Exam 3

Animals Maintain a Steady Internal Environment

  • Internal Stability: Animal bodies function most effectively within a narrow range of internal conditions. When these conditions deviate too far from the optimal state, it can lead to physiological distress or death.
  • Standard Human Body Temperature: In humans, the typical body temperature is approximately 98.6 ∘F98.6\,^{\circ}F.
  • Homeostasis: This is the process by which animals regulate their internal environment to maintain a stable, constant condition despite changes in the external environment.
  • Thermal Regulation Extremes:
    • Hyperthermia (Fever): This occurs when the temperature of the body becomes too high. It is characterized by symptoms such as sweating, as the body attempts to dissipate heat to return to its set point.
    • Hypothermia: This occurs when the temperature of the body becomes too low. It is characterized by shivering, as the body attempts to generate heat through rapid muscle contraction to return to the set point.

How Does Homeostasis Work?

  • Negative Feedback Loop: This is the most common method of maintaining homeostasis. It occurs when a system responds to a change by returning to its original state, or by decreasing the rate at which the change is occurring.
    • The Set Point: The body has a specific "set point" for various factors (like temperature or blood sugar). When levels move away from this point, negative feedback mechanisms are triggered.
    • Example (Too Hot): If the body reaches 101 ∘F101\,^{\circ}F, the pancreas or thermal sensors trigger responses like sweating to cool the body back toward the set point.
    • Example (Too Cold): The body initiates shivering to produce metabolic heat and bring the temperature back up to the set point.
  • Blood Sugar Regulation: The body controls blood sugar (glucose) levels through a negative feedback loop involving the pancreas and liver.
    • Lowering Blood Sugar: To lower blood sugar, the pancreas releases insulin. Insulin facilitates the uptake of glucose by cells and the storage of glucose as glycogen in the liver.
    • Raising Blood Sugar: To raise blood sugar, the pancreas releases glucagon. This hormone signals the liver to break down stored glycogen into glucose to be released into the bloodstream.
  • Positive Feedback Loop: A less common strategy where the body move further away from the set point in response to a stimulus. It does not stop but keeps going to reach a specific endpoint before returning the body to a normal state.
    • Example (Childbirth): During labor and delivery, contractions trigger the release of hormones that lead to even stronger contractions. This cycle continues until the baby is born, at which point the body returns to homeostasis.

Circulatory System Overview

  • Core Components: The circulatory system is comprised of three main parts:
    1. The Pump: The heart.
    2. Transport Vessels: The blood vessels (arteries, veins, and capillaries).
    3. Transport Fluid: Blood.
  • Functions of Transport: The circulatory system is responsible for moving several vital substances throughout the body, including:
    • Oxygen (O2O_2)
    • Carbon dioxide (CO2CO_2)
    • Hormones
    • Nutrients
    • Waste products

Blood: A Mixture of Cells and Fluid

  • Total Volume: On average, a human has approximately 55 to 6 quarts6\,\text{quarts} of blood circulating constantly.
  • Primary Function: Transportation of essential materials to and from cells.
  • Components of Blood: Blood can be separated into two primary areas:
    • Plasma: The liquid portion of the blood that contains water, proteins, nutrients, and waste.
    • Packed Cells: The cellular portion of the blood, consisting of red blood cells, white blood cells, and platelets.

Cell Types Found in Blood

  • Production: All blood cells are derived from stem cells located in the bone marrow and are produced at a high rate.
  • Red Blood Cells (RBCs):
    • Hemoglobin: RBCs contain this protein, which is responsible for picking up oxygen in the lungs and delivering it to tissues.
    • Structure: An individual hemoglobin molecule consists of four polypeptide chains arranged to provide four "iron seats" where oxygen molecules attach.
    • Unique Features: RBCs have a short lifespan and lack a nucleus or other organelles. This lack of internal structure maximizes the space available for hemoglobin, thereby increasing the oxygen-carrying capacity.
  • White Blood Cells (WBCs): These cells are primary components of the immune system and are involved in defending the body against pathogens.
  • Platelets:
    • Nature: Platelets are not true cells but are cellular fragments.
    • Function: They are essential for blood clotting.
    • The Clotting Process: Clotting is a complex cascade involving various proteins and cells:
      1. Platelets adhere to the site of a vessel injury.
      2. Prothrombin is converted into thrombin.
      3. Thrombin acts as an enzyme to convert the soluble protein fibrinogen into the insoluble, stringy protein fibrin.
      4. Fibrin creates a mesh that traps cells and forms a clot.

