Summary of Human Systems Background Information Levels of Organization/: atom, molecule, organelles, cell, tissue, organ, organ system, organism Tissue Types: epithelial, nervous, connective, muscle Homeostasis: our systems maintain a steady state so that they can all work at their highest level of functioning to promote the health and survival of the organism Feedback loops: how our systems maintain homeostasis The Integumentary System Function The major functions of the integumentary system include: protection, vitamin D production, and temperature regulation. It is also a sensory organ. The integumentary system consists of hair, skin, and nails. The skin consists of the epidermis, the dermis, and the subcutaneous layers. In addition, there is a top layer of dead skin cells for added protection. Sebaceous glands, sweat glands, melanocytes (that produce melanin) are all located in the dermal layer, along with nerves and hair follicles. The subcutaneous layer consists mostly of nerves and adipose (fat) cells. 1
The Muscular System Function The major job of the muscular system is movement and it is also involved in temperature regulation Muscle cells are called muscle fibers due to their elongated shape. They contain special fibrils call actin and myosin, which are responsible for muscle contraction. The sliding filament theory describes how a muscle contracts actin slides past myosin when ATP and Ca bind to them. Muscle contraction is triggered by the nervous system. The major classes of muscles include: smooth, skeletal, and cardiac. Smooth and cardiac muscles are involuntary, meaning you do not control their contraction. Skeletal and cardiac muscle have stripes known as striations. Cardiac muscle refers to the heart, an example of a smooth muscle can be found in the digestive tract and the female reproductive tract, and skeletal muscles include the triceps and biceps. Major muscles in the muscular system include: bicep, tricep, pectoralis major, deltoid, quadriceps, rectus abdominus, external obliques The Skeletal System Function The skeletal systems main jobs include structure/support, movement, the production of blood cells, and protection. Bone is made up of minerals and collagen fibers and comes in two forms: compact bone and spongy bone. Marrow in the middle of the bone is the site of blood cell production. A thin layer called the periosteum covers the bone and the bone contains Haversian canals in the middle of each Haversian system (circular component of bone) that contain blood vessels and nerves. Our skeletal first starts out as cartilage, which is then replaced by bone producing cells (osteoblasts) that produce osteocytes, mature bone cells. Osteoclasts are cells that break down bone, and their activity increases with age. If the osteoclasts and osteoblasts are not in synch, you can wind up with too much bone being broken down without being replaced, leading to brittle bones, also known as osteoporosis. The skeleton can be broken down into two main parts, the axial skeleton and appendicular skeleton. Joints are places where two bones meet and can come in various forms: fixed, gliding, pivot, ball and socket, and hinge. Major bones of the skeleton include: cranium, spine, ribs, pelvis, humerus, radius, ulna, clavicle, femur, tibia, fibia, carpals, and tarsals. 2
The Nervous System Function This system directs and coordinates the activity of all the other systems in response to changing environmental conditions/needs The brain is divided into many different regions, called lobes, with each one responsible for various activities/functions. The brain stem, cerebrum, cerebellum are the three major divisions of the brain. Electrochemical impulses and chemicals known as neurotransmitters are responsible for signal transmission throughout the nervous system. Brain cells are called neurons and consist of a cell body, axon, and many branching dendrites. The axon is covered with a myelin sheath that allows the chemical pulses to travel quickly from one neuron to the next. Major organs of this system include the brain, spinal cord, nerves Feedback loops are a large part of the nervous system. Sensory receptors send messages to the central and/or peripheral nervous system which then send a signal back through a motor neuron which causes a muscle movement (think of a reflex). You have many sensory receptors all over your body that relay messages to the brain based on temperature, pain, touch/stretch, light or the presence of chemicals. 3
The Endocrine System Function This system uses chemical messengers to coordinate activities of the various systems The endocrine system consists of different glands that produce and secrete chemicals that influence the output of target cells. A hormone can have very different effects on different cells of the body and these influences can be enormous (puberty!). Many hormones are steroids, meaning they are a type of lipid, which allows them to go directly through the cell membrane (also a lipid) and go straight into the nucleus of a cell to direct protein synthesis. The major organs of the endocrine system include the hypothalamus, the anterior and posterior pituitary gland, thyroid, the parathyroids, adrenal glands, the pancreas, and the gonads (male: testes or female: ovaries). 4
