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235 Cards in this Set
- Front
- Back
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Alimentary canal |
Mouth, pharynx, esophagus, stomach, small intestine, and large intestine |
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Accessory digestive organs |
Teeth, tongue, gallbladder, salivary glands, liver, and pancreas |
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Ingestion |
Selective intake of food |
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Mechanical digestion |
Physical breakdown of food into smaller pieces |
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Chemical digestion |
Catabolic breakdown of food |
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Absorption |
Movement of nutrients from the GI tract to the blood or lymph |
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Defecation |
Elimination of indigestible solid wastes |
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Propulsion |
- Gross movements of material through the GI tract - Includes swallowing, peristalsis and segmentations |
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Histology of the alimentary canal (esophagus to anal canal) |
From the lumen outward: 1) mucosa 2) submucosa 3) muscularis externa 4) serosa |
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Function of the muscularis externa |
- Longitudinal and circular muscles setup - Push substances through the canal in churning fashion |
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Mucosa |
- Moist epithelial layer that lines the lumen of the alimentary canal - Moistened by glandular tissues |
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Major functions of mucosa |
1) Secretion of mucus 2) Absorption of the end products of digestion 3) Protection against infectious disease |
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Three layers of the mucosa |
1) An inner epithelium 2) Lamina propria (connective tissue) 3) Muscularis mucosae (smooth muscle) |
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Epithelial lining |
Consists of simple columnar epithelium and mucus-secreting goblet cells |
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The mucus secretions |
- Protect digestive organs from digesting - Ease food along the tract (i.e. bolus) |
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Stomach and small intestine mucosa contain |
- Enzyme-secreting cells and - Hormone-secreting cells (making them endocrine and digestive organs) - Paracrine and endocrine functions |
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Lamina propria |
- Loose areolar and reticular connective tissue - Nourish the epithelium and absorb nutrients - Contains lymph nodes (part of MALT) important in defense against bacteria |
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Muscularis mucosae |
- Enhance surface area for contact with food - Smooth muscle cells that produce local movements of mucosa |
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Submucosa |
Dense connective tissue containing elastic fibers, blood and lymphatic vessels, lymph nodes, and nerves |
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Muscularis externa |
Responsible for segmentation and peristalsis (double layer of smooth muscle) |
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Serosa |
- The protective visceral peritoneum - Replaced by the fibrous adventitia in the esophagus - Retroperitoneal organs have both an adventitia and serosa (“outside” the peritoneal cavity) |
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Enteric nervous system |
- Composedof two major intrinsic nerve plexuses - Submucosal nerve plexus – regulates glands and smooth muscle in the mucosa - Myenteric nerve plexus – major nerve supply that controls GI tract mobility |
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Segmentation and peristalsis |
- Largely automatic involving local reflex arcs inervating the myenteric nerve plexus (SHORT reflexes) - Linked to the CNS via autonomic reflex arcs (LONG reflexes) |
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Mesentery |
Double layer of peritoneum that provides: - Vascular and nerve supplies to the viscera - A means to hold digestive organs in place and store fat - Include dorsal and ventral mesenteries, and the greater and lesser omentum |
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Oral Cavity (mouth) |
Tongue, teeth, salivar,y glands, cheeks, lips, and palate |
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Esophagus |
- 30 cm muscular tube, extending from cricoid cartilage to cardiac region of stomach - Passes the bolus from mouth to stomach using peristalsis |
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Teeth |
- 32 adult teeth - Involved in mastication |
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Tongue |
- Very muscular, yet agile - Lingual papillae are the sites of taste buds - Lingual frenulum attaches tongue to floor of mouth - Involved in mastication |
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Cheek, lips and palate |
Involved in mastication |
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Salivary glands and saliva |
- Composition of saliva: - 99% water - Salivary amylase - Made of serous or mucus producing cells - Lysozyme and IgA (inhibit bacteria) - Electrolytes (to maintain pH) |
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Three salivary glands |
- Parotid - Sublingual - Submandibular |
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Deglutition (swallowing) |
- Swallowing reflex is complex and is centered in medulla and pons - Involves suspension of breathing, epiglottis and peristaltic movements - Mediated by ANS |
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Two phases of swallowing |
Two phases: 1) Buccal: bolus formation 2) Pharyngeal-esophageal: bolus driven downward |
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Stomach
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Physical breakdown of food continues, chemical breakdown of proteins begins and food is converted to chyme |
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Parts of the stomach |
- Cardiac region – surrounds the cardiac orifice - Fundus – dome-shaped region beneath the diaphragm - Body – midportion of the stomach - Pyloric region – made up of the antrum and canal which terminates at the pylorus - The pylorus is continuous with the duodenum through the pyloric sphincter |
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Muscularis externa of the stomach |
- Has an additional oblique layer that: - Allows the stomach to churn, mix, and pummel food physically - Breaks down food into smaller fragments |
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Epithelial lining of the stomach |
Goblet cells that produce a coat of alkaline mucus |
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Mucosa of the stomach |
