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 fibers, 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, forming cross-bridges, and pull the actin filaments inward, shortening the sarcomere.

• Function: Sarcomeres shorten during contraction, producing force and movement.

• 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, the sarcomeres shorten, pulling the forearm upward.

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) at neuromuscular junction.

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

  3. Calcium ions are released from the sarcoplasmic reticulum.

  4. Calcium enables actin-myosin interaction, leading to 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.

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

Blood Flow and Oxygen Transport

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

• Practice: Trace blood flow: lungs → left atrium → left ventricle → aorta → body.

Mechanics of Breathing

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

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air flows out.

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

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

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

Respiratory Diseases and Disorders

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

• Impact: Diseases can impair gas exchange and reduce oxygen supply.

Human Digestive System

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 for digestion.

• 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: Pancreatic amylase digests carbohydrates in the small intestine.

Metabolic Rates and Nutrition

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

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

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

Example: BMR is higher in individuals with more muscle mass.

Digestion Processes

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

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

Example: Peristalsis moves food from the esophagus to the stomach.

Human Genetics and Inheritance

Basic Concepts and Structures

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

• Genes: Segments of DNA encoding traits; composed of nucleotide sequences.

• Chromosomes: DNA-protein complexes carrying genes; humans have 23 pairs.

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

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

• Karyotype: Visual representation of chromosome number and structure.

Example: Down syndrome is caused by an extra chromosome 21 (trisomy 21).

Genotype, Phenotype, and Punnett Squares

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

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

• Punnett Square: Diagram used to predict genetic crosses.

Example: Crossing Aa x Aa yields a 3:1 ratio of dominant to recessive phenotypes.

Alleles and Laws 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.

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 located on sex chromosomes (e.g., X-linked traits).

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

Example: Hemophilia is an X-linked recessive disorder.

Table: Comparison of Dominant and Recessive Alleles

Allele Type	Expression	Example
Dominant	Expressed in heterozygous and homozygous states	Brown eyes (B)
Recessive	Expressed only in homozygous state	Blue eyes (bb)

Additional info: Polygenic traits often show continuous variation, such as height or skin color.