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 and generate heat. The sliding filament mechanism is central to muscle contraction.

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

• Actin and Myosin Filaments: Actin provides the track for myosin heads to attach and pull, causing contraction.

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

• Function: Sarcomeres enable muscles to contract and generate force.

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

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

Example: During bicep contraction, sarcomeres shorten as myosin pulls actin filaments inward.

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential in motor neurons triggers muscle contraction.

• Order of Events:

  1. Motor neuron releases neurotransmitter (acetylcholine).

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

  3. Calcium ions are released from the sarcoplasmic reticulum.

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

  5. Myosin binds to actin, causing contraction.

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

Example: Shivering increases muscle activity to generate heat.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (movement occurs), tension remains constant.

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

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

Human Respiratory System

Significance and Mechanics of Breathing

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide.

• Breathing: Essential for cellular respiration and energy production.

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

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

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

Example: The diaphragm contracts during inhalation, increasing thoracic volume.

Mechanics of Inspiration and Expiration

• Inspiration: Diaphragm and intercostal muscles contract, thoracic cavity expands, lung pressure decreases, air flows in.

• Expiration: Muscles relax, thoracic cavity decreases, lung pressure increases, air flows out.

Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

Oxygen-Rich Blood Flow Through the Heart

• Pathway: Oxygenated blood from lungs enters left atrium, passes to left ventricle, then pumped to body.

Example: Pulmonary veins carry oxygen-rich blood to the heart.

Respiratory Diseases and Disorders

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

• Significance: Affect gas exchange and overall health.

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 macromolecules; produced in salivary glands, stomach, pancreas, small intestine.

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

Example: Amylase in saliva begins starch digestion.

Metabolic Rates and Nutrition

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

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

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

Example: BMR is measured after fasting and rest.

Digestion Processes

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

• Molecule Digestion: Carbohydrates, proteins, and fats are digested in different regions by specific enzymes.

Example: Peristalsis pushes food from esophagus to stomach.

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 trait.

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

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

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

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

Example: Down syndrome is detected by karyotyping.

Genotype, Phenotype, and Punnett Squares

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

• Phenotype: Observable traits.

• Punnett Square: Diagram predicting genetic crosses.

Example: Crossing Aa x Aa yields 1:2:1 genotype ratio.

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 assort independently.

Example: Mendel's pea plant experiments demonstrated these laws.

Complex Patterns of Inheritance

• 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 modify phenotypic expression.

• Linked Genes: Genes located close together on a chromosome tend to be inherited together.

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

• Sex-Linked Genes: Genes on sex chromosomes (e.g., X-linked traits).

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

Example: Color blindness is an X-linked trait.

Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype
Dominant/Recessive	AA, Aa, aa	Dominant trait (AA, Aa), Recessive trait (aa)
Incomplete Dominance	RR, RW, WW	Red (RR), Pink (RW), White (WW)
Codominance	IAIB	Both traits expressed (e.g., AB blood type)
Polygenic	Multiple genes	Continuous variation (e.g., height)

Additional info: Table entries inferred for clarity and completeness.