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.

• 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, pulling the filaments past each other.

• Actin and Myosin: Actin provides the track; myosin uses ATP to "walk" along actin, causing contraction.

• Substructures: Z-line, M-line, A-band, I-band, H-zone; each plays a role in sarcomere function.

• 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.

Muscle Contraction Mechanism

Muscle contraction is initiated by electrical impulses from motor neurons.

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

• Order of Events:

  1. Motor neuron releases acetylcholine at neuromuscular junction.

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

  3. Calcium ions released from sarcoplasmic reticulum.

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

  5. Myosin binds to actin, ATP is hydrolyzed, filaments slide.

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle tension increases, but length does not change (no movement).

Example: Lifting a weight is isotonic; holding a weight steady is isometric.

Major Muscle Groups and Functions

• Muscle Groups: Biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, gluteals, etc.

• Body Cavities: Diaphragm separates thoracic and abdominal cavities.

Human Respiratory System

Significance of Breathing

Breathing supplies oxygen for cellular respiration and removes carbon dioxide, essential for life.

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

• Respiratory Diseases: Asthma, bronchitis, pneumonia, emphysema, etc.

Structure and Function of Respiratory System

• Upper Respiratory Tract: Nose, nasal cavity, pharynx, larynx; filters, warms, and moistens air.

• Lower Respiratory Tract: Trachea, bronchi, bronchioles, lungs; conducts air and facilitates gas exchange.

• Intercostal Muscles: Located between ribs; contract during inhalation to expand chest cavity.

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.

• Deoxygenated blood returns to right atrium, right ventricle, then to lungs for oxygenation.

Human Digestive System

Structure and Function

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 produced in salivary glands, stomach, pancreas, small intestine.

• Function: Speed up breakdown of carbohydrates, proteins, fats.

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

Surface Area and Digestion

• Large Surface Area: Villi and microvilli in small intestine increase absorption efficiency.

Metabolic Rates

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

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

Equation: $\text{BMR} = \text{Energy expenditure at rest}$

Nutrition and "My Plate"

• "My Plate": USDA guideline for balanced nutrition: fruits, vegetables, grains, protein, dairy.

Digestion Process and Peristalsis

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

• Molecule Digestion: Carbohydrates, proteins, fats digested in mouth, stomach, small intestine.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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

• Gene: Segment of DNA coding for a trait.

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

• Genome: Complete set of genes in an organism.

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

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (alleles).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram to predict genetic crosses.

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

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• Dominant Disorders: Often lethal if homozygous.

• Recessive Disorders: Can persist in population.

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles expressed equally.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can affect phenotypic expression.

Linked Genes and Meiosis

• Linked Genes: Genes located close together on same 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 affect males more.

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

Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Dominant	AA, Aa	Trait expressed	Huntington's disease
Recessive	aa	Trait expressed	Cystic fibrosis
Incomplete Dominance	Aa	Intermediate	Red + white = pink flowers
Codominance	AB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color

Additional info: Table entries inferred for clarity and completeness.