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 functional unit of muscle fibers, composed of actin (thin) and myosin (thick) filaments.

• Actin and Myosin Filaments: Actin provides the track for myosin heads to attach and pull, causing contraction.

• Sliding Mechanism: Myosin heads bind to actin, forming cross-bridges, and pull the actin filaments inward, shortening the sarcomere.

• Function of Sarcomere: Responsible for muscle contraction and force generation.

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

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

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential that triggers muscle contraction.

• Order of Events:

  1. Motor neuron releases neurotransmitter (acetylcholine).

  2. Muscle cell membrane depolarizes, generating an action potential.

  3. Calcium ions are released from the sarcoplasmic reticulum.

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

  5. Myosin binds to actin, causing contraction.

• Heat Generation: Most body heat is generated by muscle activity.

Types of Muscle Contractions

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

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

Summary Table: Muscle Contraction Types

Type	Length Change	Movement
Isotonic	Yes	Yes
Isometric	No	No

Key Formula

Muscle force is proportional to the number of cross-bridges formed:

$F \propto n_{cross-bridges}$

Human Respiratory System

Significance of Breathing

Breathing is essential for oxygen intake and carbon dioxide removal, supporting cellular respiration and energy production.

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

• Respiratory Diseases: Includes asthma, bronchitis, pneumonia, and others.

Structures of the Respiratory System

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, larynx. Functions: air filtration, humidification, and vocalization.

• Lower Respiratory System: Includes trachea, bronchi, lungs, alveoli. Functions: gas exchange, air conduction.

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.

Blood Flow Through the Heart

• Order of Flow:

  1. Oxygen-rich blood enters left atrium from lungs.

  2. Moves to left ventricle.

  3. Pumped out to body via aorta.

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.

• Accessory Organs: Liver, pancreas, gallbladder.

• Function of Enzymes: Catalyze breakdown of macromolecules; produced in salivary glands, stomach, pancreas, small intestine.

• Large Surface Area: Increases absorption efficiency (e.g., villi in small intestine).

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.

Digestion Mechanics

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

• Molecule Digestion: Carbohydrates, proteins, and fats are digested in specific regions by specific enzymes.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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

• Gene: Segment of DNA coding for a trait.

• Chromosome: Structure carrying genes; humans have 23 pairs.

• Genome: Complete set of genetic material.

• 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.

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Tool to predict genetic outcomes.

• 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 are inherited independently.

Dominance, Codominance, and Polygenic Inheritance

• Dominant Allele Disorders: Can be lethal if expressed.

• Recessive Disorders: May persist due to carriers.

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

Environmental Impact and Linked Genes

• Environment: Can affect phenotypic expression.

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

• New Allele Combinations: Occur during meiosis via crossing over.

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.

Summary Table: Dominance Relationships

Type	Phenotype in Heterozygote
Dominant	Dominant trait expressed
Recessive	Recessive trait expressed only if homozygous
Incomplete Dominance	Intermediate phenotype
Codominance	Both traits fully expressed

Key Formula

Probability of trait inheritance (simple Mendelian):

$P = \frac{n_{desired}}{n_{total}}$

Example: In a cross between two heterozygotes (Aa x Aa), the probability of offspring being homozygous recessive (aa) is $\frac{1}{4}$.