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: 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) → Muscle cell depolarization → Calcium release → Actin-myosin interaction → Contraction.

• Electrical Impulses: Action potentials trigger calcium release from the sarcoplasmic reticulum, enabling contraction.

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

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

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

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

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

Sarcomere Substructures and Functions

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

• A-band: Contains the length of the myosin filaments.

• I-band: Contains only actin filaments.

• H-zone: Area with only myosin, disappears during contraction.

Action Potential in Motor Neuron

• Action Potential: Electrical signal generated by the movement of ions across the neuron membrane.

• Initiation: Triggered by neurotransmitter release at the neuromuscular junction.

Muscle Contraction Sequence

• 1. Nerve impulse arrives at neuromuscular junction.

• 2. Acetylcholine released, binds to muscle cell receptors.

• 3. Muscle cell depolarizes, action potential spreads.

• 4. Calcium released from sarcoplasmic reticulum.

• 5. Calcium binds to troponin, exposing actin binding sites.

• 6. Myosin binds to actin, ATP hydrolyzed, contraction occurs.

Formula:

$\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Human Respiratory System

Significance of Breathing

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

• Oxygen: Required for cellular respiration and energy production.

• Carbon Dioxide: Waste product, must be expelled to maintain pH balance.

Respiratory System Structures

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

• Lower Respiratory System: Includes trachea, bronchi, lungs, alveoli. Functions: conduct air, gas exchange.

Blood Flow Through the Heart

• Oxygen-rich blood enters left atrium → left ventricle → aorta → systemic circulation.

• Deoxygenated blood returns via vena cava → right atrium → right ventricle → pulmonary artery → lungs.

Mechanics of Breathing

• Inhalation: Diaphragm contracts, intercostal muscles lift rib cage, lung volume increases, pressure decreases, air enters.

• Exhalation: Diaphragm relaxes, rib cage lowers, lung volume decreases, pressure increases, air exits.

• Pressure Change Formula:

$\text{Pressure} \propto \frac{1}{\text{Volume}}$

• Intercostal Muscles: Assist in expanding and contracting the thoracic cavity during breathing.

Respiratory Diseases and Disorders

• Asthma: Inflammation and narrowing of airways.

• Emphysema: Damage to alveoli, reduced 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, churns food.

• 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 in Digestion

• Function: Catalyze breakdown of macromolecules.

• 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 specific conditions.

"My Plate" Purpose

• Guides healthy eating by illustrating food group proportions.

Digestion of Molecules

• Carbohydrates: Digested in mouth and small intestine.

• Proteins: Digested in stomach and small intestine.

• Fats: Digested in small intestine with bile and lipases.

Peristalsis

• Definition: Wave-like muscle contractions moving food through 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, carries genes.

• 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 (alleles present).

• Phenotype: Observable traits.

Punnett Square Function

• Predicts probability of offspring genotypes and phenotypes.

Dominant and Recessive Alleles

• Dominant: Expressed if present.

• Recessive: Expressed only if both alleles are recessive.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Allele Disorders

• Dominant Disorders: Lethal if one copy causes disease.

• Recessive Disorders: Can persist if carriers are unaffected.

Non-Mendelian Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

Environmental Impact

• Environment can modify phenotypic expression (e.g., nutrition, temperature).

Linked Genes and Meiosis

• Linked Genes: Genes close together on a chromosome, inherited together.

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

Sex-linked Genes

• Located on sex chromosomes (X or Y), often affect males more.

Nondisjunction

• Definition: Failure of chromosomes to separate during meiosis.

• Impact: Results in abnormal chromosome numbers (e.g., Down syndrome).

Inheritance Pattern	Genotype	Phenotype
Dominant	AA, Aa	Trait expressed
Recessive	aa	Trait expressed
Incomplete Dominance	Aa	Intermediate phenotype
Codominance	AB	Both traits expressed
Polygenic	Multiple genes	Continuous variation

Example: Blood type inheritance (codominance), skin color (polygenic).