Final Exam Review Sheet PDF

# Exam 4 review sheet + final exam review sheet ## 1. Know what the study of the digestive system is called and the functions of the digestive system - **Gastroenterology**- the study of the digestive tract and the diagnosis and treatment of its disorders - **Digestive system**- the organ system t...

# Exam 4 review sheet + final exam review sheet ## 1. Know what the study of the digestive system is called and the functions of the digestive system - **Gastroenterology**- the study of the digestive tract and the diagnosis and treatment of its disorders - **Digestive system**- the organ system that processes food, extracts nutrients from it, and eliminates the residue ## 2. 5 stages of digestion (functions): - **Ingestion**- selective intake of food - **Digestion**- mechanical and chemical breakdown of food into a form usable by the body - **Absorption**- uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph - **Compaction**- absorbing water and consolidating the indigestible residue into feces - **Defecation**- elimination of feces ## 3. Know the difference between chemical and mechanical digestion and where they occur in the body - **Mechanical**- physical breakdown of food into smaller particles - Cutting/grinding action of teeth, churning action of stomach and small intestines, and exposes more food surface to the action of digestive enzymes - **Chemical**- breaks dietary macromolecules into their monomers (residues). Carried out by digestive enzymes produced by salivary glands, stomach, pancreas, and small intestine - Results in polysaccharides into monosaccharides proteins into amino acids, and fats into monoglycerides and fatty acids ## 4. Know the basic structural plan for the tissue layers of the digestive tract **a. 2 subdivisions:** - **Digestive tract (alimentary canal)** - 30ft long muscular tube extending from mouth to anus, includes mouth, pharynx, esophagus, stomach, small and large intestine - Gl tract includes stomach and intestines - **Accessory organs** - Include teeth, tongue, salivary glands, liver, gallbladder, and pancreas **b. Basic structural plan from deep to superficial:** - **Mucosa**- epithelium (simple columnar in stomach/intestines to secrete and absorb nutrients, nonkeratinized stratified squamous in mouth, esophagus, and anal canal to resist abrasion), lamina propria (thin layer of loose connective areolar tissue found in the oral mucosa), and muscularis mucosae (smooth muscle that facilitate expulsion of glandular secretions; creates grooves when tensed to increase surface area). MALT- abundant in lymphocytes and lymphatic nodules. Lines lumen - **Submucosa**- loose connective tissue; contains blood vessels, lymphatic vessels, nerves, and variety of cells. Supplies blood to mucosal layer - **Muscularis externa**- inner circular layer and outer longitudinal layer. Moves food through the digestive tract by contracting and relaxing. Smooth muscle - Inner circular layer- thickens in some places to form valves (sphincters) that regulate the passage of material through the tract - Outer longitudinal layer- responsible for motility that propels food and residue through tract - **Serosa**- areolar tissue and mesothelium. Prevents friction during movement **c. Regulation of digestive tract:** - **Neural:** short (myenteric) reflexes- stretch or chemical stimulation acts through myenteric plexus to stimulate peristaltic contractions of swallowing - Long (vagovagal) reflexes- parasympathetic stimulation of digestive motility and secretion - **Hormonal:** chemical messengers secreted into bloodstream and stimulate distant parts of the digestive tract (gastrin and secretin) - **Paracrine secretions:** chemical messengers that diffuse through the tissue fluid to stimulate nearby target cells ## 5. Know what suspends the stomach and intestines to the abdominal wall - **Mesenteries**- connective tissue sheets that loosely suspend stomach and intestines from abdominal wall - Allows stomach and intestines to undergo strenuous contractions, allows freedom of movement in abdominal cavity, and holds abdominal viscera in proper relationship to each other ## 6. Know the function of the buccal cavity (mouth) - **Function:** ingestion (food intake), other sensory responses to food including mechanical and chemical digestions, swallowing, speech, and respiration - **Labial frenulum:** median fold that attaches each