The parietal cells or oxyntic cells are large, rounded cells located upon the surface of gastric glands. These cells secrete $\mathrm{HCl}$ (which converts inactive pepsinogen into active pepsin) and Castle's Intrinsic Factor or CIF (which helps in the absorption of vitamin- $B_{12}$ or cyanocobalamine). If somehow, parietal cells become partially non-functional, the patient will suffer from achlorhydria (no $\mathrm{HCl}$ ) or hypochlorhydria (less $\mathrm{HCl}$ ). This will result in the non-activation of pepsinogen due to which proteins will not be adequately hydrolysed into proteoses and peptones. Lack of CIF will cause vitamin- $\mathrm{B}_{12}$ deficiency, which will result in pernicious anaemia.