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Human Organ Systems
Nervous SystemThe nervous system is composed of the brain, spinal cord, nerves, and sensory organs. It's main function is to coordination the body's activities, detect all stimuli and form responses to them. The brain is the control center of the the nervous system. Human Brain The Central Nervous System is made up of the brain and spinal cord. The spinal cord transports sensory and motor information from other parts of the body to the brain.
The brain only weighs 3 pounds, but is composed of more than 12
billion neurons and 50 billion supporting glial cells. With the spinal
cord, the brain monitors and regulates many unconscious bodily processes
such as heart rate and breathing, and coordinates most voluntary
movements. Most important, it is the site of consciousness and of all
the intellectual functions that allow humans to think and create.
The brain produces electrical signals, which, together with chemical reactions, let the parts of the body communicate. Nerves send these signals throughout the body. The Nerve Cell
Each neuron consists of a nucleus situated in the cell body, where outgrowths called processes originate from. The main one of these processes is the axon, which is responsible for carrying outgoing messages from the cell. This axon can originate from the central nervous system (CNS) and extend all the way to the body's extremities, providing an efficient highway for messages. Dendrites are smaller secondary processes that grow from the cell body and axon. On the end of these dendrites lie the axon terminals, which plug into a cell where the electrical signal from a nerve cell to the target cell can be made. This 'plug' (the axon terminal) connects into a receptor on the target cell and can transmit information between cells. The Autonomic Nervous System is divided into 3 parts:
Spinal Cord Vertebrae
Skeletal System
The skeletal system consists of the bones, tendons, ligaments, and cartilage. It's main function is to support the body and provide protection for the internal organs.
Muscular System
The muscular system consists of skeletal muscles. These muscles attach to the skeleton and provide movement and locomotion. There are 3 main types of muscle tissue as you will see listed below. Muscle Tissue
Integumentary SystemHair, Skin, and Nails
The integumentary system consists of the skin and its derivatives; hair and nails. This system is the body's first line of defense against foreign invaders and protects against mechanical injury, infection (disease) and also prevents the inner organs from drying out by retaining body fluids. Your skin also plays an important role to eliminate waste products, regulate body temperature and protects the body from harmful ultraviolet rays from the sun. Everyone, young and old, should minimize exposure to the sun and protect themselves from Ultraviolet Radiation. UVA and UVB rays damage the DNA in skin cells and can lead to deadly forms of skin cancer (Melanoma Carcinoma). Sun exposure increases the fine lines on skin, known as wrinkles, and accelerates the timeline of the aging process. Prevention is easily achieved by limiting the amount of time you are exposed to UV rays and by using products that help prevent exposure to UVA and UVB rays. With this said, it is understandable why it is important to take care of your skin! Secretions from the sebaceous and sweat glands maintain the pH on the skin's surface at the pH of about 3 to 5. This acidic surface keeps many invaders from making a home on your skin. Your body's natural flora of bacteria have adapted to this acidic surface.
Digestive System
The digestive system begins at the mouth and ends at the anus. Consists of mouth, pharynx, esophagus, stomach, intestines, liver, pancreas, and anus. The main function of the digestive system is to process food through ingestion through the mouth, digestion, in the stomach, absorption of water and nutrients in the intestines, and elimination through the anus. Larynx
Anterior Posterior
Gallbladder
Excretory System
The excretory system is responsible for the disposal of metabolic wastes and the regulation of osmotic balance of the blood. This organ system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys are bean shaped and lie in the superior lumbar region of the posterior abdominal wall. The right kidney is crowded by the liver and is slightly inferior to the left kidney. The average kidney is about the size of a large bar of soap. The convex portion of the kidney shown in the photograph is called the lateral portion. The concave portion is called the renal hilus. This is where the renal artery, renal vein and renal pelvis leave the kidney. The smaller image displays the kidneys, adrenal gland (superior to kidney) which is part of the endocrine system, the inferior vena cava, aorta, ureter, and urinary bladder. The kidneys filer waste particles from the blood and send toxins, excess water, and metabolic wastes out of the body in the form of urine, while the useful substances from the filtrate are sent back into the blood. The three nitrogenous compounds that are eliminated from the body are urea, uric acid and creatinine. Eliminating wastes is only one job of the kidneys, they also regulate the volume and chemical makeup of the blood by maintaining equilibrium between acids and bases and between water and salts.
Respiratory System
The respiratory system consists of the lungs, trachea, and other breathing tubes. It main function is gas exchange; simply put, the uptake of oxygen and the disposal or removal of carbon dioxide. When you breath in you inhale the oxygen that the lungs need to re-supply red blood cells with oxygen, which is then transported to the rest of the body. When you breath out or exhale, you are getting rid of the carbon dioxide that the body is trying to eliminate. The respiratory system works in conjunction with the circulatory system.
Image: Encyclopaedia Britannica, 2008
Circulatory System
The circulatory system consists of the heart, blood vessels and blood. It's main function is to distribute materials throughout the body.
