Author Archives: Alila Medical Media

Coronary Circulation and Revascularization, with Animation

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The heart pumps out oxygen-rich blood through the aorta to nourish the entire body. It also supplies itself via a network of blood vessels called the coronary circulation. The two main vessels – the left and right coronary arteries – branch out from the aorta shortly after it exits the heart, right above the aortic valve.
The right coronary artery provides blood supply to the right atrium, and gives rise to:
– the marginal artery nourishing the lateral aspect of the right side of the heart,
– and the posterior interventricular artery, or posterior descending artery, supplying the posterior aspect of both ventricles and part of the interventricular septum.
The right coronary artery also supplies the SA node and AV node in the majority of people.
The left coronary artery splits into 2 major branches:
– the anterior interventricular artery, or anterior descending artery, supplying the anterior walls of both ventricles and most of the interventricular septum. This artery contributes the most to the left ventricle and is therefore the most critical vessel of the heart.
– the circumflex artery curves toward the posterior surface, providing for the left atrium and posterior walls of the left ventricle.
Coronary circulation is of utmost importance as it is required for normal function of the heart, which supplies blood to the entire body. A blocked coronary artery may cause life-threatening myocardial infarction, or heart attack. The most common cause of blockage is the accumulation of fat deposits on the wall of blood vessels, in a condition known as coronary heart disease.
Several procedures are available to treat coronary heart disease and restore normal blood supply to the heart. The most commonly performed are angioplasty and vascular bypass surgery.
Coronary angioplasty, also known as percutaneous coronary intervention, PCI, is a minimally invasive endovascular procedure used to widen narrowed or blocked coronary arteries. A deflated balloon attached to a catheter is passed through the femoral artery in the groin to the site of blockage, where the balloon is inflated, opening the artery. A stent may also be inserted together with the balloon and left in place to keep the artery open permanently. PCI is the procedure of choice for emergency treatment.
Coronary bypass, or vascular bypass, is a surgical procedure performed to create an alternative route for the blood to flow beyond the site of blockage. An artery graft from the patient’s chest, or a vein graft from the patient’s leg may be used for this purpose. Vascular bypass is usually performed in patients with severe coronary heart disease to prevent heart attacks, but it may also be used during or after a heart attack.

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Overview of the immune system, with animation.

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The immune system is the body’s defense system. It protects the body from disease-causing organisms, called pathogens. The protection has several layers.
First, invading pathogens meet with a number of surface barriers, which consist of physical, chemical, and biological obstacles designed to keep them out. The primary physical barrier is the skin, which covers the entire body. Body systems that are open to outside environment, such as the respiratory, digestive, urinary and reproductive system, each have their own mechanisms to prevent entrance of microbes: mucous membranes trap them, sneezing or coughing reflex expels them, while urine mechanically flushes them out.
Chemical barriers include stomach acid and various antimicrobial substances in sweat, saliva, tears and other body fluids.
The skin and mucous membranes are also heavily inhabited by the body’s normal flora, which competes with pathogens for nutrition and space, providing biological barriers.
If an organism manages to get past the surface barriers, for example, via a splinter that pierces through the skin, it will meet with the innate component of the immune system, which mounts an immediate, but non-specific response. If this fails to contain the infection, another layer of defense, called the adaptive, or acquired, immune response comes into play. The adaptive response takes longer to be activated, but is more effective as it specifically targets the invading pathogen. It also leaves the body with a “memory” of the pathogen, so it can react faster the next time the same pathogen attacks.
The major players of the immune system are the white blood cells, or leukocytes. All leukocytes derive from hematopoietic stem cells in the bone marrow. Each of them has different roles in the immune response.
The first response of the innate immune system is inflammation. Resident macrophages, which constantly patrol body tissues, ingest the pathogen and release inflammatory chemicals, called cytokines, which attract other immune cells to the site of injury. Basophils, eosinophils and mast cells release their own cytokines, amplifying inflammation. Cytokines dilate blood vessels, increasing blood flow and are responsible for clinical signs of inflammation such as redness and swelling. They act on endothelial cells of blood vessels and serve as chemical cues for migration of neutrophils – the major phagocytes involved in first-line defense. Activated endothelial cells attach to neutrophils in the flow, slowing them down, before getting them to squeeze through the vessel wall. Neutrophils engulf bacteria and destroy them with enzymes or toxic peroxides. They may also release highly reactive oxygen species in a phenomenon known as oxidative burst, which kills pathogens faster and more efficiently. The neutrophils themselves, however, also die in the process, their debris forming pus on the injury site.
The adaptive immune response starts with the so-called “antigen-presenting cells”, of which dendritic cells are most effective. Resident dendritic cells on the site of infection swallow up pathogens, cut them into pieces, called antigens, and display them on their surface. These dendritic cells are then picked up by lymphatic capillaries and travel to lymph nodes, where they present the antigens to a matching T-cell. The pathogen itself may also travel to a lymph node where it may encounter a matching B-cell. The match-finding process underlies the specificity of adaptive immune response. T-cells and B-cells exist in billions of variations, each carries a unique surface protein, which acts like a key. Among these billions of keys, only the ones that can bind to, or unlock, the invading pathogen, are activated. Activated T-cells and B-cells undergo differentiation and proliferation, called clonal expansion. This process produces memory cells, ready for future infections by the same pathogen; and effector cells, which include activated cytotoxic T-cells and plasma B cells producing antibodies; both of these are specific to the pathogen. Antibodies and cytotoxic T-cells then leave the lymph node for the bloodstream to be delivered to the site of infection. Antibodies attach to pathogens and either target them for destruction or neutralize them. Cytotoxic T-cells release toxins to kill infected host cells.

