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

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 involves the interaction of actin and myosin filaments within the sarcomere.

• Sarcomere: The basic contractile unit of muscle fiber, defined by the area between two Z-lines.

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

• Myosin Filaments: Thick filaments with heads that bind to actin, pulling them to shorten the sarcomere.

• Sliding Mechanism: Myosin heads attach to actin, forming cross-bridges and pulling actin filaments inward, causing contraction.

• Function of Sarcomere: Facilitates muscle contraction through the coordinated sliding of actin and myosin.

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

Muscle Contraction and Action Potentials

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

• Mechanism: The action potential travels down the neuron, causing the release of neurotransmitter (acetylcholine) at the neuromuscular junction, which initiates an electrical impulse in the muscle fiber.

• Order of Events:

  1. Action potential arrives at 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.

Example: Reflex actions, such as pulling your hand away from a hot object, involve rapid muscle contraction initiated by nerve impulses.

Muscle Types of Contractions

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while the tension remains constant. Produces movement.

• Isometric Contraction: Muscle length remains the same while tension increases. No movement occurs.

Example: Lifting a weight (isotonic) vs. holding a weight steady (isometric).

Muscle Groups and Body Cavities

• Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, etc.

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

Heat Generation

• Most body heat is generated by muscle activity, especially during shivering or exercise.

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen for cellular respiration and removing carbon dioxide, a metabolic waste product.

• Oxygen: Required for aerobic metabolism in cells.

• Carbon Dioxide: Must be expelled to maintain pH balance.

Respiratory System Structures and Functions

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

• Lower Respiratory System: Includes the trachea, bronchi, bronchioles, and lungs. Responsible for conducting air to the alveoli where gas exchange occurs.

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: Air moves from high to low pressure; during inhalation, lung pressure drops below atmospheric pressure, and vice versa for exhalation.

• 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 to the left ventricle, and is pumped throughout the body.

Respiratory Diseases and Disorders

• Common disorders include asthma, bronchitis, emphysema, and pneumonia.

Human Digestive System

Major Structures and Functions

• Mouth: Begins mechanical and chemical digestion.

• Esophagus: Transports food to the stomach via peristalsis.

• Stomach: Mixes food with gastric juices for protein digestion.

• Small Intestine: Main site for digestion and absorption; large surface area due to villi and microvilli.

• Large Intestine: Absorbs water and 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 such as amylase, protease, and lipase break down carbohydrates, proteins, and fats, respectively.

• Produced in the salivary glands, stomach, pancreas, and small intestine.

Surface Area and Digestion

• Large surface area in the small intestine (due to villi and microvilli) 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).

Dietary Guidelines

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

Peristalsis

• Involuntary, wave-like muscle contractions that move food through the digestive tract.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Chromosome: A structure composed of DNA and 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.

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

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

Inheritance Patterns

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

• Dominant Allele: Expressed when present (e.g., AA or Aa).

• Recessive Allele: Expressed only when homozygous (aa).

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

• Heterozygous: Two different alleles (Aa).

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 are inherited independently if on different chromosomes.

Non-Mendelian Inheritance

• Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., red x white = pink flowers).

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

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

• Environmental Impact: Phenotype can be influenced 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 Chromosomal Disorders

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y), often affecting traits like color blindness.

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

Genetic Disorders

• Dominant Allele Disorders: Can be lethal if one copy causes disease (e.g., Huntington's disease).

• Recessive Disorders: Remain prevalent due to carriers (heterozygotes) who do not express the disorder (e.g., cystic fibrosis).

Sample Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Mendelian (Dominant/Recessive)	AA, Aa, aa	Dominant or recessive trait	Widow's peak
Incomplete Dominance	RR, Rr, rr	Intermediate phenotype	Snapdragon flower color
Codominance	IAIB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color

Key Equations

• Hardy-Weinberg Equation:

$p^2 + 2pq + q^2 = 1$

Where p and q are the frequencies of two alleles in a population.

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard Human Biology curricula.