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 functional unit of muscle fibers, composed of actin (thin) and myosin (thick) filaments.
Actin and Myosin: Actin filaments provide sites for myosin heads to attach and pull, causing contraction. Myosin filaments have heads that bind to actin and use ATP to generate force.
Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.
Electrical Impulses: Action potentials in motor neurons trigger the release of calcium ions in muscle cells, initiating contraction.
Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, and others.
Muscle Heat Generation: Most body heat is generated by muscle activity, especially during contraction.
Muscle Contraction Sequence: Nerve impulse → Action potential → Calcium release → Actin-myosin interaction → Contraction.
Isotonic vs. Isometric Contractions: Isotonic contractions produce movement (muscle changes length), while isometric contractions produce tension without movement (muscle length remains constant).

Example: During running, quadriceps contract isotonicly to extend the knee, while holding a plank involves isometric contraction of core muscles.

Muscle Unit Structures and Functions

Muscle Fiber: Single muscle cell, contains many myofibrils.
Myofibril: Rod-like unit within muscle fiber, made of repeating sarcomeres.
Sarcomere Substructures: Z-line, A-band, I-band, H-zone, M-line.
Function of Sarcomere: Contracts and relaxes to produce movement.

Example: The biceps brachii contracts to flex the forearm at the elbow.

Muscle Contraction Mechanisms

Action Potential: Electrical signal in motor neuron triggers neurotransmitter release (acetylcholine) at neuromuscular junction.
Calcium Release: Electrical impulse causes sarcoplasmic reticulum to release Ca2+, enabling actin-myosin binding.
Order of Events: Nerve impulse → Acetylcholine release → Muscle cell depolarization → Calcium release → Contraction.

Example: Lifting a weight involves coordinated action potentials and muscle contractions.

Muscle Types and Functions

Isotonic Contraction: Muscle changes length, moves load.
Isometric Contraction: Muscle tension increases, length unchanged.
Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities.

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 lungs to heart, then distributed to body.
Gas Exchange: Occurs in alveoli of lungs.

Example: During exercise, breathing rate increases to meet oxygen demand.

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, lungs, alveoli. Functions: conduct air, gas exchange.

Example: The trachea conducts air to the lungs; alveoli exchange gases.

Mechanics of Breathing

Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume, decreasing lung pressure, air flows in.
Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air flows out.
Pressure Changes:
Intercostal Muscles: Assist in expanding and contracting rib cage during breathing.

Example: Deep breathing uses both diaphragm and intercostal muscles.

Respiratory Diseases and Disorders

Common Disorders: Asthma, bronchitis, pneumonia, emphysema.
Impact: Affect airflow, gas exchange, and overall health.

Blood Flow Through the Heart

Order: Pulmonary veins → Left atrium → Left ventricle → Aorta → Body → Right atrium → Right ventricle → Pulmonary artery → Lungs.

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 via peristalsis.
Stomach: Secretes acid and enzymes, churns food.
Small Intestine: Main site of nutrient absorption.
Large Intestine: Absorbs water, forms feces.

Example: Carbohydrates are digested in the mouth and small intestine.

Accessory Organs and Functions

Liver: Produces bile, processes nutrients.
Gallbladder: Stores and releases bile.
Pancreas: Produces digestive enzymes and hormones.

Enzymes in Digestion

Function: Speed up breakdown of food molecules.
Production Sites: Salivary glands, stomach, pancreas, small intestine.

Example: Amylase digests starch; pepsin digests proteins.

Surface Area and 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.

Example: BMR is measured after fasting and rest.

"My Plate" Purpose

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

Digestion Process and Peristalsis

Peristalsis: Wave-like muscle contractions move food through 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 and Alleles

Punnett Square: Diagram predicting genetic crosses.
Alleles: Variants of a gene; dominant alleles mask recessive alleles.
Homozygous: Two identical alleles.
Heterozygous: Two different alleles.

Mendelian Laws

Law of Segregation: Alleles separate during gamete formation.
Law of Independent Assortment: Genes for different traits assort independently.

Dominant and Recessive Disorders

Dominant Disorders: Expressed with one dominant allele; can be lethal.
Recessive Disorders: Expressed only with two recessive alleles; can persist in population.

Non-Mendelian Inheritance

Incomplete Dominance: Heterozygote shows intermediate phenotype.
Codominance: Both alleles fully expressed.
Polygenic Inheritance: Multiple genes influence a trait.
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: Genes on sex chromosomes, often X-linked.
Nondisjunction: Failure of chromosomes to separate during meiosis, leading to abnormal chromosome numbers in gametes.

Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Mendelian (Dominant/Recessive)	AA, Aa, aa	Dominant or recessive trait	Widow's peak
Incomplete Dominance	AA, Aa, aa	Intermediate phenotype	Pink snapdragon flowers
Codominance	AA, AB, BB	Both traits expressed	AB blood type
Polygenic	Multiple genes	Continuous variation	Skin color
Sex-linked	XAXa, XaY	Trait linked to sex chromosome	Color blindness

Example: Hemophilia is a recessive X-linked disorder.