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 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: Facilitates muscle contraction by shortening during activation.

• 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 in motor neurons triggers muscle contraction.

• Order of Events:

  1. Motor neuron releases neurotransmitter (acetylcholine).

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

  3. Calcium ions released from sarcoplasmic reticulum.

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

  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).

• Function: Isotonic contractions produce movement; isometric contractions stabilize joints.

Example

• During lifting a weight, the biceps undergo isotonic contraction; holding a weight steady involves isometric contraction.

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 distributed to the body.

• Importance: Cellular respiration requires oxygen; removal of CO2 prevents toxicity.

Structures of the Respiratory System

• 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, decreasing lung pressure, air flows in.

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air flows out.

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

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

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, pneumonia, emphysema.

• Impact: Affect airflow, gas exchange, and overall health.

Example

• During exercise, breathing rate increases to supply more oxygen and remove excess CO2.

Human Digestive System

Major Structures and Functions

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

• Main Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum.

• Accessory Organs: Liver, pancreas, gallbladder. Functions: produce enzymes, bile, and aid digestion.

Enzymes and Digestion

• Function: Enzymes catalyze breakdown of macromolecules.

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

Surface Area and Digestion

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

Metabolic Rates

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

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

• Equation: $\text{BMR} = \text{Energy expenditure at rest}$

"My Plate" Purpose

• Purpose: Guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion Process and Peristalsis

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

• Digestion: Chemical and mechanical breakdown of food into absorbable molecules.

Example

• Carbohydrates are digested by amylase in the mouth and pancreas; proteins by pepsin in the stomach.

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

• Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Genotype and Phenotype

• Genotype: Genetic makeup (alleles).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram to predict genetic crosses.

• Dominant Allele: Expressed trait when present.

• Recessive Allele: Expressed only when homozygous.

• 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.

Inheritance Patterns

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

• Sex-linked Genes: Genes on sex chromosomes, often X-linked.

Meiosis and Allele Combinations

• New Combinations: Crossing over during meiosis creates genetic diversity.

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

Example Table: Dominant vs. Recessive Alleles

Allele Type	Expression	Example
Dominant	Expressed in heterozygous and homozygous	Brown eyes (B)
Recessive	Expressed only in homozygous	Blue eyes (b)

Example

• Hemophilia is a sex-linked recessive disorder; sickle cell anemia shows codominance.