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 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.

• Sliding Filament Theory: Myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

• Function: Sarcomeres enable muscles to contract and generate force.

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

Action Potential and Muscle Contraction

Muscle contraction is initiated by an action potential in a motor neuron, which triggers a cascade of events in the muscle fiber.

• Action Potential: An electrical signal travels down the motor neuron, reaching the neuromuscular junction.

• Release of Acetylcholine: The signal causes release of acetylcholine, which binds to receptors on the muscle cell membrane.

• Electrical Impulse: This generates an electrical impulse in the muscle cell, leading to calcium release from the sarcoplasmic reticulum.

• Calcium's Role: Calcium enables myosin to bind to actin, starting contraction.

• Order of Events: Nerve impulse → Acetylcholine release → Muscle cell depolarization → Calcium release → Sarcomere contraction.

Example: The knee-jerk reflex involves rapid action potential transmission and muscle contraction.

Types of Muscle Contractions

Muscle contractions can be classified as isotonic or isometric.

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant. Produces movement.

• Isometric Contraction: Muscle length remains unchanged while tension increases. No movement occurs.

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

Muscle Groups and Body Cavities

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

• Muscles Sectioning Cavities: The diaphragm separates the thoracic and abdominal cavities.

Heat Generation

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

• System Responsible: The muscular system is the primary source of heat production.

Human Respiratory System

Significance of Breathing

Breathing is essential for oxygen intake and carbon dioxide removal, supporting cellular respiration and energy production.

• Oxygen: Required for aerobic metabolism in cells.

• Carbon Dioxide: Waste product expelled during exhalation.

Respiratory System Structures

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, and larynx. Functions in air filtration, humidification, and vocalization.

• Lower Respiratory System: Includes trachea, bronchi, bronchioles, and lungs. Functions in gas exchange and air conduction.

Example: The nasal cavity warms and moistens incoming air.

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.

Example: During exercise, breathing rate increases to meet oxygen demand.

Blood Flow and Oxygen Transport

• Oxygen-rich Blood: Flows from lungs to left atrium, then left ventricle, and out to the body via the aorta.

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

Respiratory Diseases and Disorders

• Common Disorders: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia, and lung cancer.

• Impact: Affect gas exchange and breathing efficiency.

Human Digestive System

Major Structures and Functions

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

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

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

• Functions: Mechanical and chemical digestion, nutrient absorption, waste elimination.

Example: The pancreas produces digestive enzymes and bicarbonate.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion. Examples: amylase (salivary glands), pepsin (stomach), lipase (pancreas).

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

Surface Area and Digestion

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

Metabolic Rates

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

• Standard Metabolic Rate (SMR): Energy expenditure under standardized conditions.

• Equation: $\text{BMR} = \text{Body weight} \times \text{Energy factor}$

"My Plate" Purpose

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

Digestion Process and Peristalsis

• Digestion: Breakdown of carbohydrates, proteins, and fats by enzymes.

• Peristalsis: Rhythmic contractions of smooth muscle that propel food through the digestive tract.

Example: Swallowing initiates peristalsis in the esophagus.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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

• Gene: A segment of DNA encoding a specific trait.

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

• Genome: The complete set of genetic material in an organism.

Homologous Chromosomes and Karyotype

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

• Karyotype: The visual representation of all chromosomes in a cell, used to detect chromosomal abnormalities.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: The observable traits resulting from the genotype.

Punnett Square and Alleles

• Punnett Square: A diagram used to predict the outcome of genetic crosses.

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

• Dominant Allele: Expressed when present (e.g., A).

• Recessive Allele: Expressed only when both alleles are recessive (e.g., aa).

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

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

• Law of Segregation: Each parent passes one allele for each gene to offspring.

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

Inheritance Patterns

• Incomplete Dominance: Heterozygotes show intermediate phenotype (e.g., pink flowers from red and white parents).

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

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

• Environmental Impact: Environment can affect phenotypic expression (e.g., nutrition, temperature).

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), often affecting traits like color blindness.

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

Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Dominant/Recessive	AA, Aa, aa	Dominant or recessive trait	Widow's peak
Incomplete Dominance	RR, RW, WW	Intermediate phenotype	Pink snapdragon flowers
Codominance	IAIB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color

Additional info: Table entries inferred for clarity and completeness.