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. 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: Actin filaments provide sites for myosin heads to attach and pull, causing contraction. Myosin filaments have heads that bind to actin and use ATP to generate force.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

• Order of Events in Muscle Contraction:

  1. Action potential travels down motor neuron.

  2. Release of neurotransmitter (acetylcholine) at neuromuscular junction.

  3. Depolarization of muscle cell membrane.

  4. Release of calcium ions from sarcoplasmic reticulum.

  5. Calcium binds to troponin, exposing binding sites on actin.

  6. Myosin binds to actin, ATP is hydrolyzed, and contraction occurs.

• Electrical Impulses: Action potentials in motor neurons trigger muscle contraction by causing release of calcium ions.

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

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

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

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

Example: During exercise, muscles contract repeatedly, generating heat and causing movement.

Human Respiratory System

Structure and Function

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide. It consists of upper and lower structures, each with specific functions.

• Upper Respiratory Structures: Nose, nasal cavity, pharynx, larynx. Functions include filtering, warming, and humidifying air.

• Lower Respiratory Structures: Trachea, bronchi, lungs, alveoli. Functions include conducting air and facilitating gas exchange.

• Significance of Breathing: Provides oxygen for cellular respiration and removes carbon dioxide, a metabolic waste.

• Blood Flow Through Heart: Oxygen-rich blood enters left atrium, passes to left ventricle, and is pumped to the body. Oxygen-poor blood returns to right atrium, moves to right ventricle, and is sent to lungs for oxygenation.

• Pressure Changes in Lungs: Inhalation decreases pressure inside lungs, drawing air in; exhalation increases pressure, pushing air out.

• Intercostal Muscles: Located between ribs, contract during inhalation to expand chest cavity, relax during exhalation.

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

• Mechanics of Expiration: Diaphragm relaxes, intercostal muscles relax, thoracic cavity decreases, air exits lungs.

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

Example: During vigorous activity, breathing rate increases to meet oxygen demands.

Human Digestive System

Structure and Function

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It includes primary and accessory organs.

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

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas. These produce enzymes and other substances aiding digestion.

• Enzymes: Biological catalysts produced in salivary glands, stomach, pancreas, and small intestine. They speed up breakdown of carbohydrates, proteins, and fats.

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

• Metabolic Rates:

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

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

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

• Digestion of Molecules: Carbohydrates, proteins, and fats are digested in different parts of the digestive tract by specific enzymes.

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

Example: After eating, peristalsis moves food from the esophagus to the stomach for further digestion.

Human Genetics and Inheritance

Genetic Concepts and Mechanisms

Genetics is the scientific study of heredity and variation in organisms. Human inheritance is governed by genes, chromosomes, and various genetic laws.

• Genes: Segments of DNA that code for proteins; basic units of heredity.

• Chromosomes: Structures in cells that contain genes; humans have 23 pairs.

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

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

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

• Genotype: Genetic makeup of an individual.

• Phenotype: Observable traits resulting from genotype and environment.

• Punnett Square: Diagram used to predict genetic crosses and inheritance patterns.

• Dominant vs. Recessive Alleles: Dominant alleles mask recessive alleles in heterozygotes. Homozygous: two identical alleles; heterozygous: two different alleles.

• Law of Segregation: Alleles separate during gamete formation.

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

• Incomplete Dominance: Heterozygotes show intermediate phenotype.

• Codominance: Both alleles are fully expressed in heterozygotes.

• Polygenic Inheritance: Traits controlled by multiple genes.

• Environmental Impact: Environment can influence phenotypic expression.

• Linked Genes: Genes located close together on the same chromosome; inherited together.

• New Allele Combinations: Crossing over during meiosis creates new allele combinations.

• Sex-linked Genes: Genes located on sex chromosomes; often show unique inheritance patterns.

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

Example: A Punnett Square can predict the probability of a child inheriting a genetic disorder.

Sample Table: Dominant vs. Recessive Alleles

Allele Type	Expression in Heterozygote	Example Trait
Dominant	Trait expressed	Widow's peak
Recessive	Trait masked	Attached earlobes

Sample Punnett Square Equation

For a monohybrid cross:

$\begin{array}{c|cc} & A & a \\ \hline A & AA & Aa \\ a & Aa & aa \end{array}$

Additional info: Academic context and explanations have been expanded for clarity and completeness.