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The Lymphatic System – Circulatory and Immune Functions, with Animation

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In a nutshell, the lymphatic system is a drainage system that removes excess fluid from body tissues and returns it to the bloodstream. It is actually a subsystem of both the circulatory and immune system.
The major purpose of the circulatory system is to bring oxygen and nutrients to body tissues and remove wastes. This exchange happens in the smallest blood vessels called the capillaries. Blood plasma containing nutrients moves out of capillaries at the arterial end of capillary beds, while tissue fluid containing wastes reabsorbs back in at the venous end. However, not all of the fluid is drawn back to the bloodstream at this point. About 15% of it is left in the tissues and would cause swelling if accumulated. This is where the lymphatic system comes into play, it picks up the excess fluid and returns it to the circulatory system.
Unlike the blood circulatory system, which is a closed loop, the lymphatic system is a one-direction, open-ended network of vessels. Lymphatic vessels begin as lymphatic capillaries made of overlapping endothelial cells. The overlapping flaps function as a one-way valve. When fluid accumulates in the tissue, interstitial pressure increases pushing the flaps inward, opening the gaps between cells, allowing fluid to flow in. As pressure inside the capillary increases, the endothelial cells are pressed outward, closing the gaps, thus preventing backflow. Unlike blood capillaries, the gaps in lymphatic capillaries are so large that they allow bacteria, immune cells such as macrophages, and other large particles to enter. This makes the lymphatic system a useful way for large particles to reach the bloodstream. It is used, for example, for dietary fat absorption in the intestine.
Once inside lymphatic vessels, the recovered fluid is called lymph. Lymph flow is enabled by the same forces that facilitate blood flow in the veins. It goes from lymphatic capillaries to larger and larger lymphatic vessels and eventually drains into the bloodstream via the subclavian veins. On the way, it passes through a number of lymph nodes, which serve as filters, cleansing the fluid before it reaches the bloodstream.
Lymph nodes are small bean-shaped structures scattered throughout the lymphatic network. They are most prominent in the areas where the vessels converge. Lymph nodes contain macrophages and dendritic cells that directly “swallow up” any pathogens, such as bacteria or viruses, that may have been taken up from an infected tissue. They also contain lymphocytes: T-cells and B-cells, which are involved in adaptive immune response, a process that produces activated lymphocytes and antibodies specific to the invading pathogen. These are then carried by the lymph to the bloodstream to be distributed wherever they are needed.
The lymphatic system also includes lymphoid organs. Primary lymphoid organs – the thymus and bone marrow, are the sites of lymphocyte production, maturation and selection. Selection is the process in which lymphocytes learn to distinguish between self and non-self, so they can recognize and destroy pathogens without attacking the body’s own cells. Mature lymphocytes then leave the primary for the secondary lymphoid organs – the lymph nodes, spleen, and lymphoid nodules – where they encounter pathogens and become activated.

