Human Digestion Process

Mastication and Mechanical Digestion

• Mastication is the chewing process that breaks food into smaller pieces to aid digestion.
• Mechanical digestion involves physical breakdown through chewing, churning in the stomach, and muscle movements along the digestive tract.

Salivary Enzymes

• Salivary amylase starts the breakdown of starches into simpler sugars like maltose.
• Salivary lipase initiates fat digestion by breaking triglycerides into fatty acids and glycerol.

Food Processing and Passage

• A bolus is a rounded mass of food formed after mixing with saliva, ready for swallowing.
• The pharynx connects the nasal cavity and mouth to the esophagus and trachea.

Esophagus and Stomach Functions

• The esophagus is a muscular tube transporting food to the stomach.
• Peristalsis refers to wavelike contractions that propel food through the digestive tract.
• The stomach mixes food with gastric juices, initiating protein digestion and controlling passage into the small intestine.

Stomach Cellular Functions

• Parietal cells produce hydrochloric acid, creating an acidic environment.
• Chief cells secrete pepsinogen, the precursor to pepsin, which breaks down proteins.
• Gastrin is a hormone that stimulates gastric acid secretion.
• Mucus protects and lubricates stomach tissues.

Chyme and Small Intestine Structure

• Chyme is a semi-fluid mixture of partially digested food and gastric juices moving to the small intestine.
• Microvilli are projections in the small intestine that increase surface area for absorption.

Nutrient Absorption

• Fat-soluble vitamins (K, A, D, E) dissolve in fats and are stored in body tissues.
• Lacteals absorb fats and fat-soluble vitamins into the lymphatic system.

Gut Microbiome and Waste Removal

• Gut flora is a diverse community of microorganisms in the gastrointestinal tract aiding digestion and immune function.
• The rectum stores feces prior to elimination, controlled by anal sphincters.

Enteric Nervous System

• The enteric nervous system regulates gastrointestinal functions independently of the central nervous system.

Liver and Gallbladder Functions

• The liver performs metabolic functions: bile production, detoxification, and nutrient storage.
• Bile emulsifies fats for better digestion and absorption.
• Albumin, a protein produced by the liver, transports substances in the bloodstream.
• The gallbladder stores and concentrates bile.

Pancreas and Digestive Enzymes

• The pancreas produces digestive enzymes and hormones like insulin and glucagon.
• Brush-border enzymes on intestinal cells help break down complex molecules into absorbable nutrients.

Kidney Function and Structure

• Nephrons filter, reabsorb, and secrete substances to form urine.
• Filtration in the nephron forms urine from filtered blood.
• Secretion involves transferring substances into the renal tubules for elimination.
• Absorption reclaims useful substances into the bloodstream.

Nephron Anatomy

• Bowman’s capsule surrounds the glomerulus, collecting filtered fluid.
• The glomerulus is a network of tiny blood vessels for filtration.
• Starling’s forces regulate fluid movement across capillary walls in the kidney.

Renal Tubule Segments

• The proximal convoluted tubule reabsorbs water, ions, and nutrients.
• Loop of Henle facilitates additional water and ion reabsorption; has descending (water permeable) and ascending (ion permeable) limbs.
• Distal convoluted tubule fine-tunes electrolyte balance and water reabsorption via hormones.
• The collecting duct further concentrates urine.

Kidney Regions and Hormonal Regulation

• The medulla contains renal pyramids and loops of Henle; the cortex houses glomeruli and convoluted tubules.
• The renal capsule protects the kidney.
• Aldosterone regulates sodium and potassium levels; renin helps control blood pressure.
• Antidiuretic hormone (ADH) regulates water reabsorption in the kidneys.

Osmoregulation

• Osmoregulation maintains fluid and ion balance for internal stability and cell function.

Gel Electrophoresis

• A technique for separating mixture components based on size and charge.
• Utilizes a gel matrix, commonly made of polyacrylamide (PAGE), as the medium.

Electric Charges

• The cathode is the negatively charged side, attracting positive ions.
• The anode is the positively charged side, attracting negative ions.

