The Structure of the Skin

Skin layers:

1. epidermis

2. dermis

3. subcutis

showing a

a. hair follicle

b. sweat gland

c. sebaceous gland

The skin consists of an outer, protective layer (epidermis) and an inner, living layer (dermis). The top layer of the epidermis is composed of dead cells containing keratin, the horny scleroprotein that also makes up hair and nails.

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The SKIN

In zootomy and dermatology, skin is the largest organ of the integumentary system made up of multiple layers of epithelial tissues that guard underlying muscles and organs.Skin pigmentation varies among populations, and skin type can range from dry skin to oily skin.

The adjective cutaneous literally means "of the skin" (from Latin cutis, skin).
Because it interfaces with the environment, skin plays a very important role in protecting (the body) against pathogens. Its other functions are insulation, temperature regulation, sensation, synthesis of vitamin D, and the protection of vitamin B folates.
Severely damaged skin will try to heal by forming scar tissue. This is often discolored and depigmented

The skin is an organ of double-layered tissue stretched over the surface of the body and protecting it from drying or losing fluid, from harmful external substances, and from extremes of temperature. The inner layer, called the dermis, contains sweat glands, blood vessels, nerve endings (sense receptors), and the bases of hair and nails. The outer layer, the epidermis, is only a few cells thick; it contains pigments, pores, and ducts, and its surface is made of dead cells that it sheds from the body. (Hair and nails are adaptations arising from the dead cells.) The sweat glands excrete waste and cool the body through evaporation of fluid droplets; the blood vessels of the dermis supplement temperature regulation by contracting to preserve body heat and expanding to dissipate it. Separate kinds of receptors convey pressure, temperature, and pain. Fat cells in the dermis insulate the body, and oil glands lubricate the epidermis.
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The Male Organ

The organs of the male reproductive system enable a man to have sexual intercourse and to fertilize female sex cells (eggs) with sperm. The gonads, called testicles, produce sperm. Sperm pass through a long duct called the vas deferens to the seminal vesicles, a pair of sacs that lies behind the bladder. These sacs produce seminal fluid, which mixes with sperm to produce semen. Semen leaves the seminal vesicles and travels through the prostate gland, which produces additional secretions that are added to semen. During male orgasm the penis ejaculates semen.

The Reproductive System

The human male reproductive system is a series of organs located outside of the body and around the pelvic region of a male that contribute towards the reproductive process.
The male contributes to reproduction by producing spermatozoa. The spermatozoa then fertilize the egg in the female body and the fertilized egg (zygote) gradually develops into a fetus, which is later born as a child

Reproduction is accomplished by the union of male sperm and the female ovum. In coitus, the male organ ejaculates more than 250 million sperm into the vagina, from which some make their way to the uterus. Ovulation, the release of an egg into the uterus, occurs approximately every 28 days; during the same period the uterus is prepared for the implantation of a fertilized ovum by the action of estrogens. If a male cell fails to unite with a female cell, other hormones cause the uterine wall to slough off during menstruation. From puberty to menopause, the process of ovulation, and preparation, and menstruation is repeated monthly except for periods of pregnancy. The duration of pregnancy is about 280 days. After childbirth, prolactin, a hormone secreted by the pituitary, activates the production of milk.
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The Pituitary Gland

The pituitary gland, or hypophysis, (from Greek hupophuein, to grow up beneath) is an endocrine gland about the size of a pea. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity (sella turcica) covered by a dural fold (diaphragma sellae).

The pituitary fossa, in which the pituitary gland sits, is situated in the sphenoid bone in the middle cranial fossa at the base of the brain.

The pituitary gland secretes hormones regulating homeostasis, including trophic hormones that stimulate other endocrine glands. It is functionally connected to the hypothalamus by the median eminence.

The hypophysis is also the top cell of the suspensor in a dicot embryo, which will differentiate to form part of the root cap.

Called the master gland, the pituitary secretes hormones that control the activity of other endocrine glands and regulate various biological processes. Its secretions include growth hormone.
a. (which stimulates cellular activity in bone, cartilage, and other structural tissue); thyroid

stimulating hormone
b. (which causes the thyroid to release metabolism-regulating hormones); antidiuretic hormone
c. (which causes the kidney to excrete less water in the urine); and prolactin
d. (which stimulates milk production and breast development in females).
The pituitary gland is influenced both neurally and hormonally by the hypothalamus.

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The Endocrine System

The endocrine system is an integrated system of small organs that involve the release of extracellular signaling molecules known as hormones. The endocrine system is instrumental in regulating metabolism, growth, development and puberty, tissue function, and also plays a part in determining mood. The field of medicine that deals with disorders of endocrine glands is endocrinology, a branch of the wider field of internal medicine.
In addition to the integrative action of the nervous system, control of various body functions is exerted by the endocrine glands. An important part of this system, the pituitary, lies at the base of the brain.

This master gland secretes a variety of hormones, including the following:
(1) a hormone that stimulates the thyroid gland and controls its secretion of thyroxine, which dictates the rate at which all cells utilize oxygen;
(2) a hormone that controls the secretion in the adrenal gland of hormones that influence
the metabolism of carbohydrates, sodium, and potassium and control the rate at which substances are exchanged between blood and tissue fluid;
(3) substances that control the secretion in the ovaries of estrogen and progesterone
and the creation in the testicles of testosterone;
(4) the somatotropic, or growth, hormone, which controls the rate of development of
the skeleton and large interior organs through its effect on the metabolism of
proteins and carbohydrates;
(5) an insulin inhibitor—a lack of insulin causes diabetes mellitus.

