📘 Subject: Human Anatomy and Physiology I
UNIT1: Human Anatomy & Physiology I
- Introduction to Human Body
- Cell & Tissue Level of Organization
- Integumentary & Skeletal Systems
- Muscular System
- Nervous System
- Cardiovascular System
- Respiratory System
- Digestive System
🧠 Unit 1: Introduction to Human Body
This unit lays the foundation for understanding the human body’s structure and function, covering organization levels, terminology, and basic systems.
🧩 1.1 Definition and Scope of Anatomy and Physiology
Anatomy is the branch of biology concerned with the structure of organisms and their parts.
Example: Studying bones, muscles, or organs.
Physiology deals with the functions and processes of those parts.
Example: How the heart pumps blood.
🧠 Why important?
Together, they help in understanding how the human body works, how diseases affect it, and how drugs act.
🏗️ 1.2 Levels of Structural Organization
Human body is organized in six levels:
Chemical Level – Atoms and molecules (e.g., water, proteins).
Cellular Level – Basic structural unit (e.g., muscle cells, nerve cells).
Tissue Level – Groups of similar cells (e.g., epithelial tissue).
Organ Level – Two or more tissues (e.g., stomach).
System Level – Related organs (e.g., digestive system).
Organism Level – One complete individual.
💡 Remember:
Atom → Molecule → Cell → Tissue → Organ → System → Organism
🧭 1.3 Basic Life Processes
Essential functions to maintain life:
| Life Process | Explanation |
|---|---|
| Metabolism | Sum of all chemical reactions in body |
| Responsiveness | Ability to detect & respond to stimuli |
| Movement | Motion of the body & organs |
| Growth | Increase in size and number of cells |
| Differentiation | Specialization of cells |
| Reproduction | Formation of new cells or new organisms |
🌍 1.4 Homeostasis: Definition and Feedback Systems
Homeostasis is the body’s ability to maintain a stable internal environment.
Example: Maintaining body temperature at ~37°C.
🔄 Types of Feedback Mechanisms:
Negative Feedback – Opposes the change.
Example: Body cools down when overheated.
Positive Feedback – Enhances the change.
Example: Oxytocin release during childbirth.
🗺️ 1.5 Anatomical Terminology
Used to describe body positions and directions:
| Term | Meaning |
|---|---|
| Anatomical Position | Standing erect, arms at side, palms forward |
| Superior / Inferior | Above / Below |
| Anterior / Posterior | Front / Back |
| Medial / Lateral | Toward midline / Away from midline |
| Proximal / Distal | Closer to / Away from attachment point |
| Superficial / Deep | Near surface / Far from surface |
💡 Use diagrams to learn!
🧍 1.6 Body Planes and Sections
Used for anatomical study:
Sagittal Plane – Divides body into left and right
Frontal Plane (Coronal) – Divides into front and back
Transverse Plane (Horizontal) – Divides into top and bottom
📌 Helps in medical imaging like CT or MRI scans.
🧱 1.7 Body Cavities and Organs
Main body cavities:
| Cavity | Contains… |
|---|---|
| Cranial | Brain |
| Vertebral | Spinal cord |
| Thoracic | Lungs, Heart |
| Abdominal | Stomach, Liver, Kidneys |
| Pelvic | Bladder, Reproductive organs |
🧪 Cavities are lined with membranes that protect internal organs.
🧪 1.8 Introduction to Cells and Tissues (Overview only; detailed in next units)
Cells – Basic unit of life (e.g., nerve cells, muscle cells)
Tissues – Groups of cells with common function:
Epithelial, Connective, Muscular, Nervous
✅ Summary Points
Anatomy = Structure | Physiology = Function
Structural organization: Chemical → Organism
Homeostasis = Internal balance via feedback
Use anatomical terms for accurate description
Body planes/cavities help in clinical studies
Unit 2: Cell and Tissue Level of Organization
In this unit, we explore the cell—the smallest living unit—and how collections of cells form tissues that carry out specific functions in the body. Understanding these basics is essential before moving on to organs and systems.
2.1 Structure and Function of the Cell
A cell is like a tiny factory, with different “departments” (organelles) performing specialized tasks. Every cell in your body carries out core functions such as energy production, waste removal, and information processing.
2.1.1 Plasma Membrane
Description: A thin, flexible barrier surrounding the cell.
Function: Controls what enters and leaves. It maintains the internal environment by allowing nutrients in, keeping waste and harmful substances out, and enabling communication with other cells.
Analogy: Think of it as the security gate of a factory, checking trucks that enter and exit.
2.1.2 Cytoplasm and Cytoskeleton
Cytoplasm: A jelly-like fluid that fills the cell and holds organelles in place. It provides space for chemical reactions.
Cytoskeleton: A network of protein fibers (microfilaments, intermediate filaments, microtubules) that gives the cell shape and enables movement of organelles within the cell.
Function: Supports cell structure, helps in intracellular transport, and contributes to cell division and movement.
2.1.3 Nucleus
Description: The cell’s control center, enclosed by its own membrane called the nuclear envelope.
Function: Stores the cell’s genetic material (DNA). DNA contains instructions for making proteins, which determine cell structure and function. The nucleus also directs all activities by controlling gene expression.
