Chapter 19 & 25: The Endocrine System PDF

Chapter 19: The Endocrine System: Introduction: The nervous system and the endocrine system work together to monitor and adjust physiological activities for the regulation of homeostasis. The nervous system performs short term “crisis management” while endocrine regulates longer...

Chapter 19: The Endocrine System: Introduction: The nervous system and the endocrine system work together to monitor and adjust physiological activities for the regulation of homeostasis. The nervous system performs short term “crisis management” while endocrine regulates longer-term, ongoing metabolic processes. Endocrine cells release chemicals called hormones that alter metabolic activities of tissues and organs. Overview of the Endocrine System The Endocrine System consists of all endocrine cells and tissues. They release their secretory products into interstitial fluid. Hormones can be divided into four groups based on their chemical structure: amino acid derivatives, peptide hormones, steroids, and eicosanoids. Cellular activities and metabolic reactions are controlled by enzymes. Hormones exert their effects by modifying the activities of target cells (cells that are sensitive to that particular hormone). Endocrine activity can be controlled by (1) neural activity (2) positive feedback (rare) or (3) complex negative feedback mechanisms. The Hypothalamus and Endocrine Regulation The hypothalamus regulates endocrine and neural activities. It (1) controls the output of the suprarenal (adrenal) medulla, an endocrine component of the sympathetic division of the ANS; (2) produces two hormones of its own (ADH and oxytocin), which are released from neurohypothesis (posterior lobe); and (3) controls the activity of the adenohypophysis  (anterior lobe) through the production of regulatory hormones (releasing hormones, or RH, and inhibiting hormones, or IH) The Pituitary Gland The pituitary gland releases 9 important peptide hormones.2 are synthesized in the hypothalamus and released at the neurohypothesis and seven are synthesized in the adenohypophysis. The Neurohypophysis The neuro hypothesis contains the axon of some hypothalamic neurons. Neurons within the supraoptic and paraventricular nuclei Manufacture.Anti diuretic hormone.And oxytocin, respectively. ADH decreases the amount of water lost at the kidney. It is released in response to a rise in the concentration of electrolytes in the blood or a fall in blood volume. In women, oxytocin stimulates smooth muscle cells in the uterus and contractile cells in the mammary glands. It is released in response to stretched uterine muscles and/or suckling of an infant. In men, it stimulates prostatic smooth muscle contractions. The Adenohypophysis The adeno hypothesis can be subdivided into the large pars distalis, the slender pars intermedia, and the pars tuberalis. The entire adenohypophysis is highly vascularized. In the floor of the hypothalamus in the tuberal area, neurons release regulatory factors into the surrounding interstitial fluids. Endocrine cells in the adenohypophysis are controlled by releasing factors, inhibitory factors (hormones), or some combination of the two. These secretions  enter the circulation through fenestrated capillaries that contain open spaces between their epithelial cells. Blood vessels, called portal vessels, form an unusual vascular arrangement that connects the hypothalamus and anterior lobe of the pituitary gland.This complex is the hypophyseal portal system. It ensures that all of the blood entering the portal vessels will reach the intended target cells before returning to the general circulation. Important hormones released by the pars distalis include (1) thyroid-stimulating hormone (TSH), which triggers the release of thyroid hormones; (2) adrenocorticotropic hormones (ACTH), which stimulates the release of glucocorticoid by the suprarenal gland; (3) follicle-stimulating hormone (FSH), which stimulates estrogen secretion (estradiol) and egg development in women and sperm production in men; (4) luteinizing hormone (LH), which causes ovulation and production of progestins (progesterone) in women and androgens (testosterone) in men (together, FSH and LH are called gonadotropins); (5) prolactin (PRL), which stimulates the development of mammary glands and the production of milk; and (6) growth hormone (GH, or somatotropin), which stimulates cells growth and replication. Melanocyte-stimulating hormone (MSH), released by the pars intermedia, stimulates melanocytes to produce melanin. The Thyroid Gland The thyroid glands lies inferior to the thyroid cartilage of the larynx. It consists of two lobes connected by a narrow isthmus.  