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The Endocrine System, Overview with Animation

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The endocrine system is one of the two systems that are responsible for communication and integration between various body tissues, the other being the nervous system. Endocrine communication is achieved by means of chemical messengers called hormones. Hormones are produced in endocrine glands and secreted into the bloodstream to reach body tissues. A hormone can travel wherever the blood goes, but it can only affect cells that have receptors for it. These are called target cells. There are 2 major types of hormones: steroid hormones derived from cholesterol and are lipid-soluble; and non-steroid hormones derived from peptides or amino-acids and are water-soluble. Lipid-soluble steroid hormones can cross the cell membrane to bind to their receptors inside the cell, either in the cytoplasm or nucleus. Steroid hormone receptors are typically transcription factors. Upon forming, the hormone/receptor complex binds to specific DNA sequences to regulate gene expression, and thus mediating cellular response. On the other hand, water-soluble non-steroid hormones are unable to cross the lipid membrane and therefore must bind to receptors located on the surface of the cell. The binding triggers a cascade of events that leads to production of cAMP, a second messenger that is responsible for cellular response to hormone. It does so by changing enzyme activity or ion channel permeability.
Major endocrine glands include: the hypothalamus, pituitary gland, pineal gland, thyroid and parathyroid glands, thymus, adrenal gland, islets of the pancreas, and testes in men or ovaries in women. The endocrine system also includes hormone-secreting cells from other organs such as kidneys and intestine.
Except for the hypothalamus and the pituitary, different endocrine glands are involved in different, more or less independent, processes. For example, the pancreas produces insulin and glucagon that keep blood sugar levels in check; the parathyroid glands produce hormones that regulate calcium and phosphorus; thyroid hormones control metabolic rates; while the ovaries and testes are involved in reproductive functions. On the other hand, the hypothalamus and pituitary gland play a more central, integrative role. The hypothalamus is also part of the brain. It secretes several hormones, called neuro-hormones, which control the production of other hormones by the pituitary. Thus, the hypothalamus links the nervous system to the endocrine system. The pituitary is known as the master gland because it controls the functions of many other endocrine glands. (See “Hypothalamus and Pituitary Gland video for details!)
A major role of the endocrine system is to maintain the body’s stable internal conditions, or homeostasis, such as blood sugar levels or serum calcium levels. To do this, it utilizes negative feedback mechanisms, which work very much like a thermostat: the heater is on when the temperature is low, off when it’s high. For example, when blood glucose level is high, such as after a meal, glucose induces insulin release from the pancreas. Insulin helps body cells consume glucose, clearing it from the blood. Low blood glucose can no longer act on the pancreas, which now stops releasing insulin. Another example is the regulation of thyroid hormones levels which are induced by a pituitary hormone called thyroid-stimulating hormone, TSH. TSH, in turn, is under control of thyrotropin-releasing hormone, TRH, from the hypothalamus. When thyroid hormone levels are too high, they suppress the secretion of TSH and TRH, consequently inhibiting their own production.

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Pathology of Different Types of Shock, with animation

