Bhashya
अथ प्राण उच्यते— प्राणः मुखनासिकासंचारी हृद-यवृत्तिः प्रणयनात्प्राणः, अपनयनान्मूत्रपुरीषादेरपानः अ-धोवृत्तिः आ नाभिस्थानः, व्यानः व्यायमनकर्मा व्यानःप्राणापानयोः संधिः वीर्यवत्कर्महेतुश्च, उदानः उत्कर्षोर्ध्वग-मनादिहेतुः आपादतलमस्तकस्थान ऊर्ध्ववृत्तिः, समान समंनयनाद्भुक्तस्य पीतस्य च कोष्ठस्थानोऽन्नपक्ता, अन इत्येषांवृत्तिविशेषाणां सामान्यभूता सामान्यदेहचेष्टाभिसंबन्धिनीवृत्तिः— एवं यथोक्तं प्राणादिवृत्तिजातमेतत्सर्वं प्राण एव ।प्राण इति वृत्तिमानाध्यात्मिकः अन उक्तः ; कर्म च अस्य
In plain words
Now we define the vital force. Prāṇa is the breath that moves through the mouth and nose, centered in the heart—so named because it draws life forward. Apāna is the downward force that carries away waste, operating from the navel downward. Vyāna is the pervasive energy that governs physical exertion, acting as the bridge between inhalation and exhalation. Udāna is the upward-rising force that lifts us, spanning from the soles of our feet to the crown of the head. Samāna is the equalizer, centered in the digestive tract, which evenly distributes the nourishment of what we eat and drink. Underlying all these specialized movements is the basic breath, 'Ana,' which sustains the general motion of the body. All these distinct functions are nothing but the one vital force. This inner, living presence that holds these functions is what we call the breath; and its work...
Close to the Sanskrit
Now the vital force is described: Prāṇa, moving through the mouth and nose, is the activity of the heart, so called because of leading forward; Apāna, because of carrying away urine, feces, etc., is the downward activity, located up to the navel; Vyāna, whose action is stretching, is the junction of Prāṇa and Apāna and the cause of vigorous actions; Udāna is the cause of pulling up and upward movement, located from the soles of the feet to the head, being the upward activity; Samāna, because of carrying equally what is eaten and drunk, is located in the stomach as the digester of food; 'Ana' is the common activity of these specific modifications, connected with the general movements of the body—thus, this entire group of activities such as Prāṇa is only Prāṇa. The possessor of these activities, operating within the body, is called 'Ana' as Prāṇa; and its action...