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. Muscle contraction is based on the sliding filament mechanism within muscle cells (muscle fibers).

• Sarcomere: The basic contractile unit of muscle, 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; 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).

Example: During contraction, the I-band and H-zone shorten, but the A-band remains the same length.

Muscle Contraction and Action Potentials

• Action Potential: An electrical signal generated in a motor neuron, leading to muscle contraction.

• Neuromuscular Junction: The synapse where a motor neuron communicates with a muscle fiber, releasing neurotransmitters (e.g., acetylcholine) to trigger an action potential in the muscle cell.

• Order of Events:

  1. Action potential travels down motor neuron.

  2. Neurotransmitter released at neuromuscular junction.

  3. Muscle cell membrane depolarizes, generating its own action potential.

  4. Calcium ions released from sarcoplasmic reticulum.

  5. Calcium binds to troponin, exposing binding sites on actin.

  6. Myosin heads bind to actin, initiating contraction.

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle length remains the same (no movement, but tension increases).

• Heat Generation: Most body heat is generated by muscle activity, especially during contraction.

Example: Shivering is an involuntary muscle contraction that generates heat.

Major Muscle Groups and Functions

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

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

Human Respiratory System

Significance and Function of Breathing

The respiratory system enables gas exchange, supplying oxygen to the body and removing carbon dioxide.

• Breathing: Essential for cellular respiration, which produces ATP (energy) for bodily functions.

• Respiratory Diseases: Include asthma, bronchitis, emphysema, and pneumonia, which impair gas exchange.

Structures of the Respiratory System

• Upper Respiratory Tract: Includes nose, nasal cavity, pharynx, and larynx. Functions: filter, warm, and humidify air.

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

• Intercostal Muscles: Located between ribs; contract during inhalation to expand the chest cavity.

• Diaphragm: Main muscle of respiration; contracts to increase thoracic volume during inhalation.

Mechanics of Breathing

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

• Exhalation (Expiration): Muscles relax, thoracic volume decreases, pressure increases, pushing air out.

• Pressure Changes: Air flows from high to low pressure; during inhalation, lung pressure drops below atmospheric pressure.

Example: During exercise, breathing rate and depth increase to meet oxygen demand.

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 Blood Flow: Right atrium → right ventricle → lungs (oxygenation) → left atrium → left ventricle → body.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

• Main Organs: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas. These produce enzymes and substances aiding digestion.

• Enzymes: Biological catalysts that speed up chemical digestion; produced in the mouth (amylase), stomach (pepsin), pancreas (lipase, proteases), and small intestine.

• Large Surface Area: Villi and microvilli in the small intestine increase surface area for nutrient absorption.

Digestive Processes

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

• Digestion of Molecules: Carbohydrates, proteins, and fats are broken down by specific enzymes in different parts of the digestive system.

Metabolic Rates and Nutrition

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

• Standard Metabolic Rate (SMR): The metabolic rate under specific conditions (e.g., at a certain temperature).

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Genetics is the scientific study of heredity and variation in organisms.

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

• Chromosome: A structure composed of DNA and proteins; humans have 23 pairs (46 total).

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

• 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, Phenotype, and Inheritance Patterns

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

• Phenotype: The observable traits or characteristics.

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

• Dominant Allele: Expressed if present (e.g., A).

• 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 and Non-Mendelian Inheritance

• 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.

• 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, height).

• Environmental Influence: Environment can affect phenotypic expression (e.g., nutrition, temperature).

Linked Genes, Sex-Linked Traits, and Chromosomal Abnormalities

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

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y), often affecting males more (e.g., hemophilia).

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

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

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

Example: A cross between two heterozygous parents (Aa x Aa) yields a 3:1 ratio of dominant to recessive phenotypes.

Additional info: The above notes expand on the review guide by providing definitions, examples, and context for each concept, ensuring a comprehensive understanding suitable for exam preparation.