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 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.

Example: During bicep contraction, the sarcomeres shorten, pulling the forearm upward.

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 (thermogenesis).

Example: Shivering increases muscle activity to generate heat.

Types of Muscle Contractions

Muscle contractions can be classified based on movement and tension.

• Isotonic Contraction: Muscle changes length (movement occurs), tension remains constant.

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

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

Human Respiratory System

Significance and Mechanics of Breathing

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

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

• Lower Respiratory Structures: Trachea, bronchi, lungs; conduct air and facilitate gas exchange.

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

• Diaphragm: Main muscle for inspiration; contracts to increase thoracic volume.

Example: During inspiration, the diaphragm contracts, creating negative pressure in the lungs.

Blood Flow and Gas Exchange

Oxygen-rich blood is transported from the lungs to the heart and then to the body.

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

• Pressure Changes: Inhalation decreases lung pressure, drawing air in; exhalation increases pressure, pushing air out.

Example: Oxygen enters alveoli, diffuses into capillaries, and is carried by hemoglobin.

Respiratory Diseases and Disorders

Various diseases affect the respiratory system, impacting breathing and gas exchange.

• Asthma: Inflammation and narrowing of airways.

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

• Pneumonia: Infection of lung tissue.

Example: Asthma attacks cause difficulty in breathing due to constricted airways.

Human Digestive System

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; produce enzymes and bile for digestion.

• Enzymes: Biological catalysts produced in salivary glands, stomach, pancreas, and small intestine.

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

Example: Pancreatic amylase digests carbohydrates in the small intestine.

Metabolic Rates and Nutrition

Metabolic rates measure energy expenditure; nutrition guidelines help maintain health.

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

• Standard Metabolic Rate: Energy used under standard conditions.

• "My Plate": USDA guideline for balanced nutrition.

Example: BMR is higher in individuals with more muscle mass.

Digestion Processes

Digestion involves mechanical and chemical breakdown of food.

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

• Enzyme Function: Enzymes break down carbohydrates, proteins, and fats.

Example: Peristalsis moves food from the esophagus to the stomach.

Human Genetics and Inheritance

Basic Concepts and Structures

Genetics studies heredity and variation in organisms. Genes and chromosomes are central to inheritance.

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

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

Example: Down syndrome is detected by karyotyping.

Genotype, Phenotype, and Punnett Squares

Genotype refers to genetic makeup; phenotype is the observable trait. Punnett Squares predict inheritance patterns.

• Genotype: Combination of alleles (e.g., AA, Aa, aa).

• Phenotype: Physical expression of genotype.

• Punnett Square: Diagram used to predict offspring genotypes.

Example: Crossing Aa x Aa yields 1:2:1 genotype ratio.

Alleles and Laws of Inheritance

Alleles can be dominant or recessive, influencing trait expression. Mendel's laws govern inheritance.

• Dominant Allele: Expressed when present (e.g., A).

• Recessive Allele: Expressed only when homozygous (e.g., aa).

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes on different chromosomes assort independently.

Example: Brown eyes (dominant) vs. blue eyes (recessive).

Patterns of Inheritance

Traits can be inherited in various ways, including incomplete dominance, codominance, polygenic inheritance, and sex-linkage.

• 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).

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

• Linked Genes: Genes close together on a chromosome tend to be inherited together.

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

Example: Hemophilia is a sex-linked disorder.

Environmental Impact and New Allele Combinations

Environment can influence phenotypic expression, and meiosis creates new allele combinations.

• Environmental Impact: Nutrition, temperature, and other factors can affect traits.

• Meiosis: Crossing over and independent assortment generate genetic diversity.

Example: Identical twins may have different phenotypes due to environmental factors.

Sample Table: Types of Inheritance

Type	Genotype	Phenotype
Dominant/Recessive	AA, Aa, aa	Dominant trait (AA, Aa), Recessive trait (aa)
Incomplete Dominance	RR, RW, WW	Red (RR), Pink (RW), White (WW)
Codominance	AB	Both traits expressed (e.g., AB blood type)
Polygenic	Multiple genes	Continuous variation (e.g., height)

Sample Equation: Mendelian Probability

Probability of a recessive phenotype in a monohybrid cross:

$P = \frac{1}{4}$

Additional info: Academic context and examples were added to clarify concepts and provide self-contained explanations.