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: Actin filaments provide the track, while myosin filaments use ATP to "walk" along actin, causing contraction.

• Sliding Filament Theory: Myosin heads bind to actin, pull, and release, shortening the sarcomere and thus the muscle.

• Order of Muscle Contraction: Nerve impulse → Action potential in motor neuron → Release of neurotransmitter (acetylcholine) → Action potential in muscle fiber → Calcium release from sarcoplasmic reticulum → Myosin-actin interaction → Contraction.

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

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

Example: During exercise, muscle contractions increase body temperature due to ATP hydrolysis.

Muscle Groups and Functions

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

• Muscles Sectioning 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).

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: Area with only myosin filaments.

Function of Sarcomere: Facilitates muscle contraction through the interaction of actin and myosin.

Action Potential in Motor Neuron

• Action Potential: Electrical signal generated by the movement of ions across the neuron's membrane.

• Neurotransmitter Release: Acetylcholine is released at the neuromuscular junction, triggering muscle contraction.

Summary Table: Muscle Contraction Types

Type	Muscle Length	Movement
Isotonic	Changes	Yes
Isometric	Constant	No

Human Respiratory System

Significance of Breathing

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

• Oxygen: Required for cellular respiration and energy production.

• Carbon Dioxide Removal: Prevents toxic buildup.

Respiratory System Structures

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

• Lower Respiratory System: Includes trachea, bronchi, 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

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

Blood Flow Through the Heart

• Oxygen-rich blood: Flows from lungs → left atrium → left ventricle → aorta → body.

• Oxygen-poor blood: Returns via veins → right atrium → right ventricle → lungs.

Respiratory Diseases and Disorders

• Examples: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food via peristalsis.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for nutrient absorption.

• Large Intestine: Water absorption and feces formation.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Pancreas: Secretes digestive enzymes and hormones.

• Gallbladder: Stores and releases bile.

Enzymes in Digestion

• Function: Catalyze breakdown of macromolecules.

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

Surface Area in Digestion

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

Metabolic Rates

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

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

My Plate

• Purpose: Dietary guideline for balanced nutrition.

Peristalsis

• Definition: Wave-like muscle contractions that move food through the digestive tract.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

• Gene: Segment of DNA coding for a trait.

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

• Genome: Complete set of genetic material.

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pair of chromosomes with same genes but possibly different alleles.

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (e.g., AA, Aa, aa).

• Phenotype: Observable traits.

Punnett Square

• Function: Predicts genetic outcomes of crosses.

Dominant and Recessive Alleles

• Dominant: Expressed if present (e.g., AA or Aa).

• Recessive: Expressed only if homozygous (aa).

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

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

• Environmental Impact: Environment can affect phenotypic expression.

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

• Definition: Genes located on sex chromosomes (X or Y).

• Example: Hemophilia is X-linked recessive.

Nondisjunction

• Definition: Failure of chromosomes to separate properly during meiosis.

• Impact: Results in abnormal chromosome numbers (e.g., Down syndrome).

Summary Table: Mendelian Inheritance Patterns

Pattern	Genotype	Phenotype
Dominant	AA, Aa	Dominant trait
Recessive	aa	Recessive trait
Incomplete Dominance	Aa	Intermediate
Codominance	AB	Both traits expressed

Example: A Punnett Square can be used to predict the probability of offspring inheriting a particular trait.

Additional info: For more detailed study, students should practice applying these concepts to real-world scenarios and genetic problems.