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Shock, also called circulatory shock, is a life-threatening clinical state characterized by body-wide deficiency of blood supply, causing oxygen deprivation, buildup of waste products, and eventual organ failure if untreated.
Shock may have different causes and hence its classification into different types:
– Hypovolemic, or low volume shock happens when the circulating blood volume is severely reduced. This can be caused by:
+ External blood loss, such as after an injury,
+ Internal blood loss such as that results from a ruptured blood vessel, ruptured ectopic pregnancy, pancreatitis …
+ Or fluid loss from major burns, excessive vomiting, diarrhea or urination.
– Cardiogenic shock occurs when the heart fails to pump sufficiently. This can result from a sudden heart attack, or an end-stage development in various heart conditions.
– Obstructive shock is caused by an obstruction of blood flow in a major circulatory circuit.
– Distributive shock results from excessive dilation of blood vessels, or vasodilation, which decreases blood pressures. Distribution shock can have different causes, the most common being sepsis, anaphylaxis and damage to the central nervous system (neurogenic):
+ In sepsis, the immune system is overwhelmed by an infection that gets out of control, and responds with a systemic cytokine release that causes vasodilation and fluid leakage from capillaries.
+ In anaphylaxis, the immune system overreacts to an allergen, releasing massive amounts of histamine, which has similar effects to cytokines. Peanut allergy is a common cause of anaphylaxis.
+ Neurogenic shock typically occurs as a result of a spinal cord injury. As the autonomic nervous system is damaged, the sympathetic tone that normally keeps blood vessels constricted is lost, causing vasodilation and hypotension.
Common symptoms of shock include low blood pressures and signs of organ damage such as confusion, reduced urine output and cold, sweaty, mottled or bluish skin, although distributive shocks due to sepsis or anaphylaxis may initially produce warm or flushed skin. This is because the infection in sepsis usually comes with fever, and the allergic reaction in anaphylaxis is accompanied by hives. Distributive shocks may also differ from other types of shock by having, at least initially, normal or high cardiac output.
As the body tries to compensate for hypotension, fast heart rates and rapid breathing may be observed. Diagnosis may also be assisted by blood tests for blood lactate levels. This is because in the absence of oxygen, the body switches to an alternative way of producing cellular energy, called anaerobic metabolism, in which glucose is broken down only partially producing lactic acid. Blood tests may also indicate signs of organ damage, or infection in case of sepsis.
Shock is a medical emergency and requires immediate treatments which aim to increase blood pressures and treat the underlying cause.

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How obesity and physical inactivity cause prediabetes and diabetes

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Diabetes refers to a group of conditions characterized by high levels of blood glucose, commonly known as blood sugar. Glucose comes from digestion of carbohydrates in food, and is carried by the bloodstream to various body tissues. But glucose cannot cross the cell membrane to enter the cells on its own; to do so, it requires assistance from a hormone produced by the pancreas called insulin. Binding of insulin to its receptor on a target cell triggers a signaling cascade that brings glucose transporters to the cell membrane, creating passageways for glucose to enter the cells. In most tissues, muscles for example, glucose is used as an energy source, while in the liver and adipose tissue, it is also stored for later use, in the form of glycogen and fats.  When the body is in the fasted state, the liver produces and secretes glucose into the blood, while adipose tissues release free fatty acids to the liver where they are converted into additional metabolic fuel.

Diabetes happens when insulin is either deficient or its action is compromised. Without insulin, glucose cannot enter the cells; it stays in the blood, causing high blood sugar levels.

There are 2 major types of diabetes. Type 1 is when the pancreas does not produce enough insulin; and type 2 is when the body’s cells do not respond well to insulin – they are insulin-resistant. Both types are caused by a combination of genetic and environmental factors but genetics plays a major role in type 1, while lifestyle is a predominant risk factor for type 2. For this reason, type 1 diabetes usually starts suddenly in childhood, while type 2 progresses gradually during adulthood, going through a so called pre-diabetic stage, which is defined as borderline blood sugar levels: higher than normal, but lower than diabetic. Pre-diabetes is very common, and while not always developing into full-blown diabetes, over time, it can cause much the same damage to the body. Unhealthy lifestyle is the trigger of pre-diabetes and the main driving force behind its progression to diabetes type 2. The key factors are obesity and physical inactivity.

There are at least 2 ways by which obesity can cause insulin resistance and high blood glucose.

First, in obesity, fat cells have to process more nutrients than they can manage and become stressed. As a result, they release inflammatory mediators, known as cytokines. Cytokines interfere with the signaling cascade by insulin receptor, blocking the action of insulin, thereby causing the cells to become less responsive to insulin.

Second, excess adipose tissue releases abnormally large amount of free fatty acids to the liver – an event that normally happens only when the body is fasting. This tricks the liver into producing and releasing more glucose into the blood. High blood glucose stimulates further insulin secretion. Constant high insulin levels de-sensitize body tissues, causing insulin insensitivity.

Intra-abdominal fat appears to produce more fatty acids and cytokines, and therefore has more severe effect on blood glucose, than subcutaneous, or peripheral fat. For this reason, large waist size is a greater risk factor than high body mass index.

