Degenerative changes in the physiology of the elderly are a reflection of the aging process, and as aging progresses, diminished functional reserves of major organ systems are evident. The structural and functional changes in organs brought about by aging significantly lower the threshold for the development of clinical diseases, and together with subclinical diseases that are not yet evident, they reduce the reserve capacity of the elderly to maintain the internal homeostasis of the body. With increasing age, chronic diseases in the elderly gradually accumulate and tend to progress acutely or even fall into a vicious circle. 1. Cardiovascular system As the aging process progresses, a series of physiological and pathological changes can occur in the cardiovascular system. From age 30 to 70, the ventricular wall loses nearly 35% of its cardiomyocytes, and the density of capillaries decreases with age, leading to ischemic injury. Compensatory hypertrophy of the remaining cardiomyocytes. Increased interstitial connective tissue matrix, increased collagen and even amyloidosis, increased cardiac stiffness, decreased compliance, decreased myocardial contractility, decreased cardiac output, and susceptibility to postural hypotension. The systolic function, as well as ejection fraction, cardiac output, and stroke volume of the left ventricle at rest in healthy elderly people do not show significant changes, whereas cardiac output decreases approximately 1.2 L/min per decade during exercise, probably due to poor myocardial chronotropy and force variability during stress, increased cardiac afterload, reduced aortic compliance, and increased left ventricular wall pressure. In contrast to systolic function, diastolic impairment is present in the elderly at rest, requiring greater filling pressures to compensate according to the Frank-Starling law. Disturbed myocyte alignment, asynchronous electrical activity, and abnormal calcium transport further affect diastolic compliance and filling parameters. Diastolic function can deteriorate with age due to coexisting structural changes, such as mitral or aortic valve disease, hypertension, atrial arrhythmias, or age-related amyloidosis, all of which can affect hemodynamic status. Alterations in vascular endothelial cell function due to aging often coexist with hypertension, hypercholesterolemia, and the effects of atherosclerosis on endothelial function. Thickening of the intima of arteries in the elderly, growth of smooth muscle in the intima, increase in collagen fibers, atherosclerosis and deposition of calcium in the elastic layer cause dilatation of large arteries with tortuosity, smaller lumen of small arteries, vascular sclerosis, decreased diastolic function and elevated vascular resistance, which predispose to decreased perfusion of the heart, brain, liver, kidney and other organs. The detection rate of coronary arteriosclerotic heart disease increases significantly in older adults over 60 years of age, and many of these patients may be asymptomatic. Aortic valve calcification and stenosis are highly prevalent in the elderly. Increased systolic pressure increases the cardiac load, and left ventricular hypertrophy prevents diastolic ventricular filling, which limits the increase in beat-to-beat output under stressful conditions. With increasing age, apoptosis, increased deposition of collagen and adipose tissue, decreased cardiac sinus node viability, and loss of cardiac conduction fibers continue. Starting at age 60 years, the number of sinus node pacing cells decreases significantly and fibers increase. At age 75, only 10% of the pacemaker cells are present in young adults. The atrioventricular node, atrioventricular bundle and bundle branches have varying degrees of fibrosis and some calcification, which can lead to cardiac conduction disturbances. As a result, PR and QT intervals, prolonged QRS time, bundle branch block, and T-wave hypoplasia are common on the ECG in older adults. Studies have also confirmed an increasing incidence of atrial fibrillation between the ages of 50 and 80 years, an increasing trend in the occurrence of atrial and ventricular premature contractions, and the development of short-onset supraventricular tachycardia in more than 33% of healthy individuals over the age of 60 years. Neither the density of beta-adrenergic receptors nor the ratio of beta1 to beta2 receptors changed with age, but the response of aging cardiomyocytes to beta-adrenergic stimulation was diminished. The effects of adrenaline on myocardial contraction rate, heart rate, and vascular tone decline with age. In healthy individuals, cardiac output can increase with exercise until age 90, but maximum heart rate decreases with age (approximately once per minute per year), so that stress-induced changes in cardiac output rely heavily on increases in output per beat. However, cardiac contractility is reduced in the elderly, and cardiac function is easily affected when blood volume changes are caused by blood loss, dehydration, or rapid diuresis. 