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 called muscle fibers that contract to produce movement. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic functional unit of a muscle fiber, 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 and movement.

• Substructures: Z-line, M-line, A-band, I-band, and H-zone are key sarcomere regions.

Example: During contraction, the sarcomere shortens as actin and myosin slide past each other.

Action Potential and Muscle Contraction

Muscle contraction is initiated by an action potential in a motor neuron, which triggers electrical impulses in the muscle fiber.

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

• Order of Events: 1. Nerve impulse arrives at neuromuscular junction. 2. Acetylcholine is released. 3. Muscle cell depolarizes. 4. Calcium ions are released from the sarcoplasmic reticulum. 5. Sliding filament mechanism activates.

• Electrical Impulses: Cause release of calcium ions, which enable actin-myosin interaction.

Example: The release of acetylcholine at the neuromuscular junction triggers muscle contraction.

Types of Muscle Contractions

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

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

Example: Lifting a weight is isotonic; holding a weight steady is isometric.

Muscle Groups and Functions

• Major Muscle Groups: Biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, gluteals.

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

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

Human Respiratory System

Significance of Breathing

Breathing is essential for oxygen intake and carbon dioxide removal, supporting cellular respiration and energy production.

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

• Respiratory Diseases: Disorders include asthma, bronchitis, emphysema, pneumonia.

Structures of the Respiratory System

• Upper Respiratory Tract: Nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.

• Lower Respiratory Tract: Trachea, bronchi, bronchioles, lungs, alveoli. Functions: gas exchange, air conduction.

Example: The alveoli are the site of oxygen and carbon dioxide exchange.

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.

Example: During inspiration, lung pressure drops below atmospheric pressure, drawing air in.

Blood Flow Through the Heart

• Order: Pulmonary veins → left atrium → left ventricle → aorta → body tissues → vena cava → right atrium → right ventricle → pulmonary artery → lungs.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food via peristalsis.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Absorbs nutrients; large surface area increases efficiency.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores bile.

• Pancreas: Produces digestive enzymes and hormones.

Enzymes and Digestion

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

• Function: Break down carbohydrates, proteins, fats.

Example: Amylase breaks down starch in the mouth.

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.

Peristalsis

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

"My Plate"

• Purpose: Dietary guideline for balanced nutrition.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

• Gene: Segment of DNA coding for a trait.

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

• Genome: Complete set of genetic material.

• Homologous Chromosomes: Pair of chromosomes with same genes, one from each parent.

Karyotype

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

Genotype and Phenotype

• Genotype: Genetic makeup (alleles).

• Phenotype: Observable traits.

Punnett Square

• Function: Predicts genetic outcomes of crosses.

Dominant and Recessive Alleles

• Dominant Allele: Expressed if present.

• Recessive Allele: Expressed only if homozygous.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Mendelian Laws

• 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

• Sex-linked Genes: Located on sex chromosomes; often affect males more.

Nondisjunction

• Nondisjunction: Failure of chromosomes to separate during meiosis; leads to abnormal chromosome numbers in gametes.

Term	Definition
Gene	Segment of DNA coding for a trait
Chromosome	DNA molecule with proteins; humans have 23 pairs
Genotype	Genetic makeup (alleles)
Phenotype	Observable traits
Homozygous	Two identical alleles
Heterozygous	Two different alleles
Dominant Allele	Expressed if present
Recessive Allele	Expressed only if homozygous
Incomplete Dominance	Intermediate phenotype in heterozygotes
Codominance	Both alleles fully expressed
Polygenic Inheritance	Trait influenced by multiple genes
Sex-linked Gene	Located on sex chromosomes
Nondisjunction	Failure of chromosome separation in meiosis

Example: Hemophilia is a sex-linked disorder, more common in males.

Additional info: Academic context and definitions were expanded for clarity and completeness.