Major Vessels of the Circulatory System

  • Arteries:
    • Characteristics: Thick-walled and muscular to withstand high pressure.
    • Function: Carry blood away from the heart.
  • Capillaries:
    • Characteristics: Extremely thin-walled (single cell layer thick) and narrow.
    • Function: The site of gas, nutrient, and waste exchange between the blood and the surrounding tissues.
  • Veins:
    • Characteristics: Thinner walls than arteries; they contain valves.
    • Function: Carry blood back toward the heart.
    • Purpose of Valves: Valves prevent the backflow of blood, ensuring it moves in one direction toward the heart, even against the force of gravity.

Blood Pressure

  • Definition: Blood pressure is the measurement of the force applied by the blood against the walls of the arteries.
  • Readings: Represented by two numbers (Systolic/Diastolic\text{Systolic} / \text{Diastolic}):
    • Systolic Pressure: The pressure in the arteries while the heart ventricles are contracting.
    • Diastolic Pressure: The pressure in the arteries while the heart is at rest between beats.
  • Blood Pressure Thresholds:
    • Hypertension (High Blood Pressure): Characterized by readings above 140/90 mmHg140/90\,\text{mmHg}. It can lead to heart disease, kidney failure, and stroke.
    • Hypotension (Low Blood Pressure): Characterized by readings below 90/60 mmHg90/60\,\text{mmHg}. Symptoms include dizziness and fainting.
  • Relative Pressure: Arteries have the highest pressure because they receive blood directly from the heart's pumping action.

The Lymphatic System

  • Overview: A system of vessels carrying a fluid called lymph.
  • Function 1: Recycling Fluid: The system collects excess interstitial fluid (the fluid surrounding cells) and returns it to the bloodstream via the subclavian veins. This prevents fluid accumulation (edema) in tissues.
  • Function 2: Fighting Illness: Lymphatic organs and vessels help filter pathogens and house immune cells.

Structure of the Heart

  • Chambers: The human heart has four chambers:
    • Atria (Right and Left): The upper chambers that receive blood entering the heart.
    • Ventricles (Right and Left): The lower, muscular chambers that pump blood out of the heart.
  • Septum: A thick wall that separates the right and left sides of the heart. This prevents the mixing of deoxygenated blood (right side) with oxygenated blood (left side).
  • Valves:
    • Atrioventricular (AV) Valves: Located between the atria and the ventricles. They prevent blood from flowing back into the atria when the ventricles contract.
    • Semilunar Valves: Located at the exits of the heart (the pulmonary artery and the aorta). They prevent blood from flowing back into the ventricles after they relax.
    • Heart Sounds: The "lub" sound is caused by the closing of the AV valves; the "dup" sound is caused by the closing of the semilunar valves.
    • Heart Murmur: Caused by blood leaking backward through a valve that does not close properly.
  • Electrical Control:
    • SA Node (Sinoatrial Node): Known as the natural pacemaker, located in the right atrium. It generates electrical signals spontaneously without nerve stimulation, causing the atria to contract.
    • AV Node (Atrioventricular Node): Receives the signal from the SA node and passes it to the ventricles, causing them to contract.

The Circuits of the Heart

  • Pulmonary Circuit:
    • Deoxygenated blood is brought to the right side of the heart.
    • The right ventricle pumps blood to the lungs.
    • Blood releases CO2CO_2 and absorbs O2O_2 (gas exchange).
  • Systemic Circuit:
    • Oxygenated blood returns from the lungs to the left side of the heart.
    • The left ventricle pumps blood to the tissues and organs of the entire body.
    • Tissues use the oxygen and produce CO2CO_2 and waste, which enter the blood.
    • Deoxygenated blood returns to the right side of the heart.

