Physiology: Homeostasis, Nervous, Sensory, Muscle, Bone, Endocrine, Energetics, Digestive, Respiratory, Cardiovascular, Reproductive, Renal, Immune Systems
Homeostasis, Nervous, and Sensory Systems
Homeostasis and Feedback Loops:
- Negative Feedback Loops: Essential for maintaining homeostasis. The effector decreases the stimulus. The set point is crucial.
- Positive Feedback Loops: Typically detrimental, the effector increases the stimulus. The set point is less critical.
- Pathophysiology: The opposite of homeostasis.
Reflexes: Involuntary, unlearned responses to specific stimuli.
Nervous System Divisions:
- CNS: Brain and spinal cord.
- PNS: Peripheral nerves, sensory, and effector neurons.
- Efferent Division: Signals from CNS to effectors. Includes:
- Somatic NS: Innervates skeletal muscle, excitatory, single neuron.
- Autonomic NS: Innervates smooth muscle, cardiac muscle, and glands, excitatory or inhibitory, 2-neuron chain to ganglia.
- Autonomic NS Subdivisions:
- Sympathetic NS: Fight or flight.
- Enteric NS: GI tract.
- Parasympathetic NS: Rest and digest.
- Afferent Division: Signals from stimulus to CNS.
Neuron Types:
- Sensory Neurons: Receive and transmit information about the environment or internal state.
- Interneurons: Process information and transmit it to different body regions.
- Motor Neurons: Signal muscles or glands to cause a response.
Graded Potentials: Variable amplitude and duration, conducted decrementally, no threshold or refractory period, caused by gated ion channels (voltage, ligand, mechanically gated).
Action Potentials: Brief, all-or-none depolarization, has a threshold and refractory period, conducted without decrement.
Saltatory Conduction: Action potentials jump from node to node along the axon.
Synaptic Potentials:
- EPSPs: Opens Na+ channels, cell becomes less negative.
- IPSPs: Opens Cl- and/or K+ channels, cell becomes more negative.
Presynaptic Factors: Precursor molecules, membrane potential, Ca2+, activation receptors, drugs/diseases.
Sensory Acuity: Ability to distinguish between stimuli.
Hearing:
- Outer Ear: Sound is reflected by the pinna, amplified in the ear canal, and vibrates the tympanic membrane.
- Middle Ear: Ear ossicles amplify sound and vibrate the oval window.
- Inner Ear: Vibrations pass through the cochlea, causing vibrations of the basilar membrane and displacing hair cells in the Organ of Corti.
Muscle, Bone, Endocrine, and Energetics
Motor Neuron Axon Terminal:
- Action potential reaches the axon terminal.
- Voltage-gated Ca2+ channels open.
- Vesicles release ACh into the synapse.
- ACh binds to nAChR on the muscle cell.
- nAChR activation causes an action potential.
- Action potential travels along the muscle cell membrane and T-tubules.
- Action potential enters DHPRs, which are connected to ryanidine receptor channels.
- Ryanidine receptor channels open, releasing Ca2+ into the cytosol.
- Ca2+ binds to troponin, exposing binding sites on actin.
- Ca2+ pumps return Ca2+ to the sarcoplasmic reticulum.
Anterior Pituitary Hormones:
- FSH & LH: Stimulate gonads.
- TSH: Stimulates thyroid.
- GH: Stimulates growth and metabolism.
- ACTH: Stimulates adrenal cortex.
- Prolactin: Stimulates breast development and milk production.
Amine Hormones: Thyroid and catecholamines.
Thyroid Hormones: Regulate metabolic rate, growth, and brain development.
Catecholamines: Derived from tyrosine.
Peptide Hormones: Coded in the genome, stored in vesicles.
Steroid Hormones: Produced in the adrenal cortex and gonads from cholesterol.
Adrenal Cortex Hormones:
- Aldosterone: Salt balance in kidneys.
- Cortisol/Corticosterone: Glucose metabolism.
- DHEA/Androgens: Sexual development and puberty.
Gonadal Hormones:
- Estradiol: Growth, sexual development, and puberty.
- Testosterone: Growth, sexual development, and puberty.
Muscle Proteins:
- Tropomyosin: Blocks myosin binding sites on actin.
- Troponin: Binds calcium and moves tropomyosin.
