Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system enables movement, posture, and heat production through the contraction of muscle fibers. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic contractile unit of muscle fiber, composed of actin (thin) and myosin (thick) filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

• Actin and Myosin: Actin forms the thin filaments, while myosin forms the thick filaments with protruding heads that attach to actin during contraction.

• Substructures of Sarcomere: Includes Z-lines (boundaries), M-line (center), A-band (length of myosin), I-band (actin only), and H-zone (myosin only).

• Function: The sarcomere's shortening generates force for muscle contraction.

Example: During bicep contraction, sarcomeres in muscle fibers shorten, pulling the forearm upward.

Action Potentials and Muscle Contraction

Muscle contraction is initiated by electrical signals called action potentials.

• Action Potential in Motor Neuron: Triggered by a stimulus, leading to the release of neurotransmitter (acetylcholine) at the neuromuscular junction.

• Electrical Impulse in Muscle Unit: Acetylcholine binds to receptors on the muscle cell membrane, causing depolarization and propagation of an action potential along the sarcolemma.

• Release of Calcium: The action potential triggers the release of Ca2+ from the sarcoplasmic reticulum, enabling myosin-actin interaction.

• Order of Events: Nerve impulse → Acetylcholine release → Muscle cell depolarization → Ca2+ release → Cross-bridge formation → Sliding of filaments → Muscle contraction.

Example: Tapping the knee causes a reflex action potential, leading to muscle contraction and leg extension.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant; produces movement (e.g., lifting a weight).

• Isometric Contraction: Muscle tension increases but length remains the same; no movement occurs (e.g., holding a plank position).

Muscle Groups and Body Cavities

• Major Muscle Groups: Include biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, deltoids, gluteals, etc.

• Muscles Sectioning Body Cavities: The diaphragm separates the thoracic and abdominal cavities; intercostal muscles are located between ribs.

Heat Generation

• Most body heat is generated by muscle activity, especially during shivering (involuntary muscle contractions).

Human Respiratory System

Significance of Breathing

Breathing supplies oxygen for cellular respiration and removes carbon dioxide, a waste product of metabolism.

• Oxygen: Essential for ATP production in cells.

• Carbon Dioxide Removal: Prevents acidification of body fluids.

Structures of the Respiratory System

• Upper Respiratory Tract: Includes nose, nasal cavity, pharynx, and larynx. Functions: filters, warms, and humidifies air.

• Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, and lungs. Functions: conducts air to alveoli for gas exchange.

Mechanics of Breathing

• Inhalation (Inspiration): Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, drawing air in.

• Exhalation (Expiration): Muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.

• Pressure Changes: $P = \frac{nRT}{V}$ (Ideal Gas Law; as volume increases, pressure decreases, and vice versa).

• Intercostal Muscles: Assist in expanding and contracting the rib cage during breathing.

Blood Flow and Gas Exchange

• Oxygen-rich Blood Flow: Oxygenated blood returns from the lungs to the left atrium, then left ventricle, and is pumped to the body.

• Order of Flow: Pulmonary veins → Left atrium → Left ventricle → Aorta → Systemic circulation.

Respiratory Diseases and Disorders

• Include asthma, bronchitis, emphysema, pneumonia, and lung cancer.

• Disorders can impair gas exchange and oxygen delivery.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical breakdown, saliva begins starch digestion.

• Esophagus: Transports food to stomach via peristalsis.

• Stomach: Churns food, secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for digestion and absorption; large surface area due to villi and microvilli.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile for fat emulsification.

• Gallbladder: Stores and releases bile.

• Pancreas: Produces digestive enzymes and bicarbonate.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion (e.g., amylase, protease, lipase).

• Production Sites: Salivary glands, stomach, pancreas, small intestine.

Surface Area and Digestion

• Large surface area in the small intestine (villi, microvilli) increases nutrient absorption efficiency.

Metabolic Rates

• Basal Metabolic Rate (BMR): Energy expended at rest to maintain vital functions.

• Standard Metabolic Rate (SMR): Metabolic rate under specific conditions (e.g., fasting, resting, non-stressed).

Dietary Guidelines

• "My Plate": A visual guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Peristalsis

• Wave-like muscle contractions that move food through the digestive tract.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

• Gene: A segment of DNA that codes for a specific protein or trait.

• Chromosome: A DNA molecule with associated proteins; humans have 23 pairs.

• Genome: The complete set of genes or genetic material in an organism.

Genetics and Inheritance

• Genetics: The scientific study of heredity and variation.

• Inheritance: Transmission of genetic information from parents to offspring.

• Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.

• Karyotype: A visual display of all chromosomes in a cell, used to detect chromosomal abnormalities.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: The observable traits or characteristics (e.g., brown eyes).

Punnett Squares and Alleles

• Punnett Square: A diagram used to predict the outcome of a genetic cross.

• Alleles: Different forms of a gene; can be dominant or recessive.

• Homozygous: Two identical alleles (AA or aa).

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

• Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

Patterns of Inheritance

• Dominant Disorders: Caused by dominant alleles; often lethal if homozygous.

• Recessive Disorders: Can persist in populations as carriers are unaffected.

• Incomplete Dominance: Heterozygotes show intermediate phenotype (e.g., pink flowers from red and white parents).

• Codominance: Both alleles are fully expressed (e.g., AB blood type).

• Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).

• Environmental Impact: Environment can affect gene expression (e.g., nutrition influencing height).

• Linked Genes: Genes located close together on the same chromosome tend to be inherited together.

• New Allele Combinations: Crossing over during meiosis creates genetic diversity.

• Sex-linked Genes: Genes located on sex chromosomes (X or Y); often show different inheritance patterns in males and females.

• Nondisjunction: Failure of chromosomes to separate during meiosis, leading to abnormal chromosome numbers (e.g., Down syndrome).

Term	Definition	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, aa
Phenotype	Observable trait	Tall, short
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Allele expressed if present	A in Aa
Recessive	Allele expressed only if homozygous	a in aa

Additional info: Some explanations and examples have been expanded for clarity and completeness, based on standard human biology curricula.