lip to the gum between the anterior incisors - **Vestibule:** space between cheek or lips and the teeth ## 7. Know the function of the tongue and the different types of papillae - **Tongue**- muscular, bulky, but remarkably agile and sensitive organ that manipulates food between teeth while it avoids being bitten. Can extract food particles from the teeth after a meal and is sensitive enough to feel stray hair in a bite of food - **Lingual papillae**- bumps and projections on the tongue that are the sites of the taste buds - **Vallate papillae**- V-shaped row that mark the boundary between the body and root of the tongue - **Lingual frenulum**- median fold that attaches the body to the floor of the mouth - **Fungiform**- contain taste buds and sensory cells; found on sides and tip of the tongue - **Filiform**- most common type. Provide friction for chewing and have keratinized squamous epithelium - **Foliate**- small bumps with 4-5 short, vertical folds with many taste buds. Located near back of tongue and line the sides - **Circumvallate**- located at back of the tongue closer to throat. Largest papillae - **Intrinsic muscles** produce subtle tongue movements of speech and are contained entirely within the tongue - **Extrinsic muscles** have origins elsewhere and insertions in the tongue and produce stronger movements of food manipulation - **Lingual glands**- serous and mucous glands that secrete a portion of the saliva - **Body**- anterior 2/3s of the tongue that occupies oral cavity - **Root**- posterior 1/3 of the tongue that occupies oropharynx. Contains lingual tonsils ## 8. Know the enzymes for the digestion of starch and fat - **Salivary amylase**: begins starch digestion in the mouth - **Lingual lipase**: activated by stomach acid and digests fat after food is swallowed - **Lysozyme**: enzyme that kills bacteria ## 9. Know how many deciduous and adult teeth we have. - **20 deciduous (baby teeth); 32 adult teeth (16 on top and bottom)** - **2 pair of incisors** used to bite off a piece of food (pointed) - **1 pair of canines** that puncture and shred food (chisel-like cutting teeth) - **2 pair of premolars** for crushing and grinding (broad surface) - **3 pairs of molars** for crushing and grinding (broader surface) - **Teeth** develop beneath gums and erupt in predictable order beginning with incisors (erupt from 6-30 months). All deciduous teeth are replaced between 6-32 years of age - **Third molars (wisdom teeth)** erupt from age 17-25 and may be impacted due to crowding against neighboring teeth preventing them from erupting ## 10. Know the muscles that control mastication. - **Mastication**- breaks down food into smaller pieces to be swallowed and exposed more surface to the action of digestive enzymes. First step in mechanical digestion. Food stimulates oral receptors that trigger an involuntary chewing reflex - **Masseter and temporalis** elevate teeth to crush food - **Medial and lateral pterygoids and masseter** swing teeth in side-to-side grinding action of molars ## 11. Know the anatomical features of what makes up teeth - **Regions:** - **Crown**- portion above gum - **Root**- portion below gum, embedded in alveolar - **Neck**- point where crown, root, and gum meet - **Gingival sulcus**- space between tooth and gum - **Dentin**- hard yellowish tissue that makes up most of the tooth - **Enamel**- covers crown and neck. Noncellular secretion formed during development - **Cementum**- covers root - **Root canal**- located in roots leading to pulp cavity in the crown. Contains nerves and blood vessels - **Apical foramen**- pore at the basal end of each root canal - **Occlusion**- meeting of the teeth with the mouth closed ## 12. Know the function of the periodontal ligament, alveolus, and gingiva - **Alveolus**- tooth socket in bone - **Periodontal ligament**- anchors tooth firmly in alveolus and allows slight movement under pressure of chewing - **Gingiva (gums)**- cover alveolar bone ## 13. Know the function of the pharynx. - **Muscular funnel** that connects oral cavity to esophagus and allows entrance of air from nasal cavity to larynx (digestive and respiratory tracts intersect) ## 14. Know the function of the esophagus and the lower esophageal sphincter - **Straight muscular tube** 25-30cm long. Extends from pharynx to cardiac orifice of stomach, passing through esophageal hiatus in diaphragm - **Lower esophageal sphincter**- food