First-degree atrioventricular block
First-degree AV block occurs when there is a delay, but not disruption, as the electrical signal moves between the atrium and the ventricles through the AV node. On ECG, this is defined by a PR interval greater than 200 msec. Additionally, there are no dropped, or skipped, beats. Second-degree atrioventricular block
Second-degree AV block occurs when the electrical signal between the atria and ventricles is even more impaired than in a first-degree AV block. In a second-degree AV block, the impairment results in a failure to conduct an impulse, which causes a skipped beat. Mobitz I
Mobitz I is characterized by a progressive yet reversible block of the AV node. On ECG, this is defined by progressive prolongation of the PR interval, with a resulting dropped beat (the PR interval gets longer and longer until a beat is finally dropped, or skipped).Some patients are asymptomatic; those who have symptoms respond to treatment effectively. There is a low risk of a Mobitz I AV block leading to heart attack and complete heart block. Mobitz II
Mobitz II is caused by a sudden, unexpected failure of the His-Purkinje cells to conduct the electrical impulse. On ECG, the PR interval is unchanged from beat to beat, but there is a sudden failure to conduct the signal to the ventricles, and resulting in random skipped beat.The risks and possible effects of Mobitz II are much more severe than Mobitz I in that it can lead to severe heart attack.
It is present in the stratum corneum and fat cells of dermis and superficial fascia. Hemoglobin (also spelled haemoglobin): It is found in blood and is not a pigment of the skin but develops a purple colour. Oxyhemoglobin: It is also found in blood and is not a pigment of the skin. It develops a red colour.There is a correlation between the geographic distribution of UV radiation (UVR) and the distribution of indigenous skin pigmentation around the world. Areas that highlight higher amounts of UVR reflect darker-skinned populations, generally located nearer towards the equator. Areas that are far from the tropics and closer to the poles have lower concentration of UVR, which is reflected in lighter-skinned populations.In the same population it has been observed that adult human females are considerably lighter in skin pigmentation than males. Females need more calcium during pregnancy and lactation, and vitamin D which is synthesized from sunlight helps in absorbing calcium. For this reason it is thought that females may have evolved to have lighter skin in order to help their bodies absorb more calcium.The Fitzpatrick scale is a numerical classification schema for human skin colour developed in 1975 as a way to classify the typical response of different types of skin to ultraviolet (UV) light:

Ageing
As skin ages, it becomes thinner and more easily damaged. Intensifying this effect is the decreasing ability of skin to heal itself as a person ages. Among other things, skin ageing is noted by a decrease in volume and elasticity.