Phases of lung development

1.      Embryonic : 

                                           i.     In utero

                                         ii.     3- 5 weeks

                                        iii.     Formation of primitive lung tissue and vascular connection

                                        iv.     Trachea and bronchi differentiation

2.     Pseudo glandular:

                                           i.     In utero

                                         ii.     05-16 weeks

                                        iii.     Formation of conducting air way

                                        iv.     Immature neural network

                                          v.     Appearance of type-II pneumocyte

3.      Canalicular:

                                           i.     In utero

                                         ii.     17-26 weeks

                                        iii.     First gas exchanging acini and pulmonary capillaries are forming.

                                        iv.      Vascular and lymphatic system develop alongside the bronchial tree.

                                          v.     Appearance of type-I pneumocyte.

                                        vi.     Beginning of surfactant production

4.     Saccular :

                                           i.     In utero

                                         ii.     27-36 weeks

                                        iii.     Alveolar saccule formation

                                        iv.     Maturation of surfactant system

                                          v.     Breathing effort begin.

                                        vi.     ECM formation

5.      Alveolar :

                                           i.     At birth

                                         ii.     37 weeks to 3+ years

                                        iii.     Mature alveolar formation

                                        iv.     Reduction of interstitial tissue.

                                          v.     Proliferation and expansion of capillary, nerve and gas exchange area.

                                        vi.     ECM formation.

Hormones of metabolic homeostasis at a glance

1.                   Insulin; which decrease blood glucose concentration

2.                   Glucagon; increase blood glucose concentration

3.                   Catecholamines ; increase blood glucose concentration

4.                   Cortisol ; increase blood glucose concentration

5.                   Growth hormone ; increase blood glucose concentration

Urea cycle at a glance

Substrate—NH₃

Product--Urea

Site--Liver,

Compartment—Mitochondria & Cytoplasm

Nature--anabolic

Rate limiting enzyme—Carbamoylphosphate  synthase 1

Energy needed—03 ATP

Regulator—N-acetyl glutamate

Importance:

1.      Conversion of toxic NH₃ into no toxic urea

2.      Disposal of two waste products; NH₃ and Co₂

3.      Synthesis of argentine

4.      Synthesis of proline

5.      Interaction of TCA cycle

·         TCA cycle  Co₂ and ATP for urea cycle

·         Urea cycle provides fumerate for TCA cycle