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.

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

• Function of Sarcomere: Generates force for muscle contraction through the cyclical interaction of actin and myosin.

Muscle Contraction and Action Potentials

• Action Potential: An electrical signal initiated in a motor neuron, leading to muscle contraction.

• Mechanism: The action potential travels down the motor neuron, causing the release of neurotransmitter (acetylcholine) at the neuromuscular junction, which triggers an action potential in the muscle fiber.

• Calcium Release: The muscle action potential causes the sarcoplasmic reticulum to release Ca2+, enabling myosin-actin binding.

• Order of Events: Nerve impulse → Acetylcholine release → Muscle action potential → Ca2+ release → Cross-bridge formation → Sliding of filaments → Contraction.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant; produces movement.

• Isometric Contraction: Muscle length remains the same while tension increases; no movement occurs.

Muscle Groups and Body Cavities

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

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

Heat Production

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

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen for cellular respiration and removing carbon dioxide, a metabolic waste product.

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

Structures of the Respiratory System

• Upper Respiratory System: Includes the nose, nasal cavity, pharynx, and larynx. Functions: filters, warms, and humidifies air; provides resonance for speech.

• Lower Respiratory System: Includes the trachea, bronchi, bronchioles, and lungs. Functions: conducts air to alveoli, site of 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 < atmospheric pressure; during exhalation, lung pressure > 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 from the lungs enters the left atrium, passes to the left ventricle, and is pumped through the aorta to the body.

Respiratory Diseases and Disorders

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

Human Digestive System

Major Structures and Functions

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

• Functions: Ingestion, digestion, absorption, and elimination of food and nutrients.

Accessory Organs

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

• Functions: Produce enzymes and bile to aid digestion.

Enzymes and Digestion

• Digestive Enzymes: Biological catalysts that break down macromolecules; produced in the mouth (amylase), stomach (pepsin), pancreas (lipase, proteases), and small intestine.

Surface Area and Digestion

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

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 (e.g., fasting, resting, specific temperature).

Nutrition Guidelines

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

Digestion Process and Peristalsis

• Digestion: Mechanical and chemical breakdown of food into absorbable molecules.

• Peristalsis: Coordinated, rhythmic contractions of smooth muscle that propel food through the digestive tract.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

• 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.

• Genetics: The scientific study of heredity and variation.

Homologous Chromosomes and Karyotypes

• Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles; one from each parent.

• 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).

Punnett Squares and Patterns of Inheritance

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

• Dominant Allele: Expressed when 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).

Mendelian Laws

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

• Law of Independent Assortment: Genes for different traits are inherited independently if on different chromosomes.

Allele Interactions and Inheritance Patterns

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

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

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

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

Linked Genes and Genetic Variation

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

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

Sex-Linked Genes and Nondisjunction

• 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 in gametes (e.g., Down syndrome).

Genetic Disorders

• Dominant Disorders: Can be lethal if one copy of the allele causes disease (e.g., Huntington's disease).

• Recessive Disorders: Remain prevalent because carriers (heterozygotes) do not show symptoms (e.g., cystic fibrosis).

Example: Punnett Square for a Monohybrid Cross

	A	a
A	AA	Aa
a	Aa	aa

Interpretation: Shows the possible genotypes of offspring from parents with genotypes Aa x Aa.

Additional info: For more complex inheritance patterns (e.g., dihybrid crosses, polygenic traits), larger Punnett squares or probability calculations are used.