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) → Depolarization of muscle cell membrane → Calcium release from sarcoplasmic reticulum → Actin-myosin interaction → Contraction.

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

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

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

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle length remains the same (no movement, tension increases).

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

Sarcomere Substructures and Functions

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

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

• I-band: Contains only actin filaments.

• A-band: Contains both actin and myosin filaments.

Function: Sarcomeres contract to produce muscle movement.

Action Potential in Motor Neuron

• Action Potential: Rapid change in membrane potential that propagates along the neuron.

• Initiation: Triggered by stimuli, leading to neurotransmitter release at neuromuscular junction.

Example: Acetylcholine is released, causing muscle cell depolarization.

Muscle Contraction Sequence

• 1. Nerve impulse arrives at neuromuscular junction.

• 2. Acetylcholine released, binds to receptors.

• 3. Muscle cell depolarizes, action potential spreads.

• 4. Calcium released from sarcoplasmic reticulum.

• 5. Actin and myosin interact, contraction occurs.

Actin and Myosin Functions

• Actin: Forms thin filaments, provides binding sites for myosin.

• Myosin: Forms thick filaments, uses ATP to pull actin.

Equation:

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

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.

• Carbon Dioxide: Waste product, must be expelled.

Blood Flow Through the Heart

• Oxygen-rich blood enters left atrium → left ventricle → aorta → body tissues.

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

Equation:

$ \text{O}_2 + \text{Glucose} \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{Energy} $

Upper and Lower Respiratory Structures

• Upper: Nose, nasal cavity, pharynx, larynx. Functions: filter, warm, humidify air.

• Lower: Trachea, bronchi, lungs, alveoli. Functions: gas exchange, air conduction.

Pressure Changes During Breathing

• Inhalation: Diaphragm contracts, thoracic cavity expands, pressure decreases, air enters.

• Exhalation: Diaphragm relaxes, thoracic cavity contracts, pressure increases, air exits.

Intercostal Muscles

• Function: Assist in expanding and contracting the rib cage during breathing.

• Inhalation: Contract to lift ribs.

• Exhalation: Relax to lower ribs.

Mechanics of Inspiration and Expiration

• Inspiration: Active process, diaphragm and intercostals contract.

• Expiration: Usually passive, muscles relax.

Respiratory Diseases and Disorders

• Examples: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.

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

• Purpose: Guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion of Molecules

• Carbohydrates: Digested by amylase, absorbed as glucose.

• Proteins: Digested by pepsin, trypsin, absorbed as amino acids.

• Fats: Digested by lipase, absorbed as fatty acids and glycerol.

Peristalsis

• Definition: Wave-like muscle contractions that 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, 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).

• Phenotype: Observable traits.

Punnett Square Function

• 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.

Laws of Genetics

• 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: Prevalent due to carriers.

Incomplete Dominance and Codominance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

Polygenic Inheritance

• Definition: Trait controlled by multiple genes (e.g., skin color).

Environmental Impact on Phenotype

• Environment: Can influence gene expression (e.g., nutrition, temperature).

Linked Genes and New Allele Combinations

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

• Meiosis: Crossing over creates new allele combinations.

Sex-linked Genes

• Definition: Genes located on sex chromosomes (X or Y).

• Example: Color blindness, hemophilia.

Nondisjunction

• Definition: Failure of chromosomes to separate during meiosis.

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

Term	Definition	Example
Genotype	Genetic makeup	AA, Aa, aa
Phenotype	Physical expression	Brown eyes, blue eyes
Dominant allele	Expressed if present	A
Recessive allele	Expressed only if homozygous	a
Homozygous	Same alleles	AA or aa
Heterozygous	Different alleles	Aa
Incomplete dominance	Intermediate phenotype	Pink flowers (red x white)
Codominance	Both alleles expressed	AB blood type
Polygenic inheritance	Multiple genes affect trait	Height, skin color
Sex-linked gene	On X or Y chromosome	Hemophilia
Nondisjunction	Chromosomes fail to separate	Trisomy 21