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 functional unit of muscle fibers, 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 as myosin heads attach to actin and pull, shortening the sarcomere.

• Order of Events: Nerve impulse → Action potential in motor neuron → Release of neurotransmitter (acetylcholine) → Depolarization of muscle cell membrane → Calcium release from sarcoplasmic reticulum → Actin-myosin interaction → Contraction.

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

Action Potential and Electrical Impulses

Muscle contraction is initiated by electrical signals from motor neurons.

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

• Motor Neuron: Releases acetylcholine at the neuromuscular junction, triggering muscle cell depolarization.

• Electrical Impulse: Causes calcium ions to be released, enabling actin-myosin binding.

Example: The release of calcium from the sarcoplasmic reticulum is essential for contraction.

Muscle Groups and Body Cavities

Muscles are organized into groups that perform specific functions and may section body cavities.

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

• Body Cavities: Diaphragm separates thoracic and abdominal cavities.

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 is isotonic; holding a weight steady is isometric.

Heat Generation

Muscles generate most of the body's heat through contraction.

• Thermogenesis: Heat produced as a byproduct of ATP hydrolysis during muscle activity.

Sarcomere Substructures

The sarcomere contains several substructures:

• Z-line: Defines the boundaries of each sarcomere.

• A-band: Contains the length of the myosin filaments.

• I-band: Contains only actin filaments.

• H-zone: Area with only myosin, disappears during contraction.

Human Respiratory System

Significance of Breathing

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

• Oxygen: Required for cellular respiration and energy production.

• Carbon Dioxide: Waste product expelled during exhalation.

Respiratory System Structures

The respiratory system is divided into upper and lower regions, each with specific functions.

• Upper Respiratory: Includes nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.

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

Mechanics of Breathing

Breathing involves changes in lung pressure and muscle activity.

• Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume, decreasing pressure, air flows in.

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

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

Intercostal Muscles

Intercostal muscles assist in expanding and contracting the rib cage during breathing.

• During Inhalation: External intercostals contract, lifting ribs.

• During Exhalation: Internal intercostals contract (forced exhalation), lowering ribs.

Blood Flow Through the Heart

Oxygen-rich blood flows through the heart in a specific sequence.

• Sequence: Pulmonary veins → Left atrium → Left ventricle → Aorta → Body tissues.

Respiratory Diseases and Disorders

Common respiratory diseases include asthma, bronchitis, pneumonia, and emphysema.

• Asthma: Inflammation and narrowing of airways.

• Emphysema: Damage to alveoli, reduced gas exchange.

Human Digestive System

Major Structures and Functions

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

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes, churns food.

• Small Intestine: Main site of 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 in Digestion

Enzymes catalyze the breakdown of food molecules.

• Amylase: Breaks down carbohydrates (produced in salivary glands, pancreas).

• Protease: Breaks down proteins (produced in stomach, pancreas).

• Lipase: Breaks down fats (produced in pancreas).

Surface Area in Digestion

Large surface area in the small intestine (villi, microvilli) increases nutrient absorption.

Metabolic Rates

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

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

"My Plate" Purpose

"My Plate" is a guide for balanced nutrition, emphasizing proper proportions of food groups.

Peristalsis

Peristalsis is the wave-like muscle contraction that moves food through the digestive tract.

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, carries genes.

• Genome: Complete set of genetic material in an organism.

Homologous Chromosomes and Karyotype

• 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 (alleles present).

• Phenotype: Observable traits.

Punnett Square

Punnett Squares predict genetic outcomes of crosses.

Parent Genotype	Possible Offspring
AA x aa	All Aa
Aa x Aa	AA, Aa, aa

Dominant and Recessive Alleles

• Dominant Allele: Expressed if present (e.g., AA or Aa).

• Recessive Allele: Expressed only if homozygous (aa).

• Homozygous: Two identical alleles (AA or aa).

• Heterozygous: Two different alleles (Aa).

Mendelian 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 (e.g., pink flowers).

• Codominance: Both alleles expressed (e.g., AB blood type).

• Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).

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

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

Environmental Impact on Phenotype

Environment can influence gene expression and phenotype (e.g., nutrition, temperature).

Meiosis and New Allele Combinations

Meiosis creates genetic diversity through crossing over and independent assortment.

Nondisjunction

Nondisjunction is the failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers in gametes.

• Example: Down syndrome (trisomy 21).