Types of Gel Electrophoresis

• SDS-PAGE: Involves sodium dodecyl sulfate to denature proteins and impart uniform negative charge.
• Reducing SDS-PAGE: Similar to SDS-PAGE but includes a reducing agent to break disulfide bonds.
• Native-PAGE: Preserves protein structure, allowing examination of native forms without denaturation.
• Isoelectric Focusing: Separates proteins based on their isoelectric point (pI), where they have no net charge.

Blotting Techniques

• Northern Blot: Identifies specific RNA strands post-gel electrophoresis.
• Southern Blot: Identifies specific DNA strands post-gel electrophoresis.
• Western Blot: Identifies specific proteins post-gel electrophoresis.

Antibody Techniques

• Primary Antibody: The initial antibody that binds to a target protein.
• Secondary Antibody: Conjugated with a label (fluorescent/enzyme) to facilitate detection of the primary antibody.

Molecular Techniques

• Sanger Method: Sequencing technique for determining DNA sequences.
• Primer: Short DNA/RNA strand essential for initiating DNA replication.
• Reverse Transcriptase: Enzyme that synthesizes DNA from an RNA template.
• Polymerase Chain Reaction (PCR): Amplifies specific DNA sequences to generate numerous copies.
• cDNA Library: Contains genes of interest stored in host cells, typically bacteria.

Enzyme-Linked Immunosorbent Assays (ELISA)

• Indirect ELISA: Detects antibody binding by using a secondary, reporter-linked antibody.
• Direct ELISA: Uses reporter-linked primary antibody for direct observation of binding.
• Sandwich ELISA: Measures antigen concentration by sequential addition of immobilized antibody, antigen, and labeled antibody.

Genetic Manipulation Techniques

• Bacterial Transformation: Bacteria uptake genetic material from the environment.
• Plasmids: Circular DNA molecules used as vectors in genetic engineering.
• Restriction Enzymes/Endonucleases: Enzymes that cut DNA at specific sequences.

Separation Techniques

• Centrifugation: Separates components by spinning; creates pellet (dense substances) and supernatant (less dense substances).
• Chromatography: Isolates a substance from a mixture based on interactions with stationary and mobile phases.
  • Mobile Phase: Liquid carrying the substance of interest.
  • Stationary Phase: Immobilized medium that interacts with the substance.
  • Gel Filtration (Size Exclusion) Chromatography: Separates based on size using porous beads.
  • Ion-Exchange Chromatography: Separates by charge using charged stationary phases.
    • Anion-Exchange: Attracts negatively charged molecules.
    • Cation-Exchange: Attracts positively charged molecules.
  • Affinity Chromatography: Isolates targets using a stationary phase with a specific affinity for the substance.

Elution

• The process of detaching a substance of interest from the stationary phase to allow it to exit the chromatography column.

Muscle Tissue

• Skeletal muscle enables voluntary movement and is innervated by the somatic nervous system.
• Smooth muscle operates involuntarily, controlled by the autonomic nervous system.
• Cardiac muscle, located in the heart, contains intercalated discs for coordinated contractions.

Muscle Contraction

• Contractile velocity refers to the speed at which muscle fibers contract.
• The actin-myosin crossbridge cycle involves ATP cleavage and binding, leading to muscle contraction.
• Myosin forms thick filaments, while actin forms thin filaments, both vital to the crossbridge cycle.
• Troponin and tropomyosin regulate muscle contraction by controlling the interaction between actin and myosin.

Muscle Physiology

• Oxygen debt occurs when the oxygen demand by muscles exceeds supply during energy production.
• Sarcoplasmic reticulum stores Ca2+ ions essential for muscle contraction and is integral to the sarcomere structure.
• The power stroke is the movement of myosin heads, shortening the sarcomere as ADP and inorganic phosphate are released.
• Shivering generates heat through small muscle contractions, aiding in thermoregulation.

Bone Structure and Function

• Bones are categorized into spongy and compact varieties; spongy bone contains red bone marrow for hematopoiesis.
• Osteons are the basic units of compact bone, featuring Haversian canals for blood vessel housing.
• Osteoblasts form bone, while osteoclasts resorb bone matrix; their activities are regulated by calcitonin and parathyroid hormone (PTH).

Ossification

• Intramembranous ossification occurs within fibrous membranes, forming flat bones.
• Endochondral ossification involves cartilage models replaced by bone tissue, primarily in long bones.

