Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

Human Muscular System

Muscle Structure and Function

The human muscular system enables movement, maintains posture, and generates heat. Muscles are composed of muscle fibers, which contain myofibrils made up of repeating units called sarcomeres.

• Sarcomere: The basic contractile unit of muscle fiber, defined by the area between two Z-lines. It contains actin (thin) and myosin (thick) filaments.

• Actin and Myosin: Actin filaments serve as tracks for myosin heads to pull, while myosin filaments have heads that bind to actin and use ATP to generate force.

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

• Major Muscle Groups: Include the biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and gluteals.

Muscle Contraction Mechanism

• Action Potential: An electrical signal generated in a motor neuron that triggers muscle contraction.

• Neuromuscular Junction: The synapse where a motor neuron communicates with a muscle fiber, releasing neurotransmitters (e.g., acetylcholine) to initiate contraction.

• Order of Events:

  1. Action potential arrives at the neuromuscular junction.

  2. Acetylcholine is released, causing depolarization of the muscle cell membrane.

  3. Calcium ions are released from the sarcoplasmic reticulum.

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

  5. Myosin heads bind to actin, performing a power stroke using ATP.

  6. Muscle contracts as sarcomeres shorten.

• Isotonic vs. Isometric Contractions:

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

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

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

• Muscles and Body Cavities: The diaphragm separates the thoracic and abdominal cavities and is essential for respiration.

Key Terms and Structures

• Sarcomere Substructures: Z-line, M-line, A-band, I-band, H-zone.

• Function of Sarcomere: To facilitate contraction through the sliding filament mechanism.

Example: During a bicep curl, the biceps brachii contracts (isotonic contraction), shortening the muscle and moving the forearm.

Human Respiratory System

Significance of Breathing

Breathing supplies oxygen to the body and removes carbon dioxide, supporting cellular respiration and energy production.

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

Structures of the Respiratory System

• Upper Respiratory System: Includes the nose, nasal cavity, pharynx, and larynx. Functions include filtering, warming, and humidifying air.

• Lower Respiratory System: Includes the trachea, bronchi, bronchioles, and lungs. Functions include conducting air to the lungs and facilitating gas exchange.

Mechanics of Breathing

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

• Exhalation (Expiration): Diaphragm and intercostal muscles relax, decreasing thoracic volume and increasing lung pressure, pushing air out.

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

• Intercostal Muscles: Assist the diaphragm in expanding and contracting the chest cavity during breathing.

Respiratory Diseases and Disorders

• Common disorders include asthma, bronchitis, pneumonia, and emphysema.

Blood Flow Through the Heart (Oxygen-Rich Blood)

1. Oxygenated blood from the lungs enters the left atrium via the pulmonary veins.

2. Passes through the mitral valve into the left ventricle.

3. Pumped through the aortic valve into the aorta and distributed to the body.

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

Human Digestive System

Major Structures and Functions

• Mouth: Begins mechanical and chemical digestion.

• Esophagus: Transports food to the stomach via peristalsis.

• Stomach: Mixes food with gastric juices for protein digestion.

• Small Intestine: Main site for digestion and nutrient absorption; large surface area due to villi and microvilli.

• Large Intestine: Absorbs water and forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores and releases bile.

• Pancreas: Produces digestive enzymes and bicarbonate.

Digestion and Enzymes

• Enzymes: Biological catalysts that speed up digestion; produced in the salivary glands, stomach, pancreas, and small intestine.

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

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

Metabolic Rates

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

• Standard Metabolic Rate (SMR): The metabolic rate under standardized conditions, often used for comparison among species.

Nutrition Guidelines

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

Example: Amylase in saliva begins the breakdown of starches in the mouth.

Human Genetics and Inheritance

Basic Concepts

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

• Chromosome: A structure made of DNA and proteins that carries genetic information; humans have 23 pairs.

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

• Genetics: The scientific study of heredity and variation.

Chromosome Structure and Function

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

• Karyotype: An organized profile of an individual's chromosomes, used to detect chromosomal abnormalities.

Genotype and Phenotype

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

• Phenotype: The observable traits or characteristics (e.g., brown eyes).

Inheritance Patterns

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

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

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

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

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

• Law of Independent Assortment: Genes for different traits are inherited independently of each other.

Complex Inheritance

• Incomplete Dominance: Heterozygotes show an 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).

• Environmental Influence: Phenotype can be affected by environmental factors (e.g., nutrition, sunlight).

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

• Sex-Linked Genes: Genes located on sex chromosomes (e.g., color blindness on the X chromosome).

Genetic Disorders and Variation

• Lethal Dominant Disorders: Caused by dominant alleles; often rare because affected individuals may not survive to reproduce.

• Recessive Disorders: Can persist in populations because carriers (heterozygotes) do not show symptoms.

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

• New Allele Combinations: Crossing over during meiosis creates genetic diversity.

Sample Table: Types of Inheritance

Type	Description	Example
Complete Dominance	Dominant allele masks recessive	Widow's peak hairline
Incomplete Dominance	Intermediate phenotype	Pink snapdragon flowers
Codominance	Both alleles expressed	AB blood type
Polygenic	Multiple genes affect trait	Skin color
Sex-linked	Gene on X or Y chromosome	Hemophilia

Example: A Punnett square can predict the probability of offspring inheriting a genetic disorder.

Equation (Probability of genotype in monohybrid cross):

$P(AA) = p^2$ $P(Aa) = 2pq$ $P(aa) = q^2$

Additional info: These equations represent Hardy-Weinberg equilibrium for allele frequencies in a population.