The Circulatory System Function This system transports nutrients, gases, and wastes in/out/around the body. It is also involved in temperature regulation. The circulatory system consists of blood vessels called arteries, veins, and capillaries that transport materials to/from the body cells. Blood itself is a mixture of erythrocytes (RBCs), leukocytes (WBCs), platelets, proteins, nutrients, gases, wastes, and water. The heart pumps the blood throughout the body and to the lungs, where waste gases can be expelled and oxygen inhaled. The structure of the heart includes two ventricles, two atria, a septum, and a connection to pulmonary arteries/veins and the aorta and vena cava. The heart itself is controlled by pacemaker cells, but can be affected by input from the nervous/endocrine systems. Arteries have layers of muscle around them while veins do not. Veins contain valves to help push blood back up to the heart. Capillaries are only one cell thick to allow body cells to exchange materials easily. The major organs of the circulatory system include: the heart, arteries, veins, and capillaries 5
The Immune (Lymphatic) System Function The major function of this system is to recognize and destroy foreign invaders and abnormal self cells. Immune cells are made in the bone marrow and mature either in the bone marrow (B cells) or in the thymus gland (T cells). These cells are very specialized, with each type capable of recognizing one specific antigen (cell identification markers) and destroying that foreign cell. Other immune cells (macrophages) use phagocytosis to swallow any foreign cell antigen they encounter (they are nonspecific). B cells release antibodies to fight foreign invaders while T cells can attack the foreign invaders directly. T cells also look for self cells that display foreign or abnormal antigens, which would indicate a viral infection or cancer. The major organs of this system include the lymph nodes, lymphatic vessels, bone marrow, spleen and thymus. The immune system reaction to invaders includes both nonspecific and specific defenses. Non specific defenses include inflammation, fever, sweat, and tears. Specific defenses include the B and T cell actions listed above. Vaccines are given to provide passive immunity to someone (it is called active immunity when you make your own antibodies to fight disease). A vaccine is simply a cocktail of heat killed pathogens (a bacteria, etc.) that cannot cause disease because it is dead but can be recognized as foreign by the body. The B cells will then make antibodies against that pathogen which will circulate in the bloodstream for up to 10 or even 20 years (when you then get a booster shot ). Vaccines help prevent disease by having the antibodies ready to respond quickly to a pathogen. Without them, a person could get very sick during the 10-12 days it would normally take for enough antibodies to be produced to actually kill the pathogen (see p. 375) Bacteria, fungus, and protists cause disease by invading tissues (living between/among cells) and releasing toxins. Viruses actually enter cells, hide there away from immune system detection, and use the cell as a factory to make their own viral proteins until they finally explode the cell with each newly made virus moving on to invade another cell HIV is the virus that causes AIDs. HIV can lay dormant inside a person s cells for years until becoming active and causing the disease symptoms we call AIDs. HIV is transferred through blood contact, the main ways are due to blood contact from childbirth or other exposures, unsafe sexual practices and unsafe needle/injection practices 6
Function This system is responsible for gas exchange. The Respiratory System The respiratory system consists of two lungs (five lobes) that contain small sacs called alveoli, where oxygen and carbon dioxide are exchanged. To take a breath, the body signals the diaphragm to contract, expanding the thoracic cavity and pulling air into the lungs. To exhale, the diaphragm relaxes, pushing back up in the cavity and forcing air out of the lungs. The major organs of the respiratory system include the lungs, trachea, bronchi, bronchioles, and diaphragm. 7
The Digestive System Function The digestive system is involved in the physical and chemical breakdown of food and the absorption of nutrients and fluids. Many enzymes are involved in the breakdown of food, with each type breaking down a different type of food protein, lipid, or carbohydrate. Each of the organs involved either produces/secretes one of these enzyme (liver, pancreas) or is involved in the physical breakdown of the food (stomach, mouth). Other areas (small and large intestines) are responsible for the reabsorption of nutrients and fluids before the remaining waste is exported to the excretory system for removal. The major organs of the digestive system include the mouth, epiglottis, esophagus, liver, stomach, pancreas, and the small and large intestines. The Excretory System Function The function of this system is to collect, concentrate, and excrete metabolic wastes, and regulate water/electrolyte concentrations This system is critical for the health of the body nephrons are responsible for the concentration of wastes and reabsorption of water and minerals that occurs in the kidneys. Liquid wastes are then delivered to the urinary bladder to be expelled while the water and minerals are returned to the blood flow. The major organs of this system consist of the renal arteries and veins, the kidneys, ureter, urinary bladder, and urethra. 8