Sedentary lifestyle, apart from having indirect effect by causing weight gain, has its own direct impact on insulin resistance. This is because physical activity is required to maintain healthy blood sugar levels. Physical activity increases energy demand by the muscles, which consume glucose from the blood, and subsequently from glucose storage in the liver and adipose tissue. High energy expenditure helps to clear up faster the spikes of blood glucose that follow every meal. High energy demand also promotes better cellular response to insulin, increasing insulin sensitivity. Studies have shown that physical inactivity, even for a short period of time, results in consistently higher spikes of blood sugar after meals, which can trigger pre-diabetic changes in healthy individuals, or speed up transition from pre-diabetes to diabetes. More importantly, this happens not only to over-weight patients, but also to people with seemingly healthy weight. This is probably because inactivity reduces muscle mass and replaces it with adipose tissue, thus having serious effects on blood sugar levels while still maintaining an overall normal weight.

The bottom line is, in order to prevent diabetes, weight management must be combined with physical activity or exercise.

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Mechanism of Hearing, with Animation

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Sounds are produced by vibrating objects. The vibrations of a sound source cause the surrounding air molecules to move back and forth, creating a series of alternating regions of high and low pressures. A sound wave is basically a pressure wave – it propagates in the form of fluctuations in air pressures.
The loudness of a sound is determined by the amplitude of sound waves, which represents the strength of vibrations produced by the sound source. The stronger the vibrations, the higher the amplitude of sound waves, the louder the sound.
The pitch of a sound is related to the frequency of sound waves, which indicates how fast the sound source vibrates. The higher the frequency, the higher the pitch. Frequency is measured in hertz. A young human ear can detect sounds in the range of 20 to 20,000 hertz. Some animal species can hear frequencies well beyond this range.
Hearing is the process by which the ear transforms sound vibrations into nerve impulses that can be interpreted by the brain as sounds. The human ear has 3 distinct regions, called the outer, middle, and inner ear.
The outer ear funnels sound waves through the auditory canal to the tympanic membrane, also called eardrum, which separates the outer ear from the middle ear. The eardrum is attached to a chain of three small bones in the middle ear, called the ossicles: the malleus, incus, and stapes. Sound waves cause the tympanic membrane to vibrate, and the vibrations are transmitted through the three bones to the oval window, where the inner ear begins. Since the eardrum is much larger in area than the oval window, the sound pressure that arrives at the oval window is much greater than the original pressure received by the eardrum. This amplification is essential for the stapes to push against the higher resistance of the fluid in the inner ear.
The organ of hearing in the inner ear is the cochlea, essentially a long tube that is coiled up in a spiral to save space. The cochlea is composed of three fluid-filled chambers. The central chamber, known as the cochlear duct, is where mechanical vibrations are transformed into nerve impulses. There are four rows of hair cells within the cochlear duct, supported on the basilar membrane. The movements back and forth of the stapes push on the fluid in the cochlear duct, causing the basilar membrane, and the hair cells, to move up and down. These movements bend the cilia of hair cells, opening the mechanically-gated potassium channels on their surface. Influx of potassium depolarizes the cells, stimulating them to send nerve impulses to the cochlear nerve and on to the brain.
Our ability to differentiate sounds of different loudness and pitch depends on the ability of the cochlea to respond differently to different amplitudes and sound frequencies. Louder sounds cause more hair cells to move and generate greater nerve signals to the brain. Different frequencies stimulate different parts of the basilar membrane, which acts like a set of piano strings. The basilar membrane is narrowest and stiffest at the base, near the oval window; and widest and most flexible at the far end. High-frequency sounds with more energy can move the stiffer part of the membrane, while low-frequency sounds can only move the more flexible part. Thus, high-pitch sounds excite nerve fibers that are closer to the oval window, while low-pitch sounds send signals through the fibers at the far end.

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Sinus Node Dysfunction (Sick Sinus Syndrome), with Animation

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The heart electrical signals are initiated in its natural pacemaker – the sinoatrial node, or SA node, and travel through the atria to reach the atrioventricular node, or AV node. The AV node passes the signals onto the bundle of His, which then splits into two branches that conduct the impulses to the two ventricles.

