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Human Body Systems
Transcript of Human Body Systems
The Digestive System has two main functions:
By: Ian Harvey
- breaking down large food molecules into smaller usable molecules
- the diffusion of small molecules into the body's cells
Organs in the Digestive System
- the beginning of digestion. Food is mechanically broken down to be more easily digested.
Organs in the Digestive System (continued)
- made up of three segments...
: first segment. Site of continuous digestion by means of enzymes, bile, and peristalsis.
: lower two segments. Absorb nutrients into the bloodstream.
Diagram of the Digestive System
- release saliva into the mouth, keeping the digestive system moist, beginning the breaking down of food in the mouth, and lubricating the passage of food from the mouth to stomach.
- the "throat." Receives food from the mouth. Performs the act of swallowing, closing off the trachea and allowing food to enter the esophagus.
- tube connecting the mouth to the stomach. Moves food to the stomach through a series of muscle contractions called peristalsis.
- food enters from the esophagus and is digested by means of acid, enzymes, and muscle contractions.
- processes nutrients absorbed from the small intestine and produces bile which is used to digest fats.
- secretes digestive enzymes into the duodenum (part of the small intestine) and produces insulin, a hormone that metabolizes sugar.
- stores and concentrates bile before releasing it into the duodenum to absorb and digest fats.
- made up of three parts...
: connects small and large intestine. Moves undigested food, vitamins, and water into
Ascending, Transverse, and Descending Colon
: most functions of the large intestine occur here. Water and vitamins are absorbed and alkaline solutions and antibodies are produced. Stool is formed here.
: connects large intestine to rectum. Forces the stool produced in colon to the rectum.
- stores stool until they are to be expelled from the body.
- controls the storage and eventually the release of stool from the body.
- ringlike muscles surrounding and able to contract or close a bodily passage or opening. Control the movement of food through the digestive system.
Distinguishing Between the Organs in the Digestive Tract and the Accessory Organs
alivary glands, liver, pancreas,
are considered accessory organs because although they are directly involved in digestion, food does not pass through them.
Physical vs. Chemical Digestion
Once food is ingested,
begins immediately through the process of chewing. This breaks down food into smaller pieces which are more easily broken down and digested. Furthermore, peristalsis churns the food in the stomach and allows it to better mix with digestive juices and enzymes.
Sites of Digestion
takes the smaller pieces of food created by physical digestion and breaks them down even further. These processes break down proteins, carbohydrates, and lipids into their building blocks. This is accomplished by means of enzymatic hydrolysis, allowing these building blocks and nutrients to be absorbed into the body and/or bloodstream through the walls of the digestive tract.
Food passes through the
mouth, pharynx, esophagus, stomach, small
large intestines, rectum,
, making them part of the digestive tract.
When carbohydrates enter the mouth, salivary amylase begins breaking down the polysaccharides in the food.
Once proteins enter the stomach, digestion begins. Hydrochloric acid and pepsinogen interact to form the enzyme pepsin. The proteins then begin to be broken down into amino acids through the process of hydrolysis.
Lipid digestion begins in the stomach. The stomach enzyme gastric lipase is important to this process. Up to 30% of digestion can occur here.
No further digestion occurs in the stomach. The acid in the stomach kills bacteria in the food and salivary amylase is no longer active. The food is now known as chyme.
The chyme then enters the small intestine, causing the pancreas to release pancreatic amylase, breaking down the polysaccharides into disaccharides. The small intestine then releases enzymes called lactase, sucrase, and maltase, breaking the disaccharides down into monosaccharides. These simple sugars and then absorbed by the small intestine.
Carbohydrates that have not been digested and absorbed that reach the large intestine are then partly broken down by intestinal bacteria.
Proteins continue on to the small intestine where protein digestion continues. Trypsin, a pancreatic protease enzyme, is secreted by the pancreas. This enzyme continues hydrolysis in the duodenum, further breaking down the proteins into amino acids.
These amino acids are small enough to pass through the lining of the small intestine, and are therefore absorbed into the bloodstream and carried where necessary in the body.
Once lipids move to the intestines, emulsification begins. Bile salts separate the lipid into smaller pieces to be digested more easily.
Pancreatic lipase is largely responsible for breaking down the lipids into smaller, absorbible molecules. These are then absorbed through the intestines.
Whipple's disease is a rare bacterial infection primarily affecting the small intestine. It can also affect the heart, lungs, brain, joints, and eyes. Left untreated, Whipple's disease is fatal.
This autoimmune disorder affects around 1 percent of people globally, according to Genetics Home Reference. It's an abnormal sensitivity to gluten, a protein in wheat, barley, and rye.
cause Whipple's disease.
infection can cause internal sores, also called lesions, and the thickening of tissues. Villi, which are tiny fingerlike projections that line the small intestine, take on an abnormal, clublike appearance. The damaged intestinal lining fails to properly absorb nutrients, causing diarrhea and malnutrition.