pauses at this point because of constriction - Prevents stomach contents from regurgitating into the esophagus. Heartburn is the burning sensation produced by acid reflux into the esophagus - **Swallowing (deglutition)** involves over 22 muscles in the mouth, pharynx, and esophagus and has a swallowing center consisting of a pair of nuclei in the medulla oblongata that coordinates swallowing by communicating with muscles of the pharynx and esophagus. Involves cranial nerves IX, X, and XII - **2 phases** - **Buccal**- under voluntary control. Tongue collects food, presses it against palate forming bolus and pushes it posteriorly. Food accumulates in oropharynx in front of blade of the epiglottis, epiglottis tips posteriorly and bolus slides around it through laryngeal opening to enter laryngopharynx and stimulates tactile receptors to activate next phase - **Pharyngoesophageal phase**- involuntary. Three actions prevent food/drink from reentering the mouth or entering the nasal cavity or larynx (root of tongue blocks oral cavity, soft palate rises and blocks nasopharynx, and infrahyoid muscles pull larynx up to meet epiglottis while laryngeal folds close airway). Bolus is driven downward by constriction of the upper, then middle, then lower pharyngeal constrictors then enters to esophagus and stretches it to stimulate peristalsis (muscular contraction that pushes bolus ahead of it and is entirely involuntary). Liquid reaches stomach in 1-2 seconds while food reaches in 4-8 seconds. Lower esophageal sphincter relaxes to let food pass into the stomach when it reaches the lower end of the esophagus ## 15. Know the function of the stomach. - **Muscular sac** in upper left abdominal cavity immediately inferior to diaphragm. Primarily functions as a food storage organ (internal volume of about 50mL when empty, 1.0-1.5L after a typical meal, up to 4L when extremely full and extend nearly as far as the pelvis). Begins chemical digestion of protein and fat. **Chyme**- soupy/pasty mixture of semi digested food in the stomach - **4 regions:** - **Cardiac region**- small area within about 3cm of cardiac orifice - **Fundic region (fundus)**- dome-shaped portion superior to esophageal attachment the stomach - **Body (corpus)**- makes up greatest part of the stomach - **Pyloric region**- narrower pouch at inferior end (contains pyloric sphincter that regulates the passage of chyme into duodenum) - **Gastric juice**- 2-3L per day produced by gastric glands, mainly a mixture of water, HCI, and pepsin. Has a high concentration of hydrochloric acid and has a pH of 0.8 (very acidic) ## 16. Enzymes for protein and fat digestion - **Hydrochloric acid**- activates pepsin and lingual lipase and helps break up connective tissues and plant cell walls to form chyme. Contributes to nonspecific disease resistance by destroying most ingested pathogens - **Pepsinogen**- secreted by chief cells. HСІ removes some of its amino acids and forms pepsin - **Pepsin**- digests proteins into shorter peptide chains (protein digestion is completed in small intestine). Has an autocatalytic effect- as some pepsin is formed, it converts more pepsinogen into more pepsin - **Gastric lipase**- produced by chief cells. This and lingual lipase play a minor role in digesting dietary fats. Digests 10-15% of dietary fats in the stomach (rest is digested in small intestine) ## 17. Know what the intrinsic factor is for. - **Glycoprotein** secreted by parietal cells that's essential to the absorption of vitamin B12 by the small intestine ## 18. Know the GI tract hormones: - **Gastrin** - secreted by G-cells in the duodenum and stomach when exposed to large quantities of incompletely digested proteins. Functions include increased stomach motility and stimulates production of gastric acids and enzymes - **Secretin**- released when chyme arrives in the duodenum. Functions include increased pancreatic buffer secretions, stimulates secretion of bile by the liver, and reduces gastric motility and gastric secretions - **Gastric inhibitory peptide (GIP)**- secreted when fats and carbs enter the small intestine. Functions include stimulating duodenal gland activity, stimulates lipid synthesis in adipose tissue, and increases glucose use by skeletal muscles ## 19. Know the three ways to treat gastritis - **Gastritis**- inflammation of the stomach, which can lead to a peptic ulcer as pepsin and hydrochloric acid erode the