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

• Sliding Filament Theory: Myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

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

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

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

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential that triggers muscle contraction.

• Order of Events: Nerve impulse → release of neurotransmitter (acetylcholine) → depolarization of muscle cell → calcium release → contraction.

• Release of Molecules: Calcium ions are released from the sarcoplasmic reticulum, enabling contraction.

Example: The neuromuscular junction is where the motor neuron communicates with the muscle fiber.

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: Isotonic contractions are used in walking; isometric contractions occur when holding a plank position.

Muscle Groups and Body Cavities

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

Additional info: The diaphragm is essential for breathing, and intercostal muscles assist in expanding the rib cage.

Human Respiratory System

Significance of Breathing

Breathing is vital for oxygen intake and carbon dioxide removal, supporting cellular respiration.

• Oxygen Transport: Oxygen-rich blood is pumped from the lungs to the heart, then distributed to tissues.

• Respiratory Diseases: Includes 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: gas exchange and air conduction.

Example: The cilia in the trachea help remove particles from inhaled air.

Mechanics of Breathing

• Inhalation: Diaphragm contracts and moves downward, intercostal muscles expand the rib cage, decreasing lung pressure and drawing air in.

• Exhalation: Diaphragm relaxes, rib cage contracts, increasing lung pressure and expelling air.

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

Intercostal Muscles: Assist in expanding and contracting the chest during breathing.

Blood Flow Through the Heart

• Order of Flow: Pulmonary veins → left atrium → left ventricle → aorta → body tissues → vena cava → right atrium → right ventricle → pulmonary artery → lungs.

Additional info: Oxygen-rich blood enters the left side of the heart and is pumped to the body.

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: Liver, pancreas, gallbladder. Functions: produce enzymes, bile, and aid digestion.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion. 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: Amylase breaks down starch in the mouth; lipase digests fats in the small intestine.

Metabolic Rates

• Basal Metabolic Rate (BMR): Energy used at rest to maintain vital functions.

• Standard Metabolic Rate (SMR): Energy used under specific conditions (e.g., fasting, resting).

Equation: $\text{BMR} = \text{weight (kg)} \times \text{energy factor}$

Digestion Process and Peristalsis

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

• Digestion: Mechanical and chemical breakdown of food into absorbable molecules.

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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

• Gene: A segment of DNA coding for a specific 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, 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: Crossing Aa x Aa yields a 3:1 ratio of dominant to recessive phenotypes.

Dominant and Recessive Alleles

• 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).

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Patterns of Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., pink flowers).

• 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 and Meiosis

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

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

Sex-linked Genes and Nondisjunction

• Sex-linked Genes: Genes located on sex chromosomes (X or Y); often affect males more.

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

Term	Definition
Gene	Segment of DNA coding for a protein
Chromosome	DNA molecule with associated proteins
Genotype	Genetic makeup
Phenotype	Observable traits
Homozygous	Identical alleles
Heterozygous	Different alleles
Dominant	Expressed allele
Recessive	Masked allele
Polygenic	Trait controlled by multiple genes
Codominance	Both alleles expressed
Incomplete Dominance	Intermediate phenotype
Nondisjunction	Failure of chromosome separation

Additional info: Disorders caused by dominant alleles may be lethal if expressed, while recessive disorders can persist in populations due to carriers.