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: Actin filaments provide sites for myosin heads to attach and pull, causing contraction. Myosin filaments have heads that bind to actin and use ATP to generate force.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, forming cross-bridges, and pull the actin filaments inward, shortening the sarcomere.

• Order of Events in Muscle Contraction: 1. Nerve impulse triggers action potential in motor neuron. 2. Release of neurotransmitter (acetylcholine) at neuromuscular junction. 3. Action potential spreads across muscle cell membrane. 4. Calcium ions released from sarcoplasmic reticulum. 5. Calcium binds to troponin, exposing binding sites on actin. 6. Myosin binds to actin, ATP is hydrolyzed, and contraction occurs.

• Electrical Impulses: Action potentials in motor neurons initiate muscle contraction by causing release of calcium ions.

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

• Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities; intercostal muscles are between ribs.

• Isotonic vs. Isometric Contractions: Isotonic contractions produce movement (muscle changes length), while isometric contractions produce tension without movement (muscle length remains constant).

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

Example: During running, leg muscles contract isotonicly to move limbs, generating heat and maintaining body temperature.

Table: Types of Muscle Contractions

Type	Description	Result
Isotonic	Muscle changes length	Movement
Isometric	Muscle length unchanged	No movement, increased tension

Human Respiratory System

Structure and Function

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide. It consists of upper and lower structures, each with specific functions.

• Upper Respiratory Structures: Nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air; protect lower airways.

• Lower Respiratory Structures: Trachea, bronchi, lungs, alveoli. Functions: conduct air, facilitate gas exchange.

• Intercostal Muscles: Located between ribs; contract during inhalation to expand chest cavity, relax during exhalation.

• Diaphragm: Main muscle for breathing; contracts to increase thoracic volume during inspiration.

• Mechanics of Breathing: Inhalation: diaphragm and intercostal muscles contract, lung volume increases, pressure decreases, air enters. Exhalation: muscles relax, lung volume decreases, pressure increases, air exits.

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$; air flows from high to low pressure.

• Oxygen-rich Blood Flow: Oxygenated blood returns from lungs to left atrium, then left ventricle, then pumped to body.

• Significance of Breathing: Essential for cellular respiration and energy production.

• Respiratory Diseases: Includes asthma, bronchitis, pneumonia, emphysema.

Example: During exercise, breathing rate increases to supply more oxygen and remove excess carbon dioxide.

Table: Structures of the Respiratory System

Structure	Location	Function
Nose/Nasal cavity	Upper	Filters, warms, humidifies air
Pharynx	Upper	Passage for air and food
Larynx	Upper	Voice production, airway protection
Trachea	Lower	Conducts air to bronchi
Bronchi	Lower	Distributes air to lungs
Lungs	Lower	Gas exchange
Alveoli	Lower	Site of gas exchange

Human Digestive System

Structure and Function

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It includes primary and accessory organs.

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

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas. Functions: produce enzymes, bile, and other substances for digestion.

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

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

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

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

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

Example: After eating, peristalsis moves food from esophagus to stomach, where enzymes begin protein digestion.

Table: Digestive System Structures and Functions

Structure	Function
Mouth	Mechanical breakdown, saliva starts digestion
Esophagus	Transports food to stomach
Stomach	Protein digestion, churns food
Small Intestine	Digestion, nutrient absorption
Large Intestine	Water absorption, waste formation
Liver	Produces bile, processes nutrients
Pancreas	Produces digestive enzymes
Gallbladder	Stores and releases bile

Human Genetics and Inheritance

Basic Concepts

Genetics is the scientific study of heredity and variation in organisms. Human inheritance is governed by genes, chromosomes, and various genetic laws.

• 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: Chromosome pairs with same genes but possibly different alleles.

• Karyotype: Visual representation of chromosomes; used to detect abnormalities.

• Genotype: Genetic makeup (alleles present).

• Phenotype: Observable traits.

• Punnett Square: Diagram to predict genetic crosses.

• Dominant Allele: Expressed if present; Recessive Allele: Expressed only if homozygous.

• Homozygous: Two identical alleles; Heterozygous: Two different alleles.

• Law of Segregation: Alleles separate during gamete formation.

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

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

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

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

• Linked Genes: Genes located close together on same chromosome; inherited together.

• Meiosis: New allele combinations arise from crossing over.

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

• Nondisjunction: Failure of chromosomes to separate during meiosis; leads to abnormal chromosome numbers (e.g., Down syndrome).

Example: A Punnett Square can predict the probability of a child inheriting a recessive disorder.

Table: Genetic Terms and Definitions

Term	Definition
Gene	DNA segment coding for a trait
Allele	Variant form of a gene
Genotype	Genetic makeup
Phenotype	Physical expression of genotype
Homozygous	Identical alleles
Heterozygous	Different alleles
Karyotype	Chromosome display
Punnett Square	Predicts genetic crosses

Formula:

$\text{Probability of trait} = \frac{\text{Number of favorable outcomes}}{\text{Total possible outcomes}}$

Additional info: Polygenic traits often show continuous variation, and environmental factors can modify gene expression. Nondisjunction can result in trisomy or monosomy conditions.