stomach wall - **Treatments:** antibiotics when caused by Helicobacter pylori, proton-pump inhibitors (pantoprazole), and Bismuth-sulfide (Pepto-Bismol). And avoid NSAIDS like ibuprofen :) ## 20. Know the features which protects the lining of the stomach from the acidic environment - **Mucous coat**- thick, highly alkaline mucus resists action of acid and enzymes - **Tight junctions**- between epithelial cells, prevent gastric juice from seeping between them - **Epithelial cell replacement**- stomach epithelial cells live only 3-6 days. Sloughed off into chyme and digested with food and are replaced rapidly by cell division in gastric pits ## 21. Know the microanatomy of what each cell type produces in the stomach - **Simple columnar epithelium** covers mucosa. Apical regions on surface cells are filled with mucin. Swells with water and becomes mucus after secretion - **Mucosa and submucosa** are flat when stomach is full, but form longitudinal wrinkles called gastric rugae when empty - **Muscularis externa** has three layers consisting of outer longitudinal, middle circular, and inner oblique layers - **Gastric pits**- depression in gastric mucosa; have 2-3 tubular glands that open into the bottom of each one - **Mucus cells**- secrete mucous - **Regenerative (stem) cells**- divide rapidly and produce continual supply of new cells that replace dead ones - **Parietal cells**- secrete hydrochloric acid, intrinsic factor, and ghrelin (hunger hormone) - **Chief cells** (most numerous)- secrete gastric lipase and pepsinogen - **Enteroendocrine cells (G cells)**- secrete hormones and paracrine messengers that regulate digestion ## 22. Know the function of the pyloric sphincter. - **Regulates passage of chyme into duodenum** ## 23. Know the function of the duodenum. - **Nearly all chemical digestion and nutrient absorption occurs in small intestine (longest part of the digestive tract). Small refers to the diameter, not length** - **Duodenum**- begins at pyloric valve (major and minor duodenal papilla distal to pyloric valve) and receives major and minor pancreatic ducts respectively. - **Receives stomach contents, pancreatic juice, and bile.** Neutralizes stomach acid - **Fats** are physically broken up (emulsified) by the bile acids - **Pepsin is inactivated by increased pH and pancreatic enzymes take over job of chemical digestion** ## 24. Know how the small intestine adapts to nutrient absorption and digestion - **Lumen is lined with simple columnar epithelium** - **Muscularis externa** has thick inner circular layer and a thinner outer longitudinal layer - **Large internal surface area for effective digestion and absorption:** three types of internal fold or projections - **Circular folds (plicae circulares)**- increase surface area by factor of 2-3 - **Villi**- increase surface area by factor of 10. Fingerlike projections 0.5-1mm tall. Make mucosa look fuzzy and are covered with two types of epithelial cells (absorptive cells or enterocytes with microvilli and goblet cells that secrete mucus) - Epithelia are joined by tight junctions that prevent digestive enzymes from seeping between them. Core of villi is filled with areolar tissue of the lamina propria (embedded in tissue are an arteriole, capillary network, venule, and lymphatic capillary called a lacteal) - **Microvilli**- increase surface area by factor of 20 - **Brush border enzymes** are contained in the plasma membrane by microvilli and carry out some of the final stages of enzymatic digestion. Not released into lumen and is involved in contact digestion (chyme must contact brush border for digestion to occur). - **Duodenal glands in submucosa of duodenum secrete an abundance of bicarbonate-rich mucus that neutralizes stomach acid and shields the mucosa from erosive effects.