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

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system relies on specialized cells and structures to produce movement. The sliding filament mechanism is central to muscle contraction.

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

• Actin and Myosin: Proteins that interact to produce contraction. Myosin heads bind to actin, pulling the filaments past each other.

• Sliding Filament Theory: Muscle contraction occurs as myosin heads attach to actin and pull, shortening the sarcomere.

• Substructures: Includes Z-lines, M-line, A-band, I-band, and H-zone, each with specific roles in contraction.

• Function: Sarcomeres shorten during contraction, generating force.

Example: During biceps contraction, sarcomeres in muscle fibers shorten, causing the arm to bend.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

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

• Mechanism: Motor neuron releases acetylcholine, triggering depolarization in the muscle cell membrane.

• Order of Events:

  1. Motor neuron releases neurotransmitter.

  2. Muscle cell depolarizes.

  3. Calcium ions released from sarcoplasmic reticulum.

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

  5. Myosin binds to actin, contraction occurs.

Example: Nerve impulse causes muscle contraction in the leg during walking.

Types of Muscle Contractions

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

• Isometric Contraction: Muscle tension increases, but length does not change. No movement produced.

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

Muscle Groups and Functions

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

• Body Cavities: Muscles such as the diaphragm section off the thoracic and abdominal cavities.

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

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen to tissues and removing carbon dioxide.

• Oxygen: Required for cellular respiration and energy production.

• Carbon Dioxide: Waste product expelled during exhalation.

Respiratory System Structures

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

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

Example: The nasal cavity filters dust and pathogens from inhaled air.

Mechanics of Breathing

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

• 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.

Blood Flow and Gas Exchange

• Oxygen-rich Blood: Flows from lungs to left atrium, then left ventricle, then systemic circulation.

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

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, pneumonia, emphysema.

• Impact: Affect airflow, gas exchange, and overall health.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for nutrient absorption.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Pancreas: Secretes digestive enzymes and hormones.

• Gallbladder: Stores and releases bile.

Enzymes and Digestion

• Function: Catalyze breakdown of macromolecules.

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

Example: Amylase breaks down starch in the mouth.

Surface Area and Digestion

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

Metabolic Rates

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

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

Example: BMR is measured after fasting and rest.

"My Plate" Purpose

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

Digestion of Molecules and Peristalsis

• Digestion: Carbohydrates, proteins, and fats are broken down by specific enzymes.

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

• Gene: Segment of DNA coding for a trait.

• Chromosome: Structure containing DNA; humans have 23 pairs.

• Genome: Complete set of genetic material in an organism.

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pair of chromosomes with same genes but possibly different alleles.

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (allele combination).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram predicting genetic crosses.

• Dominant Allele: Expressed trait if present.

• Recessive Allele: Expressed only if homozygous.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Laws of Genetics

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can affect phenotypic expression.

Linked Genes and Meiosis

• Linked Genes: Genes located close together on a chromosome, inherited together.

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

Sex-linked Genes and Nondisjunction

• Sex-linked Genes: Located on sex chromosomes, often X-linked.

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

Term	Definition
Gene	Segment of DNA coding for a trait
Chromosome	Structure containing DNA
Genotype	Genetic makeup
Phenotype	Observable trait
Homozygous	Two identical alleles
Heterozygous	Two different alleles
Dominant	Expressed if present
Recessive	Expressed only if homozygous
Incomplete Dominance	Intermediate phenotype
Codominance	Both alleles expressed
Polygenic	Trait influenced by multiple genes
Sex-linked	Gene on sex chromosome
Nondisjunction	Failure of chromosome separation

Example: Color blindness is a sex-linked trait, often inherited through the X chromosome.