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 actin filaments inward, causing contraction.
Function of Sarcomere: Facilitates muscle contraction through the coordinated sliding of actin and myosin.

Example: During biceps contraction, sarcomeres shorten as actin and myosin slide past each other.

Action Potentials and Muscle Contraction

Muscle contraction is initiated by electrical impulses called action potentials, which originate in motor neurons.

Action Potential: A rapid change in membrane potential that travels along neurons and muscle fibers.
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+, enabling actin-myosin interaction.
Order of Events: Nerve impulse → Acetylcholine release → Muscle action potential → Ca2+ release → Cross-bridge formation → Contraction.

Example: Reflex actions involve rapid transmission of action potentials to muscles.

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).

Example: Holding a plank position involves isometric contraction; walking involves isotonic contraction.

Muscle Groups and Body Cavities

Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, gluteals, 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, 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 < 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: Pulmonary veins → Left atrium → Left ventricle → Aorta → Systemic circulation.
Gas Exchange: Occurs in alveoli; O2 diffuses into blood, CO2 diffuses out.

Respiratory Diseases and Disorders

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

Human Digestive System

Major Structures and Functions

Mouth: Mechanical and chemical digestion begins here.
Esophagus: Transports food to stomach via peristalsis.
Stomach: Secretes acid and enzymes; churns food.
Small Intestine: Main site of 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

Function: Enzymes break down macromolecules into absorbable units.
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.
Standard Metabolic Rate (SMR): Energy expenditure under standardized conditions.

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 specific enzymes.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Gene: A segment of DNA that codes for a protein or functional RNA.
Chromosome: DNA molecule with associated proteins; humans have 23 pairs.
Genome: The complete set of genetic material in an organism.

Genetics Terminology

Genotype: The genetic makeup of an individual (e.g., AA, Aa, aa).
Phenotype: Observable traits resulting from genotype and environment.
Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.
Karyotype: Visual representation of all chromosomes in a cell; used to detect chromosomal abnormalities.

Inheritance Patterns

Punnett Square: Tool to predict genetic crosses and offspring genotypes.
Dominant Allele: Expressed when present (e.g., A).
Recessive Allele: Expressed only when homozygous (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 segregate during gamete formation.
Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

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: Phenotype can be influenced by environmental factors (e.g., nutrition, sunlight).

Linked Genes and Genetic Variation

Linked Genes: Genes located close together on the same chromosome; tend to be inherited together.
New Allele Combinations: Crossing over during meiosis creates new allele combinations.

Sex-linked Genes and Chromosomal Disorders

Sex-linked Genes: Genes located on sex chromosomes (X or Y); often show different inheritance patterns in males and females.
Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers (e.g., Down syndrome).

Term	Definition	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, aa
Phenotype	Observable trait	Tall, short, blood type
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed allele	A in Aa
Recessive	Masked by dominant	a in Aa

Example: Cystic fibrosis is a recessive disorder; a person must inherit two defective alleles to express the disease.

Additional info: Some dominant allele disorders are lethal because a single copy of the mutated gene disrupts essential functions. Recessive disorders persist because carriers (heterozygotes) do not show symptoms and can pass the allele to offspring.