Cross-Bridge Cycle:
- Resting State: Myosin heads energized, tropomyosin blocks binding sites.
- Cross-Bridge Binding: Ca2+ binds to troponin, exposing binding sites.
- Power Stroke: ADP and Pi dissociate, myosin head moves actin.
- Cross-Bridge Release: ATP binds to myosin, releasing actin.
Digestive, Respiratory, and Cardiovascular Systems
Digestive System Functions: Digestion, motility, absorption, secretion.
Digestive Enzymes:
- Pepsin: Digests proteins.
- Lipase: Digests fats.
- Trypsin, Chymotrypsin, Elastase: Digest proteins.
- Carboxypeptidase: Splits off terminal amino acids.
- Amylase: Breaks down polysaccharides.
Stomach Secretions:
- HCL: Dissolves stomach contents, kills bacteria.
- Gastrin: Released by G cells.
- Histamine: Produced in ECL cells.
- Somatostatin: Produced in stomach, intestine, and pancreas.
GI System Control: Volume and composition of luminal contents, neural regulation (CNS and ENS), hormonal regulation.
Liver Functions: Secretes bile, processes nutrients, filters old red blood cells, synthesizes plasma proteins.
Hepatic Portal System: Drains blood from the GI tract to the liver.
GI Tract Layers:
- Mucosa: Epithelium, lamina propria.
- Submucosa: Connective tissue, blood vessels, submucosal plexus.
- Muscularis Externa: Smooth muscle layers, myenteric plexus.
- Serosa: Connective tissue, serous fluid.
Cephalic Phase Stimuli: Sight, smell, taste, or thoughts of food.
Respiratory System Functions: Provides O2, eliminates CO2, regulates [H+], defends against microbes, influences chemical messengers, traps blood clots.
Steps of Respiration:
- Ventilation.
- Gas exchange in lungs.
- Gas transport.
- Gas exchange in tissues.
- Cellular utilization of O2 and production of CO2.
Gas Diffusion Factors: Increased surface area, pressure difference, solubility, decreased membrane thickness.
Respiratory Zones:
- Conducting Zone: Moves air, no gas exchange.
- Respiratory Zone: Gas diffusion.
Hemoglobin vs Myoglobin: Hemoglobin has a sigmoid curve, myoglobin has a hyperbolic curve.
Oxygen Transport Steps: Delivery to lungs, diffusion into blood, transport to tissues, diffusion into cells.
Pleura:
- Visceral Pleura: Attached to lungs.
- Parietal Pleura: Attached to thoracic wall and diaphragm.
Intra-pleural Pressure: Always around 4 mmHg or less.
Lung Compliance: The inverse of stiffness, increased by surfactant.
Cardiovascular System Functions: Circulates oxygen, nutrients, removes waste, protects against disease, clots blood, transports hormones, regulates temperature.
Poiseuille’s Equation: Flow = ∆P/R.
Heart Excitation Sequence:
- SA node initiates action potentials.
- Signal travels to AV node.
- AV node fires, signal travels down the bundle of His.
- Purkinje fibers excite ventricles.
- Ventricles relax and repolarize.
SA Node: Pacemaker, generates activity without afferent input.
Rhythmic Cardiac Cycling: Funny Na+ channels, t-type Ca2+ channels, L-type Ca2+ and K+ channels.
Cardiac Cycle:
- Diastole: Ventricular filling/relaxation.
- Systole: Ventricular ejection/contraction.
Cardiac Cycle Steps:
- Diastole 1: Ventricular filling.
- Systole 2: Isovolumetric ventricular contraction.
- Systole 3: Ventricular ejection.
- Diastole 4: Isovolumetric ventricular relaxation.
Frank Starling Law: Stroke volume increases with end-diastolic volume.
DPG: Binds to hemoglobin more strongly when deoxygenated.
Reproductive, Renal, and Immune Systems
Reproductive Hormones: Androgens, estrogens, gonadotropins, progesterones.
Androgens: Testosterone, DHEA, androstenedione, DHT.
Testosterone: Produced by Leydig cells, stimulates male characteristics.
DHEA and Androstenedione: Formed in the adrenal gland, initiate puberty.
Dihydrotestosterone (DHT): Derived from testosterone, more potent.
Estrogens: Estradiol, estrone, estriol.
Estradiol: Produced by the ovary, growth hormone for breasts, uterus, ovaries.