Common signs and symptoms: joint pain, diarrhea, weight loss, abdominal pain, fever, fatigue, and anemia.
Whipple's disease is treated with long-term antibiotics that kill T. whipplei bacteria. Standard therapy for Whipple's disease involves initial treatment with intravenous antibiotics for 2 weeks, followed by daily oral antibiotic treatment for 1 to 2 years.
One case per million per year.
Symptoms include: diarrhea, malabsorption, weight loss, abdominal pain and swelling, and food intolerance.
The inflammation it causes carries a risk of some gastrointestinal cancers. While celiac disease tends to cluster in families, experts have found no inheritance pattern. Diagnosis follows blood tests and/or tissue biopsy. Treatment consists of following a strict, gluten-free diet.
it influences almost every cell, organ, and function of our bodies. The endocrine system is instrumental in regulating mood, growth and development, tissue function, metabolism, and sexual function and reproductive processes through the excretion of hormones.
Function of the Endocrine System:
-The tendency of an organism or a cell to regulate its internal conditions, usually by a system of feedback controls, so as to stabilize health and functioning, regardless of the outside changing conditions
The endocrine system provides the essential mechanism of homeostasis, integrating body activities and at the same time ensuring that the composition of the body fluids bathing the constituent cells remains constant.
The endocrine system is responsible for releasing hormones that regulate aspects of homeostasis, such as body temperature, water content, and blood sugar levels.
Negative feedback decreases the deviation from an ideal normal value, and is important in maintaining homeostasis. Most endocrine glands are under the control of negative feedback mechanisms.
When conditions change in an environment regulated by a negative feedback mechanism, the mechanism detects this change. It is then activated, returning the environment to its ideal conditions. Once this condition is reached, the mechanism is deactivated.
An example of negative feedback is the regulation of the blood calcium level. The parathyroid glands secrete parathyroid hormone, which regulates the blood calcium amount. If calcium decreases, the parathyroid glands sense the decrease and secrete more parathyroid hormone. The parathyroid hormone stimulates calcium release from the bones and increases the calcium uptake into the bloodstream from the collecting tubules in the kidneys. Conversely, if blood calcium increases too much, the parathyroid glands reduce parathyroid hormone production. Both responses are examples of negative feedback because in both cases the effects are negative (opposite) to the stimulus.
- Antidiuretic hormone: promotes retention of water by kidneys.
- Parathormone: raises blood calcium levels
- Thyroxin (T3 and T4): controls metabolic rate
- Thymosin: stimulates T lymphocytes
- Glucagon: breakdown of glycogen into glucose
- Epinephrine (adrenaline): raises blood sugar level by increasing rate of glycogen breakdown by liver
- Estrogen: stimulates uterine lining, promotes development and maintenance of primary and secondary characteristics of female
- Androgens: support sperm production and promote secondary sex characteristics
Glucose is liberated from dietary carbohydrate such as starch or sucrose by hydrolysis within the small intestine, and is then absorbed into the blood. Elevated concentrations of glucose in blood stimulate release of insulin, and insulin acts on cells thoughout the body to stimulate uptake, utilization and storage of glucose.
A well-known effect of insulin is to decrease the concentration of glucose in blood.
Like the receptors for other protein hormones, the receptor for insulin is embedded in the plasma membrane. The insulin receptor is composed of two alpha subunits and two beta subunits linked by disulfide bonds. The alpha chains are entirely extracellular and house insulin binding domains, while the linked beta chains penetrate through the plasma membrane.
The insulin receptor is a tyrosine kinase. In other words, it functions as an enzyme that transfers phosphate groups from ATP to tyrosine residues on intracellular target proteins. Binding of insulin to the alpha subunits causes the beta subunits to phosphorylate themselves (autophosphorylation), thus activating the catalytic activity of the receptor. The activated receptor then phosphorylates a number of intracellular proteins, which in turn alters their activity, thereby generating a biological response.
In type 1 diabetes, the body does not produce insulin.
Type 1 diabetes is usually diagnosed in children and young adults, and was previously known as juvenile diabetes. Only 5% of people with diabetes have this form of the disease.
With the help of insulin therapy and other treatments, even young children can learn to manage their condition and live long, healthy lives.
If you have type 2 diabetes your body does not use insulin properly. This is called insulin resistance. At first, your pancreas makes extra insulin to make up for it. But, over time it isn't able to keep up and can't make enough insulin to keep your blood glucose at normal levels.
Type 2 diabetes is the most common form of diabetes.
Diabetes is a problem with your body that causes blood glucose (sugar) levels to rise higher than normal. This is also called hyperglycemia.
