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 and structures to produce movement and generate heat. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic contractile unit of muscle, composed of actin (thin) and myosin (thick) filaments.

• Actin and Myosin: Proteins that interact to produce contraction. Myosin heads bind to actin, pulling the filaments past each other.

• Sliding Filament Theory: Muscle contraction occurs as myosin heads attach to actin and pull, shortening the sarcomere.

• Structure Identification: Key structures include the sarcolemma, sarcoplasmic reticulum, T-tubules, and mitochondria.

• Major Muscle Groups: Examples include biceps, triceps, quadriceps, hamstrings, pectorals, and abdominals.

Example: During bicep contraction, the sarcomeres shorten as actin and myosin filaments slide past each other.

Electrical Impulses 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 acetylcholine → depolarization of sarcolemma → calcium release → actin-myosin interaction → contraction.

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

• Isotonic vs. Isometric Contractions: Isotonic contractions produce movement; isometric contractions generate tension without movement.

Example: Shivering is an isometric contraction that generates heat.

Muscle Cavities and Contraction Types

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

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

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

Human Respiratory System

Significance and Structure of Breathing

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide.

• Upper Respiratory Structures: Nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.

• Lower Respiratory Structures: Trachea, bronchi, lungs, alveoli. Functions: conduct air, gas exchange.

• Breathing Mechanics: Inhalation increases lung volume, decreases pressure; exhalation decreases volume, increases pressure.

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

Example: During inspiration, the diaphragm contracts and moves downward, increasing thoracic volume.

Blood Flow and Gas Exchange

• Oxygen-rich Blood Flow: Oxygenated blood returns from lungs to left atrium → left ventricle → systemic circulation.

• Respiratory Diseases: Examples include asthma, bronchitis, pneumonia, and emphysema.

Mechanics of Breathing

• Inspiration: Diaphragm and intercostal muscles contract, thoracic cavity expands, air enters lungs.

• Expiration: Muscles relax, thoracic cavity decreases, air is expelled.

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.

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

• Enzymes: Catalyze breakdown of macromolecules; produced in salivary glands, stomach, pancreas, small intestine.

• Surface Area: Increased by villi and microvilli in small intestine, enhancing absorption.

Example: Amylase in saliva begins starch digestion in the mouth.

Metabolic Rates and Digestion

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

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

• "My Plate": Dietary guideline for balanced nutrition.

• Peristalsis: Wave-like muscle contractions moving 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: Segment of DNA coding for a protein or trait.

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

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

• Homologous Chromosomes: Chromosome pairs with similar genes, one from each parent.

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

Genotype, Phenotype, and Inheritance Patterns

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable traits resulting from genotype and environment.

• Punnett Square: Diagram predicting genetic crosses.

• Dominant Allele: Expressed trait when present.

• Recessive Allele: Expressed only when two copies are present.

• Homozygous: Two identical alleles for a trait.

• Heterozygous: Two different alleles for a trait.

Mendelian Laws and Allele Expression

• Law of Segregation: Alleles separate during gamete formation.

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

• Dominant Disorders: Often lethal if homozygous; recessive disorders can persist in populations.

Complex Inheritance Patterns

• Incomplete Dominance: Heterozygote shows 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: Phenotype can be influenced by environment (e.g., nutrition, temperature).

• Linked Genes: Genes located close together on a chromosome tend to be inherited together.

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

• Sex-linked Genes: Genes located on sex chromosomes; often affect males more (e.g., hemophilia).

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

Sample Table: Dominant vs. Recessive Alleles

Allele Type	Expression	Example
Dominant	Expressed if at least one allele is present	Huntington's disease
Recessive	Expressed only if both alleles are present	Cystic fibrosis

Sample Equation: Probability of Inheritance

Probability of offspring inheriting a trait (using Punnett Square):

$ P = \frac{\text{Number of desired genotype}}{\text{Total number of possible genotypes}} $

Additional info: Academic context and examples were added to clarify and expand upon brief review points.