RESPIRATORY SYSTEM

DEPARTMENT OF HISTOLOGY, CYTOLOGY AND EMBRYOLOGY TATIANA GLOBA

Functions:- Provides gas exchange

- Olfaction

- Blood storage (well blood supply)

- Blood clotting (synthesis in the lungs of thromboplastin and heparin)

- Endocrine (synthesis of biologically active substances which act on bronchi tonus)

- Immune or protective (presence of lymphocytes, macrophages)

Two principle subdivisions of the respiratory system

1. AIR CONDUCTING PORTIONa. Nasal cavity, oral cavityb. Nasopharynx, oropharynx, and larynxc. Trachead. Bronchi (main, lobar, segmental, subsegmental)e. Terminal bronchioles

These provide a passageway to and from lungsThese components also "condition" the inspired air (i.e. moistens, removes particles and some noxious gases, warms air)

2. RESPIRATORY PORTION (RESPIRATORY ACINUS – morpho-functional unit)- 12-18 acini make a lobulea. respiratory bronchioles (3-4 orderb. alveolar ductsc. alveolar sacs d. alveoli used for gas exchange

Provide gas exchange

MUSCULOELASTIC VENTILATION APPARATUS -muscles, e.g. intercostals and diaphragm, used for moving air in and out of the lungs.

SIMPLE PSEUDOSTRATIFIED COLUMNAR CILIATED EPITHELIUM

• Columnar ciliated cells – are most numerous. On the apical surface have cilia, that move mucus back toward oral area. Function: cleaning of the air.

• Basal cells - thought to be stem cells that will divide to provide replacements for dead or lost cells of the epithelium.

• Goblet cells (mucus secreting) are interspersed among the more numerous columnar ciliated cells. Produce mucous.

SIMPLE PSEUDOSTRATIFIED COLUMNAR CILIATED EPITHELIUM

In addition, there are other types of cells:

– Endocrine cells – produce serotonin, noradrenalin.

– Brush cells - lack cilia, have apical microvilli, arelocated in the distal portion of bronchial tree -possible endocrine or sensory function(chemoreceptors).

– Non-ciliated Clara cells are present in terminal andrespiratory bronchioles – possible produce surfactant.

– Dendritic cells (Langerhan’s) – antigen-presentationcells, stimulate proliferation of T-lymphocytes.

cl = cilia, gc = goblet cell, bm = basement membrane

NASAL CAVITYThe Nasal cavity is divided into three structurally and functionally different parts.• the vestibules • the respiratory region• the olfactory region

LARYNXAn irregular tube that connects pharynx to the trachea. Laryngeal wall consists of:

• Mucosa• Cartilages• Intrinsic muscles

The larynx comprises two folds which protrude into the airway.1. The upper fold is the false vocal cord which is

covered by columnar ciliated respiratory epitheliumand contains sero-mucous glands.

2. The lower fold is the true vocal cord.

TRUE VOCAL CORD

contains the vocalis muscle and vocalisligament which are responsible for moving thetrue cord so that it becomes distant from orcloser to the true cord on the other side, thuscontrolling the pitch of the sound made.are covered by stratified epithelium which ismore resistant to the effects of physical traumacaused by the free margins of the true cordscontacting each other during speech.

VENTRICLE

Between the true and false cords is anarrow cleft, the ventricle whichterminates in a blind-ending saccule.

The ventricle is lined by respiratory typecolumnar epithelium, and containsseromucous glands.

Laryngeal mucosa

Lamina Propria Consists of fine connective tissue and

contains: Scattered lymphatic nodules Many simple branched tubulo-alveolar

glands of mixed variety Nine cartilages:o 3 paired and 3 unpaired.

Epiglottis Unpaired cartilage (elastic), covered on both sideby mucosa comprising of epithelium and laminapropria.

Epithelium of EpiglottisAnterior (lingual) surface and upper part ofposterior (laryngeal) surface are covered bystratified squamous non keratinized epithelium.

Lower half of the posterior surface is covered bythe respiratory epithelium.

Epiglottis Lamina Propria

Contains tubulo-alveolar glands of mixed type mainly on the posterior surface.

