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 called muscle fibers that contract to produce movement. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic functional unit of a muscle fiber, composed of actin and myosin filaments.

• Actin Filaments: Thin filaments that interact with myosin during contraction.

• Myosin Filaments: Thick filaments with heads that bind to actin, pulling them to cause contraction.

• Sliding Filament Theory: Myosin heads attach to actin, forming cross-bridges, and pull actin filaments inward, shortening the sarcomere.

Function of the Sarcomere: To facilitate contraction by allowing actin and myosin to slide past each other.

Example: During biceps contraction, sarcomeres shorten, causing the muscle to contract and the arm to bend.

Action Potential and Muscle Contraction

Muscle contraction is initiated by an action potential in a motor neuron, which triggers electrical impulses in the muscle fiber.

• Action Potential: A rapid change in membrane potential that travels along the neuron and muscle cell.

• Order of Events:

  1. Motor neuron releases acetylcholine at the neuromuscular junction.

  2. Muscle cell membrane depolarizes, generating an action potential.

  3. Calcium ions are released from the sarcoplasmic reticulum.

  4. Calcium enables actin-myosin interaction, leading to contraction.

Electrical Impulses: Cause release of calcium ions, which are essential for contraction.

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

Types of Muscle Contractions

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

• Isometric Contraction: Muscle tension increases, but length does not change. No movement produced.

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

Muscle Heat Generation

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

• The muscular system is the primary contributor to thermogenesis.

Muscles and Body Cavities

• Certain muscles, such as the diaphragm, section off body cavities (e.g., 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 that must be expelled.

Respiratory System Structures

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

• Lower Respiratory System: Includes trachea, bronchi, bronchioles, and lungs. Functions in gas exchange.

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 the lungs to the left atrium, then left ventricle, and is pumped to the body.

• Practice tracing blood flow through the heart: right atrium → right ventricle → lungs → left atrium → left ventricle → body.

Respiratory Diseases and Disorders

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

• These affect airflow, gas exchange, or lung tissue.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for digestion and absorption.

• 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 hormones.

Enzymes and Digestion

• Enzymes catalyze breakdown of macromolecules.

• Produced in salivary glands, stomach, pancreas, and small intestine.

Surface Area in Digestion

• Large surface area (villi and microvilli in small intestine) increases absorption efficiency.

Metabolic Rates

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

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

"My Plate" Purpose

• Guides healthy eating by illustrating food group proportions.

Digestion of Molecules and Peristalsis

• Carbohydrates, proteins, and fats are digested by specific enzymes.

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

• Gene: Segment of DNA coding for a trait.

• Chromosome: DNA molecule with associated proteins; humans have 23 pairs.

• Genome: Complete set of genetic material.

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pair of chromosomes with 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.

• Dominant Allele: Expressed when present.

• Recessive Allele: Expressed only when homozygous.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• 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 and Meiosis

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

• New allele combinations arise during meiosis via crossing over.

Sex-linked Genes and Nondisjunction

• Sex-linked Genes: Located on sex chromosomes, often X-linked.

• 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/Recessive	AA, Aa, aa	AA/Aa: dominant; aa: recessive	Widow's peak
Incomplete Dominance	RR, RW, WW	RW: intermediate	Snapdragon flower color
Codominance	IAIB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color

Additional info: Table entries inferred for clarity and completeness.