2. Respiratory system The respiratory system gradually ages with age. The airway mucosa and glands atrophy, the filtering and heating function of airflow decreases or is lost, so that the overall airway defense function decreases, which easily causes upper respiratory tract infections. Tracheal and bronchial mucosa atrophy, elastic tissue reduction, fibrous tissue hyperplasia, submucosal gland and smooth muscle atrophy, bronchial cartilage calcification, hardening, lumen expansion, small airway-like cells increase in number, hypersecretion, mucus retention, increased airflow resistance, prone to expiratory dyspnea, often causing small airway atrophy and closure. Due to the poor excretion of secretions in the lumen, the chance of infection increases, and the inner diameter becomes large and barrel-shaped. The thorax is hardened by calcification of the ribs and spine, and the mucosal epithelium and mucus glands are degenerated, so the lumen expands and the anterior and posterior diameters become larger in a barrel shape. The alveolar wall becomes thinner, the alveolar cavity expands, the elasticity decreases, the weight of lung tissue decreases, the respiratory muscle atrophies, and the elastic retraction force of the lung decreases, resulting in lower lung volume, increased residual air volume, degeneration of the cough reflex and ciliary motor function, and weakened cough and reflex function in the elderly, which increases the secretions and foreign bodies retained in the lungs and makes them susceptible to infection. The residual air volume and dead space ventilation/tidal volume increase in the elderly, the alveolar diffusion capacity decreases, and the ventilation function decreases, as shown by the decrease in arterial partial pressure of oxygen with age [PaO2=(100-years/3)mmHg] and the increase in alveolar arterial oxygen gradient. Exertional expiratory volume in one second (FEV1) decreases by 10 ml per year after 30 years of age and by more than 20 ml per year in smokers. In the elderly, chemoreceptor reactivity is reduced and the ventilatory response to hypoxia and hypercapnia is diminished. Respiratory disease is a common disease in the elderly and an important cause of death in elderly patients. With the global social and economic development, many respiratory diseases are not only decreasing but also increasing year by year. The proportion of smoking is higher in the elderly population, and the incidence of chronic obstructive pulmonary disease, tuberculosis, lower respiratory tract infections, and lung cancer increases significantly with age. The elderly are also more prone to respiratory failure in acute exacerbations of chronic respiratory diseases and in exacerbations of other systemic diseases. Pulmonary atelectasis and aspiration pneumonia are more likely to occur in the elderly in cases of surgery, fracture, and bed rest, and pulmonary embolism is an important cause of death among the elderly. Epidemiological survey data show that more than half of the elderly over 65 years of age suffer from sleep disorders, shallow and slow breathing during sleep or pause, which causes recurrent episodes of hypoxia, hypercapnia, acidemia, which can lead to sudden death in severe cases, and damage to organs of the heart, lungs, brain and kidneys, which is one of the important causative factors for the development of hypertension, coronary heart disease, stroke and Alzheimer’s disease. 3, renal system With the increase in age, under the combined effect of physiological aging and various metabolic disorders and other factors, kidney tissue structure and its function are significantly changed, the human body after the age of 40, the kidney functions are progressive decline. Clearance tests have shown that renal blood flow in humans decreases progressively from the age of 40, decreasing by 10% every 10 years, and the renal blood flow in 90-year-olds is only 50% of that in young people. Between the ages of 30 and 50, the number of surviving functional glomeruli gradually decreases, and the number of capillary collaterals per unit area also decreases, while the thylakoid component increases, the basement membrane thickens, and the small arteries become vitreous, resulting in focal glomerulosclerosis. The number of glomeruli with sclerosis or vitreous changes is already as high as 30% in healthy-looking 80-year-olds. At the same time, the proximal tubules are gradually atrophied, the distal tubules are dilated and some diverticula or cysts are formed; in addition, common age-related diseases such as hypertension and diabetes can accelerate the process of glomerular and renal arteriosclerosis in the elderly population. Decreased renal function in the elderly also includes decreased glomerular filtration rate (GFR), decreased urine concentration and dilution capacity, decreased renin response to volume, and decreased tubular capacity to secrete NH+4. In the elderly, muscle tissue groups are atrophied and creatinine production is significantly reduced, so even though GFR is significantly reduced, blood creatinine levels may be nearly normal. The decreased thirst perception, decreased urinary concentration, and decreased renin response to volume in elderly patients make it easy to develop hypovolemia and hypotension in cases of fluid loss such as blood loss, vomiting, diarrhea, and gastrointestinal decompression. The reduced dilution capacity of the kidneys and the decreased ability to handle sodium make it easy for elderly patients to develop water retention and hyponatremia during massive infusions, pulmonary edema or cerebral edema in the presence of cardiovascular or central nervous system disease, and hypernatremia in the presence of water restriction or a high sodium diet. The ability of the kidneys to secrete NH+4 is impaired, making the compensatory capacity of elderly patients significantly reduced in the event of acidosis. The relaxed bladder and enlarged prostate gland in the elderly make them prone to frequent urination, urgent urination and increased nocturia, which can lead to acute urinary retention and urinary tract infections. 