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.

• 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 and movement.

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

Example: During contraction, the sarcomere shortens as actin and myosin slide past each other.

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 → calcium release → actin-myosin interaction → contraction.

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

Example: The neuromuscular junction transmits the signal from nerve to muscle.

Types of Muscle Contractions

Muscle contractions can be classified based on movement and tension.

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

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

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

Muscle Groups and Functions

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

• Body Heat Generation: Muscular system is the primary source of body heat via ATP hydrolysis.

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

Human Respiratory System

Significance of Breathing

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

• Oxygen Transport: Oxygen-rich blood is circulated from lungs to heart and then to tissues.

• Importance: Supports cellular respiration and energy production.

Structures of the Respiratory System

• Upper Respiratory Tract: Includes nose, pharynx, larynx; filters, warms, and moistens air.

• Lower Respiratory Tract: Includes trachea, bronchi, lungs; site of gas exchange.

Example: The alveoli in the lungs are the primary site for oxygen and carbon dioxide 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.

Respiratory Diseases and Disorders

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

• Impact: Affect gas exchange and overall health.

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.

• Main Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum.

• Accessory Organs: Liver, pancreas, gallbladder; produce enzymes and bile.

Enzymes and Digestion

• Function: Catalyze breakdown of macromolecules.

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

Example: Amylase breaks down starch in the mouth.

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.

Equation: $\text{BMR} = \text{Body weight} \times \text{Energy per kg}$

"My Plate" Purpose

• Purpose: Guide for balanced nutrition and healthy eating habits.

Digestion Process and Peristalsis

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

• Molecule Digestion: Carbohydrates, proteins, and fats are digested in different regions by specific enzymes.

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: Structure carrying genes; humans have 23 pairs.

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

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pair of chromosomes with the same genes but possibly different alleles.

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (allele combination).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram used to predict genetic crosses.

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

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Genetic Laws

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes for different traits are inherited independently.

Dominant and Recessive Disorders

• Dominant Disorders: Expressed with one dominant allele; can be lethal.

• Recessive Disorders: Require two recessive alleles; may persist due to carriers.

Complex 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 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 affect males more.

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

Term	Definition	Example
Gene	Segment of DNA coding for a trait	Eye color gene
Allele	Variant form of a gene	Brown or blue eye allele
Genotype	Genetic makeup	AA, Aa, aa
Phenotype	Observable trait	Brown eyes
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed allele	A
Recessive	Masked allele	a
Codominance	Both alleles expressed	AB blood type
Incomplete Dominance	Intermediate phenotype	Pink flowers (red x white)
Polygenic	Multiple genes affect trait	Height, skin color
Sex-linked	Gene on sex chromosome	Hemophilia

Additional info: Academic context and definitions were expanded for clarity and completeness.