Spring 2025 Focused Review Notes Exam 1 PDF

Spring 2025 Page 1 of 11 Focused Review Notes Exam 1 – Spring 2025 CONCEPTS TO FOCUS ON FOR EXAM 1 NOTE: I include MOST of these concepts in the review, but may not touch on some if fairly straight forward. However, review ALL of these concepts. – PLEASE...

Spring 2025 Page 1 of 11 Focused Review Notes Exam 1 – Spring 2025 CONCEPTS TO FOCUS ON FOR EXAM 1 NOTE: I include MOST of these concepts in the review, but may not touch on some if fairly straight forward. However, review ALL of these concepts. – PLEASE REACH OUT TO YOUR COURSE FACULTY IF YOU HAVE ANY QUESTIONS!!! MARK YOUR CALENDARS: Exam 1 opens Tuesday, February 4 at 8 am and closes Friday, February 7 at 8 am CENTRAL TIME. Your exam score will be posted by Saturday, February 8 at 5 pm Central time. WEEKS 1, 2, AND 3 CONTENT COVERED ON EXAM 1: Chapters: 1, 2, 3, 4, 5, 6 Cellular Biology/Alterations MAIN COMPONENTS OF THE CELL Nucleus contains the nucleolus, a small, dense structure composed largely of RNA. Primary function of the nucleus is cell division and control of genetic information. Protects this vital genetic information and is in charge of replication and repair of deoxyribonucleic acid (DNA). Ribosomes are RNA-protein complexes (nucleoproteins) that are synthesized in the nucleolus and secreted into the cytoplasm through pores in the nuclear envelope called nuclear pore complexes (NPCs). Their chief function is to provide sites for cellular protein synthesis. Golgi complex (or Golgi apparatus) is a network of flattened, smooth membranes and vesicles frequently located near the nucleus of the cell. Proteins from the endoplasmic reticulum are processed and packaged into small membrane-bound sacs or vesicles called secretory vesicles. The Golgi complex is a refining plant and directs traffic (e.g., protein, polynucleotide, polysaccharide molecules) in the cell. Lysosomes maintain cellular health: ✔​ efficient removal of toxic cellular components ✔​ removal of useless organelles, ✔​ signals cellular adaptation They are signaling hubs of a sophisticated network for cellular adaptation and maintenance of metabolic homeostasis. The signaling functions have far-reaching implications for metabolic regulation in health and in disease. Mitochondria are organelles responsible for cellular respiration and energy production. THINK Adenosine triphosphate (ATP = energy) – ATP functions as the energy-transferring molecule.  Spring 2025 Page 2 of 11 Cellular Metabolism: All of the chemical tasks of maintaining essential cellular functions are referred to as cellular metabolism. The energy-using process of metabolism is called anabolism (ana = upward), and the energy-releasing process is known as catabolism (cata = downward). Metabolism provides the cell with the energy it needs to produce cellular structures. Dietary proteins, fats, and starches (i.e., carbohydrates) are hydrolyzed in the intestinal tract into amino acids, fatty acids, and glucose, respectively. These constituents are then absorbed, circulated, and incorporated into the cell, where they may be used for various vital cellular processes, including the production of ATP Role of Adenosine Triphosphate: What is best known about ATP is its role as a universal “fuel” inside living cells. It is the energy-carrying molecule! This fuel, or energy, drives biological reactions necessary for cells to function. For a cell to function, it must be able to extract and use the chemical energy in organic molecules. ATP not only stores energy but also transfers it from one molecule to another. Energy stored by carbohydrate, lipid, and protein is catabolized and transferred to ATP. CELLULAR ADAPTATION Atrophy: Physiologic atrophy: For example, the thymus gland undergoes physiologic atrophy during childhood. Uterus decreases in size after childbirth. Tonsils shrink in adolescents. Pathologic atrophy occurs as a result of decreases in workload, use, pressure, blood supply, nutrition, & hormonal stimulation. FOR EXAMPLE: Individuals immobilized in bed for a prolonged time exhibit a type of skeletal muscle atrophy called disuse atrophy. Hypertrophy: (increase in size of cell) Another cellular adaptation that can actually be beneficial is hypertrophy of myocardial cells (called myocytes) such as in endurance training – this is referred to as physiologic