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 and generate heat. The sliding filament mechanism is central to muscle contraction.

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

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

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

• Order of Events: Nerve impulse → Action potential in motor neuron → Release of neurotransmitter (acetylcholine) → Depolarization of muscle cell membrane → Calcium release from sarcoplasmic reticulum → Actin-myosin interaction → Contraction.

• Electrical Impulses: Action potentials trigger calcium release, which enables contraction.

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

• Muscles Sectioning Body 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, tension increases).

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

Example: During running, isotonic contractions of leg muscles propel the body forward, while isometric contractions stabilize joints.

Sarcomere Substructures and Functions

• 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.

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

• Pressure Changes:

  • Inhalation: Lung pressure decreases, air flows in.

  • Exhalation: Lung pressure increases, air flows out.

• Mechanics of Breathing:

  • Inspiration: Diaphragm contracts, chest cavity expands.

  • Expiration: Diaphragm relaxes, chest cavity contracts.

• Respiratory Diseases: Includes asthma, bronchitis, pneumonia, 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 → systemic circulation.

• Deoxygenated blood returns via the right atrium → right ventricle → pulmonary artery → lungs.

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: Liver, pancreas, gallbladder – produce enzymes and bile for digestion.

• Enzymes: Biological catalysts produced in salivary glands, stomach, pancreas, small intestine; speed up digestion.

• Large Surface Area: Villi and microvilli in the small intestine increase absorption efficiency.

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

• Metabolic Rates:

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

  • Standard Metabolic Rate: Energy used under standard conditions.

• "My Plate": USDA guideline for balanced nutrition.

Example: The pancreas releases digestive enzymes into the small intestine to break down carbohydrates, proteins, and fats.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Genetics is the scientific study of heredity and variation in organisms. Genes are segments of DNA that code for traits, located on chromosomes.

• Gene: DNA sequence coding for a protein or trait.

• Chromosome: Structure carrying genetic information; humans have 23 pairs.

• Genome: Complete set of genes in an organism.

• Homologous Chromosomes: Pairs with the same genes but possibly different alleles.

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

Genotype, Phenotype, and Punnett Squares

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

• Phenotype: Observable traits (e.g., brown eyes).

• Punnett Square: Diagram used to predict genetic crosses.

Example Punnett Square Table

	A	a
A	AA	Aa
a	Aa	aa

Alleles and Laws of Inheritance

• Dominant Allele: Expressed when present (e.g., A).

• Recessive Allele: Expressed only when homozygous (e.g., aa).

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

• Heterozygous: Two different alleles (Aa).

• Law of Segregation: Alleles separate during gamete formation.

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

Patterns of Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., pink flowers from red and white parents).

• 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 affect phenotypic expression (e.g., nutrition, temperature).

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

• 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 (e.g., Down syndrome).

Example: A child inherits cystic fibrosis if both parents carry the recessive allele.

Additional info: The notes above expand on brief review points with academic context, definitions, and examples for clarity and completeness.