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

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Human Muscular System

Muscle Cell Structure and Sliding Filament Mechanism

The human muscular system enables movement, posture, and heat production. Muscle contraction is explained by the sliding filament theory, which describes how actin and myosin filaments interact within the sarcomere.

Sarcomere: The basic contractile unit of muscle fiber, composed of overlapping actin (thin) and myosin (thick) filaments.
Sliding Filament Mechanism: During contraction, myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.
Actin and Myosin: Actin forms the thin filaments; myosin forms the thick filaments with heads that attach to actin during contraction.
Muscle Unit Structures: Includes the sarcolemma (cell membrane), sarcoplasmic reticulum (stores Ca2+), T-tubules (conduct impulses), and mitochondria (energy supply).

Example: The biceps brachii contracts to flex the forearm by shortening its sarcomeres.

Action Potentials and Muscle Contraction

Muscle contraction is initiated by electrical impulses called action potentials, which travel from motor neurons to muscle fibers.

Action Potential: A rapid change in membrane potential that travels along neurons and muscle fibers.
Neuromuscular Junction: The synapse where a motor neuron communicates with a muscle fiber, releasing acetylcholine to trigger an action potential in the muscle.
Calcium Release: Action potentials cause the sarcoplasmic reticulum to release Ca2+, enabling myosin-actin interaction.
Order of Events: Nerve impulse → Acetylcholine release → Muscle action potential → Ca2+ release → Cross-bridge formation → Contraction.

Example: Tapping the patellar tendon triggers a reflex arc, causing the quadriceps to contract.

Types of Muscle Contractions

Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant; produces movement (e.g., lifting a weight).
Isometric Contraction: Muscle tension increases, but length does not change; no movement occurs (e.g., holding a weight steady).

Example: Holding a plank position involves isometric contraction of core muscles.

Muscle Groups and Body Cavities

Major Muscle Groups: Deltoids, pectorals, biceps, triceps, quadriceps, hamstrings, gluteals, abdominals, etc.
Muscles Sectioning Cavities: The diaphragm separates the thoracic and abdominal cavities.

Heat Production

Most body heat is generated by muscle activity, especially during shivering (involuntary muscle contractions).

Human Respiratory System

Significance of Breathing

Breathing supplies oxygen for cellular respiration and removes carbon dioxide, a metabolic waste product.

Oxygen: Essential for ATP production in mitochondria.
CO2 Removal: Prevents acidification of body fluids.

Respiratory System Structures and Functions

Upper Respiratory Tract: Includes the nose, nasal cavity, pharynx, and larynx. Functions: filters, warms, and humidifies air; vocalization.
Lower Respiratory Tract: Includes the trachea, bronchi, bronchioles, and lungs. Functions: conducts air to alveoli, site of gas exchange.

Mechanics of Breathing

Inhalation (Inspiration): Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, drawing air in.
Exhalation (Expiration): Muscles relax, thoracic volume decreases, lung pressure increases, pushing air out.
Pressure Changes: (Boyle's Law: pressure and volume are inversely related in a closed system).
Intercostal Muscles: Assist in expanding and contracting the rib cage during breathing.

Blood Flow and Gas Exchange

Oxygen-rich blood returns from the lungs to the left atrium, then left ventricle, and is pumped to the body.
Gas exchange occurs in alveoli by diffusion.

Respiratory Diseases and Disorders

Examples: Asthma, emphysema, pneumonia, bronchitis, lung cancer.
Disorders can affect airflow, gas exchange, or lung tissue.

Human Digestive System

Major Structures and Functions

Mouth: Mechanical and chemical digestion begins.
Esophagus: Transports food to stomach via peristalsis.
Stomach: Mixes food, secretes acid and enzymes.
Small Intestine: Main site of digestion and absorption; large surface area due to villi and microvilli.
Large Intestine: Absorbs water, forms feces.

Accessory Organs

Liver: Produces bile for fat digestion.
Gallbladder: Stores and releases bile.
Pancreas: Produces digestive enzymes and bicarbonate.

Enzymes and Digestion

Enzymes: Biological catalysts that speed up digestion (e.g., amylase, lipase, protease).
Produced in salivary glands, stomach, pancreas, and small intestine.

Surface Area and Digestion

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

Metabolic Rates

Basal Metabolic Rate (BMR): Energy expended at rest to maintain vital functions.
Standard Metabolic Rate (SMR): Energy expenditure under standardized conditions (often used in animal studies).

Nutrition Guidelines

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

Digestion Process and Peristalsis

Food is mechanically and chemically broken down, then moved through the digestive tract by peristalsis (wave-like muscle contractions).

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Gene: A segment of DNA that codes for a protein or functional RNA.
Chromosome: A DNA molecule with associated proteins; humans have 23 pairs.
Genome: The complete set of genetic material in an organism.

Genetics Terminology

Genotype: The genetic makeup of an individual (e.g., AA, Aa, aa).
Phenotype: The observable traits resulting from the genotype and environment.
Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.
Karyotype: A visual display of all chromosomes in a cell, used to detect chromosomal abnormalities.

Inheritance Patterns

Dominant Allele: Expressed if present (e.g., AA or Aa).
Recessive Allele: Expressed only if both alleles are recessive (e.g., aa).
Homozygous: Two identical alleles (AA or aa).
Heterozygous: Two different alleles (Aa).

Punnett Squares

Used to predict the probability of offspring genotypes and phenotypes from parental crosses.

Mendelian Laws

Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.
Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

Non-Mendelian Inheritance

Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., red x white flowers = pink).
Codominance: Both alleles are fully expressed in heterozygotes (e.g., AB blood type).
Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color, height).
Environmental Influence: Phenotype can be affected by environmental factors (e.g., nutrition, sunlight).

Linked Genes and Genetic Variation

Linked Genes: Genes located close together on the same chromosome tend to be inherited together.
New Allele Combinations: Crossing over during meiosis creates new combinations of alleles.

Sex-Linked Genes and Nondisjunction

Sex-Linked Genes: Genes located on sex chromosomes (X or Y); often show different inheritance patterns in males and females.
Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers (e.g., Down syndrome).

Term	Definition	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, aa
Phenotype	Observable trait	Tall, short, blood type
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed if present	A in Aa
Recessive	Expressed only if homozygous	a in aa

Additional info: Some dominant allele disorders (e.g., Huntington's disease) are lethal because a single copy of the mutant allele causes disease. Recessive disorders (e.g., cystic fibrosis) persist because carriers (heterozygotes) are unaffected and can pass the allele to offspring.