Components:
Chromatin: DNA wrapped around proteins; condenses into chromosomes during cell division.
Nucleolus: A dense region where ribosomes (protein factories) begin to form.
2.1.4 Mitochondria
Description: Often called the “powerhouse” of the cell.
Function: Produce adenosine triphosphate (ATP), the chemical energy “currency” of the cell, through a process called cellular respiration.
Note: Cells with high energy needs (e.g., muscle cells) contain many mitochondria.
2.1.5 Endoplasmic Reticulum (ER)
Rough ER: Studded with ribosomes.
Function: Synthesizes proteins destined for secretion or for use in the cell membrane.
Smooth ER: Lacks ribosomes.
Function: Synthesizes lipids (fats) and detoxifies certain chemicals (in liver cells, for example).
2.1.6 Golgi Apparatus
Description: A stack of flattened membrane sacs.
Function: Modifies, sorts, and packages proteins and lipids received from the ER. It then directs them to their final destinations inside or outside the cell (like a postal sorting center).
2.1.7 Ribosomes
Description: Small structures made of RNA and protein, either floating in the cytoplasm or attached to the rough ER.
Function: Manufacture proteins by reading the genetic instructions from messenger RNA.
2.1.8 Lysosomes and Peroxisomes
Lysosomes: Contain digestive enzymes.
Function: Break down worn-out organelles, debris, and foreign invaders such as bacteria.
Peroxisomes: Contain enzymes that neutralize toxic substances.
Function: In liver cells, they help detoxify alcohol and other poisons; break down fatty acids.
2.1.9 Centrosomes and Centrioles
Description: The centrosome contains a pair of centrioles.
Function: Organize microtubules and are essential for proper chromosome separation during cell division.
2.2 Cell Division
Cells must divide for growth, repair, and reproduction. There are two main types of cell division:
2.2.1 Mitosis (Somatic Cell Division)
Purpose: Produces two genetically identical daughter cells from one parent cell. Used for growth and replacing damaged or dead cells.
Phases:
Prophase: Chromatin condenses into visible chromosomes; nuclear envelope begins to break down; spindle fibers form.
Metaphase: Chromosomes align at the cell’s equator, attached to spindle fibers.
Anaphase: Sister chromatids (identical halves of each chromosome) are pulled apart toward opposite poles.
Telophase: Nuclear envelopes reform around each set of chromosomes; chromosomes begin to unwind.
Cytokinesis: The cytoplasm divides, resulting in two separate cells.
2.2.2 Meiosis (Germ Cell Division)
Purpose: Produces gametes (sperm and egg) with half the chromosome number of the parent cell (haploid). This variation is critical for genetic diversity in offspring.
Key Difference: Involves two rounds of division (meiosis I and II) and results in four non-identical daughter cells.
2.3 Types of Tissues
When similar cells group together, they form tissues. There are four primary tissue types in the human body:
2.3.1 Epithelial Tissue
Function: Covers body surfaces and lines cavities; forms glands.
Characteristics: Cells are tightly packed with minimal extracellular matrix.
Types by Shape:
Squamous: Flat, thin cells (e.g., lining of blood vessels).
Cuboidal: Cube-shaped (e.g., kidney tubules).
Columnar: Tall, column-like (e.g., lining of the intestine).
Arrangement:
Simple: One cell layer (for diffusion or absorption).
Stratified: Multiple layers (for protection).
2.3.2 Connective Tissue
Function: Supports, binds, and protects organs and other tissues.
Features: Cells are scattered within an extracellular matrix composed of fibers (collagen, elastic) and ground substance.
Examples:
Loose (Areolar): Cushions organs and provides support.
Dense Regular: Tendons and ligaments; strong in one direction.
Adipose: Fat storage, insulation, cushioning.
Cartilage: Flexible support (e.g., in joints, ear).
Bone: Rigid support and protection.
Blood: Fluid matrix (plasma) carrying cells and nutrients.
2.3.3 Muscular Tissue
Function: Generates force and movement.
Types:
Skeletal Muscle: Voluntary control, striated appearance, attached to bones.
Cardiac Muscle: Involuntary, striated, found only in heart; cells interconnected for coordinated contractions.
Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs (e.g., stomach, blood vessels).
2.3.4 Nervous Tissue
Function: Detects stimuli and transmits electrical impulses to coordinate body activities.
Cells:
Neurons: Conduct impulses; consist of a cell body, dendrites (receive signals), and an axon (sends signals).
Neuroglia (Glial Cells): Support, nourish, and protect neurons.
Unit 3: Integumentary and Skeletal Systems
In this unit, we examine the body’s first line of defense (the integumentary system) and its supporting framework (the skeletal system). You will learn about skin structure and function, types of bones and joints, and how these systems work together to protect and move the body.
3.1 Integumentary System
The integumentary system consists of the skin and its appendages (hair, nails, and glands). It protects internal organs, regulates temperature, and provides sensory information.
3.1.1 Layers of the Skin
Epidermis
The outermost layer composed primarily of keratinocytes.
Divided into strata (from deep to superficial):
Stratum basale: Single row of stem cells; site of new cell production.
Stratum spinosum: Several layers of polygonal cells; provides strength and flexibility.