** - **Large population of defensive lymphocytes throughout lamina propria and submucosa of small intestine intercepts pathogens before they can invade the bloodstream and aggregate into lymphatic nodules in the ileum called Peyer Patches** ## 25. Know how minerals are absorbed. - **Minerals (electrolytes) are absorbed all along the small intestine** - **Na+** cotransported with sugars and amino acids while Cl- is exchanged for bicarbonate reversing chloride- bicarbonate exchange occurs in stomach - **Iron and calcium are absorbed as needed** ## 26. Know the hormones responsible for the regulation of pancreatic juice and bile secretion - **Three stimuli** are chiefly responsible for the release of pancreatic juice and bile - **Acetylcholine (ACh)** from vagus and enteric nerves - **Cholecystokinin (CCK)**- secreted by mucosa of duodenum in response to arrival of fats in small intestine (stimulates pancreatic acini to secrete enzymes and strongly stimulates gallbladder) - **Secretin**- released from duodenum in response to acidic chyme arriving from the stomach. Stimulates ducts of both liver and pancreas to secrete more sodium bicarbonate. Raising pH to level pancreatic and intestinal digestive enzymes required ## 27. Know the bile and pancreatic juice pathways including all papillae and sphincters - **Pancreatic duct runs lengthwise through the middle of the gland and joins the bile duct at the hepatopancreatic ampulla which allows pancreatic juice and bile to mix.** Hepatopancreatic sphincter (sphincter of Oddi) controls release of both bile and pancreatic juice into the duodenum and closes to prevent food from entering ampulla - **Major duodenal papilla**- opening in the duodenum where the bile and pancreatic juices enter (also called papilla of Vater) - **Accessory pancreatic duct:** smaller duct that branches from the main pancreatic duct, opens independently into the duodenum. Bypasses sphincter and allows pancreatic juice to be released into duodenum even when bile is not ## 28. Know the function of pancreatic juices - **Alkaline mixture of water, enzymes zymogens, sodium bicarbonate, and other electrolytes** - **Acini** secrete enzymes and zymogens. **Ducts** secrete bicarbonate which buffers HCl arriving from the stomach - **Break down complex carbohydrates, proteins, and fats** ## 29. Know the pancreatic zymogens - **Trypsinogen**- secreted into intestinal lumen, converted into trypsin by enzyme secreted by mucosa of small intestine. Autocatalytic- converts trypsinogen into still more trypsin - **Chymotrypsinogen**- converted to trypsinogen by trypsin - **Procarboxypeptidase**- converted to carboxypeptidase ## 30. Know the pancreatic enzymes for digestion - **Pancreatic amylase- digests starch** - **Pancreatic lipase- digests fat** - **Ribonuclease and deoxyribonuclease- digest RNA and DNA respectively** ## 31. Know how much water is taken in and how much is excreted? - **Digestive tract** receives about 9L of water/day - 0.7L, 1.6L in drink, 6.7L in gastrointestinal secretions - 8L is absorbed by small intestine and 0.8L by large intestine - 0.2L voided in daily fecal output - **Diarrhea**- large intestine absorbs too little water (feces passes through too quickly if intestine is irritated and contains high concentrations of a solute (lactose)) - **Constipation**- fecal movement is slow, too much water is reabsorbed, and feces becomes hardened ## 32. Know the function of the ileocecal sphincter. - "**Valve of no return**. Food in stomach triggers gastroileal reflex that enhances segmentation in the ileum and relaxes the valve. As cecum fills with residue, pressure pinches the valve shut (prevents reflux of cecal contents into the ileum) - **Segmentation**- movement in which stationary ringlike constrictions appear in several places along the intestine. Relax and form new constrictions form elsewhere, most common kind of intestinal contraction. Purpose is to mix and churn (not move material along as in peristalsis) - **Pacemaker cells** in muscularis externa set rhythm of segmentation - Contractions about 12 times per minute in the duodenum, 8-9 times per minute in ileum - When most nutrients have been absorbed and little remains but undigested residue, segmentation declines and peristalsis begins - **Gradual movement of contents toward colon** - **Peristaltic wave** begins in duodenum, travels 10-70 cm and dies out, followed by another wave starting further down the tract - **Migrating motor complex**- successive, overlapping waves of contraction. Milk chyme toward colon over a period of 2 hours - **Ileocecal valve is usually closed** ## 33. Know the function of the cecum. - **Absorb water, salts, and electrolytes from waste material received from the small intestine.