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, posture, and heat production. Muscle contraction is based on the sliding filament mechanism within muscle cells.

• Sarcomere: The basic contractile unit of muscle fiber, 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, shortening the sarcomere.

• Actin and Myosin: Actin forms the thin filaments, while myosin forms the thick filaments with protruding heads that interact with actin.

• Substructures of Sarcomere: Includes Z-line (boundary), M-line (center), A-band (length of myosin), I-band (actin only), and H-zone (myosin only).

• Function of Sarcomere: Generates force for muscle contraction by shortening during contraction.

Example: During biceps contraction, sarcomeres in muscle fibers shorten, pulling the forearm upward.

Muscle Contraction and Electrical Impulses

• Action Potential: An electrical signal generated in a motor neuron, leading to muscle contraction.

• Neuromuscular Junction: The synapse where a motor neuron communicates with a muscle fiber, releasing neurotransmitters (e.g., acetylcholine).

• Order of Events:

  1. Action potential arrives at the neuromuscular junction.

  2. Acetylcholine is released, binding to receptors on the muscle cell membrane.

  3. Muscle cell membrane depolarizes, generating an 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 (shortens or lengthens) while tension remains constant (e.g., lifting a weight).

  • Isometric: Muscle length remains the same while tension increases (e.g., holding a weight steady).

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

Example: Shivering is an involuntary isometric contraction that generates heat.

Major Muscle Groups and Functions

• Major Muscle Groups: Deltoids (shoulder), pectorals (chest), biceps/triceps (arms), abdominals, quadriceps/hamstrings (legs), gluteals (buttocks).

• Muscles Sectioning Body Cavities: The diaphragm separates the thoracic and abdominal cavities.

Human Respiratory System

Significance and Function of Breathing

The respiratory system enables gas exchange, supplying oxygen to the body and removing carbon dioxide.

• Breathing: Essential for cellular respiration, which produces ATP for energy.

• Respiratory Diseases: Include asthma, bronchitis, emphysema, and pneumonia, which impair gas exchange.

Structures of the Respiratory System

• Upper Respiratory Tract: Includes the nose, nasal cavity, pharynx, and larynx. Functions: filtering, warming, and humidifying air.

• Lower Respiratory Tract: Includes the trachea, bronchi, bronchioles, and lungs. Functions: conducting air to alveoli for gas exchange.

• Intercostal Muscles: Located between ribs; contract during inhalation to expand the chest cavity, relax during exhalation.

• Diaphragm: Main muscle of respiration; contracts to increase thoracic volume during inhalation.

Mechanics of Breathing

• Inhalation (Inspiration): Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing pressure, drawing air in.

• Exhalation (Expiration): Muscles relax, thoracic volume decreases, pressure increases, pushing air out.

• Pressure Changes: Air flows from high to low pressure; described by Boyle's Law: $P_1V_1 = P_2V_2$

Example: During exercise, breathing rate increases to meet oxygen demand.

Blood Flow and Gas Exchange

• Oxygen-Rich Blood Flow: Oxygenated blood returns from the lungs to the left atrium, then to the left ventricle, and is pumped to the body.

• Order of Blood Flow Through Heart: Right atrium → right ventricle → lungs (via pulmonary artery) → left atrium → left ventricle → body (via aorta).

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: Salivary glands, liver, gallbladder, pancreas. Functions: produce enzymes and bile to aid digestion.

• Enzymes: Biological catalysts that speed up digestion; produced in the mouth (amylase), stomach (pepsin), pancreas (lipase, proteases), and small intestine.

• Large Surface Area: Villi and microvilli in the small intestine increase surface area for nutrient absorption.

Digestive Processes

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

• Digestion of Molecules: Carbohydrates, proteins, and fats are broken down by specific enzymes in different parts of the digestive system.

Metabolic Rates and Nutrition

• Basal Metabolic Rate (BMR): The energy expended at rest to maintain vital body functions.

• Standard Metabolic Rate (SMR): The metabolic rate under specific conditions (e.g., at a certain temperature).

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

Example: The pancreas releases insulin to help regulate blood glucose after a meal.

Human Genetics and Inheritance

Basic Genetic Concepts

• Gene: A segment of DNA that codes for a specific protein or trait.

• Chromosome: A structure composed of DNA and proteins; humans have 23 pairs.

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

• Genotype: The genetic makeup of an individual (e.g., AA, Aa, aa).

• Phenotype: The observable traits or characteristics (e.g., blue eyes).

• Karyotype: A visual representation of all chromosomes in a cell, used to detect chromosomal abnormalities.

Inheritance Patterns

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

• Punnett Square: A tool to predict the probability of offspring genotypes and phenotypes.

• Dominant vs. Recessive Alleles: Dominant alleles mask the effect of recessive alleles in heterozygotes.

• Homozygous: Two identical alleles (AA or aa); Heterozygous: Two different alleles (Aa).

• 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.

Complex Inheritance and Genetic Disorders

• Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., pink flowers from red and white parents).

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

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

• Environmental Influence: Phenotype can be affected by environmental factors (e.g., nutrition, temperature).

• Linked Genes: Genes located close together on the same chromosome tend to be inherited together.

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y), often affecting males more (e.g., hemophilia).

• Nondisjunction: Failure of chromosomes to separate during meiosis, leading to abnormal chromosome numbers (e.g., Down syndrome).

• Lethal Dominant Disorders: Often result in early death, so are rare; Recessive Disorders: Can persist if carriers are unaffected.

Sample HTML Table: Dominant vs. Recessive Alleles

Term	Description	Example
Dominant Allele	Expressed in heterozygous or homozygous state	Widow's peak (W)
Recessive Allele	Expressed only in homozygous state	Attached earlobes (e)

Example: A Punnett square can predict the probability of a child inheriting cystic fibrosis if both parents are carriers.

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard human biology curricula.