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 describes how actin and myosin filaments interact within the sarcomere.

• Sarcomere: The basic contractile unit of muscle fiber, composed of actin (thin) and myosin (thick) filaments.

• Sliding Filament Mechanism: Myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere and causing contraction.

• 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).

• Muscle Unit Structures: Muscle fiber, myofibril, sarcomere, and associated connective tissues.

Example: During biceps contraction, the sarcomeres shorten as myosin pulls actin inward.

Action Potentials and Muscle Contraction

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

• Mechanism: Action potential travels down the neuron, causing release of neurotransmitter (acetylcholine) at the neuromuscular junction, triggering depolarization of the muscle cell membrane.

• Order of Events:

  1. Motor neuron releases acetylcholine.

  2. Muscle cell membrane depolarizes.

  3. Calcium ions released from sarcoplasmic reticulum.

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

  5. Myosin binds to actin, initiating contraction.

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

Types of Muscle 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 produced.

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

Major Muscle Groups and Functions

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

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

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.

• Carbon Dioxide Removal: Prevents acidification of body fluids.

Respiratory System Structures and Functions

• Upper Respiratory System: Nasal cavity (filters, warms, humidifies air), pharynx (passageway), larynx (voice box, airway protection).

• Lower Respiratory System: Trachea (windpipe), bronchi (air passageways), lungs (gas exchange), alveoli (site of gas exchange).

Mechanics of Breathing

• Inhalation (Inspiration): Diaphragm and intercostal muscles contract, thoracic cavity volume increases, lung pressure decreases, air flows in.

• Exhalation (Expiration): Diaphragm and intercostal muscles relax, thoracic cavity volume decreases, lung pressure increases, air flows out.

• Pressure Changes: Air moves from high to low pressure; described by Boyle's Law: $P_1V_1 = P_2V_2$

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

Blood Flow and Gas Exchange

• Oxygen-Rich Blood Flow: Pulmonary veins → left atrium → left ventricle → aorta → systemic circulation.

• Gas Exchange: Occurs in alveoli; oxygen diffuses into blood, carbon dioxide diffuses out.

Respiratory Diseases and Disorders

• Examples: Asthma, bronchitis, emphysema, pneumonia.

• Impact: Affect airflow, gas exchange, or lung tissue.

Human Digestive System

Major Structures and Functions

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

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

• Functions: Ingestion, digestion, absorption, elimination.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion (e.g., amylase, pepsin, lipase).

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

Surface Area and Digestion

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

Metabolic Rates

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

• Standard Metabolic Rate (SMR): Metabolic rate under standardized conditions (often used in animals).

Nutrition and "My Plate"

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

Digestion Process and Peristalsis

• Digestion: Breakdown of food into absorbable molecules by mechanical and chemical means.

• 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 that codes for a protein or trait.

• Chromosome: 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 Terminology

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

• Phenotype: The observable traits or characteristics.

• 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.

Mendelian Inheritance

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

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

• Recessive Allele: Expressed only when two copies are present (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.

Patterns of 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, height).

• 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, often inherited together.

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

Sex-Linked Genes and Nondisjunction

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

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

Table: Comparison of Dominant and Recessive Alleles

Term	Dominant Allele	Recessive Allele
Expression	Expressed if present (AA or Aa)	Expressed only if homozygous (aa)
Example	Widow's peak (W)	Straight hairline (w)
Disorders	Some are lethal (e.g., Huntington's)	Can persist in population (e.g., cystic fibrosis)

Additional info: This guide expands on the review points by providing definitions, mechanisms, and examples for each major topic, suitable for exam preparation in a Human Biology course.