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.

• Substructures: Includes Z-lines, M-line, A-band, I-band, and H-zone, each with specific roles in contraction.

• Example: During contraction, the I-band and H-zone decrease in width, while the A-band remains constant.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

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

• Order of Events: Motor neuron releases acetylcholine → depolarization of muscle cell → calcium release from sarcoplasmic reticulum → actin-myosin interaction → contraction.

• Electrical Impulses: Cause release of calcium ions, which enable actin and myosin binding.

• Example: The neuromuscular junction is where the motor neuron communicates with the muscle fiber.

Muscle Groups and Functions

Muscles are organized into groups based on their location and function.

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

• Body Cavities: Muscles such as the diaphragm section the thoracic and abdominal cavities.

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

Types of Muscle Contractions

Muscle contractions can be classified based on whether the muscle changes length.

• Isotonic Contraction: Muscle changes length (movement occurs), e.g., lifting a weight.

• Isometric Contraction: Muscle does not change length (no movement), e.g., holding a weight steady.

• Function: Isotonic produces movement; isometric stabilizes joints.

Summary Table: Muscle Contraction Types

Type	Muscle Length Change	Example
Isotonic	Yes	Bicep curl
Isometric	No	Plank hold

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 that must be expelled.

• Example: Without breathing, cells cannot produce ATP efficiently.

Respiratory System Structures

The respiratory system is divided into upper and lower regions, each with specific functions.

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

• Lower Respiratory: Includes trachea, bronchi, lungs. Functions: gas exchange, air conduction.

• Significance: Each structure ensures efficient and safe passage of air.

Mechanics of Breathing

Breathing involves changes in lung pressure and muscle activity.

• Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing pressure, drawing air in.

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

• Pressure Change Equation:

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

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

Blood Flow and Gas Exchange

Oxygen-rich blood flows through the heart and is distributed to tissues.

• Order of Flow: Pulmonary veins → left atrium → left ventricle → aorta → body tissues.

• Example: Oxygenated blood returns from lungs to heart before being pumped to the body.

Respiratory Diseases and Disorders

Various diseases affect the respiratory system, impacting breathing and gas exchange.

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

• Significance: Understanding these helps in prevention and treatment.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

• Major Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum.

• Accessory Organs: Liver, pancreas, gallbladder.

• Function: Each organ contributes to digestion and absorption.

Enzymes and Digestion

Enzymes catalyze the breakdown of food molecules.

• Produced by: Salivary glands, stomach, pancreas, small intestine.

• Function: Speed up chemical reactions, e.g., amylase breaks down starch.

Surface Area and Digestion

Large surface area in the small intestine enhances nutrient absorption.

• Structures: Villi and microvilli increase surface area.

• Example: More surface area allows more efficient absorption of nutrients.

Metabolic Rates

Metabolic rate measures energy expenditure.

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

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

• Equation:

$\text{BMR} = \frac{\text{Energy expenditure}}{\text{Time}}$

My Plate and Nutrition

"My Plate" is a guide for balanced nutrition.

• Purpose: Helps individuals plan healthy meals with appropriate proportions of food groups.

Digestion Process and Peristalsis

Digestion involves mechanical and chemical breakdown, aided by peristalsis.

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

• Structures: Esophagus, intestines.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

Genetics is the study of heredity and variation in organisms.

• Gene: Segment of DNA coding for a trait.

• Chromosome: Structure containing DNA; humans have 23 pairs.

• Genome: Complete set of genetic material in an organism.

• Homologous Chromosomes: Pairs with same genes but possibly different alleles.

• Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Genotype and Phenotype

Genotype refers to genetic makeup; phenotype is the observable trait.

• Genotype: Combination of alleles (e.g., AA, Aa, aa).

• Phenotype: Physical expression (e.g., brown eyes).

Punnett Square and Alleles

Punnett Squares predict genetic outcomes.

• Dominant Allele: Expressed if present (e.g., A).

• Recessive Allele: Expressed only if homozygous (e.g., aa).

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

• Heterozygous: Two different alleles (Aa).

Summary Table: Allele Expression

Genotype	Phenotype (Dominant)	Phenotype (Recessive)
AA	Dominant trait	-
Aa	Dominant trait	-
aa	-	Recessive trait

Mendelian Laws

Inheritance follows specific laws.

• Law of Segregation: Alleles separate during gamete formation.

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

Patterns of Inheritance

Traits can be inherited in various ways.

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

• Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).

• Environmental Impact: Environment can affect phenotypic expression.

Linked Genes and Meiosis

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

• Linked Genes: Modify inheritance patterns.

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

Sex-linked Genes and Nondisjunction

Sex-linked genes are found on sex chromosomes; nondisjunction affects chromosome number.

• Sex-linked Genes: Traits associated with X or Y chromosomes (e.g., color blindness).

• 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.