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

Human Muscular System

Muscle Cell Structure and Sliding Filament Mechanism

The human muscular system enables movement, posture, and heat production. Muscle contraction is based on the sliding filament mechanism within muscle cells (muscle fibers).

• Muscle Fiber: A single muscle cell, containing many myofibrils.

• Sarcomere: The basic contractile unit of muscle, defined by Z-lines. It contains actin (thin) and myosin (thick) filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, pulling the actin filaments toward the center of the sarcomere, shortening the muscle.

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

• Function of the Sarcomere: To generate force and shorten during muscle contraction.

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

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical signals (action potentials) from motor neurons.

• Action Potential: A rapid change in membrane potential that travels along the neuron and muscle fiber.

• Neuromuscular Junction: The synapse where a motor neuron communicates with a muscle fiber, releasing the neurotransmitter acetylcholine (ACh).

• Calcium Release: Action potentials trigger the release of Ca2+ from the sarcoplasmic reticulum, enabling myosin to bind to actin.

• Order of Events: Nerve impulse → ACh release → Muscle fiber action potential → Ca2+ release → Cross-bridge formation → Contraction.

Example: Tapping the knee causes a reflex action potential, leading to contraction of the quadriceps muscle.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant. Produces movement.

• Isometric Contraction: Muscle tension increases, but length does not change. No movement occurs.

Example: Lifting a weight (isotonic); holding a weight steady (isometric).

Muscle Groups and Body Cavities

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

• Muscles Sectioning Body Cavities: The diaphragm separates the thoracic and abdominal cavities.

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.

• Oxygen: Essential for ATP production in cells.

• Carbon Dioxide: Must be expelled to maintain pH balance.

Structures of the Respiratory System

• Upper Respiratory Tract: Nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air; voice production.

• Lower Respiratory Tract: Trachea, bronchi, bronchioles, lungs, alveoli. Functions: air conduction, gas exchange.

Example: The cilia in the trachea help trap and move particles out of the airway.

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: $P_1V_1 = P_2V_2$ (Boyle's Law: pressure and volume are inversely related in the lungs).

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

Blood Flow and Gas Exchange

• Oxygen-rich 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 → Body tissues.

Respiratory Diseases and Disorders

• Examples include asthma, bronchitis, emphysema, pneumonia, and lung cancer.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to the stomach via peristalsis.

• Stomach: Secretes acid and enzymes; churns food.

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

• Large Intestine: Absorbs water and forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• 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).

• Produced in the salivary glands, stomach, pancreas, and small intestine.

Surface Area and Digestion

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

Metabolic Rates

• Basal Metabolic Rate (BMR): Energy expended at rest.

• Standard Metabolic Rate (SMR): Energy expenditure 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 coding for a protein or trait.

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

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

• Genetics: The scientific study of heredity and variation.

Homologous Chromosomes and Karyotypes

• 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 (allele combination) of an organism.

• Phenotype: The observable traits or characteristics.

Punnett Squares and Inheritance Patterns

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

• Dominant Allele: Expressed if present (e.g., AA or Aa).

• Recessive Allele: Expressed only if both alleles are recessive (e.g., aa).

• 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.

Non-Mendelian Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., red + white = pink flowers).

• 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 phenotypic expression (e.g., nutrition, temperature).

Linked Genes and Genetic Variation

• Linked Genes: Genes located close together on the same chromosome, inherited together.

• New Allele Combinations: Crossing over during meiosis creates new allele combinations.

Sex-linked Genes and Chromosomal Disorders

• 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, or aa
Phenotype	Observable trait	Tall or short plant
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: This guide expands on the review points by providing definitions, examples, and context for each major topic, suitable for exam preparation in a Human Biology course.