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 (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 filaments and pull them inward, shortening the sarcomere.

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

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

• Function of Sarcomere: Generates force for muscle contraction by shortening during the sliding of filaments.

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

Muscle Contraction Mechanism

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

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

• Order of Events:

  1. Action potential travels down motor neuron.

  2. Acetylcholine is released at neuromuscular junction.

  3. Muscle fiber membrane depolarizes, generating an action potential.

  4. Calcium ions are released from the sarcoplasmic reticulum.

  5. Calcium binds to troponin, shifting tropomyosin and exposing actin binding sites.

  6. Myosin heads bind to actin, forming cross-bridges.

  7. ATP hydrolysis powers the sliding of filaments.

  8. Muscle contracts; process repeats as long as calcium and ATP are present.

• Heat Generation: Most body heat is generated by muscle contractions (shivering thermogenesis).

Isotonic vs. Isometric Contractions:

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

• Isometric: Muscle length remains the same while tension increases (e.g., holding a weight steady).

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

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

Human Respiratory System

Significance and Structure

The respiratory system enables gas exchange, supplying oxygen for cellular respiration and removing carbon dioxide.

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, and larynx. Functions: filter, warm, and humidify air; protect lower airways.

• Lower Respiratory System: Includes trachea, bronchi, bronchioles, and lungs. Functions: conduct air to alveoli, where gas exchange occurs.

Breathing Mechanics:

• 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, pushing air out.

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

• Intercostal Muscles: Located between ribs; assist in expanding and contracting the chest 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.

• Oxygen-poor blood returns to the right atrium, then right ventricle, and is pumped to the lungs for oxygenation.

Respiratory Diseases and Disorders: Include asthma, bronchitis, emphysema, pneumonia, and lung cancer.

Human Digestive System

Structure and Function

The digestive system breaks down food into nutrients for absorption and energy.

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

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas. Functions: produce enzymes, bile, and other substances for digestion.

• Enzymes: Biological catalysts that speed up digestion; produced in salivary glands, stomach, pancreas, and small intestine.

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

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

Metabolic Rates:

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

• Standard Metabolic Rate (SMR): Energy expenditure under standardized conditions (often used in animal studies).

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

Human Genetics and Inheritance

Basic Concepts

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

• Chromosome: A structure of DNA and protein carrying genetic information; humans have 23 pairs.

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

• Genetics: The scientific study of heredity and variation.

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

• Karyotype: An organized profile of an individual's chromosomes, used to detect chromosomal abnormalities.

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

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

Mendelian Inheritance

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

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

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

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

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

• Heterozygous: Two different alleles (Aa).

• 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.

Complex Inheritance Patterns

• Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., red x white flowers = pink).

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

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

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

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

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

• 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	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, aa
Phenotype	Observable trait	Tall, short, brown eyes
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed allele	A in Aa
Recessive	Masked by dominant	a in Aa

Example: In a cross between two heterozygous parents (Aa x Aa), the Punnett square predicts a 3:1 ratio of dominant to recessive phenotypes.

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