One capillary and the tissue cylinder it feeds, cut along and across: laminar flow, red cells, haemoglobin saturation and the oxygen profile out to the far tissue. Educational, not medical advice.
The science
Poiseuille flow. For laminar flow in a round tube Q = pi r^4 dP / (8 mu L), mean speed v = Q / (pi r^2) and a parabolic profile u(rho) = dP (r^2 - rho^2) / (4 mu L) whose centreline speed is twice the mean. Halving the radius cuts the flow 16-fold at fixed pressure.
Blood viscosity. The apparent viscosity uses the Pries et al. in-vitro fit as a function of tube diameter and haematocrit (Fahraeus-Lindqvist effect), multiplied by a plasma viscosity of 1.2 mPa s.
Oxygen carriage. Saturation follows the Hill curve S = P^n / (P^n + P50^n) with n = 2.7, P50 = 26.8 mmHg. Along the capillary the haemoglobin-bound oxygen delivered per second is Q * 1.34 * 0.33 * Ht * (S_in - S) and equals what the tissue cylinder has consumed up to that point, M * pi (R^2 - rc^2) * x.
Krogh cylinder. Steady radial diffusion with uniform consumption M gives P(r) = Pc - M/(4 D alpha) [ 2 R^2 ln(r/rc) - (r^2 - rc^2) ] between the capillary wall rc and the cylinder edge R, with zero flux at R. Where this falls to zero the tissue is anoxic.
Simplifications. Rigid round tube, steady flow, no pulsatility, no autoregulation, uniform consumption, dissolved oxygen ignored in the balance, and the diffusion constant D alpha = 4.4e-10 mL O2 / (cm s mmHg) is a model value. The vertical scale of the longitudinal view is exaggerated. Not for clinical use.