Respiratory Challenges and Fick's Law

Respiration Challenges in Different Environments

• Aquatic environments present challenges for respiration due to lower oxygen availability, slower diffusion rates, and temperature-dependent oxygen solubility.
• Terrestrial environments pose challenges related to water loss and maintaining moist respiratory surfaces.

Fick's Law of Diffusion

• Fick's Law (Q = DA(P1-P2)/L) dictates the rate of gas diffusion.
• Q = rate of diffusion.
• D = diffusion coefficient.
• A = area of diffusion surface.
• P1-P2 = partial pressure difference.
• L = distance between locations

Partial Pressure

• Partial pressure is the concentration of gases in a mixture, driving diffusion.
• Atmospheric pressure at sea level is 760 mm Hg.
• Oxygen makes up ~20.9% of air, so its partial pressure at sea level is ~159 mm Hg.
• At high altitudes, atmospheric pressure decreases, reducing the partial pressure of oxygen (e.g., Mount Everest: 253 mm Hg atmospheric pressure, 53 mm Hg O2 partial pressure)

Diffusion in Water vs. Air

• The diffusion coefficient (D) varies with the medium; oxygen diffuses slower in water than in air.
• Oxygen partial pressure in water cannot exceed that of the surrounding air; water is denser and less soluble to oxygen.
• Higher temperatures reduce oxygen solubility in water, exacerbating respiration challenges for aquatic organisms.
• Fish hypoxia is more common in hot months.

Respiratory Structure Adaptations

• Respiratory structures often feature branching networks to maximize surface area (A) for diffusion.

Dual Pump of Fish

• Fish use a dual pump mechanism for ventilation.

Countercurrent Flow

• Countercurrent flow in fish gills maximizes oxygen extraction from water by maintaining a concentration gradient.

Evolution of Buccal Pump

• The buccal pump evolved alongside the development of lungs in some species.

Aspiration Pump and Tidal Ventilation

• The aspiration pump and tidal ventilation are respiratory mechanisms.

Bohr Effect

• The Bohr effect relates to hemoglobin's oxygen-binding affinity relative to pH.
• Lower pH (more acidic) reduces hemoglobin's affinity for O2, promoting oxygen release in tissues with high CO2 levels.
• Higher pH (less acidic) increases hemoglobin's affinity for O2, facilitating oxygen uptake in the lungs.
• In tissues, CO2 reacts with water to form carbonic acid, lowering pH and promoting oxygen unloading.
• In the lungs, high PO2 causes hemoglobin to bind O2 and release H+, reversing the reaction and releasing CO2. This process helps maintains constant blood pH.

Carbon Dioxide Transport

• CO2 is transported in red blood cells as bicarbonate, increasing acidity.
• H+ ions bind to hemoglobin, reducing its affinity for O2.
• The Bohr effect increases O2 unloading at metabolically active cells that produce CO2.
• In the lungs, high PO2 causes hemoglobin to bind O2 and release H+, reversing the reaction and releasing CO2 during exhalation.

Osmolarity and Osmoregulation

• Osmolarity refers to the solute concentration of a solution, which affects water movement across membranes.
• In hypertonic solutions (high solute concentration outside the cell), water moves out of the cell, causing it to shrink.

Nitrogenous Waste

• Nitrogenous wastes are toxic and must be excreted.
• Ammonia is water-soluble and easily excreted by aquatic organisms.

Excretory Systems in Invertebrates

• Protonephridia (e.g., in Planaria): Flame cells with cilia draw in extracellular fluid, followed by selective reabsorption and secretion, with dilute urine excreted via pores.
• Metanephridia (e.g., in annelids): Coelomic fluid enters nephrostome, with selective reabsorption and secretion in tubules, and waste exits via nephridiopore.
• Malpighian tubules (e.g., in insects): Active transport of uric acid, Na+, and K+ pulls water, with minimal water loss due to ion reabsorption in the hindgut/rectum.