** Mixes contents with mucus to lubricate waste - **Appendix** attached at lower end of the cecum. Densely populated with lymphocytes and is a significant source of immune cells ## 34. Know the function of the ascending, transverse, descending, and sigmoid colon - **Ascending colon**- absorb water and nutrients from indigestible food material and solidifies it into stool - **Transverse colon**- absorb nutrients, synthesize vitamins, absorb nutrients into gut to maintain healthy population of bacteria, and moves wastes through haustral churning - **Descending colon**- stores stool until it can be eliminated from the body during a bowel movement - **Sigmoid colon**- S-shaped portion leading down into pelvis. Stores fecal wastes until it's ready to leave the body ## 35. Know the different cells for mucus production - **Mucus-secreting goblet cells** ## 36. Know the function of the rectum and anal canal - **Rectum**- portion ending at anal canal (has three curves and three infoldings called the transverse rectal folds (rectal valves)) - **Anal canal**- final 3cm of large intestine - **Anal columns and sinuses**- exude mucus and lubricant into anal canal during defecation - **Internal anal sphincter:** smooth muscle of muscularis externa - **External anal sphincter**- skeletal muscle of pelvic diaphragm - **Hemorrhoids**- permanently distended veins that protrude into the anal canal or form bulges external to the anus ## 37. Know the specific tissue for the anal canal - **Mucosa**- simple columnar epithelium through entire large intestine - **Anal canal** contains nonkeratinized stratified squamous epithelium in its lower half to provide abrasion resistance - **No circular folds or villi to increase surface area in large intestine** - **Lamina propria and submucosal layers** have large amount of lymphatic tissue that provides protection from the bacteria that densely populate the large intestine ## 38. Know the function of the stomach. - **Gastric motility-** - **Swallowing center** of medulla oblongata signals stomach **to relax** - **Food stretches** stomach activating **receptive-relaxation response** (resists stretching briefly, but relaxes to hold more food) - **Stomach** shows rhythm of peristaltic contractions controlled by **pacemaker cells** in the longitudinal layer of muscularis externa. - **Gentle ripple** of contraction every 20 seconds churns and mixes food with gastric juice, becomes stronger contractions at pyloric region, after 30 minutes, contractions become quite strong - **Churn food, mix it with gastric juice, and promote its physical breakup and chemical digestion** - **Squirts about 3ml of chyme into duodenum at a time** ## 39. Know the function of the small intestine - **Intestinal motility-** - **Contractions** of small intestine have three functions: mix chyme with intestinal juice, bile, and pancreatic acid to neutralize acid and digest nutrients more effectively, to churn chyme and bring it in contact with the mucosa for contact digestion and nutrient absorption, and to move residue toward the large intestine - **Segmentation**- movement in which stationary ringlike constrictions appear in several places along the intestine. Relax and new constrictions form elsewhere (most common kind of intestinal contraction). Purpose is to mix and churn, not to move material along in peristalsis - **Pacemaker cells** in muscularis externa set rhythm of segmentation. Contractions about 12 times per minute in the duodenum, 8-9 times per minute in ileum - When most nutrients have been absorbed and little remains but undigested residue, segmentation declines and peristalsis begins - **Gradual movement of contents toward colon** - **Peristaltic wave beings in duodenum, travels 10-70cm and dies out, followed by another wave starting further down the tract** - **Migrating motor complex**- successive, overlapping waves of contraction. Milk chyme toward colon over a period of 2 hours - **Ileocecal valve is usually closed** ## 40. Know the function of the large intestine - **Takes about 12-24 hours** to reduce the residue of a meal into feces (doesn't chemically change residue, reabsorbs water and electrolytes) - **Feces consist** of 75% water and 25% solids (30% bacteria, 30% undigested fiber, 10-20% fat, small amount of mucus, and sloughed epithelial cells) - **Mass movements** occur 1-3 times a day. Triggered by gastrocolic and duodenocolic reflexes - Filling of stomach and duodenum stimulates motility of the colon, accounts for urge to defecate often felt soon after a meal, and moves residue for several centimeters with each contraction ## 41. Know the functions of the kidneys - **Filters blood plasma, separates waste from useful chemicals, returns useful substances to blood, eliminates waste.