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

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, pull, and slide the filaments past each other, 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 → Binding of calcium to troponin → Exposure of actin binding sites → Myosin binds and pulls actin → Muscle contraction.

• Electrical Impulses: Action potentials trigger calcium release, which initiates contraction.

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

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

• 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 enabling locomotion.

Sarcomere Substructures and Functions

• Z-line: Defines the boundaries of each sarcomere.

• M-line: Center of the sarcomere, anchors myosin filaments.

• H-zone: Region with only myosin filaments.

• I-band: Region with only actin filaments.

• A-band: Region where actin and myosin overlap.

Function: Sarcomeres contract by shortening, enabling muscle movement.

Action Potential and Muscle Contraction

• Action Potential: Electrical signal in motor neuron triggers muscle contraction.

• Mechanism: Depolarization opens voltage-gated calcium channels, leading to neurotransmitter release and muscle activation.

Formula:

$\Delta V = V_{final} - V_{initial}$

Additional info: The change in membrane potential ($\Delta V$) is essential for action potential propagation.

Human Respiratory System

Significance of Breathing

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

• Oxygen Transport: Oxygen is carried by hemoglobin in red blood cells.

• Carbon Dioxide Removal: CO2 is expelled during exhalation.

Example: During exercise, increased breathing rate supplies more oxygen and removes excess CO2.

Respiratory System Structures

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

• Lower Respiratory System: Includes trachea, bronchi, bronchioles, and lungs. Functions: conduct air to alveoli, site of gas exchange.

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: $P_{in} < P_{atm}$ during inhalation; $P_{in} > P_{atm}$ during exhalation.

• Intercostal Muscles: Assist in expanding and contracting the rib cage.

Formula:

$P_{in} = P_{atm} - \Delta P$

Additional info: $P_{in}$ is intrapulmonary pressure; $P_{atm}$ is atmospheric pressure.

Blood Flow Through the Heart

• Oxygen-rich blood: Flows from lungs to left atrium → left ventricle → aorta → body tissues.

• Oxygen-poor blood: Returns via veins to right atrium → right ventricle → lungs.

Respiratory Diseases and Disorders

• Asthma: Inflammation and narrowing of airways.

• Emphysema: Damage to alveoli, reducing gas exchange.

• Pneumonia: Infection of lung tissue.

• Chronic Obstructive Pulmonary Disease (COPD): Progressive airflow limitation.

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: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for nutrient absorption.

• Large Intestine: Absorbs water, forms feces.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores and releases bile.

• Pancreas: Produces digestive enzymes and hormones.

Enzymes and Digestion

• Function: Enzymes catalyze breakdown of macromolecules.

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

Example: Amylase breaks down starch in the mouth; pepsin digests proteins in the stomach.

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 specific conditions.

Formula:

$BMR = 70 \times (Body\ Weight\ in\ kg)^{0.75}$

Additional info: BMR varies with age, sex, and activity level.

"My Plate" Purpose

• My Plate: Visual guide 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 protein.

• 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 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 to predict genetic crosses.

• Dominant Allele: Expressed trait when present.

• Recessive Allele: Expressed only when homozygous.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Law of Segregation and Law of Independent Assortment

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can modify phenotypic expression.

• Linked Genes: Genes located close together on a chromosome tend to be inherited together.

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

• Sex-linked Genes: Genes located on sex chromosomes (e.g., X-linked traits).

• 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 trait (AA, Aa); Recessive trait (aa)	Widow's peak
Incomplete Dominance	RR, RW, WW	Red (RR), Pink (RW), White (WW)	Flower color in snapdragons
Codominance	IAIB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color
Sex-linked	XRXr, XrY	Trait more common in one sex	Color blindness

Additional info: Table summarizes key inheritance patterns and examples.