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

Human Muscular System

Muscle Cell Structure and Sliding Filament Mechanism

The human muscular system enables movement, posture, and heat production. Muscle contraction is explained by the sliding filament theory, which describes how actin and myosin filaments interact within the sarcomere.

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

• Sliding Filament Mechanism: During contraction, 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.

• Muscle Unit Structures: Includes the sarcolemma (cell membrane), sarcoplasmic reticulum (stores Ca2+), T-tubules (transmit action potentials), and mitochondria (energy supply).

Example: The biceps brachii contracts when myosin heads pull actin filaments inward, shortening the muscle.

Action Potentials and Muscle Contraction

• Action Potential: An electrical signal generated in a motor neuron, leading to the release of neurotransmitters at the neuromuscular junction.

• Initiation: Acetylcholine is released, causing depolarization of the muscle cell membrane and triggering an action potential in the muscle fiber.

• Calcium Release: The action potential travels along T-tubules, causing the sarcoplasmic reticulum to release Ca2+, which enables actin-myosin binding.

• Order of Events: Nerve impulse → Acetylcholine release → Muscle cell depolarization → Ca2+ release → Actin-myosin interaction → Contraction.

Example: During a reflex, a nerve impulse rapidly triggers muscle contraction via this sequence.

Muscle Contraction Types and Heat Production

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

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

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

Major Muscle Groups and Body Cavities

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

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

Human Respiratory System

Significance and Structure of Breathing

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

• Significance: Oxygen is essential for ATP production; CO2 removal prevents acidosis.

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

• Lower Respiratory Structures: Trachea, bronchi, bronchioles, alveoli – conduct air and enable 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, pushing air out.

• 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.

Example: During exercise, breathing rate and depth increase to meet oxygen demand.

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.

• Gas Exchange: Occurs in alveoli, where O2 diffuses into blood and CO2 diffuses out.

Respiratory Diseases and Disorders

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

• Impact: These conditions impair gas exchange and oxygen delivery.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

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

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas – produce enzymes and bile to aid digestion.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up chemical breakdown of food; produced in the mouth (amylase), stomach (pepsin), pancreas (lipase, proteases), and small intestine.

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

Metabolic Rates and Nutrition

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

• Standard Metabolic Rate (SMR): Energy expenditure under standardized conditions (often used in animal studies).

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

Digestion Process and Peristalsis

• Digestion: Begins in the mouth, continues in the stomach and small intestine, with enzymes breaking down carbohydrates, proteins, and fats.

• Peristalsis: Rhythmic contractions of smooth muscle that propel 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: 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 genetic material in an organism.

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

• Karyotype: A visual representation 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 resulting from the genotype.

• Punnett Square: A diagram used to predict the probability of offspring genotypes and phenotypes.

Alleles and Patterns of Inheritance

• Allele: Different forms of a gene (dominant or recessive).

• Dominant Allele: Expressed if present (e.g., AA or Aa).

• Recessive Allele: Expressed only if both alleles are recessive (e.g., aa).

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws and Exceptions

• 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.

• Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., red x white = pink flowers).

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

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

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

Linked Genes, Sex-Linked Genes, and Chromosomal Abnormalities

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

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y), affecting inheritance patterns (e.g., color blindness).

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

Allele Combinations and Genetic Disorders

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

• Dominant Disorders: Lethal if expressed in homozygous state; rare in population.

• Recessive Disorders: Can persist if carriers are unaffected (heterozygotes).

Term	Definition	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, aa
Phenotype	Observable trait	Tall, short, blood type
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed if present	A in Aa
Recessive	Expressed only if homozygous	a in aa

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