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. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic functional unit of muscle fibers, 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: Includes Z-lines, M-line, A-band, I-band, and H-zone, each with specific roles in contraction.

• Function: The sarcomere shortens during contraction, producing force.

• Example: During biceps contraction, sarcomeres shorten, pulling the forearm upward.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical signals called action potentials.

• Motor Neuron: Releases neurotransmitter (acetylcholine) at the neuromuscular junction, triggering an action potential in the muscle cell.

• Order of Events: Nerve impulse → Acetylcholine release → Muscle cell depolarization → Calcium release → Actin-myosin interaction → Contraction.

• Electrical Impulses: Cause release of calcium ions from the sarcoplasmic reticulum.

• Example: A reflex causes rapid muscle contraction via this pathway.

Types of Muscle Contractions

Muscle contractions can be classified based on whether the muscle changes length.

• Isotonic Contraction: Muscle changes length (e.g., lifting a weight).

• Isometric Contraction: Muscle does not change length (e.g., holding a weight steady).

• Function: Isotonic produces movement; isometric maintains posture.

Muscle Groups and Body Cavities

Major muscle groups include those that section body cavities and enable movement.

• Examples: Diaphragm (separates thoracic and abdominal cavities), intercostal muscles (between ribs).

Heat Generation

Most body heat is generated by muscle activity, especially during contraction.

• System: Muscular system is the primary source of heat.

Summary Table: Muscle Contraction Types

Type	Muscle Length Change	Example
Isotonic	Yes	Lifting a dumbbell
Isometric	No	Holding a plank

Human Respiratory System

Significance of Breathing

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

• Importance: Oxygen is required for cellular respiration; CO2 must be expelled to maintain pH balance.

Respiratory System Structures

The respiratory system is divided into upper and lower regions, each with specific functions.

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

• Lower Respiratory: Includes trachea, bronchi, lungs. Functions: conduct air, gas exchange.

• Significance: Each structure ensures efficient and safe passage of air.

Mechanics of Breathing

Breathing involves changes in lung pressure and muscle activity.

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

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

• Pressure Change Equation:

$\Delta P = P_{atm} - P_{lung}$

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

Blood Flow and Oxygen Transport

Oxygen-rich blood flows from the lungs to the heart, then to the body.

• Pathway: Pulmonary veins → Left atrium → Left ventricle → Aorta → Body tissues.

Respiratory Diseases and Disorders

Common disorders include asthma, bronchitis, pneumonia, and emphysema.

• Impact: Affect airflow, 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.

• Function: Each organ contributes to digestion and absorption.

Enzymes and Digestion

Enzymes catalyze the breakdown of food molecules.

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

• Example: Amylase (carbohydrates), pepsin (proteins), lipase (fats).

Surface Area and Digestion

Large surface area in the small intestine (villi, microvilli) increases nutrient absorption.

• Function: Maximizes contact with digested food.

Metabolic Rates

Metabolic rate measures energy expenditure.

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

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

"My Plate" Purpose

"My Plate" is a nutritional guide for balanced eating.

• Purpose: Promotes healthy proportions of food groups.

Digestion Process and Peristalsis

Peristalsis is the wave-like muscle contraction that moves food through the digestive tract.

• Function: Ensures continuous movement and mixing of food.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

Genetics is the 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.

Homologous Chromosomes and Karyotype

Homologous chromosomes carry the same genes but may have different alleles.

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

Genotype and Phenotype

Genotype is the genetic makeup; phenotype is the observable trait.

• Example: Genotype AA or Aa; phenotype = dominant trait.

Punnett Square and Alleles

Punnett Squares predict genetic outcomes.

• Dominant Allele: Expressed when present (A).

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

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

Two fundamental laws govern inheritance.

• Law of Segregation: Alleles separate during gamete formation.

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

Dominant and Recessive Disorders

Some dominant disorders are lethal; recessive disorders can persist due to carrier status.

• Example: Huntington's disease (dominant), cystic fibrosis (recessive).

Non-Mendelian Inheritance

Traits can be influenced by incomplete dominance, codominance, polygenic inheritance, and environmental factors.

• 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 and Meiosis

Linked genes are inherited together; crossing over during meiosis creates new allele combinations.

• Sex-linked Genes: Located on sex chromosomes; affect traits like color blindness.

Nondisjunction

Nondisjunction is the failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers in gametes.

• Example: Down syndrome (trisomy 21).

Summary Table: Types of Inheritance

Type	Expression	Example
Dominant	Trait appears if allele present	Huntington's disease
Recessive	Trait appears only if homozygous	Cystic fibrosis
Incomplete Dominance	Intermediate phenotype	Pink snapdragon flowers
Codominance	Both alleles expressed	AB blood type
Polygenic	Multiple genes contribute	Skin color