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

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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 pull the actin filaments inward, causing contraction.
Function of Sarcomere: To generate force and shorten during muscle contraction.

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

Action Potentials and Muscle Contraction

Muscle contraction is initiated by electrical impulses called action potentials, which travel from motor neurons to muscle fibers.

Action Potential: A rapid change in membrane potential that travels along neurons and muscle cells.
Initiation: Motor neuron releases neurotransmitter (acetylcholine) at the neuromuscular junction, triggering an action potential in the muscle cell membrane.
Calcium Release: Action potential causes the sarcoplasmic reticulum to release Ca2+ ions, enabling actin-myosin interaction.
Order of Events: Nerve impulse → Acetylcholine release → Muscle action potential → Ca2+ release → Cross-bridge formation → Contraction.

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

Muscle Types of Contraction

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).

Muscle Groups and Body Cavities

Major Muscle Groups: Deltoids, pectorals, biceps, triceps, quadriceps, hamstrings, gluteals, 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 metabolic waste product.

Oxygen: Essential for ATP production in cells.
CO2 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 alveoli, site of gas exchange.

Mechanics of Breathing

Inhalation (Inspiration): Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, causing air to flow in.
Exhalation (Expiration): Diaphragm and intercostal muscles relax, decreasing thoracic volume and increasing lung pressure, pushing air out.
Pressure Changes: Air moves from high to low pressure; during inhalation, lung pressure < atmospheric pressure; during exhalation, lung pressure > 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 from lungs → pulmonary veins → left atrium → left ventricle → aorta → body tissues.

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: Secretes acid and enzymes; churns food into chyme.
Small Intestine: Main site of nutrient 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

Function: Enzymes break down macromolecules into absorbable units (e.g., amylase for starch, proteases for proteins, lipases for fats).
Production Sites: Salivary glands, stomach, pancreas, small intestine.

Surface Area and Digestion

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

Metabolic Rates

Basal Metabolic Rate (BMR): Energy expended at rest to maintain vital functions.
Standard Metabolic Rate (SMR): Energy expenditure under standardized conditions (often used in animal studies).

Nutrition Guidelines

"My Plate": A visual guide 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.
Molecule Digestion: Carbohydrates, proteins, and fats are digested in specific regions by specialized enzymes.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Gene: A segment of DNA that codes for a specific protein or trait.
Chromosome: A structure composed of DNA and proteins; 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 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).

Punnett Squares and Mendelian Laws

Punnett Square: A diagram used to predict the outcome of genetic crosses.
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 two copies are present (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).
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: Environmental factors can influence gene expression (phenotype).

Term	Definition	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, or aa
Phenotype	Observable trait	Brown eyes
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed when present	A in Aa
Recessive	Expressed only when homozygous	a in aa

Key Equations

Mendelian Probability:

Hardy-Weinberg Equation:

where p and q are the frequencies of two alleles in a population.

Additional info: Some explanations and examples have been expanded for clarity and completeness, based on standard college-level Human Biology content.