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 (fibers).

• 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 filaments and pull them inward, shortening the sarcomere.

• Actin and Myosin: Actin forms thin filaments; myosin forms thick filaments with heads that attach to actin during contraction.

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

Example: During a biceps curl, sarcomeres in the biceps muscle shorten, causing the arm to flex.

Muscle Contraction Mechanism

• Action Potential: An electrical signal generated in a motor neuron triggers muscle contraction.

• Neuromuscular Junction: The site where a motor neuron communicates with a muscle fiber, releasing neurotransmitter (acetylcholine) to initiate contraction.

• Order of Events:

  1. Action potential travels down motor neuron.

  2. Acetylcholine is released into synaptic cleft.

  3. Muscle fiber 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, performing a power stroke.

  7. ATP is required for myosin head detachment and re-cocking.

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle length remains the same (no movement, tension increases).

• Heat Generation: Most body heat is generated by muscle activity (shivering thermogenesis).

Example: Holding a plank is an isometric contraction; lifting a weight is isotonic.

Major Muscle Groups and Functions

• Major Groups: Deltoids, pectorals, biceps, triceps, quadriceps, hamstrings, gluteals, abdominals, etc.

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

Human Respiratory System

Significance and Structure

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide. It is divided into upper and lower respiratory tracts.

• Upper Respiratory Structures: Nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air; voice production.

• Lower Respiratory Structures: Trachea, bronchi, bronchioles, lungs, alveoli. Functions: conduct air to lungs, gas exchange.

Example: The nasal cavity filters dust and pathogens from inhaled air.

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, air is expelled.

• Pressure Changes: Air flows from high to low pressure; during inhalation, lung pressure drops below atmospheric pressure.

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

Example: Forced exhalation (blowing out candles) uses abdominal and intercostal muscles.

Blood Flow and Gas Exchange

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

• Gas Exchange: Occurs in alveoli; oxygen diffuses into blood, carbon dioxide diffuses out.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, emphysema, pneumonia, lung cancer.

• Significance: Impair gas exchange, reduce oxygen delivery, and may be life-threatening.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It includes the alimentary canal and accessory organs.

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

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

• Functions: Ingestion, digestion, absorption, elimination.

Example: The pancreas secretes digestive enzymes into the small intestine.

Enzymes and Digestion

• Digestive Enzymes: Proteins that catalyze breakdown of macromolecules (e.g., amylase, lipase, protease).

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

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

Metabolic Rates and Nutrition

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

• Standard Metabolic Rate (SMR): Similar to BMR but measured under specific conditions (e.g., fasting, resting, non-stressed).

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

Digestive Processes

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

• Molecule Digestion: Carbohydrates, proteins, and fats are digested in specific regions by specific enzymes.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Genetics is the scientific study of heredity and variation. Genes are DNA segments that code for traits; chromosomes are DNA-protein structures carrying genes.

• Gene: A sequence of DNA that codes for a protein or functional RNA.

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

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

• 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.

Genotype, Phenotype, and Inheritance Patterns

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

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

• Punnett Square: A tool to predict genetic crosses and offspring ratios.

• Dominant vs. Recessive Alleles: Dominant alleles mask recessive ones in heterozygotes.

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

Mendelian Laws and Exceptions

• 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.

• Incomplete Dominance: Heterozygotes show 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 trait (e.g., skin color).

• Environmental Impact: Environment can affect phenotypic expression (e.g., nutrition, temperature).

Chromosomal and Genetic Variations

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

• New Allele Combinations: Crossing over during meiosis creates new allele combinations.

• 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	Allele expressed in heterozygote	A in Aa
Recessive	Allele masked in heterozygote	a in Aa

Example: A Punnett square can predict the probability of offspring inheriting a genetic disorder.

Additional info: For equations related to genetics, the probability of a genotype can be calculated using the binomial expansion: $P = n! \div [k!(n-k)!] \cdot p^k \cdot q^{n-k}$, where n is the number of trials, k is the number of successes, p is the probability of success, and q is the probability of failure.