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

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Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system enables movement, posture, and heat production. Muscle contraction is based on the sliding filament mechanism within muscle cells (fibers).

Muscle Fiber Structure: Each muscle fiber contains myofibrils, which are composed of repeating units called sarcomeres.
Sarcomere: The functional unit of muscle contraction, bordered by Z-lines. Contains 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 forms the thin filaments; myosin forms the thick filaments with protruding heads that attach to actin during contraction.

Example: During a biceps curl, the sarcomeres in the biceps muscle shorten, pulling the forearm upward.

Action Potentials and Muscle Contraction

Action Potential: An electrical signal generated in a motor neuron that triggers muscle contraction.
Neuromuscular Junction: The synapse where a motor neuron communicates with a muscle fiber, releasing neurotransmitters (e.g., acetylcholine).
Sequence of Events:
1. Action potential travels down the motor neuron.
2. Neurotransmitter is released into the synaptic cleft.
3. Muscle fiber membrane depolarizes, generating its own action potential.
4. Calcium ions are released from the sarcoplasmic reticulum.
5. Calcium binds to troponin, exposing binding sites on actin.
6. Myosin heads bind to actin, initiating contraction.

Isotonic vs. Isometric Contractions:

Isotonic: Muscle changes length (movement occurs).
Isometric: Muscle length remains the same (no movement, but tension increases).

Heat Production: Most body heat is generated by muscle activity due to energy loss as heat during ATP hydrolysis.

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

Muscles and Body Cavities: The diaphragm separates the thoracic and abdominal cavities and is essential for breathing.

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.
Carbon Dioxide: Must be expelled to maintain blood pH and prevent toxicity.

Respiratory System Structure and Function

Upper Respiratory Tract: Includes the nose, nasal cavity, pharynx, and larynx. Functions in filtering, warming, and humidifying air.
Lower Respiratory Tract: Includes the trachea, bronchi, bronchioles, and lungs. Responsible for gas exchange.

Significance: Each structure ensures efficient delivery of oxygen and removal of carbon dioxide.

Mechanics of Breathing

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

Blood Flow and Gas Exchange

Oxygen-rich Blood Flow: Oxygenated blood returns from the lungs to the left atrium, passes to the left ventricle, and is pumped to the body.
Gas Exchange: Occurs in alveoli where oxygen diffuses into blood and carbon dioxide diffuses out.

Respiratory Diseases and Disorders

Common Disorders: Asthma, bronchitis, emphysema, pneumonia.
Impact: These conditions impair gas exchange and oxygen delivery.

Human Digestive System

Major Structures and Functions

Mouth: Mechanical and chemical digestion begins here.
Esophagus: Transports food to the stomach via peristalsis.
Stomach: Secretes acid and enzymes for protein digestion.
Small Intestine: Main site for digestion and nutrient absorption; large surface area due to villi and microvilli.
Large Intestine: Absorbs water and forms feces.

Accessory Organs

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

Enzymes and Digestion

Function: Enzymes catalyze the breakdown of macromolecules (carbohydrates, proteins, fats).
Production Sites: Salivary glands, stomach, pancreas, small intestine.

Surface Area and Digestion

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

Metabolic Rates

Basal Metabolic Rate (BMR): Energy expended at rest.
Standard Metabolic Rate (SMR): Energy expenditure under standardized conditions.

Nutrition Guidelines

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

Digestion Process and Peristalsis

Peristalsis: Wave-like muscle contractions that move food through the digestive tract.
Molecule Digestion: Carbohydrates, proteins, and fats are digested in specific regions by specialized enzymes.

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: The scientific study of heredity and variation.

Homologous Chromosomes and Karyotypes

Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.
Karyotype: An organized profile of an individual's chromosomes, used to detect chromosomal abnormalities.

Genotype and Phenotype

Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).
Phenotype: The observable traits resulting from the genotype.

Punnett Squares and Mendelian Laws

Punnett Square: A diagram used to predict the outcome of genetic crosses.
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.

Alleles and Inheritance Patterns

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

Non-Mendelian Inheritance

Incomplete Dominance: Heterozygote shows an intermediate phenotype (e.g., red x white = pink).
Codominance: Both alleles are fully expressed (e.g., AB blood type).
Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).
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).

Genetic Disorders

Dominant Disorders: Can be lethal if one copy is enough to cause disease (e.g., Huntington's disease).
Recessive Disorders: Can persist in populations because carriers (heterozygotes) do not show symptoms (e.g., cystic fibrosis).

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: This guide expands on the review points by providing definitions, mechanisms, and examples for each system and concept, ensuring a comprehensive overview suitable for exam preparation.