hypertrophy. Pathologic hypertrophy that occurs secondary to hypertension (HTN): Pathologic hypertrophy results from chronic hemodynamic overload, such as from HTN or heart valve dysfunction. When Left Ventricular Hypertrophy (LVH) occurs secondary to hypertension, it represents pathologic hypertrophy. Prolonged cardiac hypertrophy progresses to contractile dysfunction, hemodynamics are altered, and finally heart failure. In contrast to physiologic hypertrophy, where the myocardial matrix is preserved, pathologic hypertrophy is associated with increased interstitial fibrosis, cell death, and abnormal cardiac function. Hyperplasia: (increase in the number of cells) results from an increased rate of cellular division. As a response to a stimulus (e.g., injury), hyperplasia occurs when the damage is severe or prolonged or when it results in cell death. Hyperplasia requires that cells undergo mitosis, a process wherein a single cell divides into two identical cells. The main mechanism for hyperplasia is the production of hormones or growth factors, which stimulate the remaining cells after injury or cell loss to synthesize new cell components and, ultimately, to divide. Another mechanism is increased output of new cells from tissue stem cells. Mature cells have differing capacity for hyperplastic (mitotic) growth. Pathological: Benign prostatic hyperplasia (BPH). Metaplasia: (replacement of cells) normal columnar ciliated epithelial cells of the bronchial lining have been replaced by stratified squamous epithelial cells. Can be reversed if irritant stopped. CELLULAR INJURY Hypoxia, or the lack of sufficient oxygen within cells, is the single most common cause of cellular injury and is a prominent feature of pathological states encountered in bacterial infection, inflammation, wounds, cardiovascular defects, and cancer. Hypoxia can result from several circumstances, such as reduced oxygen content in the ambient air, loss of hemoglobin, decreased red blood cell (RBC) production, respiratory and cardiovascular diseases. The most common cause of hypoxia is ischemia, or a reduced supply of blood and therefore oxygen  Spring 2025 Page 3 of 11 (decreased perfusion). Hypoxia negatively impacts normal physiological processes: differentiation, angiogenesis, proliferation, erythropoiesis, and overall cell viability. Mitochondria are the primary consumers of oxygen. Ethanol (alcohol use disorder): Liver enzymes metabolize ethanol to toxic acetaldehyde. Acetaldehyde is a highly toxic substance and known carcinogen. Chronic alcohol consumption breaks down the gut barrier function (causing leaky gut), which leads to impaired gut motility, delaying gastric emptying time; induces chemical gastritis; and impaired absorption of nutrients (e.g., folic acid, thiamine, vitamin B6, magnesium, and phosphorus). Folic acid deficiency, in particular, is problematic in persons consuming large quantities of alcohol. Ethanol alters folic acid (folate) homeostasis by decreasing intestinal absorption of folate, and increasing the loss of folate through urinary and fecal excretion. Folic acid deficiency becomes especially serious when alcohol is consumed during pregnancy and may contribute to fetal alcohol syndrome. Magnesium is the second most abundant micronutrient in the human body, and deficiency is almost universal in individuals with high levels of alcohol consumption and/or liver disease. Urinary excretion of magnesium is increased secondary to alcohol consumption, and total body stores of magnesium become depleted. Radiation: Ionizing radiation is emitted by x-rays, γ-rays, and alpha and beta particles (which are emitted from atomic nuclei in the process of radioactive decay). A main pathologic mechanism is the subsequent damage to DNA (VERY BAD!). It also generates free radicals. Free radicals play a major role in the initiation and progression of diseases. A free radical is an electrically uncharged atom or group of atoms having an unpaired electron. Having one unpaired electron makes the molecule unstable; thus, to stabilize, it gives up an electron to another molecule or steals one. Therefore, it is capable of injurious chemical bond formation with proteins such as fragmentation and folding, lipids, carbohydrates—key molecules in membranes and nucleic acids. They cause DNA damage and mutations. Antioxidants contribute to protections