Stratum granulosum: Cells contain keratohyalin granules; begin to die and form a waterproof barrier.
Stratum lucidum: Thin, translucent layer found only in thick skin (palms, soles).
Stratum corneum: 20–30 layers of dead, flattened cells filled with keratin; resists abrasion and water loss.
Dermis
A connective tissue layer beneath the epidermis, composed of two regions:
Papillary region: Loose areolar tissue; contains dermal papillae that project into the epidermis to nourish it and form fingerprints.
Reticular region: Dense irregular connective tissue; provides strength, elasticity, and houses blood vessels, nerves, and glands.
Hypodermis (Subcutaneous Layer)
Loose connective tissue with abundant adipose cells.
Functions as energy storage, insulation, and cushioning; anchors skin to underlying structures.
3.1.2 Skin Appendages
Hair and Hair Follicles
Hair develops from follicles in the dermis.
Roles include protection (scalp hair), sensory input (body hair), and thermoregulation.
Nails
Composed of hard keratin; protect fingertip and enhance fine touch.
Glands
Sebaceous (Oil) Glands: Secrete sebum to lubricate skin and hair; usually associated with hair follicles.
Sweat Glands:
Eccrine glands: Widely distributed; produce watery sweat for thermoregulation.
Apocrine glands: Located in axilla and groin; secrete viscous fluid into hair follicles, activated at puberty.
3.1.3 Functions of the Integumentary System
Protection
Physical barrier against pathogens, chemicals, and mechanical injury.
Melanin in epidermis protects against ultraviolet radiation.
Thermoregulation
Sweat evaporation and blood vessel dilation or constriction regulate body temperature.
Sensation
Specialized receptors detect touch, pressure, temperature, and pain.
Metabolic Functions
Synthesis of vitamin D in response to ultraviolet light.
Excretion
Sweating removes small amounts of waste products (urea, salts).
3.2 Skeletal System
The skeletal system provides structural support, protects organs, allows movement, and serves as a reservoir for minerals.
3.2.1 Functions of Bone
Support: Framework for the body and attachment for muscles.
Protection: Encases vital organs (e.g., skull protects brain).
Movement: Bones serve as levers acted upon by muscles.
Mineral Storage: Reservoir for calcium and phosphorus.
Blood Cell Production: Red marrow produces red blood cells, white blood cells, and platelets.
Energy Storage: Yellow marrow stores lipids.
3.2.2 Classification of Bones
Long Bones: Longer than they are wide (e.g., femur, humerus).
Short Bones: Approximately equal length and width (e.g., carpals, tarsals).
Flat Bones: Thin, flattened, often curved (e.g., sternum, cranial bones).
Irregular Bones: Complex shapes (e.g., vertebrae, facial bones).
Sesamoid Bones: Embedded in tendons (e.g., patella).
3.2.3 Gross Anatomy of a Long Bone
Diaphysis: Shaft composed of compact bone surrounding a central medullary cavity containing marrow.
Epiphyses: Ends of the bone, composed of spongy bone with a thin outer layer of compact bone; joint surfaces covered by articular cartilage.
Metaphysis: Region between diaphysis and epiphysis; contains the epiphyseal plate (growth plate) in growing bones.
Periosteum: Dense irregular connective tissue covering external bone surfaces (except at joint surfaces); contains osteogenic cells.
Endosteum: Delicate membrane lining the medullary cavity.
3.2.4 Microscopic Structure and Cells of Bone
Compact Bone: Organized into osteons (Haversian systems)—cylindrical structures with a central canal (blood vessels and nerves) surrounded by concentric lamellae.
Spongy Bone: Meshwork of trabeculae; spaces filled with marrow.
Bone Cells:
Osteogenic Cells: Stem cells that differentiate into osteoblasts.
Osteoblasts: Bone-forming cells; secrete osteoid (organic matrix).
Osteocytes: Mature bone cells; maintain bone matrix within lacunae.
Osteoclasts: Large cells that resorb (break down) bone; important for remodeling and calcium release.
3.2.5 Bone Development and Growth
Intramembranous Ossification: Bone develops directly from mesenchymal tissue (forms flat bones of skull and clavicle).
Endochondral Ossification: Bone forms by replacing hyaline cartilage (forms most bones).
Longitudinal Growth:
Occurs at the epiphyseal plate through proliferation of chondrocytes, cartilage calcification, and replacement by bone.
Appositional Growth:
Increase in bone thickness by activity of osteoblasts beneath the periosteum.
3.2.6 Joints (Articulations)
Joints are points where two or more bones meet. They are classified structurally and functionally:
Structural Classification:
Fibrous Joints: Bones joined by dense connective tissue; little or no movement (e.g., sutures of skull).
Cartilaginous Joints: Bones joined by cartilage; limited movement (e.g., intervertebral discs).
Synovial Joints: Bones separated by a fluid-filled joint cavity; freely movable.
Functional Classification:
Synarthrosis: Immovable (fibrous).
Amphiarthrosis: Slightly movable (cartilaginous).
Diarthrosis: Freely movable (all synovial joints).
Features of Synovial Joints:
Joint capsule (fibrous layer and synovial membrane).
Synovial fluid for lubrication.
Articular cartilage covering bone ends.