Symptoms include: urinating often, feeling very thirsty or hungry, extreme fatigue, blurry vision, cuts/bruises that are slow to heal, weight loss (type 1), tingling/pain/numbness in the hands or feet (type 2)
Hypothyroidism (underactive thyroid) is a condition in which your thyroid gland doesn't produce enough of certain important hormones.
Women, especially those older than age 60, are more likely to have hypothyroidism. Hypothyroidism upsets the normal balance of chemical reactions in your body. It seldom causes symptoms in the early stages, but, over time, untreated hypothyroidism can cause a number of health problems, such as obesity, joint pain, infertility and heart disease.
Accurate thyroid function tests are available to diagnose hypothyroidism, and treatment of hypothyroidism with synthetic thyroid hormone is usually simple, safe and effective.
The main function of the excretory system is to remove waste products of metabolism from the body thus preventing damage to its tissues.
: Filtering of the blood takes place within nephrons in the kidneys. Each nephron contains a cluster of capillaries called a glomerulus. A cup-shaped sac called a Bowman's capsule surrounds each glomerolus. The blood that flows through the glomerulus is under great pressure. This causes glomerulus, water, glucose and urea to enter the Bowman's capsule. White blood cells, red blood cells and proteins remains in the blood. As the blood continues through the blood vessels, it winds around the renal tubule. During this time, reabsorption occurs. Glucose and chemicals, such as potassium, sodium, hydrogen magnesium and calcium are reabsorbed into the blood. Almost all the water removed during filtration returns to the blood during the reabsorption phase. The kidneys control the amount of liquid in our bodies. Now only wastes are in the nephron. These wastes are called urine and include urea, water and inorganic salts. The cleansed blood goes into veins that carry the blood from the kidneys and back to the heart.
: are muscular ducts that propel urine from the kidneys to the urinary bladder. In the adult, the ureters are usually 25–30 cm (10–12 in) long.
: The urinary bladder is the organ that collects urine excreted by the kidneys prior to disposal by urination. It is a hollow muscular, and elastic organ, and sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra.
: A tube that carries urine from the bladder to the outside of the body.
It is the type of excretion in which ammonia is the main nitrogenous waste material. Such animals are called ammonotetic.
It is found in aquatic animal groups like sponges, coelentrates, crustaceans, echinoderms, bony fish, tadpole larvae and salamander.
Ammonia is produced as a result of catabolism of proteins, especially in the liver cells by oxidative deamination of excess of amino acids in the presence of oxidase enzyme.
Ammonia is highly toxic and must be metabolised or expelled from the body as soon as possible.
Ammonia is highly soluble in water and a very large volume of water is needed by the animal to dissolve ammonia. 1 gm of ammonia needs about 300 - 500 ml of water. But this is not a problem for animals living in an aqueous habitat which are generally found to be ammonotelic.
It is a type of excretion where urea is the main nitrogenous waste material. Animals showing ureotelism are called ureotelic animals.
Generally found in land animals which can afford to excrete sufficient volume of water or to concentrate urea in considerable quantity in the urine. It is commonly found in man, whales, seals, desert mammals like kangaroo rats, camels, toads, frogs, cartilagenous fishes, aquatic and semi aquatic reptiles like alligator, terrapins and turtles.
In the liver of the animals, ammonia is detoxified to form urea by the orrithine cycle. Urea is far less toxic than ammonia and so can remain inside the body for a longer period without causing any ill effects inside the body.
1 gm of urea needs about 50 ml of water to the expelled out.
Elimination of uric acid as the main nitrogenous waste material is called uricotelism. Animals showing uricotelism are called uricotelic animals.
It is a common method seen in birds, land reptiles, insects, land snails and some land crustaceans.
Uric acid is formed from ammonia mostly in the liver and to some extent in the kidneys. The process is highly energy dependant, but is much less toxic than both ammonia and urea and it is almost insoluble in water and can be eliminated from the body in nearly a solid state, saving a lot of water. Since kidneys can handle the nitrogenous wastes only in solution, reptiles and birds pass a dilute solution of uric acid into the cloaca, where water is absorbed and solid uric acid is eliminated along with faeces. The faecal matter of certain birds like cormorants, pelicans and gannets called guano has been used for the commercial extraction of uric acid. Islands off the coast of South America are covered with guano.
Man also excretes a small amount of uric acid in his urine formed by the catabolism of nucleic acids.
Processes of the Nephron
Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into Bowman's capsule. Specialized cells of Bowman's capsule are modified into podocytes, which, along with split pores, increase the rate of filtration. Filtration occurs by diffusion and is passive and nonselective. The filtrate contains everything small enough to diffuse out of the glomerulus and into Bowman's capsule, including glucose, salts, vitamins, waste such as urea, and other small molecules. From Bowman's capsule, the filtrate travels into the proximal tubule.