Contains gastric pits, which contain gastric glands that secrete: - Gastric juice - Mucus - Gastrin and other hormones |
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Mucous neck cells |
- In the gastric glands - Secretes alkaline mucus |
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Parietal (oxyntic) cells |
- In the gastric glands - Secrete HCl and intrinsic factor - HCl maintains the acidity needed for enzymes like pepsinogen |
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Chief (zymogenic) cells |
- In the gastric glands - Produce pepsinogen - Pepsinogen is activated to pepsin by: HCl in the stomach - Pepsin itself by a positive feedback mechanism - Pepsin breaks down protein |
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Enteroendocrine cells |
Secrete gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), and somatostatin into the lamina propria |
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Stomach lining conditions |
The stomach is exposed to the harshest conditions in the digestive tract |
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What the stomach does to keep from digesting itself |
- A thick coat alkaline mucus on the stomach wall - Epithelial cells that are joined by tight junctions - Pervents penetrance of gastric juices - Gastric glands that have cells impermeable to HCl - Damaged or old epithelial cells are quickly replaced - Replaced by actively dividing cells |
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Regulation of gastric secretion |
Neural and hormonal mechanisms regulate the release of gastric juice |
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Stimulatory and inhibitory events of digestion occur in three phases |
- Cephalic (reflex) phase: prior to food entry - Input from a higher brain center - Gastric phase: once food enters the stomach - Intestinal phase: as partially digested food enters the duodenum |
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Cephalic phase
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- Via vagal stimulation from the medulla - Excitatory events include: - Sight or thought of food - Stimulation of taste or smell receptors - Inhibitory events include: - Loss of appetite or depression - Decrease stimulation of the parasympathetic division |
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Excitatory events of the gastric phase |
- Stomach distension (over distension of the stomach can cause vomiting) - Activation of stretch receptors (neural activation) - Activation of chemoreceptors by peptides, caffeine, and rising pH: - Release of gastrin (hormone) to the blood - Acetylcholine and histamine - ALL THREE ABOVE STIMULATE PARIETAL CELLS TO MAKE HCl!! |
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Inhibitory events of the gastric phase |
- A pH lower than 2 (too low; result of “loss” of buffering peptides when stomach empties) - Emotional upset which overrides the parasympathetic division (fear, anxiety, etc…stimulates sympathetic division) |
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Anatomy of small intestine |
- Runs from pyloric sphincter to the ileocecal valve - Has three subdivisions: duodenum, jejunum, and ileum - The jejunum extends from the duodenum to the ileum - The ileum joins the large intestine at the ileocecal valve |
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Microscopy anatomy of small intestine |
- Structural modifications of the small intestine wall increase surface area - Plicae circulares: deep circular folds of the mucosa and submucosa - Villi: fingerlike extensions of the mucosa - Microvilli: tiny projections of absorptive mucosal cells’ plasma membranes |
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Mucosa of small intestine |
- Absorptive cells and goblet cells - Absorptive cells have microvilli, which contain BRUSH BORDER ENZYMES, integral components of SI digestion - Interspersed T cells (intraepithelial lymphocytes), and - Enteroendocrine cells (secrete hormones) |
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Intestinal crypts of small intestine |
Secrete intestinal juice -> important for continuing digestion |
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Peyer's patches |
Found in the submucosa |
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Brunner’s glands |
In the duodenum secrete alkaline mucus (neutralize stomach acid) |
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Intestinal juice |
- Secreted by intestine glands in response to distension or irritation of the mucosa - Slightly alkaline and isotonic with blood plasma - Is largely water, enzyme-poor, but contains mucus |
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Liver |
- The largest gland in the body - Superficially has four lobes – right, left, caudate, and quadrate |
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Associated structures of the liver |
- The lesser omentum anchors the liver to the stomach - The hepatic blood vessels enter the liver at the porta hepatis - The gallbladder rests in a recess on the inferior surface of the right lobe |
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Bile leaves the liver via |
- Hepatic ducts which fuse into the common hepatic duct - The common hepatic duct fuses with the cystic duct - These two ducts form the bile duct |
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Microscopic anatomy of liver
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- Hexagonal-shaped liver lobules are the structural and functional units of the liver - Composed of hepatocyte (liver cell) plates radiating outward from a central vein - Portal triads are found at each of the six corners of each liver lobule - Liver sinusoids – enlarged, leaky capillaries located between hepatic plates - Kupffer cells – hepatic macrophages found in liver sinusoids |
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Portal triads |
- Bile duct - Hepatic artery – supplies oxygen-rich blood to theliver - Hepatic portal vein – carries venous blood withnutrients from digestive viscera - Secreted bile flows between hepatocytes toward the bile ducts in the portal triads |
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Functions of hepatocytes |
1) Production of bile 2) Processing bloodborne nutrients 3) Storage of fat-soluble vitamins 4) Detoxification |
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Hepatitis |
- Inflammation of the liver, often due to viral infection - Hepatitis-causing viruses are catalogued as HVA through HVF - HVA and HVE are transmitted enterically and cause self-limiting infections - Transmitted via blood transfusions, contaminated needles, and sexual contact, and increases the risk of liver cancer - Hepatitis B and C produce chronic liver infection - Nonviral hepatitis caused by drug toxicity and wild mushroom poisoning |
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Cirrhosis |
