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

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system relies on specialized cells called muscle fibers that contract to produce movement. The sliding filament mechanism is central to muscle contraction.

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

• Actin and Myosin: Proteins that interact to produce contraction. Myosin heads bind to actin, pulling the filaments past each other.

• Sliding Filament Theory: Muscle contraction occurs as myosin heads attach to actin, forming cross-bridges and pulling actin filaments inward.

• Order of Events: Nerve impulse → Action potential in motor neuron → Release of neurotransmitter (acetylcholine) → Depolarization of muscle cell membrane → Calcium release from sarcoplasmic reticulum → Cross-bridge formation → Contraction.

• Electrical Impulses: Action potentials trigger calcium release, which enables contraction.

• Heat Generation: Most body heat is generated by muscle activity, especially during contraction.

Muscle Groups and Functions

• Major Muscle Groups: Include biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and gluteals.

• Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (movement occurs).

• Isometric Contraction: Muscle length remains the same (no movement, but tension increases).

• Function: Isotonic produces movement; isometric stabilizes joints and maintains posture.

Sarcomere Substructures

• Z-line: Defines the boundaries of a sarcomere.

• A-band: Contains the length of the myosin filaments.

• I-band: Contains only actin filaments.

• H-zone: Central region with only myosin.

Key Terms and Functions

• Action Potential: Electrical signal that triggers muscle contraction.

• Motor Neuron: Nerve cell that initiates muscle contraction.

Example: During running, quadriceps contract isotonicly to extend the knee, while abdominal muscles contract isometrically to stabilize the torso.

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen to tissues and removing carbon dioxide.

• Oxygen Transport: Oxygen-rich blood is pumped from the lungs to the heart, then distributed to the body.

• Importance: Cellular respiration requires oxygen; carbon dioxide must be expelled to maintain pH balance.

Structures of the Respiratory System

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, and larynx. Functions: filter, warm, and humidify air.

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

Mechanics of Breathing

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

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

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

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, pneumonia, emphysema.

• Impact: Affect airflow, gas exchange, and overall health.

Blood Flow Through the Heart

• Order: Pulmonary veins → Left atrium → Left ventricle → Aorta → Body tissues → Right atrium → Right ventricle → Pulmonary artery → Lungs.

Example: During exercise, increased breathing rate enhances oxygen delivery and carbon dioxide removal.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

• Major Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

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

• Function: Each organ contributes to digestion, absorption, or excretion.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion. Examples: amylase (saliva), pepsin (stomach), lipase (pancreas).

• Production Sites: Salivary glands, stomach, pancreas, small intestine.

Surface Area and Digestion

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

Metabolic Rates

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

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

"My Plate" Purpose

• My Plate: A guide for balanced nutrition, emphasizing proper proportions of food groups.

Digestion of Molecules and Peristalsis

• Digestion: Carbohydrates, proteins, and fats are broken down by specific enzymes in different digestive organs.

• Peristalsis: Rhythmic contractions of smooth muscle that propel food through the digestive tract.

Example: After eating, peristalsis moves food from the esophagus to the stomach, where pepsin begins protein digestion.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Genetics is the scientific study of heredity and variation in organisms.

• Gene: A segment of DNA encoding a specific trait.

• Chromosome: DNA molecule with associated proteins, carrying many genes.

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

• Homologous Chromosomes: Chromosome pairs with the same gene sequence, one from each parent.

Karyotype, Genotype, and Phenotype

• Karyotype: Visual representation of chromosomes, used to detect abnormalities.

• Genotype: Genetic makeup of an organism (allele combination).

• Phenotype: Observable traits resulting from genotype and environment.

Punnett Square and Alleles

• Punnett Square: Diagram used to predict genetic crosses.

• Alleles: Variants of a gene; can be dominant or recessive.

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

• Heterozygous: Two different alleles (e.g., Aa).

Laws of Genetics

• Law of Segregation: Each parent passes one allele for each gene to offspring.

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

Dominant and Recessive Alleles

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

• Recessive Allele: Expressed only when homozygous (e.g., aa).

• Lethal Dominant Disorders: Often eliminated quickly; recessive disorders can persist as carriers are unaffected.

Complex Patterns of Inheritance

• 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).

• Environmental Impact: Phenotype can be influenced by environment (e.g., nutrition, temperature).

Linked Genes and Meiosis

• 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: Located on sex chromosomes (X or Y); often affect males more.

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

Punnett Square Table Example

Parent Genotype	Offspring Genotype	Offspring Phenotype
AA x aa	All Aa	All dominant trait
Aa x Aa	AA, Aa, aa	Dominant and recessive traits
Aa x aa	Aa, aa	Dominant and recessive traits

Example: In humans, brown eyes (B) are dominant to blue eyes (b). A cross between Bb and bb parents yields 50% Bb (brown) and 50% bb (blue) offspring.

Additional info: Polygenic traits such as height are influenced by multiple genes and environmental factors.