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 and generate heat. The sliding filament mechanism is central to muscle contraction.

• Sarcomere: The basic contractile unit of muscle fibers, composed of actin (thin) and myosin (thick) filaments.

• Actin and Myosin Filaments: Actin provides the track for myosin heads to attach and pull, causing contraction.

• Sliding Filament Theory: Myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

• Muscle Heat Generation: Most body heat is generated by muscle contractions, especially in skeletal muscle.

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

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

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

Muscle Contraction Mechanism

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential in motor neurons triggers muscle contraction.

• Order of Events:

  1. Motor neuron releases neurotransmitter (acetylcholine).=

  2. Muscle cell membrane depolarizes, generating an action potential.

  3. Calcium ions released from sarcoplasmic reticulum.

  4. Calcium binds to troponin, exposing actin binding sites.

  5. Myosin binds to actin, ATP hydrolysis powers contraction.

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle length remains constant (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.

Human Respiratory System

Significance of Breathing

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

• Oxygen Transport: Oxygen-rich blood is pumped from the lungs to the heart, then distributed to the body.

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

Example: Oxygen is required for cellular respiration, which produces ATP.

Structures of the Respiratory System`

• 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.

Significance: Each structure ensures efficient gas exchange and protection from pathogens.

Mechanics of Breathing

• Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume, decreasing lung pressure.

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

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

Example: During inspiration, lung pressure drops below atmospheric pressure, drawing air in.

Blood Flow Through the Heart

• Order of Oxygen-rich Blood Flow:

  1. Pulmonary veins

  2. Left atrium

  3. Left ventricle

  4. Aorta

  5. Systemic circulation

Example: Oxygenated blood returns from the lungs to the left side of the heart.

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), pancreas (produces digestive enzymes), gallbladder (stores bile).

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.

Surface Area and Digestion

• Large Surface Area: Villi and microvilli in the small intestine increase absorption efficiency.

Example: The small intestine's surface area is greatly increased by villi.

Metabolic Rates

• Basal Metabolic Rate (BMR): Energy expended at rest.

• Standard Metabolic Rate (SMR): Energy expenditure under specific conditions.

Example: BMR is measured after fasting and rest.

"My Plate" Purpose

• My Plate: A guide for balanced nutrition, emphasizing proper proportions of food groups.

Digestion Process and Peristalsis

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

Example: Peristalsis pushes food from the esophagus to the stomach.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

Genetics is the scientific study of heredity and variation in organisms.

• Gene: A segment of DNA coding for a specific protein.

• Chromosome: DNA molecule with associated proteins, carrying genetic information.

• Genome: The complete set of genes in an organism.

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

• Karyotype: The number and appearance of chromosomes in a cell.

Example: Humans have 23 pairs of chromosomes.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism.

• Phenotype: The observable traits of an organism.

Example: Genotype AA, Aa, or aa; phenotype could be brown or blue eyes.

Punnett Square and Alleles

• Punnett Square: Diagram used to predict genetic crosses.

• Alleles: Different forms of a gene.

• Dominant Allele: Expressed when present.

• Recessive Allele: Expressed only when homozygous.

• Homozygous: Two identical alleles (AA or aa).

• Heterozygous: Two different alleles (Aa).

Example: Brown eyes (dominant), blue eyes (recessive).

Mendelian Laws

• Law of Segregation: Each parent passes one allele for each gene to offspring.

• Law of Independent Assortment: Genes for different traits are inherited 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 affect phenotypic expression.

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

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

Example: Skin color is polygenic; hemophilia is X-linked.

Meiosis and Allele Combinations

• Meiosis: Cell division producing gametes with new allele combinations.

• Nondisjunction: Failure of chromosomes to separate, leading to abnormal chromosome numbers.

Example: Down syndrome results from nondisjunction.

Punnett Square Table Example

Parent Genotype	Offspring Genotype	Offspring Phenotype
AA x aa	All Aa	Dominant trait
Aa x Aa	AA, Aa, aa	3:1 ratio (dominant:recessive)
Aa x aa	Aa, aa	1:1 ratio

Additional info: This table illustrates basic Mendelian inheritance using a Punnett Square.