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, composed of actin (thin) and myosin (thick) filaments.

• Actin and Myosin: Proteins that interact to produce contraction. Myosin heads bind to actin, pulling the filaments past each other.

• Sliding Filament Theory: Muscle contraction occurs as myosin heads attach to actin and pull, shortening the sarcomere.

• Order of Events: Nerve impulse → Action potential in motor neuron → Release of neurotransmitter (acetylcholine) → Muscle cell depolarization → Calcium release → Actin-myosin interaction → Contraction.

• Electrical Impulses: Action potentials trigger calcium release from the sarcoplasmic reticulum, enabling contraction.

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

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

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

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

Example: Lifting a weight (isotonic); holding a weight steady (isometric).

Key Terms and Functions

• Sarcomere Function: Facilitates contraction by shortening during muscle activity.

• Actin: Provides sites for myosin attachment.

• Myosin: Uses ATP to pull actin filaments.

Additional info: ATP is required for myosin head detachment and re-cocking during contraction cycles.

Human Respiratory System

Significance and Structure

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide. It consists of upper and lower structures, each with specific functions.

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

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

• Breathing: Essential for cellular respiration and energy production.

• Oxygen-rich Blood Flow: Oxygenated blood returns from lungs to left atrium → left ventricle → systemic circulation.

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.

Respiratory Diseases and Disorders

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

• Impact: Affect gas exchange and breathing efficiency.

Example: Asthma causes constriction of airways, reducing airflow.

Human Digestive System

Structure and Function

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It includes primary and accessory organs.

• Major Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum.

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

• 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.

• Peristalsis: Rhythmic contractions move food through the digestive tract.

Metabolic Rates and Nutrition

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

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

• "My Plate": Nutrition guide for balanced diet.

Example: Pancreatic amylase digests carbohydrates in the small intestine.

Additional info: Enzymes are specific to substrates; e.g., proteases for proteins, lipases for fats.

Human Genetics and Inheritance

Basic Concepts

Genetics studies heredity and variation. Genes, chromosomes, and alleles determine traits and inheritance patterns.

• Gene: DNA segment coding for a protein.

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

• Genome: Complete set of genetic material.

• Homologous Chromosomes: Pair with same genes, may have different alleles.

• Karyotype: Chromosome display; used to detect abnormalities.

• Genotype: Genetic makeup.

• Phenotype: Observable traits.

Inheritance Patterns

• Punnett Square: Diagram to predict genetic crosses.

• Dominant Allele: Expressed if present.

• Recessive Allele: Expressed only if homozygous.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes on different chromosomes assort independently.

Complex Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can modify phenotypic expression.

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

• Meiosis: New allele combinations arise via crossing over.

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

• Nondisjunction: Failure of chromosomes to separate; leads to abnormal chromosome numbers in gametes.

Sample Table: Dominant vs. Recessive Alleles

Allele Type	Expression	Example
Dominant	Expressed in heterozygote	Widow's peak
Recessive	Expressed only in homozygote	Attached earlobe
Codominant	Both alleles expressed	AB blood type
Incomplete Dominance	Intermediate phenotype	Pink snapdragon flowers

Example: Sickle cell anemia is caused by a recessive allele; color blindness is X-linked.

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