4.Digestive system Elderly people have atrophy of esophageal muscles, weakened contraction, poor swallowing function, relaxation of cardia sphincter, delayed emptying of esophagus, increased dilatation of esophagus and contraction without propulsion. The atrophy and degeneration of gastric mucosa and glandular cells, the decrease of main cells and mural cells, and the decrease of gastric juice secretion in the elderly cause mechanical damage to the gastric mucosa, impairment of the formation of the mucus bicarbonate barrier, making the gastric mucosa easily damaged by gastric acid and pepsin, reducing the digestive and sterilizing effects of pepsin, and reducing the release of pancreatin, causing gastric mucosa erosion, ulceration, and bleeding, coupled with the partial or total loss of endocrine secretion function The loss of the ability to absorb vitamin B12 causes megaloblastic anemia and hematopoietic disorders. Due to the decrease of gastric acid secretion, the absorption of calcium, iron and vitamin D is reduced, which makes it easy for malnutrition to occur and can lead to iron deficiency anemia and osteochondrosis in the elderly. The secretory function of the pancreas tends to age more rapidly in the elderly, and the activity of lipolysis and gluconeolysis decreases, which seriously affects the digestion and absorption of starch, protein and fat; degeneration of pancreatic islet cells, reduced insulin secretion and decreased tolerance to glucose increase the risk of insulin-dependent diabetes. The digestive glands are more responsive to nerve reflexes than to humoral stimuli, and gastric emptying slows down. As a result, the digestive capacity of the elderly is weakened and appetite gradually decreases. The gastrointestinal blood flow in the elderly is reduced, about 60% in 80 years old, the gastrointestinal smooth muscle tone is insufficient and peristalsis is weakened, so constipation often occurs. The quality of the liver is reduced in the elderly, the number of hepatocytes is reduced and the number of degenerated connective tissue is increased, which easily causes liver fibrosis and sclerosis, liver function is reduced, the ability to synthesize protein is decreased, the enzyme activity of some hepatocytes is reduced, the liver detoxification function is decreased, which easily causes drug-related liver damage, and because of the poor digestion and absorption function of the elderly, it easily causes protein and other nutritional deficiencies, which leads to liver fat deposition. The vitality of liver microsomal enzyme system, which is closely related to drug metabolism, decreases in the elderly, and the response to induction is weakened. The gallbladder wall and bile duct wall become thicker and less elastic, and because they contain a large amount of cholesterol, they are prone to cholecystitis and cholelithiasis, and inflammation of the bile duct can cause the pancreas to digest itself and become acute pancreatitis. 5, the mental nervous system with age brain tissue atrophy, the number of brain cells decreased. It is generally believed that the brain nerve cells stop dividing after birth, and since the age of 20, they lose 0.8% per year and selectively decrease with the type and location of their existence. 60 years old, the number of cortical nerves and cells decreases by 20% to 25%, the cerebellar cortical nerve cells decrease by 25%, and the total number of nerve cells decreases by up to 45% in elderly people over 70 years old, with enlarged ventricles, thickened meninges and lipofuscin deposits. The brain ventricles are enlarged, the meninges are thickened, lipofuscin deposits are increased, the metabolism of the cells is obstructed, the cerebral arteries are hardened, the resistance to blood circulation is increased, and the blood supply to the brain is reduced, resulting in cerebral softening. The ability of various neurotransmitters in the brain of the elderly has decreased, leading to forgetfulness, mental retardation, inattention, poor sleep, mental character change, slow movement, motor tremor, dementia, etc. The number of synapses in the brain decreases and degenerative changes occur, slowing down the nerve conduction speed, leading to slow reaction to external things and decreased coordination of movement in the elderly. With the ageing of plant nerve degeneration and dysfunction, the balance of internal organs such as fluid circulation, gas exchange, absorption and excretion of substances, growth and reproduction, etc. is imbalanced. The acuity of touch, proprioception, vision and hearing of the elderly is reduced, the threshold of taste and smell is significantly increased, and the conduction signal to the center is significantly reduced, thus reducing the working ability of the elderly. Only slower rhythmic activities and lighter work can be performed. The unique psychological characteristics of the elderly: 1, the memory of the elderly, especially the near memory decreases significantly, insensitive to new things, imagination decline; 2, easy to fluctuate mood, especially the life and death of friends and relatives, bereavement, etc. will make them depressed, lose interest in life, coupled with frailty, sudden changes in the habits of retirement can make them inferior, useless, old and decrepit feeling, suffering from depression. All thoughts are lost, and some people also have the idea of suicide. 