Connective Tissues

• Tendons attach muscles to bones; ligaments connect bones to other bones.
• Both tendons and ligaments are composed of strong, flexible collagen.

Skin Layers

• The epidermis is the outermost skin layer, composed of five strata.
• The dermis contains essential structures such as sweat glands, hair follicles, blood vessels, and sensory nerve endings.
• The hypodermis anchors skin to underlying muscles and stores adipose tissue.

Thermoregulation Mechanisms

• Piloerection raises hair to trap heat, aiding in temperature regulation.
• Evaporative cooling dissipates heat through sweat evaporation.
• Vasodilation increases blood vessel diameter, enhancing heat transfer to the skin's surface for cooling.

Endoderm

• Forms the epithelial lining of the digestive system, playing a crucial role in digestion and nutrient absorption.
• Represents the epithelial lining of the respiratory tract, essential for gas exchange and respiratory function.
• Contributes to the development of vital organs, including the liver, which aids in metabolic processes and detoxification.
• Involved in the formation of the pancreas, an organ crucial for digestion and blood sugar regulation.
• Responsible for the development of the stomach, which is integral to food storage and digestion.

Mesoderm

• Gives rise to the musculoskeletal system, providing structure and support for body movement.
• Forms the circulatory system, including the heart and blood vessels, facilitating transport of nutrients and oxygen.
• Develops the gonads, which are necessary for reproduction and hormone production.
• Creates linings of body cavities, ensuring protection and separation of internal organs.
• Forms the adrenal cortex, which is vital for hormone production related to stress and metabolism.

Ectoderm

• Leads to the formation of the integumentary system, which includes the skin, hair, and nails, protecting the body from the environment.
• Responsible for the development of the nervous system, controlling bodily functions and responses to stimuli.
• Contributes to the epithelial lining of the mouth and anus, maintaining important roles in digestion and waste elimination.

HPG Axis and Hormones

• The hypothalamus, anterior pituitary gland, and gonads form the HPG axis, crucial for endocrine control.
• GnRH (gonadotropin-releasing hormone) is released by the hypothalamus, stimulating the anterior pituitary.
• FSH (follicle-stimulating hormone) and LH (luteinizing hormone) are produced by the anterior pituitary and play key roles in regulating gametogenesis.

Male Reproductive System

• Testes: Male reproductive glands responsible for sperm production and hormone secretion.
• Spermatogenesis occurs in seminiferous tubules and involves spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa.
• Sertoli cells support and nourish developing sperm and are stimulated by FSH.
• Leydig cells produce testosterone in response to LH stimulation.

Sperm Structure and Function

• Spermatozoa are mature male reproductive cells, capable of fertilizing an egg.
• The acrosome contains enzymes to penetrate the egg, while the flagellum provides motility.
• The vas deferens transports sperm to the ejaculatory duct.

Female Reproductive System

• Ovaries: Female reproductive organs responsible for ova production and hormone secretion.
• Oogenesis involves oogonia developing into primary oocytes and secondary oocytes, which can be fertilized.
• Polar bodies are discarded cells from meiotic divisions that do not contribute to reproduction.

Fertilization and Early Development

• Fertilization occurs when a sperm cell merges with an ovum, forming a zygote.
• Acrosomal reactions allow sperm to penetrate the zona pellucida, while cortical reactions prevent polyspermy.
• Zygote undergoes cleavage, forming a multicellular organism, and becomes an embryo by the end of eight weeks.

Stages of Development

• Morula: A ball of tightly packed cells formed from the zygote.
• Blastocyst: Structure with a blastocoel, inner cell mass (ICM), and trophoblast; leads to implantation.
• Pluripotent cells can develop into various body cell types, while totipotent cells can give rise to all cell types, including extraembryonic tissues.

Gastrulation and Germ Layers

• Gastrulation forms three germ layers: endoderm, mesoderm, and ectoderm.
• The primitive streak establishes the body's axis; the archenteron will become the gastrointestinal tract.
• Endoderm forms internal organ linings, mesoderm yields muscles and bones, and ectoderm creates skin and nervous system structures.

Neurulation and Organ Development

• Notochord forms in the mesoderm and contributes to vertebral column development.
• Neural folds create the neural tube, which develops into the brain and spinal cord.
• Neural crest cells migrate from the neural tube, forming various body tissues.

