 Hz, which are difficult or impossible for adults to hear. As humans age, presbycusis or age related hearing frequency loss begins, starting at around age 18 in most individuals and continuing throughout life.