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 and generates heat through the contraction of muscle fibers. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic functional unit of muscle fibers, 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 provides the track for myosin to pull, while myosin uses ATP to generate force.

• Substructures: Includes Z-lines, M-line, A-band, I-band, and H-zone, each with specific roles in contraction.

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

Example: During exercise, muscle contractions increase heat production, helping maintain body temperature.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential that triggers muscle contraction.

• Order of Events: Nerve impulse → release of neurotransmitter (acetylcholine) → depolarization of muscle cell → calcium release → contraction.

• Electrical Impulses: Cause release of calcium ions from the sarcoplasmic reticulum, enabling actin-myosin interaction.

Example: The neuromuscular junction is where the motor neuron communicates with the muscle fiber.

Types of Muscle Contractions

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

• Isometric Contraction: Muscle length remains the same (no movement), e.g., holding a weight steady.

Example: Isotonic contractions are used in walking; isometric contractions occur when holding a plank position.

Major Muscle Groups and Functions

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

• Body Cavities: Muscles such as the diaphragm section the thoracic and abdominal cavities.

Human Respiratory System

Significance of Breathing

Breathing is essential for oxygen intake and carbon dioxide removal, supporting cellular respiration and energy production.

• Oxygen Transport: Oxygen-rich blood is pumped from the lungs to the heart and then to the body.

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

Structures of the Respiratory System

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

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

Example: The cilia in the trachea help remove particles from inhaled air.

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 Through the Heart

• Order: Pulmonary veins → left atrium → left ventricle → aorta → body tissues → vena cava → right atrium → right ventricle → pulmonary artery → lungs.

Human Digestive System

Major Structures and Functions

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

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

• Accessory Organs: Liver, pancreas, gallbladder; produce enzymes and bile for 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 into absorbable molecules.

Example: Amylase breaks down starch in the mouth; pepsin digests proteins in the stomach.

Surface Area and Digestion

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

Metabolic Rates

• Basal Metabolic Rate (BMR): The energy expended at rest.

• Standard Metabolic Rate (SMR): The energy expended under standardized conditions.

Example: BMR is measured after fasting and rest; SMR may be measured under specific environmental conditions.

"My Plate" and Nutrition

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

Digestion Mechanics

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

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

• Chromosome: DNA molecule with associated proteins; humans have 23 pairs.

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

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

• Karyotype: The visual representation of chromosomes in a cell.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism.

• Phenotype: The observable traits of an organism.

Punnett Square and Alleles

• Punnett Square: A diagram used to predict genetic crosses.

• Alleles: Variants of a gene; can be dominant or recessive.

• Homozygous: Two identical alleles for a trait.

• Heterozygous: Two different alleles for a trait.

Mendelian Laws

• Law of Segregation: Each parent passes one allele for each gene to offspring.

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

Patterns of Inheritance

• Dominant Disorders: Often lethal if homozygous; e.g., Huntington's disease.

• Recessive Disorders: Can persist in populations; e.g., cystic fibrosis.

• Incomplete Dominance: Heterozygotes show intermediate phenotype.

• Codominance: Both alleles are 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 tend to be inherited together.

• Sex-linked Genes: Genes located on sex chromosomes; e.g., hemophilia.

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

Meiosis and Genetic Variation

• New Allele Combinations: Crossing over and independent assortment during meiosis create genetic diversity.

Sample Table: Types of Genetic Inheritance

Type	Description	Example
Dominant	One allele masks the other	Huntington's disease
Recessive	Both alleles must be present	Cystic fibrosis
Incomplete Dominance	Intermediate phenotype	Red and white flowers produce pink
Codominance	Both alleles expressed	AB blood type
Polygenic	Multiple genes affect trait	Skin color

Additional info: Academic context and examples were added to clarify brief review points and ensure completeness for exam preparation.