** - **Regulates blood volume and pressure** by eliminating or conserving water. Regulates the osmolarity of the body fluids by controlling the relative amount of water and solutes eliminated - **Secretes enzyme, renin to activate hormonal mechanisms that control blood pressure and electrolyte balance** - **Secretes erythropoietin to stimulate RBC cell production** - **Collaborates with lungs** to regulate pCO2 and acid-base balance of body fluids - **Contributes to calcium homeostasis** - **Three protective connective tissue coverings:** renal fascia (binds to abdominal wall), perirenal fat capsule (cushions kidney and holds it in place), and fibrous capsule (encloses kidney protecting it from trauma and infection) ## 42. Know all the nitrogenous wastes that are excreted by the urinary system - **Waste**- any substance that's useless to the body or present in excess of the body's needs - **Metabolic waste**- waste substance produced by the body - **Uric acid**-product of nucleic acid catabolism - **Creatinine**- product of creatine phosphate catabolism - **Blood urea nitrogen (BUN)**- expression of the level of nitrogenous waste in the blood. Normal concentration of blood urea is 10-20mg/dL - **Nitrogenous waste:** waste product produced when proteins and nucleic acids are broken down and metabolized. Consists of ammonia, urea, and uric acid - **Urea formation**- proteins à amino acids à NH2 removed forms ammonia, liver converts ammonia to urea - **Proteins are broken down into amino acids which get converted into ammonia (toxic to the body). Ammonia gets broken down into nontoxic urea by arginase** ## 43. Know the anatomical pathway through the kidney and the specific physiological response (ie. – permeability, electrolyte reabsorption/excretion, osmolarity) - **Renal tubule**- duct that leads away from the glomerular capsule and ends at the tip of the medullary pyramid. Divided into 4 regions (PCT, nephron loop, and DCT are parts of one nephron) - **Proximal convoluted tubule**- most coiled region - **Nephron loop (loop of henle)**- Long U-shaped portion of the renal tubule - **Distal convoluted tubule**- shorter and less coiled the PCT. End of the nephron - **Collecting duct**- receives fluid from many nephrons and DCT as it passes back into the medulla. Numerous collecting ducts converge toward the tip of the medullary pyramid - **Papillary duct**- formed by merger of several collecting ducts - 30 papillary ducts end in the tip of each papilla. Collecting and papillary ducts lined with simple cuboidal epithelium - **Anatomical pathway:** - **Renal artery**- blood enters the kidney through the renal artery at the hilum - **Renal artery branches** into smaller blood vessels that reach the nephrons - **Each nephron contains a glomerulus** to filter the blood - **Glomerulus is highly permeable** to small molecules like electrolytes and water (and urea) - **Primary electrolyte** that's filtered and excreted is potassium - **Osmolarity of the glomerulus:** 300 mOsm/L - **Fluid filtered out of the blood** travels through the proximal convoluted tube, passes through the loop of henle, and then the distal convoluted tubule to reach the collecting duct - **PCT- highly permeable** to water and most solutes - Reabsorbs calcium paracellularly - Excretes sodium - Osmolarity of PCT: ~300mOsm/L - **Descending limb**- highly permeable to water, but not salt - **Loop of Henle**- highly permeable to water - Excretes sodium chloride and potassium - Osmolarity of the Loop of Henle: 1,200mOsm/L - **Ascending limb**- highly permeable to sodium, potassium, and chloride - Thick segment reabsorbs calcium - Excretes sodium, chloride, and small amounts of potassium - **Filtered blood leaves the kidney through the renal vein and flows back to the heart** - **Urine leaves the kidneys and travels through the ureters to the bladder for storage** - **Distal convoluted tubule**- water permeable. Permeability is regulated by ADH which allows for increased water reabsorption - Reabsorbs calcium transcellularly - Primarily excretes potassium. Regulated by aldosterone - Aldosterone stimulates potassium secretion by increasing sodium reabsorption - Sodium-potassium pump in DCT actively transports sodium out of the cell and potassium into it - **Osmolarity of DCT:** less than 300mOsm/L. Around 100mOsm/L - **Osmolarity of the collecting duct** is around 