Additional Developmental Processes

• Gestation refers to the pregnancy period; organogenesis is the development of organs.
• Parturition is the childbirth process; the amniotic sac surrounds the embryo for protection.
• Determination and differentiation define a cell's commitment to its specific type and function.
• Morphogens influence differentiation; inducers release morphogens, while responders undergo differentiation.
• Apoptosis is programmed cell death vital for tissue remodeling during development.

Regulatory Mechanisms

• Negative Feedback: A process where the output of a system counteracts changes, maintaining stability or homeostasis.
• Positive Feedback: A regulatory mechanism in which output amplifies the initial stimulus, potentially leading to an escalation away from the original state.

Hormonal Signaling

• Hormones: Chemical messengers produced by glands that circulate in the bloodstream to target cells, eliciting specific biological responses.
• Autocrine Signaling: A cell secretes signaling molecules that bind to its own receptors or those of similar neighboring cells.
• Paracrine Signaling: Cells release signaling molecules that affect nearby cells, facilitating communication within the same tissue.

Types of Bioactive Compounds

• Peptides: Compounds made of two or more amino acids linked by peptide bonds; include peptide hormones, typically short proteins.
• GPCR: G-protein coupled receptors, family of cell surface receptors important in many signaling pathways.

Cholesterol and Gland Functions

• Cholesterol: A lipid crucial for building cell membranes and serves as a precursor for steroid hormones.
• Exocrine Glands: Secrete substances outward through ducts (e.g., sweat glands).
• Endocrine Glands: Release hormones directly into the bloodstream, affecting distant target tissues.

Pancreas and Hormonal Roles

• Pancreas: Functions as both an endocrine and exocrine organ, producing insulin and digestive enzymes.
• Islets of Langerhans: Clusters of cells in the pancreas, including α, β, and δ cells, responsible for producing insulin, glucagon, and somatostatin.
• Insulin: Regulates blood sugar by facilitating glucose uptake into cells.
• Glucagon: Increases blood glucose levels by stimulating glycogen breakdown in the liver.
• Somatostatin: Inhibits the release of hormones including insulin and glucagon.

Brain and Pituitary Regulation

• Hypothalamus: Brain region controlling physiological functions and regulating the pituitary gland's activity via hormone release.
• Hypophyseal Portal System: Blood vessels connecting hypothalamus and anterior pituitary, allowing direct communication.
• Relevant Hormones:
  • FSH: Follicle-stimulating hormone.
  • LH: Luteinizing hormone.
  • ACTH: Adrenocorticotropic hormone.
  • TSH: Thyroid-stimulating hormone.
  • Prolactin: Stimulates milk production in mammary glands.
  • Endorphins: Natural painkillers released in response to stress or pain.

Growth and Reproductive Hormones

• GHRH: Growth hormone-releasing hormone.
• hGH: Human growth hormone.
• hCG: Human chorionic gonadotropin.
• Oxytocin: Stimulates milk release and aids uterine contractions during childbirth.
• ADH: Antidiuretic hormone, also known as vasopressin.

Thyroid and Parathyroid Hormones

• T3 and T4: Triiodothyronine and thyroxine, hormones that regulate metabolism.
• Calcitonin: Promotes bone formation and reduces blood calcium levels.
• Parathyroid Hormone (PTH): Increases blood calcium levels.

Adrenal Hormones

• Adrenal Cortex: Outer layer producing cortisol and aldosterone, vital for metabolism and blood pressure regulation.
• Adrenal Medulla: Inner part producing epinephrine and norepinephrine, involved in the "fight-or-flight" response.
• Aldosterone: Regulates electrolyte balance and blood pressure.
• Cortisol: Regulates metabolism and immune response.
• Epinephrine and Norepinephrine: Catecholamines involved in stress response and neurotransmission.
• Catecholamines: Derivatives of tyrosine, including epinephrine and norepinephrine.

Regulatory Axes and Systems

• HPA Axis: Hypothalamic-pituitary-adrenal axis, regulating stress response.
• HPG Axis: Hypothalamic-pituitary-gonadal axis, pivotal for reproductive functions.
• RAAS: Renin-angiotensin-aldosterone system, regulating blood pressure and fluid balance.
• CRH (CRF): Corticotropin-releasing hormone/factor, involved in the stress response.