- A diffuse and progressive chronic inflammation of the liver - Typically results from chronic alcoholism or severe chronic hepatitis - The liver becomes fatty and fibrous, and its activity is depressed - Scar tissue obstructs blood flow in the hepatic portal system causing portal hypertension - Scar tissue is common to chronic inflammation |
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Gallbladder |
- Thin-walled, green muscular sac on the ventral surface of the liver - Stores and concentrates bile by absorbing its water and ions - Releases bile via the cystic duct which flows into the bile duct |
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Bile |
- Synthesized by liver, stored in gall bladder - Gall bladder releases bile when stimulated by fats in duodenum |
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Composition of bile |
- A yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes - Bile salts are cholesterol derivatives that: 1) Emulsify fat 2) Facilitate fat and cholesterol absorption 3) Help solubilize cholesterol - Enterohepatic circulation recycles bile salts - Chief bile pigment is bilirubin, a waste product of heme |
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Cholecystokinin (CCK) and secretin |
- Acidic, fatty chyme causes the duodenum to release these into the bloodstream - CCK causes: the gallbladder to contract and the hepatopancreatic sphincter to relax - Bile enters the duodenum |
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Bilesalts and secretin |
Transported in blood; stimulate the liver to produce bile |
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Vagal stimulation |
- Causes weak contractions of the gallbladder - Bile released from the duodenum |
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Chyme |
- Extremely hypertonic: highly concentrated - Mass movement of water leads to increase in blood volume - Chyme is highly regulated when entering the intestine - Pancreatic juice (basic) neutralizes the acidity of chyme |
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Pancreas |
- Lies deep to the greater curvature of the stomach - Head is encircled by the duodenum and the tail abuts the spleen |
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Exocrine function of pancreas
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- Secretes pancreatic juice which breaks down all categories of foodstuff - Acini (clusters of secretory cells) contain zymogen granules with digestive enzymes |
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Endocrine function of pancreas |
Release of insulin and glucagon |
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Cells of pancreatic digestion |
- Duct Cells: bicarbonate secretion, water - Acinar Cells: zymogens - trypsinogen, chymotrypsinogen procarboxypeptidase - These zymogens iffer in their cleavage sites for peptides - Also by acinar cells: lipase, amylase, nuclease |
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Regulation of pancreatic secretion |
- Secretin and CCK are released when fatty or acidic chyme enters the duodenum - CCK and secretin enter the bloodstream - Upon reaching the pancreas: CCK induces the secretion of enzyme-rich pancreatic juice; Secretin causes secretion of bicarbonate-rich pancreatic juice - Vagal stimulation also causes release of pancreatic juice |
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Segmentation |
- Common motion of small intestine - Initiated by intrinsic pacemaker cells (Cajal cells) - Moves contents steadily toward the ileocecal valve |
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Peristalisis |
- After nutrients have been absorbed - Begins with each wave starting distal to the previous - Meal remnants, bacteria, mucosal cells, and debris are moved into the large intestine |
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Intestinal motility |
- Local enteric neurons of the GI tract coordinate intestinal motility - Cholinergic neurons cause: contraction and shortening of the circular muscle layer in the muscularis externa |
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Gastroileal reflex and gastrin |
- Relax the ileocecal sphincter - Allow chyme to pass into the large intestine - As cecum fills, pressure causes sphincter to close, preventing reflux into the SI |
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Chemical Digestion |
- Catabolic process in which large food molecules are broken down to their chemical building blocks (monomers), which can be absorbed by the GI tract lining - Accomplished by enzymes secreted by both intrinsic and accessory glands into the lumen of the alimentary canal - Enzymatic breakdown of food molecules is called hydrolysis because it involves the addition of a water molecule to each molecular bond to be broken |
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Carbohydrate digestion |
- Enzymes used: salivary amylase, pancreatic amylase, and brush border enzymes - Absorption: via co transport with Na+, and facilitated diffusion - Enter the capillary bed in the villi - Transported to the liver via the hepatic portal vein |
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Protein digestion |
- Enzymes used: pepsin in the stomach and enzymes acting in the small intestine - Pancreatic enzymes – trypsin, chymotrypsin, and carboxypeptidase - Brush border enzymes – aminopeptidases, carboxypeptidases, and dipeptidases - Absorption: similar to carbohydrates |
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Fats digestion |
- Enzymes/chemicals used: bile salts (physical emulsifier) and pancreatic lipase (enzyme) - Bile breaks down fat globules into emulsification droplets - Pancreatic lipase than breaks fat into fatty acids and monoglycerides |
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Fats absorption
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- Fatty acids and monoglycerides enter intestinal cells via diffusion using micelles as a “taxi” to the wall - Once inside, the triglycerides are resynthesized - They combine with proteins within the cells, forming chylomicrons (lipoproteins) - Resulting chylomicrons are extruded and picked up by the lacteals and transported via lymph |
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Nucleic acid digestion |
- Absorbed in villi and transported to liver via hepatic portal vein - Enzymes used: pancreatic ribonucleases and deoxyribonuclease in the small intestine - Absorption – active transport via membrane carriers |
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Absorption of electrolytes |
Most ions are actively absorbed along the length of small intestine |
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Sodium absorption |
Coupled with absorption of glucose and amino acids |
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Ionic iron absorption |
Transported into mucosal cells where it binds to ferritin |
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Anions absorption |
Passively follow the electrical potential established by sodium |
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Potassium absorption |
Diffuses across the intestinal mucosa in response to osmotic gradients |
