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 called muscle fibers that contract 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: Include biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and gluteals.
Muscles Sectioning Body Cavities: Diaphragm (separates thoracic and abdominal cavities), intercostal muscles (between ribs).
Isotonic vs. Isometric Contractions: Isotonic contractions produce movement (muscle changes length), isometric contractions produce tension without movement (muscle length remains constant).
Body Heat Generation: Most body heat is generated by muscle activity, especially during contraction.

Example: During exercise, muscle contractions increase heat production, helping maintain body temperature.

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.
A-band: Length of myosin filaments, includes overlap with actin.
I-band: Region with only actin filaments.

Function: The sarcomere shortens during contraction, producing force and movement.

Action Potential and Muscle Contraction

Action Potential: Electrical signal in motor neuron triggers release of acetylcholine at neuromuscular junction.
Calcium Release: Electrical impulse causes sarcoplasmic reticulum to release calcium, enabling actin-myosin binding.

Example: The sequence of events from nerve impulse to muscle contraction is essential for voluntary movement.

Isotonic vs. Isometric Contractions

Isotonic: Muscle changes length, moves a load (e.g., lifting a weight).
Isometric: Muscle generates tension without changing length (e.g., holding a weight steady).

Example: Holding a plank position is isometric; performing a bicep curl is isotonic.

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.

Structures of the Respiratory System

Upper Respiratory Tract: Includes nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.
Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, lungs, alveoli. Functions: conduct air, gas exchange.

Example: The alveoli are the site of gas exchange between air and blood.

Mechanics of Breathing

Inhalation: Diaphragm contracts and moves downward, intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, drawing air in.
Exhalation: Diaphragm relaxes, intercostal muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.
Pressure Changes:

Function of Intercostal Muscles: Assist in expanding and contracting the rib cage during breathing.

Blood Flow Through the Heart

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

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

Mouth: Mechanical breakdown, saliva starts digestion.
Esophagus: Transports food via peristalsis.
Stomach: Chemical digestion with acid and enzymes.
Small Intestine: Main site of nutrient absorption.
Large Intestine: Water absorption, feces formation.

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

My Plate: Dietary guideline for balanced nutrition.

Peristalsis

Definition: Wave-like muscle contractions moving food through digestive tract.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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 genetic outcomes of crosses.

Example Punnett Square Table

	A	a
A	AA	Aa
a	Aa	aa

Dominant and Recessive Alleles

Dominant: Expressed if present (e.g., AA or Aa).
Recessive: Expressed only if homozygous (aa).
Homozygous: Two identical alleles (AA or aa).
Heterozygous: Two different alleles (Aa).

Mendelian Laws

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 fully expressed (e.g., AB blood type).
Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).
Environmental Impact: Environment can affect phenotypic expression.

Linked Genes and Meiosis

Linked Genes: Genes located close together on same chromosome, inherited together.
New Allele Combinations: Crossing over during meiosis creates genetic diversity.

Sex-linked Genes and Nondisjunction

Sex-linked Genes: Located on sex chromosomes, often X-linked.
Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers in gametes.

Example: Down syndrome results from nondisjunction of chromosome 21.