Accessory ligaments and bursae.
4.1 Types of Muscle Tissue
The human body contains three distinct muscle tissue types, each with unique structure and control:
Skeletal Muscle
Control: Voluntary (under conscious control)
Appearance: Striated (alternating light and dark bands)
Location: Attached to bones via tendons
Function: Produces body movements, maintains posture, stabilizes joints, and generates heat
Cardiac Muscle
Control: Involuntary (autonomic control)
Appearance: Striated with branching fibers and intercalated discs
Location: Walls of the heart (myocardium)
Function: Pumps blood through the heart chambers and into blood vessels
Smooth Muscle
Control: Involuntary
Appearance: Non-striated (smooth) with spindle-shaped cells
Location: Walls of hollow organs (e.g., blood vessels, gastrointestinal tract, bladder, uterus)
Function: Moves substances through internal passageways, regulates vessel diameter, controls organ volume
4.2 Gross Anatomy of a Skeletal Muscle
A skeletal muscle is an organ composed of muscle fibers (cells), connective tissue, blood vessels, and nerves. From the outside in:
Epimysium: Dense irregular connective tissue sheath surrounding the entire muscle
Perimysium: Connective tissue partition dividing the muscle into bundles called fascicles
Endomysium: Fine layer of reticular connective tissue surrounding each individual muscle fiber
Each muscle fiber contains multiple nuclei (resulting from fusion of precursor cells) and numerous mitochondria to meet high energy demands.
4.3 Microscopic Structure of Skeletal Muscle Fiber
A single muscle fiber exhibits the following key features:
Sarcolemma: Plasma membrane of the muscle fiber
Sarcoplasm: Cytoplasm containing glycogen (energy storage) and myoglobin (oxygen-binding pigment)
Myofibrils: Cylindrical structures filling most of the fiber’s volume; composed of repeating units called sarcomeres
Sarcoplasmic Reticulum (SR): Specialized endoplasmic reticulum that stores and releases calcium ions (Ca²⁺)
T‑tubules (Transverse tubules): Invaginations of the sarcolemma that conduct electrical impulses into the fiber’s interior
4.4 Sarcomere and Filament Organization
The sarcomere is the basic functional unit of muscle contraction, defined by Z‑discs on each end. Within each sarcomere:
Thin Filaments: Primarily actin filaments anchored at the Z‑disc
Thick Filaments: Myosin filaments centrally located, overlapping the thin filaments
A Band: Length of the thick filament (includes areas of overlap with thin filaments)
I Band: Region containing only thin filaments, bisected by the Z‑disc
H Zone: Central part of the A band with only thick filaments
M Line: Protein complex at the center of the H zone anchoring thick filaments
4.5 Sliding Filament Mechanism of Contraction
Muscle contraction occurs as thick and thin filaments slide past one another, shortening each sarcomere. The process involves:
Neuromuscular Junction Activation
Motor neuron releases acetylcholine (ACh) into the synaptic cleft
ACh binds receptors on the sarcolemma, triggering an action potential
Excitation–Contraction Coupling
Action potential travels along the sarcolemma and down T‑tubules
SR releases Ca²⁺ into the sarcoplasm
Cross-Bridge Cycling
Ca²⁺ binds to troponin on thin filaments, causing tropomyosin to move and expose myosin‑binding sites on actin
Cross-bridge formation: Myosin head binds actin
Power stroke: Myosin head pivots, pulling thin filament toward the center of the sarcomere; ADP and inorganic phosphate (Pi) released
Cross-bridge detachment: ATP binds myosin head, causing it to release actin
Recovery stroke: ATP is hydrolyzed to ADP + Pi, cocking the myosin head for the next cycle
Relaxation
ACh is degraded by acetylcholinesterase, ending the action potential
Ca²⁺ is actively pumped back into the SR
Troponin‑tropomyosin complex re‑covers binding sites on actin, preventing further cross-bridge formation
4.6 Energy Sources for Contraction
Muscle fibers require ATP for cross-bridge cycling and Ca²⁺ transport. ATP is regenerated by:
Creatine Phosphate (Phosphocreatine) System
Quick transfer of Pi from creatine phosphate to ADP
Provides energy for up to ~15 seconds of intense activity
Anaerobic Glycolysis
Glucose breakdown to pyruvate and lactate in the cytosol
Yields 2 ATP per glucose; supports activity for ~30–60 seconds
Aerobic Respiration
Occurs in mitochondria with O₂
Pyruvate enters the citric acid cycle, producing up to ~36 ATP per glucose
Supports prolonged, lower-intensity activity
4.7 Muscle Fiber Types
Skeletal muscle fibers differ in contraction speed and fatigue resistance:
Type I (Slow Oxidative)
High myoglobin content (“red fibers”), many mitochondria, rich blood supply
Slow contraction speed, highly fatigue‑resistant; suited for endurance (posture, marathon running)
Type IIa (Fast Oxidative‑Glycolytic)
Intermediate characteristics: moderate myoglobin, mitochondria, and resistance to fatigue; fast contraction
Type IIb (Fast Glycolytic)
Low myoglobin, few mitochondria, high glycolytic enzyme content
Fast contraction speed, fatigue quickly; suited for short, powerful bursts (sprinting, weight lifting)
Unit 5: Nervous System
In this unit we explore how the body detects, processes, and responds to internal and external stimuli. We cover the organization of the nervous system, the structure and function of its cellular components, and the mechanisms by which nerves conduct signals and communicate.
