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

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system enables movement, posture, and heat production. Muscle contraction is based on the sliding filament mechanism within muscle cells (fibers).

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

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

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

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

• 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.

Muscle Contraction Mechanism

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

• Neuromuscular Junction: The synapse where a motor neuron communicates with a muscle fiber, releasing neurotransmitter (acetylcholine) to initiate contraction.

• Order of Events:

  1. Action potential travels down motor neuron.

  2. Acetylcholine released into synaptic cleft.

  3. Muscle fiber membrane depolarizes.

  4. Calcium ions released from sarcoplasmic reticulum.

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

  6. Myosin heads bind to actin, pulling filaments (power stroke).

  7. ATP binds to myosin, releasing it from actin and resetting the cycle.

• Heat Generation: Most body heat is generated by muscle contractions (shivering thermogenesis).

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

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

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant; produces movement (e.g., lifting a weight).

• Isometric Contraction: Muscle length remains the same while tension increases; no movement occurs (e.g., holding a weight steady).

Table: Comparison of Isotonic and Isometric Contractions

Type	Muscle Length Change	Movement Produced
Isotonic	Yes	Yes
Isometric	No	No

Human Respiratory System

Significance of Breathing

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

• Oxygen: Essential for aerobic metabolism 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: filters, warms, and humidifies air; provides resonance for speech.

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

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 drops below atmospheric pressure.

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

Equation: Boyle's Law (relationship between pressure and volume):

$P_1 V_1 = P_2 V_2$

Blood Flow and Gas Exchange

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

• Gas Exchange: Occurs in alveoli by diffusion.

Respiratory Diseases and Disorders

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

• Impact: Affect airflow, gas exchange, or lung tissue.

Human Digestive System

Major Structures and Functions

• Main Organs: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

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

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

Enzymes and Digestion

• Digestive Enzymes: Proteins that catalyze breakdown of food molecules; produced in salivary glands, stomach, pancreas, and small intestine.

• Examples: Amylase (carbohydrates), pepsin (proteins), lipase (fats).

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): Energy expended at rest to maintain vital functions.

• Standard Metabolic Rate (SMR): Metabolic rate under standardized conditions (e.g., specific temperature, fasting).

Nutrition and "My Plate"

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

Digestion Process and Peristalsis

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

• 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 functional RNA.

• Chromosome: A structure of DNA and protein carrying genetic information; humans have 23 pairs.

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

• Genetics: The scientific study of heredity and variation.

Homologous Chromosomes and Karyotypes

• 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 resulting from the genotype and environment.

Punnett Squares and Mendelian Laws

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

• 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.

Alleles and Patterns of Inheritance

• Dominant Allele: Expressed when present (e.g., AA or Aa).

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

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

• Heterozygous: Two different alleles (Aa).

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., pink flowers from red and white parents).

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

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

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

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

Genetic Disorders and Variation

• Lethal Dominant Disorders: Rare because affected individuals often die before reproducing.

• Recessive Disorders: Can persist in populations because carriers (heterozygotes) 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 during meiosis creates genetic diversity.

• Environmental Impact: Environment can influence gene expression (phenotype).

Table: Mendelian vs. Non-Mendelian Inheritance Patterns

Pattern	Description	Example
Mendelian (Simple Dominance)	One allele is dominant over the other	Widow's peak hairline
Incomplete Dominance	Heterozygote is intermediate	Pink snapdragon flowers
Codominance	Both alleles expressed	AB blood type
Polygenic	Multiple genes affect trait	Skin color
Sex-linked	Gene on X or Y chromosome	Color blindness

Example: A Punnett square can predict the probability of offspring inheriting a genetic disorder.

Equation: Probability of genotype (for a 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, mechanisms, and examples for each major topic, suitable for exam preparation in Human Biology.