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Calcium absorption |
- Is related to blood levels of ionic calcium Is regulated by Vitamin D and parathyroid hormone (PTH) - Important: GLU2 and KCC1 |
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Absorption of water |
- 95% of water is absorbed in the small intestine by osmosis - Water moves in both directions across intestinal mucosa - Net osmosis occurs whenever a concentration gradient is established by active transport of solutes into the mucosal cells - Water uptake is coupled with solute uptake, and as water moves into mucosal cells, substances follow along their concentration gradients |
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Malabsorption of nutrients |
- Results from: Anything that interferes with delivery of bile or pancreatic juice or - Factors that damage the intestinal mucosa 1) Bacterial infection 2) Gluten enteropathy (adult celiac disease) – gluten damages the intestinal villi and reduces the length of microvilli; treated by eliminating gluten from the diet (all grains but rice and corn) |
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Unique features of large intestine |
- Teniae coli – three bands of longitudinal smooth muscle in its muscularis - Haustra – pocket like sacs caused by the tone of the teniae coli - Epiploic appendages – fat-filled pouches of visceral peritoneum |
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Subdivisions of large intestine |
Cecum, appendix, colon, rectum, and anal canal |
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Cecum |
- Saclike - Lies below the ileocecal valve in the right iliac fossa - Contains a wormlike vermiform appendix |
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Regions of the colon |
Ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, and sigmoid colon |
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Anchor of transverse and sigmoid portions |
Via mesenteries called mesocolons |
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Anal canal |
The last segment of the large intestine, opens to the exterior at the anus |
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Two spincters of the anus |
- Internal anal sphincter composed of smooth muscle: innervated by the spine - External anal sphincter composed of skeletal muscle: innervated by cerebral cortex - Closed except during defecation |
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Bacterial flora of the large intestine |
- Ferment indigestible carbohydrates - Release irritating acids and gases (flatus) - Synthesize B complex vitamins and vitamin K |
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Functions of large intestine |
- Other than digestion of enteric bacteria, no further digestion takes place - Vitamins, water, and electrolytes are reclaimed - Its major function is propulsion of fecal material toward the anus - Colon is not essential for life |
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Haustral contractions |
- Slow segmenting movements that move the contents of the colon - Haustra sequentially contract as they are stimulated by distension - Contract from proximal to distal - Baroreceptors |
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Presence of food in the stomach and SI |
- Activates the gastrocolic and duodenocolic reflexes - Initiates peristalsis that forces contents toward the rectum |
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Diarrhea |
- Changes the way water is absorbed in the colon - Stool passes through too quickly |
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Constipated or delayed |
High absorption of water |
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Two reflexes of defecation |
- Intrinsic defecation reflex - Parasympathetic defecation reflex |
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Distension of rectal walls caused by feces |
- Stimulates contraction of the rectal walls - Relaxes the internal anal sphincter - Voluntary signals stimulate relaxation of the external anal sphincter and defecation occurs |
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Function of bile |
- Bile salts work to EMULSIFY fats - Break big globules of fats to small and micro globules of fat - Allows tremendously more surface area for lipases to break down fats into triglycerides |
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Kidney functions |
- Filter 200 liters of blood daily - Excrete toxins, metabolic wastes,& excess ions - Regulate volume & chemicalmakeup of blood - Maintain balance between water& salts, acids & bases - Gluconeogenesis during prolongedfasting - Produce Renin (regulate bloodpressure) - Produce Erythropoietin (RBCproduction) - Activation of vitamin D |
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Supporting tissue (outer to inner) |
1) Anterior renal fascia 2) Adipose capsule 3) Renal capsule |
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Circulation |
Larger divisions of the renal circulation converge on the nephrons through sequentially smaller vessels |
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Afferent arteriole |
Terminal vessel which feeds the glomerulus of the nephron |
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Functional unit of kidney |
- Nephron 1) Renal corpuscle 2) Renal tubule |
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Renal corpuscle |
- Glomerulus - Glomerular capsule (BOWMAN’S capsule) |
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Renal tubule |
- Proximal convoluted tubule (PCT) - Loop of Henle - Distal Convoluted Tubule (DCT) |
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Collecting duct |
1) Intercalated cells - Cuboidal cells with microvilli - Function in maintaining the acid-base balance of the body 2) Principal cells - Cuboidal cells without microvilli - Help maintain the body’s water and salt balance |
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Two types of nephrons |
1) Cortical:Capsules found close to cortex; loops dip into medulla 2) Juxtamedullary:Capsules found close to medulla; loops dip well into medulla; maintain a salinity gradient important for waterconservation |
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Processes of urine formation |
1) Glomerular filtration 2) Tubular reabsorption and secretion 3) Water conservation |
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Glomerular filtration |
Creates plasmalike filtrate of the blood |
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Tubular reabsorption |
- Removes useful solutes from the filtrate, returns them to the blood - Tubular secretion: removes additional wastes from the blood and adds them to the filtrate |
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Water conservation |
Removes water from the urine and returns to blood; concentrates waste |
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Filtrate (in capsule and tubule) |