The posterior lobe of the pituitary secretes vasopressin, which acts on the kidney to control the volume of urine; a lack of vasopressin causes diabetes insipidus, which results in the passing of large volumes of urine.
The posterior lobe also elaborates oxytocin, which causes contraction of smooth muscle in the intestines and small arteries and is used to bring about contractions of the uterus in childbirth.

Other glands in the endocrine system are the pancreas, which secretes insulin, and the parathyroid, which secretes a hormone that regulates the quantity of calcium and phosphorus in the blood.
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The Stomach

Located on the left side of the body, under the diaphragm, the stomach is a muscular, saclike organ that connects the esophagus and small intestine. Its main function is to break down food. Cells in the stomach lining secrete enzymes, hydrochloric acid, and other chemicals to continue the digestive process begun in the mouth and produce mucus to keep these substances from digesting the lining itself.

The Digestive and Excretory System

Digestion is the breaking down of food in the body, into a form that can be absorbed and used or excreted. It is also the process by which the body breaks down food into smaller components that can be absorbed by the blood stream. In mammals, preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to break down starches. The stomach continues to break food down mechanically and chemically through the churning of the stomach and mixing with enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with excretion

The excretory system is an organ system that performs the function of excretion, the bodily process of discharging nitrogeneous wastes. It is responsible for the elimination of the nitrogeneous waste products of metabolism as well as other non-useful nitrogeneous materials. The main components of the excretory system are your two kidneys, two tubes that carry urine called ureters, the bladder, and the urethra.

The energy required for maintenance and proper functioning of the human body is supplied by food. After it is broken into fragments by chewing (see Teeth) and mixed with saliva, digestion begins. The food passes down the gullet into the stomach, where the process is continued by the gastric and intestinal juices. Thereafter, the mixture of food and secretions, called chyme, is pushed down the alimentary canal by peristalsis, rhythmic contractions of the smooth muscle of the gastrointestinal system.

The contractions are initiated by the parasympathetic nervous system; such muscular activity can be inhibited by the sympathetic nervous system. Absorption of nutrients from chyme occurs mainly in the small intestine; unabsorbed food and secretions and waste substances from the liver pass to the large intestines and are expelled as feces. Water and water-soluble substances travel via the bloodstream from the intestines to the kidneys, which absorb all the constituents of the blood plasma except its proteins. The kidneys return most of the water and salts to the body, while excreting other salts and waste products, along with excess water, as urine.
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The Human Lungs

Human Lungs Air travels to the lungs though a series of tubes and airways. The two branches of the trachea, called bronchi, subdivide within the lobes into smaller and smaller air vessels. They terminate in alveoli, tiny air sacs surrounded by capillaries. When the alveoli inflate with inhaled air, oxygen diffuses into the blood in the capillaries to be pumped by the heart to the tissues of the body, and carbon dioxide diffuses out of the blood into the lungs, where it is exhaled.

The Respiratory System

In humans and other mammals, the respiratory system consists of the airways, the lungs, and the respiratory muscles that mediate the movement of air into and out of the body. Within the alveolar system of the lungs, molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous environment and the blood. Thus, the respiratory system facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation. The system also helps to maintain the acid-base balance of the body through the efficient removal of carbon dioxide from the blood.

Respiration is carried on by the expansion and contraction of the lungs; the process and the rate at which it proceeds are controlled by a nervous center in the brain.
In the lungs, oxygen enters tiny capillaries, where it combines with hemoglobin in the red blood cells and is carried to the tissues. Simultaneously, carbon dioxide, which entered the blood in its passages through the tissues, passes through capillaries into the air contained within the lungs. Inhaling draws into the lungs air that is higher in oxygen and lower in carbon dioxide; exhaling forces from the lungs air that is high in carbon dioxide and low in oxygen. Changes in the size and gross capacity of the chest are controlled by contractions of the diaphragm and of the muscles between the ribs.

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The Immune System

A scanning electron microscope image (photo)

single neutrophil (yellow)

engulfing anthrax bacteria (orange).

An immune system is a collection of mechanisms within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function properly. Detection is complicated as pathogens adapt and evolve new ways to successfully infect the host organism.

To survive this challenge, multiple mechanisms evolved that recognize and neutralize pathogens. Even simple unicellular organisms such as bacteria possess enzyme systems that protect against viral infections. Other basic immune mechanisms evolved in ancient eukaryotes and remain in their modern descendants, such as plants, fish, reptiles, and insects. These mechanisms include antimicrobial peptides called defensins, phagocytosis, and the complement system. More sophisticated mechanisms, however, developed relatively recently, with the evolution of vertebrates.

The immune systems of vertebrates such as humans consist of many types of proteins, cells, organs, and tissues, which interact in an elaborate and dynamic network. As part of this more complex immune response, the vertebrate system adapts over time to recognize particular pathogens more efficiently. The adaptation process creates immunological memories and allows even more effective protection during future encounters with these pathogens. This process of acquired immunity is the basis of vaccination.

Disorders in the immune system can result in disease. Immunodeficiency diseases occur when the immune system is less active than normal, resulting in recurring and life-threatening infections. Immunodeficiency can either be the result of a genetic disease, such as severe combined immunodeficiency, or be produced by pharmaceuticals or an infection, such as the acquired immune deficiency syndrome (AIDS) that is caused by the retrovirus HIV. In contrast, autoimmune diseases result from a hyperactive immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include rheumatoid arthritis, diabetes mellitus type 1 and lupus erythematosus. These critical roles of immunology in health and disease are areas of intense scientific study.

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The NERVOUS System Organization

The Peripheral Nervous System
1.) Sensory Neurons-(Afferent)
2.) Motor Neurons-(efferent)
2a. Autonomic nervous system
2b. Somatic nervous system
b1.) Sympathetic nervous system
b2.) Parasympathetic Nervous system

The Central Nervous System
a.) Brain
b.) Spinal Cord