Thyroid Follicles and Thyroid Hormones The thyroid glands contain numerous thyroid follicles. Cells of the follicles manufacture thyroglobulin and store it within the colloid (a viscous fluid containing suspended proteins) in the follicle cavity. The cells also transport iodine from the extracellular fluids into the cavity, where it complexes with tyrosine residues of the thyroglobulin molecules to form thyroid hormones. When stimulated by the TSH, the follicular cells reabsorb the thyroglobulin, break down the protein, and release the thyroid hormones, thyroxine (TX or T4) and triiodothyronine (T3) into the circulation. The C Thyrocytes of the Thyroid Gland The C thyrocytes of the thyroid follicles produce calcitonin (CT), which helps lower calcium ion concentrations in the body fluids by inhibiting osteoclast activities and stimulating calcium ion excretion at the kidneys. Actions of calcitonin are opposed by those of the parathyroid hormone produced by the parathyroid glands. The Parathyroid Glands Four parathyroid glands are embedded in the posterior surface of the thyroid gland. The parathyroid (principal) cells of the parathyroid produce parathyroid hormone (PTH) in response to lower-than-normal concentrations of calcium ions. Oxyphil cells of the parathyroid have no known function. PTH (1) stimulates osteoclast activity, (2) stimulates osteoblast activity, to a lesser degree and, (3) reduces calcium loss in the urine, and (4) promotes calcium absorption in the intestine by stimulating calcitriol production.  The parathyroid glands and the C Thyrocites of the thyroid gland maintain calcium ion levels within relatively narrow limits. The Thymus The thymus, embedded in a connective tissue mass in the thoracic cavity, produces several hormones that stimulate the development and maintenance of normal immunological defenses. Thymosins produced by the thymus promote the development and maturation of lymphocytes. The Suprarenal Glands A single suprarenal (adrenal) gland rests on the superior border of each kidney. Each suprarenal gland is surrounded by a fibrous capsule and is subdivided into a superficial cortex and an inner medulla. The Cortex of the Suprarenal Gland The cortex of the suprarenal gland manufactures steroid hormones called adrenocortical steroids (corticosteroids). The cortex can be subdivided into three separate areas: (1) the outer zona glomerulosa releases mineralocorticoids (MC), principally aldosteron, which restricts sodium and water losses at the kidneys, sweat glands, digestive tract, and salivary gland. The zona glomerulosa responds to the presence of the hormone angiotensinII, which appears after the enzyme renin has been secreted by kidney spells exposed to a decline in blood volume and/or blood pressure. (2) The middle zona fasciculata produces glucocorticoids (GC), notably cortical and corticosterone. All of these hormones accelerate the rates of both glucose synthesis and glycogen formation, especially in liver cells. (3)  The inner zona reticularis produces small amounts of sex hormones called androgens. The significance of the small amounts of androgens produced by the suprarenal glands remains uncertain. The Medulla of the Suprarenal Gland Each medulla of the suprarenal gland contains clusters of chromaffin cells, which resemble sympathetic ganglia neurons. They secrete either epinephrine (75-80%) or norepinephrine (20-25%). These catecholamines trigger cellular energy utilization and the mobilization of energy reserves. Endocrine Functions of the Kidneys and Heart Endocrine cells in both the kidney and the heart produce hormones that are important for the regulation of blood pressure and blood volume, blood oxygen levels, and calcium and phosphate ion absorption. The kidney produces the enzyme renin and the peptide hormone erythropoietin when blood pressure or blood oxygen levels in the kidneys decline, and it secretes the steroid hormone calcitriol when parathyroid hormone is present. Renin catalyzes the conversion of circulating angiotensinogen to angiotensin I. In ling capillaries, it is converted to angiotensin II, the hormone that stimulates the production of aldosterone in the suprarenal cortex. Erythropoietin (EPO) stimulates red blood cell production by the bone marrow. Calcitriol stimulates the absorption of the calcium and phosphate in the digestive tract. Specialised muscle cells of the heart produce atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) when blood pressure or blood volume becomes excessive. These hormones stimulate water and sodium ion loss at the kidneys, eventually reducing blood volume. The Pancreas and Other Endocrine Tissues of the Digestive System The lining of the digestive tract, the liver, and the pancreas produce exocrine secretions that are essential to the normal breakdown and absorption of food. The Pancreas The pancreas is a nodular organ occupying a space between the stomach and small intestine. It contains both exocrine and endocrine cells. The exocrine pancreas secretes an enzyme-rich fluid into the lumen of the digestive tract. Cells of the endocrine pancreas form clusters called pancreatic islets (Islets of langerhans). Each islet contains four cell types: alpha cells produce glucagon to raise blood glucose levels; beta cells secrete insulin to lower blood glucose levels; delta cells secrete somatostatin (growth hormone-inhibiting hormone) to inhibit the production and secretion of glucagon and insulin; and F cells secrete pancreatic polypeptide (PP) to inhibit gallbladder contractions and regulate the production of some pancreatic enzymes. PP may also