Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

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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.
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 a bicep curl, the sarcomeres in the biceps muscle shorten, producing movement.

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.
Calcium Release: Electrical impulse causes calcium ions to be released from the sarcoplasmic reticulum, enabling contraction.

Formula: (change in membrane potential)

Muscle Groups and Body Heat

Muscles are grouped by function and location. Most body heat is generated by muscle activity.

Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, etc.
Heat Generation: Muscular system accounts for most human body heat via metabolic activity.

Types of Muscle Contractions

Muscle contractions can be classified as isotonic or isometric.

Isotonic Contraction: Muscle changes length (movement occurs).
Isometric Contraction: Muscle length remains the same (no movement, but tension increases).

Example: Holding a weight steady is isometric; lifting it is isotonic.

Muscles and Body Cavities

Diaphragm: Separates thoracic and abdominal cavities; essential for breathing.
Intercostal Muscles: Located between ribs; assist in expanding and contracting the chest cavity.

Human Respiratory System

Significance of Breathing

Breathing is vital 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 System: Includes nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.
Lower Respiratory System: Includes trachea, bronchi, lungs. 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 and decreasing pressure, drawing air in.
Exhalation: Muscles relax, thoracic volume decreases, pressure increases, air is expelled.
Pressure Change Formula: (Boyle's Law)

Intercostal Muscles

Function: Expand and contract the rib cage during breathing.
During Inhalation: Contract to lift ribs.
During Exhalation: Relax, allowing ribs to fall.

Blood Flow and Oxygen Transport

Oxygen-rich Blood: Flows from lungs to left atrium, left ventricle, then to body tissues.
Order of Flow: Pulmonary veins → left atrium → left ventricle → aorta → systemic circulation.

Respiratory Diseases and Disorders

Common Disorders: Asthma, bronchitis, pneumonia, emphysema.
Impact: Affect airflow, gas exchange, and overall health.

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: Mixes and digests food with acids and enzymes.
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 and Digestion

Function: Speed up chemical breakdown of food.
Production Sites: Salivary glands, stomach, pancreas, small intestine.

Surface Area in Digestion

Large Surface Area: Villi and microvilli in small intestine increase absorption efficiency.

Metabolic Rates

Basal Metabolic Rate (BMR): Energy used at rest.
Standard Metabolic Rate (SMR): Energy used under standardized conditions.

Formula:

"My Plate" Purpose

My Plate: USDA guideline for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion of Molecules and Peristalsis

Digestion: Carbohydrates, proteins, and fats are broken down by specific enzymes.
Peristalsis: Wave-like muscle contractions move 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 (allele combination).
Phenotype: Observable traits.

Punnett Square and Alleles

Punnett Square: Diagram used to predict genetic outcomes.
Alleles: Variants of a gene; can be dominant or recessive.
Homozygous: Two identical alleles.
Heterozygous: Two different alleles.

Law of Segregation and Independent Assortment

Law of Segregation: Each parent passes one allele for each gene to offspring.
Law of Independent Assortment: Genes for different traits are inherited independently.

Dominant and Recessive Alleles

Dominant Allele: Expressed when present.
Recessive Allele: Expressed only when both alleles are recessive.
Lethal Dominant Disorders: Often eliminated quickly; recessive disorders can persist if carriers are unaffected.

Incomplete Dominance, Codominance, Polygenic Inheritance

Incomplete Dominance: Heterozygote shows intermediate phenotype.
Codominance: Both alleles are fully expressed (e.g., blood type AB).
Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).

Environmental Impact and Linked Genes

Environment: Can affect phenotypic expression (e.g., nutrition, temperature).
Linked Genes: Genes located close together on a chromosome tend to be inherited together.

Meiosis, Sex-linked Genes, and Nondisjunction

Meiosis: Produces gametes; new allele combinations arise via crossing over.
Sex-linked Genes: Located on sex chromosomes; often affect males more (e.g., hemophilia).
Nondisjunction: Failure of chromosomes to separate properly, leading to abnormal chromosome numbers in gametes.

Table: Comparison of Dominant vs. Recessive Alleles

Type	Expression	Example
Dominant	Expressed if at least one allele is present	Huntington's disease
Recessive	Expressed only if both alleles are recessive	Cystic fibrosis

Table: Major Structures of the Digestive System

Structure	Function
Mouth	Mechanical and chemical digestion
Esophagus	Transports food
Stomach	Mixes and digests food
Small Intestine	Absorbs nutrients
Large Intestine	Absorbs water, forms feces

Table: Respiratory System Structures

Structure	Region	Function
Nose	Upper	Filters, warms, humidifies air
Pharynx	Upper	Passage for air and food
Larynx	Upper	Voice production
Trachea	Lower	Conducts air to lungs
Bronchi	Lower	Branches to lungs
Lungs	Lower	Gas exchange

Additional info: Academic context and definitions were added to expand brief review points into full explanations, including formulas and tables for clarity.