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. The sliding filament mechanism is central to muscle contraction.

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

• Actin and Myosin: Proteins that interact to produce contraction. Myosin heads bind to actin, pulling the filaments past each other.

• Sliding Filament Theory: Muscle contraction occurs as myosin heads attach to actin and pull, shortening the sarcomere.

• Substructures: Includes Z-lines, A-band, I-band, H-zone, and M-line, each with specific roles in contraction.

• Muscle Unit Structures: Muscle fiber, myofibril, sarcolemma, sarcoplasmic reticulum.

Example: During contraction, the sarcomere shortens as actin and myosin slide past each other, resulting in muscle shortening.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

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

• Motor Neuron: Releases neurotransmitter (acetylcholine) at the neuromuscular junction, causing depolarization of the muscle cell membrane.

• Order of Events: Nerve impulse → Acetylcholine release → Muscle cell depolarization → Calcium release from sarcoplasmic reticulum → Actin-myosin interaction → Contraction.

• Electrical Impulses: Cause release of calcium ions, which enable actin-myosin binding.

Example: A nerve impulse causes a muscle to contract by triggering calcium release and actin-myosin interaction.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (movement occurs), tension remains constant.

• Isometric Contraction: Muscle length remains the same, tension increases (no movement).

Example: Lifting a weight is isotonic; holding a weight steady is isometric.

Muscle Groups and Functions

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

• Body Cavities: Muscles such as the diaphragm section the thoracic and abdominal cavities.

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

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 to the body.

• Importance: Cellular respiration requires oxygen; removal of CO2 prevents toxicity.

Structures of the Respiratory System

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

• Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, lungs, alveoli. Functions: conduct air, gas exchange.

Example: The alveoli are the site of gas exchange between air and blood.

Mechanics of Breathing

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

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

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

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

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, pneumonia, emphysema.

• Effects: Impair gas exchange, reduce 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.

• Functions: Mechanical and chemical digestion, absorption, excretion.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion. Examples: amylase (saliva), pepsin (stomach), lipase (pancreas).

• Production Sites: Salivary glands, stomach, pancreas, small intestine.

Surface Area and Digestion

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

Metabolic Rates

• Basal Metabolic Rate (BMR): Energy expended at rest.

• Standard Metabolic Rate (SMR): Energy expenditure under specific conditions.

Example: BMR is measured after fasting and rest; SMR may be measured during activity.

"My Plate" and Nutrition

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

Digestion Processes

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

• Molecule Digestion: Carbohydrates, proteins, and fats are broken down by specific enzymes in different regions.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Genetics is the scientific study of heredity and variation in organisms.

• Gene: A segment of DNA encoding a specific 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, one from each parent.

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

Genotype and Phenotype

• Genotype: Genetic makeup (allele combination).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram used to predict genetic crosses.

• Alleles: Variants of a gene; can be dominant or recessive.

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

• Heterozygous: Two different alleles (e.g., Aa).

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• Dominant Allele Disorders: Can be lethal if expressed in homozygous form.

• Recessive Disorders: May persist due to carriers.

• Incomplete Dominance: Heterozygotes show intermediate phenotype.

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

• 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 tend to be inherited together.

• New Allele Combinations: Occur during meiosis via crossing over.

• Sex-linked Genes: Located on sex chromosomes; often affect males more.

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers in gametes.

Sample Punnett Square Table

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

Parent 1	Parent 2	Offspring Genotype	Offspring Phenotype
Aa	Aa	AA, Aa, aa	Dominant, Dominant, Recessive
AA	aa	Aa	Dominant
aa	aa	aa	Recessive

Additional info: Table entries inferred for clarity and completeness.