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, composed of actin (thin) and myosin (thick) filaments.

• Actin and Myosin: Actin filaments provide sites for myosin heads to attach and pull, causing contraction. Myosin filaments have heads that bind to actin and use ATP to generate force.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, pull the filaments together, and shorten the sarcomere.

• Electrical Impulses: Action potentials in motor neurons trigger the release of calcium ions in muscle cells, initiating contraction.

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

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

• Isotonic vs. Isometric Contractions: Isotonic contractions produce movement (muscle changes length), while isometric contractions produce tension without movement (muscle length remains the same).

Example: During running, isotonic contractions move the legs, while isometric contractions stabilize the torso.

Additional info: The sarcoplasmic reticulum releases calcium ions in response to electrical impulses, enabling contraction.

Order of Events in Muscle Contraction

• 1. Action potential arrives at the motor neuron.

• 2. Acetylcholine is released at the neuromuscular junction.

• 3. Muscle cell membrane depolarizes.

• 4. Calcium ions are released from the sarcoplasmic reticulum.

• 5. Myosin binds to actin, ATP is hydrolyzed, and contraction occurs.

Muscles and Body Cavities

• Certain muscles, such as the diaphragm, section body cavities (e.g., thoracic and abdominal cavities).

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 throughout the body.

• Respiratory Structures: The upper respiratory system (nose, pharynx, larynx) filters, warms, and humidifies air. The lower respiratory system (trachea, bronchi, lungs) conducts air and facilitates 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 exercise, breathing rate increases to meet oxygen demand.

Respiratory Diseases and Disorders

• Common disorders include asthma, chronic obstructive pulmonary disease (COPD), pneumonia, and lung cancer.

Blood Flow Through the Heart

• Oxygen-rich blood flows from the lungs to the left atrium, then to the left ventricle, and is pumped out to the body.

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.

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

• Surface Area: Large surface area in the small intestine (villi and microvilli) increases nutrient absorption.

Metabolic Rates

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

• Standard Metabolic Rate (SMR): The energy expended under standardized conditions.

Example: "My Plate" is a guideline for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion Processes

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

• Molecule Digestion: Carbohydrates, proteins, and fats are broken down by specific enzymes in different digestive structures.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Gene: A segment of DNA that codes for a specific protein.

• Chromosome: A 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: The visual representation of chromosomes in a cell.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism.

• Phenotype: The observable traits of an organism.

Punnett Square and Alleles

• Punnett Square: A diagram used to predict the outcome of genetic crosses.

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

• Homozygous: Two identical alleles for a trait.

• Heterozygous: Two different alleles for a trait.

Mendelian Laws

• Law of Segregation: Each parent passes one allele for each gene to offspring.

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

Inheritance Patterns

• Dominant and Recessive Disorders: Dominant allele disorders can be lethal; recessive disorders may persist due to carriers.

• Incomplete Dominance: Heterozygotes show intermediate phenotype.

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

• Polygenic Inheritance: Traits controlled by multiple genes (e.g., skin color).

• Environmental Impact: Environment can influence phenotypic expression.

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

• Meiosis and Allele Combinations: Crossing over during meiosis creates new allele combinations.

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

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

Sample Table: Dominant vs. Recessive Alleles

Allele Type	Expression	Example Disorder
Dominant	Expressed if at least one allele is present	Huntington's disease
Recessive	Expressed only if both alleles are present	Cystic fibrosis

Additional info: Nondisjunction can result in conditions such as Down syndrome (trisomy 21).