against damage caused by free radicals. Apoptosis versus Necrosis. The two main types of cell death are necrosis and apoptosis. Apoptosis: Approximately 10 billion new cells are created every day, and the same number destroyed. Usually physiological role. A programmed cell death that is regulated or programmed. Usually, a normal physiological process of the elimination of unwanted cells. Necrosis: Usually pathologic (culmination of irreversible cell injury). Characterized by rapid loss of the plasma membrane structure, organelle swelling, mitochondrial dysfunction. Hypoxia is the #1 major cause of cellular injury leading to necrosis. EXAMPLE of necrosis is cell death during a myocardial infarction (heart attack). Aging and the cell/tissues. Every physiological processes can be shown to function less efficiently. Effects of aging depends on how we care for ourselves and genetics! ✔​ Senescence causes loss of tissue-repair capacity ✔​ Increase in stem cell exhaustion ✔​ Peripheral vascular resistance increases. ✔​ Delayed emptying of stomach. ✔​ Decreased immune response to T-dependent antigens  Spring 2025 Page 4 of 11 ✔​ Increased accumulation of pro-inflammatory tissue Fluids & Electrolytes, Acid and Base Balance Fluid balance Vulnerable populations to fluid imbalances: Infants: ✔​ 75-80% TBW ✔​ They have a high metabolic rate. ✔​ Their kidneys are not mature enough to counter fluid losses. Older adults: thirst sensation is diminished MAJOR PLAYERS IN THE PROCESS OF FLUID BALANCE: Hydrostatic pressure - At the arterial end of capillaries, fluid moves from the intravascular space into the interstitial space because capillary hydrostatic pressure (blood pressure) is higher than the capillary oncotic pressure. Hydrostatic pressure facilitates the outward movement of water from the capillary to the interstitial space and is mainly influenced by blood pressure. Oncotic pressure is heavily influenced by plasma proteins (albumin). Low plasma albumin causes edema, especially in the lower extremities, as a result of a reduction in plasma oncotic pressure. Renin angiotensin-aldosterone system (RAAS) - When circulating blood volume or blood pressure is reduced, renin, an enzyme secreted by the juxtaglomerular cells of the kidney, is released in response to sympathetic nerve stimulation and decreased perfusion of the renal vasculature. Aldosterone (think sodium) - Hormonal regulation of sodium and potassium balance is influenced by aldosterone. When circulating blood volume or blood pressure is reduced: Aldosterone causes sodium (Na+) and water resorption (hangs on to Na+ and water), AND thus increases blood pressure and blood volume. However, sacrifices potassium by increasing excretion thus hypokalemia. Hyperaldosteronism causes: Hypokalemia, hypernatremia, and fluid volume excess. Hypoaldosteronism causes: Hyperkalemia, hyponatremia, and fluid volume deficit. Antidiuretic hormone (ADH (think water): Secretion of ADH and the perception of thirst are stimulated by a decrease in plasma volume, increase in serum sodium, decreased blood pressure (so decreased perfusion). Natriuretic peptides are hormones that include atrial natriuretic peptide (ANP) produced by the myocardial atria, brain natriuretic peptide (BNP) produced by the myocardial ventricles, and urodilatin within the kidney. Natriuretic peptides decrease blood pressure and increase sodium and water excretion. (Counteracts the RAAS – it is an ANTAGONIST OF THE RAAS) ELECTROLYTES Sodium (Na+)  Spring 2025 Page 5 of 11 Regulator of fluids, nerve impulse conduction, acid-base balance, cellular chemical reactions, and transport of substances across the cellular membrane. Hyponatremia is associated with hypoaldosteronism, loss of sodium, inadequate intake, and some medications. Sodium depletion usually causes hypoosmolality with an associated movement of water into cells (cellular swelling with potential for rupture) and cellular function is altered. Clinical manifestations are related to altered action potential in neurons and muscles so impaired nerve conduction and neurologic changes. Nausea, vomiting with less severe hyponatremia. More severe lethargy, seizures, coma. FYI: major cause of morbidity and mortality in intensive care and older patients. Hypernatremia: central nervous system is most serious, and some are the same as hyponatremia such as