- Contains all plasma components except protein - Loses water, nutrients, andessential ions to become urine |
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Urine (once it reaches the collecting tubule) |
Contains metabolic waste and uneeded substances |
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Efficiency of glomerular filtration |
- Its filtration membrane is significantly more permeable - Glomerular blood pressure is higher - It has a higher net filtration pressure - Plasma proteins are not filtered and are used to maintain oncotic pressure of the blood |
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Two main factor contribute to increased permeability: |
1) Fenestrations in the blood capillary 2) Filtration slits in the capsular epithelium, formed by the pedicels of the podocytes - Pedicels allow for increased permeability |
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Capsular pressure |
Pressure in a confined space |
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Colloid osmotic pressure |
Bulk and large macromolecules |
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We only excrete 1-2L of this filtrate daily as urine. What does this mean? |
- Women form 150L/day of filtrate - Most of the filtrate is reabsorbed in the kidneys – significant resorption of the filtrate. Volume is decreased also since it is concentrated. HIGHLY EFFICIENT SYSTEM – TAKES BACK IRON, SALTS, ETC. |
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If the GFR (glomerular filtration rate) is too high: |
Needed substances cannot be reabsorbed quickly enough and are lost in the urine |
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If the GFR is too low: |
Everything is reabsorbed, including wastes that are normally disposed of |
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Three mechanisms control the GFR |
1) Renal autoregulation (intrinsic system) 2) Neural controls – external inputs 3) The renin-angiotensin system (hormonal mechanism) |
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Autoregulation entails two types of control |
1) Myogenic – responds to changes in pressure in the renal blood vessels (afferent arterioles) - Afferent arterioles are closer to the GFR - Senses changes in afferent arterioles specifically 2) Tubuloglomerular feedback – senses changes in the juxtaglomerular apparatus - JG cells of the capillary - Macula Densa cells of the capsular epithelium |
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Juxtaglomerular apparatus (JGA) |
- Where the distal tubule lies against the afferent (sometimes efferent) arteriole - Macula densa - Tall, closely packed distal tubule cells - Lie adjacent to JG cells - Function as chemoreceptors or osmoreceptors -> Physically make up the lining of the lumen of DCT and release chemicals to regulate salt concentration - Secrete a paracrine messenger that stimulates JG cells - Mesangial cells may serve as messengers between macula densa and JG cells |
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Arteriole walls have juxtaglomerular (JG) cells |
- Enlarged, smooth muscle cells - Have secretory granules containing renin - Act as mechanoreceptors -> Secrete renin -> Specialized cells – intertwine with arterioles -> Can detect some sort of physical attribute |
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When the sympathetic nervous system is at rest |
- Renal blood vessels are maximally dilated - Autoregulation mechanisms prevail |
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When the sympathetic nervous system is under stress |
- Norepinephrine is released by the SNS - Epinephrine is released by the adrenal medulla - Afferent arterioles constrict and filtration is inhibited |
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Sympathetic nervous system also regulates this system |
Stimulates the renin-angiotensin mechanism by causing the JG cells to release renin |
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Renin-angiotensin system |
- Is triggered when the JG cells release renin - Renin acts on angiotensinogen to release angiotensin I - Angiotensin I is converted to angiotensin II |
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Angiotensin II |
- Causes mean arterial pressure to rise - Stimulates the adrenal cortex to release aldosterone which causes sodium retention - Stimulates the secretion of antidiuretic hormone, which promotes water reabsorption - Both systemic and glomerular hydrostatic pressures rise - Vasoconstricts arterioles to nephron, altering GFR - Stimulates sense of thirst |
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Tubular reabsorption |
- About 65% of filtrate is “given back” to the peritubular capillaries inthe PCT (remainder is reabsorbed in loop and DCT) - Some water and ion reabsorption is hormonally controlled; some is actively reabsorbed. - Reabsorption may be an active (requires ATP) or passive process |
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In tubular reabsorption, transported substances move through three membranes |
1) Luminal and basolateral membranes of tubule cells 2) Endothelium of peritubular capillaries - All organic nutrients are reabsorbed |
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Reabsorption by PCT cells |
Reabsorption can occur either through the cytoplasm of the cells (transcellular) or between epithelial cells (paracellular) |
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In PCT, active pumping of Na+ drives reabsorption of: |
- Water by osmosis (obligatory) - Anions and fat-soluble substances by diffusion - Organic nutrients and selected cations by secondary active transport - The NON-ATP consuming Na symports/antiports on luminal side of tubule depend on ATP consuming sodium/potassium pumps on basolateral side. |
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A transport maximum (Tm): |
- Reflects the number of carriers in the renal tubules available - Exists for nearly every substance that is actively reabsorbed - Most of the time, we don’t reach anywhere near the max for substances |
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Substances are not reabsorbed if they: |
1) Lack carriers 2) Are not lipid soluble 3) Are too large to pass through membrane pores |
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Important nonabsorbed substances |
Urea (half is absorbed), creatinine (too big), and uric acid (absorbed, but given back) |
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Tubular secretion |
Essentiallyreabsorption in reverse, where substances move from peritubular capillaries ortubule cells into filtrate |
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Tubular secretion is important for: |
- Disposing of substances not already in the filtrate - Eliminating undesirable substances such as urea and uric acid - Ridding the body of excess potassium ions - Controlling blood pH - Ridding body of pollutants, antibiotics, and other drugs |
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Regulating water loss |