3, personality change, people in old age, mental activities from the tendency to change things outside, gradually turned to “inward” trend, stay in the past, cling to the old habits, self-imposed, can be a change in the past personality, like two. This is related to the degeneration of the frontal lobe of the cerebral cortex. 4. Behavior change. Due to the decay of the cerebral cortex, the instinctive activities of the lower cortex controlled by the cortex are dominant, so some elderly people will appear some behaviors like children. 6.Endocrine system and metabolism The endocrine function of the elderly is reduced mainly by the activity of hypothalamus-pituitary-gonadal (testes, ovaries) system, reduced thyroid function, reduced adrenal cortex function, reduced sensitivity to insulin and glucose tolerance, reduced secretion of sex hormones and sexual dysfunction. The hypothalamus is the plant nerve center in the body, and its function declines, causing the secretion of various hormone-releasing hormones to be reduced or their effects to be diminished, and the functions of the pituitary gland and subordinate target glands, which are regulated by the hypothalamus, are also comprehensively reduced, thus causing the onset and development of aging. With aging, the number of receptors in the hypothalamus decreases, the response to both glucocorticoids and blood glucose decreases, and the threshold for negative feedback inhibition increases. The pituitary gland increases in fibrous tissue and iron deposition with aging, and the feedback receptor sensitivity of the hypothalamic-pituitary axis decreases. In men over the age of 50, their testosterone secretion from the interstitial cells of the testes decreases, the number of receptors decreases, or their sensitivity decreases, resulting in a gradual decline in sexual function. In women, estrogen decreases sharply between the ages of 35 and 40, drops to its lowest level at the age of 60, and stabilizes at a low level after the age of 60. In the elderly, the thyroid gland loses weight, the follicles become smaller, the synthesis of hormones decreases significantly, and the binding power of tissue target cells is also reduced. The thyroid gland’s ability to assimilate iodine is reduced in the elderly, and total serum triiodothyronine (T3) is significantly lower than that of adults. As a result, metabolism becomes slower, and if the diet is large, body mass tends to increase, and symptoms such as fear of cold, dry skin, slow heartbeat, and lethargy tend to occur. With hypothyroidism, which increases blood cholesterol, atherosclerosis can be aggravated. The adrenal cortex mainly secretes aldosterone in the globus pallidus, cortisol in the fasciculus, and trace amounts of adrenal androgens in the reticular cortex. Aldosterone concentrations in the blood decrease in the elderly, while cortisol does not change meaningfully with increasing age. In contrast, androgen secretion by the human adrenal cortex decreases linearly with age after 20 years of age, and the response of the adrenal reticular formation to ACTH is significantly reduced in the elderly. As the adrenocortical function decreases in the elderly, the content of steroid hormones and their metabolites in the blood and urine decreases with age, and therefore, the ability to cope with trauma, infection and other harmful stimuli is poor, and the ability to maintain a stable internal environment is reduced. The pancreatic function of the pancreas decreases with ageing, and insulin secretion decreases, and the binding power of insulin receptors in the hepatocytes of the elderly is significantly lower than that of the young, and the sensitivity to the released insulin decreases, and the ability to respond to insulin decreases, thus reducing glucose tolerance and increasing the incidence of diabetes in the elderly. It is also believed that after glucose injection in the elderly, insulin secretion is mostly less active insulinogen, as well as increased concentration of anti-insulin substances in the blood. The release of parathyroid hormone from the parathyroid glands in the elderly is significantly reduced, as is the secretory response to low blood calcium, suggesting that the function of the parathyroid glands declines in old age. Older adults, especially older women, are prone to osteoporosis after menopause. The main reason for this is the reduced secretion of estrogen, which cannot counteract the action of the parathyroid glands and causes calcium loss from bone. Malabsorption of calcium and vitamin D are both causes of osteoporosis in the elderly. The overall body water in the elderly decreases, especially the proportion of intracellular fluid to body weight. In men aged 65 to 85 years and weighing 40 to 80 kg, the volume of intracellular fluid is 25% to 30% of body weight, while for women of the same age and weight intracellular fluid is about 20% to 25% of body weight. In the absence of acute stress and other conditions affecting the water-electrolyte balance, the daily basal metabolic requirements, calculated per liter of intracellular fluid, are: 100 ml of water, 418 kJ of calories, 3 g of protein, 30 mmol of sodium, and 2 mmol of potassium. fluid and electrolytes in elderly patients should be closely monitored and adjusted according to changes in their condition and pathophysiological status.