coma and seizures. Potassium (K+) K+ is the major determinant of the resting membrane potential necessary for transmission of nerve impulses. The ratio of K+ in the ICF to K+ in the ECF is the major determinant of the resting membrane potential, which is necessary for the transmission and conduction of nerve impulses, maintenance of normal cardiac rhythms, and skeletal and smooth muscle contraction. Clinical manifestations of potassium imbalances: think heart --- cardiac functioning. ALSO, a HUGE contributor to acid-base balance, for example: An increase in hydrogen ions (acidosis) in the blood causes the body to shift hydrogen ions into the cell in exchange for potassium. Hyperkalemia: Oliguric kidney failure (little to no urine output!) and Addison’s disease (decreased production of aldosterone thus body holds onto K+). Hyperkalemia should be investigated when there is a history of renal disease, massive trauma, insulin deficiency, Addison disease, use of potassium salt substitutes, or metabolic acidosis. SHIFT: In states of acidosis, hydrogen ions shift into the cells in exchange for ICF potassium. Hypokalemia: Decreased intake: starvation or anorexia nervosa, inadequate replacement. Increased renal loss: renal tubular failure, K+-losing diuretics, hyperaldosteronism, vomiting, diarrhea. SHIFT: from ECF to ICF: respiratory/metabolic alkalosis. Insulin promotes cellular uptake of K+. For example: When administering insulin in diabetic ketoacidosis (DKA) – watch for decreased ECF potassium! Calcium, Phosphate, Magnesium CAUSES MANIFESTATIONS Calcium Calcium (calming) is a necessary ion for many fundamental metabolic processes. It is the major cation associated with the structure of bones and teeth. It serves as an enzymatic cofactor for blood clotting and is required for hormone secretion and the function of cell receptors. Plasma membrane stability, permeability, and repair are directly related to calcium ions, as is the transmission of nerve impulses and the contraction of muscles. Hypocalcemia Increased neuromuscular excitability; tetany, tingling, muscle Inadequate intestinal absorption, massive blood spasms (particularly in hands, feet, and facial muscles), intestinal administration, decreases in PTH and vitamin D cramping, hyperactive bowel sounds; osteoporosis and fractures;  Spring 2025 Page 6 of 11 CAUSES MANIFESTATIONS levels; nutritional deficiencies, elevated severe cases show convulsions and tetany; prolonged QT calcitonin level; pancreatitis interval, cardiac arrest Hypercalcemia Hyperparathyroidism; bone metastases with calcium resorption from breast, prostate, renal, and cervical cancer; excess vitamin D; many Many nonspecific; fatigue, weakness, lethargy, anorexia, nausea, tumors that produce PTH; calcium-containing constipation; impaired renal function, kidney stones; antacids dysrhythmias, bradycardia, cardiac arrest; bone pain Calcium and phosphorous balance is influenced by parathyroid hormone (PTH), calcitonin, and vitamin D Phosphate Think “energy” ATP (adenosine triphosphate) and oxygen transport 2,3 DPG (2,3 diphosphoglycerate) Hypophosphatemia Conditions related to reduced capacity for oxygen transport by Intestinal malabsorption related to vitamin D red blood cells and disturbed energy metabolism; leukocyte and deficiency, long-term alcohol use disorder; platelet dysfunction; deranged nerve and muscle function; in increased renal excretion of phosphate severe cases, irritability, confusion, numbness, coma, associated with hyperparathyroidism convulsions; possibly respiratory failure (because of muscle weakness), cardiomyopathies, bone resorption (leading to rickets or osteomalacia) (Same as hypercalcemia) Hyperphosphatemia Acute or chronic renal failure with significant loss of glomerular filtration (kidneys main Symptoms primarily related to low serum calcium levels (caused excretory organ for phosphate); long-term use by high phosphate levels) similar to symptoms of hypocalcemia; of laxatives or enemas containing phosphates; when prolonged, calcification of soft tissues in lungs, kidneys, hypoparathyroidism joints. (Same as hypocalcemia) Magnesium Magnesium (calming) is a cofactor in intracellular enzymatic reactions, protein synthesis, and neuromuscular excitability. Improves myocardial metabolism, reduces peripheral vascular resistance, and inhibits platelet function.  