Secretion occurs in the proximal and distal tubules. It is the active, selective uptake of certain drugs and toxic molecules that did not get filtered into Bowman's capsule. The proximal tubule also secretes ammonia to neutralize the acidic filtrate
Reabsorption is the process by which most of the water and solutes that initially entered the tubule during filtration are transported back into the peritubular capullaries and, thus, back to the body. This process begins in the proximal convoluted tubule and continues in the loop of Henle and collecting tubule. The main function of the loop of Henle is to move salts from the filtrate and accumulate them in the medulla surrounding the loop of Henle and the collecting tubule. In this way, the loop of Henle acts as a countercurrent exchange mechanism, maintaining a steep salt gradient surrounding the loop. This gradient ensures that water molecules will continue to flow out of the collecting tubule of the nephron, thus creating hypertonic urine and conserving water. The longer the loop of Henle, the greater is the reabsorption of water.
Excretion is the removal of metabolic wastes, for example, nitrogenous wastes. Everything that passes into the collecting tubule is excreted from the body. From the collecting tubule or duct, urine passes through the ureter to the urinary bladder. Urine is temporarily stored in the urinary bladder until it passes out of the body via the urethra.
Diagram of Kidney
: The specific function of each glomerulus is to bring blood (and the waste products it carries) to the nephron.
: Fluids from blood in the glomerulus are collected in the Bowman's capsule and further processed along the nephron to form urine.
Proximal Convoluted Tubule
: Reabsorbes glucose, amino acids, phosphate, potassium, urea, and other organic solutes from the filtrate.
Loop of Henle
: Reabsorbs water from filtrate to create a more concentrated urine.
Distal Convoluted Tubule
: Regulates pH and water by absorbing bicarbonate and secreting hydrogen ions.
: Gathers all material that has not returned to the blood through the tubular membranes. It regulates electrolytes such as chloride, potassium, hydrogen ions, and bicarbonate. Its end product is usually urine.
: Nephritis is the inflammation of one or both kidneys. Herein the organs of body get affected through autoimmune disorders. Out of the disorders, lupus nephritis is a potentially serious condition. In this, the auto immune system of the body attacks body tissues, organs and body cells. The result is pain at the start and body organ damage for continued diseases.
Signs and Symptoms
: Smelly urine, Pain in lower abdomen, Blood in urine
: The overall annual incidence rate was 0.40 per 100,000 population per year, with a rate of 0.68 in women and 0.09 in men.
: Antibiotics can be used to treat this condition. When the disorder is caused by lupus, steroids may also have to be used.
: The inflammation of the bladder is known as cystitis. The bladder is the storage place for the urine until it is discharged by voluntary action of body. The urge to urinate is not an automatic action and hence bladder always has some quantity of urine. The bladder is the place where bacteria can grow easily leading to inflammation of bladder.
Signs and Symptoms
: pain or difficulty when urinating, foul-smelling urine, pain or soreness of abdomen, cloudy urine, blood in urine
: Three to 8 million women in the United States may have interstitial cystitis. This prevalence number, presented at the 2009 American Urological Association Annual Meeting in Chicago, represents about 3 to 6 percent of all U.S. women.
: Cystitis is normally treated with antibiotics for bacteria. The removal of contributing causes can also form part of treatment.
The purpose of the immune system is to keep infectious microorganisms, such as certain bacteria, viruses, and fungi, out of the body, and to destroy any infectious microorganisms that do invade the body
The organs involved with the immune system are called the lymphoid organs, which affect growth, development, and the release of lymphocytes.
(two glands located at the back of the nasal passage)
(a small tube that is connected to the large intestine)
(the arteries, veins, and capillaries through which blood flows)
(the soft, fatty tissue found in bone cavities)
(small organs shaped like beans, which are located throughout the body and connect via the lymphatic vessels)
(a network of channels throughout the body that carries lymphocytes to the lymphoid organs and bloodstream)
(lymphoid tissue in the small intestine)
(a fist-sized organ located in the abdominal cavity)
(two lobes that join in front of the trachea behind the breast bone)
(two oval masses in the back of the throat)
The human immune response system recognizes pathogensT cells and antigens and acts to remove, immobilize, or neutralize them. The immune system is antigen-specific (responding to specific molecules on a pathogen) and has memory (its defense to a pathogen is encoded for future activation). The immune system relies on several components to fight an infecting pathogen. T cells are lymphocytes that circulate between the blood, lymph, and lymphoid organs to trigger a systemic immune response with antigen-receptors on the T cell membrane. B cells are lymphocytes that activate the primary immune response when antigens bind to their receptors, causing the B cells to proliferate. Daughter cells of B cells later differentiate into antibody-releasing plasma cells. B cells also comprise the immune system's memory
Antibodies, also called immunoglobulins, are divided into five classes by structure and function, enabling them to recognize a wide spectrum of antigens. Antibody functions include complement fixation that can lead to antigen-cell lysis (rupture) and can cause inflammation. Antibodies also generate a neutralization response where viruses and bacteria are destroyed by phagocytes. Agglutination, or clumping together, of foreign cells are caused by B cells' promotion of complex cross-linking of antibodies binding to antigens. These agglutinated cells are phagocytized. B cells are cloned in massive quantities for a single specific antigen.
