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 fibers, 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, forming cross-bridges, and pull the actin filaments inward, 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.

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

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

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

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

• Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities; intercostal muscles are between ribs.

Example: During running, isotonic contractions of leg muscles propel the body forward, while isometric contractions stabilize joints.

Electrical Impulses and Action Potentials

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

• Motor Neuron: Initiates action potential by releasing acetylcholine.

• Electrical Impulse Mechanism: Depolarization leads to calcium release, which is essential for contraction.

Example: The action potential in a motor neuron causes the release of acetylcholine, which depolarizes the muscle cell membrane.

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen to tissues and removing carbon dioxide.

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

• Respiratory Structures:

  • Upper Respiratory System: Includes nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.

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

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

• Pressure Changes: Inhalation decreases lung pressure, drawing air in; exhalation increases pressure, expelling air.

• Mechanics of Inspiration: Diaphragm contracts, chest expands, air enters lungs.

• Mechanics of Expiration: Diaphragm relaxes, chest contracts, air leaves lungs.

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

Example: During exercise, breathing rate increases to supply more oxygen and remove excess carbon dioxide.

Blood Flow Through the Heart

• Order of Oxygen-Rich Blood Flow:

  1. Oxygenated blood from lungs enters left atrium.

  2. Flows into left ventricle.

  3. Pumped out through aorta to body tissues.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It consists of the alimentary canal and accessory organs.

• Alimentary Canal: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

• Enzymes: Proteins that catalyze digestion; produced in salivary glands, stomach, pancreas, small intestine.

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

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

• 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.

Example: The pancreas produces digestive enzymes that break down carbohydrates, proteins, and fats in the small intestine.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Genetics is the scientific study of heredity and variation. Genes are segments of DNA that code for traits, located on chromosomes.

• Gene: A DNA sequence coding for a protein or trait.

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

Example: Down syndrome is detected by karyotyping, showing an extra chromosome 21.

Genotype, Phenotype, and Punnett Squares

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

• Phenotype: Observable traits (e.g., brown eyes).

• Punnett Square: Diagram used to predict genetic crosses.

Example: A cross between Aa and aa parents yields 50% Aa and 50% aa offspring.

Alleles and Laws of Inheritance

• Dominant Allele: Expressed when present (e.g., A).

• Recessive Allele: Expressed only when homozygous (e.g., aa).

• Homozygous: Two identical alleles (AA or aa).

• Heterozygous: Two different alleles (Aa).

• Law of Segregation: Alleles separate during gamete formation.

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

Patterns of Inheritance

• 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: Genes located close together on a chromosome; inherited together.

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

• Nondisjunction: Failure of chromosomes to separate during meiosis; leads to abnormal chromosome numbers.

Example: Color blindness is a sex-linked trait, more common in males due to X-linked inheritance.

Sample Punnett Square Table

The Punnett Square is used to predict the probability of offspring genotypes from parental crosses.

Parent 1	Parent 2	Offspring Genotype	Offspring Phenotype
Aa	aa	50% Aa, 50% aa	50% dominant trait, 50% recessive trait
AA	aa	100% Aa	100% dominant trait

Additional info: In polygenic inheritance, traits like height are influenced by multiple genes and environmental factors.

Key Equations

• Muscle Contraction (ATP Hydrolysis): $\mathrm{ATP} \rightarrow \mathrm{ADP} + \mathrm{P_i} + \text{energy}$

• Gas Exchange (Partial Pressure): $\mathrm{P_{O_2}}$ and $\mathrm{P_{CO_2}}$ represent partial pressures of oxygen and carbon dioxide in blood.

• Genetic Probability: $\text{Probability} = \frac{\text{Number of desired outcomes}}{\text{Total number of outcomes}}$