Spring 2025 Page 7 of 11 CAUSES MANIFESTATIONS Hypomagnesemia Malnutrition, malabsorption syndromes, alcohol use disorder, urinary losses (renal tubular Behavioral changes, irritability, increased reflexes, muscle dysfunction, loop diuretics) cramps, ataxia, nystagmus, tetany, convulsions, tachycardia Hypermagnesemia Usually, renal insufficiency or kidney failure with Lethargy, drowsiness; loss of deep tendon reflexes; nausea and little or NO urine output!! (Mg+ excreted by vomiting; muscle weakness; bradycardia; respiratory distress; kidneys and intestines); also, excessive intake heart block, cardiac arrest of magnesium-containing antacids ACID-BASE IMBALANCE An acid-base imbalance is not a disorder in and of itself, it is a diagnostic sign. In order to correct the imbalance, treatment is targeted at resolving the cause of the imbalance (see table below for causes and pathophysiology of each imbalance). The body will compensate at all costs to maintain a range of 7.35-7.45. Perfect pH is 7.40 – less than 7.40 is considered acidosis; greater than 7.40 is alkalosis when evaluating pH during an exacerbation of a disease entity. Causes Pathophysiology RESPIRATORY ACIDOSIS ​ ↑ CO2 retention from hypoventilation ​ Examples below of poor ventilatory status ​ Compensatory response (lungs in (hypoventilation) that cause retention of carbon dioxide trouble, kidneys try to help) is ↑ HCO3− (CO2) thus unable to eliminate a powerful acid via the retention by kidney, but this is not an lungs!! immediate compensatory mechanism and does take some time to be effective. ✔​Respiratory failure – hypoventilation UGH! However, with chronic respiratory conditions such as chronic obstructive ✔​Chronic respiratory disease (e.g., COPD) pulmonary disease (COPD), kidneys are very effective. ✔​Barbiturate or sedative overdose ​ Kidneys secrete hydrogen ions (H+). ✔​Respiratory muscle weakness ​ Bicarbonate is regenerated by the kidneys.  Spring 2025 Page 8 of 11 Causes Pathophysiology RESPIRATORY ALKALOSIS ​ Compensatory response (lungs in Examples below of increased elimination of carbon trouble, kidneys try to help) is ↑ HCO3− dioxide (CO2) - loss of too much acid from the body excretion by kidney through the lungs (hyperventilation). ​ Hyperventilation – causes: hypoxia, anxiety, fear, pain, fever ​ Stimulated respiratory center (e.g., septicemia, stroke, meningitis, encephalitis, brain injury) METABOLIC ACIDOSIS ​ Gain of fixed acid, inability to excrete acid or loss of base INCREASED ACID load = BICARBONATE LOSS Compensatory response (kidneys in ELEVATED ANION GAP (NORMAL ANION GAP) trouble, lungs try to help) is ↑ CO2 Increased hydrogen ion (H+) excretion by lungs called Kussmaul load Good way to remember: Diarrhea respirations – the patient presents KILU with increased rate and depth of K = Ketoacidosis (diabetes respirations. Vomiting – trying to get Renal failure mellitus) rid of acid! I = Ingestions (ethylene glycol, salicylates) L = Lactic acidosis (shock) U = Uremia METABOLIC ALKALOSIS ​ Loss of strong acid or gain of base ​ Vomiting – loss of acid (pH of stomach contents = 2) ​ Compensatory response (kidneys in ​ Nasogastric suctioning trouble, lungs try to help) is ↑ CO2 retention by lungs ​ Diuretic therapy ​ Hypokalemia ​ Any condition that elevates aldosterone or mineralocorticoids (which enhance sodium [Na] reabsorption and potassium [K] and hydrogen ion [H +] excretion) can elevate HCO 3 −.  Spring 2025 Page 9 of 11 GENETICS GENETIC PRINCIPLES General overview: Identification of a specific genetic lesion can lead to effective prevention and support early screening. Presence of a genetic component can alter the course of disease through prevention and lowering risk factors. Also, a family history of a disease may mean that the person is more likely to develop the disease earlier in life: for example: a person with a first-degree relative with Alzheimer disease has double the risk. Elements of Formal Genetics 1. Alleles are different forms of genes located at the same locus on the chromosome. 2. At any given locus in a somatic cell, an individual has two genes, one from each parent. An individual may be homozygous or heterozygous for a locus. 