lab 05 diagrams AP 2

Trachea and esophagus: transverse section

Trachea is a round tube with C-shaped hyaline cartilage, open side facing back. The esophagus is a flattened tube directly behind (posterior to) the trachea, touching the open side where the trachealis muscle is.

Trachea and esophagus: sagittal section

The trachea runs in front (anterior) and the esophagus lies behind (posterior) it, both in front of the vertebral column.

Essential difference: conducting vs respiratory division

Conducting division only carries air to the gas-exchange area (no gas exchange; warms, humidifies, filters). Respiratory division is where gas exchange actually occurs across thin walls.

Significance of pleural membrane and fluid in ventilation

Pleural fluid creates surface tension that holds the visceral pleura (lung) to the parietal pleura (chest wall), so the lungs expand and recoil with the thoracic cavity. It also lubricates to reduce friction.

Location of lungs relative to heart and diaphragm

Lungs fill the thoracic cavity on both sides of the heart (in the mediastinum). The bases rest on the relaxed, dome-shaped diaphragm; the apices extend slightly above the clavicles.

Trachea histology

Lined by pseudostratified ciliated columnar epithelium with goblet cells. Beneath it: lamina propria, mucus glands, and C-shaped hyaline cartilage rings (with chondrocytes). The trachealis (smooth muscle) closes the gap at the back.

Full pathway of O2: outside the body to the cells

Air -> nose/mouth -> pharynx -> larynx -> trachea -> bronchi -> bronchioles -> alveoli -> across respiratory membrane into pulmonary capillary -> pulmonary veins -> left atrium -> left ventricle -> aorta -> systemic arteries -> systemic capillaries -> across capillary wall into body cells

Full pathway of CO2: cells to outside the body

Body cells -> systemic capillaries -> veins -> vena cava -> right atrium -> right ventricle -> pulmonary trunk -> pulmonary arteries -> pulmonary capillaries -> across respiratory membrane into alveoli -> bronchioles -> bronchi -> trachea -> larynx -> pharynx -> nose/mouth -> exhaled

Five stages of respiration

1) Ventilation 2) External respiration 3) Transport 4) Internal respiration 5) Cellular respiration

Ventilation

Movement of air into and out of the lungs (atmosphere <-> alveoli). O2 moves in, CO2 moves out. Occurs in the airways and lungs.

External respiration

Gas exchange in the lungs between alveoli and pulmonary capillaries. O2 moves from alveoli into blood; CO2 moves from blood into alveoli.

Transport

Blood carries O2 and CO2 between the lungs and body tissues via the cardiovascular system. O2 is mostly bound to hemoglobin; CO2 is mostly carried as bicarbonate.

Internal respiration

Gas exchange between systemic capillaries and body cells. O2 moves from blood into cells; CO2 moves from cells into blood.

Cellular respiration

Cells use O2 to break down glucose and make ATP, producing CO2 and water. C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + ATP

Relationship between CO2 and cellular respiration

CO2 is a waste product of cellular respiration (made in the mitochondria when glucose is broken down) and must be carried away and exhaled.

Relaxed diaphragm shape and position

Dome-shaped, bulging up into the thoracic cavity. The lungs sit superior to it on either side of the heart (mediastinum).

Left lung vs right lung (lobes)

Left lung has 2 lobes (superior, inferior); right lung has 3 lobes (superior, middle, inferior).

Why is the left lung smaller?

It has a cardiac notch (indentation) to make room for the heart, which tilts toward the left.

Parietal pleura

Outer layer of the pleural membrane; lines the thoracic wall, diaphragm, and mediastinum.

Visceral pleura

Inner layer of the pleural membrane; covers the surface of the lungs.

Pleural cavity

Thin space between parietal and visceral pleura, filled with pleural (serous) fluid.

Three purposes of the pleural membranes

1) Pleural fluid reduces friction as lungs expand and recoil. 2) Fluid surface tension holds the lungs to the thoracic wall so they expand with it during ventilation. 3) Compartmentalizes each lung, limiting spread of infection and protecting the lungs.

What resists excessive expansion of the lungs?

The elastic fibers (elastic connective tissue) in the lungs, which recoil, along with stretch receptors that signal the brain to stop inhaling.

What actually prevents food from entering the larynx during swallowing?

The vocal folds and vestibular folds (false vocal cords) close the glottis, and the larynx elevates so the airway is sealed. The epiglottis only helps a little.

Purpose of cartilaginous rings in trachea and bronchi

Keep the airway open (patent) so it doesn't collapse when pressure changes during breathing.

Why are tracheal rings C-shaped (incomplete)?

The open part faces posteriorly toward the esophagus so the esophagus can expand into the trachea when food is swallowed. The trachealis muscle closes the gap.

Position of trachea vs esophagus

The trachea is anterior to the esophagus; the esophagus lies posterior to the trachea, in front of the vertebral column.

Left vs right primary bronchus

Right: shorter, wider, more vertical. Left: longer, narrower, more horizontal (angled around the heart).

Which bronchus is aspirated food most likely to enter?

