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 and generate heat. 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 in motor neuron → Release of neurotransmitter (acetylcholine) → Muscle cell depolarization → Calcium release → Actin-myosin interaction → Contraction.

• Electrical Impulses: Action potentials trigger calcium release from the sarcoplasmic reticulum, enabling contraction.

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

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

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

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

Example: Lifting a weight is isotonic; holding a weight steady is isometric.

Sarcomere Substructures and Functions

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

• M-line: Center of the sarcomere, anchors myosin.

• I-band: Contains only actin filaments.

• A-band: Contains both actin and myosin.

Function: Sarcomeres contract to produce movement.

Action Potential in Motor Neuron

• Action Potential: Electrical signal generated by ion movement across neuron membranes.

• Initiation: Triggered by neurotransmitter release and depolarization.

Formula:

$\Delta V = IR$ (Ohm's Law, relates voltage change to current and resistance in neurons)

Human Respiratory System

Significance of Breathing

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

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

• Respiratory Structures:

  • Upper Respiratory: Nose, pharynx, larynx – filter, warm, and humidify air.

  • Lower Respiratory: Trachea, bronchi, lungs – conduct air and enable gas exchange.

• Intercostal Muscles: Located between ribs; contract during inhalation to expand chest cavity.

• Diaphragm: Contracts and flattens during inhalation, increasing thoracic volume.

• Pressure Changes:

  • Inhalation: Lung pressure decreases, air enters.

  • Exhalation: Lung pressure increases, air exits.

• Mechanics of Inspiration: Diaphragm and intercostal muscles contract, chest expands.

• Mechanics of Expiration: Muscles relax, chest contracts, air is expelled.

Formula:

$P_1V_1 = P_2V_2$ (Boyle's Law: pressure and volume relationship in lungs)

Respiratory Diseases and Disorders

• Asthma: Inflammation and narrowing of airways.

• Emphysema: Damage to alveoli, reduced gas exchange.

• Pneumonia: Infection of lung tissue.

• Chronic Obstructive Pulmonary Disease (COPD): Progressive airflow limitation.

Oxygen-Rich Blood Flow Through the Heart

• Oxygenated blood from lungs → 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.

  • Gallbladder: Stores bile.

  • Pancreas: Produces digestive enzymes.

Enzymes in Digestion

• Function: Catalyze breakdown of macromolecules.

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

Surface Area in Digestion

• Large Surface Area: Villi and microvilli in small intestine increase absorption efficiency.

Metabolic Rates

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

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

"My Plate" Purpose

• My Plate: Visual guide 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 of smooth muscle 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 trait.

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

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

• Homologous Chromosomes: Paired chromosomes with same genes, possibly different alleles.

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (allele combination).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram to predict genetic crosses.

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

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Law of Segregation and Law of Independent Assortment

• 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: Expressed when present.

• Recessive: Expressed only when homozygous.

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

Incomplete Dominance, Codominance, and 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, Sex-Linked Genes, and Nondisjunction

• Meiosis: Process creating gametes; new allele combinations arise via crossing over.

• Sex-Linked Genes: Located on sex chromosomes; often affect males more.

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

Example: Down syndrome results from nondisjunction of chromosome 21.

Term	Definition
Genotype	Genetic makeup of an organism
Phenotype	Observable traits
Homozygous	Two identical alleles
Heterozygous	Two different alleles
Dominant	Allele expressed when present
Recessive	Allele expressed only when homozygous
Incomplete Dominance	Intermediate phenotype in heterozygotes
Codominance	Both alleles fully expressed
Polygenic Inheritance	Trait controlled by multiple genes

Formula:

$\text{Probability of trait} = \frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}}$

Additional info: Academic context and definitions were expanded for clarity and completeness.