Innate vs. Acquired Immunity
refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen's appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells that attack foreign cells in the body. The innate immune response is activated by chemical properties of the antigen.
develops through exposure to specific foreign microorganisms, toxins, and/or foreign tissues), which are "remembered" by the body's immune system. When that antigen enters the body again, the immune system "remembers" exactly how to respond to it, such as with chickenpox. Once a person is exposed to chickenpox or the chickenpox vaccine, the immune system will produce specific antibodies against chickenpox. When that same person is exposed to chickenpox again, the immune system will trigger the release of the particular chickenpox antibodies to fight the disease.
Types of Immunity
Active vs. Passive Immunity
: Antibodies are transferred to an individual from someone else. Examples are maternal antibodies that pass through the placenta to the developing fetus or through breast milk to the baby. Also, a person with a weak immune system often recieves an injection of gamma globulin, which are antibodies culled from many people, to boost the weak immune system.
: The individual makes his or her own antibodies after being ill and recovering or after being given an immunization or vaccine. A vaccine contains dead or live viruses or enough of the outer coat of a virus to stimulate a full immune response and to impart lifelong immunity.
Humoral vs. Cell-Mediated Immunity
response (or antibody‐mediated response) involves B cells that recognize antigens or pathogens that are circulating in the lymph or blood (“humor” is a medieval term for body fluid). The response follows this chain of events:
Antigens bind to B cells.
Interleukins or helper T cells costimulate B cells. In most cases, both an antigen and a costimulator are required to activate a B cell and initiate B cell proliferation.
B cells proliferate and produce plasma cells. The plasma cells bear antibodies with the identical antigen specificity as the antigen receptors of the activated B cells. The antibodies are released and circulate through the body, binding to antigens.
B cells produce memory cells. Memory cells provide future immunity.
response involves mostly T cells and responds to any cell that displays aberrant MHC markers, including cells invaded by pathogens, tumor cells, or transplanted cells. The following chain of events describes this immune response:
Self cells or APCs displaying foreign antigens bind to T cells.
Interleukins (secreted by APCs or helper T cells) costimulate activation of T cells.
If MHC‐I and endogenous antigens are displayed on the plasma membrane, T cells proliferate, producing cytotoxic T cells. Cytotoxic T cells destroy cells displaying the antigens.
If MHC‐II and exogenous antigens are displayed on the plasma membrane, T cells proliferate, producing helper T cells. Helper T cells release interleukins (and other cytokines), which stimulate B cells to produce antibodies that bind to the antigens and stimulate nonspecific agents (NK and macrophages) to destroy the antigens.
B and T Lymphocytes
All cells, including immune cells such as lymphocytes, are produced in the bone marrow (the soft, fatty tissue found in bone cavities). Certain cells will become part of the group of lymphocytes, while others will become part of another type of immune cells known as phagocytes. Once the lymphocytes are initially formed, some will continue to mature in the bone marrow and become "B" cells. Other lymphocytes will finish their maturation in the thymus and become "T" cells. B and T cells are the two major groups of lymphocytes which recognize and attack infectious microorganisms.
Once mature, some lymphocytes will be housed in the lymphoid organs, while others will travel continuously around the body through the lymphatic vessels and bloodstream.
Although each type of lymphocyte fights infection differently, the goal of protecting the body from infection remains the same. The B cells actually produce specific antibodies to specific infectious microorganisms, while T cells kill infectious microorganisms by killing the body cells that are affected. In addition, T cells release chemicals, called lymphokines, which trigger an immune response to combat cancer or a virus, for example.
Lymphocytes - a type of infection-fighting white blood cell - are vital to an effective immune system. Lymphocytes "patrol" the body for infectious microorganisms.
Antibiotics don't work on viruses because of how viruses are constructed. While antibiotics work by impairing its target microorganisms ability to live and reproduce. Since viruses don't "live" in the same way as other organisms and only reproduce by hijacking the cellular reproductive capabilities of organisms, antibiotics are ineffective against viruses
Antibiotics can be used to treat bacterial infections. However, antibiotics are ineffective in treating virus-related illnesses. In addition, antibiotics treat specific bacteria and overuse or misuse of antibiotics can lead to drug-resistant bacteria. It is important that antibiotics are taken properly and for the duration of the prescription. If antibiotics are stopped early, the bacteria may develop a resistance to the antibiotics.
