Other General Biology - NCLEX-PN

Aldosterone is a mineralcorticoid hormone secreted by the adrenal cortex in response to aldosterone II. An rise in plasma angiotensin levels will effect an elevation in blood volume (and hence blood pressure) by increasing the resorption of sodium and water in the kidney and increasing renal excretion of potassium.

While normal function is possible with a urinary output as little as 500ml/day, normal urinary output is between 1000-2000ml per day, with 1200ml being average with adequate fluid intake.

The majority of nutrients and electrolytes from food are absorbed n the small intestine. The remaining material passes into the large intestine for further transformation into stool. The liver and stomach are important sites of digestion and metabolism but are not the primary site of nutrient and electrolyte absorption.

The large intestine serves multiple functions. Large amounts of water are resorbed from stool via aquaporins in the large intestine mucosa, and the remaining matter is passed via a series of slow waves toward the rectum for excretion. In addition the large intestine houses trillions of both beneficial and pathogenic intestinal bacteria and fungi.

Stool that has passed through the large intestine is stored in the rectal ampulla, a dilated portion of the rectum inferior to the sigmoid colon and superior to the anal canal. From there it can be passed into the anal canal and excreted via the anus. The haustra coli are segments or pouches formed along the length of the small intestine, demarcated by the smooth muscle of the taenia coli.

The internal anal sphincter is a ring of involuntary smooth muscle that spends the majority of its time in a state of perpetual contraction. It relaxes only when the rectal ampulla is distended. Passage of stool is then controlled by the voluntary constriction of the external anal sphincter.

The muscular sphincter that keeps stomach contents from regurgitating into the esophagus is the lower esophageal sphincter. The upper esophageal sphincter separates the esophagus from the pharynx, the pyloric sphincter separates the stomach from the small intestine, and the ileocecal valve separates the small intestine from the large intestine.

Ghrelin is a hormone produced primarily in the stomach and small intestine. It is secreted when the stomach is empty, triggering a feeling of hunger. When the stomach is stretched, secretion of ghrelin is inhibited. Leptin is a hormone secreted by adipose cells to signal satiety. Gastrin triggers the secretion of stomach acid during digestion, and cholecystokinin (CKK) is a hormone with various roles in the process of digestion, primarily acting as a hunger suppressant and a trigger for the release of digestive enzymes and bile.

The ileocecal sphincter/valve separates the small intestine from the large intestine. The lower esophageal sphincter, also known as the cardiac sphincter, separates the esophagus from the stomach, while the pyloric sphincter separates the stomach from the small intestine.

The system of coordinated peristaltic waves that slowly sweeps food through the small intestine for digestion is called the migrating motor complex. Disorderly motion of this complex can result in a wide variety of gastrointestinal complaints such as vomiting, dumping syndrome, bloating, or indigestion. Segmentation contractions mix the contents of the colon for more absorption, while mass movements serve to propel feces towards the rectum.

By the time the contents of the digestive tract ender the colon, the majority of food digestion is complete. The colon then serves primarily to absorb water and electrolytes and to prepare feces for excretion.

The portions of the small intestine, in order from superior to inferior, are the duodenum, the jejunum, and the ileum. The cecum is not a part of the small intestine at all but rather the beginning of the large intestine.

The duodenum wraps around the pancreas.

The pudendal nerve innervates the external anal sphincter and is responsible for a person's ability to voluntarily control defecation. Dysfunction of the pudendal nerve has been associated with fecal incontinence or constipation. The other nerves listed are all part of the pelvic floor but do not directly innervate the anal sphincter.

The majority of absorption of nutrients in the small intestine occurs mainly in duodenum and the jejunum. The ileum is still a site of some absorption, though it is far less than nutrient absorption in the superior parts of the small intestine. The cecum is part of the large intestine.

The areas of the stomach, from superior to inferior, are the fundus, the body, and the pyloric antrum. The rugae are folds in the stomach that increase its surface area and expandability.

The hepatic portal vein is the main vein the carries nutrient-rich blood from the digestive tract to the liver for further processing. The other veins listed are all smaller veins that drain the stomach, small intestine, and spleen into the portal vein.

The ligament of Treitz suspends the duodenum, while the splenorenal ligament goes between the left kidney and the spleen. Ligamentum flava are ligaments present in the spinal cord.

Gastrin is produced by the G cells of the stomach. Parietal cells of the stomach secrete hydrochloric acid, while chief cells secrete pepsinogen and chymosin. Beta-islet cells of the pancreas produce glucagon.