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: 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.

• Substructures: Includes Z-lines, A-band, I-band, H-zone, and M-line, each with specific roles in contraction.

• Example: During contraction, the I-band and H-zone decrease in width, while the A-band remains constant.

Action Potential 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: Motor neuron releases acetylcholine → depolarization of muscle cell → calcium release → actin-myosin interaction → contraction.

• Electrical Impulses: Cause release of calcium ions from the sarcoplasmic reticulum.

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

Types of Muscle Contractions

Muscle contractions can be classified based on whether the muscle changes length.

• Isotonic Contraction: Muscle changes length (movement occurs).

• Isometric Contraction: Muscle does not change length (no movement, but tension increases).

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

Major Muscle Groups and Functions

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

• Muscles Sectioning Cavities: Diaphragm separates thoracic and abdominal cavities.

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 throughout the body.

• Example: Oxygen enters alveoli → diffuses into capillaries → carried by hemoglobin.

Structures of the Respiratory System

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

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

Mechanics of Breathing

• Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume, 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.

Respiratory Diseases and Disorders

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

• Example: Asthma involves constriction of airways, reducing airflow.

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, anus.

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

• Function: Each organ contributes to digestion, absorption, or excretion.

Enzymes and Digestion

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

• Example: Amylase (saliva), pepsin (stomach), lipase (pancreas).

Surface Area and Digestion

• Large Surface Area: Villi and microvilli in the small intestine increase surface area for absorption.

Metabolic Rates

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

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

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

Nutrition and "My Plate"

• "My Plate": A guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion Mechanics

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

• Example: Swallowing initiates peristalsis in the esophagus.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Genetics is the scientific study of heredity and variation in organisms.

• Gene: A segment of DNA coding for a trait.

• Chromosome: DNA molecule with associated proteins, carrying many genes.

• Genome: The complete set of genes in an organism.

• Homologous Chromosomes: Chromosome pairs with the same genes, one from each parent.

• Karyotype: Visual representation of chromosomes; humans have 46 (23 pairs).

Genotype and Phenotype

• Genotype: Genetic makeup (alleles present).

• Phenotype: Observable traits.

• Example: Genotype: Aa; Phenotype: dominant trait expressed.

Punnett Squares and Alleles

• Punnett Square: Diagram used to predict genetic crosses.

• Dominant Allele: Expressed when present ($A$).

• Recessive Allele: Expressed only when homozygous ($a$).

• 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.

Patterns of Inheritance

• 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 the same chromosome, inherited together.

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

Sex-linked Genes and Nondisjunction

• Sex-linked Genes: Genes located on sex chromosomes (X or Y).

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

• Example: Down syndrome results from nondisjunction of chromosome 21.

Term	Definition	Example
Genotype	Genetic makeup of an organism	AA, Aa, aa
Phenotype	Observable traits	Brown eyes, blue eyes
Dominant Allele	Expressed when present	A
Recessive Allele	Expressed only when homozygous	a
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Incomplete Dominance	Intermediate phenotype	Red + White = Pink flowers
Codominance	Both alleles expressed	AB blood type
Polygenic Inheritance	Trait controlled by multiple genes	Skin color
Sex-linked Gene	Located on X or Y chromosome	Hemophilia
Nondisjunction	Failure of chromosomes to separate	Down syndrome