HIV stands for human immunodeficiency virus. It kills or damages the body's immune system cells. AIDS stands for acquired immunodeficiency syndrome. It is the most advanced stage of infection with HIV.
HIV most often spreads through unprotected sex with an infected person. It may also spread by sharing drug needles or through contact with the blood of an infected person. Women can give it to their babies during pregnancy or childbirth.
The first signs of HIV infection may be swollen glands and flu-like symptoms. These may come and go a month or two after infection. Severe symptoms may not appear until months or years later.
At the end of 2009, an estimated 1,148,200 persons aged 13 and older were living with HIV infection in the United States, including 207,600 (18.1%) persons whose infections had not been diagnosed.
In 2011, the estimated number of persons diagnosed with AIDS in the United States was 32,052. Of these, 24,088 AIDS diagnoses were among adult and adolescent males, 7,949 were among adult and adolescent females, and 15 diagnoses were among children aged less than 13 years.
There is no cure, but there are many medicines to fight both HIV infection and the infections and cancers that come with it. People can live with the disease for many years.
Severe Combined Immunodeficiency (SCID)
Severe Combined Immunodeficiency, is a primary immune deficiency. The defining characteristic is usually a severe defect in both the T- & B-lymphocyte systems. This usually results in the onset of one or more serious infections within the first few months of life. These infections are usually serious, and may even be life threatening, they may include pneumonia, meningitis or bloodstream infections. Children affected by SCID can also become ill from live viruses present in some vaccines. These vaccines (such as Chickenpox, Measles, Rotavirus, oral polio and BCG, etc.) contain viruses and bacteria that are weakened and don’t harm children with a healthy immune system. In patients with SCID however, these viruses and bacteria may cause severe, life-threatening infections.
Severe combined immunodeficiency (SCID) is very rare, affecting between 50 and 100 children born in the U.S. every year. Because it is a genetic disorder (caused by an error in the genes), in affected children, the condition is present at birth.
Some treatment options include basic precautions such as avoiding crowds, dirty places, ill people, and maintaining cleanliness; antibody infusions; stem cell/bone marrow transplants; and gene therapy.
At the most basic level, the function of the nervous system is to transmit signals from one cell to others, or from one part of the body to others.
Central and Peripheral System
The Neuron and Reflex Arc
Central Nervous System:
Peripheral Nervous System:
-the complex of nerve tissues that controls the activities of the body. In vertebrates it comprises the brain and spinal cord.
-the part of the vertebrate nervous system constituting the nerves outside the central nervous system and including the cranial nerves, spinal nerves, and sympathetic and parasympathetic nervous systems.
Neurotransmitters and Postsynaptic Potential
Polarization of the Neuron's Membrane
Cell membranes surround neurons just as any other cell in the body has a membrane. When a neuron is not stimulated — it's just sitting with no impulse to carry or transmit — its membrane is polarized. Being polarized means that the electrical charge on the outside of the membrane is positive while the electrical charge on the inside of the membrane is negative. The outside of the cell contains excess sodium ions (Na+); the inside of the cell contains excess potassium ions (K+).
When the neuron is inactive and polarized, it's said to be at its resting potential. It remains this way until a stimulus comes along.
When a stimulus reaches a resting neuron, the gated ion channels on the resting neuron's membrane open suddenly and allow the Na+ that was on the outside of the membrane to go rushing into the cell. As this happens, the neuron goes from being polarized to being depolarized.
Each neuron has a threshold level — the point at which there's no holding back. After the stimulus goes above the threshold level, more gated ion channels open and allow more Na+ inside the cell. This causes complete depolarization of the neuron and an action potential is created. In this state, the neuron continues to open Na+ channels all along the membrane. When this occurs, it's an all-or-none phenomenon. "All-or-none" means that if a stimulus doesn't exceed the threshold level and cause all the gates to open, no action potential results; however, after the threshold is crossed, there's no turning back: Complete depolarization occurs and the stimulus will be transmitted.
After the inside of the cell becomes flooded with Na+, the gated ion channels on the inside of the membrane open to allow the K+ to move to the outside of the membrane. With K+ moving to the outside, the membrane's repolarization restores electrical balance, although it's opposite of the initial polarized membrane that had Na+ on the outside and K+ on the inside. Just after the K+ gates open, the Na+ gates close; otherwise, the membrane couldn't repolarize.
When the K+ gates finally close, the neuron has slightly more K+ on the outside than it has Na+ on the inside. This causes the membrane potential to drop slightly lower than the resting potential, and the membrane is said to be hyperpolarized because it has a greater potential. (Because the membrane's potential is lower, it has more room to "grow."). This period doesn't last long, though (well, none of these steps take long!). After the impulse has traveled through the neuron, the action potential is over, and the cell membrane returns to normal (that is, the resting potential).
