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 (thin) and myosin (thick) filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin filaments and pull them inward, shortening the sarcomere.

• Actin and Myosin: Actin provides the track for myosin movement; myosin uses ATP to generate force.

• Order of Events: Nerve impulse → Action potential → Calcium release → Myosin-actin interaction → Muscle contraction.

• Electrical Impulses: Action potentials in motor neurons trigger calcium release from the sarcoplasmic reticulum.

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

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

• 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 is isotonic; holding a weight steady is isometric.

Sarcomere Substructures

• Z-line: Defines the boundaries of a sarcomere.

• A-band: Contains the length of the myosin filaments.

• I-band: Contains only actin filaments.

• H-zone: Central region with only myosin.

Function: The sarcomere shortens during contraction, producing force.

Action Potential in Motor Neuron

• Initiation: Action potential is generated by the influx of sodium ions.

• Transmission: Travels down the axon to the neuromuscular junction.

• Release: Triggers release of neurotransmitter (acetylcholine).

Formula: $\Delta V = IR$ (Ohm's Law, relates voltage change to current and resistance in neurons)

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.

• Carbon Dioxide Removal: Waste gas is expelled during exhalation.

Structures of the Respiratory System

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

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

Mechanics of Breathing

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

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

• Pressure Changes: $P_1V_1 = P_2V_2$ (Boyle's Law: pressure and volume are inversely related)

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

Example: During inspiration, lung pressure drops below atmospheric pressure, drawing air in.

Respiratory Diseases and Disorders

• Asthma: Inflammation and narrowing of airways.

• Emphysema: Damage to alveoli, reduced gas exchange.

• Pneumonia: Infection of lung tissue.

Blood Flow Through the Heart

• Oxygen-rich blood enters the left atrium → left ventricle → aorta → systemic circulation.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food via peristalsis.

• Stomach: Secretes acid and enzymes; churns food.

• Small Intestine: Main site of nutrient absorption.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores and releases bile.

• Pancreas: Produces digestive enzymes and hormones.

Enzymes in Digestion

• Function: Catalyze breakdown of macromolecules.

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

Surface Area in Digestion

• Importance: Increased surface area (villi, microvilli) enhances nutrient absorption.

Metabolic Rates

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

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

"My Plate" Purpose

• Guideline: Visual tool for balanced nutrition.

Peristalsis

• Definition: Wave-like muscle contractions moving food through the digestive tract.

Example: Swallowing food initiates peristalsis in the esophagus.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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.

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pair of chromosomes with same 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

• Function: Predicts genetic outcomes of crosses.

Example Table: Dominant vs. Recessive Alleles

Allele Type	Genotype	Phenotype
Dominant	AA, Aa	Trait expressed
Recessive	aa	Trait expressed only if homozygous

Laws of Inheritance

• Law of Segregation: Alleles separate during gamete formation.

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

Dominant and Recessive Disorders

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

• Recessive Disorders: Expressed only if both alleles are recessive; can persist in populations.

Incomplete Dominance and Codominance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed (e.g., blood type AB).

Polygenic Inheritance

• Definition: Trait controlled by multiple genes (e.g., skin color).

Environmental Impact on Phenotype

• Influence: Environment can modify gene expression (e.g., nutrition, temperature).

Linked Genes and New Allele Combinations

• Linked Genes: Genes located close together on a chromosome, inherited together.

• Meiosis: Crossing over creates new allele combinations.

Sex-linked Genes

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

• Example: Color blindness is X-linked.

Nondisjunction

• Definition: Failure of chromosomes to separate during meiosis.

• Impact: Results in abnormal chromosome numbers (e.g., Down syndrome).

Formula: $2^n$ (Number of possible gamete combinations, where n = number of heterozygous pairs)