100-1,200mOsm/L ## 44. Know the blood pathway from the renal artery to renal vein - **Renal artery** divides into segmental arteries that give rise to interlobar arteries (up renal columns and between pyramids) and arcuate arteries over pyramids) - **Branch into afferent arterioles** that each supply one nephron and leads to a ball of capillaries called the glomerulus - **Blood is drained** from glomerulus by efferent arterioles that lead to either peritubular capillaries or vasa recta around a portion of the renal tubule - **Interlobular veins or directly into arcuate veins**- interlobular veins to segmental veins - **Renal vein empties** into inferior vena cava - **In the cortex**- the peritubular capillaries branch off of the efferent arterioles supplying the tissue near the glomerulus (PCT and DCT) - **In the medulla**, the efferent arterioles give rise to the vasa recta which supplies the nephron loop portion of the nephron ## 45. Know the inner and outer layer of bowman's capsule. - **Renal corpuscle** consists of glomerulus and two-layered glomerular (Bowman) capsule that encloses the glomerulus - **Parietal (outer) layer** consists of simple squamous epithelium - **Visceral (inner) layer** consists of elaborate cells called podocytes that wrap around the capillaries of the glomerulus - **Capsular space** separates the two layers of Bowman's capsule ## 46. Understand glomerular filtration - **Glomerular filtrate collects in capsular space, flows into PCT** - **3 barriers** that make up filtration membrane through which fluid passes: - **Fenestrated endothelium of glomerular capillaries**- filtration pores exclude blood cells and is highly permeable - **Basement membrane**- excludes molecules greater than 8nm (most proteins). Blood plasma is 7% protein, the filtrate is 0.03% protein - **Filtration slits**- podocyte cell extensions (pedicels) wrap around the capillaries to form a barrier layer with filtration slits. Negatively charged with additional obstacle for large anions - **Glomerular filtration rate (GFR)**- amount of filtrate formed per minute by the kidneys. 180L/day (male) and 150L/day (females) - **Controlled by 3 mechanisms:** - **Autoregulation**- myogenic mechanism (JG cells and mesangial cells) and tubuloglomerular (macula densa cells of the DCT) - **Myogenic mechanism**- afferent arteriole restricts blood flow into glomerulus when arteriole blood pressure increases - **Juxtamedullary apparatus**- mesangial cells, JG cells, and macula densa - **Macula densa**- patch of cells at the end of the nephron loop on the side of the tubules facing the arterioles. Senses variations in flow or fluid composition and secretes a paracrine signal that stimulates JG cells - **Juxtaglomerular (JG) cells**- smooth muscle cells in afferent arterioles - When stimulated by the macula, they dilate or constrict the arterioles. Contain granules of renin, which they secrete in response to drops in blood pressure - **Mesangial cells**- in cleft between afferent and efferent arterioles and among capillaries of glomerulus - Connected to macula densa and JG cells by gap junctions and communicate by means of paracrine signals. Constrict or relax capillaries to regulate flow - **Sympathetic control**- SNS and epinephrine constrict afferent arterioles during exercise or blood loss - **Hormonal control**- renin-angiotensin- aldosterone-system restores BP and BV when there's a drop in BP ## 47. Know the specific features of PCT and DCT - **Proximal convoluted tubule**- arises from glomerular capsule. Longest and most coiled region. Contains simple cuboidal epithelium with prominent microvilli for majority of absorption - **Tubular reabsorption:** - **Regulates pH** by absorbing bicarbonate and secreting hydrogen ions - **Reabsorbs 65% of sodium and water** by Na/K ATPase pump - **Reabsorbs 100% of organic solutes** (glucose and amino acids) by cotransport - **Reabsorbs 65% of potassium** by solvent drag and simple diffusion - **Reabsorbs 80% of phosphate** - **Distal convoluted tubule**- begins shortly after ascending limb reenters the cortex. Contains cuboidal epithelium without microvilli. End of the nephron. Has a larger lumen and more mitochondria - **Tubular reabsorption:** - **Regulates pH** by absorbing bicarbonate and secreting hydrogen ions - **Reabsorbs sodium** (aldosterone) and secretes potassium - **Calcium regulation** via parathyroid hormone ## 48. Know