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The Organ Systems of the Human Body
What Are Organ Systems?
An organ system is a level of organisation found in our body. There are four levels of organisation within the body:
- A cell is a group of organelles working together to perform a particular function;
- A tissue is a group of cells working together;
- An organ is a group of tissues working together;
- An organ system is a group of organs working together to perform a particular task.
Most of my science pupils know the names of several organs by the time they arrive in high school at 11 years old. My first job when teaching human biology is to teach my pupils how these organs work together and why they work together.
So why do we need our organ systems to work together? The usual response from the kids is "to keep us alive!" Whilst correct, this is a very simplistic view that needs improvement. All living things perform the same 7 life processes:
Our organ systems divide up the different life processes between them. Each organ system relies on all the others to carry out the tasks it cannot do by itself.
Organ Systems and the Life Processes
Nervous System, Integumentary System
Respiratory System, Cardiovascular System
The Circulatory System
Organs of the Circulatory system:
- Heart (CV)
- Blood Vessels (CV)
- Lymph Glands (L)
- Thymus (L)
- Spleen (L)
The circulatory system is made up of the cardiovascular system (CV) and the Lymphatic system (L). This system is responsible for transporting nutrients and gases to the cells and tissues of the body, and removing waste products.
Fast Fact: The tissue that makes up your heart is myogenic - it will beat on its own!
The Respiratory System
Organs of the Respiratory System:
- Intercostal muscles
The respiratory system provides oxygen for all your cells, and removes carbon dioxide from the body. The lungs are adapted to provide as large a surface area as possible to maximise diffusion. The small sacs in the lungs (alveoli) are only a cell thick to allow oxygen to diffuse into the blood and carbon dioxide to diffuse out.
Fast Fact: The lungs provide a surface area of over 70m2 in an adult - this is the size of a tennis court!
The Gastrointestinal System
Organs of the GI System:
- Small and Large Intestine
The gastrointestinal system is responsible for digestion of our food. Digestion is the process of breaking down food into nutrients that can be readily absorbed and used by the body. Most of the nutrients are absorbed in the small intestine, whereas the large intestine reabsorbs as much water as possible. The liver and pancreas aid digestion by producing bile (to digest fat) and enzymes, respectively.
Fast Fact: The small intestine can be up to 20ft (6m) in length!
The Musculoskeletal System
Organs of the musculoskeletal system:
- Bones in skeleton.
The musculoskeletal system is a combination of the muscles and skeleton. The skeleton not only provides a rigid structure for the muscles to pull on, but provides protection to vulnerable internal organs such as the brain, lungs and heart. Muscles come in two varieties: skeletal and smooth. Skeletal muscle is under our conscious control and are attached to bones by rings of tissue called ligaments. Smooth muscle forms the walls of organs such as the stomach; this muscle cannot be controlled and is called involuntary.
Fast Fact: There are 206 bones in an adult body, but babies have more than 300 bones or cartilage elements!
Organ Systems in Our Body - Detailed Video
The Urinary/Excretory System
Organs of the Excretory System:
- Vena Cava and Aorta
The kidneys are the major organs of the excretory system; they filter the blood removing urea, excess salt and water. These waste products are stored in the bladder until they can be excreted from the body. The two major blood vessels of the body, the aorta and vena cava supply the kidneys with blood.
Fast Fact: Healthy urine is sterile - it contains fluids and salts, but no bacteria or viruses...so it is safe to drink?
Organs of the Reproductive Systems
Male Reproductive System
Female Reproductive System
The Reproductive Systems
The human reproductive system is the only organ system that differs between the sexes. It allows couples to produce fertile offspring to continue the species. Women are born with their full complement of immature eggs (between 400,000 and 2 million), inside their ovaries*. Men constantly produce sperm from puberty at the rate of around 1,500 sperm per second.
Fast Fact: While a woman may be born with 2 million eggs, only around 500 eggs will develop over the course of her fertile life.
The Endocrine System
Organs of the Endocrine System:
- Pineal Gland
- Pituitary gland
- Thyroid gland
- Adrenal glands
The human endocrine system is a collection of glands that secrete hormones - the chemical messengers of the human body. These molecules cause chemical changes in cells with the appropriate receptors. For example, growth hormones secreted by the pituitary gland signal certain cells to divide for growth. The adrenal glands release adrenaline (epinephrine) under stress to trigger the fight-or-flight response. The endocrine system works together with the nervous system to send messages around the body.
Fast Fact: There are around 50 different hormones in the human body.
The Immune System
Organs of the Immune System:
- Tonsils and adenoids
- Lymph nodes
- Bone Marrow
- White blood cells (not an organ)
The immune system defneds the body against attacks from foreign bodies (bacteria and viruses). The lymph glands and bone marrow work together to create and store the various types of white blood cell required to properly defend the body.
Fast Fact: It is thought that new cancer therapies can be developed by modifying and targetting the body's own immune system - this could lead to cancer treatments with no side-effects.
The Nervous System
Organs of the Nervous System:
- Spinal cord
The nervous system is high-speed broadband compared to the postal service that is the endocrine system. It transmits electrical messages at high speed from throughout the body. There are four different types of nerves:
- Cranial nerves run from the brain to the sense organs of the head.
- Central nerves are found in the brain and spinal cord.
- Autonomic Nerves run from the spinal cord to the lungs, heart, digestive, bladder and sex organs. These send messages that are not under conscious control.
- Peripheral nerves connect the spinal cord to the limbs - these messages are under conscious control and are used for things such as movement.
Fast Fact: The brain contains over 100 billion neurons!
The Integumentary System
The integumentary system includes:
- Blood vessels
- Sweat and oil glands
The skin is the largest organ of the body - it makes up 16% of your body weight - and one of our most important sense organs. It also regulates body temperature, provides a physical barrier to pathogens, protects internal organs and helps to retain moisture.
Fast Fact: The outer layer of the skin is made of dead cells - we shed around 30,000-40,000 an hour (out of 1.6 trillion skin cells). This forms most of the dust in your house. Over a year you shed around 3.6kg (8lbs) of dead skin.