Innate Immune System

• Provides general protection against diseases without recognizing specific pathogens.
• Lysozyme is a protein in saliva that breaks down bacterial cell walls.

Leukocytes (White Blood Cells)

• Primary cells of the immune system; crucial for defense.
• Neutrophils are the most abundant white blood cells, first responders that phagocytize bacteria.
• Lymphocytes are the second most common and include natural killer cells that target virus- and tumor-infected cells.

Monocytes and their Derivatives

• Monocytes can differentiate into macrophages (large phagocytic cells) and dendritic cells (antigen presenters).
• Eosinophils target parasitic infections, while basophils trigger allergic responses by releasing histamine.
• Mast cells, similar to basophils, are found mainly in mucous membranes and connective tissues.

Phagocytosis and Immune Signaling

• Phagocytes engulf and destroy pathogens through phagocytosis.
• The complement system tags pathogens with proteins, promoting phagocyte recruitment.
• Opsonization refers to proteins attaching to pathogens for easier recognition by phagocytes.

Cytokines and Inflammation

• Cytokines are signaling proteins that coordinate immune responses.
• Inflammation occurs in response to injury or pathogens, increasing blood flow and immune cell availability.

Adaptive Immune System

• Features the ability to adapt and learn to recognize specific pathogens.
• Naïve B cells are unexposed to antigens, while plasma cells are activated B cells producing antibodies.
• Memory B cells remain dormant until re-exposure to the same antigen, allowing for a quicker response.

Immune Response Dynamics

• The primary immune response is slower as naïve B cells encounter antigens for the first time.
• The secondary immune response is expedited due to the presence of memory B cells.

Immune System Properties

• Humoral immunity involves B cells and antibody production, while cell-mediated immunity involves T cells.
• Positive selection ensures T cells accurately respond to antigens, while negative selection eliminates overly aggressive T cells to prevent autoimmunity.

T Cell Types and Functions

• Helper T cells (CD4+) activate other immune cells by binding to MHC class II proteins.
• Killer T cells (CD8+) destroy infected cells by identifying presented antigens through MHC class I.

Antigen Recognition

• Major histocompatibility complex (MHC) proteins present antigens on cell surfaces; MHC class I is found in all cells, while MHC class II is specific to immune cells.
• Antigen-presenting cells, such as macrophages and dendritic cells, display antigens to activate T cells.

Blood Cell Formation and Types

• Hematopoiesis is the process of blood cell production in the bone marrow.
• Erythrocytes are red blood cells responsible for oxygen transport.

Antibodies (Immunoglobulins)

• Five classes of antibodies with a Y-shaped structure; they recognize specific antigens through their variable regions.
• The constant region influences the antibody class and stabilizes its structure.

Epitopes and Paratopes

• Epitopes are specific regions on antigens that antibodies recognize.
• Paratopes are regions on antibodies that bind to antigens, diverging through random recombination to enable diverse antibody formation.

Autoimmune Disorders

• Occur when immune cells mistakenly attack healthy body cells, examples include lupus, multiple sclerosis, and rheumatoid arthritis.

Central Nervous System (CNS)

• Comprises the brain and spinal cord, responsible for processing and transmitting information to and from the body.

Peripheral Nervous System (PNS)

• Consists of nerves and ganglia outside the CNS, connecting it to the rest of the body supporting sensorimotor functions.

Spinal Nerve Roots

• Dorsal Roots: Carry sensory information from the body to the spinal cord.
• Ventral Roots: Exit the spinal cord carrying motor information to the body.

Brain Anatomy

• Cerebral Cortex: Outer layer of the cerebrum, involved in higher brain functions like thinking and memory.
• Frontal Lobe: Responsible for executive functions, reasoning, motor skills, and expressive language.
• Parietal Lobe: Processes sensory information, spatial awareness, and perception.
• Occipital Lobe: Mainly processes visual information.
• Temporal Lobe: Associated with auditory processing, memory, and language comprehension.

Brain Regions

• Corpus Callosum: Connects the left and right hemispheres, facilitating interhemispheric communication.
• Wernicke’s Area: Involved in language comprehension; damage leads to Wernicke’s aphasia, impairing understanding of language.
• Broca’s Area: Involved in speech production; damage results in Broca’s aphasia, leading to difficulty in speech coherence.

