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 and generates heat through the contraction of muscle fibers. The sliding filament mechanism is central to muscle contraction.

• 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.

• Actin and Myosin: Actin provides the track, while myosin uses ATP to generate force.

• Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, and others.

• Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities.

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential that triggers muscle contraction.

• Order of Events: Nerve impulse → release of neurotransmitter (acetylcholine) → depolarization → calcium release → contraction.

• Heat Generation: Most body heat is produced by muscle activity.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (movement occurs).

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

Sarcomere Substructures

• Z-line: Defines the boundaries of a sarcomere.

• A-band: Contains myosin filaments.

• I-band: Contains actin filaments.

Example: During bicep curl, the sarcomeres shorten as actin and myosin slide past each other.

Human Respiratory System

Significance of Breathing

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

• Oxygen Transport: Oxygen-rich blood is pumped from the lungs to the heart, then distributed to the body.

Structures of the Respiratory System

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

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

Mechanics of Breathing

• Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure.

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

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

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

Respiratory Diseases and Disorders

• Examples: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.

Blood Flow Through the Heart

• Order: Pulmonary veins → left atrium → left ventricle → aorta → body.

Example: During exercise, breathing rate increases to supply more oxygen.

Human Digestive System

Major Structures and Functions

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

• Major Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum.

• Accessory Organs: Liver, pancreas, gallbladder.

Enzymes and Digestion

• Function: Enzymes catalyze the breakdown of macromolecules.

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

Surface Area and Digestion

• Large Surface Area: Villi and microvilli in the small intestine increase absorption efficiency.

Metabolic Rates

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

• Standard Metabolic Rate (SMR): Energy used under specific conditions.

"My Plate" Purpose

• My Plate: A guide for balanced nutrition, emphasizing proper proportions of food groups.

Digestion Process and Peristalsis

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

Example: The pancreas releases digestive enzymes into the small intestine to break down fats, proteins, and carbohydrates.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Gene: A segment of DNA coding for a trait.

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

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

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

• Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Genotype and Phenotype

• Genotype: Genetic makeup (e.g., AA, Aa, aa).

• Phenotype: Observable traits (e.g., eye color).

Punnett Square and Alleles

• Punnett Square: Diagram to predict genetic crosses.

• Dominant Allele: Expressed trait when present.

• Recessive Allele: Expressed only when homozygous.

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes for different traits are inherited independently.

Inheritance Patterns

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

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

• Environmental Impact: Environment can affect phenotypic expression.

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

• Sex-linked Genes: Genes located on sex chromosomes (e.g., X-linked traits).

Meiosis and Genetic Variation

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

• Nondisjunction: Failure of chromosomes to separate properly, leading to abnormal chromosome numbers in gametes.

Sample Punnett Square Table

Parent Genotype	Offspring Genotype	Offspring Phenotype
AA x aa	All Aa	All dominant phenotype
Aa x Aa	AA, Aa, aa	3:1 dominant:recessive
Aa x aa	Aa, aa	1:1 dominant:recessive

Example: Cystic fibrosis is a recessive disorder; sickle cell anemia shows codominance.

Additional info: The notes above expand on brief review points to provide academic context and explanations suitable for exam preparation.