Cardiovascular system:
increased heart rate, blood pressure, risks of arrhythmia. The heart has to work harder and faster and this stress can have deleterious effects on an older animal.

Gastrointestinal system:
slowing of gastric transit time and increased intestinal secretions lead to vomiting, anorexia, risk of gastric ulceration, constipation.

Immune system: impaired.
This leads to increased risk of infection, enhances metastatic tumour spread, increased risk of tumour occurrence in animals in remission.

increased metabolism and oxygen consumption. Breakdown of muscle, fat and glucose stores. AS a result delayed wound healing, weight loss and increased tissue breakdown. Weak old dogs become weaker!

increased respiratory rate and depth of breathing increases. Increased risk of pneumonia.

urine retention, water and sodium retention. Electrolyte imbalances.