The refractory period is when the Na+ and K+ are returned to their original sides: Na+ on the outside and K+ on the inside. While the neuron is busy returning everything to normal, it doesn't respond to any incoming stimuli. It's kind of like letting your answering machine pick up the phone call that makes your phone ring just as you walk in the door with your hands full. After the Na+/K+ pumps return the ions to their rightful side of the neuron's cell membrane, the neuron is back to its normal polarized state and stays in the resting potential until another impulse comes along.
Although an impulse travels along an axon electrically, it crosses a synapse chemically. The cytoplasm at the terminal branch ofthe presyaptic neuron contains many vesicles, each containing thousands of molecules of neurotransmitter. Depolarization of the presynaptic membrane causes Ca++ ions to rush into the terminal branch through calcium-gated channels. This sudden rise in Ca++ levels stimulates the vesicles to fuse with the presynaptic membrane and release the neurotransmitter by exocytosis into the synaptic cleft. Once in the synapse, the neurotransmitter bonds with receptors on the photosynaptic side, altering the membrane potential of the postsynaptic cell and resulting in a response. Depending on the type of receptors and the ion channels they control, the postsynaptic cell will be either inhibited or excited.
Shortly after the neurotransmitter is released into the synapse, it is destroyed by an enzyme called esterase and recycled by the presynaptic neuron. The neurotransmitter at all neuromuscular junctions is acetylcholine. Other neurotransmitters are serotonin, epinephrine, norepinephrine, and dopamine. In addition, the neurotransmitter acetylcholine stimulates some cells to release the gas nitric oxide, which, in turn, stimulates other cells. A single postsynaptic neuron may reveive 1,000 impulses from presynaptic neurons, releasing a variety of different neurotransmitters. All of these impulses are integrated and summed up into either hyperpolarization or hypopolarization.
EPSP vs. IPSP
An excitatory postsynaptic potential (EPSP) is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell. A postsynaptic potential is defined as excitatory if it makes it easier for the neuron to fire an action potential.
They are the opposite of inhibitory postsynaptic potentials (IPSPs), which usually result from the flow of negative ions into the cell. An Inhibitory Postsynaptic Potential (commonly abbreviated as IPSP) is the change in membrane voltage of a postsynaptic neuron which results from synaptic activation of inhibitory neurotransmitter receptors.
A postsynaptic potential is considered inhibitory when the resulting change in membrane voltage makes it more difficult for the cell to fire an action potential, lowering the firing rate of the neuron.
-Alzheimer's is a type of dementia that causes problems with memory, thinking and behavior. Symptoms usually develop slowly and get worse over time, becoming severe enough to interfere with daily tasks. It is the most common form of dementia, a general term for memory loss and other intellectual abilities serious enough to interfere with daily life. Alzheimer's disease accounts for 50 to 80 percent of dementia cases.
Signs and Symptoms:
-The most common early symptom of Alzheimer's is difficulty remembering newly learned information because Alzheimer's changes typically begin in the part of the brain that affects learning. As Alzheimer's advances through the brain it leads to increasingly severe symptoms, including disorientation, mood and behavior changes; deepening confusion about events, time and place; unfounded suspicions about family, friends and professional caregivers; more serious memory loss and behavior changes; and difficulty speaking, swallowing and walking.
-Alzheimer's has no current cure, but treatments for symptoms are available and research continues. Although current Alzheimer's treatments cannot stop Alzheimer's from progressing, they can temporarily slow the worsening of dementia symptoms and improve quality of life for those with Alzheimer's and their caregivers. Today, there is a worldwide effort under way to find better ways to treat the disease, delay its onset, and prevent it from developing.
-An estimated 5.2 million Americans have Alzheimer's disease in 2014, including approximately 200,000 individuals younger than age 65 who have younger-onset Alzheimer's. Almost two-thirds of American seniors living with Alzheimer's are women. Of the 5 million people age 65 and older with Alzheimer's in the United States, 3.2 million are women and 1.8 million are men.
Usually there are five parts of a reflex arc:
- sense organ in skin, muscle, or other organ
- carries impulse towards central nervous system
- carries impulse within central nervous system
- carries impulse away from central nervous system
- structure by which animal responds (muscle, gland, etc).
Example of how it works is the knee-jerk test:
The pathway for this reflex arc starts at a stretch receptor within the tendon. Hitting this receptor stimulates it, which causes it to send a nerve impulse along a sensory neuron to the spinal cord. Within the spinal cord, the nerve impulse passes from the sensory neuron to a motor neuron and travels back to the thigh muscle. When the impulse arrives at the thigh muscle, it causes it to contract and jerk the lower part of the leg upward. The person is aware that this is happening, so sensory impulses do travel from the spinal cord to the brain, but there is nothing that can be done to stop it happening.
