Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

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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 (thin) and myosin (thick) filaments.
Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin filaments and pull them inward, shortening the sarcomere.
Actin and Myosin: Actin provides the track, while myosin uses ATP to generate force and movement.
Order of Events: Nerve impulse → Action potential → Calcium release → Myosin-actin interaction → Muscle contraction.
Electrical Impulses: Action potentials in motor neurons trigger calcium release from the sarcoplasmic reticulum, enabling contraction.
Major Muscle Groups: Include biceps, triceps, quadriceps, hamstrings, pectorals, and abdominals.
Body Heat Generation: Most body heat is generated by muscle activity, especially during contraction.
Muscles Sectioning Cavities: Diaphragm separates thoracic and abdominal cavities.
Isotonic vs. Isometric Contractions:
- Isotonic: Muscle changes length (movement occurs).
- Isometric: Muscle length remains the same (no movement, but tension increases).

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

Sarcomere Substructures

Z-line: Defines the boundaries of a sarcomere.
A-band: Contains the length of the myosin filaments.
I-band: Contains only actin filaments.
H-zone: Area with only myosin, disappears during contraction.

Function: The sarcomere shortens during contraction, producing force.

Action Potential in Motor Neuron

Initiation: Triggered by neurotransmitter release (acetylcholine) at the neuromuscular junction.
Propagation: Electrical impulse travels along the muscle membrane, leading to 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 Structures:
- Upper Respiratory: Nose, pharynx, larynx – filter, warm, and humidify air.
- Lower Respiratory: Trachea, bronchi, lungs – conduct air and facilitate gas exchange.
Intercostal Muscles: Located between ribs, contract during inhalation to expand the chest cavity.
Pressure Changes: Inhalation decreases lung pressure, drawing air in; exhalation increases pressure, expelling air.
Mechanics of Inspiration: Diaphragm contracts, chest expands, air enters.
Mechanics of Expiration: Diaphragm relaxes, chest contracts, air exits.
Respiratory Diseases: Include asthma, bronchitis, pneumonia, and emphysema.

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

Blood Flow Through the Heart

Oxygen-rich blood enters the left atrium → left ventricle → aorta → body tissues.
Deoxygenated blood returns via veins to the right atrium → right ventricle → lungs for oxygenation.

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.
Accessory Organs: Liver, pancreas, gallbladder – produce enzymes and bile for digestion.
Enzymes: Catalyze breakdown of carbohydrates, proteins, and fats; produced in salivary glands, stomach, pancreas, and small intestine.
Surface Area: Villi and microvilli in the small intestine increase surface area for absorption.
Peristalsis: Wave-like muscle contractions move food through the digestive tract.
Metabolic Rates:
- Basal Metabolic Rate (BMR): Energy used at rest.
- Standard Metabolic Rate (SMR): Energy used under specific conditions.
"My Plate": USDA guideline for balanced nutrition.

Example: The pancreas releases digestive enzymes into the small intestine to aid in food breakdown.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

Gene: Segment of DNA coding for a trait.
Chromosome: Structure containing DNA; humans have 23 pairs.
Genome: Complete set of genetic material in an organism.
Homologous Chromosomes: Paired chromosomes with genes for the same traits.
Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Genotype and Phenotype

Genotype: Genetic makeup (alleles present).
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: Each parent passes one allele for each trait to offspring.
Law of Independent Assortment: Genes for different traits are inherited independently.

Patterns of Inheritance

Dominant Disorders: Expressed with one dominant allele; can be lethal.
Recessive Disorders: Require two recessive alleles; can persist in populations.
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.
Meiosis: New allele combinations arise from 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 Table: Types of Genetic Inheritance

Inheritance Type	Genotype	Phenotype	Example
Dominant	AA, Aa	Trait expressed	Huntington's disease
Recessive	aa	Trait expressed	Cystic fibrosis
Incomplete Dominance	Aa	Intermediate	Pink snapdragon flowers
Codominance	AB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Height, skin color

Key Equations

Muscle Contraction: ATP hydrolysis provides energy for myosin movement.
Genotype Probability (Punnett Square):

Additional info: Academic context and examples were added to clarify and expand upon brief review points.