Vertebrate Nephron

• The vertebrate nephron maintains extracellular fluid homeostasis.
• Filtrate flows through Bowman’s capsule, proximal convoluted tubule, Loop of Henle, distal convoluted tubule, and collecting duct.
• Urine flows from the collecting duct.

Nephron Function

• Filtration: From glomerulus to Bowman’s capsule.
• Reabsorption: From renal tubule to circulation.
• Secretion: From circulation to renal tubule.
• Excretion: From collecting duct.

Concentrated/Dilute Urine

• Dilute urine contains more water and less waste; concentrated urine has less water and more waste.
• In the collecting duct, water is reabsorbed into the blood down the descending loop.
• Salts are actively pumped out of the ascending loop into the tissue, diluting it with the gradient; the concentration of urine is adjusted in the collecting duct.
• ADH in the collecting duct signals cells to insert aquaporins, allowing more water to be reabsorbed into the bloodstream.
• Low ADH levels result in more dilute urine.

Regulation of ADH

• High osmolarity (dehydration) triggers ADH release.
• Osmoreceptors in the hypothalamus detect blood osmolarity.
• Baroreceptors in blood vessels detect changes in blood pressure and inhibit ADH production when blood pressure increases and promote it with decrease.
• ADH increases the permeability of collecting duct cells and distal tubule cells to water.

Immunology: Animal Defense Systems

• The innate immune response is non-specific and rapid, while the adaptive immune response is specific and slower.
• Deadly human pathogens include HIV, influenza virus, smallpox virus, bubonic plague, tuberculosis, and malaria.
• Wildlife pathogens and diseases include snake fungal disease, chytrid fungus in amphibians, bat white nose syndrome, elk hoof disease, pneumonia in big horn sheep, and avian influenza.

Elements of the Innate Immune Response

• Lysozymes are secreted into mucus and rupture bacterial cell walls.
• The complement system involves proteins made by the liver that tag pathogens for phagocytosis, recruit phagocytes, and lyse invading cells.
• Defensins are proteins that insert into the pathogen's cell membrane and create pores, making it permeable.
• Interferons are proteins produced by infected cells that prevent the spread of infection to neighboring cells.

Immune Response

• The immune response includes recognition of self vs. non-self, activation of cells and molecules to fight invaders, and effector mechanisms to destroy the invader.

Lymphatic System

• The lymphatic system includes lymphatic vessels, lymph nodes, thymus, bone marrow, and spleen.
• It collects interstitial fluid (lymph) and returns it to the circulatory system, containing WBCs and platelets but not RBCs.

White Blood Cells

• White blood cells (leukocytes) include granulocytes, monocyte-derived cells, and lymphocytes.
• B and T cells, the main cells of the adaptive immune response, are primarily found in lymph nodes and are derived from bone marrow.

Key Players in Coordinating Adaptive Response

• Major histocompatibility complex (MHC) proteins display foreign antigens on the surface of cells, allowing T cells to identify infected cells.
• T cell receptors are proteins on the surface of T cells that recognize antigens presented by MHC proteins.
• Antibodies (immunoglobulins, Ig) are proteins produced by B cells that bind to foreign molecules (antigens).
• Cytokines are protein hormones used for communication between immune cells, inducing responses in target cells.
• MHC proteins present antigens of intracellular parasites on the surface of infected cells.

Adaptive Immune Response

• The adaptive immune response includes humoral (B cell antibodies) and cellular (T cell receptor binding) responses.
• It exhibits specificity, recognition of self/non-self, ability to deal with many pathogens, and memory.

Antibodies

• Antibodies neutralize pathogens, opsonize pathogens for phagocytosis, and activate the complement system.

Generating Diversity

• Diversity of antibodies arises from the selection and combination of genes from multiple coding regions (V, D, and J genes) during B cell maturation in bone marrow and T cell maturation in the thymus.
• Clonal selection refers to the proliferation of B or T cells with antibodies or receptors that "match" the antigen.
• Memory cells ensure a rapid response to the next encounter with the same antigen.