The SA node is composed of two major cell types: P, for pacemaker, cells generate electrical impulses; and T, for transitional, cells transmit these signals to the right atrium and subsequently to the rest of the cardiac conduction system. Sinus node dysfunction occurs when any of these cells cease to function properly: failure to produce electrical impulses by P cells leads to sinus pause or sinus arrest, while delay or failure of signal transmission by T cells results in SA exit blocks.

On an ECG, sinus pause or arrest can be seen as a brief absence of P waves, which can last for seconds to minutes. In most cases, a downstream pacemaker in the atria, atrioventricular junction, or ventricles, will take over the pacing function, producing so-called escape beats or rhythms, and thus preserving heart rate and function until the SA node recovers and fires again; but long pauses may cause dizziness, fainting and possibly cardiac arrest.

In SA exit blocks, the SA node discharges normally, but the impulses are slow to reach the atrium, or completely interrupted before reaching the atrium. There are three degrees of SA blocks, similar to the 3 degrees observed with AV blocks.

  • In first-degree SA block, there is an abnormal delay between the firing of the SA node and transmission to the atrium. Because SA node firing is not significant enough to be seen on a standard 12-lead ECG, this type of block cannot be detected on a surface ECG.
  • In second-degree SA block type I, the electrical signals are delayed further and further with each heartbeat until a P wave is missing altogether. Due to the diminution in the increment of the delay, the P-P intervals are progressively shortened before the dropped P wave. This pattern results in pauses and the appearance of grouped beats. The duration of each pause is less than two P-P cycles.
  • In second-degree SA block type II, some of the electrical signals do not reach the atrium. On an ECG, this is seen as intermittent dropped P waves; the pauses are multiple, usually twice, of the P-P interval.
  • Third-degree SA block is a complete block; P waves are absent. This type of SA exit block is indistinguishable from a sinus arrest.

Sinus node dysfunction is most commonly due to degeneration or scarring of the SA node tissue, which can result from aging, other heart diseases or diabetes. Other causes may include certain medications or an excessive vagal tone.

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Unsaturated versus Saturated versus Trans Fats, with Animation

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Contrary to popular belief, not all fats cause heart diseases and are bad. In fact, most fats, in adequate amounts, are required for normal bodily functions, especially brain functions. There are also good fats that actually decrease the risks for cardiovascular diseases.

A fat molecule is composed of a glycerol head and three fatty acid tails, each of which is a long hydrocarbon chain – a carbon skeleton bound to hydrogen atoms. When all the carbons are fully bound to hydrogens, the fatty acid is said to be saturated – all the bonds between carbon atoms are single, and the hydrocarbon chain has a straight shape. A fat molecule made entirely of saturated fatty acids is a saturated fat. Due to their straight tails, saturated fats are compact and solid at room temperature.

On the other hand, when the hydrocarbon chain has fewer hydrogens, it is said to be unsaturated. Instead of binding to a maximum number of hydrogens, some carbon atoms bind to each other via a double bond. The presence of double bonds may bend the hydrocarbon chain, creating gaps between molecules, making them less compact. As a result, unsaturated fats are usually liquid at room temperature. A fat molecule that contains only one double bond is a monounsaturated fat, while one that has multiple double bonds is polyunsaturated.

Dietary fats provide fatty acids for the synthesis of the cell membrane – a vital component of all animal cells. The gaps in unsaturated fatty acids provide membrane fluidity, facilitating membrane transport and cellular signaling. While both types of fats are needed for an optimal composition of the cell membrane, too much saturated fat, which is commonly the case in a typical American diet, would make the membrane rigid and hinder cellular responsiveness. Membrane fluidity is most important in the nervous system, where neuronal response requires extremely fast cellular communication.  A certain ratio of unsaturated to saturated fatty acids is also required for the formation of myelin – the insulating material that wraps around axons of neurons and speeds up the conduction of electrical signals.

The body is capable of synthesizing all the fatty acids it needs, with the exception of polyunsaturated fatty acids omega-3 and omega-6, which must be obtained from the diet. These are known as essential fatty acids.

In general, unsaturated fats are healthier than saturated fats. Unsaturated fats decrease the risks for heart disease by reducing the amount of bad cholesterol, LDL, and increasing the good cholesterol, HDL; while saturated fats increase both good and bad cholesterol. But not all unsaturated fats are equal. In fact, a type of unsaturated fat, known as trans-fat, is the unhealthiest of all!

A double bond can give rise to 2 possible configurations: cis and trans. Cis is when the 2 hydrogen atoms are on the same side of the bond, while trans is when they are on the opposite sides. A cis double bond bends the fatty acid molecule, while the somewhat more symmetric trans configuration does not. A trans-fat is therefore similar in structure to a saturated fat. More importantly, trans-fats rarely occur in nature so the body does not have the necessary enzymes to break them down. Diets rich in trans-fats increase the bad cholesterol LDL and reduce the good cholesterol HDL, having the most detrimental effect on blood vessels.

Trans-fats are found mainly in partially hydrogenated oil products, such as margarine. Because unsaturated fats are less stable and spoil faster, food manufacturers add hydrogens to make them more saturated through a process known as partial hydrogenation. This process not only prolongs shelf-life of vegetable oils, but also turns them into solid, or semi-solid products, which are preferred by commercial bakers for their low cost and wide range of different textures. Unfortunately, partial hydrogenation also converts some of the cis double bonds into trans configuration, producing trans-fats. The FDA has officially banned production of partially hydrogenated oils in June 2018, but products made earlier may still be in use until January 2020.

 

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Effects of Exercise on the Brain, with Animation

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Apart from body fitness, physical exercise also has beneficial effects on the brain. A regular routine of aerobic exercise can improve memory, thinking skills, moods; and have protective effects against aging, injuries and neurodegenerative disorders.

It is noteworthy that these effects are specific to “aerobic” exercise – the kind of exercise that accelerates heart rate and respiratory rate, such as running, cycling, swimming… Non-aerobic activities, such as stretching or muscle building, do not have the same effect. The effects appear to result from increased blood flow to the brain and subsequent increase in energy metabolism. A certain degree of intensity is required to achieve the beneficial outcome.

Aerobic exercise increases the production of several growth factors of the nervous tissue, known as neurotrophic factors, among which BDNF, for Brain-Derived Neurotrophic Factor, has a central role. BDNF exerts a protective effect on existing neurons, and stimulates formation of new neurons from neural stem cells in a process called neurogenesis.

BDNF appears to coordinate its action with at least 2 other growth factors: insulin-like growth factor 1, IGF-1, and vascular endothelial growth factor, VEGF, whose expression levels also increase following aerobic exercise. BDNF interacts with IGF-1 to induce neurogenesis, while VEGF stimulates growth of new blood vessels, a process known as angiogenesis. Together these processes improve survival of existing neurons, produce new brain tissue, and constitute the brain’s enhanced plasticity that underlies the exercise-induced protective effect against aging, degenerative diseases and injuries.

Changes in BDNF levels are observed throughout the brain but are most remarkable in the hippocampus, the area that is responsible for memory retention and learning. In fact, regular exercise has been shown to increase the size of the hippocampus and improve cognitive functions.

While acute exercise, defined as a single workout, can produce significant changes in BDNF levels and subsequent improvements in learning performance; a regular exercise program progressively increases BDNF baseline level and make its response steadier overtime. It appears that some cognitive functions are enhanced immediately after a single workout, while others only improve following a consistent exercise routine.

The immediate effect of acute exercise is most remarkable on the body’s affective state. A single bout of exercise can promote positive emotions, suppress negative feelings, reduce the body’s response to stress, and sometimes, after intense exercise, induce a euphoric state known as “runner’s high” sensation. These effects may persist for up to 24 hours, and are thought to result from exercise-induced upregulation of several neurotransmitters involved in mood modulation. These include:

  • Dopamine – a neurotransmitter of the brain reward pathways;
  • Serotonin, commonly known as the substance of well-being andhappiness, whose low levels in the brain have been associated with depressive disorders;
  • Beta-endorphin, or endogenous morphine, an endogenous opioid;
  • and anandamide, an endogenous cannabinoid, a substance related to psychoactivechemicals in marijuana. Endogenous opioids and cannabinoids are involved in pain modulation, stress and anxiety reduction and are believed to underlie the “runner’s high” sensation.
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