- Hormonally by: 1) Aldosterone - Retains salt - Stimulates renin production 2) ADH 3) Atrial Natriuretic peptide (ANP) - Antagonizes ADH - Inhibits renin - Causes vasodilation of glomerular arterioles, increasing GFR |
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ADH Mechanism |
- Antidiuretic hormone (ADH) inhibits diuresis - ADH is the signal to produce concentrated urine - ADH causes aquaporin channel proteins to be inserted into collecting duct membranes - The kidneys’ ability to respond to ADH depends upon the high medullary osmotic gradient |
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Aldosterone |
- Secreted by adrenal cortex (a mineralocorticoid) - Stimulates Na reabsorption, followed by Cl- reabsorption - Water follows - Elicits effects on the DCT and collecting duct - Decreases urine volume (works with ADH) |
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Formation of concentrated urine |
- By the time the filtrate reaches the loop of Henle, the amount and floware reduced by 65% but it is still isosmotic - The solute concentration in the loop of Henle ranges from 300 mOsmto 1200 mOsmdue to an osmotic gradient - Dissipation of the medullary osmotic gradient is prevented because theblood in the vasa recta equilibrates with the interstitial fluid |
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Major function of loop of Henle |
To create an osmotic gradient between cortical-medullary area of kidney |
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The descending loop of Henle: |
- Is relatively impermeable to solutes - Is permeable to water |
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The ascending loop of Henle |
- Is impermeable to water - Actively transports sodium chloride into the surrounding interstitial fluid |
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Major function of loop of Henle |
Create an osmotic gradient between cortical-medullary area of kidney |
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Creation of osmotic gradient |
Dependent upon Na, K and urea molecules in medulla |
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Collecting ducts |
- Have to pass through highly concentrated medullaryarea - In the presence of ADH, CD are more permeable to water than NaCl; therefore water goes out, and salt stays behind - Important to concentrate urine and conserve water |
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Dilute urine |
- In the ascending loop of Henle - No ADH being secreted - Collecting ducts remain impermeable to water; no further water reabsorption occurs - Dilute urine is created by allowing this filtrate to continue into the renal pelvis - Urine osmolality can be as low as 50 mOsm (one-sixth that of plasma) |
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Chemicals that enhance the urinary output include: |
- Any substance not reabsorbed - Substances that exceed the ability of the renal tubules to reabsorb it |
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Osmotic diuretics include: |
- High glucose levels – carries water out with the glucose - Alcohol – inhibits the release of ADH - Caffeineand most diuretic drugs – inhibit sodium ion reabsorption - Lasix – inhibits Na+-K+-2Cl- symporters |
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Three layers of the bladder |
1) Transitional epithelial mucosa 2) Thick muscular layer 3) Fibrous adventitia |
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Bladder |
- Distensible and collapses when empty - Urine accumulates and bladder expands without significant rise in internal pressure |
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Micturition (Voiding or Urination) |
Has both voluntary and involuntary control |
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During micturition, stretch receptors in bladder signal two centers in brain
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- ANS centers in spinal cord that promote urination (involuntary) and the pons, which integrates info from other brain areas (voluntary) - Efferent signaling from spinal cord via parasympathetic ganglion causes detrusor muscle to contract and the internal urethral sphincter to relax. (INVOLUNTARY) - External urethral sphincter must open (VOLUNTARY) |
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Normal pH of body fluids |
- Arterial blood is 7.4 - Venous blood and interstitial fluid is 7.35 - Intracellular fluid is 7.0 |
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Alkalosis or alkalemia |
Arterial blood pH rises above 7.45 |
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Acidosis or acidemia |
Arterial pH drops below 7.35 (physiological acidosis) |
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Concentration of hydrogen ions is regulated sequentially by: |
1) Chemical buffer systems – act within seconds 2) The respiratory center in the brain stem – acts within 1–3 minutes 3) Renal mechanisms – require hours to days to effect pH changes |
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Chemical buffer systems |
- Strong acids – all their H+ is dissociated completely in water - Weak acids – dissociate partially in water and are efficient at preventing pH changes - Strong bases – dissociate easily in water and quickly tie up H+ - Weak bases – accept H+ more slowly (e.g., HCO3¯ and NH3) |
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Three major chemical buffer systems |
1) Bicarbonate buffer system 2) Phosphate buffer system 3) Protein buffer system (like hemoglobin) |
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Resist change in pH
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- One or two molecules that act to resist pH changes when strong acid or base is added - Any drifts in pH are resisted by the entire chemical buffering system |
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Physiological buffer systems |
- The respiratory system regulation of acid-base balance is a physiological buffering system - There is a reversible equilibrium between: Dissolved carbon dioxide and water Carbonic acid and the hydrogen and bicarbonate ions |
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During carbon dioxide unloading |
Hydrogen ions are incorporated into water |
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When hypercapnia or rising plasma H+ occurs: |
- Deeper and more rapid breathing expels more carbon dioxide
- Hydrogen ion concentration is reduced |
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Alkalosis causes |
Slower, more shallow breathing, causing H+ to increase |
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Respiratory system impairment causes |
Acid-base imbalance(respiratory acidosis or respiratory alkalosis) |
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Chemical buffers can tie up excess acids or bases, but |
They cannot eliminate them from the body |
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The lungs can eliminate carbonic acid |
By eliminating carbon dioxide |
