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, defined by the area between two Z-lines.

• Actin Filaments: Thin filaments that interact with myosin for contraction.

• Myosin Filaments: Thick filaments with heads that bind to actin, pulling them to shorten the sarcomere.

• Sliding Mechanism: Myosin heads attach to actin, forming cross-bridges and pulling actin filaments inward, causing muscle contraction.

• Function of Sarcomere: To generate force and shorten during contraction, enabling movement.

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

Action Potentials and Muscle Contraction

• Action Potential: An electrical signal generated in a motor neuron that triggers muscle contraction.

• Mechanism: The action potential travels down the neuron, causing the release of neurotransmitter (acetylcholine) at the neuromuscular junction, which initiates an electrical impulse in the muscle cell.

• Order of Events:

  1. Motor neuron releases acetylcholine.

  2. Muscle cell membrane depolarizes.

  3. Calcium ions are released from the sarcoplasmic reticulum.

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

  5. Myosin binds to actin, initiating contraction.

Example: Reflex actions, such as pulling your hand away from a hot object, involve rapid action potentials and muscle contractions.

Muscle Types of Contractions

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

• Isometric Contraction: Muscle length remains the same while tension increases. No movement occurs.

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

Muscle Groups and Body Cavities

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

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

Heat Generation

• Most body heat is generated by muscle activity, especially during shivering or exercise.

Human Respiratory System

Significance of Breathing

Breathing supplies oxygen for cellular respiration and removes carbon dioxide, a waste product of metabolism.

• Oxygen: Essential for ATP production in cells.

• Carbon Dioxide Removal: Prevents acidification of body fluids.

Respiratory System Structures and Functions

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, and larynx. Functions in filtering, warming, and humidifying air.

• Lower Respiratory System: Includes trachea, bronchi, bronchioles, and lungs. Functions in gas exchange.

Mechanics of Breathing

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

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

• Pressure Changes: Air flows from high to low pressure; during inhalation, lung pressure is lower than atmospheric pressure.

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

Blood Flow and Gas Exchange

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

Respiratory Diseases and Disorders

• Common disorders include asthma, bronchitis, pneumonia, emphysema, and lung cancer.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins here.

• Esophagus: Transports food to the stomach via peristalsis.

• Stomach: Mixes food with gastric juices for protein digestion.

• Small Intestine: Main site for digestion and absorption; large surface area due to villi and microvilli.

• Large Intestine: Absorbs water and forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores and releases bile.

• Pancreas: Produces digestive enzymes and bicarbonate.

Enzymes and Digestion

• Enzymes break down carbohydrates, proteins, and fats into absorbable units. Produced in the mouth, stomach, pancreas, and small intestine.

Surface Area in Digestion

• Large surface area (villi, microvilli) in the small intestine increases nutrient absorption efficiency.

Metabolic Rates

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

• Standard Metabolic Rate (SMR): Energy expenditure under standardized conditions.

"My Plate"

• Guideline for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion Process and Peristalsis

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Chromosome: Structure made of DNA and proteins; humans have 23 pairs.

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

Genetics and Inheritance

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

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

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

• Karyotype: A visual display of all chromosomes in a cell, used to detect chromosomal abnormalities.

Punnett Squares and Patterns of Inheritance

• Punnett Square: A tool to predict the probability of offspring genotypes and phenotypes.

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

• Recessive Allele: Expressed only if both alleles are recessive (e.g., aa).

• 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 separate during gamete formation.

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

Non-Mendelian Inheritance

• Incomplete Dominance: Heterozygote shows 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 trait (e.g., skin color).

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

Linked Genes and Genetic Variation

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

• New Allele Combinations: Crossing over during meiosis creates new combinations of alleles.

Sex-Linked Genes and Nondisjunction

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y), often affecting traits like color blindness.

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

Genetic Disorders

• Some dominant allele disorders are lethal (e.g., Huntington's disease), while some recessive disorders persist due to carriers (e.g., cystic fibrosis).

Sample Punnett Square Table

	A	a
A	AA	Aa
a	Aa	aa

Purpose: Predicts offspring genotypes from parental alleles.

Key Equations

• Probability of genotype (for monohybrid cross): $P = \frac{\text{Number of desired genotype}}{\text{Total number of possible genotypes}}$

Additional info: This guide expands on the review points by providing definitions, examples, and context for each concept, ensuring a comprehensive understanding suitable for exam preparation.