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 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.

• Order of Events: Nerve impulse → Action potential in motor neuron → Release of neurotransmitter (acetylcholine) → Muscle cell depolarization → Calcium release → Actin-myosin interaction → Contraction.

• Electrical Impulses: Action potentials trigger calcium release from the sarcoplasmic reticulum, enabling contraction.

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

Example: During exercise, muscle contractions increase heat production, helping maintain body temperature.

Muscle Groups and Functions

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

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

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 is isometric; performing a bicep curl is isotonic.

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: Include asthma, bronchitis, pneumonia, and emphysema.

Structures of the Respiratory System

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

• Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, and lungs. Functions: conduct air, 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.

Example: During inspiration, the diaphragm moves downward, increasing lung volume.

Blood Flow Through the Heart

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

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.

• Enzymes: Proteins that catalyze digestion; produced in salivary glands, stomach, pancreas, small intestine.

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

Metabolic Rates

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

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

Example: BMR is measured after fasting and rest; SMR may be measured during activity.

Digestion Processes

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

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

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 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 chromosomes; used to detect abnormalities.

Genotype and Phenotype

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

• Phenotype: Observable traits (e.g., eye color).

Punnett Square and Alleles

• Punnett Square: Diagram to predict genetic crosses.

• Alleles: Variants of a gene; can be dominant or recessive.

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Patterns of Inheritance

• Dominant Allele Disorders: Often lethal if homozygous.

• Recessive Disorders: Can persist in populations due to carriers.

• 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 affect phenotypic expression.

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

• Sex-linked Genes: Genes on sex chromosomes; often affect males more.

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

Meiosis and Genetic Variation

• New Allele Combinations: Crossing over and independent assortment during meiosis create genetic diversity.

Term	Definition	Example
Genotype	Genetic makeup of an organism	AA, Aa, aa
Phenotype	Observable traits	Brown eyes, blue eyes
Dominant Allele	Expressed when present	A in Aa
Recessive Allele	Expressed only when homozygous	a in aa
Codominance	Both alleles expressed	AB blood type
Incomplete Dominance	Intermediate phenotype	Pink flowers from red and white parents

Additional info: Academic context and definitions were expanded for clarity and completeness.