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Only the ________ can rid the body of metabolic acids (phosphoric, uric, and lactic acids and ketones) and prevent metabolic acidosis |
- Kidneys - Ultimate acid-base regulatory organs |
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The most important renal mechanisms for regulating acid-base balance are |
- Conserving (reabsorbing) or generating new bicarbonate ions - Excreting bicarbonate ions |
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Losing a bicarbonate ion is the same as |
Gaining a hydrogen ion |
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Hydrogen ion secretion occurs in |
PCT and in type A intercalated cells |
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Hydrogen ions come from the |
Dissociation of carbonic acid |
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Reabsorption of Bicarbonate |
- Carbonic acid formed in filtrate dissociates to release carbon dioxide and water - Carbon dioxide then diffuses into tubule cells, where it acts to trigger further hydrogen ion secretion |
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Two mechanisms carried out by type A intercalated cells generate new bicarbonate ions |
Both involve renal excretion of acid via secretion and excretion of hydrogen ions or ammonium ions (NH4+) |
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In response to acidosis: |
- Kidneys generate bicarbonate ions and add them to the blood - An equal amount of hydrogen ions are added to the urine |
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Generating new bicarbonate ions using ammonium ion excretion |
- This method uses ammonium ions produced by the metabolism of glutamine in PCT cells - Each glutamine metabolized produces two ammonium ions and two bicarbonate ions - Bicarbonate moves to the blood and ammonium ions are excreted in urine |
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Respiratory acidosis and alkalosis |
- Result from failure of the respiratory system to balance pH - PCO2 is the single most important indicator of respiratory inadequacy - NormalP CO2 fluctuates between 35 and 45 mm Hg - Values above 45 mm Hg signal respiratory acidosis - Values below 35 mm Hg indicate respiratory alkalosis |
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Respiratory acidosis is the most common cause of acid-base imbalance |
Occurs when a person breathes shallowly, or gas exchange is hampered by diseases such as pneumonia, cystic fibrosis, or emphysema |
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Hyperventilation |
Common cause of respiratory alkalosis |
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Metabolic acidosis |
- All pH imbalances except those caused by abnormal blood carbon dioxide levels - Metabolic acid-base imbalance –bicarbonate ion levels above or below normal (22–26 mEq/L) - Metabolic acidosis is the second most common cause of acid-base imbalance - Typical causes are ingestion of too much alcohol and excessive loss of bicarbonate ions - Other causes include accumulation of lactic acid, shock, ketosis in diabetic crisis, starvation, and kidney failure |
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Most hydrogen ions originate from cellular metabolism |
- Breakdown of phosphorus-containing proteins releases phosphoric acid into the ECF - Anaerobic respiration of glucose produces lactic acid - Fat metabolism yields organic acids and ketone bodies - Transporting carbon dioxide as bicarbonate releases hydrogen ions |
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Concentration of hydrogen ions is regulated sequentially by: |
- Chemical buffer systems – act within seconds - The respiratory center in the brain stem – acts within 1-3 minutes - Renal mechanisms – require hours to days to effect pH changes |
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Acidosis |
- H+ diffuses into cells and drives out K+, elevating K+ concentration in ECF - H+ buffered by protein in ICF, causes membrane hyperpolarization, nerve and muscle cells are hard to stimulate; CNS depression may lead to death |
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Alkalosis |
H+ diffuses out of cells and K+ diffuses in, membranes depolarized, nerves overstimulate muscles causing spasms, tetany, convulsions, respiratory paralysis |
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Buffer systems |
- Strong acids – all their H+ is dissociated completely in water - Weak acids – dissociate partially in water and are efficient at preventing pH changes - Strong bases – dissociate easily in water and quickly tie up H+ - Weak bases – accept H+ more slowly (e.g., HCO3¯ and NH3) |
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Three major chemical buffer systems |
- Bicarbonate buffer system - Phosphate buffer system - Protein buffer system |
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Bicarbonate buffer system |
A mixture of carbonic acid (H2CO3) and its salt, sodium bicarbonate (NaHCO3) (potassium or magnesium bicarbonates work as well); important ECF buffer |
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In bicarbonate buffer, if strong acid is added |
- Hydrogen ions released combine with the bicarbonate ions and form carbonic acid (a weak acid) - The pH of the solution decreases only slightly - Drops to ~7.2 |
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In bicarbonate buffer, if strong base is added |
- It reacts with the carbonic acid to form sodium bicarbonate (a weak base) - The pH of the solution rises only slightly |
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Phosphate buffer system |
- Sodium salts of dihydrogen phosphate (H2PO4¯), a weak acid Monohydrogen phosphate (HPO42¯), a weak base - This system is an effective buffer in urine and intracellular fluid - Nearly identical to bicarbonate |
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Protein buffer system |
- Plasma and intracellular proteins are the body’s most plentiful and powerful buffers - Some amino acids of proteins have: free organic acid groups (weak acids), and groups that act as weak bases (e.g., amino groups) - Amphoteric molecules are protein molecules that can function as both a weak acid and a weak base |
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Respiratory acidosis and alkalosis |
- Resultfrom failure of the respiratory system to balance pH - PCO2 isthe single most important indicator of respiratory inadequacy |
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PCO2 levels |
- Normal PCO2 fluctuates between 35 and 45 mm Hg - Values above 45 mm Hg signal respiratory acidosis - Values below 35 mm Hg indicate respiratory alkalosis |
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Respiratory acidosis |
- Most common cause of acid-base imbalance - Occurs when a person breathes shallowly, or gas exchange is hampered by diseases such as pneumonia, cystic fibrosis, or emphysema |
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Respiratory alkalosis |