Coronavirus Entry Into Cells

• Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) gains entry into cells via a hormone 'receptor'.

ACE2

• ACE2 is a membrane enzyme/receptor that breaks down angiotensin.
• Actions on lung epithelial tissue involve ACE2 converting Ang II to Ang1-7, which acts through Mas receptors to counter the effects of Ang II on lung tissue.

Allergic Reactions

Failure of Self Recognition

• In insulin-dependent diabetes mellitus (Type I diabetes), the immune response kills beta cells that produce insulin, leading to increased blood glucose levels.

Autoimmune Failure

• In Hashimoto’s thyroiditis, immune cells attack thyroid tissue, resulting in lethargy, fatigue, weight gain, and depression; a goiter may form initially.

Muscle Types

• Skeletal muscle: Voluntary, striated, multinucleate.
• Cardiac muscle: Involuntary, striated, uninucleate, with intercalated discs.
• Smooth muscle: Involuntary, not striated, uninucleate; controls movement in the gut, glands, bladder, and blood vessels.

Microscopic Muscle Structure

Muscle Contraction: Sliding Filaments

• Tropomyosin wraps around actin; troponin-Ca2+ binding alters its position

Skeletal Muscle Contraction

• Neural input initiates skeletal muscle contraction.
• The motor end plate is involved in neural input.

Muscle ATP Sources

• Preformed ATP and creatine phosphate (donates phosphate to ADP).
• Glycolytic system: Metabolizes carbs to pyruvate (or lactate), yielding less ATP.
• Oxidative system: Metabolizes carbs and fats to H2O and CO2, yielding more ATP.
• The system used governs endurance and is characteristic of white vs. red muscle.

Gametogenesis

• Gametogenesis involves spermatogenesis in males.
• Gametogenesis involves oogenesis in females.
• In many species, including humans, the primary oocyte is arrested in early stages of meiosis and does not complete meiosis until puberty (just before ovulation).

Male Sex Organs

• Seminal fluid (semen or ejaculate) is composed of fluids that support sperm and facilitate fertilization; less than 5% of semen volume is sperm.
• Additional fluids (sugars, mucus, enzymes, acid neutralizers) come from the seminal vesicles, prostate, and bulbourethral glands.

Spermatogenesis

• Spermatogenesis takes place in the seminiferous tubules.
• Sertoli cells provide nourishment for developing sperm and secrete chemicals that promote sperm development
• Leydig cells are outside seminiferous tubules and produce androgens.

Male Gonadal Hormones

• Androgens, like testosterone, are responsible for the development of external genitalia and secondary sexual traits (deep voice, facial hair, musculature).
• They are controlled by a classic negative feedback loop that also includes inhibin produced by Sertoli cells.
• Gonadal hormones also regulate spermatogenesis and reproductive behavior.

Female Sex Organs

• When the egg is fertilized by sperm, it is a secondary oocyte (n) and subsequently completes meiosis followed by fusion of the haploid nuclei.
• The dividing zygote forms the blastocyst.
• The blastocyst implants in the endometrium.

Ovarian Cycle

• Just before ovulation, the primary oocyte completes the first meiotic division, forming a haploid secondary oocyte.

Graafian Follicle

• The antrum is fluid-filled and has high concentrations of steroids.
• Thecal cells and granulosa cells are collectively "follicular" cells.
• Thecal cells produce androgens.
• Granulosa cells convert androgens to estrogens.
• After ovulation, the follicular cells form the corpus luteum and begin producing estrogens and progesterone, causing proliferation of the endometrium.

Hormones in Embryo Development

• The developing embryo produces a hormone that "rescues" the corpus luteum.
• If hCG is not produced, the corpus luteum degrades, forming the corpus albicans.
• hCG is the target of most pregnancy tests.

Feedback Control of Gonadal Hormones in Females

• Control of estrogen and progesterone production is similar to males.
• Unlike males, there is negative AND positive feedback.
• Positive feedback is associated with estrogens (not progesterone) and stimulates ovulation.