Urinary and digestive systems

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A small percentage of the bicarbonate is reabsorbed in the collecting ducts and in the intercalated cells of the distal tubule. The bicarbonate is a product of dissociation of carbonic acid which is formed by the action of carbonic anhydrase on water and carbon dioxide. In the tubular lumen, hydrogen ions combine with bicarbonate to form weak carbonic acid. The acid then dissociates into water and carbon dioxide and the gas diffuses through the membranes. Endocrine gland connections to the renal system The renal system is connected to the endocrine system through the pituitary and the adrenal glands. The adrenal cortex secretes aldosterone which is important in water balance. The pituitary gland secretes anti-diuretic hormone (ADH). The two hormones act by regulating the volume of water that is either reabsorbed or excreted in the kidneys. Decreased water intake or increased re-absorption of sodium causes a decrease in blood volume and an increased osmolality. In turn, chemo-receptors in the hypothalamus are stimulated and they synthesize ADH which is stored and released by the pituitary glands. Increased secretion of aldosterone results in increased re-absorption of sodium ions in the kidneys which increases the osmolality. This causes the release of ADH if the osmolality rises beyond normal levels which lead to decreased resorption of sodium and increased absorption of water (Class notes 367). Why we do not pass urine as much in hot weather as in cold weather In hot weather, our bodies lose a lot of water through sweating in an attempt to cool of the body. This results in a state of general dehydration in the body. The amount of urine produced per day is proportional to the amount of water that we take. The decreased amount of water correlates to the decreased volumes and frequency of urination as less amounts of water are excreted through the kidneys (Class notes 357). During cold seasons, the body is trying to reduce heat loss. A lot of energy in form of heat is lost during sweating. Water that is lost in the cooling process is conserved in the body and in an attempt to regulate water volumes in the body it is lost through renal secretion hence increased urine volumes and increased urinating frequency. Micturition and defecation reflexes The micturition reflex basically involves a pathway of impulses from a stretched bladder to the sacral region of spinal cord and then back to the bladder. The first reflex is stretch reflex where the walls of the bladder stretch due to increasing volume sending an impulse to the sacral region of the spinal cord. This activates parasympathetic neurons from the spinal cord to the bladder causing contraction of the smooth muscle on bladder wall to contract. Sensory signals from spinal cord stimulate ascending pathways to cerebellum and pons which results in a conscious desire to urinate. The external urinary sphincter relaxes releasing urine into the urethra. Defecation reflex Mass movement of food in the colon stimulates the defecation reflex. Presence of feces in the rectum causes stretch which stimulates both parasympathetic and local reflexes. There is a resulting contraction of rectum and the internal anal sphincter relaxes forcing the feces out (Class notes 336). The external sphincter also relaxes and defecation is achieved through peristalsis in rectum and increased abdominal pressure. Effect of alcohol consumption on urine production Alcohol increases urine production as it inhibits production of antidiuretic hormone in the