help control the rate of nutrient absorption by the GI tract. Insulin lowers blood glucose by increasing the rate of glucose uptake and utilization by most body cells; glucagon raises blood glucose levels by increasing the rates of glycogen breakdown and glucose synthesis in the liver. Somatostatin reduces the rate of hormone secretion by alpha and beta cells and slows food absorption and enzyme secretion in the digestive tract. The Endocrine Tissues of the Reproductive System Testes  The interstitial cells of the male testes produce androgens. Testosterone is the most important androgen. It promotes the production of functional sperm, maintains reproductive-tract secretory glands, influences secondary sexual characteristics, and stimulates muscle growth. The hormone inhibin, produced by nurse (sustentacular) cells in the testes, interacts with FSH from the anterior lobe of the pituitary gland to maintain sperm production at normal levels. Ovaries Oocytes develop in follicles in the female ovary; follicle cells surrounding the oocytes produce estrogens, especially estradiol. Estrogens support the maturation of the oocytes and stimulate the growth of the uterine lining. Active follicles secrete inhibin, which suppresses FSH release by negative feedback. After ovulation, the follicle cells remaining within the ovary reorganize into a corpus luteum, which produces a mixture of estrogens and progestins, especially progesterone. Progesterone facilitates the movement of a fertilized egg through the uterine tube to the uterus and stimulates the preparation of the uterus for implantation. The Pineal Gland The pineal gland (epiphysis cerebri) contains secretory cells called pinealocytes, which synthesize melatonin. Melatonin slows the maturation of sperm, eggs, and reproductive organs by inhibiting the production of FSH- and LH-releasing factors from the hypothalamus. Additionally, melatonin may establish circadian rhythms. Hormones and Aging The endocrine system shows relatively few functional changes with advanced age. The most dramatic endocrine changes are the rise in reproductive hormone levels in puberty and the decline in reproductive hormone levels at menopause. ★ Chapter 19 - Clinical Terms: ○ Diabetes insipidus: ○ Diabetes mellitus: ○ Goiter: ○ Type 1 Diabetes: ((Insulin-dependent diabetes mellitus (IDDM) (also known as Type 1 diabetes or juvenile-onset diabetes)): ○ Myxedema: ○ Type 2 Diabetes: ((Non-insulin-dependent diabetes mellitus (NIDDM) (also known as Type 2 diabetes or maturity-onset diabetes)). Chapter 25: The Endocrine System Introduction The digestive system consists of the muscular digestive tract and various accessory organs. An Overview of the Digestive System Histological Organization of the Digestive Tract The major layers of the digestive tract are the mucosa (formed by the mucosal epithelium and lamina propria), submucosa (areolar tissue), the muscularis externa (a region of smooth muscle fibers), and (in the peritoneal cavity) a serous membrane called the serosa. Muscularis Layers and theMovement of Digestive Materials The smooth muscle cells of the digestive tract are capable of plasticity, which is the ability to tolerate extreme stretching. The digestive system contains visceral smooth muscle tissue, in which the muscle cells are arranged in sheets and contain no motor innervation. The presence of pacemaker (interstitial) cells allows for rhythmic waves of contraction that spread through the entire muscular sheet. The muscularis externa propels materials through the digestive tract through the contractions of peristalsis. Segmentation movements in areas of the small intestine churn digestive materials. The Peritoneum The serosa, also known as the visceral peritoneum, is continuous with the parietal peritoneum that lines the inner surfaces of the body wall.  Fused double sheets of peritoneal membrane called mesenteries suspend portions of the digestive tract. Organs of the abdominal cavity may have a variety of relationships with the peritoneum, including intraperitoneal, retroperitoneal, and secondarily retroperitoneal. The Oral Cavity The functions of the oral cavity include (1) analysis of potential foods; (2) mechanical processing using the teeth, tongue, and palatal surfaces, (3) lubrication by mixing with mucus and salivary secretions; and (4) digestion by salivary enzymes. Structures of the oral cavity include the tongue, salivary glands, and teeth. Anatomy of the Oral Cavity The oral cavity (buccal cavity) is lined by a stratified squamous epithelium. The bard and soft palates form the roof of the oral cavity. The tongue aids in mechanical processing and manipulation of food as well as sensory analysis. The superior surface (dorsum) of the body of the tongue is covered with papillae. The inferior portion of the tongue contains a thin fold of mucous membrane called the lingual frenulum. Intrinsic and extrinsic tongue muscles are controlled by the hypoglossal nerve. The parotid, sublingual, and submandibular salivary glands discharge their secretions into the oral cavity. The parotid salivary glands release salivary amylase, which begins the breakdown of carbohydrates.  