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.

• Order of Events: Nerve impulse → action potential → calcium release → myosin-actin interaction → contraction.

• Electrical Impulses: Action potentials in motor neurons trigger calcium release from the sarcoplasmic reticulum.

• Heat Generation: Most body heat is generated by muscle activity, especially during contraction.

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

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle tension increases, but length does not change (no movement).

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

Sarcomere Substructures and Functions

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

• A-band: Contains the length of the myosin filaments.

• I-band: Contains only actin filaments.

• H-zone: Area with only myosin, disappears during contraction.

Action Potential and Muscle Contraction

• Action Potential: Electrical signal in motor neuron triggers muscle contraction.

• Mechanism: Acetylcholine released at neuromuscular junction → depolarization → calcium release → contraction.

Equation:

$\Delta V = V_{final} - V_{initial}$

Additional info: ATP is required for both contraction and relaxation of muscle fibers.

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 Structures:

  • Upper Respiratory: Nose, pharynx, larynx – filter, warm, and humidify air.

  • Lower Respiratory: Trachea, bronchi, lungs – conduct air and facilitate gas exchange.

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

• Pressure Changes: Inhalation decreases lung pressure, drawing air in; exhalation increases pressure, expelling air.

• Mechanics of Inspiration: Diaphragm contracts, chest expands, air enters.

• Mechanics of Expiration: Diaphragm relaxes, chest contracts, air exits.

• Respiratory Diseases: Includes asthma, bronchitis, pneumonia, and emphysema.

Example: During exercise, breathing rate increases to meet oxygen demand.

Blood Flow Through the Heart

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

Equation:

$P = \frac{F}{A}$

Additional info: Breathing also helps regulate blood pH by controlling CO2 levels.

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 – produce enzymes and bile.

• Enzymes: Catalyze breakdown of carbohydrates, proteins, and fats; produced in salivary glands, stomach, pancreas, small intestine.

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

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

• Metabolic Rates:

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

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

• "My Plate": Dietary guideline for balanced nutrition.

Example: The pancreas releases amylase to digest carbohydrates in the small intestine.

Equation:

$\text{BMR} = 70 \times (\text{body weight in kg})^{0.75}$

Additional info: Digestive enzymes are specific to substrate and optimal pH.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Gene: Segment of DNA coding for a protein.

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

• Genome: Complete set of genes in an organism.

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

• Karyotype: Visual representation of chromosome number and structure.

Genotype, Phenotype, and Punnett Squares

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

• Phenotype: Observable traits (e.g., brown eyes).

• Punnett Square: Diagram to predict genetic crosses.

Alleles and Patterns of Inheritance

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

• Recessive Allele: Expressed only when homozygous (e.g., aa).

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

• Heterozygous: Two different alleles (Aa).

• Law of Segregation: Alleles separate during gamete formation.

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

Complex Patterns and Disorders

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

• 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, inherited together.

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

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

Example: Color blindness is a sex-linked recessive trait.

Inheritance Pattern	Genotype	Phenotype
Dominant	AA, Aa	Trait expressed
Recessive	aa	Trait expressed
Incomplete Dominance	Aa	Intermediate trait
Codominance	AB	Both traits expressed
Polygenic	Multiple genes	Continuous variation

Equation:

$\text{Probability of trait} = \frac{\text{Number of favorable outcomes}}{\text{Total outcomes}}$

Additional info: Nondisjunction can result in conditions like Down syndrome (trisomy 21).