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 (muscle fibers).

• 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, shortening the sarcomere.

• Actin and Myosin: Actin forms the thin filaments; myosin forms the thick filaments with protruding heads that attach to actin during contraction.

• Substructures of Sarcomere: Includes Z-lines (boundaries), M-line (center), A-band (length of myosin), I-band (actin only), and H-zone (myosin only).

• Function of Sarcomere: Generates force for muscle contraction by shortening during the sliding of filaments.

Example: During biceps contraction, sarcomeres in muscle fibers shorten, causing the muscle to contract and the arm to flex.

Action Potentials and Muscle Contraction

Muscle contraction is initiated by electrical signals called action potentials.

• Action Potential in Motor Neuron: A rapid change in membrane potential that travels along the neuron, triggering neurotransmitter release at the neuromuscular junction.

• Electrical Impulses in Muscle Unit: The action potential spreads along the muscle fiber membrane (sarcolemma), leading to calcium ion release from the sarcoplasmic reticulum.

• Order of Events in Muscle Contraction:

  1. Action potential arrives at neuromuscular junction.

  2. Acetylcholine is released, binding to receptors on the muscle cell membrane.

  3. Depolarization of sarcolemma triggers calcium release.

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

  5. Myosin heads bind to actin, initiating contraction.

• Heat Generation: Most body heat is generated by muscle contractions (thermogenesis).

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant; produces movement (e.g., lifting a weight).

• Isometric Contraction: Muscle tension increases but length does not change; no movement occurs (e.g., holding a weight steady).

Major Muscle Groups and Body Cavities

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

• Muscles Sectioning Body Cavities: The diaphragm separates the thoracic and abdominal cavities.

Human Respiratory System

Significance and Function of Breathing

Breathing supplies oxygen for cellular respiration and removes carbon dioxide, a waste product of metabolism.

• Importance: Oxygen is essential for ATP production; CO2 removal prevents acid-base imbalance.

Structures of the Respiratory System

• Upper Respiratory Tract: Includes nose, nasal cavity, pharynx, and larynx. Functions: filters, warms, and humidifies air.

• Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, and lungs. Functions: conducts air to alveoli for gas exchange.

Mechanics of Breathing

• Inhalation (Inspiration): Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, drawing air in.

• Exhalation (Expiration): Muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.

• Pressure Changes: Air flows from high to low pressure; during inhalation, lung pressure drops below atmospheric pressure.

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

Blood Flow and Gas Exchange

• Oxygen-Rich Blood Flow: Oxygenated blood returns from the lungs to the left atrium, then to the left ventricle, and is pumped to the body.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, emphysema, pneumonia, and lung cancer affect breathing efficiency.

Human Digestive System

Major Structures and Functions

• Main Organs: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

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

• Function of Enzymes: Biological catalysts that speed up the breakdown of food molecules; produced in salivary glands, stomach, pancreas, and small intestine.

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

Digestion and Absorption

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

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

Metabolic Rates and Nutrition

• Basal Metabolic Rate (BMR): The energy expended at rest to maintain vital body functions.

• Standard Metabolic Rate (SMR): The metabolic rate under specific conditions (e.g., at a certain temperature).

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

• Gene: A segment of DNA that codes for a specific protein or trait.

• Chromosome: A structure composed of DNA and proteins; humans have 23 pairs.

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

• Genetics: The scientific study of heredity and variation in organisms.

Inheritance and Chromosome Structure

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

• Karyotype: A visual display of all chromosomes in a cell, used to detect chromosomal abnormalities.

Genotype, Phenotype, and Punnett Squares

• Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: The observable traits or characteristics.

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

Alleles and Patterns of Inheritance

• Dominant Allele: Expressed trait when at least one copy is present (e.g., A).

• Recessive Allele: Expressed only when two copies are present (e.g., aa).

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

• Heterozygous: Two different alleles (Aa).

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

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

Complex Patterns of Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., red x white = pink flowers).

• Codominance: Both alleles are fully expressed (e.g., AB blood type).

• Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color, height).

• Environmental Impact: Environment can affect gene expression (e.g., nutrition influencing height).

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

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

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y), often show different inheritance patterns in males and females.

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

Table: Comparison of Inheritance Patterns

Pattern	Description	Example
Complete Dominance	Dominant allele masks recessive	Widow's peak hairline
Incomplete Dominance	Heterozygote is intermediate	Pink snapdragon flowers
Codominance	Both alleles expressed equally	AB blood type
Polygenic	Multiple genes affect trait	Skin color
Sex-linked	Gene on X or Y chromosome	Color blindness

Key Equations

• Mendelian Monohybrid Cross Ratio: $\frac{3 \text{ dominant} : 1 \text{ recessive}}$

• Probability of Genotype (Punnett Square): $\text{Probability} = \frac{\text{Number of desired outcomes}}{\text{Total possible outcomes}}$