Saliva lubricates the mouth, solubilizes food, dissolves chemicals, flushes the oral surfaces, and helps control bacteria. Salivation is usually controlled by the autonomic nervous system. Dentine forms the basic structure of a tooth. The crown is coated with enamel, and the root with cement. The neck marks the boundary between the root and the crown. The periodontal ligament anchors the tooth in an alveolar socket. Mastication (chewing) occurs through the contact of the opposing occlusal surfaces of the teeth. There are four types of teeth, each with specific functions: incisors, for cutting; cuspids (canines) for tearing; bicuspids (premolars), for crushing; and molars, for grinding. The first set of teeth to appear are called deciduous teeth (primary, milk, or baby teeth), the temporary teeth of the primary dentition.These are replaced by the adult secondary dentition, termed permanent teeth. Mastication forces the food across the surfaces of the teeth until it forms a bolus that can be swallowed easily. The Pharynx Skeletal muscles involved with swallowing include the pharyngeal constrictor muscles and the palatopharyngeus, stylopharyngeus, and palatal muscles. The Swallowing Process Deglutition (swallowing) has three phases. The buccal phase begins with the compaction of a bolus and its movement into the pharynx.The pharyngeal phase involves the elevation of the larynx, reflection of the epiglottis, and closure of the glottis. Finally, the esophageal phase involves  the opening of the upper esophageal sphincter and peristalsis moving the bolus down the esophagus to the lower esophageal sphincter. The Esophagus The esophagus is a hollow muscular tube that transports food and liquid to the stomach, through the esophageal hiatus, an opening in the diaphragm. Histology of the Esophageal Wall The wall of the esophagus is formed by mucosa, submucosa, muscularis externa, and adventitia layers. The Stomach The stomach has three major functions: (1) bulk storage of ingested matter, (2) mechanical breakdown of resistant materials, and (3) chemical digestion through the disruption of chemical bonds using acids and enzymes. Anatomy of the Stomach The stomach is divided into four regions: the cardia, the fundus, the body, and the pylorus. The pyloric sphincter guards the exit from the stomach. The mucosa and submucosa are thrown into longitudinal folds, called rugae. The muscularis layer is formed of three bands of smooth muscle: a longitudinal layer, a circular layer, and an inner oblique layer. The mesenteries of the stomach are the greater omentum and the lesser omentum. Three branches of the celiac trunk supply blood to the stomach: the left gastric artery, the splenic artery, and the common hepatic artery. Histology of the Stomach  Simple columnar epithelia line all portions of the stomach. Shallow depressions, called gastric pits, contain the gastric glands of the fundus and body. Parietal cells secrete intrinsic factors and hydrochloric acid. Chief cells secrete pepsinogen, which acids in the gastric lumen convert to the enzyme pepsin. G cells of the stomach secrete the hormone gastrin. Regulation of the Stomach The production and secretion of gastric juices are directly controlled by the CNS and the celiac plexus. The release of the local hormones secretin and cholecystokinin inhibits gastric secretion but stimulates secretion by the pancreas and liver. The Small Intestine Regions of the Small Intestine The small intestine includes the duodenum, the jejunum, and the ileum. Support of the Small Intestine The superior mesenteric artery and superior mesenteric vein supply numerous branches to the segments of the small intestine. The mesentery properly supports the branches of the superior mesenteric artery and vein, lymphatics, and nerves that supply the jejunum and ileum. Histology of the Small Intestine The intestinal mucosa bears transverse folds, called plicae circulares. The mucosa of the small intestine forms small projections, called intestinal villi, that increase the surface area for absorption. Each villus contains a  terminal lymphatic called a lacteal. Pockets called intestinal crypts (crypts of Lieberkühn) house enteroendocrine, goblet, and stem cells. The regions of the small intestine have histological specializations that determine their primary functions.The duodenum (1) contains submucosal duodenal (Brunner's)glands that aid the crypts in producing mucus and (2) receives the secretions of the common bile ductand pancreatic duct. The ileum contains large groups of aggregated lymphoid nodules (Peyer's patches) within the lamina propria. (see Figures 25.1/25.4/25.11/25.13/25.15/25.21a,d) Regulation of the Small Intestine Intestinal juice moistens the chyme, helps buffer acids, and dissolves digestive enzymes and the products of digestion. The Large Intestine The large intestine (large bowel) begins as a pouch inferior to the terminal portion of the ileum and ends at the anus. The main functions of the large intestine are to (1) reabsorb water and compact feces, (2) absorb vitamins by bacteria, and (3) store fecal material prior to defecation. (see Figures 