5.1 Organization of the Nervous System
Structural Divisions
Central Nervous System (CNS): Brain and spinal cord. Processes information and issues commands.
Peripheral Nervous System (PNS): All neural tissue outside the CNS. Connects the CNS with receptors, muscles, and glands.
Functional Divisions
Sensory (Afferent) Division: Carries information from sensory receptors toward the CNS.
Somatic sensory – from skin, muscles, joints
Visceral sensory – from organs
Motor (Efferent) Division: Transmits commands from CNS to effectors (muscles, glands).
Somatic motor – voluntary control of skeletal muscle
Autonomic motor – involuntary control of smooth muscle, cardiac muscle, glands
Sympathetic (“fight or flight”)
Parasympathetic (“rest and digest”)
5.2 Neuron: Structure and Function
A neuron is the basic functional cell of the nervous system, specialized for rapid communication.
Cell Body (Soma): Contains nucleus and organelles; integrates incoming signals.
Dendrites: Branch‑like extensions that receive input from other neurons or receptors and convey it toward the cell body.
Axon: Long process that conducts nerve impulses away from the soma. May be wrapped in a myelin sheath.
Axon Hillock: Junction of soma and axon; where action potentials originate.
Collateral Branches: Side branches that allow one neuron to communicate with multiple targets.
Axon Terminals (Synaptic Boutons): Release neurotransmitter to communicate with other cells.
5.3 Neuroglia (Glial Cells)
Neuroglia support and protect neurons, maintain the extracellular environment, and participate in repair.
In the CNS:
Astrocytes: Maintain blood–brain barrier, regulate ion and nutrient concentrations, repair tissue.
Oligodendrocytes: Form myelin sheaths around CNS axons, increasing conduction speed.
Microglia: Resident macrophages; remove debris and pathogens.
Ependymal Cells: Line ventricles of the brain and central canal of the spinal cord; produce and circulate cerebrospinal fluid (CSF).
In the PNS:
Schwann Cells: Myelinate PNS axons; aid in regeneration after injury.
Satellite Cells: Surround neuron cell bodies in ganglia; regulate nutrient and waste exchange.
5.4 Resting Membrane Potential
The resting membrane potential is the electrical difference across the neuronal membrane when the cell is not transmitting a signal (typically –70 mV).
Origin:
Unequal distribution of ions (Na⁺, K⁺, Cl⁻, organic anions) across the membrane.
Membrane more permeable to K⁺ than to Na⁺, allowing more positive charge to leak out.
Na⁺/K⁺-ATPase pumps maintain ion gradients (3 Na⁺ out, 2 K⁺ in).
Significance:
Stores potential energy used to generate action potentials.
5.5 Action Potential: Generation and Conduction
An action potential is a rapid, self‑propagating change in membrane potential that travels along the axon.
Threshold and Depolarization:
Stimulus raises membrane potential to threshold (about –55 mV).
Voltage‑gated Na⁺ channels open, Na⁺ rushes in, causing rapid depolarization toward +30 mV.
Repolarization:
Voltage‑gated Na⁺ channels inactivate; voltage‑gated K⁺ channels open.
K⁺ exits the cell, membrane potential returns toward negative.
Hyperpolarization:
K⁺ channels remain open briefly, overshooting resting level.
Membrane potential becomes slightly more negative than resting.
Return to Resting State:
K⁺ channels close; Na⁺/K⁺ pump and leak channels restore original ion distribution.
Conduction:
Continuous Conduction: In unmyelinated axons, action potential moves by successive depolarization of adjacent segments.
Saltatory Conduction: In myelinated axons, action potential “jumps” between nodes of Ranvier, increasing speed.
5.6 Synapse and Neurotransmission
A synapse is the junction where one neuron communicates with another cell (neuron, muscle, gland).
Presynaptic Events:
Arrival of action potential at axon terminal opens voltage‑gated Ca²⁺ channels.
Ca²⁺ influx triggers synaptic vesicles to fuse with the membrane and release neurotransmitter into the synaptic cleft.
Synaptic Cleft:
Narrow extracellular space; neurotransmitter diffuses across.
Postsynaptic Events:
Neurotransmitter binds to receptors on postsynaptic membrane.
Ionotropic receptors: Ligand‑gated ion channels; direct changes in ion flow.
Metabotropic receptors: G‑protein‑coupled; initiate second‑messenger cascades.
Excitatory Postsynaptic Potential (EPSP): Depolarizes membrane (e.g., glutamate).
Inhibitory Postsynaptic Potential (IPSP): Hyperpolarizes membrane (e.g., GABA).
Termination:
Enzymatic degradation (e.g., acetylcholinesterase).
Reuptake into presynaptic cell.
Diffusion away from the synapse.
5.7 Central Nervous System Structures
Brain:
Cerebrum: Conscious thought, memory, voluntary movement.
Diencephalon: Thalamus (sensory relay), hypothalamus (homeostasis).
Brainstem: Midbrain, pons, medulla oblongata (basic life functions).
