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 Filament Theory: Myosin heads attach to actin, forming cross-bridges, and pull actin filaments inward, shortening the sarcomere.

Function of the Sarcomere: To facilitate contraction by allowing actin and myosin to slide past each other.

Example: During biceps contraction, sarcomeres shorten, causing the muscle to pull on the forearm.

Muscle Contraction Mechanism

• Action Potential: An electrical signal generated in the motor neuron, triggering muscle contraction.

• Order of Events:

  1. Motor neuron releases acetylcholine at the neuromuscular junction.

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

  3. Action potential travels along the sarcolemma and into T-tubules.

  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.

• Electrical Impulses: Cause release of calcium ions, which are essential for contraction.

Isotonic vs. Isometric Contractions:

• Isotonic: Muscle changes length (e.g., lifting a weight).

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

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

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

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, and larynx. Functions: filter, warm, and humidify air.

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

Example: The alveoli are the site of oxygen and carbon dioxide exchange.

Mechanics of Breathing

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

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.

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

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

Blood Flow and Oxygen Transport

• Oxygen-rich blood: Flows from lungs to left atrium, then left ventricle, then systemic circulation.

• Order of Flow: Pulmonary veins → left atrium → left ventricle → aorta → body.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.

• Significance: Affect gas exchange and overall health.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for digestion and absorption.

• Large Intestine: Absorbs water and forms feces.

Accessory Organs: Liver, pancreas, gallbladder. Functions: produce bile, enzymes, and regulate digestion.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion. Produced in salivary glands, stomach, pancreas, and small intestine.

• Function: Break down carbohydrates, proteins, and fats.

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

Metabolic Rates

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

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

"My Plate": A 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 different regions by specific enzymes.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

• Gene: Segment of DNA coding for a trait.

• Chromosome: Structure containing DNA; humans have 23 pairs.

• Genome: Complete set of genetic material in an organism.

• Genetics: Scientific study of heredity and variation.

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pairs with same genes but possibly different alleles.

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

Genotype and Phenotype

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

• Phenotype: Observable traits (e.g., eye color).

Punnett Square and Alleles

• Punnett Square: Diagram to predict genetic crosses.

• 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).

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• 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.

Linked Genes and Meiosis

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

• New Allele Combinations: Crossing over during meiosis creates genetic diversity.

Sex-linked Genes and Nondisjunction

• Sex-linked Genes: Located on sex chromosomes, often X-linked.

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers in gametes.

Table: Comparison of Inheritance Patterns

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

Example: Nondisjunction can result in Down syndrome (trisomy 21).

Additional info: Table entries and some explanations expanded for academic completeness.