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 Z-lines. It contains overlapping actin (thin) and myosin (thick) filaments.

• Sliding Filament Mechanism: During contraction, 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-line, M-line, A-band, I-band, and H-zone, each with specific roles in contraction.

• Muscle Heat Generation: Most body heat is generated by muscle contractions, especially during shivering.

• Major Muscle Groups: Examples include biceps brachii, quadriceps femoris, pectoralis major, and rectus abdominis.

Example: During a biceps curl, the biceps brachii contracts, shortening the sarcomeres and pulling the forearm upward.

Action Potentials and Muscle Contraction

Muscle contraction is initiated by electrical impulses called action potentials, which travel from motor neurons to muscle fibers.

• Action Potential: A rapid change in membrane potential that travels along the neuron and muscle cell membrane.

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

• Order of Events:

  1. Action potential arrives at neuromuscular junction.

  2. Acetylcholine is released, binding to receptors on the muscle cell membrane.

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

  4. Calcium ions are released from the 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, tension increases).

Example: Holding a heavy object steady involves isometric contraction; lifting it involves isotonic contraction.

Muscles and Body Cavities

• Diaphragm: Separates thoracic and abdominal cavities; essential for breathing.

• Intercostal Muscles: Located between ribs; assist in expanding and contracting the thoracic cavity during respiration.

Human Respiratory System

Significance of Breathing

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

• Oxygen: Required for aerobic metabolism in cells.

• Carbon Dioxide 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. Responsible for gas exchange.

Mechanics of Breathing

• Inhalation (Inspiration): Diaphragm contracts and moves downward; intercostal muscles contract, expanding the chest cavity. Lung volume increases, pressure decreases, and air flows in.

• Exhalation (Expiration): Diaphragm and intercostal muscles relax, chest cavity volume decreases, pressure increases, and air is expelled.

• Pressure Changes: Governed by Boyle's Law: $P_1V_1 = P_2V_2$

Blood Flow and Gas Exchange

• Oxygen-rich Blood Flow: Oxygenated blood returns from the lungs to the left atrium, passes to the left ventricle, and is pumped to the body.

• Gas Exchange: Occurs in alveoli by diffusion.

Respiratory Diseases and Disorders

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

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

• Function: Enzymes catalyze the breakdown of macromolecules (carbohydrates, proteins, fats).

• 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 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

• Definition: Coordinated, rhythmic contractions of smooth muscle that propel food through the digestive tract.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

• Gene: A segment of DNA that codes for a protein or functional RNA.

• Chromosome: A 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 individual (e.g., AA, Aa, aa).

• Phenotype: The observable traits resulting from the genotype.

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

• Karyotype: A visual representation 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 gamete receives one allele from each gene pair.

• 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 flowers).

• 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	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, aa
Phenotype	Observable trait	Tall, short, blood type
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed when present	A
Recessive	Expressed only when homozygous	a

Additional info: Some dominant allele disorders (e.g., Huntington's disease) are lethal because the dominant allele causes disease even if only one copy is present. Recessive disorders (e.g., cystic fibrosis) persist because carriers (heterozygotes) do not show symptoms but can pass the allele to offspring.