Blood is a connective tissue, the ground substance is plasma, and the blood cells are called formed elements. Plasma makes up 55% and cellular/formed elements make up 45%. The three formed elements are erythrocytes, leukocytes and platelets, which develop from a single population of pluripotent stem cells in the red marrow of bones. This marrow is found in the ribs, vertebrae, breastbone, and pelvis of the fetus. The pluripotent stem cells are unique because they have the potential to develop into any type of blood cell or cells that produce platelets. Erythrocytes (red blood cells) Leukocytes (white blood cells)
*Know that as a rule of thumb, bacterial infections cause granulocytosis and viral infections cause lymphocytosis. There are exceptions to this, but this is a very basic (and important) concept.
Platelets (thrombocytes)
BLOOD PATHWAY BLOOD VESSELS BLOOD VESSEL STRUCTURE Vascular System -Three Basic Layers: Tunica Intima (with endothelial lining), Tunica Media (smooth muscle), Tunica Adventitia (outer connective tissue). Elastic Arteries vessel wall contains large amounts of elastin (a protein fiber). Muscular Arteries diameter ranges from .3mm - 1cm, they have less elastin than elastic arteries, and more smooth muscle in the tunica media. Arterioles diameter is less than .3 mm, and tunica media consists of 5 or fewer layers of smooth muscle. Capillaries have a diameter only slightly larger than the diameter of an erythrocyte, consisting only of a tunica intima. They form capillary bed and are the site for gas and nutrient exchange. Venules collect blood from capillaries. Veins are formed when venules merge together, composed of tunica intima, and most veins have valves to prevent back flow.
Immune System
The immune and lymphatic system consist of bone marrow, lymph nodes, thymus, spleen, lymph vessels, and white blood cells. It's main function is fighting infection and cancer. better known as the body's defense system.
The lymphatic and immune systems are so closely related that we will place them under the same heading. The main components of the lymphatic system are the lymphatic vessels. Think of the these vessels as the highway in which the disease organisms travel. It is through the lymphatic vessels that escaped fluid from blood vessels is returned to the blood stream. These vessels run all through the human body collecting a fluid called lymph. This fluid travels in a one-way direction toward the heart (due to flap-like mini-valves which prevent backflow) and empties into the great veins in the base of the neck. The lymphatic vessels also return leaked proteins from the surrounding blood capillaries back to the bloodstream. The lymphatic system has no organ (like the heart) to pump lymph through the body, and therefore relies on the pulsing of surrounding blood vessels, body movement and muscle contractions to move or squeeze fluid through the vessels. The main components of the immune system are lymphocytes, lymphoid tissue, and lymphoid organs (spleen, lymph nodes, thymus, tonsils, lymphoid nodules in the small intestine, and the appendix). Think of the lymphoid tissue and organs as the parking garage or battle ground where the disease organisms are detained and ultimately destroyed. Artificially Acquired Immunity
Endocrine System
The endocrine system consists of many glands; the pituitary, thyroid, adrenal glands, pancreas, and ovaries/testicles (which also secrete hormones). These chemicals regulate:
It was not until the early 1900's that the existence of these substances became known. Since then, over 30 human hormones have been identified, and we have developed the ability to extract them from tissues and synthesize them in the lab. In humans, most hormones are produced by certain glands called endocrine glands. Doctors that specialize in the evaluation and treatment of hormone conditions are called endocrinologists. In humans and animals, hormones control a number of bodily functions including growth, development, and reproduction. In plants, hormones mainly regulate growth. Decreased production of these chemical messengers can lead to serious diseases and even death.
Reproductive SystemsThe reproductive system consists of the ovaries, testes, and other associated organs. It's main function is reproduction.
The cervix is lined with a layer of cells called epithelial cells.
Epithelial cells are a general type of cells found throughout the body,
and they vary in shape and size depending on where they are. In the
cervix, the epithelial cells inside the canal are very different from
the cells that line the part of the cervix that borders the vagina. In
the canal the cells are tall and are referred to as columnar epithelium.
On the outside wall of the cervix, where the cervix meets the vagina the
epithelial cells are flat, or squamous. A very delicate area of the
cervix is called the squamous columnar junction, where the tall columnar
cells end and the flat, squamous cells begin. It is here that
pre-cancerous lesions are usually detected and where cells are sampled
for Pap smear screening.
The male pelvis is narrower, deeper and has thicker, stronger bones
than the female pelvis. The male reproductive glands, testes, lie within
the scrotum, which is outside the body between the legs. The testes
produce sperm and male hormones. From the testes, sperm pass into a
coiled tube called the epididymis where they mature and are stored until
ejaculation through the urethra or until reabsorbed by the body. The
prostate is about the size of a walnut. It lies just below the urinary
bladder and surrounds the upper part of the urethra.
The Ear
Human DiseasesMany foreign invaders such as bacteria, viruses, pathogens in the air, and abnormal body cells can cause disease. Scientists from research and development (R&D) teams all over the world are constantly working on new ways to defeat/control these intrusions.
Other Anatomy Resources
Mrs.
King's BioWeb |
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Metabolism
& growth 
Last modified: August 07, 2010