Question

1.Describe the pulmonary and bronichial circulation structure and function

2. Identify the major structure of the upper respiratory tract and their functions.

Answer 1

1) Describe the Pulmonary and Bronchial Circulation and Structure ?

Introduction: The main function of the Pulmonary circulation is respiratory gas exchange, a vital function that the lungs take over from the placenta at birth. The structure of the Pulmonary circulation is highly adopted to fulfill this role. It receives entire cardiac output from the right ventricle during each cardiac cycle, and this mixed venous blood is delivered at high flow but low pressure to the delicate alveolar structures where gas exchange occurs.Blood flow is matched closely to the regional ventilation within the lung to optimize maintain systemic arterial oxygenation.

Structure of the Pulmonary Circulation:

1. The Pulmonary arteries and bronchi together with lympahatics, run in a single connective sheath in the centre of pulmonary segments and lobules, the so called " Broncho vascular bundle ",

2.The conventional pulmonary arteries branch dichotomously and symmetrically, along with the airways and they also give off extra branches between the conventional branching points called 'Supra numeracy' or short branches,

3. The intrapulmonary veins pursue a different course along the edges of lobules and segments in the interlobular septa. The branching pattern of veins is similar to that of the Pulmonary arteries.

4. The branching pattern of the Pulmonary arteries can be described by two approaches, they are

a) divergent approach where main pulmonary artery called generation 1,2,3, etc,

b) Convergent approach - where peripheral branch numbered order - 1, it increases up to 17 that main pulmonary artery, with a diameter from 13 micro meter to 30,000 um . These pre capillary vessels are involved in disease process that affect the pulmonary circulation.

5. The wall structure of the Pulmonary arteries changes along their length depending on the function of the vessel,

- Elastic arteries - ( order 17 - 13) Large arteries contain adventitial, muscular and intimal layers,

- muscular arteries - ( Order 13 - 3) small arteries, possess only internal and external laminae,

- Partial muscular arteries ( orders 5-3), contains smooth muscle fibers, leading to incomplete muscular coat,

- Non muscular arteries ( Order 5-1), contains no elastic laminae, smooth muscle replaced by pericytes whose basement membrane fuses with that of the endothelial cell lining the vascular lumen.

Pulmonary Veins: similar to  that of the arteries, but with only 15 orders, because 4 pulmonary veins converge on the left atrium without joining up to form an additional 2 orders,

- veins do not have the an internal elastic laminae,

- their walls contain more elastic and less muscular tissue.

Capillarynetwork: 300 million precapillary vessels lead into a network of alveolar septal capillaries with a blood volume (150ml) equal to that in the Pulmonary arterial or venous systems.

- the capillary surface area is about 125M2 ,

- Alveolar capillaries have thick and thin side, thin side consists of cytoplasmic extensions of the luminal endothelial and alveoli epithelial cell lining.

Distribution of Pulmonary circulation;

Blood flow within the lungs is heterogeneous in distribution, that heterogeneity based on two factors, they are:

1. Gravity dependent flow,

2. Gravity independent flow.

Regulation of Pulmonary vasomotor tone: pulmonary circulation differ from systemic circulation, is fully dilated under normal conditions.

- Circulating and local production of vasodilators and vadi constrictors contributing to the resting tone.

- the autonomic nervous system interacts with humoral mediators and he amp dynamic forces for the control of pulmonary vascular tone, autonomic interaction of the lung being via parasympathetic and sympathetic nerves in the periarterial plexus.

*** play a vital role in Hypoxic pulmonary vasoconstriction and ventilation perfusion relationships ***.

Pulmonary Vascular Resistance (PVR):

The pulmonary circulation is a high flow , low pressure system whose pvr is one tenth of systemic vascular resistance (SVR).

PVR= Ppa-Ppv/QP,

PVR is the mean pulmonary arterial - venous pressure difference ( Ppa-Ppv) to mean pulmonary blood flow (QP).

Summary of the Answer:  The normal pulmonary circulation distributed the deoxygenated blood at low pressure and high flow to the pulmonary capillaries for gas exchange.The structure of Pulmonary vessels vary with their function,PVR is the one tenth of SVR being the great contribution to resistance, many neural and humoral mediators can influence the pulmonary circulation including nitric acid and prostacyclin, alveolar hypoxia causes construction of small pulmonary arteries where as systemic arteries dilate when hypoxic. Despite large regional differences in the matching of ventilation perfusion is maintained remarkably steady at around 0.85.

Q)2) Identify major structure of the Upper respiratory tract and their functions?

A) The upper respiratory tract contains the following structures. They are mainly:

1) Conchae,

2) Glotitis,

3) Larynx, Vocal Cords and

4) Trechea, Bronchi and Bronchioles.

All the respiratory passageways open to allow easy passage of air to and from alveoli, hence the structures of respiratory systems should have good physiological functions. If we observe the major structures of URT are

Treachea - to keep the trachea from collapsing, multiple cartilage rings extend about sixth of the way around the treachea

Bronchi and Bronchioles: In all areas of trechea and bronchioles composed mainly by smooth muscle,

- Many obstructive diseases result from narrowing of smaller bronchi and bronchioles,

- under normal respiratory conditions air flow easily 1 cm of water pressure gradient from the aveoli to the atmosphere is sufficient to enough air flow for breathing,

- yet in disease conditions, the smaller bronchioles play greater role in air flow resistance for two reasons,

1. Because their small size, easily occluded,

2. Because they have greater percentage of smooth muscle in the walls, they constrict easily.

Nervous and local control of bronchioles: sympathetic nerve and beta receptors produced hormones like epinephrine,

Parasymapthetic construction of bronchioles by thevagal nerve penetrate parenchyma,

Local secretory factors: Histamine and mast cells. They are slow reactive anaphylaxis and allergic reactions respectively.

In the URT Brochiiles play a vital role in pathological conditions.

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