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 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.
Function: Sarcomeres shorten during contraction, generating force.
Example: During biceps contraction, sarcomeres in muscle fibers shorten, causing the arm to bend.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

Action Potential: A rapid change in membrane potential that travels along the neuron and muscle cell.
Mechanism: Motor neuron releases neurotransmitter (acetylcholine), triggering an action potential in the muscle cell.
Order of Events: Nerve impulse → Acetylcholine release → Muscle cell depolarization → Calcium release → Actin-myosin interaction → Contraction.
Electrical Impulses: Cause release of calcium ions from the sarcoplasmic reticulum, enabling contraction.
Example: Reflex action, such as knee-jerk, involves rapid muscle contraction following nerve stimulation.

Types of Muscle Contractions

Muscle contractions can be classified based on movement and tension.

Isotonic Contraction: Muscle changes length (movement occurs), tension remains constant.
Isometric Contraction: Muscle length remains the same, tension increases (no movement).
Example: Lifting a weight (isotonic); holding a weight steady (isometric).

Muscle Groups and Functions

Major muscle groups include skeletal, cardiac, and smooth muscles, each with distinct functions.

Skeletal Muscles: Voluntary movement, attached to bones.
Cardiac Muscle: Heart contraction.
Smooth Muscle: Found in organs, controls involuntary movements.
Body Heat Generation: Most body heat is generated by muscle activity (thermogenesis).
Muscles Sectioning Cavities: Diaphragm separates thoracic and abdominal cavities.

Human Respiratory System

Significance of Breathing

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

Oxygen: Required for cellular respiration and energy production.
Carbon Dioxide: Waste product, must be expelled to maintain pH balance.
Example: During exercise, increased breathing supplies more oxygen to muscles.

Respiratory System Structures

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

Upper Respiratory System: Includes nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.
Lower Respiratory System: Includes trachea, bronchi, lungs. Functions: conduct air, gas exchange.
Significance: Structures ensure efficient and clean air delivery to lungs.

Mechanics of Breathing

Breathing involves changes in lung pressure and muscle activity.

Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume, decreasing pressure, air enters lungs.
Exhalation: Muscles relax, thoracic volume decreases, pressure increases, air exits lungs.
Pressure Changes:
Intercostal Muscles: Assist in expanding and contracting rib cage during breathing.
Example: Deep breathing during stress increases oxygen intake.

Blood Flow and Gas Exchange

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

Pathway: Lungs → Pulmonary veins → Left atrium → Left ventricle → Aorta → Body.
Gas Exchange: Occurs in alveoli; oxygen enters blood, carbon dioxide leaves.

Respiratory Diseases and Disorders

Various diseases affect respiratory function.

Examples: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.
Impact: Reduced gas exchange, breathing difficulties.

Human Digestive System

Major Structures and Functions

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

Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.
Accessory Organs: Liver, pancreas, gallbladder.
Functions: Mechanical and chemical digestion, nutrient absorption.
Example: Stomach secretes acid and enzymes to digest proteins.

Enzymes and Digestion

Enzymes catalyze the breakdown of food molecules.

Produced by: Salivary glands, stomach, pancreas, small intestine.
Function: Speed up digestion of carbohydrates, proteins, fats.
Example: Amylase breaks down starch in the mouth.

Surface Area and Digestion

Large surface area in the small intestine enhances nutrient absorption.

Villi and Microvilli: Increase surface area for absorption.
Example: Small intestine absorbs most nutrients due to its extensive surface area.

Metabolic Rates

Metabolic rate measures energy expenditure.

Basal Metabolic Rate (BMR): Energy used at rest.
Standard Metabolic Rate (SMR): Energy used under specific conditions.
Formula:

Nutrition and "My Plate"

"My Plate" is a guide for balanced nutrition.

Purpose: Encourages proper proportions of food groups.
Example: Half plate fruits and vegetables, quarter grains, quarter protein.

Digestion Mechanics

Peristalsis moves food through the digestive tract.

Peristalsis: Wave-like muscle contractions.
Function: Propels food from esophagus to stomach and 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 carrying genes; humans have 23 pairs.
Genome: Complete set of genetic material.
Homologous Chromosomes: Pair with same genes, may have different alleles.
Karyotype: Visual representation of chromosomes.
Example: Down syndrome is caused by an extra chromosome 21.

Genotype and Phenotype

Genotype is the 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 (A).
Recessive Allele: Expressed only if homozygous (a).
Homozygous: Two identical alleles (AA or aa).
Heterozygous: Two different alleles (Aa).
Example: Cross Aa x Aa yields 3:1 dominant:recessive ratio.

Genetic Laws and Inheritance Patterns

Mendelian laws govern inheritance.

Law of Segregation: Alleles separate during gamete formation.
Law of Independent Assortment: Genes assort independently.
Incomplete Dominance: Heterozygote shows intermediate phenotype.
Codominance: Both alleles expressed (e.g., AB blood type).
Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).
Environmental Impact: Environment can modify phenotypic expression.

Linked Genes, Meiosis, and Sex-linked Traits

Genes on the same chromosome are linked; meiosis creates new allele combinations.

Linked Genes: Inherited together unless crossing over occurs.
Sex-linked Genes: Located on sex chromosomes (X or Y).
Nondisjunction: Failure of chromosomes to separate, leading to abnormal chromosome numbers.
Example: Color blindness is X-linked; Turner syndrome results from nondisjunction.

Term	Definition	Example
Gene	DNA segment coding for a trait	Eye color gene
Allele	Variant form of a gene	A or a
Genotype	Genetic makeup	AA, Aa, aa
Phenotype	Physical trait	Brown eyes
Homozygous	Same alleles	AA or aa
Heterozygous	Different alleles	Aa
Dominant	Expressed allele	A
Recessive	Masked allele	a
Codominance	Both alleles expressed	AB blood type
Incomplete Dominance	Intermediate phenotype	Pink flowers
Polygenic	Multiple genes	Skin color
Sex-linked	On sex chromosome	Color blindness