Cerebellum: Coordination of movement and balance.
Spinal Cord:
Conveys information between brain and PNS; responsible for reflex actions.
Protective Coverings:
Meninges: Three layers—dura mater (tough), arachnoid mater (web‑like), pia mater (delicate).
Cerebrospinal Fluid (CSF): Cushions the CNS; flows in subarachnoid space and ventricles.
5.8 Peripheral Nervous System Components
Cranial Nerves (I–XII): Emerge from the brain; perform sensory, motor, or mixed functions (e.g., optic nerve for vision).
Spinal Nerves (31 pairs): Exit the spinal cord; branch into dorsal (sensory) and ventral (motor) roots.
Autonomic Nervous System:
Sympathetic Division: Prepares body for stress (“fight or flight”).
Parasympathetic Division: Conserves energy and promotes “rest and digest.”
Unit 6: Cardiovascular System
In this unit you will learn how blood is circulated throughout the body by the heart and blood vessels, how its components function, and how pressure and flow are regulated.
6.1 Components of Blood
Plasma
The liquid matrix (about 55 % of blood volume), consisting of water, dissolved proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, hormones, and waste products.
Functions: transport medium for cells and solutes; maintenance of osmotic balance and pH.
Formed Elements
Red Blood Cells (Erythrocytes)
Biconcave, enucleate cells filled with hemoglobin.
Function: transport oxygen (via oxyhemoglobin) and carbon dioxide.
Lifespan ~120 days; removed by spleen and liver.
White Blood Cells (Leukocytes)
Five major types grouped into two categories:
Granulocytes (neutrophils, eosinophils, basophils)—contain cytoplasmic granules and a multilobed nucleus; involved in phagocytosis, allergic responses, and inflammation.
Agranulocytes (lymphocytes, monocytes)—lack visible granules; lymphocytes mediate immune responses, monocytes become macrophages in tissues.
Platelets (Thrombocytes)
Cell fragments derived from megakaryocytes; circulate for ~7–10 days.
Function: initiate blood clotting (hemostasis) by forming a platelet plug and providing a surface for fibrin deposition.
6.2 Heart: Anatomy and Conduction
Gross Anatomy
Located in the mediastinum, roughly the size of a fist, enclosed by the pericardium.
Four chambers:
Right atrium receives deoxygenated blood from the body (via superior/inferior venae cavae).
Right ventricle pumps deoxygenated blood to the lungs via the pulmonary trunk.
Left atrium receives oxygenated blood from the pulmonary veins.
Left ventricle pumps oxygenated blood into the aorta for systemic distribution (thickest wall).
Valves ensure unidirectional flow: tricuspid, pulmonary, mitral (bicuspid), and aortic valves.
Cardiac Conduction System
Sinoatrial (SA) node (“pacemaker”) in the right atrial wall initiates each heartbeat.
Impulse spreads through atria to the atrioventricular (AV) node, then via the Bundle of His, right and left bundle branches, and Purkinje fibers to the ventricular myocardium.
Electrical events correspond to the ECG: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).
6.3 Cardiac Cycle and Heart Sounds
Phases of the Cardiac Cycle
Atrial Systole: Atria contract, topping off ventricular volume.
Isovolumetric Ventricular Contraction: Ventricles contract with all valves closed, pressure rises.
Ventricular Ejection: Semilunar valves open; blood is ejected into arteries.
Isovolumetric Ventricular Relaxation: Ventricles relax; semilunar valves close (“dub” sound).
Ventricular Filling: AV valves open; passive filling begins, followed by atrial systole (“lub” sound when AV valves close at start of ventricular contraction).
Heart Sounds
First sound (“lub”): closure of tricuspid and mitral valves.
Second sound (“dub”): closure of pulmonary and aortic valves.
6.4 Blood Vessels and Blood Pressure
Types of Vessels
Arteries: carry blood away from the heart; thick walls to withstand high pressure.
Arterioles: small branches that regulate flow into capillary beds via vasoconstriction/vasodilation.
Capillaries: single-layer endothelium for exchange of gases, nutrients, and waste between blood and tissues.
Venules and Veins: return blood to the heart; contain valves to prevent backflow and serve as blood reservoirs.
Blood Pressure
Systolic Pressure: peak arterial pressure during ventricular contraction.
Diastolic Pressure: minimum arterial pressure during ventricular relaxation.
Regulation:
Neural control via baroreceptor reflex in carotid sinus and aortic arch.
Hormonal control (e.g., epinephrine, angiotensin II, atrial natriuretic peptide).
Local autoregulation by metabolites (e.g., nitric oxide, lactic acid).
6.5 Microcirculation and Lymphatics
Microcirculation
Arterioles → Metarterioles → Capillary beds → Thoroughfare channels → Venules.
Capillary Exchange:
Diffusion (O₂, CO₂), filtration (hydrostatic pressure), reabsorption (osmotic pressure).
Lymphatic System
Returns interstitial fluid (lymph) to the bloodstream; transports dietary lipids from the digestive tract; participates in immune responses via lymph nodes.
Lymph vessels collect fluid through blind‑ended capillaries, pass it through lymph nodes, and ultimately drain into the subclavian veins.