Estrone: Main estrogen in postmenopausal people.
Estriol: High levels during pregnancy.
Gonadotropins: LH and FSH, produced in the anterior pituitary.
LH and FSH Effects on Testes: LH stimulates testosterone, FSH stimulates sperm and inhibin.
LH and FSH In Ovaries: LH triggers ovulation, FSH essential for egg maturation.
Progesterones: Essential for maintaining pregnancy.
Ovarian Cycling: Follicular phase, ovulation, luteal phase.
Selection of the Dominant Follicle: Feedback loop acting on all follicles.
Ovulation: LH surge stimulates ovulation.
Luteal Phase: Corpus luteum produces hormones.
Corpus Luteum: Temporary endocrine structure.
Pregnancy – Fertilization: Occurs in the fallopian tube.
Implantation: Embryo produces HCG.
Placenta: Gas and nutrient exchange between parent and infant.
Parturition (Birth): Three positive feedback loops.
Lactation: Stimulated by suckling.
Kidney Functions: Maintain water and ion balance, produce erythropoietin, produce vitamin D.
Nephrons: Functional units of the kidney.
Juxtamedullary Nephrons: Long loop of Henle.
Cortical Nephrons: Short loop of Henle.
Urine Formation: Glomerular filtration, tubular secretion, tubular reabsorption.
Filtration: Forces for and against.
Reabsorption: Most filtrate is reabsorbed.
Tubular Reabsorption: Paracellular and transcellular transport.
Tubular Secretion: Substances move from capillaries to lumen.
Tubule Labor Division: Proximal tubule and loop of Henle, distal tubule and collecting duct.
Urine Formation: Proximal tubule, loop of Henle, distal tubule, collecting duct.
Vasopressin: Increases water reabsorption.
Aldosterone: Stimulates Na+ reabsorption.
Regulating Na+ Levels: Renin-angiotensin system.
Immune System: Innate and adaptive.
Innate Immune System: Unspecific response, preventative, cellular, chemical pathways.
Cells: White blood cells (leukocytes).
Macrophages: Phagocytosis, secrete toxins, process antigens.
Dendritic Cells: Phagocytosis, process antigens.
Neutrophils: Phagocyte, release vasodilators and chemotaxins.
Phagocytosis: Intracellular killing of microbes.
Toll-like Receptors: Recognize pathogen-associated molecular patterns (PAMPs).
Mast Cells: Release histamine and other chemicals involved in inflammation.
Cytokines: Protein messengers of the immune system.
Inflammation: Response to injury or infection.
Vasodilation: Increased delivery of proteins and leukocytes.
Interferons: Type I and Type II, antiviral proteins.
Complement Cascade: Proteins activated by pathogens.
Adaptive Immune System: Lymphocytes (B cells and T cells).
Antigen: Triggers an adaptive immune response.
Generalized Adaptive Immune Response: Lymphocyte activation, clonal expansion, attack antigens.
Primary Lymphoid Organs: Initial site of lymphocyte development.
Secondary Lymphoid Organs: Store and activate lymphocytes.
Lymphatic System: Accumulates cellular debris and antigens.
Lymphocyte Maturation: B cells in bone marrow, T cells in thymus.
Humoral-Mediated Immunity: B cells secrete antibodies.
Cell-Mediated Immunity: T cells kill antigen-bearing cells.
Helper T Cells: Activate B cells and T cells.
NK Cells: Target virus-infected and cancer cells.
Active Immunity: Memory cells allow for rapid response.
Passive Immunity: Antibodies from one individual to another.
Blood Typing: Carbohydrate chains on red blood cells act as antigens.
Autoimmune Diseases: Mediated by autoantibodies and self-reactive T cells.
Additional Information
Shwachman-Diamond Syndrome: Affects bones, pancreas, and bone marrow, due to alterations in the SBDS gene.
21-Hydroxylase Deficiency (Congenital Adrenal Hyperplasia): Deficiency in enzymes required for cortisol synthesis.
Marfan Syndrome: Genetic disorder resulting in defective connective tissue, caused by mutation in fibrillin 1 gene.
Tetanus: Caused by Clostridium tetani, blocks neurotransmitters, causing muscle spasms.
Duchenne’s Muscular Dystrophy: Muscular weakness, mutation in the dystrophin gene.