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

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system relies on specialized cells called muscle fibers that contract to produce movement. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic functional unit of muscle fibers, composed of actin and myosin filaments.

• Actin Filaments: Thin filaments that interact with myosin during contraction.

• Myosin Filaments: Thick filaments with heads that bind to actin, pulling them to cause contraction.

• Sliding Mechanism: Myosin heads attach to actin, forming cross-bridges, and pull actin filaments inward, shortening the sarcomere.

Function of the Sarcomere: To facilitate muscle contraction through the coordinated movement of actin and myosin.

Example: During biceps contraction, sarcomeres shorten, causing the muscle to contract and the arm to bend.

Action Potential and Muscle Contraction

Muscle contraction is initiated by an action potential in a motor neuron, which triggers electrical impulses in muscle fibers.

• Action Potential: A rapid change in membrane potential that travels along the neuron and muscle cell.

• Order of Events:

  1. Motor neuron releases acetylcholine at the neuromuscular junction.

  2. Muscle cell membrane depolarizes, generating an action potential.

  3. Electrical impulse triggers release of calcium ions from the sarcoplasmic reticulum.

  4. Calcium binds to troponin, exposing binding sites on actin.

  5. Myosin binds to actin, causing contraction.

Isotonic vs. Isometric Contractions:

• Isotonic: Muscle changes length (movement occurs).

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

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

Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and others.

Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities.

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen to tissues and removing carbon dioxide.

• Oxygen: Required for cellular respiration and energy production.

• Carbon Dioxide: Waste product that must be expelled.

Respiratory System Structures

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.

• Lower Respiratory System: Includes trachea, bronchi, lungs. Functions: conduct air, gas exchange.

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

Mechanics of Breathing:

• Inspiration: Diaphragm and intercostal muscles contract, increasing thoracic volume, decreasing lung pressure, air flows in.

• Expiration: Muscles relax, thoracic volume decreases, lung pressure increases, air flows out.

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

Blood Flow Through the Heart: Oxygen-rich blood enters left atrium, passes to left ventricle, then pumped to body.

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

Human Digestive System

Major Structures and Functions

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

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food via peristalsis.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for nutrient absorption.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs: Liver (produces bile), pancreas (produces digestive enzymes), gallbladder (stores bile).

Enzymes: Biological catalysts produced in salivary glands, stomach, pancreas, small intestine; speed up digestion.

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

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

Metabolic Rates:

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

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

"My Plate": Dietary guideline for balanced nutrition.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Gene: Segment of DNA coding for a trait.

• Chromosome: Structure carrying genes; humans have 23 pairs.

• Genome: Complete set of genetic material.

• Homologous Chromosomes: Pair of chromosomes with same genes, one from each parent.

• Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Genotype, Phenotype, and Punnett Squares

• Genotype: Genetic makeup (e.g., AA, Aa, aa).

• Phenotype: Observable traits.

• Punnett Square: Diagram predicting genetic crosses.

Alleles and Patterns of Inheritance

• Dominant Allele: Expressed trait (e.g., A).

• Recessive Allele: Masked unless homozygous (e.g., a).

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

• Heterozygous: Two different alleles (Aa).

Law of Segregation: Alleles separate during gamete formation.

Law of Independent Assortment: Genes for different traits assort independently.

Dominant/Recessive Disorders: Dominant disorders can be lethal; recessive disorders persist due to carriers.

Complex Patterns of Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

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

• Environmental Impact: Environment can affect phenotypic expression.

• Linked Genes: Genes located close together on a chromosome; inherited together.

• New Allele Combinations: Occur during meiosis via crossing over.

• Sex-linked Genes: Located on sex chromosomes; often affect males more.

• Nondisjunction: Failure of chromosomes to separate; leads to abnormal chromosome numbers (e.g., Down syndrome).

Sample Table: Patterns of Inheritance

Pattern	Genotype	Phenotype	Example
Dominant/Recessive	AA, Aa, aa	Dominant or recessive trait	Widow's peak
Incomplete Dominance	RR, RW, WW	Intermediate phenotype	Pink snapdragon flowers
Codominance	IAIB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color
Sex-linked	X-linked	Trait on X chromosome	Color blindness

Example: Using a Punnett Square to predict offspring genotypes for a trait with dominant and recessive alleles.

Formula for Probability:

$\text{Probability} = \frac{\text{Number of desired outcomes}}{\text{Total number of possible outcomes}}$

Additional info: Academic context and examples have been added to clarify and expand upon the review guide points.