Nervous System Divisions

• Autonomic Nervous System: Controls involuntary bodily functions (e.g., heartbeat).
  • Parasympathetic Nervous System: Promotes rest and digestion.
  • Sympathetic Nervous System: Triggers fight-or-flight responses.
• Somatic Nervous System: Governs voluntary movements and sensory information.

Neuron Structure and Function

• Soma: Neuron's cell body housing the nucleus.
• Dendrites: Receive signals from other neurons.
• Axons: Transmit signals to other cells.
• Action Potential: Electrical signal propagating along a neuron's membrane during impulse transmission.

Neural Support Cells

• Oligodendrocytes: Produce myelin in the CNS.
• Schwann Cells: Produce myelin in the PNS.
• Myelin: Fatty substance that insulates axons, increasing transmission speed.
• Nodes of Ranvier: Gaps in myelin for action potential generation.

Signal Transmission

• Saltatory Conduction: Rapid transmission of action potentials in myelinated neurons node-to-node.
• Synapse: Junction between two neurons for signal transmission via neurotransmitters.
• Synaptic Plasticity: Synapses adapt over time based on activity.
• Synaptic Pruning: Eliminating less active synapses to refine neural connections.

Ion Channels and Membrane Potential

• Potassium and Sodium Leak Channels: Allow ion movement across the membrane.
• Sodium-Potassium Pump: Maintains resting potential; pumps sodium out and potassium in.
• Hyperpolarization: Increases negative membrane potential.
• Depolarization: Decreases negative membrane potential, making it more positive.
• Repolarization: Restores membrane potential after depolarization.

Refractory Periods

• Absolute Refractory Period: No action potential possible regardless of stimulus strength.
• Relative Refractory Period: Action potential possible only with a stronger-than-usual stimulus.

Neurotransmitters and Synaptic Mechanisms

• Neurotransmitters: Chemical messengers transmitting signals between neurons.
• Temporal Summation: Multiple signals arriving quickly at a synapse.
• Spatial Summation: Signals from different synapses converging simultaneously.
• Reuptake: Removal of neurotransmitters from the synaptic cleft by the presynaptic neuron.
• Enzymatic Degradation: Breakdown of neurotransmitters by enzymes.

Neuron Types

• Afferent Neurons: Carry sensory information to the CNS.
• Efferent Neurons: Carry motor information away from the CNS.
• Interneurons: Connect afferent and efferent neurons for communication.

Reflex Arcs

• Withdrawal Reflex: Reflexive response to noxious stimuli, causing withdrawal.
• Polysynaptic Reflex Arc: Involves multiple synapses between afferent and efferent neurons.
• Monosynaptic Reflex Arc: Consists of a single synapse between afferent and efferent neurons.

Motor Control

• Upper Motor Neurons: Originate from the brain and synapse with lower motor neurons in the spinal cord.
• Lower Motor Neurons: Innervate muscles via neuromuscular junctions.
• Neuromuscular Junction: Synapse between a motor neuron and a muscle fiber.

Visual System

• Photoreceptors: Retina cells that respond to light.
• Cornea: Transparent outer layer covering the eye.
• Pupil: Regulates light entering the eye.
• Lens: Focuses light onto the retina.
• Retina: Contains photoreceptors and is sensitive to light.
• Ciliary Muscle: Changes lens shape for focusing.

Optics and Perception

• Optic Nerve: Transmits visual information from the eye to the brain.
• Optic Nerve Chiasm: Point where optic nerves partially cross, sharing signals between both brain hemispheres.

Chemical and Sensory Detection

• Retinal: Light-sensitive molecule in photoreceptors.
• Opsin: Protein that combines with retinal to form visual pigments.
• Phototransduction: Conversion of light into electrical signals in photoreceptors.

Auditory Processing

• Place Theory: Explains frequency sound perception based on cochlea location.
• Somatosensation: Includes touch, pressure, temperature, and pain sensations.

Olfactory System

• Olfactory Receptors: Detect odor molecules in the nasal cavity.
• Olfactory Bulb: Processes smell information from olfactory receptors.