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

Human Muscular System

Muscle Cell Structure and Sliding Filament Mechanism

The human muscular system enables movement, posture, and heat production. Muscle contraction is explained by the sliding filament theory, which involves the interaction of actin and myosin filaments within the sarcomere.

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

• Sliding Filament Mechanism: During contraction, myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

• Actin and Myosin: Actin forms the thin filaments, while myosin forms the thick filaments with protruding heads that attach to actin during contraction.

• Substructures of Sarcomere: Includes Z-lines (boundaries), M-line (center), A-band (length of myosin), I-band (actin only), and H-zone (myosin only).

• Function of Sarcomere: Generates force for muscle contraction by shortening during the sliding of filaments.

Example: During biceps contraction, sarcomeres in muscle fibers shorten, pulling the forearm upward.

Electrical Impulses and Muscle Contraction

• Action Potential in Motor Neuron: An electrical signal generated by the nervous system that travels down the motor neuron to the neuromuscular junction.

• Initiation of Muscle Contraction: The action potential triggers the release of acetylcholine, which binds to receptors on the muscle cell membrane, leading to depolarization and subsequent muscle contraction.

• Order of Events:

  1. Action potential arrives at neuromuscular junction.

  2. Acetylcholine is released and binds to muscle cell receptors.

  3. Muscle cell membrane depolarizes, generating an action potential.

  4. Calcium ions are released from the sarcoplasmic reticulum.

  5. Calcium binds to troponin, exposing binding sites on actin.

  6. Myosin heads bind to actin, initiating contraction.

• Heat Generation: Most body heat is generated by muscle contractions, especially during shivering.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant; produces movement.

• Isometric Contraction: Muscle tension increases, but length does not change; maintains posture or supports objects in a fixed position.

Example: Lifting a weight (isotonic); holding a weight steady (isometric).

Major Muscle Groups and Functions

• Major Muscle Groups: Deltoids (shoulder), pectorals (chest), biceps/triceps (arms), abdominals, quadriceps/hamstrings (legs), gluteals (buttocks).

• Muscles Sectioning Body Cavities: The diaphragm separates the thoracic and abdominal cavities.

Human Respiratory System

Significance and Function of Breathing

The respiratory system enables gas exchange, supplying oxygen to the body and removing carbon dioxide. Breathing is essential for cellular respiration and energy production.

• Upper Respiratory System: Includes the nose, nasal cavity, pharynx, and larynx. Functions: filters, warms, and humidifies air; provides resonance for speech.

• Lower Respiratory System: Includes the trachea, bronchi, bronchioles, and lungs. Functions: conducts air to lungs, site of gas exchange (alveoli).

Mechanics of Breathing

• Inhalation (Inspiration): Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing pressure, drawing air into lungs.

• Exhalation (Expiration): Diaphragm and intercostal muscles relax, decreasing thoracic volume and increasing pressure, pushing air out.

• Pressure Changes: Air flows from high to low pressure; during inhalation, lung pressure drops below atmospheric pressure, and during exhalation, it rises above atmospheric pressure.

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

Example: During exercise, both the diaphragm and intercostal muscles work harder to increase air intake.

Oxygen-Rich Blood Flow Through the Heart

• Oxygen-rich blood returns from the lungs via the pulmonary veins to the left atrium, passes to the left ventricle, and is pumped out through the aorta to the body.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, pneumonia, emphysema, and lung cancer.

• Effects: Impair gas exchange, reduce oxygen delivery, and may cause respiratory distress.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It consists of the alimentary canal and accessory organs.

• Major Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

• Functions: Ingestion, digestion, absorption, and elimination.

Enzymes and Digestion

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

• Function: Break down carbohydrates, proteins, and fats into absorbable units.

Surface Area and Digestion

• Large Surface Area: Villi and microvilli in the small intestine increase surface area for efficient nutrient absorption.

Metabolic Rates

• Basal Metabolic Rate (BMR): The energy expended at rest to maintain vital body functions.

• Standard Metabolic Rate (SMR): The metabolic rate under specific conditions (e.g., at a certain temperature for ectotherms).

Dietary Guidelines

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

Digestion and Peristalsis

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

• Digestion of Molecules: Carbohydrates, proteins, and fats are digested in specific regions by specialized enzymes.

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 proteins, located on chromosomes within the genome.

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

• Chromosome: A structure composed of DNA and proteins, carrying genetic information.

• Genome: The complete set of genes or genetic material in an organism.

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

• Karyotype: An organized profile of an individual's chromosomes, used to detect chromosomal abnormalities.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: The observable traits or characteristics (e.g., brown eyes, blue eyes).

Punnett Squares and Inheritance Patterns

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

• Dominant Allele: Expressed trait when at least one copy is present (e.g., A).

• Recessive Allele: Expressed only when two copies are present (e.g., a).

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

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

Complex Patterns of Inheritance

• Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., red x white = pink flowers).

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

• Polygenic Inheritance: Multiple genes influence a single trait (e.g., skin color).

• Environmental Impact: Environment can affect gene expression (e.g., nutrition influencing height).

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

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y), often showing different inheritance patterns in males and females.

Genetic Disorders and Chromosomal Abnormalities

• Lethal Dominant Disorders: Dominant alleles that cause death, often before reproductive age.

• Prevalence of Recessive Disorders: Recessive alleles can persist in populations because carriers are unaffected.

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers (e.g., Down syndrome).

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

Term	Definition	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, aa
Phenotype	Observable trait	Tall, short
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed with one or two copies	A
Recessive	Expressed only with two copies	a

Additional info: For equations related to genetics, the probability of a genotype in a monohybrid cross can be calculated using the Punnett square. For example, the probability of Aa offspring from Aa x Aa cross is:

$\text{P(Aa)} = \frac{1}{2}$