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 thin filaments; myosin forms 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.

Muscle Contraction Mechanism

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

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

• Order of Events:

  1. Action potential travels down motor neuron.

  2. Acetylcholine is released into synaptic cleft.

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

  4. Calcium ions are released from the sarcoplasmic reticulum.

  5. Calcium binds to troponin, shifting tropomyosin and exposing actin binding sites.

  6. Myosin heads bind to actin, performing a power stroke (sliding filaments).

  7. ATP binds to myosin, causing detachment and resetting the cycle.

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

Types of Muscle Contractions

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

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

Major Muscle Groups and Functions

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

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

Key Molecules and Structures

• Calcium Ions (Ca2+): Released from the sarcoplasmic reticulum, essential for contraction.

• Sarcoplasmic Reticulum: Organelle that stores and releases calcium ions.

Example:

During a biceps curl, the biceps brachii contracts (isotonic contraction), shortening the muscle and moving the forearm.

Human Respiratory System

Significance of Breathing

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

• Oxygen: Essential for ATP production in mitochondria.

• Carbon Dioxide Removal: Prevents acidification of body fluids.

Structures of the Respiratory System

• Upper Respiratory Tract: Includes nose, nasal cavity, pharynx, and larynx. Functions: filters, warms, and humidifies air; protects lower tract.

• Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, and lungs. Functions: conducts air to alveoli, site of 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 drops below atmospheric pressure.

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

Blood Flow and Gas Exchange

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

• Practice: Trace blood flow: pulmonary veins → left atrium → left ventricle → aorta → body tissues.

Respiratory Diseases and Disorders

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

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

Example:

During exercise, breathing rate increases to supply more oxygen and remove more carbon dioxide.

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: produce enzymes, bile, and other substances for digestion.

Enzymes and Digestion

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

• Function: Speed up chemical reactions, allowing efficient nutrient absorption.

Surface Area and Digestion

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

Example:

Amylase from saliva begins starch digestion in the mouth; peristalsis moves the bolus to the stomach.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

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

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

• Genetics: The scientific study of heredity and variation.

Homologous Chromosomes and Karyotypes

• Homologous Chromosomes: Chromosome pairs (one from each parent) with genes for the same traits.

• 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).

Punnett Squares and Alleles

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

• Alleles: Different forms of a gene (dominant or recessive).

• 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.

Patterns of Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., red x white = pink).

• 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, temperature).

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 genetic diversity.

Sex-Linked Genes and Nondisjunction

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y), often affecting males more (e.g., hemophilia).

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

Example:

A Punnett square can predict the probability of a child inheriting cystic fibrosis (recessive disorder) if both parents are carriers (heterozygous).

Sample Table: Types of Inheritance

Type	Description	Example
Mendelian (Dominant/Recessive)	One allele masks the other	Widow's peak hairline
Incomplete Dominance	Intermediate phenotype	Snapdragon flower color
Codominance	Both alleles expressed	AB blood type
Polygenic	Multiple genes affect trait	Skin color, height
Sex-linked	Gene on X or Y chromosome	Color blindness

Key Equations

• Probability of Inheritance (Punnett Square):

$P = \frac{\text{Number of desired outcomes}}{\text{Total possible outcomes}}$

• Basal Metabolic Rate (BMR):

$BMR = 70 \times (\text{body weight in kg})^{0.75}$

Additional info: Equations and table added for academic completeness.