Unit 7: Respiratory System
The respiratory system is responsible for bringing oxygen into the body and removing carbon dioxide. It works closely with the cardiovascular system to deliver gases to and from tissues.
7.1 Organs and Structures of the Respiratory Tract
Nose and Nasal Cavity
Functions: Warms, moistens, and filters incoming air; houses olfactory receptors for smell.
Structures: Nasal hairs trap large particles; mucous lining traps smaller dust and pathogens; conchae increase surface area and turbulence.
Pharynx
Regions:
Nasopharynx: Behind nasal cavity; conducts air.
Oropharynx: Behind oral cavity; conducts both air and food.
Laryngopharynx: Leads to larynx (air) and esophagus (food).
Larynx (Voice Box)
Cartilages: Thyroid (Adam’s apple), cricoid, and paired arytenoid cartilages.
Epiglottis: Flap that closes over the glottis during swallowing to prevent food from entering the airway.
Vocal Folds: Produce sound when air passes between them.
Trachea (Windpipe)
A rigid tube of C‑shaped cartilage rings that keeps the airway open; lined with ciliated epithelium to move mucus upward to the pharynx (mucociliary escalator).
Bronchial Tree
Primary (Main) Bronchi: Right and left branches off the trachea; each enters a lung.
Secondary (Lobar) and Tertiary (Segmental) Bronchi: Further subdivisions; cartilage support decreases as branching increases.
Bronchioles: Smallest conducting passages, lacking cartilage and lined by smooth muscle, allowing regulation of airflow.
Terminal and Respiratory Bronchioles: Lead into alveolar ducts.
Alveoli
Structure: Tiny air sacs, one cell layer thick, surrounded by capillaries.
Function: Site of gas exchange by simple diffusion. Type I pneumocytes form the wall; Type II pneumocytes secrete surfactant to reduce surface tension and prevent collapse.
Lungs and Pleura
Lobes: Right lung has three lobes; left lung has two lobes and a cardiac notch.
Pleura:
Visceral Pleura: Covers lung surface.
Parietal Pleura: Lines the thoracic cavity.
Pleural Cavity: Potential space with a thin layer of fluid that reduces friction and maintains negative pressure.
7.2 Mechanics of Breathing
Breathing (ventilation) involves changes in thoracic volume that drive air flow.
Inhalation (Inspiration)
Diaphragm: Contracts (moves downward), increasing vertical dimension of thorax.
External Intercostal Muscles: Contract, lifting ribs up and out to expand thoracic cavity laterally and anterior–posteriorly.
Result: Intrapulmonary pressure falls below atmospheric pressure, drawing air into the lungs.
Exhalation (Expiration)
Passive at Rest: Diaphragm and external intercostals relax; elastic recoil of lung tissue and thoracic cage returns them to resting position.
Forced Exhalation: Internal intercostals and abdominal muscles contract to further decrease thoracic volume and expel air.
7.3 Lung Volumes and Capacities
Measured by spirometry:
Tidal Volume (TV): Air moved in or out during normal breathing (~500 mL).
Inspiratory Reserve Volume (IRV): Additional air inhaled after a normal inspiration.
Expiratory Reserve Volume (ERV): Additional air exhaled after a normal expiration.
Residual Volume (RV): Air remaining in lungs after forced expiration (cannot be measured by spirometry).
From these, the following capacities are calculated:
Vital Capacity (VC) = IRV + TV + ERV
Total Lung Capacity (TLC) = VC + RV
Inspiratory Capacity (IC) = TV + IRV
Functional Residual Capacity (FRC) = ERV + RV
7.4 Gas Exchange and Transport
External Respiration (Alveolar Gas Exchange)
Oxygen diffuses from alveoli (high PO₂) into blood (low PO₂).
Carbon Dioxide diffuses from blood (high PCO₂) into alveoli (low PCO₂).
Transport in Blood
Oxygen:
~98% bound to hemoglobin in red blood cells.
~2% dissolved in plasma.
Carbon Dioxide:
~7% dissolved in plasma.
~23% bound to hemoglobin (carbaminohemoglobin).
~70% converted to bicarbonate (HCO₃⁻) via carbonic anhydrase in red blood cells.
Internal Respiration (Tissue Gas Exchange)
O₂ diffuses from blood (high PO₂) into tissues (low PO₂).
CO₂ diffuses from tissues (high PCO₂) into blood (low PCO₂).
7.5 Neural and Chemical Regulation of Breathing
Neural Centers
Medullary Respiratory Centers:
Dorsal Respiratory Group (DRG): Controls basic rhythm of inspiration.
Ventral Respiratory Group (VRG): Involved in forced breathing.
Pontine Respiratory Centers:
Modify activity of medullary centers to smooth transitions between inhalation and exhalation.
Chemoreceptor Input
Central Chemoreceptors (medulla): Respond to changes in cerebrospinal fluid pH (reflecting blood CO₂).
Peripheral Chemoreceptors (carotid and aortic bodies): Respond primarily to low arterial O₂, but also to high CO₂ and low pH.
Unit 8: Digestive System
In this unit, we examine how the body ingests food, breaks it down into absorbable nutrients, and eliminates waste. You will learn the structure and function of each part of the alimentary canal and associated accessory organs, as well as the processes of digestion, absorption, motility, and regulation.