3. An individual's genotype is the person's genetic makeup, and 4. The phenotype reflects the interaction of genotype and environment. Expressivity is the extent of variation in phenotype associated with a particular genotype. If the expressivity of a disease is variable, the penetrance may be complete but the severity of the disease can vary greatly. Deoxyribonucleic acid (DNA). Genes are functional regions of DNA. To serve as the basis of genetic inheritance, DNA must be able to provide a code for all the body's proteins. DNA must be able to replicate itself accurately during cell division so that the genetic code can be preserved in subsequent cell generations. A mutation is any inherited alteration of genetic material. Several different proteins are involved in DNA replication. One protein unwinds the double helix, one holds the strands apart, and others perform different distinct functions. The most important of these proteins is the enzyme known as DNA polymerase. This enzyme travels along the single DNA strand, adding the correct nucleotides to the free end of the new strand. Besides adding the new nucleotides, the DNA polymerase performs a proofreading procedure. After the new nucleotide has been added to the chain, the DNA polymerase checks to make sure that its base is actually complementary to the template base. If it is not, the incorrect nucleotide is excised and replaced with a correct one. This procedure, one of the mechanisms of DNA repair, substantially enhances the accuracy of DNA replication. Aneuploid cells are defined as those that do not contain a multiple of 23 chromosomes. Monosomy, the presence of only one copy of a given chromosome in a diploid cell, is the other common form of aneuploidy. Monosomy of any chromosome is lethal. However, newborns with trisomy of chromosomes 13, 18, or 21 can survive. This difference illustrates an important principle: loss of chromosome material has more serious consequences than duplication of chromosome material. An aneuploid cell containing three copies of one chromosome is said to be trisomy (a condition termed trisomy). The most well-known example of aneuploidy in an autosome is trisomy of the twenty-first Chromosome: Down syndrome was formerly called mongolism, but this an inappropriate term and no longer used. Individuals with this disease typically have intelligence quotients (IQs) between 25 and 70. The facial appearance is distinctive, with a low nasal bridge, protruding tongue, and flat, low-set ears. Autosomal recessive: For a recessive allele to be expressed, they must exist in a homozygous form. The most common lethal autosomal recessive disease in white children is cystic fibrosis and is more common in females.  Spring 2025 Page 10 of 11 EXAMPLE: If a male has the gene for cystic fibrosis, an autosomal recessive disorder, and the female has no gene, the child may still be a carrier. Carriers do not usually show any phenotypic signs of the disease. Because most recessive alleles are maintained in normal carriers, they are able to survive in the population from one generation to the next. Autosomal dominant: When one allele masks those of another they are in a heterozygote form. At a heterozygous locus, the dominant gene masks those of a recessive gene. For example, an autosomal dominant form of breast cancer. Genes responsible for this form of breast cancer have been mapped to chromosomes 17 (BRCA1) and 13 (BRCA2). Women who inherit a mutation in BRCA1 or BRCA2 experience a 50% to 80% lifetime risk of developing breast cancer. Breast cancer aggregates strongly in families. If a woman has one affected first-degree relative, her risk of developing breast cancer doubles. Another example is early onset Alzheimer disease (AD). Later onset AD is rapidly increasing in the United States. AD before the age of 65 is usually associated with an autosomal dominant mode of transmission. Sex chromosome aneuploidy. Some conditions are caused by genes located on the sex chromosomes, and that mode of inheritance is referred to as sex-linked. The Y chromosome contains only a few dozen genes, so most sex-linked traits are located on the X chromosome and are said to be X-linked. Females receive two X chromosomes, one from the father and one from the mother, so they can be homozygous for a disease allele at a given locus, homozygous for the normal allele at the locus, or heterozygous. A male who inherits a recessive disease allele on the X chromosome will be affected by the disease because the Y chromosome