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 when myosin heads attach to actin and pull, shortening the sarcomere.

• Substructures: Includes Z-lines, M-line, A-band, I-band, and H-zone, each with specific roles in contraction.

• Function: Sarcomeres shorten during contraction, generating force.

Example: During biceps contraction, sarcomeres in muscle fibers shorten, causing the arm to bend.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical signals called action potentials.

• Motor Neuron: Sends an action potential to the muscle fiber, triggering contraction.

• Order of Events:

  1. Action potential arrives at neuromuscular junction.

  2. Acetylcholine is released, depolarizing the muscle membrane.

  3. Electrical impulse travels along the sarcolemma and into T-tubules.

  4. Calcium ions are released from the sarcoplasmic reticulum.

  5. Calcium binds to troponin, exposing binding sites on actin.

  6. Myosin binds to actin, contraction occurs.

Example: The knee-jerk reflex involves rapid action potential transmission and muscle contraction.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant. Produces movement.

• Isometric Contraction: Muscle tension increases, but length does not change. No movement occurs.

Example: Lifting a weight (isotonic); holding a weight steady (isometric).

Muscle Groups and Functions

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

• Body Heat Generation: Muscular system is the primary source of body heat due to energy released during contraction.

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

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 in filtering, warming, and humidifying air.

• Lower Respiratory System: Includes trachea, bronchi, lungs. Functions in gas exchange.

Example: The nasal cavity filters dust and pathogens from inhaled air.

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.

Blood Flow and Gas Exchange

• Oxygen-rich Blood: Flows from lungs to left atrium, then left ventricle, then systemic circulation.

• Order of Flow: Pulmonary veins → left atrium → left ventricle → aorta → body tissues.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia, tuberculosis.

• Impact: Affect gas exchange and breathing efficiency.

Human Digestive System

Major Structures and Functions

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for nutrient absorption.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores and releases bile.

• Pancreas: Produces digestive enzymes and hormones.

Enzymes and Digestion

• Function: Catalyze breakdown of macromolecules.

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

Example: Amylase breaks down starch in the mouth.

Surface Area and 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.

Example: BMR is measured after fasting and rest.

"My Plate" Purpose

• Guideline: Promotes balanced nutrition and healthy eating habits.

Digestion Process and Peristalsis

• Peristalsis: Wave-like muscle contractions move food through digestive tract.

• Digestion: Breakdown of carbohydrates, proteins, fats by enzymes.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

• 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 but possibly different alleles.

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (alleles present).

• Phenotype: Observable traits.

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.

• Heterozygous: Two different alleles.

Genetic Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Dominant and Recessive Disorders

• Dominant Disorders: Expressed with one dominant allele; can be lethal.

• Recessive Disorders: Expressed only with two recessive alleles; can persist in populations.

Complex Patterns of Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can affect phenotypic expression.

Linked Genes and Meiosis

• Linked Genes: Genes located close together on a 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; often affect males more.

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

Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Dominant	AA or Aa	Dominant trait expressed	Huntington's disease
Recessive	aa	Recessive trait expressed	Cystic fibrosis
Incomplete Dominance	Aa	Intermediate phenotype	Red and white flowers produce pink
Codominance	AB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Height, skin color

Additional info: Table entries inferred for completeness and clarity.