Scattered taste buds are present between the epithelial cells on the posterior surface.

I. Tunica mucosa 1. simple pseudostratified columnar ciliated epithelium2. lamina propria of mucosa – loose connective tissue, contains many

lymphocytes

II. Tunica submucosa - is composed of loose connective tissueand contains the secretory components of serous and mucous glandswhose ducts empty into the tracheal lumen.

III. Tunica fibro-cartilage - C-shaped rings of hyalinecartilage; * Trachealis muscle (smooth muscle) connects the ends ofthe “C” formed by the cartilage rings. * The cartilage and musclemake the trachea a very rigid structure.

IY. Tunica adventitia

TRACHEA

Trachea

Bronchial Tree2 primary (main) bronchi enter lungs3 lobar bronchi on right and 2 on the left lung (secondary bronchi)segmental bronchi (tertiary): R: 3 in upper, 2 in middle, 5 in lower lobeL: 5 in upper, 5 in lower lobe

- subsegmental bronchi Terminal bronchioles

RESPIRATORY ACINUS

Large bronchiØ 10-15 mm

Medium bronchi Ø 5-2 mm

Small bronchi Ø < 2 mm

Tunica mucosa:1. Epithelium

Simple pseudostratifiedcolumnar ciliated epitheliumis tall.Goblet cells are numerous

Simple pseudostratifiedcolumnar ciliated epitheliumbecomes lower than in thelarge bronchi.Number of Goblet cellsdecreases

Simple is simple columnar to simple cuboidalGoblet cells are absent.

2. Muscularis internais absent appears is well developed – circularly

arranged smooth muscle cellsTunica submucosa

Mixed glands are numerous Number of glands decreases Glands are absentTunica fibro-cartilage

Lamelae of hyaline cartilage Islets of cartilage. Hyalinecartilage is changed to elastic

Is absent

BRONCHUS OF MEDIUM DIAMETER

BRONCHUS OF SMALL DIAMETER

Respiratory Components

The respiratory components consist of:Respiratory bronchiolesAlveolar ductsAlveolar sacsAlveoli

Respiratory ComponentsRespiratory bronchioles have incomplete walls such that alveoli make direct contact. This allows for gas exchange to occur.Alveolar ducts are where respiratory bronchioles branch. There is much greater space with alveoli exposed.Alveolar sacs are clusters of alveoliAlveoli are single bubble like structures

Pulmonary acinus

alveolus

LUNG

Cells of the alveolar wall

1. Alveolar type I cells - squamous epithelial cellsa. the cells across which gaseous transfer occursb. Compose about 40% of the alveolar cells, but cover about 95% of the alveolar surface area.

2. Alveolar type II cells (also called “big” cells)– a. These are roughly cuboidal with many microvilli on

their free surface– b. Synthesize and secrete a surfactant.

Surfactant

Phospholipids: coats inside of each alveolusWithout it: alveolus would collapse

Is a component of the blood-air barrierstands in the way of excretion of the blood plasma and

interstitial fluid into the lumen of alveolibactericidal action

Cells of the alveolar wall

3. Also find alveolar macrophages called dust cells - usually free in the alveolar lumen, but also in tissues between alveoli.

a. These cells act to clean fine inhaled debris from the alveolar free surface of cells by endocytotingparticles.

The blood-air barrierThis refers to the substances/structures that lie between the air in the

alveolar sacs and the blood in the capillaries.

Starting in the alveolar lumen this barrier consists of:

* Surfactant

* Type I alveolar cells lining the alveolus

* Basal lamina of both alveolar cells and capillary endothelial cells (fused in some areas)

* Non-fenestrated (continuous) endothelium of capillary

* In areas where basal lamina of the two endothelial layers are not fused, reticular and elastic fibers are present.

Alveolar Capillaries

Mechanism for gas exchangePrimary source of angiotensin converting enzyme: angiotensin I to angiotensin II– Regulation of blood volume and blood pressure

Pleura

Mesothelial cellsConnective tissue

Pleural effusion - fluidHaemothorax - bloodPneumothorax - airPleuritis - infection