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 Filaments: Actin provides the track for myosin heads to attach and pull, causing contraction.

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

• Function of Sarcomere: Facilitates muscle contraction by shortening during the sliding filament process.

• Major Muscle Groups: Includes muscles such as biceps, triceps, quadriceps, hamstrings, pectorals, and abdominals.

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

Example: During bicep contraction, the sarcomeres shorten, pulling the forearm upward.

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential that travels along the motor neuron, triggering muscle contraction.

• Order of Events:

  1. Motor neuron releases neurotransmitter (acetylcholine).

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

  3. Calcium ions are released from the sarcoplasmic reticulum.

  4. Calcium binds to troponin, exposing binding sites on actin.

  5. Myosin binds to actin, causing contraction.

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

Example: Shivering increases muscle activity to generate heat.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (movement occurs), e.g., lifting a weight.

• Isometric Contraction: Muscle length remains the same (no movement), e.g., holding a weight steady.

Example: Holding a plank position involves isometric contraction.

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.

• Respiratory Diseases: Includes asthma, bronchitis, pneumonia, and emphysema.

Structures of the Respiratory System

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, and larynx. Functions: filters, warms, and moistens air.

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

Example: The alveoli are the site of oxygen and carbon dioxide 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.

Example: During exercise, breathing rate increases to meet oxygen demand.

Human Digestive System

Major 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 of Enzymes: Catalyze breakdown of macromolecules; produced in salivary glands, stomach, pancreas, and small intestine.

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

Example: Pancreatic amylase digests carbohydrates in the small intestine.

Metabolic Rates and Digestion

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

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

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

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

Example: Swallowing initiates peristalsis in the esophagus.

Human Genetics and Inheritance

Basic Concepts

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

• Genes: Segments of DNA that code for proteins.

• Chromosomes: Structures that organize and carry genes; 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: Visual representation of chromosome number and structure.

Example: Down syndrome is identified by a karyotype showing an extra chromosome 21.

Genotype, Phenotype, and Inheritance Patterns

• Genotype: Genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: Observable traits resulting from genotype and environment.

• Punnett Square: Tool to predict genetic crosses and offspring ratios.

• Dominant Alleles: Expressed when present; Recessive Alleles: Expressed only when homozygous.

• Homozygous: Two identical alleles; Heterozygous: Two different alleles.

Example: Brown eyes (dominant) vs. blue eyes (recessive).

Mendelian Laws and Exceptions

• Law of Segregation: Alleles separate during gamete formation.

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

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

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

• Environmental Impact: Environment can modify phenotypic expression.

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

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

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

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

Example: Hemophilia is a sex-linked recessive disorder.

Genetic Inheritance Table

The following table summarizes inheritance patterns:

Inheritance Pattern	Genotype	Phenotype	Example
Dominant	AA, Aa	Trait expressed	Brown eyes
Recessive	aa	Trait expressed only if homozygous	Blue eyes
Incomplete Dominance	Aa	Intermediate phenotype	Pink flowers (from red and white parents)
Codominance	AB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color
Sex-linked	XrXr, XrY	Trait more common in males	Color blindness

Additional info: Table entries inferred for clarity and completeness.