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 and structures 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 and pull, shortening the sarcomere.

• Order of Events: Nerve impulse → Action potential → Calcium release → Myosin-actin interaction → Contraction.

• Electrical Impulses: Action potentials in motor neurons trigger calcium release from the sarcoplasmic reticulum.

• Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, and others.

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

• Isotonic vs. Isometric Contractions: Isotonic contractions produce movement; isometric contractions generate tension without movement.

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

Example: During running, leg muscles contract isotonicly to move limbs, generating heat and enabling locomotion.

Sarcomere Substructures and Functions

• 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.

Function: The sarcomere shortens during contraction, producing force.

Action Potential and Muscle Contraction

• Action Potential: Electrical signal in motor neuron triggers muscle contraction.

• Calcium Release: Action potential causes calcium ions to be released, enabling myosin-actin interaction.

• Order of Events: Nerve impulse → Action potential → Calcium release → Contraction.

Types of Muscle Contractions

• Isotonic: Muscle changes length, movement occurs.

• Isometric: Muscle length remains the same, tension increases.

Example: Holding a weight steady is isometric; lifting it is isotonic.

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 to the body.

• Gas Exchange: Occurs in alveoli; oxygen enters blood, CO2 is expelled.

Structures of the Respiratory System

• Upper Respiratory Tract: Includes nose, pharynx, larynx; filters, warms, and moistens air.

• Lower Respiratory Tract: Includes trachea, bronchi, lungs; conducts air and facilitates gas exchange.

Example: The nose filters dust and pathogens from inhaled air.

Mechanics of Breathing

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

• 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

• Asthma: Inflammation and narrowing of airways.

• Emphysema: Damage to alveoli, reducing gas exchange.

• Pneumonia: Infection of lung tissue.

Blood Flow Through the Heart

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

Human Digestive System

Major Structures and Functions

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

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes; churns food.

• Small Intestine: Main site of nutrient absorption.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile, processes nutrients.

• Gallbladder: Stores bile.

• Pancreas: Produces digestive enzymes and hormones.

Enzymes and Digestion

• Function: Enzymes catalyze breakdown of macromolecules.

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

Example: Amylase breaks down starch in the mouth.

Surface Area in Digestion

• Importance: Increased surface area (villi, microvilli) enhances nutrient absorption.

Metabolic Rates

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

• Standard Metabolic Rate (SMR): Energy used under specific conditions.

• Equation: $BMR = \text{weight (kg)} \times \text{energy factor}$

"My Plate" Purpose

• Guideline: Visual tool for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion of Molecules and Peristalsis

• Digestion: Carbohydrates, proteins, and fats are broken down by specific enzymes.

• Peristalsis: Rhythmic contractions move food through the digestive tract.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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

• Gene: Segment of DNA coding for a protein.

• Chromosome: DNA molecule with associated proteins; humans have 23 pairs.

• Genome: Complete set of genetic material in an organism.

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pair of chromosomes with same genes, one from each parent.

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (alleles).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram predicting genetic crosses.

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

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Law of Segregation and Independent Assortment

• Law of Segregation: Alleles separate during gamete formation.

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

Dominant and Recessive Alleles

• Dominant: Expressed when present.

• Recessive: Expressed only when homozygous.

• Lethal Dominant Disorders: May cause early death, reducing prevalence.

• Recessive Disorders: Can persist if carriers are unaffected.

Incomplete Dominance, Codominance, Polygenic Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

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

Environmental Impact and Linked Genes

• Environment: Can affect phenotypic expression (e.g., nutrition, temperature).

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

Meiosis and New Allele Combinations

• Crossing Over: Exchange of genetic material during meiosis creates new allele combinations.

Sex-linked Genes and Nondisjunction

• Sex-linked Genes: Located on sex chromosomes; often affect males more (e.g., hemophilia).

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers in gametes.

Table: Comparison of Dominant vs. Recessive Alleles

Type	Expression	Example
Dominant	Expressed in heterozygotes	Huntington's disease
Recessive	Expressed only in homozygotes	Cystic fibrosis

Example: A Punnett Square can predict the probability of offspring inheriting a trait.

Additional info: Polygenic traits often show continuous variation, such as height or skin color.