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 and myosin filaments.

• Actin and Myosin Filaments: Actin (thin filament) and myosin (thick filament) interact to produce contraction via the sliding filament mechanism.

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

• Function of Sarcomere: Responsible for muscle contraction and force generation.

Example: During biceps contraction, sarcomeres shorten, causing the muscle to pull on the forearm.

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 potential that travels along the neuron and muscle cell.

• Order of Events:

  1. Motor neuron releases acetylcholine at the neuromuscular junction.

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

  3. Electrical impulse triggers release of calcium ions from the sarcoplasmic reticulum.

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

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

Example: Shivering increases muscle contractions 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 (isotonic); holding a weight steady (isometric).

Major Muscle Groups and Functions

• Muscles of Body Cavities: Diaphragm (separates thoracic and abdominal cavities), intercostal muscles (between ribs).

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

Human Respiratory System

Significance of Breathing

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

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

• Importance: Cellular respiration requires oxygen to produce ATP.

Structures of the Respiratory System

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

• Lower Respiratory System: Trachea, bronchi, lungs, alveoli. Functions: conduct air, gas exchange.

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, drawing air in.

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.

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

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

Respiratory Diseases and Disorders

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

• Impact: Affect airflow, gas exchange, and overall respiratory efficiency.

Human Digestive System

Major Structures and Functions

• Digestive Tract: Mouth, esophagus, stomach, small intestine, large intestine, rectum.

• Accessory Organs: Liver, pancreas, gallbladder. Functions: produce enzymes, bile, aid digestion.

Example: The pancreas produces digestive enzymes and insulin.

Enzymes and Digestion

• Function: Enzymes break down macromolecules into absorbable units.

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

Surface Area and Digestion

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

Metabolic Rates

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

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

Equation: $\text{BMR} = \text{Energy} / \text{Time}$

"My Plate" and Nutrition

• Purpose: Guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion Process and Peristalsis

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

• Digestion: Chemical and mechanical breakdown of food into nutrients.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

• Gene: Segment of DNA coding for a protein.

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

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

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Paired chromosomes with similar genes, one from each parent.

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (alleles).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram predicting genetic crosses.

• Alleles: Variants of a gene; can be dominant or recessive.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Genetic Laws

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes assort independently during meiosis.

Dominant and Recessive Disorders

• Dominant Disorders: Expressed with one dominant allele; can be lethal.

• Recessive Disorders: Require two recessive alleles; can persist in populations.

Complex Patterns of Inheritance

• 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: Genes located on sex chromosomes (X or Y).

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

Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Dominant	AA or Aa	Trait expressed	Huntington's disease
Recessive	aa	Trait expressed	Cystic fibrosis
Incomplete Dominance	Aa	Intermediate	Snapdragon flower color
Codominance	AB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Height, skin color

Additional info: Table entries inferred for clarity and completeness.