The right primary bronchus, because it is wider, shorter, and more vertical, so objects drop straight into it.

Conducting division

Structures that only move air to the gas-exchange area (no gas exchange). Warms, humidifies, and filters air. Nasal cavity through terminal bronchioles.

Respiratory division

Structures where gas exchange occurs: respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

Structures of the respiratory division

Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli.

Upper respiratory tract

Nose, nasal cavity, paranasal sinuses, and pharynx (nasopharynx, oropharynx, laryngopharynx).

Lower respiratory tract

Larynx, trachea, bronchi, bronchioles, and lungs (alveoli).

Epithelium: vestibule of the nostril

Stratified squamous (keratinized). Protects against abrasion and traps large particles at the entrance.

Epithelium: nasal cavity

Pseudostratified ciliated columnar (respiratory epithelium) with goblet cells. Traps and moves debris with mucus; warms and humidifies air.

Epithelium: nasopharynx

Pseudostratified ciliated columnar. Air-only passage; moves mucus and trapped debris toward the throat to be swallowed.

Epithelium: oropharynx

Stratified squamous. Passage for both food and air, so it needs protection from abrasion.

Epithelium: laryngopharynx

Stratified squamous. Food and air pass through, so it needs protection from abrasion.

Epithelium: alveoli

Simple squamous. Very thin, so gases diffuse quickly across it.

What is respiratory epithelium?

Pseudostratified ciliated columnar epithelium with goblet cells, lining most of the conducting airways (nasal cavity to bronchi). Goblet cells make mucus that traps dust and microbes, and cilia sweep it.

Mucociliary escalator

Cilia beat in a coordinated upward motion, moving mucus with trapped particles toward the pharynx, where it is swallowed or coughed out. It cleans the air passages.

Great alveolar cell (type II)

Secretes surfactant, which reduces surface tension in the alveolus and prevents it from collapsing; can also replace damaged alveolar cells.

Squamous alveolar cell (type I)

Thin, flat cell that makes up most of the alveolar wall; allows rapid gas exchange between the alveolus and the capillary.

Alveolar macrophage

Phagocytic "dust cell" that removes debris, bacteria, and particles that reach the alveoli, keeping them clean.

Surfactant

Lipid-protein fluid secreted by great alveolar cells that lowers surface tension and keeps alveoli from collapsing.

Respiratory membrane

Thin barrier for gas exchange: alveolar squamous cell, fused basement membranes, and capillary endothelial cell.

Direction of O2 and CO2 at the alveolus

O2 moves from the alveolus into the capillary blood. CO2 moves from the capillary blood into the alveolus (each down its concentration gradient).

Path of air (ventilation)

Nose/mouth -> nasal cavity -> pharynx (naso-, oro-, laryngo-) -> larynx (glottis) -> trachea -> primary bronchi -> secondary bronchi -> tertiary bronchi -> bronchioles -> terminal bronchioles -> respiratory bronchioles -> alveolar ducts -> alveolar sacs -> alveoli

Structures O2 crosses in external respiration

Alveolar squamous cell (type I) -> fused basement membranes -> capillary endothelial cell -> blood (red blood cell, binds hemoglobin).

Vessel sequence for O2 during transport

Pulmonary capillaries -> pulmonary venules -> pulmonary veins -> left atrium -> left ventricle -> aorta -> systemic arteries -> arterioles -> systemic capillaries

Structures O2 crosses in internal respiration

Capillary endothelial cell -> interstitial fluid -> plasma membrane of the body cell -> into the cell (down its gradient).

What happens to O2 in cellular respiration?

It is the final electron acceptor in the mitochondria, used to make ATP; produces CO2, H2O, and ATP.

CO2 in internal respiration

CO2 diffuses from cells (high CO2) across the cell membrane, interstitial fluid, and capillary endothelium into the blood.

Vessel sequence for CO2 during transport

Systemic capillaries -> venules -> veins -> superior/inferior vena cava -> right atrium -> right ventricle -> pulmonary trunk -> pulmonary arteries -> pulmonary arterioles -> pulmonary capillaries

CO2 in external respiration

CO2 diffuses from pulmonary capillary blood across the capillary endothelium, fused basement membranes, and alveolar squamous cell into the alveolus.

Pathway of CO2 in ventilation

Alveoli -> respiratory bronchioles -> terminal bronchioles -> bronchioles -> bronchi -> trachea -> larynx -> pharynx -> nasal/oral cavity -> out. It is the reverse of the O2 pathway.

How is transport different for O2 vs CO2?

O2 is mostly (about 98%) bound to hemoglobin in red blood cells, with a small amount dissolved. CO2 is mostly (about 70%) carried as bicarbonate, with the rest bound to hemoglobin or dissolved in plasma.

Pulmonary circuit pathway

Right ventricle -> pulmonary trunk -> pulmonary arteries -> pulmonary arterioles -> pulmonary capillaries (gas exchange) -> pulmonary venules -> pulmonary veins -> left atrium

Overall purpose of breathing

To supply O2 for cellular respiration (ATP production) and remove the CO2 waste, which also helps maintain blood pH.