What structure of the eye produces tears?

The lachrymal gland, which is part of the larger lachrymal apparatus, produces tears that flow over the anterior surface of the eye. Most of this fluid evaporates, but excess amounts are collected in small ducts in the corner of the eye. Tears lubricate and cleanse the eye. In addition, tears contain lysozyme, an enzyme that is capable of destroying certain kinds of bacteria and helps fight eye infections.

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.

What hormone can be used to overcome jet lag?

Jet lag occurs when an individual’s biological clock is out of sync with local time. As a general rule it takes about a day for each hour of time zone change to recover from jet lag. Melatonin, available as a dietary supplement, is sometimes used to induce sleep when traveling. It is more useful when traveling east and may be taken before, during, or after traveling. It is best taken approximately five to seven hours before the usual bedtime in the old time zone. Travelers should consult their physicians before using melatonin. It is not recommended for pregnant or breast-feeding women and children.

How eye produces tears?

The lachrymal gland, which is part of the larger lachrymal apparatus, produces tears that flow over the anterior surface of the eye. Most of this fluid evaporates, but excess amounts are collected in small ducts in the corner of the eye. Tears lubricate and cleanse the eye. In addition, tears contain lysozyme, an enzyme that is capable of destroying certain kinds of bacteria and helps fight eye infections

What is the auditory tube and its function?

The auditory tube (Eustachian tube) connects each middle ear to the throat. This tube conducts air between the tympanic cavity and the outside of the body by way of the throat and mouth. It also helps maintain equal air pressure on both sides of the eardrum, which is necessary for normal hearing. The function of the auditory tube can be experienced during rapid change in altitude. As a person moves from a high altitude to a lower one, the air pressure on the outside of the membrane becomes greater and greater. As a result, the eardrum may be pushed inward, out of its normal position, and hearing may be impaired. When the air pressure difference is great enough, some air may force its way up through the auditory tube into the middle ear. This allows the pressure on both sides of the eardrum to equalize, and the drum moves back to its regular position. An individual usually hears a popping sound at this time, and normal hearing is restored. A reverse movement of air occurs when a person moves from a low altitude to a higher one.

What is cerumen?

Cerumen is an oily, fatty substance produced by the ceruminous glands in the outer portion of the ear canal. This compound is commonly referred to as ear wax and, together with hairs in the auditory canal, helps prevent foreign objects from reaching the delicate eardrum. Dust, dirt, bacteria, fungi, and other foreign dangers to the body all stick to the wax and do not enter the ear. Ear wax also contains a special enzyme, lysozyme, which breaks down the cell walls of bacteria. In most individuals, the ear canal is self-cleansing and there is no need to remove ear wax. However, ear wax may be impacted due to poor attempts at cleaning the ear. In such cases, the impacted ear wax should be removed by a healthcare professional.

Are body planes important for identifying anatomical structure?

In order to observe and study the structural arrangement of the internal organs, the body may be divided and sectioned (or cut) along three fundamental planes. These planes are the midsagittal (median) plane, the coronal (frontal) plane, and the transverse (horizontal) plane. The midsagittal plane divides the body lengthwise into right and left sides. A sagittal section placed off-center divides the body into asymmetrical right and left sides. The coronal plane divides the body into front (anterior) and back (posterior) sections. The transverse plane divides the body into upper (superior) and lower (inferior) sections. It is at right angles to the sagittal and frontal planes.

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.

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

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 do bones grow?

Bones form and develop through a process called ossification. There are two types of ossification: intramembranous ossification and endochondral ossification. Intramembranous ossification is the formation of bone directly on or within the fibrous connective tissue. Examples of bone formed through intramembranous ossification are the flat bones of the skull, mandible (lower jaw), and clavicle (collarbone). Endochondral ossification, from the Greek endo, meaning “within,” and khondros, meaning “cartilage,” is the transformation of the cartilage model into bone. Cartilage cells in the epiphyseal plate grow and move into the metaphysis where they are reabsorbed and replaced by bone tissue. Examples of bone formed through endochondral ossification are the long bones, such as the femur and humerus.

Which structures of the body have more bones for their size than any other part of the body?

The wrist and the hand have more bones in them for their size than any other part of the body. There are 8 carpals in the wrist between the forearm and the palm of the hand; 5 metacarpal bones that form the palm of the hand between the wrist, thumb, and fingers; and 14 phalanges or finger bones. The presence of many small bones in the wrist and hand with the many movable joints between them makes the human hand highly maneuverable and mobile.

Why is there a “popping” sound when you crack your knuckles, and is it dangerous to crack them?

A number of reasons have been given for the characteristic “popping” sound associated with someone cracking their knuckles. One reason is that when a joint is contracted, small ligaments or muscles may pull tight and snap across the bony protuberances of the joint. Another possibility is that when the joint is pulled apart, air can pop out from between the bones, creating a vacuum that produces a popping sound. A third reason, discovered by British scientists in 1971, is that when the pressure of the synovial fluid is reduced by the slow articulation of a joint tiny gas bubbles in the fluid may burst, producing the popping sound. Research has not shown any connection between knuckle cracking and arthritis. One study found that knuckle cracking may be the cause of soft tissue damage to the joint capsule and a decrease in grip strength. The rapid, repeated stretching of the ligaments surrounding the joint is most likely the cause of damage to the soft tissue. Some researchers believe that since the bones of the hand are not fully ossified until approximately age 18, children and teenager who crack their knuckles may deform and enlarge the knuckle bones. However, most researchers believe knuckle cracking does not cause serious joint damage.

Why is a woman’s voice usually higher than a man’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.

Why is it dangerous to talk while eating?

If a person talks while eating, food may be inhaled into the lungs. Normally, after food is swallowed, it passes into the pharynx and then into the esophagus. Food is prevented from entering the larynx (the passageway to the lungs) by the epiglottis, a spade-shaped cartilage flap that covers the pharynx. If food does enter the larynx, a cough reflex is usually initiated, although food may lodge in the larynx, causing a blockage of the airway.

Distinguish among the terms stimulus, sensation, and perception

A stimulus is an energy source (chemical, pressure, light wave, etc.) that activates a receptor cell (specialized nerve cell) to transmit a nerve impulse, or sensation. If the sensation arrives in the conscious part of the brain, the cerebral cortex, a perception occurs. Perception is awareness of the stimulus.Pricking one’s finger, for example, is a stimulus that activates many receptor cells to send nerve impulses
to the brain. Once these sensations reach the cerebral cortex, a person perceives (feels) pain.