Cardiovascular Disease (CVD)

  • Atherosclerosis: A condition where plaque (fat, cholesterol, etc.) builds up on arterial walls, narrowing the lumen and restricting blood flow.
  • Arteriosclerosis: The thickening and stiffening of arterial walls, which reduces elasticity and blood flow, often due to aging or high blood pressure.
  • Cholesterol and Lipoproteins:
    • High-Density Lipoprotein (HDL): "Good cholesterol." It removes excess cholesterol from the blood and carries it to the liver for excretion.
    • Low-Density Lipoprotein (LDL): "Bad cholesterol." It contributes to plaque formation in the arteries.
  • Heart Attack: Occurs when coronary arteries (which supply the heart muscle) become blocked, causing the death of heart muscle cells. These cells cannot be replaced.
  • Stroke: Caused by a blockage or rupture of arteries in the brain.
  • Treatments:
    • Stent: A small mesh tube inserted into an artery to keep it open, often during angioplasty.
    • Bypass Surgery: A surgical procedure that redirects blood flow around a blocked section of a coronary artery.
    • Medications: Various drugs to manage blood pressure or cholesterol.
  • Prevention (The ABCs):
    • A: Aspirin or Anticoagulants (to prevent clotting).
    • B: Blood pressure control.
    • C: Cholesterol control.

The Immune System Overview

  • Self vs. Non-self: The immune system identifies pathogens by distinguishing between the body's own markers ("self") and foreign markers ("non-self").
  • Three Lines of Defense:
    1. Barrier Defenses (Nonspecific)
    2. Nonspecific Defenses / Innate Immunity (Nonspecific)
    3. Specific Defenses / Adaptive Immunity (Specific)
  • Difference between Defenses: Nonspecific defenses respond the same way to all invaders; specific defenses create a targeted response tailored to a unique pathogen.

Barrier Defenses (First Line)

  • Physical Barriers:
    • Skin: A tough outer layer that is difficult to penetrate.
    • Mucous Membranes: Line the respiratory, digestive, and reproductive tracts; they trap pathogens in mucus for removal.
  • Chemical Barriers:
    • Lysozyme: Enzymes in tears and saliva that break down bacterial cell walls.
    • Stomach Acid: A highly acidic environment that destroys most ingested pathogens.
  • Biological Barriers: Beneficial microbes (normal flora) that compete with pathogens for space and nutrients.

Nonspecific Defenses (Second Line)

  • Characteristics: Immediate response and broad-spectrum protection.
  • Phagocytic Cells: Macrophpages and neutrophils that engulf and digest pathogens through phagocytosis.
  • Inflammation: Triggered by the release of histamine from mast cells. Signs include redness, heat, swelling, and pain. It recruits immune cells to the site of infection.
  • Fever: Elevated body temperature that inhibits microbial growth and speeds up tissue repair.
  • Antimicrobial Proteins:
    • Interferons: Alert neighboring cells to viral infections.
    • Complement Proteins: Assist in destroying bacteria.

Specific Defenses (Third Line)

  • Characteristics: Targeted (only attacks the specific pathogen that triggered it) and possesses memory (remembers the pathogen for future encounters).
  • Components:
    • Lymphocytes: The main players (T cells and B cells).
    • Antigens: Substances (usually proteins) that trigger the immune response.
    • Antibodies (Immunoglobulins): Proteins produced by B cells that bind to specific antigens.
  • T Cells (Cell-Mediated Immunity):
    • Helper T Cells: Stimulate B cells to produce antibodies and Cytotoxic T cells to kill.
    • Cytotoxic (Killer) T Cells: Directly destroy infected or foreign cells using perforin and granzymes.
    • Regulatory T Cells: Manage the immune response to prevent overactivity.
    • Memory T Cells: Stay in the body to provide rapid response to re-exposure.
  • B Cells (Humoral Immunity):
    • Activated B cells are called plasma cells, which mass-produce antibodies.
    • Antibody Action:
      1. Agglutination: Clumping pathogens together.
      2. Neutralization: Blocking a pathogen’s ability to infect cells.
      3. Precipitation: Making soluble antigens insoluble for easier removal by phagocytes.
  • Memory Cells: Both T and B memory cells provide a faster, more powerful response upon second exposure to a pathogen.

HIV/AIDS and the Immune System

  • Acquisition: HIV is transmitted through infectious fluids: blood, semen, vaginal fluids, and breast milk.
  • Immune Deficiency: HIV specifically infects and destroys CD4+ T cells (Helper T cells). Without these cells to coordinate the immune response, the body becomes "deficient" and susceptible to opportunistic infections and cancers (defined as AIDS).

Active and Passive Immunity

  • Active Immunity: The body produces its own antibodies. It is long-lasting due to memory cell formation.
    • Natural Active: Recovering from an illness (e.g., Chickenpox).
    • Artificial Active: Receiving a vaccine (weakened/inactive antigen).
  • Passive Immunity: Antibodies are transferred from another source. It is immediate but temporary (no memory cells).
    • Natural Passive: Antibodies passed through the placenta or breast milk.
    • Artificial Passive: Injection of serum/antibodies (e.g., Rabies treatment).

