Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system enables movement and generates heat through the contraction of muscle fibers. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic contractile unit of muscle, 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.

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

Example: During exercise, muscle contractions increase body temperature due to ATP hydrolysis.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential that triggers muscle contraction.

• Order of Events: Motor neuron releases acetylcholine → depolarization → calcium release → actin-myosin interaction → contraction.

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

Example: The neuromuscular junction transmits the signal from nerve to muscle.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (movement occurs).

• Isometric Contraction: Muscle tension increases, but length does not change (no movement).

Example: Lifting a weight is isotonic; holding a weight steady is 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 supplies oxygen for cellular respiration and removes carbon dioxide, essential for life.

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

• Respiratory Diseases: Includes asthma, bronchitis, pneumonia, and emphysema.

Structures of the Respiratory System

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

• Lower Respiratory Tract: Trachea, bronchi, lungs – conduct air and facilitate gas exchange.

Example: The cilia in the trachea help remove particles from inhaled air.

Mechanics of Breathing

• Inhalation: Diaphragm contracts, intercostal muscles expand the rib cage, lung pressure decreases, air flows in.

• Exhalation: Diaphragm relaxes, rib cage contracts, lung pressure increases, air flows out.

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

Intercostal Muscles: Assist in expanding and contracting the chest during breathing.

Blood Flow Through the Heart

• Order: Pulmonary veins → left atrium → left ventricle → aorta → body tissues.

Human Digestive System

Major Structures and Functions

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

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

• Accessory Organs: Liver, pancreas, gallbladder – produce enzymes and bile for digestion.

Enzymes and Digestion

• Function: Enzymes catalyze breakdown of macromolecules (proteins, carbohydrates, fats).

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

Example: Amylase breaks down starch in the mouth.

Surface Area and Digestion

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

Metabolic Rates

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

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

Equation: $\text{BMR} = \text{Energy expenditure at rest}$

My Plate and Nutrition

• My Plate: A guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion Mechanics

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Gene: A segment of DNA coding for a protein.

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

• Genome: The complete set of genes in an organism.

• Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.

• Karyotype: The visual display of chromosomes, used to detect abnormalities.

Genotype and Phenotype

• Genotype: The genetic makeup (alleles) of an individual.

• Phenotype: The observable traits resulting from genotype and environment.

Punnett Square and Alleles

• Punnett Square: Diagram used to predict genetic crosses.

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

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

• Heterozygous: Two different alleles (e.g., Aa).

Mendelian Laws

• Law of Segregation: Each parent passes one allele to offspring.

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

Patterns of Inheritance

• Dominant Allele Disorders: Can be lethal if expressed; e.g., Huntington's disease.

• Recessive Disorders: Remain prevalent due to carriers; e.g., cystic fibrosis.

• Incomplete Dominance: Heterozygotes show intermediate phenotype.

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

• Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).

• Environmental Impact: Environment can modify 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.

Term	Definition	Example
Genotype	Genetic makeup of an organism	AA, Aa, aa
Phenotype	Observable traits	Brown eyes, blue eyes
Homozygous	Same alleles	AA or aa
Heterozygous	Different alleles	Aa
Dominant	Expressed allele	A
Recessive	Masked allele	a
Codominance	Both alleles expressed	AB blood type
Incomplete Dominance	Intermediate phenotype	Pink flowers (red x white)
Polygenic	Multiple genes affect trait	Height, skin color

Additional info: Academic context and definitions were expanded for clarity and completeness. Table entries were inferred for common genetic terms.