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

Human Muscular System

Muscle Cell Structure and Sliding Filament Mechanism

The human muscular system enables movement, posture, and heat production. Muscle contraction is explained by the sliding filament theory, which involves the interaction of actin and myosin filaments within the sarcomere.

• Sarcomere: The basic contractile unit of muscle fiber, defined by the area between two Z-lines.

• Actin Filaments: Thin filaments that interact with myosin for contraction.

• Myosin Filaments: Thick filaments with heads that bind to actin, pulling them to shorten the sarcomere.

• Sliding Mechanism: Myosin heads attach to actin, forming cross-bridges and pulling actin filaments inward, causing contraction.

• Function of Sarcomere: Facilitates muscle contraction through the coordinated sliding of actin and myosin.

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

Action Potentials and Muscle Contraction

• Action Potential: An electrical signal generated in a motor neuron that triggers muscle contraction.

• Initiation: Action potential travels down the motor neuron, reaching the neuromuscular junction.

• Release of Neurotransmitters: Acetylcholine is released, causing depolarization of the muscle cell membrane.

• Calcium Release: Depolarization triggers the sarcoplasmic reticulum to release Ca2+, enabling actin-myosin interaction.

• Order of Events: Nerve impulse → Acetylcholine release → Muscle cell depolarization → Ca2+ release → Sarcomere contraction.

Example: Reflex actions involve rapid transmission of action potentials to muscle fibers.

Muscle Types of Contractions

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

• Isometric Contraction: Muscle length remains the same while tension increases; no movement occurs.

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

Muscle Groups and Body Cavities

• Major Muscle Groups: Biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, etc.

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

Heat Generation

• Most body heat is generated by muscle activity, especially during shivering.

Human Respiratory System

Significance of Breathing

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

• Oxygen: Essential for ATP production in cells.

• CO2 Removal: Prevents acidification of body fluids.

Respiratory System Structures and Functions

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, and larynx. Functions in filtering, warming, and humidifying air.

• Lower Respiratory System: Includes trachea, bronchi, bronchioles, and lungs. Functions in air conduction and gas exchange.

Example: The cilia in the trachea help remove particles from inhaled air.

Mechanics of Breathing

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

• Exhalation (Expiration): Diaphragm and intercostal muscles relax, decreasing thoracic volume and increasing lung pressure, pushing air out.

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$ (Air flows from high to low pressure)

• 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 to the left ventricle, and is pumped to the body.

• Gas exchange occurs in alveoli by diffusion.

Respiratory Diseases and Disorders

• Common disorders include asthma, bronchitis, emphysema, and pneumonia.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins here.

• Esophagus: Transports food to the stomach via peristalsis.

• Stomach: 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 and 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 catalyze the breakdown of macromolecules; produced in the mouth (amylase), stomach (pepsin), pancreas (lipase, proteases), and small intestine.

Surface Area and Digestion

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

Metabolic Rates

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

• Standard Metabolic Rate (SMR): Energy expenditure under standardized conditions.

Nutrition Guidelines

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

Peristalsis

• Wavelike 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 protein or trait.

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

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

Genetics Terminology

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

• Phenotype: Observable traits resulting from genotype and environment.

• 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.

Inheritance Patterns

• Punnett Square: A tool to predict genetic crosses and offspring genotypes.

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

• Recessive Allele: Expressed only when homozygous (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 x white = pink).

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

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

• Environmental Influence: Phenotype can be affected by environmental factors (e.g., nutrition, sunlight).

Linked Genes and Genetic Variation

• 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 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 properly during meiosis, leading to abnormal chromosome numbers (e.g., Down syndrome).

Term	Definition
Genotype	Genetic makeup (e.g., AA, Aa, aa)
Phenotype	Physical expression of traits
Homozygous	Two identical alleles
Heterozygous	Two different alleles
Dominant	Allele expressed when present
Recessive	Allele expressed only when homozygous
Incomplete Dominance	Intermediate phenotype in heterozygotes
Codominance	Both alleles expressed equally
Polygenic	Trait controlled by multiple genes
Sex-linked	Gene located on sex chromosome

Example: Hemophilia is a sex-linked recessive disorder more common in males.

Additional info: Some dominant allele disorders are lethal because a single copy of the mutated gene disrupts essential functions. Recessive disorders persist because carriers (heterozygotes) do not show symptoms and can pass the allele to offspring.