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, M-line, A-band, I-band, and H-zone, each with specific roles in contraction.

• Muscle Unit Structures: Muscle fiber, fascicle, endomysium, perimysium, epimysium.

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 → Actin-myosin interaction → Contraction.

• Electrical Impulses: Cause release of calcium ions from the sarcoplasmic reticulum, enabling contraction.

Example: A nerve impulse causes the release of acetylcholine, which triggers an action potential in the muscle cell.

Types of Muscle Contractions

Muscle contractions can be classified based on whether the muscle changes length.

• Isotonic Contraction: Muscle changes length (movement occurs).

• Isometric Contraction: Muscle does not change length (no movement, but tension increases).

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

• Muscles Sectioning Cavities: Diaphragm separates thoracic and abdominal cavities.

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen to tissues and removing carbon dioxide.

• Oxygen: Required for cellular respiration and energy production.

• Carbon Dioxide: Waste product removed by exhalation.

Respiratory System Structures

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

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

Example: The alveoli are the site of gas exchange in the lungs.

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.

Blood Flow and Oxygen Transport

• Oxygen-rich Blood: Flows from lungs to left atrium, left ventricle, then to body tissues.

• Order of Flow: Pulmonary veins → Left atrium → Left ventricle → Aorta → Body.

Respiratory Diseases and Disorders

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

• Impact: Affect gas exchange and breathing efficiency.

Human Digestive System

Digestive System Structures and Functions

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

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

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

• Function: Each organ contributes to digestion, absorption, or 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 used at rest.

• Standard Metabolic Rate (SMR): Energy used under standardized conditions.

• Equation: $\text{BMR} = \text{Energy expenditure at rest}$

Nutrition and "My Plate"

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

Digestion Mechanics

• 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 digestive organs.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Gene: A segment of DNA coding for a specific protein.

• 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 but possibly different alleles.

• Karyotype: Visual representation of chromosome number and structure.

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).

Genetic Laws and Inheritance Patterns

• Law of Segregation: Alleles separate during gamete formation.

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

• Dominant/Recessive Disorders: Dominant disorders can be lethal; recessive disorders may persist due to carrier status.

Complex Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can affect phenotypic expression.

Linked Genes, Meiosis, and Sex-linked Traits

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

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

• Sex-linked Genes: Genes located on sex chromosomes (e.g., X-linked traits).

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

Sample Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Dominant	AA, Aa	Dominant trait expressed	Huntington's disease
Recessive	aa	Recessive trait expressed	Cystic fibrosis
Incomplete Dominance	Aa	Intermediate phenotype	Red and white flowers produce pink
Codominance	AB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color

Additional info: Table entries inferred for clarity and completeness.