8.1 Overview and Functions
The digestive system accomplishes:
Ingestion – Taking in food via the mouth.
Propulsion – Movement of food through the tract by swallowing and peristalsis.
Mechanical Digestion – Physical breakdown of food (chewing, churning).
Chemical Digestion – Enzymatic degradation of macromolecules into monomers.
Absorption – Transport of digested nutrients into blood or lymph.
Defecation – Elimination of indigestible residues as feces.
8.2 Anatomical Regions of the Alimentary Canal
Mouth (Oral Cavity)
Teeth: mastication.
Tongue: mixes food; contains taste receptors; helps form bolus.
Salivary glands (parotid, submandibular, sublingual): secrete saliva containing amylase (carbohydrate digestion) and mucus.
Pharynx
Shared passage for food and air; pharyngeal muscles propel bolus into the esophagus.
Esophagus
Muscular tube; upper third skeletal muscle, lower two-thirds smooth muscle.
Peristaltic waves move bolus toward the stomach.
Lower esophageal (cardiac) sphincter prevents reflux.
Stomach
Regions: cardia, fundus, body, pylorus.
Rugae: folds that allow expansion.
Gastric glands in mucosa:
Mucous cells: secrete protective mucus.
Parietal cells: secrete hydrochloric acid (HCl) and intrinsic factor (for vitamin B₁₂ absorption).
Chief cells: secrete pepsinogen (inactive precursor to pepsin for protein digestion).
G cells: secrete gastrin (hormone that stimulates acid secretion and motility).
Small Intestine
Longest section (~6 m) divided into duodenum, jejunum, ileum.
Duodenum: receives chyme, bile (from liver/gallbladder), and pancreatic juice.
Jejunum & Ileum: primary sites for nutrient absorption.
Mucosal modifications:
Circular folds (plicae circulares)
Villi (finger‑like projections)
Microvilli (brush border)
Intestinal glands (Crypts of Lieberkühn) secrete intestinal juice.
Large Intestine
Regions: cecum (with appendix), ascending, transverse, descending, sigmoid colon, rectum, anal canal.
Functions: water and electrolyte absorption; formation and storage of feces; houses microbiota that produce vitamins (e.g., K, B₇).
Anus
Internal (smooth muscle) and external (skeletal muscle) anal sphincters control defecation.
8.3 Accessory Digestive Organs
Pancreas
Exocrine function: acinar cells secrete pancreatic juice containing enzymes for carbohydrate (amylase), protein (trypsin, chymotrypsin), lipid (lipase), and nucleic acid digestion, plus bicarbonate to neutralize gastric acid.
Endocrine function (in A&P II): islets secrete insulin and glucagon.
Liver
Produces bile (bile salts emulsify fats).
Metabolizes nutrients, detoxifies substances, stores glycogen and certain vitamins.
Gallbladder
Stores and concentrates bile; releases it into the duodenum via the common bile duct when stimulated by cholecystokinin.
8.4 Processes of Digestion
Mechanical Digestion
Mastication in mouth.
Churning action of stomach.
Segmentation contractions in small intestine mix chyme with digestive secretions.
Chemical Digestion
Carbohydrates: salivary and pancreatic amylases; brush‑border enzymes (maltase, sucrase, lactase) produce monosaccharides.
Proteins: pepsin in stomach; pancreatic proteases; brush‑border peptidases yield amino acids.
Lipids: emulsification by bile salts; pancreatic lipase breaks triglycerides into monoglycerides and free fatty acids.
Nucleic Acids: pancreatic nucleases and brush‑border nucleotidases convert DNA/RNA to nucleotides and bases.
8.5 Absorption and Transport
Monosaccharides and amino acids enter intestinal epithelial cells via active transport or facilitated diffusion; then enter capillaries of villi and travel to the liver via the hepatic portal vein.
Short‑chain fatty acids enter capillaries directly.
Long‑chain fatty acids, monoglycerides, and lipid‑soluble vitamins form micelles, diffuse into epithelial cells, are re‑esterified into triglycerides, packaged into chylomicrons, and enter lacteals (lymphatic capillaries) before joining the bloodstream at the thoracic duct.
8.6 Neural and Hormonal Regulation
Neural Control
Cephalic phase: sight, smell, or thought of food triggers vagus nerve to stimulate secretions and motility.
Gastric phase: food in stomach stretches its wall and raises pH, further stimulating gastrin release and acid production.
Intestinal phase: chyme entering duodenum initially stimulates and then inhibits gastric activity via enterogastric reflexes.
Hormonal Control
Gastrin (stomach): increases gastric motility and secretions.
Cholecystokinin (CCK) (duodenum): stimulates pancreatic enzyme secretion, gallbladder contraction, and satiety.
Secretin (duodenum): stimulates pancreatic bicarbonate secretion and inhibits gastric acid secretion.
Gastric inhibitory peptide (GIP): inhibits gastric motility; stimulates insulin release.
Here All the 8 Unit have been explained for this first subject:
Human Anatomy & Physiology I
Introduction to Human Body
Cell & Tissue Level of Organization
Integumentary & Skeletal Systems
Muscular System
Nervous System
Cardiovascular System
Respiratory System
Digestive System