25.1/25.4/25.11/25.13/25.16 to 25.18) The large intestine is divided into three parts: the cecum, the colon, and the rectum. The Cecum The cecum collects and stores materials arriving from the ileum. The ileum opens into the cecum at the ileal papilla, with muscles encircling the  opening forming the ileocecal valve. The appendix is attached to the cecum, and it functions as part of the lymphatic system. The Colon The colon has a larger diameter and a thinner wall than the small intestine. It bears haustra (pouches), the taeniae coli (longitudinal bands of muscle), and omental appendices, or fatty appendices of the colon (fat aggregations within the serosa). (see Figures 25.16/25.17) The colon is subdivided into four regions: ascending, transverse, descending, and sigmoid. (see Figures 25.4/25.16/25.17) The Rectum The rectum terminates in the anal canal leading to the anus.Internal and external anal sphincters control the passage of fecal material to the anus. Internal and external anal sphincters control the passage of fecal material to the anus. Distension of the rectal wall triggers the defecation reflex. Histology of the Large Intestine The major histological featuresof the colon are lack of villi, abundance of goblet cells, and distinctive mucus-secreting intestinal crypts. (see Figures 23.7/25.18) Regulation of the Large Intestine Movement from the cecum to the transverse colon occurs slowly via peristalsis and haustral churning. Movement from the transverse to the sigmoid colon occurs several times each day via mass movements. Accessory Glandular Digestive Organs The Liver  The liver performs metabolic and hematological regulation and produces bile. Its metabolic role is to regulate the concentrations of wastes and nutrients in the blood, and its hematological role is as a blood reservoir. (see Figures 25.11/25.19/25.20 and Table 25.1) The classical topographical description of the liver has the organ divided into four lobes: left, right, quadrate, and caudate. The gallbladder is located in a fossa within the posterior surface of the right lobe. New terminology for the lobular structure for liver has recently been adopted, which is based on subdivisions of the hepatic artery, portal vein, and hepatic ducts. (see Figure 25.19a,b,c,d,f) The hepatic artery proper and hepatic portal vein supply blood to the liver. Hepatic veins drain blood from the liver and return it to the systemic circuit via the inferior vena cava. (see Figures 22.15/22.22/ 25.19d) Liver cells are specialized epithelial cells, termed hepatocytes. Kupffer cells, or stellate reticuloendothelial cells, are phagocytic cell that reside in the sinusoidal lining. The liver lobule is the basic functional unit of the liver. Each loble is hexagonal in cross section and contains six porta areas, or hepatic triads. A portal area consists of a branch of the hepatic portal vein, a branch of the hepatic artery proper, and a branch of the hepatic (bile) duct. Bile canaliculi carry bile to bile ductules that lead to portal areas. The bile ducts from each lobule unite to form the left and (see Figures 25.19 to 25.21) right hepatic ducts, which merge to form the common hepatic duct. The Gallbladder  The gallbladder is a hollow muscular organ that stores and concentrates bile before excretion in the small intestine. Bile salts break apart large drops of lipids and make them accessible to digestive enzymes. Bile ejection occurs under stimulation of cholecystokinin (CCK). The gallbladder is divided into fundus, body, and neck regions.The cystic duct leads from the gallbladder to merge with the common hepatic duct to form the common bile duct. (see Figures25.15/25.19d/25.21) The wall of the gallbladder is composed of only the mucosa, lamina propria, and muscularis externa. (see Figure 25.21) The Pancreas The pancreas is divided into head, body, and tail regions. The pancreatic duct penetrates the wall of the duodenum. Within each lobule, ducts branch repeatedly before ending in the pancreatic acini (blind pockets). The accessory pancreatic duct (if present) and pancreatic duct perforate the wall of the duodenum to discharge pancreatic juice at the lesser duodenal papilla and greater duodenal papilla, respectively. (see Figures 22.15/22.22/25.16а/25.21 a/25.22) Pancreatic tissue consists of exocrine and endocrine portions. The bulk of the organ is exocrine in function, as the pancreatic acini secrete water, ions, and digestive enzymes into the small intestine. Pancreatic enzymes include lipases, carbohydrases, nucleases, and proteolytic enzymes.The major hormones produced by the endocrine portion are insulin and glucagon. Aging and the Digestive System  Normal digestion and absorption occur in elderly individuals; however, changes in the digestive system reflect age-related changes in other body systems. These include a slowed rate of epithelial stem cell division, a decrease in smooth muscle tone, the appearance of cumulative damage, an increase in cancer rates, and numerous changes in other systems. ★ Chapter 25 - Clinical Terms: ○ Achalasia: ○ Cirrhosis: ○ Colitis: ○ Esophagus: ○ Gastritis: ○ Mumps: ○ Peptic Ulcer: ○ Peritonitis: