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: Actin filaments provide sites for myosin heads to attach and pull, causing contraction. Myosin filaments have heads that bind to actin and use ATP to generate force.

• Sliding Filament Theory: Myosin heads attach to actin, pull, and release, causing the sarcomere to shorten and the muscle to contract.

• Muscle Unit Structures: Includes sarcolemma (cell membrane), sarcoplasmic reticulum (stores calcium), and T-tubules (transmit action potentials).

Example: During contraction, calcium ions are released from the sarcoplasmic reticulum, enabling myosin to bind to actin.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential that travels along the neuron and muscle cell.

• Order of Events: Motor neuron releases acetylcholine → action potential in muscle cell → calcium release → contraction.

• Electrical Impulses: Cause release of neurotransmitters and calcium ions, triggering contraction.

Example: The neuromuscular junction is where the motor neuron communicates with the muscle fiber.

Muscle Groups and Body Cavities

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

• 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).

Example: Lifting a weight is isotonic; holding a weight steady is isometric.

Heat Generation

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

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: Waste product that must be expelled.

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, alveoli. 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: Assist in expanding and contracting the rib cage during breathing.

Blood Flow and Oxygen Transport

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

Respiratory Diseases and Disorders

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

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: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile, processes nutrients.

• Gallbladder: Stores bile.

• Pancreas: Produces digestive enzymes and hormones.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion. Produced in salivary glands, stomach, pancreas, small intestine.

• Function: Break down carbohydrates, proteins, fats.

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.

Example: BMR is measured after fasting and rest; SMR may be measured during activity.

"My Plate" Purpose

• My Plate: A guide for balanced nutrition, emphasizing proper proportions of food groups.

Peristalsis

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

• Genome: Complete set of genetic material.

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pairs with same genes but possibly different alleles.

• 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.

• Alleles: Variants of a gene; can be dominant or recessive.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Mendelian 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.

Non-Mendelian Inheritance

• 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 (e.g., nutrition, temperature).

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

Meiosis and New Allele Combinations

• Meiosis: Produces gametes; crossing over creates new allele combinations.

Sex-linked Genes and Nondisjunction

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

• Nondisjunction: Failure of chromosomes to separate; leads to abnormal chromosome numbers in gametes.

Table: Comparison of Types of Inheritance

Type	Definition	Example
Mendelian (Dominant/Recessive)	One allele masks the other	Widow's peak, cystic fibrosis
Incomplete Dominance	Intermediate phenotype	Red + white flowers = pink
Codominance	Both alleles expressed	AB blood type
Polygenic	Multiple genes affect trait	Skin color, height

Additional info: Table entries inferred for clarity and completeness.