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 called muscle fibers that contract to produce movement. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic functional unit of a muscle fiber, composed of actin (thin) and myosin (thick) filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, pulling the filaments past each other.

• Actin and Myosin: Actin provides the track, while myosin uses ATP to generate force.

• Order of Events: Nerve impulse → Action potential → Calcium release → Myosin-actin interaction → Contraction.

• Electrical Impulses: Action potentials in motor neurons trigger calcium release from the sarcoplasmic reticulum.

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

Example: During exercise, muscle contractions increase heat production, helping maintain body temperature.

Muscle Groups and Functions

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

• 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 it steady is isometric.

Sarcomere Substructures

• Z-line: Defines the boundaries of a 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 to tissues and removing carbon dioxide.

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

• Respiratory Diseases: Include asthma, bronchitis, pneumonia, and emphysema.

Structures of the Respiratory System

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

• Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, and lungs. Functions: conduct air, gas exchange.

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.

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

Blood Flow Through the Heart

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

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 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

• Function: Catalyze breakdown of macromolecules.

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

Surface Area in Digestion

• Importance: Increased surface area (villi, microvilli) enhances nutrient absorption.

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

• Guidance: Visual tool for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Peristalsis

• Definition: Wave-like muscle contractions moving 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; humans have 23 pairs.

• 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).

• Phenotype: Observable traits.

Punnett Square

• Function: Predicts genetic outcomes of crosses.

Dominant and Recessive Alleles

• Dominant Allele: Expressed if present.

• Recessive Allele: Expressed only if homozygous.

• 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.

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 and Meiosis

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

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

Sex-linked Genes and Nondisjunction

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

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

Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype
Dominant/Recessive	AA, Aa, aa	AA/Aa: dominant trait; aa: recessive trait
Incomplete Dominance	RR, RW, WW	RW: intermediate trait
Codominance	AB, AA, BB	AB: both traits expressed
Polygenic	Multiple genes	Continuous variation (e.g., skin color)

Example: Sickle cell anemia is a recessive disorder; blood type AB is codominant.