Blood Types and Transfusions

  • ABO System: Based on A and B antigens.
    • Type A: A antigen; Anti-B antibodies.
    • Type B: B antigen; Anti-A antibodies.
    • Type AB: Both A and B antigens; No antibodies.
    • Type O: No antigens; Both Anti-A and Anti-B antibodies.
  • Rh Factor: Presence (Rh+Rh+) or absence (Rh−Rh-) of the Rh antigen.
  • Compatibility:
    • Universal Donor: O−O- (no A, B, or Rh antigens).
    • Universal Recipient: AB+AB+ (no anti-A, anti-B, or anti-Rh antibodies).
    • Incompatibility: Leads to agglutination (clumping), which can cause serious complications.

Immune System Malfunctions

  • Autoimmune Disorders: The immune system fails to recognize "self" and attacks the body's own tissues. Examples include Rheumatoid Arthritis, Type 1 Diabetes (destruction of pancreatic beta cells), and Lupus.
  • Allergies: Overreaction to a harmless substance (allergen). The immune system produces IgE antibodies, leading to histamine release. Severe reactions can cause anaphylaxis.

Human Reproduction

  • Male Anatomy:
    • Testes: Produce sperm and testosterone.
    • Epididymis: Sperm storage and maturation.
    • Vas Deferens: Transports sperm.
    • Glands (Seminal Vesicles, Prostate, Bulbourethral): Produce nourishing and protective seminal fluid.
  • Female Anatomy:
    • Ovaries: Produce eggs, estrogen, and progesterone.
    • Fallopian Tubes (Oviducts): Site of fertilization; transport eggs to the uterus.
    • Uterus/Endometrium: Site where the fetus develops; the lining is shed during menstruation.
    • Vagina: Birth canal.

Functions and Regulation of the Male System

  • Erection Mechanism: Arousal triggers the release of nitric oxide, causing blood vessels in the penis to dilate. Erectile tissues fill with blood and veins are compressed to maintain firmness.
  • Sperm Structure:
    • Head: Contains the nucleus (2323 chromosomes).
    • Acrosome: Cap with enzymes to penetrate the egg.
    • Midpiece: Packed with mitochondria for energy.
    • Tail: Flagellum for movement.
  • Capacitation: Physiological changes sperm undergo in the female tract (increased calcium permeability and acrosome responsiveness) to gain the ability to fertilize an egg.
  • Hormonal Control:
    • GnRH: From the hypothalamus; starts the cycle.
    • FSH: Stimulates sperm production (spermatogenesis).
    • LH: Stimulates testosterone production by Sertoli/Leydig cells.
    • Testosterone: Primary sex hormone; regulated by negative feedback.

Female Reproduction and Hormones

  • Ovarian Function: Females are born with all the eggs they will ever have. At ovulation, a follicle bursts and releases an egg.
  • Post-Ovulation: The empty follicle becomes the corpus luteum, which secretes progesterone.
  • Menstrual Cycle Phases:
    • Menstrual Phase (Days 1–5): Shedding of the endometrium.
    • Follicular Phase (Days 6–14): Follicle matures; Estrogen increases to thicken the lining.
    • Ovulation (Day 14): Egg is released.
    • Luteal Phase (Days 15–28): Corpus luteum forms; Progesterone increases.
  • Fertilization and Pregnancy:
    • Fertilization occurs in the fallopian tube.
    • Implantation happens 77 to 10 days10\,\text{days} after ovulation in the uterus.
    • The placenta secretes hCG (the hormone detected in pregnancy tests).

Birth Control and STDs

  • Contraception Methods:
    • Barrier: Condoms, diaphragms.
    • Hormonal: Pills, patches, implants (inhibit ovulation).
    • IUD: Copper or hormonal; prevent fertilization/implantation.
    • Emergency Contraception: Plan B or Ella (prevents ovulation, not an abortion).
  • Infertility: Inability to conceive after 1 year1\,\text{year} of unprotected sex.
  • STDs (Sexually Transmitted Diseases):
    • Bacterial: Chlamydia, Gonorrhea, Syphilis (Treatable with antibiotics).
    • Viral: HIV, HPV (vaccine available), Herpes (No cure; managed with antivirals).