: receives and interprets olfactory sensation, initiates voluntary commands to skeletal muscles; it is also a main location for personality traits and higher thought processes including learning, problem solving, memory, etc.
: receives and interprets auditory sensation and equilibrium sensation; it is also a main location for coordination of auditory and visual aspects of language
: receives and interprets cutaneous and somatic sensations and taste; it is also a main location for general association areas
: receives and interprets visual sensation
- the enlarged ventral projections of the frontal lobes, adjacent to the cribiform plate of the ethmoid bone, where the olfactory nerves begin.
- The connection between the cortex and the brain stem which consists of the thalamus, hypothalamus, epithalamus and pineal gland, and third ventricle
- A pair of large ovoid masses of gray matter situated in the posterior part of the diencephalon on either side of the third ventricle which process sensory impulses (except olfaction) by gating out irrelevant sensory information while directing relevant information to the cerebral cortex and it is also important in motor control
- The part of the brain which lies below the thalamus, forming the major portion of the ventral region of the diencephalon and which functions to regulate bodily temperature, water balance, carbohydrate and fat metabolism among other metabolic processes, and autonomic activities and also contributes to the regulation of internal homeostasis by neurosecretory functions which control the activity of the pituitary gland
- A thin mass of nervous tissue (gray and white matter) forming the roof of the third ventricle, and including the pineal gland; its gray matter is involved in emotional and visceral responses to odors and its white fibers form a link between the limbic system and other parts of the brain
- A small organ situated beneath the back part of the corpus callosum in the roof of the third ventricle of the brain which secretes the hormone melatonin; in the human it appears to play a role in sleep-wake cycles and may contribute to the regulation of the onset of puberty
- The upper portion of the brain stem, it contains major ascending and descending white fiber tracts, and contains gray matter nuclei involved in the reflex movements of the head and trunk in response to visual, auditory and other stimuli.
- The "bridge" between the midbrain and the medulla oblongata consists of gray matter nuclei, including the pneumotaxic area and apneustic area which help control breathing rate, and white fiber tracts.
- The lower portion of the brain stem, it contains major ascending and descending white fiber tracts and the location where most such tracts, sensory and motor, cross from right to left within the CNS; and it contains gray matter nuclei involved in the regulation of heart rate, vasomotor tone, respiratory rate, and coordination of swallowing, vomiting, coughing, sneezing, and hiccupping
of cerebellum is the portion of the cerebellum responsible for mediating unconscious proprioception. Inputs into the anterior lobe of the cerebellum are mainly from the spinal cord.
of cerebellum is the portion of the cerebellum caudal to the primary fissure. It is sometimes equated to the "neocerebellum", since phylogenetically it is the newest part of the cerebellum. It plays an important role in fine motor coordination, specifically in the inhibition of involuntary movement via inhibitory neurotransmitters. The posterior lobe receives input mainly from the brainstem (i.e., reticular formation and inferior olivary nucleus) and cerebral cortex.
is a lobe of the cerebellum consisting of the nodule and the flocculus. The two flocculi are connected to the midline structure called the nodulus by thin pedicles. It is placed on the anteroinferior surface of cerebellum. This region of the cerebellum has important connections to the vestibular nuclei and uses information about head movement to influence eye movement. Lesions to this area can result in multiple deficits in visual tracking and oculomotor control (such as nystagmus and vertigo), integration of vestibular information for eye and head control, as well as control of axial muscles for balance. This lobe is also involved in the maintenance of balance equilibrium and muscle tone.
Parkinson's disease (PD) is a chronic and progressive movement disorder, meaning that symptoms continue and worsen over time. Parkinson’s involves the malfunction and death of vital nerve cells in the brain, called neurons. Parkinson's primarily affects neurons in the an area of the brain called the substantia nigra. Some of these dying neurons produce dopamine, a chemical that sends messages to the part of the brain that controls movement and coordination. As PD progresses, the amount of dopamine produced in the brain decreases, leaving a person unable to control movement normally.
-Tremor of the hands, arms, legs, jaw and face
-Bradykinesia or slowness of movement
-Rigidity or stiffness of the limbs and trunk
-Postural instability or impaired balance and coordination
As many as one million Americans live with Parkinson's disease. Approximately 60,000 Americans are diagnosed with Parkinson's disease each year, and this number does not reflect the thousands of cases that go undetected. An estimated seven to 10 million people worldwide are living with Parkinson's disease. Incidence of Parkinson’s increases with age, but an estimated four percent of people with PD are diagnosed before the age of 50. Men are one and a half times more likely to have Parkinson's than women.
: The cause is unknown, and although there is presently no cure, there are treatment options such as medication and surgery to manage its symptoms.