Common result of hyperventilation |
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Metabolic acidosis |
- All pH imbalances except those caused by abnormal blood carbon dioxide levels - Metabolic acid-base imbalance – bicarbonate ion levels above or below normal (22-26 mEq/L) - Metabolic acidosis is the second most common cause of acid-base imbalance - Typical causes are ingestion of too much alcohol and excessive loss of bicarbonate ions - Other causes include accumulation of lactic acid, shock, ketosis in diabetic crisis, starvation, and kidney failure |
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Metabolic alkalosis |
- Risingblood pH and bicarbonate levels indicate metabolic alkalosis - Typicalcauses are: 1) Vomiting of the acid contents ofthe stomach 2) Intake of excess base (e.g., fromantacids) 3) Constipation, in which excessivebicarbonate is reabsorbed |
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Respiratory and renal compensation |
- Acid-base imbalance due to inadequacy of a physiological buffer system is compensated for by the other system - The respiratory system will attempt to correct metabolic acid-base imbalances - The kidneys will work to correct imbalances caused by respiratory disease |
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Respiratory buffer system |
- Uses reversible equilibrium: CO2 + H2O <-> H2CO3 <-> H+ + HCO3¯ - When hypercapnia or rising plasma H+ occurs: - Deeper and more rapid breathing expels more carbon dioxide - Hydrogen ion concentration is reduced - Hypocapnia / Alkalosis causes slower, more shallow breathing, causing H+ to increase |
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In metabolic acidosis: |
- The rate and depth of breathing are elevated - Blood pH is below 7.35 and bicarbonate level is low - As carbon dioxide is eliminated by the respiratory system, PCO2 falls below normal |
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In respiratory acidosis |
The respiratory rate is often depressed and is the immediate cause of the acidosis |
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In metabolic alkalosis: |
- Compensation exhibits slow, shallow breathing, allowing carbon dioxide to accumulate in the blood - Correction is revealed by: 1) High pH (over 7.45) and elevated bicarbonate ion levels 2) Rising PCO2 |
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Urinary buffer systems |
- Chemical buffers tie up excess acids or bases, but cannot eliminate them - Kidneys rid the body of metabolic acids (phosphoric, uric, and lactic acids and ketones) and prevent metabolic acidosis - Kidneys = ultimate acid-base regulatory organs - Kidneys are the only organs that can get rid of the kidneys |
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Renal response to acidosis |
- Boosts bicarbonate buffering by Resp. system - Secretes H+, reabsorbs HCO3- - In starving individual, uses amino acids to buffer |
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Renal response to alkalosis |
- Secretes HCO3-, transfers strong acid to capillary - High H+ lowers plasma HCO3- - Low HCO3- = dissociation of H2CO3 = High H+, pH returns to normal - Decreased respiratory rate |
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The most important renal mechanisms for regulating acid-base balance are: |
- Conserving (reabsorbing) or generating new bicarbonate ions - Excreting bicarbonate ions |
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Losing a bicarbonate ion |
Gaining a hydrogen ion |
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Reabsorbing a bicarbonate ion |
Losing a hydrogen ion |
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Reabsorption of bicarbonate |
- Carbonic acid formed in filtrate dissociates to CO2 + H2O - CO2 diffuses into tubule cells, where it triggers further hydrogen ion secretion |
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Generating new HCO3- ions |
- Hydrogen ion secretion occurs in the PCT and in type A intercalated cells - Two mechanisms carried out by type A intercalated cells generate new bicarbonate ions - Both involve renal excretion of acid via secretion and excretion of hydrogen ions or ammonium ions (NH4+) |
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Hydrogen ion excretion |
- Dietary hydrogen ions must be counteracted by generating new bicarbonate - The excreted hydrogen ions must bind to buffers in the urine (phosphate buffer system) - Intercalated cells actively secrete hydrogen ions into urine, which is buffered and excreted - Bicarbonate generated is: moved into the interstitial space via a cotransport system; passively moved into the peritubular capillary blood |
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In response to acidosis, kidneys |
- Generate bicarbonate ions and add them to the blood - An equal amount of hydrogen ions are added to the urine |
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Ammonium ion excretion |
- This method uses ammonium ionsproduced by the metabolism of glutamine in PCT cells - Each glutamine metabolized produces two ammonium ions and twobicarbonate ions - Bicarbonate moves to the blood and ammonium ions are excreted in urine |
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Bicarbonate ion secretion |
- When the body is in alkalosis, type B intercalated cells: - Exhibit bicarbonate ion secretion - Reclaim hydrogen ions and acidify the blood - The mechanism is the opposite of type A intercalated cells and the bicarbonate ion reabsorption process - Even during alkalosis, the nephrons and collecting ducts excrete fewer bicarbonate ions than they conserve |
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Renal compenation |
- To correct respiratory acid-baseimbalance, renal mechanisms are stepped up - Chemoreceptors detect this balance - Acidosis has high PCO2 and high bicarbonate levels - The high PCO2 is the cause of acidosis - The high bicarbonate levels indicate the kidneys are retainingbicarbonate to offset the acidosis, to offset H+ ions generated by CO2 |
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Alkalosis has low PCO2 and high pH |
The kidneys eliminate bicarbonate from the body by failing to reclaim it or by actively secreting it |
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Water content of the body |
Greatest at birth (70-80%) and declines until adulthood, when it is about 58% |
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At puberty, sexual differences in body water content |
Arise as males develop greater muscle mass |
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Homeostatic mechanisms |
Slow down with age |
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Elders are at risk for dehydration |
Because they may be unresponsive to thirst clues |
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Most frequent victims of imbalance |
The very young and the very old are the most frequent victims of fluid, acid-base, and electrolyte imbalances |