does not carry a normal allele to counteract the effects of the disease-causing allele. Consequently, males are more frequently affected by X-linked recessive diseases, with the difference becoming more pronounced as the disease becomes rarer. X inactivation sex chromosome aneuploidy is the presence of a single X chromosome and no homologous X or Y chromosome, resulting in a total of 45 chromosomes; and it causes a set of symptoms known as Turner syndrome. Because they have no Y chromosome, persons with Turner syndrome are always female. They are usually sterile, however, and have gonadal streaks rather than ovaries. Other features of the disorder include short stature, webbing of the neck in about half of cases, widely spaced nipples, coarctation (narrowing) of the aorta (in 15% to 20% of cases), edema of the feet in newborns, and sparse body hair. Their IQs are typically in the normal range, however intellectual abilities can be affected especially with impairment of spatial and mathematical reasoning ability. Teenagers with Turner syndrome are typically treated with estrogen to promote the development of secondary sexual characteristics. (DO NOT NEED TO CALCULATE THESE FOR THE EXAM, BUT DO KNOW THE DEFINITIONS). Incidence rate is the number of new cases of a disease reported during a specific period (typically 1 year) divided by the number of individuals in the population. For example, during COVID, incidence rate was calculated on a weekly basis (number of new cases of COVID in one week) Relative risk is a common measure of the effect of a specific risk factor. It is expressed as a ratio of the incidence rate of the disease among individuals exposed to a risk factor divided by the incidence of the disease among individuals not exposed to a risk factor. EXAMPLE: The incidence of death from lung cancer is 1.66 in heavy smokers (more than 25 cigarettes daily), but only 0.07 nonsmokers. The ratio of these two incidence rates is 1.66/0.07, which yields a relative risk of 23.7 deaths. Thus, it is concluded that the relative risk of dying from lung cancer increased by about 24-fold in heavy smokers compared with nonsmokers.  Spring 2025 Page 11 of 11 Recurrence rate (RR) of multifactorial inheritance. 1)​ If the expression of the disease is more severe RR is higher. 2)​ Recurrence risk becomes higher if more than one family member is affected. For example, the sibling recurrence risk for a ventricular septal defect (VSD, a type of congenital heart defect) is 3% if one sibling has been affected by a VSD but increases to approximately 10% if two siblings have been diagnosed with VSDs. 3)​ The recurrence risk for the disease usually decreases rapidly in more remotely related relatives. 4)​ Many genes and environmental factors contribute to multifactorial diseases. Epigenetics bridges DNA information and function by modifying gene expression without any alteration in DNA sequence. "Epi-"means on or above in Greek, and "epigenetic" describes factors beyond the genetic code. Epigenetic changes are modifications to DNA that regulate whether genes are turned on or off. These modifications are attached to DNA and do not change the sequence of DNA building blocks. ​ Epigenetic modification can cause individuals with the same DNA (IDENTICAL TWINS) to have different disease profiles – For example the occurrence of asthma in only one of a pair of identical twins. ​ As twins age, they demonstrate increasing differences in methylation patterns of their DNA sequences, causing increasing numbers of phenotypic differences. ​ Environmental factors, such as diet and exposure to certain chemicals, may cause epigenetic modification. ​ Epigenetic factors are behaviors and environmental factors that can change how genes work, turning them "on" or "off". These factors can include: ​ Exposure to toxins: Air pollution, diesel exhaust, cigarette smoke, plastics, BPA, heavy metals like lead or cadmium ​ Substances: Alcohol, tobacco, recreational drugs, and certain prescription medications ​ Lifestyle: Foods, physical activity, stress levels, relationships, social interactions, community support, and access to healthcare ​ Epigenetic changes can occur throughout life, both as part of normal development and aging, and due to exposure to environmental factors. These changes can affect health in different ways. YOU CAN DO THIS!!!!